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FIRST
COLLEGE COURSE
IN PHOTOGRAPHY
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Katherine Chamberlain, Sc.D.
Associate Professor of Physics
Wayne University, Detroit
Copyright, 1942, by
Katherine Chamberlain
Printed in U.S.A.
ED WA R D S B R OTHERS, IN C.
Lithoprinters
A N N A R B O R, MI C H IGAN
1942

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PRE FACE
There is a growing realization that the physical sciences
have a unique part to contribute to a liberal education and it is
therefore to be regretted that large numbers of students go through
college without ever making contact with any of these. Many, how-
ever, have neither the time nor inclination to submit to the disci-
pline of the older type of science courses that are designed pri-
marily to meet the needs of science majors. That there is a real
need for something different has been widely recognized but many
of us feel that this has been rather unsatisfactorily met by exist-
ing simplified courses. Sometimes these cover so much ground that
they are necessarily superficial and put the emphasis upon the re-
sults rather than the method of science. Usually these courses
have no laboratory work.
It is the opinion of many of us that the unique contribu-
tion that science offers to a liberal education lies in the culti-
vation of the spirit of careful inquiry, in the unprejudiced ap-
peal to experiment, and in the opportunity so frequently offered
to test our opinions and learn definitely whether or not they are
valid. But, if it is to serve this purpose, we must not rob it of
its essential quality. It is not sufficient to make it simple by
telling students the answer and having them memorize it. We must
not neglect our opportunities to correlate the work of head and
hands and we do well to remember that for many students it is in
the laboratory that inanimate remnants of knowledge come to life.
An enthusiast about photography since childhood, the author
has taught such a course on the college level for many years and
has found in it an opportunity to introduce many Students to the
subject matter and methods of the physical sciences who would not
have met these otherwise. But, it should be emphasized that the
teaching of these things to students with a limited background in
science involves a slower, more minute and patient development of
our fundamental concepts. Certainly, it should not involve the
elimination of the more difficult portions at the expense of log-
ical completeness nor the development of a vast and Superficial
cramming process. On this account, no apologies are offered for
the inclusion of the absorption law, many sensitometric Strips and
the graphs of photography. The student who has forgotten most of
iii

iV PREFACE
what he once learned about the accompanying logarithms does well to
be reminded and one who has never studied these gains something in
justifiable self-confidence if he has the stamina to learn enough
about them to appreciate their usefulness and fundamental simplicity.
More space than usual has been devoted to color photography
for two reasons. In the first place, it has an inherent fascina-
tion and interest that stimulates students to make very strenuous
efforts to master it. Here, we have something that will arouse al-
most any student to exert himself to the utmost to discover why it
is so and the learning process goes forward by leaps and bounds
under these circumstances. In the Second place, color photography
is so certain to offer many people professional opportunities in
the future that it seems very desirable from a teaching Standpoint
to show students as much as possible of the ever-broadening horizons
that lie here. -
Students frequently read too much and think too little.
So, just because photography includes a relatively limited domain
in comparison to a survey course in the physical sciences or even
a course in general physics, it is believed that it offers students
a particularly good opportunity to develop themselves by intensive
study, careful reasoning, and patient experiment. That it at the
same time offers training in a fascinating technique whose applica-
tions are almost unlimited is an additional advantage that will en-
courage the student to suffer with fortitude if the characteristic
curve should bring on an attack of growing pains.
Katherine Chamberlain
Wayne University
Detroit, Michigan
October 28, 1911.l


".º
Chapter
I.
II.
III.
IV.
WI.
VII.
VIII.
IX.
XI.
XII.
XIII.
XIV.
C ON TENTS
How Photography Began
Making a Print.
Films and Their Processing
Cameras
The Factor's that, Influence the
Sharpness of the Photographic
Image -
The Graphs of Photography .
Projection Printing .
Photographic Optics
More Photographic Optics
The Rendering of Color in Mono-
Chrome
Introductory Considerations Re-
garding Color Photography .
The Additive Processes of Color
Photography .
The Subtractive Processes Of
Color Photography .
Photography and Creative Ex-
pression
Page
18
3O
119
6||
81
... 102
178
2Ol
219
228
º
Chapter |
How PHOTOGRAPHY BEGAN
Probably there is no field in the world in which
more people are interested than photography. Those who
are taking pictures are legion and when we add to these
all who are interested in photographs, the enterprise
takes on a universality that makes it almost unique
among the occupations that man has devised for himself.
Perhaps this almost universal appeal arises because there
is latent in every one of us an urge to make pictures.
This urge can find an outlet in photography when, per-
haps, we lack the talent or training to find a means of
self-expression in an older art.
Or, possibly, the appeal lies in the mystery and
beauty of the process itself. We can expose a film in a
camera for a fraction of a second, then take it into a
dark room and watch it develop. Within a short time,
the image appears with all its wealth of detail and gra-
dation. Nobody knows precisely what has been happening
while we watched, but the wonder and mystery of the proc-
ess make an appeal to the imagination that keeps it from
seeming commonplace even after we have seen it thousands
of times.
But, in spite of this almost universal interest,
the number of those who are able to achieve a high stand-
ard of excellence is almost vanishingly small. J. Dudley
Thompson, Honorary Fellow of the Royal Photographic So-
ciety, wrote the following after acting as judge for a
Royal Photographic Salon for the twenty-first time :
"The trouble is that those who have an eye to see
a picture so often do not trouble to acquire the techni-
cal ability to make a print of sufficiently good quality,
whilst on the other hand so many who can make a really -
good print squander their efforts upon totally unsuitable
subjects, obviously having no idea whatever of pictorial
essentials. Those who can really see a picture, can


2 FIRST COLLEGE COURSE IN PHOTOGRAPHY
isolate it from all the multiplicity of Nature's details
and embody the ideal in a print of superlative and appro-
priate quality are an infinitesimal minority. I have
been criticized in the past for asserting on more than
one occasion that there are not produced in the whole
world in any one year more than one hundred photographic
prints that deserve to rank as first rate. So far from
recanting, increased experience suggests that I have been
far too liberal in my figure and that the hundred would
have to include not only those that have some originality
of vision combined with faultless technic, but a large
sprinkling of respectable repetitions of things that have
already been done better."
Perhaps the very large amount of mediocre photo-
graphic work is due to the fact that a partial mastery
of the processes is too easy. A ten-year-old child can
learn to make prints of a sort. The simplicity of the
processes fails to challenge the photographer to exert
himself to the limit of his ability. Perhaps it would
be a distinct help to photography if we had materials
that would not produce passable results when carelessly
handled. Then, there would not be quite the temptation
that there is today to use old paper or the Wrong grade,
to take a chance with old developer, to let the tempera-
ture go up or down, or to juggle with the developing
time.
Some may object that they believe in the inspira–
tion of the moment and fear that too much science Would
make the photographic process a stereotyped, mechanical
routine. Certainly, every advantage should be taken of
all the inspiration that the moment can supply. The only
point is that it is wrongly applied when it expends it –
self upon those things that are more properly in the
realm of the balance, the clock, and the thermometer.
These are all prečminent in their own fields and one who
would reproduce consistent results, disregards them at
his peril. With their help, one can pass surely and
rapidly in the direction of real proficiency with a much
Smaller expenditure of time than would be possible by
hit-or-miss experimenting. Furthermore, it should be re-
membered that a thorough mastery of a medium of expres–
sion never yet robbed anyone of what he was able to

HOW PHOTOGRAPHY BEGAN 3.
express. Rather, such mastery serves to make expression
SO effort, less that the Whole attention can be devoted to
the idea, and the means will take care of itself.
Outstanding Contributors to the Development of
Photography. A survey of the history of photography and
an exact appraisal of the value of the individual contri-
butions are complicated, as is usually the case in sci-
entific matters, by great difficulty in assigning the
exact credit due each individual that participated. Rec –
ords are often incomplete for then, as now, research
workers have often been prone to keep records intelligi-
ble to no one except themselves and notebooks having the
completeness and clarity of those of Faraday are the ex-
ception rather than the rule. Scientific journals were
not nearly so numerous as they are now and often a re-
Construction of the circumstances under which epoch–
making work was done can be arrived at only by inference
based upon old correspondence or the testimony of con–
temporaries. Often, it is very difficult to be certain
Whether a given investigator influenced one who followed
him or whether the latter worked the whole thing out in-
dependently. Occasionally national pride would appear
to have colored somewhat the evidence that has come down
to us. Perhaps the exact contribution of the individual
does not greatly matter and, certainly, controversies
regarding priority need not concern us here. Rather, our
interest should be in the nature of the problems to be
solved and the means taken for their solution to help us
to appreciate all that we have at our command today and
to comprehend something of the debt we owe to the pa-
tient enterprise of those who have preceded us. We shall
therefore mention only a few of these individuals to in-
dicate the general character of their investigations but
it should be realized that actually there were many more
who contributed a part.
Photochemical Effects. Essential to photography
was the discovery of materials that would undergo a
color change under the direct influence of light or of
Subsequent development. In addition, it was highly de-
sirable that these effects could be produced by short
exposures and that the resulting changes could be made

l; FIRST COLLEGE COURSE IN PHOTOGRAPHY
—a.
permanent. Johann Heinrich Schulze (1727) discovered
accidentally that a pasty mixture of chalk, aqua regia
and silver nitrate darkened while he examined it by
light coming through the window. Further experiments
indicated quite definitely that the effect was due to
light and not to contact with the air.
In 1765, Dr. William Lewis repeated Schulze's
experiments. This work is noteworthy begause Lewis left
notebooks describing his experiments that eventually
fell into the hands of Thomas Wedgwood, the son of the
famous potter. Carl Wilhelm Scheele (1777) exposed pa-
per impregnated with silver chloride to the light of the
solar spectrum and found that the violet portion of the
Spectrum darkened the paper about two and one-half times
as fast as the green.
The work of Wedgwood and his collaborator, Sir
Humphrey Davy, is important primarily because their ex-
periments were of assistance to William Henry Fox Talbot
who brought work covering over a century to a successful
culmination by succeeding in making pictures in a camera
with a relatively short exposure and of sufficient perma-
nence so that some are still extant today. Wedgwood and
Davy sensitized their paper by coating it alternately
With silver nitrate and common salt and appear never to
have succeeded in making a paper fast enough so that it
would make an image in a camera. Neither were they suc-
cessful in making the image permanent. Wedgwood began
his investigations at the age of nineteen and but for
his untimely death at thirty-four might easily have been
the one to carry the problem to a successful culmina-
tion. At any rate, it seems certain that he and Davy
Succeeded in making silhouettes by placing small opaque
objects on their sensitized paper and exposing to light
and that they also succeeded in making some very minute
projected images with the solar microscope.
Wedgwood and Davy, (1802) published an article"
in the Journal of the Royal Institution describing their
l. T. Wedgwood with observations by H. Davy: An Account of a Meth-
od of Copying Paintings upon Glass and of Making Copies by the
Agency of Light on Nitrate of Silver. Jour. of the Royal Insti-
tution, Wol. l.
º

HOW PHOTOGRAPHY BEGAN 5
combined researches after which Davy apparently turned
his attention to other Scientific matters.
William Henry Fox Talbot. William Henry Fox
Talbot is often called the father of modern photography
because he succeeded in presenting to the world an en-
tirely practical process for making a picture by the
agency of light. At first he tried paper in the camera
..obscura coated as Wedgwood and Davy had coated it but
found that even with an exposure of an hour or two, the
results were not satisfactory. He makes the following
statement regarding this in his book, The Pencil of
Nature . -
"The outline of the roof and chimney was marked
enough but the details of the architecture were feeble,
and the parts in shade were left blank or nearly so."
In 1855 he used paper prepared as above in the wet state
and so managed to get a satisfactory image in about ten
minutes on a bright day. These early photographs were
of miniature size but he later made larger ones that
were used as plates in his books, The Pencil of Nature
and Sun Pictures of Scotland.
In January, l859 Fox Talbot described this first
process in a paper to the Royal Society, later publish–
ing full details in the Philosophical Magazine. The
process that served to make photography a popular pas—
time indulged in even by Queen Victoria and the Prince
Consort at Windsor, came a little later. It will be
realized that photography could be little more than a
scientific plaything until the discovery of the latent
image and a method of developing it made short exposures
effective.
The following excerpts from a letter to the edi-
tor of the Literary Gazette, issue of February 19, 1841,
written by Talbot set forth the circumstances surround-
ing this discovery.
"I may as well begin by relating to you the way
in which I discovered the Process itself. One day, last
September, I had been trying pieces of sensitive paper,
prepared in different ways, in the camera obscura, allow-
ing them to remain there only a very short time, with a

6 FIRST COLLEGE COURSE IN PHOTOGRAPHY
view of finding out which was the most sensitive. One of
these papers was taken out and examined by candlelight.
There was little or nothing to be seen upon it, and I left
it lying on a table in a dark room. Returning some time
later I took up the paper, and was much surprised to see
upon it a distinct picture. I was certain that there was
nothing of the kind when I had looked at it before, and,
therefore (magic apart) the only conclusion that could be
drawn was that the picture had unexpectedly developed it-
self by a spontaneous action. Fortunately I remembered
the particular way in which this paper had been prepared,
and was therefore enabled immediately to repeat the ex-
periment. The paper, as before, when taken out of the
camera, presented hardly anything visible; but this time,
instead of leaving it, I continued to observe it by
candlelight, and had soon the satisfaction of seeing a
picture begin to appear, and all the details of it come
out one after another.
"In this experiment, the paper was used in a moist
state, but since it is much more convenient to use dry
paper if possible, I tried it shortly afterwards in a dry
state, and the result was still more extraordinary. The
dry paper appeared to be much less sensitive than the
moist, for when taken out of the camera after a short ex-
posure, say a minute or two, the sheet of paper was abso-
lutely blank.
"But nevertheless, I found that the picture ex-
isted there, although invisible; and by a chemical proc-
ess analogous to the foregoing, it was made to appear in
all its perfection. . . . . I know few things in the range
Of science more surprising than the gradual appearance of
the picture on the blank sheet, especially the first time
the experiment is witnessed."
The paper mentioned here was prepared by brush-
ing paper with silver nitrate and then dipping it into a
solution of potassium iodide. The paper was then brushed
with a mixture of silver nitrate, water, acetic acid and
gallic acid. After producing the latent image change by
an exposure of less than a minute, development was pro-
duced by more of the gallic acid solution assisted by
gentle heating. The image was made semi-permanent by
treating finally with a strong solution of sodium chlo-
ride or potassium bromide.
HOW PHOTOGRAPHY BEGAN 7
Thus, we see that a single individual within a
relatively short time solved all the problems that were
formidable stumbling blocks in the way of the develop.–
ment of photography. He succeeded in finding material
Sufficiently light sensitive so that it could be used in
a camera; he next shortened exposures greatly by discov–
ering the latent image and a method of developing it ;
and, last , he found a method of making the image perma—
nent, though not the one that we use today. It has oc –
Curred many times in the history of science after pa–
tient investigation on the part of numerous workers over
a long period has contributed many valuable fragments
that, finally, the individual appears who is able to
make a really remarkable synthesis of all that has gone
before, augmented by a very considerable amount that he
has done himself, with the result that the problem
Stands solved. All of these instances raise interesting
Questions regarding whether the successful culmination
is due primarily to the unusual talent of the man or to
his good fortune in having been born at the right time.
At least, it is noticeable that those with exceptional
creative ability nearly always exhibit rather marked
humility as if they realized that there is an overplus
in their achievements for which they do not feel respon-
Sible.
Joseph Nicephore Niepce. The work that reached
a culmination in the daguerreotype was begun by Joseph
Nicephore Niepce, probably in the second decade of the
nineteenth century. His primary objective was the pro-
duction of plates for printing that could be made by
light as a substitute for the laborious handwork re-
quired in drawing designs on stones with greasy materi-
als in the making of lithographs.
Various organic materials undergo changes render-
ing them more or less insoluble on exposure to light,
apparently by Oxidation. In some of his early investi-
gations Niepce coated metallic plates with a solution of
asphaltum in oil of lavender which was allowed to dry
and the plates were then given very long exposures in a
Camera. As a result, the coating was rendered insoluble
Where the light reached it strongly and the faintly dis–
tinguishable image was developed by bathing the plates

8 FIRST COLLEGE COURSE IN PHOTOGRAPHY
in a mixture of one part of oil of lavender and ten parts
of white petroleum. This slowly dissolved away the as-
phaltum varnish from those parts that had not been af-
fected by the light leaving what was to all intents and
purposes an acid resist such as is required' before etch-
ing a metallic plate. In fact, some of his plates were
etched and used for printing with inks. Others were
used simply to show the faint image or were treated with
suitable chemicals to darken it. The above process was
subject to considerable modification with the passage of
years and is to be regarded merely as a typical example
of Niepce's processes. At least, there can be little
doubt that he pointed the way to the development of
photo-mechanical printing.
In 1829 Niepce formed a partnership with Louis
Jacques Mande Daguerre and apparently the two worked in
collaboration until the death of Niepce in 1855. An in-
dication of the progress that had been attained is indi-
cated by the statement of Daguerre that a photographic
copy of a landscape could be made in seven or eight
hours but single monuments strongly lighted by the sun
and light in color could be taken in three, an exposure
possibly one million times that required today for a
Similar subject. Iodine was one of the chemicals used
by them and they frequently formed their images on pol-
ished metal plates so it was not long until they initiat-
ed together the experiments that led finally to the ,
daguerreotype.
The daguerreotype. The daguerreotype plate was
usually a copper plate heavily coated with silver and
highly polished. This was exposed to the fumes of io-
dine until a layer of silver iodide of suitable thick-
ness was formed upon it. At first the image formed was
the visible image that could only be produced by an ex-
cessively long exposure and it seems evident that the
discovery of the latent image and the means of develop- .
ing it are due to Daguerre alone. The date of this dis-
covery is not definitely known but the following excerpt
from a latter written to Daguerre by the son of Nicephore
Niepce three or four years after his father's death,
could scarcely have referred to anything other than the
discovery of the latent image.

HOW PHOTOGRAPHY BEGAN 9
------- ----ſ
-
"While I require almost a whole day to make One
design, you - you ask only four minutes."
The discovery was another of those happy acci-
dents so common in science when a completely fortuitous
combination of circumstances causes a significant re-
sult to pass under the observation of someone suffi-
ciently acute to appreciate its meaning. The story goes
that Daguerre had prepared a plate with the intention of
making the usual long exposure on it. A short time after
this was begun, the sky clouded over making it impossi-
ble to obtain any further result that day. Thinking
that he still possessed an unexposed plate, Daguerre
took it out of the camera in the dark room and laid it
aside to use on a future occasion. We can imagine his
amazement when he returned some time later and found vis-
ible on the plate the scene to which he had given it a
brief exposure. While many scientists have known the
exhilaration of having success catch them unawares, it
is doubtful whether there are many cases in which the de-
sired objective has been so perfectly realized at a sin–
gle stroke.
Daguerre concluded that there must be something
present in his cupboard that was capable of developing
an invisible image and subsequent investigation showed
that it was the fumes of mercury. Mercury has an appre-
Ciable vapor pressure at room temperature and what had
happened was that such fumes found their way from an un-
covered dish to the plate and formed a visible amalgam
there wherever the plate had been affected by the light.
As finally worked out by Daguerre the process
of making a daguerreotype was as follows. A brightly
polished plate of copper coated with silver was cleaned
With finely powdered pumice and olive oil, then with di-
lute nitric acid. After being washed and dried it was
buffed to a high polish and exposed to fumes of iodine.
As the coating of silver iodide thickened, it showed
various colors by interference and the process was con-
tinued until the coating was a golden brown color, the
stage of maximum sensitiveness. The exposures required
in Paris varied from three to thirty minutes. Develop-
ment was brought about by exposing the plate to the fumes

Il O FIRST COLLEGE COURSE IN PHOTOGRAPHY
of mercury in a closed container that could be heated
slightly and observation of the progress of the action
was possible through a colored glass window. When de-
Velopment was complete, the image was made permanent by
bathing the plate in sodium thiosulphate, the hypo of
today. Strictly speaking, an image formed by a mercury
amalgam is of doubtful permanence and a distinct advance
was contributed by H. L. Fizeau in 1844 who showed that
the image could be converted into a gold image by bath-
ing the plate in a water solution of gold chloride and
hypo. It is probable that most of the daguerreotypes
extant today have been gold toned.
The year 1859 will always be regarded as an
epoch-making one in the history of photography as it was
in this year that Fox Talbot and Daguerre published par-
ticulars regarding their entirely dissimilar processes
for making pictures by the agency of light. At that mo–
ment it would appear that Daguerre's process had reached
a more complete state of development as Fox Talbot did
not publish the account of his discovery of the latent
image until 1841. At any rate, the daguerreotype enjoyed
an astonishing vogue for a decade or two and then died
out completely. It seems regrettable that this was the
case for examples of great beauty have come down to us
but the competition resulting from the increased sim-
plicity and ease of duplication of results by the meth—
ods following Fox Talbot proved too much for the da–
guerreotype and the process has now only historical sig-
nificance. At the same time, it should not be forgotten
that it did much to create an interest in photography by
producing results that had a very definite charm all
their own.
There is reason to believe that the first por-
traits ever made by Daguerre's process were made by Dr.
J. W. Draper and Robert Cornelius working independently
in Philadelphia. A daguerreotype still exists made by
Draper of his sister in March, l8l40. One reason why
there is a certain charm and naturalness about daguerre-
otype portraits far superior to much of the early work
following Fox Talbot arises from the fact that it was im-
possible to retouch them. The early retouchers, unfortu-
nately, appear often to have used their tools to remove
Eºiſ -
º
ſº,
º
-
g
HOW PHOTOGRAPHY BEGAN ll
every possible element of character and originality from
their photographs. Thus, they left a lasting memorial
rather to a certain artificiality in the Victorian age
than to more lasting values in the photograph as a means
of creative interpretation.
That there were those from the very beginning,
however, who were aware of the artistic possibilities of
photography is shown by the work of such people as David
Octavius Hill. Primarily an artist, Hill conceived the
idea of using Fox Talbot's process to make a photograph-
ic record of several hundred notables of Edinburgh whom
he wished to portray in a vast historical painting Com-
memorating the founding of the Church of Scotland. This
work is significant because Hill clearly recognized that
many of the principles applied in painting could be uti-
lized in making photography a genuine means of creative
expression at the time when it was still so new that the
novelty of its accomplishments caused most people to
marvel over it and to be quite satisfied that a recog-
nizable record could be produced at all.
Fox Talbot's negatives were made of paper and it
must have been evident from the beginning that a glass
support would offer a great improvement both in trans-
parency and in freedom from a structure of its own that
would be visible in the print. Before glass could be
used, however, it was necessary to develop a coating for
the plates that would carry the light-sensitive salts in
an extremely finely divided and uniformly distributed
State. If coated directly on the glass, the chemicals
tended to form irregular crystalline clumps separated by
Other regions in which there was little or no light-
sensitive material.
Niepce de Saint Victor was the first to use a
glass plate, coating sheets of glass with white of egg
containing potassium iodide. After drying, the plate
Was immersed in silver nitrate which caused silver iodide
to be formed in the coating by a simple substitution re-
action. -
AgNOs + KI = AgI + KNOs
Development was with gallic acid and the negatives gave
good gradation and exceptionally fine grain. In fact,

12 FIRST COLLEGE COURSE IN PHOTOGRAPHY
albumen negatives have never been equalled for fineness
of grain but they were always very slow.
This was followed in l85l by the collodion wet
plate process, first used by Scott Archer. With this
was inaugurated what may be considered the heroic age of
photography for these plates had to be coated just be-
fore use and developed immediately afterward so a land-
Scape photographer had to start out accompanied not only
by a camera of decidedly generous proportions and tripod
but also by a portable darkroom and everything necessary
to coat and develop his plates. The glass had first to
be cleaned and coated with collodion containing potas–
Sium iodide. Evaporation of the solvents was so rapid
that in a minute or two the collodion became jelly-like
and set sufficiently so that it would no longer run on
the plate. It was then immersed in silver nitrate in
the dark and while still wet was exposed in the camera.
Development must also take place before the plate dries.
The following account by Frank M. Sutcliffe of his ex-
periences in making some photographs for John Ruskin
throws very interesting sidelights upon what it meant to
be a photographer in that day. *
"In the early seventies I was working for him
(John Ruskin) at Brantwood, on Coniston Lake, which he
had recently bought and improved.
"This was in the days of wet plates, when the pho- ,
tographer had to carry about with him a heavy parapher-
nalia of dark tent, water bottle, silver bath, developers,
chemically clean plate glass, and plate boxes.
"At Brantwood I made use of the gardener's pot-
ting shed as a darkroom, with a piece of red calico
pinned over the window, where the plates were sensitized
and developed, washed and dried.
"One day Mr. Ruskin said that he would like to
have a photograph of a wild strawberry plant growing by
the lakeside, a little lower down the lake than the house;
he had been making a most careful pencil drawing of this,
but he was afraid it would not last till he finished his
2. Photographic Journal, November, 1957, 60l.

HOW PHOTOGRAPHY BEGAN 13
3.
drawing. A plate, 6% x 8%, was sensitized, and John Rus-
kin, my camera, tripod and self got into his own special
boat in which he paddled about the lake. It was deeply
waterlogged; the water when we were all aboard was nearly
level with the gunwales. I hardly relished being drowned
at such an early stage of my life. I was but 20, but I
consoled myself by thinking what a grand advertisement it
would be if I lost my life in such distinguished company.
The pencil drawing of the strawberry plant is, I believe,
in the Ruskin Museum at Sheffield. w
"As everyone knows who has ever worked wet plates,
these things were spoilt if they became dry; twenty min-
utes was about as long as they would keep wet, and not so
long as that in hot weather, even when the dark slide had
been damped with glycerine and a pad of wet blotting pa–
per placed at the back of the plate.
"There was a clump of fir trees growing among the
rocks above the house at Brantwood of which Mr. Ruskin
wanted some views, so he and I climed up to photograph it;
by the time he had found a viewpoint which satisfied him,
and the plate was exposed, I was afraid the plate would be
drying and showing the usual oyster-shell markings, so
leaving John Ruskin, to bring the camera down, I rushed off
helter-skelter downhill to develop it."
Negatives of fine grain and high contrast can be
made by this process which still finds use in photo-
engraving where the inconvenience of having to coat, ex-
pose and develop in a continuous operation is not seri-
ous. For general photographic use, however, plates were
needed that could be sensitized in advance so that a
darkroom would not be needed in the field. Major C.
Russell contributed the next step by showing that it was
possible to use alkaline pyrogallol as a developer, a
developer suitable for a gelatine coated dry plate. An-
other problem was to devise a method for removing the
surplus salts from the gelatine emulsion as these would
crystallize out on the surface of a dry plate if not re-
moved. Many worked on the problems involved in produc-
ing a satisfactory dry plate and in 1878 Charles Bennett
made such plates by a process that is essentially that
used today. The removal of the surplus chemicals was
accomplished by first allowing the gelatine emulsion to

|
PLATE I
Portrait Processes of the Past Century.
Upper row.
Left. Hand drawn silhouette.
Scotland, 1835.
Center. Daguerreotype.
Canada, 1857.
Right. Ambrotype.
U.S.A., 1860.
Lower row.
Left. Tintype.
U.S.A., 1867.
Center. Gold toned print on glossy
printing out paper. (P.O.P.)
U.S.A., 1884.
Right. Silver print on developing
out paper. (D.O.P.)
U.S.A., 1902.


HOW PHOTOGRAPHY BEGAN 15
set, after which it was reduced to a finely shredded
form that made it possible to wash out the soluble salts.
It could then be remelted and used to coat plates. Since
that time, there have been notable improvements in speed,
fineness of grain and color sensitivity but no radical
changes in method. It is curious to note that the very
moderate speeds of the early dry plates were regarded as
a disadvantage by many photographers because they were
too fast !
Çn Plate I are shown reproductions representing
the various portrait processes of the past century. The
silhouette was evidently done with India ink and a brush
a few years before any practical photographic process
existed. The lighter parts were put in with gilt paint.
Daguerreotypes and ambrotypes were frequently mounted in
the same kind of plush or leatherette covered cases so,
contrary to a general belief, the case does not insure
that the photograph contained in it is actually a da–
guerreotype. In fact, even tintypes are occasionally
found that have been mounted in these cases. Daguerreo-
types have always been most highly esteemed, ambrotypes
next and tintypes, least. They can be positively dis-
tinguished by the uninitiated in several ways. Daguerre-
otypes show an image having a distinct metallic lustre
when viewed at certain angles, reveal the picture best
at a particular angle and are made on a metal plate,
usually polished copper coated with silver. The ambro-
type image is made on a glass support and can be seen
almost equally well at any angle. Here the image was
converted chemically into a light-colored, opaque com—
pound and backed with black varnish. It is viewed
through the glass support. Since daguerreotypes were
framed with protective covering glasses, in case of
doubt about identification, it is usually possible to
pry open the case and examine the enclosed photograph
directly. It should be emphasized that daguerreotypes
are valuable and should be kept where they are safe from
harm. Even then, many of them now show distinct signs
of deterioration and if one wishes to be sure of preserv —
ing the likeness, the most certain way is to have it re-
photographed by our present processes.


l6 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Old photographs on printing out paper, or P. O. P. ,
are glossy and range in tone from brown to purple accord-
ing to the treatment received in the gold toning bath.
They were usually printed by daylight and the image was
visible before development. About the only use to which
such paper is put today is in making photographer's
proofs which are merely printed and not fixed or toned
so that the image lasts for only a short time and soon
darkens if exposed to strong light. . Most of the papers
used today show no image until developed and are suffi-
ciently fast so that they can be printed by artificial
light. The tones obtainable by direct development range
from a brownish to a true black depending upon the paper
and the developer used. By subsequent toning, the orig-
inal silver image can be converted into any one of a
number of chemical compounds giving images in almost any
Color de Sired.
Systematic production of photographic materials
as a commercial enterprise began about 1880. Bromide
paper appeared about the same time as the dry plate. The
following table will serve to date a few more of the
things that photographers today take for granted.
Table Tº
Carbon printing . . . . . . . * @ C tº C e 1875
Velox . . . . . . . . . . . . . . . . . . . 1894 §
Platinum printing . . . . . . . . . . . . . 1875
First dye sensitizing . . . . . . . . . . 1875
First kodak . . . . . . . . . . . . . . . 1888
Roll film on transparent base . . . . . . 1889
Daylight loading film . . . . . . . . . . 1891
Cut film introduced . . . . . . . . . . . 1912
Panchromatic film . . . . . . . . . . . . 1901;
Supersensitive panchromatic film . . . . 1931
3. C. E. K. Mees, Photography.
º
º
#
*
º HOW PHOTOGRAPHY BEGAN 17
QUESTIONS “
º
l. Why is Fox Talbot called the "father of modern pho-
§ tography"?
{{ }; 2. Mention other examples in science in which a single
º individual has been able to make an important Syn-
§ thesis of much that has been done by his predeces-
§ SOI’S -
Sºº 3. What differences do you see in creative work in sci-
º ence and in art?
l!. Are scientific and artistic abilities diametrically
º opposed to each other or are they in reality differ-
ent forms of expression for abilities that are quite
º Similar? -
5. Mention someone who has done creative work both in
# Science and in art.
... zº 6. Should a person receive credit for accidental dis-
coveries or should these berregarded merely as lucky
accident Sº
7. What are latent images? Describe the discovery of
the latent image by Daguerre. By Fox Talbot.
º 8. Describe the process involved in making a daguerreo-
res type.
9. Why must these be held at a particular angle in order
to see the picture clearly?
lC). How do you account for the fact that the resulting
picture is a positive while the other processes in-
volving the silver halides usually yield negatives?
ll. How might we define a positive and a negative?
l2. How did Fox Talbot make positive prints?
l:5. To what extent do you think that there is danger
that too much science in photography may interfere
With art, 2 --
ll. What does J. Dudley Thompson mean when he refers to
"those who can really see a picture"?
15. The vogue of the daguerreotype lasted only for a dec-
ade or two. How do you account for the fact that
this process, which had much to commend it, fell so
rapidly into disuse?
l. The questions following each chapter are intended to serve two
purposes, to summarize the factual material and to provoke
thought. The student is urged to consider each carefully.


Chapter | |
MAK 1 N G A PRINT
As the making of a print is the final step in
the photographic process, it might seem that it would be
more logical to consider first the making of the nega-
tive. Certain practical advantages result, however,
from considering the print first. Repeated trials can
be made more rapidly and with less expense and a careful
comparison of the results obtained is likely to reveal
more to the novice from the examination of prints by re-
flected light than of films by transmitted light. More-
over, since paper and film emulsions have very similar
fundamental characteristics, it will be found that all
that can be learned from a preliminary study of the prob-
lem of print-making will be extremely helpful in nega-
tive-making as well.
At the outset it is well to emphasize that photo-
graphic processes involve so many variable factors that
a rigorous, scientific series of tests is likely to ad-
vance the novice much faster than will a much larger
amount of random experimenting. The essenge of the sci-
entific method as applied here consists in the systemat-
ic study of one of the variables at a time while the *
others are held as nearly constant as possible. A sys-
tematic series of tests made to answer clearly formu-
lated questions is likely to leave the student with a
more sustained interest and a general sense of compre-
hension of the photographic technic than can be obtained
in a more desultory way by many times as much random ex-
perimenting.
Moreover, while the kind of photographic inves-
tigations that are carried on in research laboratories
frequently require very elaborate equipment and highly
developed technic, those things that the novice needs to
learn in order to make skillful use of photography as a
medium of artistic or scientific expression require
#.
3.i
- --
F.j
l
-f
i.
18
º

MAKING A PRINT 19
§
º
little in the way of equipment that is not easily obtain-
able. The most essential requirement would appear to be
an attitude of mind that will contribute care, thorough-
ness, and a very considerable amount of capacity for
taking pains. Fortified by the possession of these and
guided by a systematic plan, it seems almost certain
that the novice can travel steadily in the direction of
real proficiency with much enjoyment and satisfaction to
himself and with a minimum of discouragement and lost
time.
Photographic Papers. Photographic paper's fall
into three general classes, chloride, bromide, and
chloro-bromide, according to the silver salt used in
their manufacture. Those used for contact printing are
the slow or chloride papers while the faster bromide pa_
pers are used for enlarging. Chloro-bromide papers are
intermediate in speed and are used for both purposes.
The precise color and contrast of chloro-bromide papers
can be modified somewhat by the treatment given them dur-
ing development and they are often preferred by experi-
enced photographers on this account. These characteris–
tics, however, make them somewhat erratic in inexperi-
enced hands so the novice is likely to find it advisable
to confine his attentions to chloride and bromide papers
until he is thoroughly competent with them.
If the silver salts were coated directly on the
paper Stock, they would have a tendency to sink into the
paper making a dead, flat image or to form crystalline
aggregates here and there resulting in an uneven distri-
bution of the light-sensitive material. By holding them
in Suspension in a colloid such as gelatine and coating.
the paper with the combination, it is possible to obtain
an extremely finely divided and uniform distribution
Overlaid on the surface of the paper. When such paper
is exposed to light through a negative, a very wonderful
and mysterious, though invisible, change occurs. In re-
gions where the negative is dark, relatively few parti-
cles are affected while many are affected in the lighter
parts. In the developer, these particles become reduced
to black, metallic silver while the remainder of the
Silver salt remains unaffected. The image can then be

2O FIRST COLLEGE COURSE IN PHOTOGRAPHY
clearly seen under the darkroom light. If such a print
were exposed to white light while still soaked with de-
veloper, it would immediately begin to blacken all over
as the light would produce the latent image change in
the silver salt that had previously been unaffected and
the developer would reduce it. Even if such a print
were carefully washed to remove the developer before ex-
posing it to white light, the image would not be perma-
nent for these silver salts gradually blacken on pro-
longed exposure to light even without the action of the
developer. As a result a fixing bath must be used im—
mediately after development to dissolve the silver salts
that have not been affected by the light without impair–
ing the reduced silver image. Finally, the print must
be thoroughly washed to remove the developer and fixing
bath. The print then consists of an image in metallic
Silver imbedded in the gelatine coating on the paper
base.
Gradation. The technical excellence of a print
is determined very largely by its range of tone or gra-
dation. By range of tone we refer to the varying grays
of the silver deposit imbedded in the gelatine coating
of the paper after development. This may extend all the
Way from the faintest distinguishable gray to deep black.
With Superior negatives, paper and developing technic,
the print is likely to include a large number of inter-
mediate tones as well. With faulty technic, poor nega-
tives or a Wrong choice of paper, the number of grays
is greatly reduced with a corresponding diminution of
that intangible factor known as print quality. In the
object photographed the number of tones might easily be
infinite. In ordinary photography, the tone differentia–
tion of the object is first enormously reduced by the
loss of color in rendering our subject in monochrome. It
is then further reduced by the limitations of the nega-
tive for no negative material is capable of rendering
the entire brightness range of a subject such as a land-
Scape that includes both bright sky light and deep shad—
OWs. The range of tone is again reduced because the num-
ber of grays that can be distinguished in the print by
reflected light is much smaller than the number that can
be distinguished in the negative by transmitted light.
º
ă
º
#
º
:
Fº
ºj
MAKING A PRINT 21
Thus, it frequently happens that the indefinitely large
number of tones of the object is finally rendered in the
print by Such a limited number of tones that the observ —
er is likely to be vaguely dissatisfied with it without ,
perhaps, fully realizing what is the matter. Just as it
is possible to play a recognizable, melody on a single
String Stretched taut on a laboratory sonometer, so it
is possible to make a photographic pºint containing not
more than four or five distinguishable tones of gray;
but neither accomplishment is likely to be notable for
its artistry because of the extremely limited range with–
in which expression is possible.
Contrast and Density. While professional pho-
tographers, particularly when working under controllable
light conditions in a studio, can standardize negative
quality, most other negatives from which acceptable
prints can be made vary so much both in contrast and
density that manufacturers supply their papers in vari-
ous contrasts to suit the needs of different kinds of
negatives. By the term "contrast" we refer to the range
of tones present in the negative or print. When this ex-
tends all the way from extremely light to extremely dark
tones, We Speak of the negative as high in contrast ––
contrasty or hard. When the range of tones used is only
part of the range which the material is capable of render–
ing, as from light to medium gray or from medium gray to
black, We Speak of it as low in contrast –-flat or soft.
Quite obviously, the tones of the subject itself might
be limited in range so that there is no reason to assume
that the full range of tones would necessarily be found
in every satisfactory negative.
Density is a measure of the light-transmitting
power of the negative; one in which the predominating
tones are the darker grays would be considered dense,
while one predominantly in lighter gray's Would be C On-
sidered thin. The denser the negative, the longer the
time required to print it. Several other reasons, to be
considered later, will show why dense negatives should
be avoided. It Will be sufficient now to State that
both very dense and very thin negatives present difficul—
ties in printing that make them undesirable. It should


22 FIRST COLLEGE COURSE IN PHOTOGRAPHY
be noted, perhaps, that contrast &nd Čensity 37°e not mu-
tually exclusive terms and that both dense flat, and
thin contrasty negatives are frequently seen. If its
range of tone extends from a medium gray to a dark gray,
a negative would be flat just as would one whose range
of tone extended from light gray to medium gray for both
lack contrast because they are using considerably less
than the total range of tones that the negative material
can render. Thin, contrasty negatives would be those
that contain some dark portions and some extremely light
portions but whose predominating tones are among the
lighter grays. -
The Contrast of Photographic Papers.
Printing papers are manufactured in different degrees of
contrast so that it is possible to select a paper that
will increase or decrease the contrast in the print if
the negative contrast is not exactly what is desired. A
normal negative may be defined as one that reproduces -
the range of tone of the original subject as completely
and accurately as the negative material is capable of
doing it. A print from such a negative should, there —
fore, be made on normal paper; that is, on paper that
will reproduce as exactly as possible the tone range of
the negative. It sometimes happens, however, because of
slight errors in exposure, development, or lighting,
that the negative compresses the tone range of the Orig-
inal so that a print on normal paper Will lack brillian-
CY. Again, a negative may be too contrasty either
because of harsh lighting or unduly prolonged develop-
ment so that its contrasts need to be toned down by the
use of a softer paper. It should perhaps be emphasized
that there is no way known of making a print, at least
by strictly photochemical process, that will introduce
more tones than are in the negative though there may
easily be less. All that a contrast paper does is to
stretch the tone scale so that the maximum and minimum
tones are farther apart while a soft paper Compresses
them. Negatives occasionally occur that have so much
contrast that the tone range is beyond the capacity of
normal paper to print in its entirety. For such cases,
soft papers are supplied that compress the tone range.
º
º
º
#* .

MAKING A PRINT 23
º "º
On Plate II are shown prints on soft, normal
and hard papers from the same negative. With soft paper,
the tone scale of this particular negative was com—
pressed too much, the dog looks dirty and the print shows
a general lack of vigor. The print on normal paper is
more pleasing because it shows additional snap and vigor.
At the same time, the darker spots on the dog and the
harness, which were medium brown, are correctly rendered
as intermediate in tone and detail is preserved in the
White hair although it no longer looks dirty. With hard
paper, the harness, the dark shadows in the hair, and
the grass are too black while much of the white hair on
the dog's legs is blank white without detail. Moreover,
while longer printing would have introduced detail into
this white hair, it could have done so only by making
the grass and harness, which are already too deep in
tone, darker than ever. In general, then, we can say
that that grade of paper should be selected that is just
capable of including the tone range of the negative
Within the scale that it can print. Under these Circum-
stances, the print will show very light grays, deep
blacks and a satisfactory range of intermediate tones
and is likely to have satisfactory brilliancy. Too hard
a paper, on the other hand will crowd some of the tones
toward the lighter or darker end of the scale producing
the effect known as "soot and white-wash." Too soft a
paper Will produce a somewhat drab tone range running,
possibly, from very light gray to medium gray.
In the above discussion, it has been as Sumed
that the range of light values in the subject is consid—
erable. That this is not necessarily the case will be
realized when we consider subjects such as flowers or
portraits in high key but it can always be said that a
normal paper should be used when we wish to reproduce
the tone scale of the negative, soft paper to compress
it and hard paper to extend it.
Sensit Ometric Tests of Photographic Materials.
While We can gain a certain amount of information re-
garding the differences in soft, normal and hard papers
by a study of comparative prints, much more can be
learned from a study of sensitometric strips such as are
reproduced below each print in Plate II. By sensitome–
try is meant the controlled determination by quantita-
tive methods of the responses of photographic materials
No. 1 Paper (Soft) No. 2 Paper (Normal) No. 4 Paper (Hard)
PLATE I
Effect of Printing the Same Negative on Soft, Normal and Hard Papers.
Note the following.
The decrease in the number of tones on the sensitometric
strips as the papers increase in contrast.
The increase in exposure necessary to produce the minimum
tone with the more contrasty papers.
The difference in the tone rendering of the white and med-
ium brown on the dog's coat with the three papers.
| 7 || || 7 || 7 || 7 || 7 || 7 || 7 º' Yº Yº Yº


:
:
:
º-
MAKING A PRINT 25
to light. Those with which the practical photographer
is most likely to be concerned are response to exposure,
response to development and graininess. In making Such
tests, pieces of the materials to be investigated are
given a series of known exposures under carefully con-
trolled and reproducible conditions. In research lab-
oratories, the equipment for such purposes may be quite
elaborate but exposures sufficiently accurate to yield
much useful information to the practical photographer
can be made with a weak light by giving the Sensitized
material a series of graduated exposures by covering the
successive portions step by step with a piece of card-
board while the light continues to print the uncovered
portion. After carefully controlled processing, they
can be studied individually or compared.
The sensit Ometric strips below each print show
the result of printing a series of graduated exposures
on pieces of the soft, normal and hard papers used in
making the prints of the dog. The enlarger used as a
light source was raised about 50 inches above the table
and the lens stopped down until a two-second exposure On
a piece of soft paper placed in the focal plane gave a
barely distinguishable gray after development. The fol—
lowing exposures were then given to strips of soft, nor-
mal and hard papers, 2, 5, 14, 6, 8, ll, lº, 22, 50, 45,
60, 90, lz0, and l80 seconds. All were given identical
processing. This exposure range is satisfactory because
it gives tones from the minimum to the maximum on all
the papers considered. Moreover, these exposure times
are in approximate geometrical progression which means
that any succession of exposures on one paper can be com-
pared with a similar succession on another regardless of
Whether they represent the same exposure times or not.
The series is a geometrical progression because each ex-
posure is obtained from the one preceding by multiplying
the latter by V2, taking the nearest integer in each
Case Since the decimal parts of a second would be mean-
ingle SS under the conditions of time measurement used
here. With every second term the exposure doubles. An—
Other factor could have been used but this one is par-
ticularly satisfactory because it makes each step on the
gray Scale clearly distinguishable from those adjacent
to it and still makes the increments of gray quite small.

26 FIRST COLLEGE COURSE IN PHOTOGRAPHY
It is not, of course, implied that the tones given rep-
resent all that a paper can render but we do Consider
that this total number will be proportional to the num-
ber of tones given on each strip. The following table
is a summary of what we can learn by a comparison of
these strips.

T TI III TV
Exposure Exposure Number of Ratio
Paper for Minimum for Maximum | Distinguish- E /E i
Gray, Emin. Gray, Emax. able Tones Iſla. X. e. f "Iſll Iſle
SOft, 2 seconds. 120 seconds l3 6O
Normal 6 " L2O t? LO 2O
Hard 3O !! 18O f : 6 6
We note the following:
l. The number of distinguishable tones diminishes as the
paper gets harder. The number of tones shown on each strip is not
all that the paper can render, of course, but a comparison of the
number shown for each makes possible an inference regarding the
Telative number attainable with each. Soft papers are capable of
rendering the greatest number of tones and are therefore desirable
whenever negative contrast is sufficient to yield a print of the
desired brilliancy. *
2. The exposure to render minimum gray increases as the pa-
per increases in contrast.
3. The exposure to render. maximum gray also increases but
not so rapidly as that for minimum gray. This is equivalent to
saying that hard paper passes from gray to black more rapidly than
soft paper. Contrasty papers do not, in general, render as many
tones as softer papers so their use should be avoided unless the
negative requires them to produce a print of the desired brillian-
Cy .
li. Column IV gives the exposure range for different papers
or the number of times the minimum exposure that is necessary to
give black. This is equivalent to saying that the hard paper will
print black when the exposure is only six times that for minimum
gray or that a negative will print the entire tone range on hard
paper when the maximum density is only six times the minimum. On
the other hand, the soft paper will not do so unless the maximum
density is sixty times the minimum.

2. A.º
º
º
§
MAKING A PRINT 27
The Color of the Silver Deposit. All who have
worked with metals in a very finely divided State, par-
ticularly when this state has been brought about by
chemical processes, are aware that there can be consid—
erable variation in the precise color, or shade, of the
deposit as the physical or chemical conditions governing
its formation vary slightly. It is not surprising,
therefore, that noticeable variations in the basic color
of the photographic image are found. The blacks range
all the way from a deep pure black, sometimes referred
to as a "blue black," through the olive blacks to those
that are distinctly brownish in tone. It is inadvisable
to be arbitrary in designating which is the best basic
tone as much depends upon the color of the paper Stock,
the character of the subject, the paper and developer
used; but a critical examination will show that many
prints suffer from a general degradation of tone that
makes them disappointing and unsatisfactory examples,
whatever the basic color sought may have been.
The following elements all contribute to the de-
velopment of satisfactory tone values. It is always
Wisest to use the developing formula recommended by the
manufacturer of the paper. Developing formulas vary
considerably in the proportions of the fundamental Con-
stituents and as each manufacturer has made Very large
numbers of carefully controlled tests of his product, he
is likely to know which developer Will produce the best
results on his paper. For satisfactory tone values, it
is also important that the developer and paper should be
fresh. It should be remembered also that development is
a chemical process that results in the decomposition of
the developer itself as print after print is made and in
the accumulation of decomposition products that retard
the rate of development. Among other results, both of
these factors retard the velocity of development and
exert an appreciable effect upon the tone of the finished
print. Another influence that changes the velocity of
development is the temperature of the developing solu-
tion, with a consequent possible change in tone. It is ,
therefore, most important to be sure that the tempera–
ture of the developer remains at all times within a de-
gree or two of 70 degrees F.

28 FIRST COLLEGE COURSE IN PHOTOGRAPHY
As one gains experience with a given paper and
developer, it is possible to learn how many prints may
be made With a certain portion of developer ; but , lack-
ing that experience, there are at least two Ways that
one may realize when the developer has reached the point
at which it is advisable to discard it. First, the rate
of development becomes noticeably slower as the develop.–
er deteriorates and it should be emphasized that increas—
ing the developing time does not provide perfect compen-
sation--a deteriorated developer always gives inferior
shadow detail. In the second place, the developer shows
definite discoloration as socn as deterioration is seri–
ous. When either or both of these effects are noticed,
the developer should be discarded, and a new portion
prepared . It is better to take a new portion of develop-
er than to add new solution to the old, as the accumula-
tion of decomposition products in the old is likely to
have a detrimental effect upon the action of new develop-
erº .
Still another cause of degraded tones in prints
is to be found in the attempt to minimize the effect of
overeexposure by shortening the time of development. While
it is true that slight errors in exposure can be compen-
Sated for by variations in developing time, this is pos–
Sible only within rather narrow limits without impair–
ment of tone, and should be resorted to only after a
faithful serving of an apprenticeship devoted to a strict
adherence to the manufacturer 's instructions. Then it
is possible to increase the contrast of a paper by a
slight decrease in exposure and a slight increase in de-
Veloping time, and to decrease it by lengthening expo-
Sure and shortening development. The student is advised,
however, not to complicate his investigations by varying
developing time until he has thoroughly mastered the
standard process under the following carefully controlled
conditions: fresh developer compounded according to the
paper manufacturer's formula, temperature within a de-
gree or two of 70 degrees Fahrenheit; and development
for the time recommended.
MAKING A PRINT 29
10.
ll.
l2.
l3.
l!.
lº.
16.
17.
l8.
l9.
20.
QUESTIONS
. What is the distinction between a novice and an
amateur 2
. What is the function of the developer?
. What is the function of the fixing bath?
. Describe the appearance of a print after development
if it were exposed long enough to cause all the Sil-
ver halide to undergo the latent image change.
How long should prints remain in the fixing bath be—
fore exposing them to white light?
. Describe the appearance of a thin, flat negative. A
dense flat negative. A thin contrasty negative. A
dense contrasty negative.
. Distinguish between contrast and density.
Why is the use of unnecessarily contrasty paper in-
advisable 2
Classify printing paper's according to the light-
Sensitive Salt, used in their manufacture.
Compare the speeds of these papers.
How may the contrast of a given paper be slightly
increased or decreased?
If a negative represented the whole tone range that
normal paper could render, what would be the effect
of printing it on hard paper?
What would be the effect of printing it on soft pa-
per?
Under what conditions is it advisable to use a paper
that will stretch the tone range?
Under what conditions is it advisable to use a paper
that will compress the tone range?
What is meant by gradation?
Can you observe any differences in the blacks ren-
dered by the soft, normal or hard papers on the
sensitometric strips on Plate II? Why do prints on
Soft paper sometimes lack really black tones?
Close examination of the series of graduated grays
On a sensitometric strip will show that the edge of
a lighter shade adjacent to a darker shade appears
lighter than the rest of the same area. Is this an
optical illusion or is it really true?
Why is it inadvisable to replenish exhausted develop –
er by adding fresh to it in making prints?
How is it possible to tell when the developer is be –
coming exhausted? The fixing bath?

Chapter | | |
[i.
F | LMS AND THE | R PROCESS IN G
- º
Gelatine has certain peculiar characteristic S ºf
very valuable for photographic purposes that we shall
next consider briefly. In the first place, it has the sº.
property of being able to dissolve large amounts of Cold
water which causes it to swell and become a jelly-like ſº
Solid without entering the liquid state. In warm Water, .*
however, gelatine appears to dissolve in Water and upon ºil.
Standing and cooling, Will set as a jelly, the final * .
consistency depending upon the relative amounts of gela— §
tine and water. When relatively small amounts of gela—
tine are used, the final product is the kind of jelly g |
familiar to all in gelatine desserts, but with larger
amounts of gelatine, it first sets as a jelly and then
dries out to form a hard, horn-like solid. This is the
concentration used in coating photographic films and
this form when immersed in the developing solutions m
takes up water again and increases somewhat in thickness.
There is undoubted increase in volume but the peculiar º
thing about it is that this is largely upward from the
Surface and only slightly laterally so that there is lit – Eºm
tle distortion of the photographic image. Such an image
appears nearly the same on a wet film and a dry one and
On drying, the gelatine shrinks back into its original
|position.
§
i.
If the solutions differ considerably in tempera-
ture, the Swelling of the gelatine may be so excessive Prº-
that it is not able to contract evenly in drying and {
leaves a surface showing minute wrinkles or ridges which .
ruin the negative as they are reproduced in printing.
This is known as reticulation and can be avoided by keep-
ing the temperature of all solutions approximately the
same and, preferably, between 65 and 70 degrees F. As a *
matter of fact, moderate swelling of the gelatine is nec – º
essary if the developer and fixing bath are to find their sº
Way to the Silver halide particles and do their work but º
sº
sº

FILMS AND THEIR PROCESSING 3]
it cannot become excessive without serious impairment of
the final result.
In tropical countries films may be hardened by
soaking in a formalin solution after developing and fix-
ing which so hardens the gelatine that it can be dried
by artificial heat. It is sometimes recommended that
the film be given a hardening in this way before develop-
ment but there is apparently danger that such a proced-
ure may so impede the developing process as to be unde-
sirable. Sodium sulphate may be added to the developer
that must be used at a high temperature and tends to les-
Sen the excessive swelling of the gelatine.
Gelatine serves several purposes in the photo-
graphic emulsion. As has already been mentioned, it
makes it possible to obtain an extremely fine-grained
and uniform distribution of the silver salts that will
produce a satisfactory image.
Experiment. Dissolve 5 grams of sodium chloride
in 100 cubic centimeters of water and 5 grams silver ni-
trate in a similar amount. Precipitate silver chloride
by mixing half of the two solutions which will form a
coarse, curd-like precipitate that soon begins to settle
Out in the bottom of the flask.
Next prepare a gelatine solution by dissolving
2 grams of gelatine in 200 cc. of Warm water, add the
remainder of the sodium chloride solution and, finally,
the silver nitrate solution. Note the finely divided
state of the precipitated silver chloride and that it re-
mains in suspension.
Apparently, however, gelatine serves other pur-
poses as well. One of these is to act as a sort of pro-
tective colloid to prevent the developer from acting
upon silver halide that has not been exposed to light.
It has been shown that the silver halides prepared with-
out exposure to light in solutions without gelatine are
completely reduced to silver by a developer. It is also
evident that the gelatine itself plays a part in deter-
mining the sensitivity of the emulsion as emulsions have
been prepared identical in every way except in the gela-
tine used that show marked differences in sensitivity to


32 FIRST COLLEGE COURSE IN PHOTOGRAPHY
light. This appears to be due to the presence in the
gelatine of minute traces of substances that either form
nuclei around which development starts or else act as
catalytic agents to start development without actually
participating in it. It can thus be said that the gela-
tine itself is something more than a mere inert carrier
for the silver halide and it is known that the precise
treatment given to the gelatine in making an emulsion
has a very marked influence upon its sensitivity.
Manufacture of Photographic Films. The exact
details of manufacture of photographic materials are
likely to be carefully guarded trade secrets but the fol—
lowing steps may be considered typical. The first step
consists in dissolving the required soluble halides in
a gelatine solution in the liquid State. Usually only a
part of the required gelatine is used here and the cal-
culated amount of silver nitrate is added which forms a
creamy suspension of silver halide in gelatine.
KBr + AgNO3 = AgBr + KNO3
The emulsion is next subjected to a process called ripen-
ing which produces a marked increase in the sensitivity
of the emulsion. This process consists in allowing the
emulsion to Stand at a particular temperature, often a
fairly high temperature, for a definite time and sensi–
tivity may also be increased by the addition of ammonia
at this point. The soluble salts shown in the equation
above have a detrimental effect upon the emulsion and
must be removed. The emulsion is, therefore, allowed to
set after ripening which causes it to assume the jelly-
like state. It can then be shredded by forcing it
through fine perforations in the bottom of a press after
which it is washed thoroughly with cold water to remove
the soluble salts. It may be allowed to stand for fur-
ther ripening after washing and is then heated and com-
bined with enough more gelatine before coating the film
to make it assume the horn-like consistency after it
sets. After the coating is done, conveyers carry the
long Strips of film into a cooler where the gelatine
Sets and then into a drying room where the film remains
until the gelatine assumes the hard, horn-like state of
finished film. It is finally cut into the desired sizes

FILMS AND THEIR PROCESSING 33
|º-
i*º* -
--
|
ºº
ºf
s--º
º§
and packed in light-proof packages. It is a Curious
fact that any or all of the conditions, physical or chem-
ical, embodied in these processes may affect the final
result to such an extent that it is not only customary
to carry out the processes themselves with rigorous ac-
curacy but even the temperature, humidity, and ventila-
tion of the workrooms must be accurately controlled. *
Classification of Films According to Color Sen—
sitivity. The foregoing discussion applies particularly
to the manufacture of what is known as an ordinary film,
one that is sensitive to blue and violet light but in-
creasingly insensitive to green and yellow and quite in-
sensitive to orange and red light. It will be realized
that such film cannot reproduce tone values such as the
eye sees in many cases as all red and orange objects
would appear black on the print and browns would be too
dark. It has been found, however, that certain dyes
greatly increase the sensitivity of such film to these
colors. Eosin and erythrosin dyes extend the sensitivi-
ty into the yellow green while the isocyanin and carbo-
cyanin dyes render the film sensitive to the whole visi-
ble spectrum. Films sensitive to yellow green are known
as Orthochromatic and include a large proportion of
those commonly used, as red is relatively infrequent in
occurrence in nature so that for many purposes lack of
sensitivity to it will not be missed. This lack permits
development by a red darkroom light. Films that are
Sensitive to the whole spectrum are known as panchromat –
ic. For Satisfactory rendering of red, brown, and orange
tones, their use is imperative and the tendency today
appears to be toward their use as all-purpose films as
their manufacture has now become so standardized that
emulsion characteristics are now reproduced and remain
essentially the same from batch to batch. Panchromatic
films of moderate speed are not injured by a brief ex-
posure to a dark green safe-light but the very fast ones
Should be handled in total darkness. Before the advent
of Very fast films, photographers were accustomed to
Watch the progress of development by the darkroom light
l. For a more complete discussion of film manufacture, see Photo-
graphic Journal, July, 1958, pp. 1159–1175.
PLATE | | |
Color Rendering of Different Films.
Top . Process.
Center. Orthochromatic .
Bottom. Panchromatic .
(The color of each cube is indicated by the
initial letter on its face.)
ſº
ſº
Q-
ſº
[ _
[º-
ſº-
ſº
[ -
[ _
[ -
Gº-
[ -
[T-
Cº-


FILMS AND THEIR PROCESSING 35
and to determine the precise moment by inspection wher.
development had progressed far enough. With the devel-
opment of the ultra-speed films, this procedure, which
was always rather difficult, became practically impossi-
ble and today most film developing is done in tanks by
time and temperature. Process panchromatic films are
obtainable for use when very high contrast is required.
These are much faster than ordinary process films and
are useful when the subject from which a high contrast
negative is to be made is colored rather than black and
White.
The exact reason that these dyes increase film
Sensitivity is somewhat uncertain. As would be expected,
the additional spectral sensitivity of the silver halide
lies in the same region as the absorption spectrum of
the dye but the two are not identical. Most dyes that
Sensitize are themselves light-sensitive so that it may
be that photochemical changes in the dye affect the sil-
ver halide particles. This might occur because the pho-
to chemical reaction product of the dye helps to decom-
pose the Silver halide. It is also possible that ex-
posure to light might cause the dye to emit electrons,
i.e., a photoelectric effect, and that these in turn
find their way to the silver halide particles and bring
about the latent image change. A third possibility is
that the dye might fluoresce primarily under the influ-
ence of the violet or ultra-violet light in such a way .
as to emit visible light that could help to contribute
to the latent image change.
Plate III shows the tone rendering of a set of
blocks each of which had been painted with dull mat
poster colors the color indicated by the initial letter
on its face. When photographed on process film, the
blocks representing green, yellow, orange and red all
appear Very dark because this film is not sensitive to
these colors. As a result, the images of these blocks
on the negative were abnormally light and corresponding-
ly dark in the print. The high contrast of this film is
indicated by the extreme difference in tone between the
light and dark blocks. On orthochromatic film, the yel
low and green blocks appear much lighter while the violet

36 FIRST COLLEGE COURSE IN PHOTOGRAPHY
and blue blocks remain light showing that this film gains
yellow and green sensitivity without sacrifice of its
sensitivity to blue and violet. The panchromatic film is
sensitive to all the colors as is indicated by the render-
ing of all the blocks by light tones. An effort was made
to select shades for the blocks that would be rendered
on the panchromatic film by about the same gray. In the
case of the yellow, however, this proved impractical and
would have necessitated the use of a yellow that was ab-
normally dark. Apparently, the panchromatic film Was ex-
tremely sensitive to yellow. Some panchromatic films are
rather lacking in sensitivity to green which may make
orthochromatic film a better choice when the predominating
color is green as in landscapes or for rendering the
greenish patterns of the oscillograph.
Classification of Film According to Speed. Films
may also be classified according to their speed as slow,
medium, fast and ultra-fast. Many people do not realize
that extreme speed in a photographic emulsion cannot be
obtained Without the sacrifice of other desirable char'-
acteristics so that their use should be restricted to
those occasions when poor light or extremely brief expo-
Sures necessitate their use. For general use, medium
speed films are to be preferred as they are definitely
Superior in contrast, gradation and grain. A summary of
the general characteristics of the different classes of
film is given below.
l. Slow. Such films are contrasty, fine-grained,
and short scaled. They are suitable for all kinds of
copying that does not involve so great a tone range as
to be beyond the limits of their capacity as their fine
grain renders detail very well and their high contrast
is especially satisfactory for rendering clear whites
and dense blacks.
2. Medium speed. These have somewhat less con-
trast, rather coarser grain and longer tone scale than
Slow films. They are sufficiently fast for all outdoor
Subjects not involving the problem of stopping rapid mo-
tion and produce brilliant, clean working negatives, capa-
ble of resolving fine detail.
5. Fast. Here, again, the trend is toward still
lower contrast and coarser grain with the compensating
º
*
tº
º

FILMS AND THEIR PROCESSING 37
:
i
advantage of shorter exposures that make this film use-
ful where relatively rapid motions must be stopped as
in portraiture, or in ordinary moving objects. Fast
film does not usually have the long tone scale of medium
speed film as it is not capable of producing as dense
blacks as the medium speed and its ability to resolve
fine detail is rather limited. It is therefore a good
plan to confine its use to the portrayal of Subjects
that necessitate a short exposure by poor light.
11. Ultra-fast. These fog rather easily and do
not produce as clean, brilliant negatives as Slower
films. They also show the coarsest grain and lowest
contrast, so their use should be confined to those OCC al-
sions when their great speed is needed.
Recently, very great improvements have been made
in films that combine both great speed and reasonably
fine grain but it would still appear to be true that
very great speed is obtainable only by some sacrifice of
fine grain, gradation and contrast, so that Such films
should be reserved for use on those occasions requiring
their speed. * In miniature photography, especially, the
necessary enlargement of the negative will reveal de-
fects that are not apparent in contact prints so that
advantage should be taken of the very fast lenses usual-
ly provided on this class of camera to use slower film
whenever possible.
Theory of Development. The precise mechanism of
the process of development is a highly controversial sub-
ject and it will be sufficient for our present purposes
to consider briefly only those aspects that are capable
of direct observation. If the undeveloped emulsion is
magnified about two thousand times, minute plate-like ,
translucent crystals can be observed distributed at ran–
dom in the gelatine. Often these show definite triangu–
lar or hexagonal forms and they are usually oriented
With their flat sides in the plane of the emulsion. De-
velopment has been watched under the microscope with spe-
Cially prepared, thin emulsion layers and slow developers
and it has been found that development will start at a
|particular point on a crystal which appears to act as a
Sort of nucleus for further development. Development is
2. Certain ultra-speed films have recently appeared that are rela-
tively high in contrast.


38 FIRST COLLEGE COURSE IN PHOTOGRAPHY
made evident by the appearance of a black Speck at some
such point and with the passage of time, this gradually
enlarges by the reduction of the silver bromide crystal
until the latter loses its crystal symmetry and becomes
completely transformed into black, amorphous, metallic
Silver .
Different developer's show marked variations in
the appearance of the developed silver under the micro-
scope, some producing particles with sharp, definite
outlines while others have a much less clearly defined
structure. Doubtless these differences have an effect
upon the grain of the enlarged, projected image. Al-
though the particles are far too small to be seen indi-
vidually, they show considerable tendency to gather into
clumps that may be large enough to be resolved by the
eye in enlargements of considerable size.
The silver bromide grains cannot all be equally
sensitive to light for, if they were, all would be ren-
dered developable by exposure and the film would be a
uniform expanse of black, after development. It might be
possible that differences in light intensity would be
apparent after development if the grains were all equal-
ly Sensitive and a weak light were only able to penetrate
the emulsion to a slight extent while a strong light
could affect the deeper layers. The microscope, however.
Shows that this is not the case for exposure to a weak
light produces developable crystals scattered here and
there throughout the emulsion, whose location can be de-
termined after development by examining a thin section
of the film under moderate magnification. In general,
it has been observed that the coarse grains are the most
Sensitive to light but whether there is any actual con-
nection between grain size and speed or whether they are
merely characteristics that appear together because the
conditions favoring the one also favor the other has not
been definitely proved.
Development is a process that progresses gradual-
ly through a series of more or less definite stages.
After the film has been in the developer for a period
Varying from a few seconds to a minute or two with dif-
ferent developers, the image begins to appear and soon
shows all its details. If the film should be removed
:º
----g
:--º... •-•---*>--º
---
-|---
sº
ſ.
Jº
º
ſº
Cºm
ſº
ſºm

FILMS AND THEIR PROCESSING 39
from the developer at this at age and fixed, the image
would be so thin and lacking in contrast that it would
be impossible to make a satisfactory print. As develop –
ment continues, the image is gradually built up as the
process of reducing the exposed silver bromide to silver
continues. This reduction goes faster in those parts
that have received the most exposure so that these grow
dark while the less strongly exposed parts remain rela—
tively light thus increasing the contrast. Gradually,
however, the development of the exposed grains slows up
when the number of exposed grains not yet developed
diminishes sufficiently. Meanwhile, another process
known as developer fog sets in. As development is pro-
longed, the unexposed crystals of silver bromide begin
to develop resulting in the appearance of a uniform de-
posit of developed silver superposed on the developed
image. With fresh film, a satisfactory developer, and
a normal developing time, the slight developer fog pro-
duced merely lengthens printing time slightly and does
no harm. If, however, the development is unduly pro-
longed in the effort to build up density in very thin
parts of the negative, a stage is reached in which de-
velopment of exposed silver bromide has become very slow
While development of unexposed particles is accelerating
When this stage is reached, it is useless to carry de-
velopment farther for from this point, developer fog
Will be contributing more to the image than will the un-
developed, exposed grains and a definite impairment of
negative quality will result.
- Constituents of a Developing Solution. In gen-
eral, a developing solution consists of four distinct
elements, the developer, the activator, the preservative,
and the restrainer. Occasionally, satisfactory develop-
ers are found that lack one or more of these but by far
the greater number include all of them. The developer
must be a Weak reducing agent for if too strong, it would
reduce the unexposed silver halide as well as the ex-
posed. It must not produce undesirable reduction prod–
ucts such as disagreeable fumes, precipitates, or any-
thing detrimental to the gelatine or image. It is very
desirable that it should have good keeping qualities and,
above all, it must be capable of producing a developed
image that will make a satisfactory print.


|O FIRST COLLEGE COURSE IN PHOTOGRAPHY
Since all developer's are unstable and C&pable of
being oxidized by the oxygen of the air, a preservative
is added in excess that is even more readily Oxidized
than the developer. Sodium sulphite is ordinarily used
and is gradually converted into sulphate in the presence
of any oxygen that may be present. The developer is
thus protected from deterioration by similar oxidation.
Experiment. Dissolve about 10 gm. of sodium car-
bonate in 100 cc. of water and add l gm. of hydroquinone.
The solution will immediately begin to turn brown because
there is no sulphite present to protect the alkaline so-
lution of the developer from oxidation by the air. Dis–
solve l gm. of hydroquinone in Water. Little or no di S-
Coloration Will be observed .
The foregoing experiment indicates that a de-
veloper in alkaline solution is much more easily oxidized
than one dissolved in Water alone. In fact, most devel-
opers have little or no developing action unless the so-
lution is alkaline which appears to be due to the fact
that the developer itself is only slightly ionized in So-
lution and is converted by the activator into a much
more highly ionized and active form. The activator most
commonly used is sodium carbonate. Potassium carbonate
has very similar characteristics but is rarely used as
it is considerably more expensive. Developers for build-
ing up very high contrast occasionally contain either so-
dium or potassium hydroxide. Developer's containing am—
monium hydroxide are fast and energetic but their use is
generally confined to color plates or other processes in
Which the original negative is converted into a positive.
The activity of such developer's varies noticeably with a
Change in the concentration of the ammonium hydroxide
and as this can evaporate from the solution, results are
Somewhat uncertain. Borax is also extensively used as
the activator in developers producing moderately fine
grain and Such developers have good keeping qualities.
The last constituent of the developer is the re-
Strainer, potassium bromide. Small amounts of potassium
bromide in a developer produce very marked differences
in the velocity with which a developer acts. Its most
important effect is to retard the tendency of developers
FILMS AND THEIR PROCESSING || 1
already noted to produce developer fog. In the case of
prints, the amount of potassium bromide used is rather
critical as too little will result in grayish White S and
too much is likely to produce greenish blacks, and to
impair gradation by making the prints more contrasty.
The effect of potassium bromide upon sensitometric
strips that receive identical exposures is marked. If
one is developed in developer without bromide, it will
show that even the unexposed portion of the paper is
a medium gray from developer fog and indicates that it
would be impossible to make a satisfactory print with such
such developer. If another strip is developed in devel-
oper containing 4 grams of bromide per liter, the min-
jimum amount recommended by the manufacturer of the pa-
per , a very satisfactory range of tones Will be obtained.
and the unexposed paper remains white. If a third strip
is developed in developer containing lº grams of bromide
per liter, not quite as many tones are rendered
as in the second case indicating beyond a doubt that
the minimum amount of bromide that Will keep the unex–
posed portions of the paper white is to be preferred.
The contrast of the paper was slightly greater with more
bromide in the developer as this sensit ometric strip
showed a smaller number of tones than the others. Just
what the action of the potassium bromide is , is rather
obscure. It has been suggested that the presence of a
common ion, Brit, in silver bromide and potassium bromide
may tend to repress the ionization of the less highly
ionized compound, silver bromide, so that more of it is
present in the molecular state. As a result, the tend—
ency of the unexposed halide to develop is retarded and
developer fog is greatly reduced. Apparently, however,
this simple explanation does not account completely for
the observed effects. *
Factors Affecting Development. Among the fac-
tors that affect development, a very important one is
temperature. It is a well-known general principle that
the velocity of many reactions is increased with a rise
in temperature. This is true of development. As a
3. Nietz. Theory of Development. Monograph Number 2, Eastman Ko-
dak Company, p. 160.

DEVELOPED II MINUTES Iº MINUTES 36 MINUTES
Negatives developed in D-76 at 68°F.
Panatomic-X film.
Exposure 1/25 second at f/6.3.
Dull daylight. 9 A.M.
Note the growth in density and in contrast
with increased development. -
Prints from the above negatives.
Velour Black #33 developed in D-55 at 70°F.
Developing time of prints 90 seconds.
Negative #1 Printed 10 seconds.
Negative #2 Printed 20 seconds.
Negative #3 Printed 40 seconds.
PLATE I W
Effect of an Increase in Developing Time
upon Identical Exposures.


FILMS AND THEIR PROCESSING l! 3
general rule, however, it is better to keep the tempera-
ture between 65°F. and 68°F. for film and between 70°F.
and 72°F. for paper. At higher temperatures, the gela—
tine tends to become too soft for safety and developer
fog appears more rapidly. On the other hand, hydroqui-
none becomes almost inactive below 60°F. so it is essen-
tial not to allow developers containing this to become
too cold. Other developer's act more slowly if too cold
and thus increase the danger of under development.
Another factor that has a very marked effect
upon the quality of the negative is the time of develop-
ment . This varies Within Wide limit, S With different de –
veloper's but with all, development passes through the
same series of stages. There is first a preliminary
stage in which the developer is penetrating the emulsion.
Then, the image begins to appear. As time goes on, the
image increases not only in density as more and more sil-
ver Salt is reduced but also in contrast, because the
more strongly exposed portions develop more rapidly than
those receiving less exposure. Plate TV shows the ap-
pearance of three negatives made from identical exposures
that were developed for ll, 18 and 56 minutes respective-
ly in D-76, a developer for which l8 minutes would be
considered the normal time. As the developing time in-
creases, the silver deposit grows denser, as would be
expected. What is also true, although not quite so ob-
vious, is that the lighter tones are not increasing in
density nearly as fast as the darker tones. As a re-
Sult, the negatives that received longer development
Show more contrast. A more definite idea of the rela—
tive densities of the three negatives may be obtained by
noting the times required to make the prints from them
shown in Plate IV . Note, also, the increase in the
Contrast in the child's face and the cat in the prints
from the negatives that had longer development.
Fresh film and development at least within a few
days of exposure insure a minimum of developer fog and
the best gradation. In tray development it is customary
to rock the tray back and forth in order to remove the
reaction products from the surface of the emulsion and
keep 1t bathed with fresh developer. In small tanks,
the same result can be attained by shaking it frequently

l; l. FIRST COLLEGE COURSE IN PHOTOGRAPHY
or by various types of mechanical agitators. Best re-
sults are attained when these act rather gently. Th9,t
agitation during development is important is shown by
the fact that identical exposures developed with and
Without it can be distinguished by the fact that the one
receiving agitation shows appreciably greater density.
As it is rather puzzling for the novice to de-
cide whether or not his negatives have been developed to
the most satisfactory density, the appearance of the
negatives on Plate IV by strong transmitted light
should be studied carefully. In a portrait, skin tex-
ture is rendered best if the negative is not too thin.
On the other hand, retouching cannot be satisfactorily
done unless the negative transmits sufficient light with
moderate illumination so that fine detail Can be seen in
the negative on the retouching stand. In general, nega-
tives that are thinner Or denser than those ShoWn. On
Plate VI do not have entirely satisfactory printing qual-
ity.
The Chemical Nature of Photographic Developers.
Nearly all the developers in common use are derivatives
of benzene or naphthalene and it is a curious fact that
compounds having identical percentage compositions exist,
one of which will be a developer and another entirely
lacking in developing power.
Most of the developers used are ortho- or paradi-
amines, diphenols or amino-phenols. A Summary of empir–
ical rules derived many years ago regarding which com—
pounds may be expected to have developing power is given
by Nietz. * These were first stated by the Lumiere
brothers and Seyewitz and while subject to some excep-
tions in the light of knowledge subsequently gained,
Still form an interesting summary.
We shall next consider the distinguishing char–
acteristics of the developer's most commonly used.
Metol. This is a fast-working developer that
builds up an image full of detail but somewhat lacking
lº. Nietz. Theory of Development. Pages 17–18.
FILMS AND THEIR PROCESSING | B
in contrast. As a result it is usually combined in the
developing solution With hydroquinone. Other names
for this developer are Elon and Rhodol.
Hydroquinone. Ordinarily this developer is much
slower in action than elon. Its outstanding character-
istic is the ability to produce negatives having very
vigorous contrast though somewhat lacking in gradation.
In combination with elon, the latter supplies the fine
detail &nd hydroquinone , the vigorous contrast . They
Work well together and have excellent keeping qualities
in full well-stoppered bottles. It should be noted that
hydroquinone loses most of its developing power below
60 degrees Fahrenheit so it is essential not to attempt
to use developers containing it below 65 degrees.
Pyrogallol. This is one of the earliest de-
velopers working in alkaline solution and gives very
good gradation and contrast. The negatives are usually
stained slightly brown which improves their printing
quality. Pyro developer's oxidize rapidly when exposed
to air and are generally used only for tank development
as they stain the hands badly.
Amidol. Amidol is unusual in that it makes a
satisfactory developing solution without alkali which
makes it desirable for use in hot climates as the alkali
in ordinary developers shows a marked tendency to soften
the gelatine excessively when the temperature is high.
It also finds extensive use in the development of lan-
tern slides and bromide enlargements as it builds up the
image rather gradually, thus allowing time to judge it
Carefully, gives a good tone, and does not stain readily.
Amidol developers are usually mixed when wanted for im–
mediate use as it does not keep well in solution.
Glycin. Glycin produces rather fine grain and
is usually used in combination with para-phenylene-
diamine as the two work well together to produce an image
Of exceptionally fine grain and good contrast.
Para-phenylene diamine. This developer has been
known for years but was not regarded as of practical


|6 FIRST COLLEGE COURSE IN PHOTOGRAPHY
importance because when used alone it is excessively
slow and produces images too low in contrast to be prac-
tical. Recently, however, it has been combined with
glycin and combinations of the two are probably more ex-
tensively used at present than any other developers to
produce the fine grain required in miniature photography.
The following summary of scientific names and
Structural formulas Will be of interest to student S of
organic chemistry.
- OH
Metol is the Sulphate of Metol
para-methylaminophenol
CeH4(OH) (NH) (CH3) ^- NH-CH3
Para-methylaminophenol
Hydroquinone
20H S
Para-dioxybenzene |
CeH4(OH)2 H H
NOH (
Pyrogallol
OH S
H OH
Adjacent tri-hydroxybenzene | |
CeBa(OH)3 º H OH
- > H 2-
Amidol
2" OH N
H NH2
Di-amido-phenol hydrochloride | | + HCl
CeHa(OH) (NH2)22 HC1 HS H
2.
NHe
Glycin
2 OH S
Para-oxy-phenyl-glycin H H
CeH4OH.NH.CH2. COOH # |
N 2-’
NH.CH2. COOH
-
w-ºw-
-----,------ ---
[...
{Tº
º
Jº
ſº
Fº
Frºm

FILMS AND THEIR PROCESSING ||7
Para-phenylene Diamine
CeH4(NH2)2 n h |
Tables are available indicating the exact de-
veloping time for all practical temperatures and strict
adherence to these is likely to yield negatives of Sat-
isfactory quality. The question arises whether under-
exposure, normal and overexposures should all receive
the same development. Careful experiment, S have indicat-
ed that this is the case and that the development that
is best for a normal exposure will bring out as much as
possible in an over or underexposure.
Another rather curious method of development, now
little used except for the reversal processes with color
film is the Watkins factorial method. According to this,
one determines the elapsed time until the first appear-
ance of the image disregarding the sky and then gives
the negative a total developing time equal to this
amount multiplied by some factor that is characteristic
of the developer and film used. This factor is deter-
mined by previous experiments or from the published
data. This method yields negatives of exceptionally uni-
form quality provided the film is sufficiently slow to
permit light enough for observation but is obviously un-
suitable for ultra-speed films or for tank development.
In conclusion, it cannot be emphasized too much
that the negative is the key to the whole photographic
process. Because of the variety of papers available,
photographers are sometimes tempted to be rather care —
le SS about negative-making and to rely upon the choice
of the printing paper to annul any defects in the con–
trast of the negative. As a matter of fact, negative de-
fects inevitably result in a loss of print quality and
While it is true that a poor negative will yield a fair
print in competent hands, the same hands could make a
Superlative print from a really first-rate negative. The
student is therefore urged to make every possible effort


||8 FIRST COLLEGE COURSE IN PHOTOGRAPHY
to master the technic of the developing process, to Cul-
tivate great capacity for taking pains and to under-
stand all the contributing factors. In many respects
the negative is far more subject to control than the
print and print-making assumes the proportions of a
pleasant pastime rather than an anxious struggle as soon
as one has mastered the art and science of making really
acceptable negatives.
QUESTIONS
l. Discuss the characteristics of gelatine.
. What causes reticulation?
3. Describe methods for preventing excessive swelling
of gelatine when it is necessary to develop at high
temperatures.
. Describe the manufacture of photographic emulsions.
5. Discuss the classification of films according to
color sensitivity.
6. Discuss the various hypotheses to account for dye
Sensitizing.
7. Under what conditions might an orthochromatic film
be preferable to a panchromatic 2
. Discuss Plate III,
. Discuss the classification of films according to
Speed.
10. Discuss the uses and abuses of ultra-speed films.
ll. Discuss the theory of development.
12. What is developer fog? How do we keep it reduced to
a minimum?
lº. Name the constituents of a developing solution and
discuss the use of each.
l!. Discuss Plate IV.
15. Discuss the effect of temperature upon development.
16. Why is photographic work diſficult in the tropics?
17. Why is agitation desirable during development?
2
|
:
18. Discuss the various methods of development and indi-
cate the advantages of each.
l9. Describe the characteristics of metol, hydroquinone,
pyrogallol, amidol, para-phenylene diamine, and gly-
Cine.
For students of organic chemistry.
20. Discuss the chemical constitution of the above de-
velopers. -
i. _{
Chapter | W
CAMERAS
In this chapter we shall consider the various
types of cameras in common use. It may be said that all
of these have their good points and their limitations
and it should be realized that the selection of one in
preference to another is finally determined not so much
by reference to an absolute standard of perfection as by
the personal preferences of the individual who is making
the choice. It is therefore advisable not to go hastily
into the selection of a camera but , rather, to make a
careful study of all the kinds available and then to
choose the one that seems to coincide most nearly With
one's own ideas. The right camera is likely to become a
very helpful companion; the wrong one is apt to prove a
calculating adversary who will defeat one if it can.
It is well to remember that the more a Camera
can do, the greater the skill demanded of the operator
to make it do it, so the very beautiful instruments of
precision that are capable of nearly anything are not
for novices. Rather, a beginning should be made with
the relatively simple and inexpensive cameras that are
not discouraging in their complexity by offering too
many adjustments that one is likely to forget. It is
also a very excellent plan to make a systematic business
of taking pictures of ordinary subjects in the ordinary
Way until one has mastered the craft. Very excellent
practice can be obtained by making snapshots of one's
friends and family and if due thought is given to light-
ing and naturalness of action and expression, such pic-
tures are likely to be considerably more than mere exer-
cises in exposure and focusing.
Until the novice has developed sufficient skill
to be able to take about seven pictures out of eight
that are correctly exposed and focused, he is wise to
confine his attentions to simple subjects such as street
19

FIGURE I
1. Look into the focusing hood. You set a
reflected image of the subject, right side up,
full picture size—to the instant of exposure
2. When the pleasingly composed image is
clear on the ground glass, the subject is in
sharp focus.
:*. The mirror reflects the image to the
ground glass. When the exposure release
is pressed, the mirror swings upward out of
the way, instantly releasing the focal plane
shutter—securing the desired picture.
the between-the-lens shutter in wide ºpen
during only the firth and sixth flashes.
4. Focus is under easy and positive control The craſlew focal plane shutter transmits all
to the very instant of exposure. the available light during the entire expºsure.
5. Superior lens gathers ample light for the F
focal plane shutter which transmits ap- |GU R E 4
preciably more light than does any other
type of shutter.
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|||}|||||||
FIGURE 6
PLATE V
TYPES OF
CAMERAS
FIGURE 9










CAMERAS 51
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scenes, architecture, outdoor family groups and pets
taken in a good light. In the first place, nothing suc-
ceeds like success in stimulating one to further effort
and, in the second, by the choice of subjects such as
these, it is comparatively easy to make negatives that
are excellent from a technical standpoint and thus es—
tablish a high standard of attainment in what is cer–
tainly the preliminary step toward good photography. If
one attempts too difficult subjects too early, he is like-
ly to congratulate himself for poor work because he got
anything at all which hinders progress. Later, in grad-
uating to more difficult subjects, he should not be
satisfied with results that are less good technically
than he has learned to expect with easier subjects. It
is to be suspected that many people take pictures for
years without ever learning to discriminate between a
first and a second-rate negative. It will be found in-
Structive to make several exposures of the same subject
using different times and to make prints of these on
various papers. Certain of these are likely to be defi-
nitely better than the others although the latter may be
Sufficiently good so that one would not be aware of
their deficiencies if better ones were not available for
comparison. The differences between good, better and
best may be slight and it takes much thoughtful, dis-
Criminating practice to appreciate them fully.
The View Camera. The view camera (Figure l,
Plate W ) in larger sizes is known to everyone from its
extensive use in professional studios but that they are
also available in sizes as small as 3# by 1% inches is
not so well known. These cameras combine great strength
and ruggedness with a very large number of possible ad-
justments. Because of these characteristics, they make
very good cameras for teaching purposes. In fact, it
seems doubtful whether anyone should feel that his pho-
tographic education is really complete until he has
Served an apprenticeship with a view camera even though
a certain ponderous clumsiness about them may make his
feeling for them mainly one of thankfulness when he is
permitted to graduate to another kind.
Lenses are mounted on small lens boards that can
be quickly detached from the camera so that it is


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CAMERAS 53.
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possible to change lenses very quickly. These cameras
invariably have a rising front which makes it possible
to make the lens move upward while the film remains
fixed. The most general use for this is in photograph-
ing tall buildings from a point so near that it is im–
possible to include the top without tipping the camera.
The general rule about tipping the camera is that it
should not be done to an extent that Will distort, the
perspective badly unless one is deliberately modernistic.
The effect of photographing a tall building from a point
across the street by tilting the camera is to cause the
perpendicular sides to converge unpleasantly because the
bottom is appreciably nearer to the camera than the top.
The rising front is simply a means of causing
the lens to travel upward in a plane parallel to the for
cal plane which tends to lessen this distortion. In or—
der to be useful, the lens must have sufficient covering
power to form a sharp image over an area considerably
larger than the film. Moving the lens an inch or two
parallel to the focal plane changes the perspective of
the Whole image so slightly that it is scarcely percepti-
ble but it can make a very marked shift in the portion
of it that is to fall on the film if the covering power
of the lens is greater than the film area. Plate VI
shows how the image appears on the film both with and
Without the use of the rising front. In the left-hand
diagram, the lens occupies its normal position and the
C Ornice and chimney are below the film while a dispro-
portionate amount of sidewalk is shown on it. In the
right-hand diagram, the rising front has been used to
shift the lens vertically upward while the film remains
in the same position as before. As a result, the roof
and cornice now appear on the film while the excessive
amount of front walk there has been greatly reduced.
For distant objects, the two views are practically iden—
tical but a very marked change has been produced in the
precise portion of the scene that is projected on the
film.
Experiment. Remove the back of a view camera
and allow the image formed by the lens to fall on a
ground glass considerably larger than the back by leav-
ing the camera unextended and holding the glass in the


5|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
focal plane. Cover the head and camera with a focusing
cloth to exclude extraneous light. Note the size of the
area over which the lens forms a sharp image and the
character of the image around the margin. Shift the
image by means of the rising front and notice whether
there are appreciable changes in it in any respect ex-
cept in its location on the ground glass.
The rising front is also convenient when we wish
to take two photographs, one above the other, on the two
halves of the same film. If the back of the Camera is
removed, it will be found that there are grooves just
inside the ground glass into which cardboard can be in-
serted to mask part of the film while an exposure is
made on the remaining part. Such cardboard does not
make the film holder light tight but is quite sufficient
to keep the covered part of the film from being fogged
during the brief interval while the other half is being
exposed. The cardboard can then be shifted to cover the
Other half after the film slide is inserted and the hold-
er removed. By so locating the camera that the first
image taken is formed on the lower half of the film with
the lens in the normal position, one can be formed on
the upper half of the same object without moving it or
the camera by using the rising front. This is often con-
Venient when we wish to make comparative exposures of
the same object under different conditions on the same
film.
At the back of the camera is one knurled head
Screw that permits the ground glass, i.e., the focal
plane, to be tilted when loosened while another can ro–
tate it about a vertical axis. These are known as the
SWing back and the side swing respectively and are useful
When one wishes to bring two objects that are at quite
different distances from the camera into focus at the
same time. If 0, and Oe, (Fig. 10) represent two ob-
jects one of which is twice as far from the camera as
the other, by tilting the ground glass just the right
amount it is possible to bring both into sharp focus at
the same time. . ,
It will be realized that the rising front, SWing
back and side swing would be of little use Without
ground glass focusing as a careful preliminary study of
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CAMERAS 55
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the image is necessary in order to be quite sure that it
is satisfactorily focused. In fact, focusing with Cam-
eras that require it is one of the most important ele-
ments in success from a technical standpoint. Ordinarily,
it will be sufficient to do it visually without a magni-
fier but it is important to remember that the minimum
distance at which the eye forms a sharp image without
undue fatigue is ten inches and to be careful not to get
too close to the ground glass. Considerable practice is
necessary before one can judge the sharpness of this
image competently. Focusing should always be done with
the lens wide open because this insures the brightest
image and gives the least depth of focus, thus making it
more apparent when focusing is not correct. For very
exact focusing, a small magnifier may be used
02
Kl
0.
Figure | O The swing back.
While there are many other things that might be
mentioned about the view camera, most of them are so
much more readily understood by an examination of the
instrument itself than by a description that it seems un-
necessary to mention them here. The best preliminary
Step toward the mastery of the view camera is to examine
One very carefully and make inquiry about anything that
is not understood.
The Box Camera. The simplest camera that can be
devised is the box camera. Equipped as they necessarily
are to Operate only as fixed focus cameras, there is lit-
tle to forget and even the most inexperienced novice is
likely to score a large percentage of successes if he
can keep himself from trying to make it take speed pic-
tures at any time or snapshots in poor light. The reason
that a lens can be satisfactory at fixed focus is that


56 FIRST COLLEGE COURSE IN PHOTOGRAPHY
the aperture at which it works is small and if this is
the case, any lens of not more than four or five inches
focal length will have everything in reasonably sharp
focus from twelve or fifteen feet to infinity. The Small
aperture should be accompanied by a rather slow shutter
to admit enough light for a good exposure under average
conditions. The Baby Brownie is rather unique in having
a curved focal plane which enables its simple lens to
form a sharp image of rather greater area than would be
possible otherwise.
The Folding Camera. Folding cameras are equipped
with bellows that permit the lenses to take the correct
position when the cameras are in use and yet fold away
in the camera case when not needed, thus greatly reduc –
ing the bulk. Another advantage of the bellows is that
it makes focusing possible which is essential with large
aperture lenses if the images formed are to be critical-
ly sharp when the lens is not stopped down. These cameras
generally use either roll films or film packs containing
a dozen separate films in a light tight package for in-
Sertion in the camera as a unit. The advantages of a
roll film camera are that films are obtainable almost
anywhere and commercial processing is on a production
basis and satisfactorily done. The disadvantages are
that it is difficult, though not impossible, to develop
part of a roll before the rest has been exposed and the
Spools must have space provided for them which makes the
Camera somewhat larger than a film pack camers taking a
picture of the same size (Figure 8, Plate V). Film
packs are less likely to be obtainable when traveling
and except in very large establishments, commercial fin-
ishing is often unsatisfactory. Processing a film pack
involves the handling of twelve separate pieces of film
and is not to be recommended if one must rely upon others
for finishing. For the serious worker who does his own
Work, however, these cameras have much to commend them.
The film pack is enclosed in a film pack adapter which
is light tight when the slide is inserted so the film
pack can be removed from the camera whenever desired for
ground glass focusing. The film pack can be opened in
the darkroom and the exposed films removed for develop-
ing Without waiting to expose the whole series. Many

CAMERAS 57
|
film pack cameras can also use cut film or plates in
suitable holders if desired. Both types of folding cam-
eras are available in any price range desired from very
inexpensive fixed focus models that have the limited
capabilities of box cameras to beautiful instruments hav-
ing very superior lenses and shutters and every contri-
vance ingenuity can devise to make them convenient.
Since the price range is so extensive, it is es—
sential to be able to judge values well in order to se–
lect wisely or else to follow the advice of someone who
can. The first important factor is the quality and
speed of the lens and shutter. Almost equally important
in these lightly built cameras is the rigidity and ac-
curacy of alignment of the movable parts for a poorly
built camera is likely to permit some lost motion after
a little use.
- The Reflex Camera. In this type of camera a mir-
ror placed at an angle of forty-five degrees between the
lens and the film deflects the lens image upward so that
it falls on a horizontal ground glass that is exactly as
far from the lens as the film. Thus, focusing on this
ground glass by racking the lens back and forth insures
an equally sharp image on the film. When an exposure is
made, the action is rather complicated as the mirror
must first spring out of the way before the shutter
opens. Figure 5, Plate V should be studied carefully.
There is inevitably a little time lag so that it is cus–
tomary to expose a very rapidly moving object when it
appears at the edge of the field of view as it will have
progressed appreciably by the time the shutter actually
OpenS.
Focal plane shutters are generally used on re-
fiex cameras as these adapt themselves better to the me–
chanical requirements of getting the mirror out of the
way before the shutter is released than between-the-lens
shutters. Such a shutter usually consists of a fabric
curtain so flexible that it can be wound up like a roller
blind. At intervals it contains metal-bound slits of
Various widths. A spring of adjustable tension actuates
the shutter and when an exposure is made, enough of the
curtain is released to allow one slit to pass across the

58 FIRST COLLEGE COURSE IN PHOTOGRAPHY
space before the lens close to the focal plane. Such
shutters have a number of advantages. In the first
place, they are very efficient admitting possibly sixty
per cent more light than a between-lens-shutter of the
Star type as the latter is wide open only for an instant
and consumes most of the time of the exposure opening
and closing.’ See Figure 4, Plate V.
Another advantage is that such shutters are very fast
and accurate. * Most important of all, possibly, is the
fact that the location of the shutter behind the lens
and close to the focal plane means that any desired vari-
ety of lenses may be used with the one shutter by merely
mounting them on separate lens boards that fit the Cam-
€ 128, .
Under certain circumstances, focal plane shutter’s
produce a peculiar kind of distortion in moving objects.
This results from the fact that the exposure is made by
a moving slit which passes across the Space in front of
the focal plane. As time must elapse while this takes
place, different parts of the moving object are not pho-
tographed at the same instant and may move along before
their part of the image is formed. Thus a circular
wheel may become elliptic though satisfactorily sharp.
'l'he special advantages of this type of camera
arise from the fact that their shutters are very fast
and that the erect image is visible until the instant
the exposure is made, a very distinct advantage when
photographing action that may change quickly.
The Speed Graphic. Closely related to the re-
flex camera is the Speed Graphic, (Figure 5, Plate V) a
camera that finds very general use among press photog-
raphers. This camera has the focal plane shutter of the
Graflex, the American reflex camera, but gains in com-
l. The best modern shutters are more efficient than this.
2. Focal plane shutters are likely to be accurate in the sense that
the shutter times are reproducible but they are often not the
times they claim to be. The shutter curtain is frequently so
designed that it accelerates and passes by the last portion of
the film at higher speed than the first. While the density dif-
ferences produced in this way are not likely to be serious in
ordinary photography, it is well to know that these peculiarities
exist and to take them into account in quantitative work.
: -#
CAMERAS 59
pactness by using finders to frame the view, thus dis–
pensing with the mirror of the reflex type. Probably
this camera meets with special favor with press photog-
raphers because it is the most compact 4 by 5 camera
that can be held in the hands during exposure and is
very rugged and dependable. The relatively large size
of the negative is a distinct advantage in press work
where speed in getting out the finished print is so much
an object, that prints may have to be made while the neg—
atives are still wet. Under these circumstances, a cam-
era that makes pictures large enough so that the prints
can be made by contact rather than projection is a dis-
tinct advantage.
The Exacta. (Figure 6, Plate W ) In the Exacta,
we find the miniature version of the reflex camera, hav-
ing all the advantages of the larger models and a con-
venient compactness that makes it convenient for photo-
micrography and various other scientific uses. It has
interchangeable lenses and various accessories including
extension tubes that adapt, it for various purposes in-
volving photographing very near objects. For this pur-
pose, the convenient ground glass focusing is especially
desirable for the depth of focus obtainable in extreme
close-ups is so limited that it is almost impossible to
focus sharply at large lens apertures without direct for
cusing. Another important advantage under these condi-
tions of any type of camera that permits direct focusing
through the taking lens is that there is no uncertainty
regarding the exact field of view because of parallax as
is always the case when one lens takes the picture and
another, necessarily displaced from it somewhat, frames
the view. -
VIEWING LENS
CAMERA LENS
Figure | | Difference in viewpoint due to
parallax.

6O FIRST COLLEGE COURSE IN PHOTOGRAPHY
ſº
Twin Lens Cameras. In the twin lens camera (Fig-
ure 7, Plate W ) we find a camera that combines many of
the good features of the reflex type with one or two of
its own. Essentially, this is a camera that has a view
finder lens of large aperture mounted directly above the
taking lens so that it offers the advantages of a large
image without the time lag necessary when a mirror must
move up out of the way before the picture can be taken.
In the less expensive models, focusing is by scale while
in the more expensive models, the finder and taking
lenses are coupled so that the taking lens is in sharp
focus whenever the viewing lens is. Having a separate
viewing lens has one important advantage in rapid action
Work in that it becomes possible to stop down the taking
lens without reducing the light forming the ground glass
image, a very important advantage if one is following
action that necessitates rapid change of focus. Such
cameras are available only in small sizes as they would
otherwise be too bulky and the finder image suffers from
parallax or lack of coincidence between taking lens and
finder images in extreme close-ups. Certain types are
equipped to compensate for this.
Miniature Cameras. There has been much discus –
sion regarding the precise definition of the miniature
camera, (Figure 9, Plate W) and the negative size that
marks the line of demarcation between miniature and larg—
er cameras. Here, we shall define a miniature camera
somewhat arbitrarily as one that takes a picture smaller
than the vest pocket size, lă inches by 2% inches and
the most usual twin lens size, 2% inches Square. Good
negatives of the sizes mentioned are large enough so
that they will make satisfactory enlargements without
exercising any of the special precautions usual and nec –
essary with extremely small negatives so it seems rea—
sonable to consider that these are not miniatures. Many
of the latter use motion picture film although this is
not invariably true. As the negatives are extremely
Small, it almost goes without saying that cameras and
lenses of very high quality must be used if the results
are to stand comparison with those obtainable with larg—
er cameras of good quality even in the hands of a skill-
ful operator.
ſº



CAMERAS 61
These cameras are really instruments of preci-
Sion. The fastest lenses and shutter’s are available and
an almost unlimited list of accessories. Handled with
sufficient skill, these little cameras can accomplish
anything that a larger camera can with the exception of
those subjects demanding a swing back or a rising front.
Pictorialists usually prefer larger cameras for those
classes of subjects in which they wish to subordinate
everything except the main objects or to gain the utmost
in photographic quality. Miniature cameras are supreme
for purposes that demand a picture in a split second or
not at all under adverse light conditions. But, just be-
cause they are so versatile, they are not the best cam—
eras for the novice who will do well to gain consider-
able skill before acquiring one. The small finder image
rather hamper's study of the picture from the point of
view of composition. Another rather curious disadvantage
arises from the cheapness of the film which tempts one
to take pictures in huge numbers without sufficient
thought. It would appear that many people photograph
with a miniature camera as aimlessly as they might fire
an air gun and the chances of getting anything meritori-
ous in this way are almost vanishingly small. At the
same time, it should not be forgotten that they will do
remarkable things. Their versatility is astonishing and
there is practically no limit to the uses to which they
may be put .
In the foregoing, the cameras discussed have
been selected because they are typical examples of their
Class. It should be realized that various manufacturers
make the different kinds, and a very excellent way of be-
coming well informed regarding them would be to examine
as many examples of each class as possible. A mere de –
Scription is a very unsatisfactory substitute for what
can be learned by an examination of the cameras them-
Selves.
Today We have at our disposal marvelous lenses,
cameras that are really instruments of precision, inex–
pensive artificial lights, films combining speed, color
Sensitivity and fine grain, color film, papers of almost
any surface or emulsion desired, and the photoelectric
exposure meter. Photography has attained a degree of

62
FIRST COLLEGE COURSE IN PHOTOGRAPHY
certainty and convenience never before known but it may
be wondered whether there is not a tendency to over-
*mphasize the importance of the equipment and to under-
emphasize the importance of the person who is to use it.
No amount of superlative equipment is a substitute for
a really competent manipulator who has a mind in good
working order. Acquiring expensive cameras without any
particular justification appears to be one of the forms
of extravagance of this age and instead of deluding one-
self into thinking that his deficiencies will disappear
by magic if the equipment is only fine enough, it is Sug-
gested that the student challenge himself to be at least
as good as what he has before he buys more.
QUESTIONS
l. Arrange the following in the order of their difficul-
|
;
ty as photographic subjects and give your reasons.
Full length view of people.
Portrait, S.
Street, Scene S.
Landscape S.
Still life .
A puppy.
An elderly dog.
A line drawing.
. Which of the above subjects are best taken in the
Shade 2
. Why is it best to select the cast shadow of something
that is not directly overhead in Question 22
. Explain the use of the rising front.
. Why must the lens on a camera that has a rising
front have surplus covering power? Describe the ef-
fect that would be produced if a lens that lacked
this surplus covering power were used on such a cam-
era.” ~
. Explain the use of the swing back and side swing.
. Why should one take a position at least 10 inches
distant when focusing on the ground glass without a
magnifier?
Is it possible to get closer in focusing with a mag-
nifier 2
10.
ll.
12.
15.
ll.
15.
16.
17.
18.
CAMERAS 63
. How does one focus with a low power microscope? When
Would this be desirable'?
Compare the advantages of reflex and twin lens cam-
eI*B.S.
Why should one "press the button" the instant a rap-
idly moving object traveling at right angles to the
line of sight first appears in the field of view
rather than at the instant it becomes centered with
a reflex camera?
When is eye level focusing imperative?
Which gives more natural perspective, eye level or
lower focusing?
How could you use a reflex camera to take a picture
behind you? Over the top of a fence slightly higher
than your head?
Compare the advantages of roll film and film pack
C81116.1°E, S.
What are focal plane shutters? What would be the
shape of the image of an automobile wheel if the di-
rection of travel of the shutter were parallel and
opposite to that of the wheel?
Explain how photographs such as those in Figure 11,
Plate W are taken.
Discuss the advantages and disadvantages of miniature
Carner’8, S.
Figure | 2 Eastman Kodak Co.



Chapter W
THE FACTORS THAT | N FLUENCE THE SHARP N ESS
0 F THE PHO TO GRAPH | C | MAGE
There are two respects in which photography
stands unique among the graphic arts. No other method
of pictorial representation remotely approaches it in
its ability to render fine detail or in the long scale
of distinguishable tones that it is able to produce. In
fact, the term "photographic," is sometimes used in a
derogatory sense and is meant to imply that too much
minute detail has been rendered. An artist would not be
at all likely to attempt to render the detail of the in-
dividual leaves of foliage in painting a landscape even
if he could and those Dutch painters who managed to de-
pict such things as lace collars so that it is almost
possible to count, the threads are not considered to have
attained the highest type of art. In many examples of
pictorial representation, photographic included, the
Work assumes an abstract quality and a certain universal-
ity because it presents its elements by suggesting them
rather than by delineating them with all possible detail.
We should also recognize that the human eye is
really a very imperfect optical instrument that forms a
rather unsharp image at best and sees with maximum defi-
nition only within an extremely narrow angle of view.
The result is that if our purpose is to render things as
the eye sees them extreme definition can easily be over-
done by a fine anastigmat lens.
Experiment. Count the number of letters that
can be seen sharply at one time on this printed page.
Note that the eye changes its viewpoint several times in
reading across a line of type even though the head does
not move .
Essentially, our problem as photographers is not
usually to render an image with all possible detail. We
t
i
º
º
s
6||
FACTORS THAT INFLUENCE SHARPNESS 65.
could, of course, make a portrait that would depict a
person as if we were examining him with a magnifying
glass. Rather, our purpose is usually to render the
subject so that the observer will neither have his at-
tention distracted by visible defects nor feel vaguely
dissatisfied because he wishes to perceive detail that
is not there.
Thus, if our intention is to delineate something
that will be satisfactory to the observer by giving him
merely a general impression rather than extremely minute
detail, no particular precautions need to be taken. If,
on the other hand, we wish to bring out everything that
our medium can render, it is essential to take certain
precautions and to understand certain fundamental prin–
ciples that underlie what we propose to do. It should
also be recognized that the attainmºnt of the ability to
make photographic materials do their utmost in rendering
fine detail or delicate gradation gives one a general
feeling of competence that is very satisfying. It also
has value in saving one from the quite common though di-
ametrically opposed delusions that the attainment of
fine technique is a relatively simple matter needing
slight attention by anyone who has artistry in his soul
or that it is a mystifying and complex aggregate having
about as much underlying logic about it as alchemy or
a Strology.
When one has once gained this skill and under-
Standing, it is always easy to reduce irrelevant detail
by the use of soft focus lenses in taking the picture or
of diffusing screens in enlarging it. It should be
emphasized, however, that the deliberate repression of
the elements that are not desired is wholly different
from the effect produced when detail is missing because
the lack of technical skill on the part of the photogra–
pher causes his picture to suffer from a complication of
minor disorders. Moreover, anyone who has ever made use
Of photography for scientific records knows that superla-
tive technical skill may make all the difference between
Success and failure. This is particularly true in spec-
troscopy where the lines that are significant are fre-
Quently of such low intensity that a developable image
can be obtained only under the most favorable conditions.


66 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Another interesting direction in which the utmost in the
rendering of detail is sought is in the work of the "F/
6|| Group," a group of photographers who work habitually
with their lenses stopped away down in order to obtain
enormous depth of field. In fact, they sometimes go to
the length of having their cameras fitted with special
diaphragms that make it possible to take their pictures
With Smaller stops than are ordinarily supplied on len-
S eS .
Factors that Affect the Sharpness and Definition
of the Negative Image. The following factors influence
appreciably the sharpness and definition of the negative
image. We shall consider the precise effect of each in
turn. Many of these will be discussed more in detail in
later chapters.
. Lighting of subject.
Size of film.
Resolving power of film.
. Quality of lens.
Stop.
(a) For maximum depth of field.
(b) For maximum resolving power.
Contrast obtained during development.
Cleanliness of lens surfaces.
8. Use of a lens hood.
:
:
Lighting of the Subject. For a three-dimensional
Subject, there must be inequalities of illumination in
order to indicate in the image plane that the subject was
not two dimensional. In portraiture this is done by gen-
erally avoiding direct front lighting and by having the
illumination upon the two sides of unequal intensity.
Great care is necessary not to make the illumination too
unequal or it will be impossible to print the resulting
negative. Dark, heavy shadows should usually be avoided.
Texture is best rendered by oblique side lighting. A
brightly lighted subject will show more detail in the
negative than it would if it were less brightly lighted.
Glare, however, must be avoided.
Size of the Film. Since there is a definite low-
er limit to the size of the detail that a film can render
º
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ENLARGED 50X
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(a) Graininess of Different Types of Film.
(b) Resolving Power of a certain Lens at Different stops





68 FIRST COLLEGE COURSE IN PHOTOGRAPHY
owing to its granular nature, it will be obvious that,
other things being equal, the larger the film the great-
er the amount of detail that we may expect in the nega-
tive. As a matter of fact, other things are rarely
equal and an advantage often exists in favor of minia–
ture cameras because of the exquisite character of the
images produced by their fine lenses. The author sus-
pects, however, that a competition between the finest
camera taking a picture 2# inches square and one taking
a picture l inch by lá inches on this question of image
definition alone Would be decided in favor of the former
because it makes a negative having about three times the
area. Of the Other.
Resolving Power of the Film. Resolving power is
defined as the ability of an optical system or a photo-
Sensitive material to render fine detail and is measured
by the angular separation between two objects that can
just be distinguished as separate. When the angle be-
comes Smaller than this, the images run together and be-
Come one more or less uniform expanse. In a negative
taken at moderate distances, one can distinguish the in-
dividual bricks in a brick wall, but if one continues to
take pictures of it from increasing distances, a point
Will eventually be reached at which it will no longer be
possible to distinguish the individual bricks. This will
be due in part to the resolving power of the lens but,
more particularly, to the resolving power of the film.
OWing to the granular nature of the photographic image, .
it can no longer resolve detail when it becomes so minute
that it approaches the dimensions of the grain clumps
themselves. Moreover, since the dimensions of the grain
Clumps vary with different kinds of film, their resolv -
ing power also varies. On Plate VII, upper half, are
50X enlargements of exact size photographs of a proc-
ess engraver's line screen made on Microfile, Pana-
tomic-X, and Super XX films. These increase in grain
Size in the Order in which they are listed. The
Screen consisted of two hundred black lines separated
by transparent spaces of approximately the same width
per inch. Note that the sharpness of the boundaries
decreases While the number of developed grains in the
White portions increases with grain size.
E.
º
* -2
#
-º-
* .
s
--
º
º
FACTORS THAT INFLUENCE SHARPNESS 69
Quality of the Lens. Lenses differ enormously
in their ability to render fine detail as would be ex-
pected from the wide range in price and it is a fair in-
ference that there is a correlation between cost and re-
solving power. In general, the resolving power of the
lens is considerably greater than that of the film. *
Moreover, if an ordinarily good lens has greater resolv-
ing power than the film, it might be wondered whether
anything is actually gained by going to the extra eX—
pense of obtaining a really superlative lens. As a mat-
ter of fact, there is justification for this for all of
the factors that contribute to the unsharpness of the
image are cumulative and a reduction in the effect of
any of these will improve the negative quality. A fine
lens is therefore able to define more on the same film
than can an ordinary lens. The frontispiece shows
the resolving power of fine-grained film and an excep-
tionally good lens. As the puppy still had its first
coat of very fine hair, the fact that it looks like hair
and not wool with this degree of enlargement pays high
tribute to the lens. A fine lens is therefore able to
define more on the same film than can an ordinary lens.
Stop. Here, a very curious contradiction occurs.
We shall show in a later chapter how stopping down a
lens increases the depth of field, that is, the distance
in object space within which it can form a satisfactori-
ly sharp image. We shall also show that an image formed
by a lens is always unsharp because of the wave nature
Of light and that this unsharpness becomes more pro-
nounced as the lens is stopped down beyond a certain op-
timum stop opening. (Plate W II ) Here, equivalent ex-
posures were made on Microfile film at different stops
of a Finlay color screen containing a geometrical array
of red, green and blue color elements so small as to be
just below the limit of visibility with the unaided eye.
The negatives were exact size and were enlarged 20X.
Note that f/9 gave the best definition and that there
is distinct deterioration both at larger and smaller
Stops. Exactly which stop this is varies with differ-
ent lenses and should be determined, particularly in
the case of enlarger lenses, if maximum performance is
de Sired. -
l. This may not be true except in the central portion of the film
alºea, ,


70 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Contrast Obtained During Development. A good
way to investigate this is to examine images identical,
except that they were developed to different degrees of
contrast, under a magnification of about fifty times with
a microscope. It will be found that the sharpness of
the outline is considerably greater when the contrast is
great.
Cleanliness of the Lens Surfaces. The interior
of the optical glass of lenses frequently shows minute
black specks which are actually minute bubbles that ap-
pear black because the light does not enter them in
traversing the lens. While they prevent the transmis–
Sion of a very minute amount of light, they are not re-
garded as detrimental as they do not impair the image.
Certain kinds of optical glass cannot be made that will
be entirely free from these bubbles. If, however, a
Coating of dust, or a faint scum of anything such as
fingerprints is found on the surface of a lens, it will
impair the image very seriously becºuse it tends to SC at –
ter a portion of the light rays and"cause them to travel
toward the image plane in directions different from those
that they would have taken had the surface been perfect –
ly clean. Camel's-hair brushes are recommended for the
preliminary cleaning of a lens before wiping it with old
linen or lens tissue because these lift the dust off
lightly. Rubbing a dusty optical surface with cloth or
tissue is apt to cause scratches because of the abrasive
nature of the dust. It is far better, however, to keep
a lens Clean than to make it, so after it has been allowed
to become dirty.
Lens Hoods. Just as extraneous light Shining
into Our eyes will impair seeing, it will impair the
image that is formed by a lens. It is therefore highly
advisable to shield a lens with a lens cap.
Experiment. Light a porch light at night and
note how much better you can see things beyond the cir–
cle of illumination with the light off than on.
Additional Factors that Influence Graininess.
While the individual silver grains of the photographic
º
* ,
C
*
s
FACTORS THAT INFLUENCE SHARPNESS 71
image are far too small to be seen except with a very
powerful microscope, they show a marked tendency to form
in clumps that are sufficiently large so that they can
be seen under moderate magnification. This phenomenon
is known as graininess and determines the degree of mag-
nification that the image will stand and still remain
free from spotted effects over surfaces that should show
a uniform tone. When these clumps are rather diffuse
and without sharply defined outlines, the negatives will
stand considerably more enlargement than they will other-
Wise. Actually, the film selected has far more influ-
ence than any of the other factors but the following ex-
erºt. Some effect .
Nature of developer.
Degree of development.
. Density of the developed image particularly
in broad plain areas.
Optics of the enlarger.
Contrast of the printing medium.
Agitation during development.
Importance of Fine-Grain Development. When neg—
atives are to be enlarged not more than four or five
times, it is unnecessary to take any particular precau–
tions to keep the grain of the negative as fine as pos–
Sible as it is inherent in the nature of the photograph-
iC image that the grains or clumps of grains will be too
Small under this much magnification to be visible. Of
recent years, however, various developments of photogra–
phy have appeared that demand magnification to such an
extent that the grain of the original image must be kept
as fine as possible or else the quality of the magni-
fied image will be seriously impaired. The first of
these is the motion picture. A single frame of silent
film is one inch by three quarters and when this is pro-
jected on a theatre screen to a screen size of twelve by
Sixteen feet, it is magnified over one hundred ninety di-
ameters. A comparison of present-day films with those
of ten or fifteen years ago will show the marked im–
provements in fineness of grain of films today. Even
today, grain is occasionally quite evident and can be
noticed in plain portions of the projected image that
are rather light in tone. As a matter of fact, some


72 FIRST COLLEGE COURSE IN PHOTOGRAPHY
motion picture producers are often Willing to sacrifice
a certain amount of fineness of grain by using the very
fast films that, though coarser in grain, have the im–
portant advantage of making it possible to Save light , a
very important element in the cost of a production. Man-
ufacturers are continually hunting for methods of film
manufacture that will minimize grain realizing that one
who could make a film that would combine the Speed, Col—
or sensitivity and gradation desired with exceptionally
fine grain could monopolize the market.
More recently, the great vogue of the miniature
camera has caused the average, non-professional photogra–
pher to become very much interested in this subject as
many feel that a miniature negative, possibly an inch by
an inch and a half in size, needs to be enlarged to
about eleven by fourteen before all that is in it can be
fully appreciated. As a result, much attention has been
given to the development of formulas and manipulative
technique that will permit such magnification without
producing unpleasant graininess. The average negative
made on coarse-grained film and developed in the Ordinary
way gives a fuzzy, unsatisfactory image if enlarged to
this extent.
For a slightly different reason, microphotography
or the production of small, legible reproductions of
large areas, requires a film having as fine grained an
image as possible. Here, the image cannot reproduce
fine detail unless its grain is considerably finer than
the smallest detail desired. At present cameras are
available that photograph a whole page of a newspaper On
a film approximately an inch and a half Square, yet every
word can be read easily when the image is projected on a
Screer, and magnified to its original size.
Fine-Grain Development. It has already been men—
tioned that if we watch the process of development of a
photographic emulsion under the microscope, we find that
development begins at some point on a silver bromide
crystal by the appearance of an amorphous black Speck
which gradually enlarges at the expense of the crystal
until the latter is completely converted into a black
deposit of silver. The microscope will also show that
º
º
*
º

º
º: FACTORS THAT INFLUENCE SHARPNESS 73
tº different developer's produce silver Čeposits that vary
-- noticeably in the physical characteristics of the re-
duced Silver .
Two avenues of approach to the problem of pro-
º ducing negatives having partic: ilarly fine grain have
r proved very productive. The first consists in substi-
H tuting for the highly ionized, sodium carbonate of devel-
r oper's such as we have been considering a less highly
#. ionized alkali such as borax. In this way it is possi-
r ble to produce a developing solution having a much lower
º reduction potential that reduces the silver of the latent
º image more slowly and with a noticeable reduction in
L. grain size. The following formula is that of a very
º well-known developer of this type. -
r Eastman D-76 Borax Developer
º Warm Water . . . . . . . . . . 750 cc.
Metol . . . . . . . . . . . . 2 grams
º Sodium Sulphite . . . . . . . 100 grams
[. Hydroquinone . . . . . . . . . 5 grams
. Borax . . . . . . . . . . . . 2 grams
Cold Water to make . . . . . . l liter
Development is from 12 to 25 minutes at 65°F. de –
pending upon the kind of film and the general density of
negative desired. Ultra-fast films require longer de-
E== velopment than ordinary films.
A modification of this formula that produces even
s finer grain is the following:
== Modified E.K. Formula D-76 (Buffered Borax)
sº Warm water . . . . . . . . . . 750 cc.
* - Metol . . . . . . . . . . . . 2 grams
º Sodium Sulphite . . . . . . . 100 grams
-- Hydroquinone . . . . . . . . . 5 grams
sº Borax . . . . . . . . . . . . 2 grams
Boric acid . . . . . . . . . . 11 grams
fă Cold water to make . . . . . . l liter
º Note that these formulas are exactly alike except
,” for the addition of the boric acid to the second. No po-
º tassium bromide is necessary in either because they have
ºs.
#4
j.

7|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
such low reduction potentials that they do not produce
appreciable developer fog and so require no restrainer.
These developers can be re-used and the quantities given
are sufficient to develop from l;00 to 500 square inches
or film. h
Even finer grain can be produced by formulas that
substitute paraphenylene diamine and glycin for the metol
and hydroquinone of ordinary formulas.
Sease #5 Formula
Warm Water . . . . . . . . 750 cc.
Sodium Sulphite . . . . . 90 grams
Paraphenylene diamine . . 10 grams
Glycin . . . . . . . . . . 6 grams
Cold water to make . . . . l liter
This developer contains neither alkali nor bro–
mide. It is a curious fact that paraphenylene diamine
has been known to have developing power for at least twen-
ty-five years but was not considered suitable for a de-
veloper because the developed image was too thin to print
satisfactorily. Combined with glycin, however, satis-
factory density can be obtained without unduly increas –
ing grain size. Paraphenylene diamine developers in gen—
eral require an increased exposure as compared to metol
hydroquinone developers to produce excessively fine
grain and while this condition is easily fulfilled in
good light, it will be realized that this requirement
would be a very serious detriment under some conditions.
Modifications of the Sease formula containing potassium
bromide are occasionally used. These will produce even
finer grain but require exposures as much as four times
normal if the maximum amount of bromide is added to the
developer.
If fine grain were the only factor to be consid—
ered in producing satisfactory miniature negatives, it
Would be a simple matter to carry out carefully con–
trolled experiments with each formula, examine the re-
Sult S With a microscope, and determine the best. As a
matter of fact, the issue is much more complicated than
at first appears for grain is only one of several factors
tº
w£f
.
: º
ºff. . . .
º
º
º
|
FACTORS THAT TMFLUENCE SHARPNESS 75
that contribute to the elusive thing known as negative
quality. Among these might be mentioned gradation,
shadow detail, printing quality, etc. Unfortunately, no
developer is superior in all respects and so the prob-
lem becomes one of making the best possible practical
compromise and this probably involves the personal equa-
tion among other things.
Other Factors that Affect Grain Si Ze'. In film
manufacture it is known that the quality of the gelatine
and the precise treatment it receives has a noticeable
effect upon grain size so it appears a fair inference
that the gelatine might also influence the development
of the image in other respects. The reduced silver par-
ticles appear to have a certain degree of mobility in
the gelatine and anything that would tend to weaken the
gelatine mesh that separates the particles would make
their tendency to clump together more marked. As a re-
Sult, development, fixing and Washing should not be un-
necessarily prolonged as this is likely to produce an
undue SWelling of the gelatine. For the same reason,
the temperature should not be too high and, especially,
Should not vary from solution to solution. Even the
Wash Water should be kept as near 65°F. as possible.
Rather Special care to harden the gelatine either by the
invariable use of a fresh acid fixing bath or by the use
of a hardening agent between development and fixing may
help to keep the grains from clumping. This also serves
another important purpose by lessening the tendency of
the surface of the film to scratch. In miniature films,
it should be remembered that even scratches so small
that they cannot be seen without a magnifier are serious.
Washing should be thorough but not unnecessarily
prolonged and drying should take place where the air cir-
culates freely but is completely free from dust. Before
drying, the surplus water should be mopped off the film
With a Viscose Sponge or other suitable absorbent that
is completely free from lint and tendency to scratch.
Another means of lessening grain size is by agi–
tation during development. As the developer acts, the
portion in contact with the film becomes weakened and
2 Ontaminated with decomposition products that are



76 FIRST COLLEGE COURSE IN PHOTOGRAPHY
detrimental to further development. The primary purpose
of agitation is therefore to keep the developer circu-
lating so that the film is continually brought into C on-
tact with fresh developer. This makes any developer act
faster and is especially useful with developers having
very low reduction potentials because it reduces develop-
ing times that might otherwise be so long as to promote
Clumping. Agitation, however, should not be too Violent
or it may have a detrimental effect upon grain size.
It will be realized that the optical system of
the enlarger has an influence upon the graininess of the
projected image and that one that is capable of produc-
ing the utmost in the way of definition may conceivably
reveal more graininess that does one that does not form
quite so perfect an image. An enlargement made with a
projection lantern would not be likely to be satisfacto-
ry on this account for this is designed to produce maxi-
mum definition and relies upon the fact that the observ —
er is some distance away to prevent his seeing too much.
Graininess is more apparent with high contrast
enlarging papers than with low contrast. Over a broad
plain area, the image will appear rather mottled as soon
as it undergoes sufficient enlargement. With a low con-
trast paper, however, this structure may be represented
by grays that are so close together that they blend
into a comparatively uniform expanse that is not un-
pleasantly mottled. With a high contrast paper, how-
ever, these grays will be farther apart in tone and the
Surface will show far too much graininess even when we
make all possible allowance for the fact that the eye is
an imperfect optical instrument.
Measurement of Graininess. In order to compare
the grain size of the particles in different emulsions
or of the same emulsion under different developing con–
ditions, it is customary to make photographs of line
charts and develop them under carefully controlled con-
ditions. Various groups of such lines are prepared run-
ning in different directions and having the number of
lines per inch vary to such a degree that the finest are
beyond the limit of resolution of any film. In the nega-
tives obtained, lines are considered resolved if the
sº FACTORS THAT INFILUENCE SHARPNESS 77
observer can be sure of the direction in which they run
even though they are unsharp. The charts are prepared
with a degree of contrast that may fairly represent that
likely to be encountered in a normal subject. The fol-
lowing tables shows the results obtained with certain
new Eastman films that have just appeared. The numerals
in the right-hand column indicate the number of lines
per millimeter that can just be distinguished as sepa-
rate.
Resolving Power
Developer D-76
Resolving Power
in lines/mm.
Super-XX © e © e s e o - º º º 55
Plus —X o e e º © e º o tº º © l;5
Panatomic-X . . . . . . . . 50
Panatomic . . . . . . . . . HO
From this table we learn that Super-XX, the
fastest of these films has the lowest resolving power
and Panatomic-X, the slowest of these new films has the
greate St. Both Plus-X and Panatomic-X are superior to
Panatomic in resolving power and also in speed while
Super-XX is only a little inferior , n resolving power
and has remarkably great speed. It thus becomes appar-
ent that the films represent distinct improvements over
their predecessor, Panatomic .
Another use that might be made of these charts
to measure resolving power lies in the opportunity they
Offer the individual photographer to test his own tech-
nic. Let him "photographic such line charts on film
Whose resolving power he knows, develop according to his
own methods and determine whether he can produce a nega-
tive that reproduces as many lines per millimeter as the
manufacturer claims. That fifty lines per millimeter is
a remarkable achievement may be more apparent if we con–
vert it to twelve hundred and fifty lines per inch. As
this is about six times as many lines per inch as the
eye can resolve, such a negative would need to be en-
larged at least six times in order to reveal the struc –
ture of the pattern to the observer.


78 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Degree of Contrast De Sirable in Miniature Nega-
tives. The exact density to which the negative is de-
veloped influences the graininess of the enlarged image.
In general, as development continues, the Silver parti-
cles gradually grow larger while the density is being
built up. It will therefore be self-evident that devel-
opment should be allowed to continue only long enough to
produce a negative of the minimum density necessary to
produce a satisfactory print. Allowing density to
progress beyond this point is likely to increase the
graininess that will be evident in a large enlargement.
In fact, some users of miniature cameras stop develop-
ment at a point where the image is still so flat from
underdevelopment that a contrast paper must be used to
get a satisfactory print. Before deciding to do this,
it is well to remember that contrast papers usually do
not reproduce as great a number of distinguishable tones
as the softer papers and that their exposure latitude is
less. The exposure therefore has to be more exact and
there may be some loss in the number of tones reproduced.
Contrast papers also reveal graininess more than soft
paper S.
Certain early experiments to discover whether
grain is more noticeable with certain densities than
With others indicate that grain will be most apparent
when the film density is such that it is transmitting
about half of the incident light. Then, the silver
grains cover the space quite completely with little over-
lapping. When the density is less than this, the grains
have Open spaces between them and so are less apparent
while with a greater density the grains cover the space
so thickly that there is considerable overlapping and
the observer is therefore less aware of their individual
Structure. This would mean in portraiture, for instance,
that an effort should be made to produce negatives in
which the broader expanses of the face are not represent-
ed by densities that will transmit one-half of the in-
cident light. Probably here a greater density is prefer-
able to a smaller one for skin texture is likely to be
poor in negatives of low density. Of negatives in gen–
eral a good test would be to examine them for shadow de-
tail and for unblocked highlights. Assuming correct ex-
posure , lack of detail in the shadows would imply
l
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FACTORS THAT INFLUENCE SHARPNESS 79
underedevelopment while highlights so black that detail
cannot be printed through them imply over-development.
Very minute scratches print out in thin nega-
tives that would not be apparent in denser negatives.
One cause of film damage that is very annoying in minia–
ture negatives arises from the formation of very minute
holes in the emulsion. These can be avoided by washing
the film for at least two minutes between developing and
fixing. It will be recalled that the developer is alka–
line and the fixing bath acid. If the film is trans-
ferred to the fixing bath while it still contains appre-
ciable amounts of developer, particularly those contain-
ing carbonate, there is a good chance that neutraliza–
tion will occur within the gelatine itself at certain
points with the evolution of enough gas to burst its way
out and produce an actual rupture of the gelatine film.
It Will be realized from all this, that there
are many mutually contradictory factors involved in Ob-
taining maximum definition and minimum grainine SS and
the experimenter does well to learn first what these are
and then to work out his own salvation in his OWn Way.
There is no perfect technique but results can be obtained
in a variety of ways that are very interesting and the
conviction that such photography is capable of far great-
er development than it has yet received lends a fascina–
tion to its pursuit that must be experienced to be fully
appreciated.
QUESTIONS
l. Determine the angle of view within which you have
sharpest vision by measuring the width of the portion
of a printed line that you see most sharply and the
Viewing distance. Solve trigonometrically or graphi- e
Cally.
2. Why Would it be inadvisable to mount a filter that was
too large by attaching it to the outer rim of the lens
cap?
5. Why is it better to express the resolving power of a
lens by an angle rather than by the linear separation
between two object, sº


8O FIRST COLLEGE COURSE IN PHOTOGRAPHY
4. Suggest subjects that would make it desirable to use
film having the highest possible resolving power.
5. Why do we not use such films all the time?
6. Under what circumstances could maximum definition be
Obtained by St Opping the lens down to the limit?
7. Under what circumstances should we stop down only
moderately in order to obtain the sharpest image?
8. To what extent is it advisable to stop down the lens
Critical definition.
9 .
l0.
ll.
l2.
l3.
l!.
lº).
l6.
l'7.
of an enlarging camera?
Discuss the effect of each of the following upon
Lighting.
Film size.
Resolving power of film.
Quality of the lens.
St. Op.
Film Contrast, .
Clean lens surfaces and bubbles in glass.
Lens hoods.
Define graininess.
Discuss the effect of the following upon graini–
Il62 S S .
l8.
l9.
20.
2l.
22.
23.
2!!.
25.
26.
Nature of the developer.
Degree of development.
Density of the image in broad plain areas.
Optics of the enlarger.
Contrast of the printing medium.
Agitation during development.
Discuss the effect of density upon graininess.
When miniature negatives are to be greatly enlarged,
why is it advantageous to use a sufficiently large
stop opening so that the exposure need not exceed
l/100 second?
Is it actually contradictory that the "F/6]
Group" uses extremely small stops to secure maximum
definition and yet Plate VII indicates that the
sharpest image is obtained at f/92 Explain.
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Chapter W I
THE GRAP iſ S OF PHO TO GRAPHY
We have already seen that it is possible to
learn a considerable amount about the response of photo-
graphic materials to light by making comparative tests
of the materials as they are ordinarily used in photog-
raphy. (Plates II and IV . ) It is also possible to
learn even more by making sensitometric strips. (Plate
II Both methods are time consuming, necessari-
ly limited in the number of materials to which they can
be applied, and rather inexact . These same methods, how-
ever, greatly refined and elaborated, are in constant
use in research and Commercial laboratories &nd, When
published, make available to the general photographer
vast amounts of valuable information provided he has
learned to comprehend it. Frequently this is presented
in graphical form which makes an extremely convenient
method for presenting large amounts of photographic data.
It is useful, however, only to those who are willing to
leave the realm of the purely empirical aspects of our
Subject, and take the trouble to learn a certain amount
Of its underlying theory. Once having done this, one
finds that he can often gain at a glance from the graphs
in Scientific articles valuable information that would
have required hours or even days to amass by the route
Of direct, personal experiment. The student is there —
fore urged to make as strenuous an effort as may be nec –
essary to master this aspect of our subject. By so do–
ing, he will Open avenues leading to his further develop.–
ment and Sources of exact information that will be for –
ever Closed to him if he does not make this effort and
remains content with what he can learn by the purely
Qualitative and empirical route.
Absorption of Light by a Neutral Medium. Before
discussing the procedure actually followed, it will be
Well to consider briefly the absorption and transmission
81


82 FIRST COLLEGE COURSE IN PHOTOGRAPHY
of light by a neutral medium, i.e. , by one that absorbs
the same fraction of the energy of all colors in visible
light. Let us imagine that we have a sheet of gelatine
that contains a sufficient quantity of gray dye so that
it absorbs half the light that falls on it and transmits
half. A single thickness, therefore, would transmit fif–
ty per cent of the incident light. If this transmitted
light is allowed to pass through another similar gela—
tine, this will in turn absorb half and transmit half so
that the amount to get through will be twenty-five per
cent of the original and, in general, as the number of
layers is increased, each transmits half of what reaches
it. Other gelatines might be secured that would trans – "
mit more or less of the incident light but the important
thing to recognize is that the fraction transmitted is
Constant and is characteristic of the particular sample
that is being used.
The following tables illustrate what will happen
to the transparency and opacity as we increase the num-
ber of layers.
Table I
LIGHT ABSORBED BY EACH LAYER
Layer Incident Light Fraction Absorbed Fraction Transmitted
First, l l x # = } #
Second # # x # = } #
Third # # x # = # #
Fourth à # x # = is is
Fifth is # x is =# sº
Table TT
TOTAL ABSORPTION BY THE NUMBER OF LAYERS CONSIDERED
Number of Layers Total Absorption Transparency Opacity
(It/To) (Io/It)
l # # 2
2 # # l;
l; # is 16
5 # # 32
º
R.

THE GRAPHS OF PHOTOGRAPHY 83
º
-§ 2. ºf
§
In Table I, it will be evident that the light incident
upon each layer will be the fraction that is transmit-
ted by the layer preceding it and that each layer will
transmit # of what reaches it. In Table II we find the
total absorption produced by all the layers through
which the light has passed. Quite obviously this would
equal the sum of the fractions absorbed by all the lay-
ers involved. Transparency and opacity are technical
terms that refer to the fraction of light transmitted,
It /Io, and the reciprocal of this quantity respectively.
We shall next plot the opacity and the transpar-
ency against the number of layers in order to discover
whether these graphs will yield any useful information.
What we wish to discover is whether any of these quanti-
ties are directly proportional to each other and, if not,
whether quantities may be derived from them that do ful—
fil this condition. This relationship would be made ap-
parent by the fact that the graph would be a straight
line. Figure l6 shows the result obtained by
º plotting the number of layers against the opacity while
| Figure 14 shows the number of layers plotted
. against the transparency. In neither case do we obtain
a Straight line, and a constant increase in the ordinate
does not result in a similar increase in the abscissa.
E Miſſ Hº
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ºxa-kº Fig. 19transparency Fig. \{OPACITY Fig, 15 DENsity
The law of absorption that we are considering
§ here is a particular example of the more general law of
; : continual decrease that applies to a great variety of
Fº phenomena that decrease at a constant rate. This law
may be stated as follows:
1.2 1.5
It E Ioe-mix.

8|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
** -smº -
It = light transmitted
Io = incident light
e = 2.718, a mathematical constant
m = the coefficient of absorption, a constant
that describes the absorptive power of the
medium.
X = the independent variable which may be the
number of layers, the thickness of the me –
dium, etc.
Table III gives these data for the case repre-
sented by Tables I and II and Figure lo shows
the graph. The latter shows that the logarithm of the
opacity is directly proportional to the number of layers
Of the absorber.
Table III
Number of layers Opacity Density (log Opacity)
2
1.
8
l6
32
:
|
:
The logarithm of the opacity is usually referred to as
the density, a term that we have used somewhat vaguely
in earlier discussions by defining it as a measure of
the light absorbing power of the photographic material.
Since it is a logarithmic expression, it is difficult
to assign a definite physical meaning to it, and it Will
probably be best to accept it as a mathematical ab–
Straction that has extremely useful characteristics, as
We shall See presently.
The Absorption of Light by the Photographic
Image. When we consider the absorption and transmission
of light by the photographic image, our problem becomes
complicated by the necessity of taking into account the
photo-chemical effect of light itself. It is a simple
matter to demonstrate by experiment that an exposure
twice as great does not produce an image twice as black.
In fact, two such negatives differ so little in density
that it is necessary to look at them rather closely to
º
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THE GRAPHS OF PHOTOGRAPHY 85
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discover which had the longer exposure. Moreover, it
Will be recalled in the case of the sensit ometric strips
that We found it advisable to make the series of succes—
sive exposures in geometrical progression by multiplying
each exposure by V2 to determine the next . This is
equivalent to saying that it takes much more additional
light to make an appreciable change in a dark tone than
in a light One.
Although analogies are a little dangerous and
must not be pushed too far, such an analogy may serve to
make this clearer. Ten additional people added to a
group of ten make an appreciable difference in its size
though they would probably be unnoticed if added to a
group of a thousand. Similarly, a relatively small num-
ber of additional silver halide particles that have
undergone the latent image change will produce a notice –
able effect on those areas where the number already af-
fected is small but not on areas where the number is al-
ready very large.
The following table represents the data obtained
from a Sensit Ometric strip containing a series of gradu-
ated exposures. This was developo in buffered borax
and the densities were measured with a Martens photome–
ter.
It will now be desirable to make various graphs
from the following table to discover which yields useful
information. The students should plot each graph indi-
cated on cross-section paper and keep it for future ref-
elſen Ce .
Table IV
Exposure Units of LOg E Density Opacity
Exposure (Log O) (Antilog D)
1/500 sec. l O .37 2.3
l/200 2.5 l; .37 2.3
1/100 5 .7 .lil 2.5
l/HO 12.5 l.l .60 H.0
1/20 25 l.l. .82 6.6
1/10 50 l.T l. OO 10.0
l/5 LOO 2. O l. 19 lj.5
l/l, 125 2. l l.26 18.2
2/5 2OO 2.3 l. 37 25.1;
l/2 250 2. li. l. 112 26.3
l 5OO 2.7 l.60 l;O.O
2 LOOO 3.0 L.78 60.5


86 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Density-Exposure Graph
Plot Column II as abscissas and Column TV as ordinates.
Opacity-Exposure Graph
Plot Column II as abscissa's and Column W as ordinates.
Opacity-Log Exposure Graph
Plot Column III as abscissas and Column W as ordinates.
Density-Log Exposure Graph
Plot Column III as abscissas and Column TV as ordinates.
The Characteristic Curve. As has already been
mentioned, whenever We Wish to make a systematic study
of the photographic image, we are primarily interested
in how it transmits light. A great many factors may af-
fect the image such as the kind of film, the developer,
the developing time, the age of the film, the tempera-
ture of the developer. Different batches of the same
film may differ appreciably from one another. Manufac –
turers and large users make routine tests on all film,
the former, to make sure that none reaches the market
that is not up to standard and the latter, to be sure
that the operating technic in the studio is not deteri-
Orating. While the average user of smaller quantities
is never likely to run these tests himself, so much in-
formation is published regarding films, papers, etc. ,
based upon these sensit ome Cric tests that any photogra–
pher will find himself amply rewarded for the trouble
taken to understand them by the ease with which he will
thereafter accumulate useful information about the ma—
terials that he uses and by an increased understanding
of the whole photographic process.
The following series of steps may be considered
typical of all such investigations.
l. Make a series of accurately known exposures
on a piece of the material to be investigated.
2. Develop under carefully controlled and repro-
ducible conditions.
5. Measure the light transmission of the differ-
ent sections and derive the photographic
densities.
4. Make a graph of the results.
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88 FIRST COLLEGE COURSE IN PHOTOGRAPHY
One way of making a series of accurately known
exposures is by means of a sector wheel which has Open-
ings cut in it so that each is twice as wide as the One
preceding it. The wheel is allowed to make one complete
revolution in front of the film to be tested which put S
a series of exposures on the film. The duration of
these will be determined by the time required by each
open portion of the sector wheel to pass in front of the
film and thus expose it to the standard light. The Speed
of the wheel is so adjusted that one rotation of the
wheel gives the required exposure range. It is a curi–
ous fact once subject to considerable argument but now
definitely settled that a series of brief, intermittent
exposures does not produce exactly the same density as a
Single exposure representing the same total exposure
time. -.
The next step consists in developing the Strip
under carefully controlled conditions so that a compari-
son of different strips will be significant. Developer,
temperature and developing time must be held constant if
different emulsions are to be compared and, in general,
conditions are so regulated that everything is held con–
Stant except the one variable that is being studied at
the moment. If this can be done, it is a fair inference
that variations in results obtained are due to the one
variable factor. Without such precautions, the result S
obtained are too complicated to be interpreted With any
certainty. -
After the film has been fixed and dried, the
densities of the different portions can be determined in
various ways. In general, these involve a measurement
of transmissions It/Io or a matching of the gray of the
unknown film with another gray that can be varied Sy S-
tematically until a match is obtained. See Experiment 14
By a very careful study of Plate VIII,it is pos-
sible to learn a great deal about the information yield-
ed by these characteristic curves because it is drawn
with unusual completeness and covers an exceptionally
long exposure range. The exposures range from #5 unit
to 2000 units since the logarithms of the exposures
range from —l to 5.5, an exposure range of a 20,000
times. The curve is divided into four regions, under-
exposure, correct exposure, overexposure and abnormal
THE GRAPHS OF PHOTOGRAPHY 89
over-exposure. Negatives fall into the first region when
all the grays are extremely light. The contrast in the
negative is then much lower than in the subject. A
longer exposure will produce a negative farther along on
this curve and contrasts will be satisfactory if the
density range falls between .5 and 2.5. If the exposure
is still longer, the subject will be represented by
densities still farther up the curve, the negative will
again be low in contrast and difficult to print because
of excessive density. Thus far, the curve is the sort
that is characteristic of a good many functions other
than photographic that start slowly, continue at a Con-
stant rate for a time and then decrease again. The re-
gion of abnormal overexposure, however, is unique. The
fact that the ordinates decrease in value here means that
exposures that are excessively great will actually pro-
duce densities that are less than those produced by
smaller exposures.
A photographer is not likely to make exposures
here while photographing ordinary subjects but it is
well to know that such a region exists in order to be on
guard against drawing erroneous conclusions when photo-
graphing very bright subjects under exceptional condi-
tions for which previous experience cannot serve as a
guide. A practical use is made of this region in the
direct copy film obtainable today to make enlarged nega-
tives directly from a negative, thus saving the time and
expense of making an intermediate positive. This film
is exposed sufficiently during manufacture to make it
possible to develop it to the density represented by C
On Plate VIII without further exposure. As a result, ex-
posure to the enlarger light will cause those portions
that receive the most light to develop lighter than those
that receive less. Portions receiving no light develop
black so the result is a positive resembling the origi-
nal in the enlarger rather than a negative. The fideli– *
ty. With which the enlargement would reproduce the tones
of the Original would depend upon the extent to which
this portion of the characteristic curve approximates a
Straight line, and it would appear to be inevitable that
contrast would be less than in the original.

90 FIRST COLLEGE COURSE IN PHOTOGRAPHY
The following table gives a Summary of informa—
tion that can be read from the characteristic Curve On
Plate VIII.
Table W
Region Range of | Range of *max. Range of Omax.
* º ºs º- Log E E Emin. Density Opacities 9min.
Under- l
exposure —l-O TO-l 10 O— .5 O-35.2 sºme ºsmº tºº -
Correct,
exposure O-2 l–l OO LOO .5–2.5 3.2–320 LOO
Over- -
exposure 2–2.9 lOO–8OO 8 2.5–2.75 || 520–560 l.T
Reversal | 2.9–3.3 || 800–2000 || 2.5 2.75–2.6 560–100 l. 11

This graph is idealized to the extent that the limits of
the various regions have been arbitrarily chosen so that
they can be represented by numbers that are easy to in-
terpret, and is presented primarily to illustrate the
principles involved. Once these are understood, it
should not be found difficult to interpret the graphs in
the literature that apply to specific materials. These
data indicate the following general principles.
l. In the range of under-exposure, the density
range is less than the log E range. As a result, nega-
tives here will be flat. As the D–log E relationship is
represented here by a curve, there will be distortion of
the tone scale.
2. The same situation exists in the region of
overexposure.
3. In the region of correct exposure, the densi-
ty range is equal to the log E range and tone rendering
will be exact. This equality exists because the slope
of the straight line portion of the curve is |B9. The
effect of other values for the slope will be discussed
further .
4. The slope represents the rate of change in D
with respect to log E and is obtained by dividing any
convenient density range by the corresponding log expo-
sure range.
THE GRAPHS OF PHOTOGRAPHY 91
The Reciproclºy. Law. It will be evident that
the exposure may be considered as the product of the in-
tensity of the light multiplied by the time that it is
allowed to fall upon the film.
E = It
This is the reciprocity law and indicates that the pho-
tographic effect produced by a weak light that falls
upon the film for a comparatively long time is the same
as that of a strong light for a time that is correspond-
ingly shortened. It is now recognized that this is not
quite true. In fact, for lights of extremely brief dura-
tion and high intensity such as the beam used in making
the sound track on motion picture film or of extremely
low intensity and long duration as in a stronomical expo-
sures, the deviations cannot be disregarded. In the
range of light values used in ordinary photography, how-
ever, the deviation is not serious and we therefore feel
justified in applying the information acquired from
Sensitometric tests to ordinary photographic subjects.
In making sensit ometric strips, it is usually
most convenient to obtain a variety of exposures by the
use of a constant light source for different lengths of
T Lime. Actual photographs, on the other hand, represent.
a variety of exposures because the light values of the
Subject vary and are all allowed to fall upon the film
for the amount of time that the shutter remains Open. In
both cases, within the range of light values encountered
in Ordinary photography with a camera, we consider that
the exposure is the product of I and t and that it is
immaterial whether I or t is the variable quantity. E
and log E on the D–log E characteristic curves represent
Sensit Ometric Strips or the light values of actual sub-
jects with equal fidelity.
The Significance of the Straight Line Portion of
the D–log E. Curve. We need to consider next precisely
Why the Straight line portion of the characteristic
curve represents correct tone rendering of the subject.
When We make a photograph our purpose is usually to
translate the light values of the subject into densities
On a negative and back into a reciprocal series of densi-
ties on a print that will represent as accurately as pos-


92 FIRST COLLEGE COURSE IN PHOTOGRAPHY
sible the range of light values of the subject. Let us
assume that we have a subject whose range of light Val-
ues is lo to l, that is, the brightest part reflects ten
times as much light as the darkest part and that we give
it a correct exposure. In this case the exposures all
fall within the region of correct exposure, log Emax. and
log Emin. Will differ by l since the maximum light value
is lo times the minimum. Next, if we develop the nega-
tive for exactly the right length of time, these expo-
sures will be converted into densities that differ from
each other by l. Taking the antilogs of these densities,
We find that the maximum opacity is lo times the minimum
or that the minimum density represented transmits lo
times as much light as the maximum. A positive transpar-
ency made from this negative and developed exactly the
correct amount of time will yield the same range of Opa-
cities in reverse Order which means that our positive
displays a range of tones that reproduces exactly the
light values of the original subject.
If, however, we had given an exposure that fell
in the regions of over- or underexposure, the density
range would not have been equal to the log E range, and
the tone scale would have been compressed. More serious
still, the tone scale would have been distorted as is
indicated by the fact that the graph is not a straight
line here and it would not have been possible to dupli–
cate the tones of the original. What would have result –
ed in the print would have been reduced contrast and a
falsification of the tone scale.
The Meaning of Gamma. In Plate VIIIwe noted that
the Straight line portion of the characteristic curve
made an angle of 45° with the horizontal and that this
meant exact equivalence between the range of values of
log E and D. We must next consider what it would mean
if the region of correct exposure had some other slope
and whether it is possible or desirable to exert any in-
fluence upon this during development. Many factors in-
fluence the precise amount of reduction of silver pro-
duced by development such as the kind of film, the de-
Veloper used, the developing time, the temperature of
the developer and the spectral quality of the light.
Quite obviously these are subject to control and it is
THE GRAPHS OF PHOTOGRAPHY 93
found that the developing time has a marked effect upon
the slope of the straight line portion of the character—
istic Curve and that it can be varied within rather wide
limits with a given film, developer, temperature and
light source by merely varying the developing time. The
term, gamma, refers to the rate of change of the density
With change in log E and is defined as follows.
Gamma is the tangent of the angle formed by the
Straight line portion of the characteristic curve with
the horizontal. Here, we are using the term, tangent,
in it S usual trigonometric sense as the side opposite di-
Vided by the side adjacent in a right tºriangle. This
right triangle may be formed by taking any convenient
log E range as the side adjacent, the corresponding
density range as the side opposite and the included por–
tion of the characteristic curve as hypotenuse. See
Plate VIII. -
Gamma = density range/log E range.
Gamma may assume useful values all the way from about .6
to 2.0 or more and is a measure of the rate of change in
density. With change in log E as indicated below.
(Pmax. - Pnin) = Gamma (log Emax. - log Emin.)
It will be readily seen, therefore, that values of gamma
less than unity represent a compression of the tone
Scale as represented by the light values of the subject
While values greater than unity represent an expansion
Of this scale. For ordinary negatives, a gamma of about
. 8 is likely to be satisfactory. This is due to the
fact that negative materials can render a longer density
range than paper prints can so that a deliberate shorten–
ing of the density range by control of the developing
time Will compress the scale sufficiently to make it pos–
Sible to reproduce the whole of it on a print even with
a high contrast subject. On the other hand, values of
gamma greater than one are desirable in negatives repro-
ducing line drawings where we wish to print clear black
lines and retain a pure white background. Another ad-
vantage about keeping gamma low is that the shortened
developing time offers less opportunity for the clumping
effect of the developed silver that results in graini-
Ile SS .

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THE GRAPHS OF PHOTOGRAPHY 95
Plate IX shows a family of characteristic curves
for Panatomic-X film developed for various times in D-76
borax developer. Note that increased developing time
results not only in increased general density as indi-
cated by the fact that corresponding points are repre-
sented by larger ordinates as developing time increases
but also in increased contrast because corresponding
points in the denser portions show greater separation
than in the thinner portions. See also Plate IV
for the appearance of negatives and prints.
Gamma Developing Curves. The information is
rarely available for determining gamma directly from an
ordinary negative as the light values of the subject are
usually known only in the most general way. In fact,
the determination of gamma after a negative had been de-
Veloped Would mean its determination after the opportun–
ity to modify it in the interest of negative quality had
already been lost. Fortunately, however, the informa-
tion regarding the developing time for particular nega-
tive materials and developers is published and the tem—
perature and time of development to produce any gamma
desired can be read from time-gamma curves such as that
shown on Plate IX. Note the differences in maximum
practical gamma produced with the three developer's shown
and the Wide variations in developing time to produce a
given gamma. These demonstrate the importance of choos-
ing the proper developer for the type of negative de-
sired and the importance of the developing time.
All that it necessary in order to develop nega-
tives to the gamma desired is to obtain time gamma
graphs representing the film and developer that we pr’O –
pose to use and read the time corresponding to this gam—
mê from the graph. Then, if the developer is carefully
compounded, fresh, and used at exactly the temperature
indicated on the graph, negative quality can be dupli-
cated with a high degree of precision.
- This matter becomes rather more C Omplicated when
; : ) one is using developers that are reused for a number of
rolls of film as it is certain that developer activity
diminishes with increasing use because of the oxidation
of the developing agent and of the accumulation of de-
composition products in the solution. For extremely ac-
curate Work, such as three-color Separation negatives,



75
N
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7
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TN
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||||||N N
2 3 4 5 6 789 10 15 20 30 40
TIME OF DEVELOPMENT (Minutes)
Eastman Kodak Coe
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0
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5
5
PLATE X
a 2 r * r * * * * * * g g g g g g g g g g g g g º º


THE GRAPHS OF PHOTOGRAPHY 97
it is therefore customary to use fresh developer each
time. For the usual run of negatives, it is usually
sufficient to compensate for the decrease in developer
activity with use by slightly increasing the developing
time with each additional roll, by adding replenishing
solutions to keep up developer strength, or by adding a
small amount of fresh developer each time it is used.
The precise details of such procedures are often pub-
lished in the direction sheets of prepared developer's
and must be learned for each developer. Nothing is less
likely to be productive than random experimentation
along these lines by those who are untrained in such pro-
Cedure S.
º If, for any reason, one wishes to develop at a
temperature slightly different from that for which the
time gamma curves have been prepared, graphs such as
those shown on Plate X are available which show the
variation of the developing time with temperature. It,
will be noted that these graphs are straight lines with
a negative slope, and that the axis of abscissa's makes
use of a logarithmic scale. All of this indicates that
the logarithm of the time of development is
proportional to the temperature. It would always be
possible, of course, to look up the logarithms of the
time and plot these against the temperature on Ordinary
rectangular coördinate paper. The use of semi-
logarithmic paper that represents the temperature by a
scale of equal parts and the time by a scale whose parts
are proportional to the logarithms of the times makes it
possible to plot such a graph without having to convert
the times into logarithms and makes it read directly in
minutes rather than in the logarithms of these.
Distinction between Gamma, and Contrast, . If a
roll of film were correctly exposed and then developed
in a strip, the negatives would all represent the same
gamma. Whether the individual negatives are flat or
contrasty depends upon the range of the light values of
the subjects. A subject whose range of such values is
long would produce a negative that utilized most of the
densities possible in the region of correct exposure
and would be high in contrast while one whose range was
low Would utilize only part of the density scale and
Would be flat. Gamma, then, depends upon the develop –
ing time while negative contrast is largely determined


98 FIRST COLLEGE COURSE IN PHOTOGRAPHY
by the range of light values in the subject itself.
There is no possible way by which we can make a high con-
trast negative from a subject low in contrast. All that
We can do is to make the contrast somewhat greater than,
equal to or less than it was in the original by a proper
choice of the gamma to which we develop it. That gamma
affects contrast cannot be denied. (Plate IV ) But,
as Suming skillful development, the principal factor in
negative contrast lies in the range of light values of
the subject itself. -
Latitude. Latitude is a measure of the varia–
tion in exposure that is possible with a given light-
Sensitive material without carrying the negative densi-
ties outside the region of correct exposure. This may
be defined as the ratio, Emax./Emin., for this region. For
the graph represented by Plate VIII, this would be loo/l
indicating that light values such that the brightest is
100 times the least bright may both be reproduced simul—
taneously in the region of correct exposure. For such a
subject, only one correct exposure is possible. If,
however, the subject had a range of light values only
one-tenth as long, it might be represented by a log E
range of 0 to l, by l to 2 or by any number of inter-
mediate ranges. All negatives so produced would have
the same contrast if developed alike and would make
prints of the same quality although they would require
different printing times. It will be realized that the
possible variation in exposure time that is possible
while still producing negatives whose densities all lie
in the region of correct exposure is much greater with
a low contrast than with a high contrast subject. It,
also depends upon the light-sensitive material for some
of these represent a much longer exposure range of cor-
rect exposure than do others. Because of the fact that
latitude depends upon these two entirely independent
factors, light range of subject and exposure range of
the sensitive material, the term is almost necessarily
somewhat vague in its precise significance. Suffice it
to say, therefore, that when a material is referred to
as having great latitude, it means that the exposure
range within the region of correct exposure is consider-
able and, as a result, exposure is not too critical and
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THE GRAPHS OF PHOTOGRAPHY 99
can be varied within reasonable limits without carrying
the negative over into densities that represent either
over- or under-exposure, unless the subject contrast is
very high.
Uses of Sensit Ometric Strips and Characteristic
Curves. While many applications of sensitometric strips
and the graphs derived from them will be apparent from
the foregoing discussion, it will perhaps be well to
conclude this chapter by mentioning a few more specific
applications. Manufacturers of photographic materials
make very extensive use of such data first, to discover
precisely the performance of their products and, second,
- to test each batch after manufacture to be certain that
it is up to standard. Film processing establishments,
especially in motion picture production run these tests
to make sure that their processing technique is satis–
factory. Color workers must make balanced separation
negatives if there is to be any hope of correct color
reproduction. All three of these negatives should be
developed to the same gamma, their light values must
fall within the density range represented by correct ex-
posure and printing is greatly simplified if they all
represent exactly comparable density ranges. All Of
this can be checked by reproducing a scale of graduated
grays on each negative and comparing them to be sure
that they are identical on each negative and that they
fall within the correct exposure range. Last , advanced
amateurs can gain much useful information regarding the
performance of materials and their own technique by mak-
ing sensit ometric strips. Here, it will ordinarily be
sufficient to make visual comparisons. Moreover, even
though one never makes density measurements himself, an
understanding of their meaning reveals much of the under-
lying philosophy of the photographic process and Con-
tributes greatly to a knowledge of what, it signifies.
QUESTIONS
l. A geometrical progression is one in which each term
can be derived from the one preceding it by multiply–
ing it by a constant factor. Show that the following
Series constitutes a geometrical progression: l, 2,
!, 8, 16, 52, 64.
:


LOO FIRST COLLEGE COURSE IN PHOTOGRAPHY
:
2.
5
6.
7.
8.
An arithmetical progression is one in which each term
can be derived from the one preceding it by adding
or subtracting a constant amount. Show that the loga-
rithms of the above numbers constitute an arithmeti-
cal progression.
For what purposes do the following classes of people
make use of characteristic curves: manufacturers of
photographic materials, processing laboratories for
motion picture film, makers of photographic prints in
color, advanced amateurs? -
Make a table showing the values of the opacity and
transparency that correspond to each of the following
densities: O. . 1 , . 2, .. 3, .4, .5, l.0, l. 5 and 2.0.
. The following questions refer to Plate VIII ,
(a) What is the maximum density obtainable with this
material?
(b) What is the density range that gives correct
tone reproduction? .
) What exposure range yields this density range?
) Determine gamma for this curve.
) What density range would have been obtained on a
negative whose exposure range extended from 100
to 200 unit S of exposure?
(f) What density range would have been obtained on a
negative whose exposure range extended from 1/10
to l unit of exposure?
Explain the meaning of gamma. Compare the light Val-
ues of the subject with the density range produced
in the negative when gamma has the following values:
. 8, 1.0, l.2.
Show that high gamma is not necessarily associated
with high contrast.
How is it possible to alter gamma?
(c
(d
(e
9. Discuss the family of characteristic curves shown on
Plate IX. Show precisely how they indicate that both
density and contrast increase with prolonged develop-
ment . .
lC). Discuss the time gamma curves on Plate IX. Which de-
ll.
veloper produces the contrast 2 For which developer
does gamma change most rapidly?
Make a table showing the developing time required to
produce gammas of . 6, .8, l. O and l.2 with developers
DK-60a, D-76 and DK-20. See Plate IX.
THE GRAPHS OF PHOTOGRAPHY 1Ol
l2.
15.
14.
15.
l6.
17.
l8.
l9.
2O.
2l.
22.
23.
24.
Why do we habitually use the portions of the expo-
sure range represented by the toe and shoulder in
making prints while we seek to avoid using any ex-
cept the straight line portion in making negatives?
Why is it possible to make more beautiful positives
as transparencies than as paper prints?
Make a table showing the equivalent developing times
for DK-60a, D-76 and DK-20 at 60°, 65°, 70° and 75° F.
See Plate X.
Explain why the permissible latitude of exposure is
greater with low contrast subjects.
If we make a positive transparency from a negative
by contact and develop it to a gamma equal to l, de-
scribe the appearance by transmitted light when they
are superposed.
Show that the regions of under- and overaexposure
both result in a compression of the tone scale.
Explain why we find it advisable with ordinary pho-
tographic subjects to develop our negatives to a gam—
ma less than l.
If you decided that a gamma of . 8 would be desirable
in developing your own negatives, how would you ob-
tain the information necessary to secure it?
Determine the exposure range and the density range
representing correct exposure for each of the family
of characteristic curves on Plate IX. Show that the
density range is equal to the exposure range multiplied
by gamma in each case.
Assume that we make a series of different exposures
of a low contrast subject, all of which lie in the
region of correct exposure, on a roll film and -
develop in a tank. How do they compare in density,
gamma, and contrast, 2
Assume that we make a series of identical correct
exposures and develop them separately for different
lengths of time. How do they compare in density,
gamma, and contrast?
How might one use sensitometric strips to compare
the performance of two developers?
How might they be used to compare two different pa–
pers? -


Chapter W I
PROJECT | ON PR | N T | NG
Until recently, a very large part of the best
photographic work was done by large cameras and contact
printing. These, however, necessarily limited the field
of work by their cumber some character and the time Con-
sumed in preparing for an exposure. More recently, the
development of fine-grained films has made it possible
to reduce the size of the camera and the negatives made
by it without an undue sacrifice of photographic quali–
ty. Along, with this has come a vast increase in the use
of enlarging cameras for printing.
While the term, "contact quality," continues to
be one of the highest tributes that can be bestowed upon
an enlargement, there are several reasons why an enlarge-
ment may actually be superior to a contact print. In
the first place, the negative resolves detail having
roughly one-sixth Che dimensions of the minimum that can
be resolved by the eye which means that a magnification
of six times is necessary to enable the observer to see
all that is actually in the negative. In the Second
place, the minimum viewing distance at which the eye can
form a sharp image is ten inches and when an enlargement
of fair size is held at this distance, the image formed
on the retina of the eye is about the size that it would
be if we were looking at the scene portrayed. When a
Small contact print is held at this same distance, and
it cannot be held closer without the use of a magnifying
glass, the retinal image is much smaller and we vaguely
realize that the enlarged photograph looks more "natural"
Without , perhaps, understanding why. Closely allied to
this is the fact that an enlargement or a magnified view
of a small print through a reading glass assumes a three-
dimensional quality not present in the unmagnified Small
print. This, too, is quite possibly due to the fact
that the retinal image approximates in size what it would
be if one were looking at the objects portrayed.
ſº
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LO2
PROJECTION PRINTING 103
Two other reasons in favor of projection prints
are the opportunities they offer for local control or
for the selection of a portion of a negative in the in-
terests of good composition.
- Factor's Determining Permissible Degree of En—
largement. Whether projection prints will stand compari-
son with contact prints made with larger cameras depends
upon a variety of factors among which the following
might be mentioned.
l. Sharpness of the negative.
2. Optical and mechanical excellence of the en-
larger.
3. Character of the subject. A photograph of a
landscape might be pleasing when a degree of
unsharpness existed that would be quite un-
Satisfactory in one of a printed page.
Technical skill of the operator.
5. Type of enlarger. Condenser enlarger's permit
the making of larger enlargements than dif-
fused light enlargers without undue loss of
sharpness.
l;
Diffused light enlargers usually magnify from li to 5
times and are more frequently used with negatives of
fair size. Miniature enlargers of the vertical type
usually permit enlargements of from 10 to 20 times, the
upper limit usually being determined by the length of
the upright supporting the lamp house. Certain types
Can be SWung around into a horizontal position and the
image projected upon a vertical screen. In that Ca. Se,
the size of the enlargement is limited only by the qual-
ity of the negative and the length of the room.
Just What degree of enlargement is desirable de-
pends not only upon the factors mentioned above but also
upon the distance at which it is to be viewed. In gener-
al, enlargement should not be carried so far that the
image becomes noticeably unsharp and graininess dis-
agreeably evident at this distance. An examination of a
negative under a microscope with a magnification of 50X
Will show that the photographic image inevitably has
Somewhat blurred edges and, as a result, the more it is
magnified, the more this becomes apparent unless at the
Same time the observer is moved farther aWay.

PHOTOPLOOD
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PLATE X |
The Enlarger.
.



PROJECTION PRINTING - 105
Optics of the Enlarger. Plate XI shows the
essential parts of an enlarger and should be studied
carefully by those who are unfamiliar with Such equip-
ment. The essential parts are listed below.
Negative holder.
. Lamp house and light Source.
Condensers or diffusing glass.
. Lens.
. Paper holder.
i
Focusing should be positive and capable of variation by
very small steps. Sharper images are formed if the neg—
ative holder does not require glass between the negative
and the lens to assist in keeping the negative flat.
Where a very intense enlarging light is required to save
time or to permit a high degree of enlargement, condenser
enlargers are usually used. Such enlargers yield images
possessing higher contrast than diffused light enlargers
and bring out all possible detail including dust specks
and scratches if these exist on the negative. They are
more expensive than diffused light enlargers and the
latter are entirely satisfactory if the desired degree
of enlargement is not too great. The diffusing glass is
essential in these to make illumination reasonably even.
Moreover, without it a badly focused image of the light
filament or the word Mazda on the tip of the bulb might
appear in each enlargement, particularly if the lens
were stopped down.
In condenser enlargers it is essential that the
condensers be matched to the focal length of the enlarg—
er lens as shown in Plate XII. The purpose of these
condensers is to make the beam of light illuminate the
negative evenly and sufficiently convergent so that as
much of it as possible will pass through the projection
lens and become effective in forming the image. In Fig-
ure l, the light just covers the negative and converges
to a point within the lens barrel. In Figure 2, the
light is converging to a point in front of the lens so
that much of it will be cut off by the bellows and the
illuminated area in the negative plane is larger than is
necessary so that much of it is useless and represents
wasted light. In Figure 5, the negative is not entirely
covered by the convergent beam and part of this will be

ENLARGER LENS
T T º
| T i
D. ID | * Yºº-DIFFUSION DISC
LKGHT RAYS —s' W | | || IF III) '
FORMHNG * { } }}}} || s—LK+T RAYS
Off FUSED IMAGE FORMING
SHARP IMAGE
ACTION OF THE DIFFUSION DISC
IN ENLARGING
DIAGRAMS SHOWING DISTRIBUTION OF | LLUMINATION
and NEGATIVE SIZES
THE NUMBER 3 CONDENSER IS PICTURED IN EACH CA$6.
DIAGONAL O!AGONAL
-º-º-º-º-º: 2-
NEGATIVE —- NEGATIVE" _*
-
3 * LENS t 4” iſ:NS
2* LENS
CORRECT |NCORRECT INCORRECT
LIGHT COMPLETELY COVERS NEGA- UGHT MORE THAN COVERS NEGATIVE, LIGHT FAILS TO COVER NEGATIVE
TIVE AND JUST FILLS LEN3. (IN TME$º HENCE, WASTEFUL. ALSO MORE THAN COMPLETELY OR TO FILL LENS. THIS
DIAGRAMS IT IS AS$UMED THAT THE FILLS LENS, SCATTERING STRAY LIGHT PRO DUCES I. G. H. W. CORN ER 5 AND
CORRECT PROJECTION UENS HAS BEEN INSIDE SELLOWS —TENDS TO REDUCE OTHER DEFECTS ON PRINT$.
CHOSEN FOR THE NEGATIVE SHOWN.) PRINT OUALITY.
FIGURE I FIGURE 2 FIGURE 3
Eastman Kodak Co.
PLATE X | |
º

PROJECTION PRINTING 107
cut off by the lens barrel. All of this indicates that
it is very essential to have condensers matched to the
focal length of the enlarger lens. It is also very es–
sential in such enlargers that all the optical parts and
the light be aligned very carefully if maximum efficien-
cy is to be secured.
Occasionally, one encounters a subject that Will
be improved in pictorial quality by deliberately making
the image less sharp in the enlargement than a direct
use of the negative would make it. A portrait, for in-
stance, might be improved by softening excessive detail.
To do this by deliberately throwing the image out of
focus is not satisfactory because an image that is en-
tirely unsharp simply lacks photographic quality. By
the use of a diffusing screen, however, it is possible
to produce an image that is partly soft and partly sharp
So that the image is firm and yet eliminates unwanted
detail. Plate XII shows how this can be done. A diffu-
Sion disc is a flat piece of glass marked with some sort
of pattern indented in the glass. The unmarked areas
transmit a sharp image while the indented portions act
as tiny lens elements that break up the sharp image pass-
ing through them so that it falls in the focal plane as
a diffuse image. The result is an image that retains
sufficient detail to be satisfactorily sharp because of
the plane portions of the disc while superposed on this
is a diffused image due to the marked portions.
Characteristics of Enlarging Papers. For pro-
jection printing, much faster papers are generally desir–
able than in contact printing. Accordingly, bromide or
Chloro-bromide papers are used. Bromide papers are
Sometimes about as fast as slow films and must be handled
by a safelight that will not fog them. They are rather
Simpler to handle than chloro-bromide papers which can
be modified somewhat in effect, during development.
With negative material, we have al-
ready learned that prolonging development results in in-
creased gamma. In the case of printing papers, however,
this could not be the case without making exposure time
more critical than is desirable. As a result, papers
are so manufactured that increase in the density of the
image Will result from prolonging development while gam-
ma remains constant. Thus, it will be possible to con-

108 FIRST COLLEGE COURSE IN PHOTOGRAPHY
tinue development if the print seems a little light and
build up higher densities without altering the relative
contrast in the print. -
It will be recalled that the term, latitude , ap-
plied to negatives had reference to the permissible
range of exposures that would make it possible to repro-
duce the light values of the subject on the straight
line portion of the characteristic curve. That such
negatives differed in general density made no differ-
ence as this could be compensated for by a regulation of
the printing time. With prints, however, a change in
general density that made the extremely light tones be-
come medium grays and caused the subject to be rendered
only in the darker tones would not be at all satisfac-
tory.
By paper latitude we mean that there is, Within
reasonable limits, a reciprocal relationship between -
exposure and developing time so that the same kind of
print can be obtained by a shorter exposure and longer
development as by a longer exposure and shorter develop-
ment. As a result, exposure is not extremely critical
and moderate differences can be compensated for by an
adjustment of the developing time, thus resulting in a
considerable reduction in the number of spoiled print S
from failure to give the correct exposure.
We must next, consider how Une characteristic
curves of different grades of a projection paper Compare
with each other. -- - - - - - - - ----- -
F i q ure | 6
Characteristic
curves of papers

PROJECTION PRINTING 109
We note, first, that the papers in-
crease in gamma in the order soft, normal, medium con-
trast and contrast. Next, the maximum tone obtainable
with soft Velour Black is not quite as black as with the
other three grades. The others differ little in this
respect. The fact that the curve for soft paper cuts
the other three means that while it will print the
faintest distinguishable gray with less exposure than
any of the others, it will not yield its maximum tone
until it has had a greater exposure.
Another important thing to realize is that it is
rarely practicable to make a print by utilizing only
the Straight line portion of the characteristic curve.
For the papers on Figure l6, doing so would deprive us
of the tones represented by minimum and maximum densi-
ties, that is, of all the lighter grays and maximum
black. We therefore find it better to sacrifice accura—
cy of tone reproduction in the lightest and darkest tones
by using the toe and shoulder of the characteristic curve
in Order to have them present at all in our photographs.
As a matter of fact, we are riot very sensitive to actual
tone values and rarely know whether the correspondence
between object and image is accurate or not. What we
do notice is contrast and gradation so too much effort
cannot be made to have the print leave nothing to be de-
sired in these respects.
Local Control in Enlargement. It frequently
happens for reasons that are beyond the control of the
photographer that the densities of portions of a negative
from which an enlargement is to be made are not ln prop-
er relation to the rest. While a judicious waiting for
the best hour of the day or for the right kind of
weather in making the negative will often avoid this, it
is not always possible. As a result, the photographer
finds it very advantageous to alter the time that he al-
lows different parts of an enlargement to be affected by
the printing light. Practically all of such procedures,
and their number is legion, are based upon two princi—
ples. The first of these is that the shadows cast by a
shield that is placed in the enlarger beam about half-
way between the lens and the image will be unsharp with
diffused edges. This lack of sharpness can be made

ll O FIRST COLLEGE COURSE IN PHOTOGRAPHY
still greater if the shield is kept moving all the time
that it is being used to shield part of the exposure.
The other principle is that the observer does not find
an alteration of printing densities objectionable provid-
ing the resulting densities represent reasonable values
and shade off gradually enough into one another so that
there is no obvious line of demarcation to show that
Something was attempted that did not quite succeed.
The simplest application of this is dodging. By
this is meant that a card is moved back and forth to
shield a portion of the image during part of the expo-
sure, the exact amount being determined by the result
desired. This was done in the Street, Scene in Old Que –
bec (Plate XIII ) . There it will be noted that the
light stucco building is in full sunlight and the darker
buildings in Shadow. As a result, it was not possible
to get any detail in the stucco without making the build-
ings on the shady side too dark. In the final print a
cardboard shield was used to cut off the light from the
less dense portion of the negative during half the expo-
sure and the shield was kept moving slightly so that
there would be no line apparent between the areas that
received different printing times.
When the area that needs extra printing is
Small, it is often possible to shield the rest of the
area with a card that has a hole cut in it and to con-
tinue printing while this card is moved about slightly.
With practice one learns to do this so that such things
as bald high lights exhibit a more satisfactory tone
without the slightest evidence that extra printing was
resorted to. The converse of this consists in shielding
a Small spot while the main area continues to print.
This can be accomplished by cutting a shield about the
Shape of the part that is to be blocked out the size
that this portion would be if projected on a plane at
the distance from the lens at which the screen is to be
held. This is supported out over the picture area by a
thin stiff wire which is kept in motion during printing
so that it does not shield any one portion long enough
to leave its image.
Control of Contrast in Print Making. While a
very slight effect may be produced with some papers in
the way of āltering print contrast by changing the de-
veloping time, this is so slight that it is hardly worth
:
film
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PROJECTION PRINTING lll
§,
º
º
§:
mentioning. It has already been pointed out that the
main effect of prolonging development with most paper's
today is merely to shift the densities from one charac-
teristic curve to another whose straight line portion is
parallel to the first. Thus, gamma remains constant and
relative contrast is not altered. The most usual way of
controlling the contrast in a print is by a suitable
choice of the grade of paper, choosing a medium hard or
hard paper if the density scale of the negative needs to
be stretched, a soft paper if it needs to be compressed
and a normal paper if it is about right. The amount of
bromide in the developer has a slight effect, With no
bromide, unexposed paper is a medium gray from developer
fog. It is thus apparent that it is never desirable
to use a paper developer with out bromide. In
general, potassium bromide slows up developer action so
that a good rule to follow is to use the minimum amount
that will prevent developer fog on unexposed portions of
the paper during the normal developing time.
The developing formula used produces some effect
and many formulas are published that claim to produce
soft, normal, or contrasty effects. In general, those
that contain more than the minimum amounts of carbonate,
hydroquinone and bromide produce greater contrast. Dilu-
tion of a developer has a tendency to lessen the contrast
of the prints while the accumulation of decomposition
products in the developer will do the same thing.
In concluding this chapter, it may not be amiss
to point out that it is in projection printing that the
photographer finds his reward for the patient apprentice-
ship he may have found largely dedicated to an infinite
capacity for taking pains. The reward is more than suf-
ficient, however, for in projection printing lies a
challenge to all the science and art that may lie latent
in his soul and an opportunity for self-expression that
is more than satisfying to its devotees.
QUESTIONS
l. Would a projector be likely to be satisfactory as an
enlarger if we built a box around it to shut in the
extraneous light? Explain.



112 _FTRST COLLEGE COURSE IN PHOTOGRAPHY
10.
ll.
l2.
l3.
Paper latitude.
. Discuss the reasons why enlargements are often more
Satisfactory than contact prints.
. Why should the condensers be changed if one changes
the focal length of the lens in a condenser enlarg—
er 2
Is it advisable to use contact papers in making pro-
jection prints?
Note the wiring diagram in the upper left-hand cor-
ner of Plate XI. Show that only the projector
light is in the circuit when the switch is thrown
to the right thus allowing it to operate at maximum
brilliance.
. Discuss the effect of throwing the switch to the
left in the same diagram. What would be a suitable
additional resistance to put in series with the pro-
jector light if it should have about the same re-
sistance as the light in order to reduce the bright-
ness of the light by the desired amount 7
. Discuss the essential parts of an enlarger.
. Discuss the relative merits of condenser and dif-
fused light enlargers.
Compare Plate XI and Fig. le. Explain what these indi-
cate regarding the effect of different developing
times upon paper and film.
What is the precise difference in the meaning of the
term, latitude, as applied to papers and to negative
materials?
Explain the significance of the fact that the char-
acteristic curve of the soft paper crosses that of
medium paper. (Figure 16. )
Discuss the methods of local control used in projec-
tion printing.
Make a list of the various factors that affect the
contrast of projection prints.
Figure l 7
º
s'

Chapter V | | |
PHOTOGRAPH | C OPT || C S
The Reflection of Light. In order to form an im-
age on the photographic film, an object must reflect or
transmit light that passes through the lens. An under-
standing of the laws of the reflection of light is there-
fore very important to a photographer. Whenever light is
reflected from a matte surface , we have diffused reflec –
tion of the light in various directions as the reflecting
elements of area are differently oriented and the surface
will have a uniform general illumination. On the other
hand, when light is reflected from a highly polished
surface the light reflected shows a distinctly direc-
tional character and if the lens is placed Where it
picks up this directed light, images of the source or
very strong highlights are likely to be seen in the for
cal plane. This is known as specular reflection. Every-
one has seen photographs of persons in Which eye glasses
are merely white disks obliterating eye detail entirely.
It is not unusual to see pictures taken by artificial
light in which the lights themselves appear by reflec –
tion in window panes or bookcases. With ground glass
focusing, these effects are easily seen and avoided.
With cameras where this is not possible, the operator
should place his eye as close to the taking lens as pos-
sible and note whether he can see objectionable reflec –
tions.
- . Laws of Reflection. Whenever light is reflected,
the angle of incidence is equal to the angle of reflec –
tion. The incident ray, the normal to the surface and
the reflected ray lie in the same plane. This means
that when we get the objectionable reflections that have
just been mentioned, the reflecting surface is so placed
and Oriented that incident rays can pass from the source
of light to the polished reflecting surface and then to
the lens according to this law of reflection. In the
ll3


ll!! FIRST COLLEGE COURSE IN PHOTOGRAPHY
case of the person Wearing glasses, a slight change in
the position of the head Will usually be sufficient to
remove objectionable reflections. When artificial
lights are used, a slight change in the position of a
light will often serve the same purpose.
Another interesting case of specular reflection
is in the catch lights in the eyes in portraiture. Such
lights, which are actually images of the source reflect –
ed by the cornea, serve to give life and brilliancy to
the eyes. It is Well to note, however, that these catch
lights are not likely to be pleasing if multiple as they
might easily be if several artificial lights are used.
The exact location of the image formed by a plane mirror
gives us additional information about the laws of re-
flection.
Experiment. Place a plane mirror in a vertical
position in the center of a piece of paper and an invert–
ed thumb tack an inch or two in front of the reflecting
surface to serve as object. Sight carefully along a ruler
at the reflected image or the tack and draw a line on the
paper to indicate the direction. From a second position,
repeat this. Next, after marking the location of the mir-
ror, remove the mirror and produce the two lines until
they meet. This intersection locates the image of the
thumb tack.
Image
º
/ 1 N
/ | N
/ | N
Æ | \
A |
C / ! \s
^ , º,
, fi`, ir's
/ ^ / . \
." 9/ i **,
/ Object N
/ N
€ / \a
4. e = 0
Position | - Position 2
Figure I 8. Location of image in plane mirror.
gº is
i.
---º
PHOTOGRAPHIC OPTICS 115
Figure 18 shows such a drawing. The two lines drawn by
sighting along the ruler represent two reflected rays
from the object. The corresponding incident rays must
go from the object to the mirror at the point at which
the reflected rays intersect it. If these are drawn
and normals erected at the points at Which they rays
intersect the mirror, the following laws of reflection
can be verified by direct measurement.
l. The image of an object in a plane mirror lies as far
behind the mirror as the object is in front.
2. The line joining the object and image is perpendicu-
lar to the surface of the mirror.
5. The angles of incidence and reflection are equal and
the incident and reflected rays lie in the same plane
as the normal to the reflecting surface.
In general, the problem of producing a pleasing
effect in photographing any subject consists in light –
ing it so that detail desired can be clearly distin-
guished, yet. Without glare, meaningless highlights or
harsh shadows. This is equivalent to saying that every-
thing must be so arranged that the object reflects the
correct amount of light in desirable directions. More —
Over, since the reflecting power of the object is not
easily changed, it is usually more practical to accom-
plish this by paying careful attention to the location
and intensity of our light sources. In general, point
light sources such as a clear glass projection lantern
bulb produce illumination with very harsh shadows while
an extended source produces much better modelling. The
reas on for this is that an extended source may be re-
garded as a large number of point sources distributed
Over a considerable area and while each individually is
Casting shadows, the aggregate effect is to have the
general illumination from some of the area reduce the
shadows produced by the rest of it so that the lighting
is much less harsh. This is one reason why lights with
large reflectors are very desirable for photographic
use. Diffusing screens of thin translucent material
placed over the lights also serve to soften and diffuse
the light reflected by the object to such a desirable
extent that it is somewhat puzzling to discover why

116 FIRST COLLEGE COURSE IN PHOTOGRAPHY
their use is not more general. Probably this is due to
the fact that the general illumination is cut down by
such screens by about fifty per cent but the sacrifice
of light is far more than compensated for by the im—
provement in quality.
The Refraction of Light. Whenever light passes
obliquely from one medium into another in which its ve-
locity is different, its direction is changed. This
bending occurs at the boundary between the two media.
A very important optical constant is the index of re-
fraction which is defined by the equation below.
Velocity in first medium
velocity in second medium
Index. Of refraction =
These velocities are usually not known with great ac-
curacy and would be exceedingly difficult to determine
directly. It is not difficult, however, to show that
they are proportional to the sines of the angles formed
by the incident ray and the refracted ray with the nor-
mal. As these angles are easily measured with any re-
quired degree of accuracy, it becomes a simple matter
to determine the index of refraction between any two
transparent media as follows:
Sine of angle of incidence
sine of angle of refraction
Index of refraction =
Example: Find the index of refraction, air-glass, if the angle of
incidence is 30° and the angle of refraction 209. Look-
ing up these angles in a table of sines, we find that sin i equals
.5 and sin r, .3H2. .
Index = .5/.312 = 1.16.
The index, glass-air, would be the reciprocal of this, .342/.5 or
.68.
When light is passing from a denser to a less
dense medium, it is unable to emerge under certain cir-
cumstances. It is a well established fact that the an-
gle of refraction is always greater than the angle of
incidence when light passes from a denser to a less
dense medium. As the angle of incidence grows greater,
:




ſºi.*
*-
º
!.
|
jº
f.
}
{
º
§fºt; .
gºjº-ß:
PHOTOGRAPHIC OPTICS 117
one will eventually be reached for which the angle of re-
fraction is ninety degrees. The ray will then emerge at
grazing incidence along the boundary between the two me—
dia as indicated by ray 2 in Figure 2. Since it is not
possible to have an angle of refraction greater than
ninety degrees, rays that meet the boundary at a still
greater angle than that indicated for ray 2 undergo re-
flection at the transparent boundary as indicated for
ray 5. This is known as total internal reflection and
that angle of incidence that results in an angle of re-
fraction of ninety degrees is the critical angle.
Less dense
medium
Denser
medium
figure 9. The path of a ray of light that meets
a boundary between a less dense and a denser medium. Note
the following.
l. Some light is always reflected at such a boundary.
2. When light is passing from a less dense to a denser me—
dium, it is bent toward the normal.
5. When light is travelling in the reverse direction, it
is bent away from the normal.
4. The change of direction takes place at the boundary be-
tween the two media. *
5. Angle l is equal to angle 3 and is greater than angle 2.






118 FIRST COLLEGE COURSE IN PHOTOGRAPHY

| 2^ Less dense
medium
2 Boundary
3
_D_T - 3- L
2 | Denser medium
º / -
C
Figure 20. Total internal reflection and the crit-
ical angle. Note the following.
1. Ray l is an ordinary refracted ray.
. Ray 2 emerges at grazing incidence.
. Angle BOC is the critical angle.
. Ray 5 has undergone total internal reflection. The
angles of incidence and reflection are equal.
Angle DOC = angle COL.
:
A close examination of any refracted rays
through a single lens or prism will show that the light
is not only deviated but that it is also dispersed so
that the rays show colored edges. This results from
the fact that the different colors in white light are
not all deviated by the same amount when they pass into
a new transparent medium and We therefore see the sepa-
rate colors When they are no longer superposed. In a
prism, this dispersion can be made very marked.
º
PHOTOGRAPHIC OPTICS - ll.9
Violet
Figure 21. Dispersion of light by a prism.
Note the following.
l. Deviation and dispersion occur at both boundaries.
2. The rays are bent in such a direction that they en-
close the thick side of the prism.
3. Violet is refracted most and red, least.
Pinhole Cameras. Especially in tropical coun-
tries where the light is very intense, it is a matter
Of common observation that a darkened enclosure int. O
Which light is admitted through a small aperture Will
show on the opposite Wall a recognizable, inverted
image of Whatever is outside. If the aperture is made
larger, the image becomes brighter but less sharp While
it changes into a bright spot resembling the hole when
the aperture is sufficiently enlarged. As a matter of
fact, there is an optimum size for the opening and the
image is also less sharp if the aperture is very minute
because of diffraction but this condition will not be
realized unless rather special precautions are taken to
make an exceedingly minute pinhole.



120 FIRST COLLEGE COURSE IN PHOTOGRAPHY

a b c d
#
e Camera
Pinhole
Figure 22. Pinhole camera. In the above drawing
of a pinhole camera, we note the following.
l. The image is inverted.
2. The image becomes larger as the image plan is moved
from a to b, c, or d. t
3. The exact location of the image plane is immaterial
as light is not focused by a pinhole camera.
Experiment: Mount an incandescent light with
clear bulb, an opaque cardboard screen that may be punched
with a darning needle and an image screen in the order in-
dicated on an optical bench. When a hole is punched in
the cardboard, an image of the filament will be seen pro-
jected on the image screen. Punching a second hole pro-
duces a second image and so on until, finally, when enough
holes are made the images overlap to such an extent that
their individual identity is lost and one sees only a
bright spot of light.
Actually, a point on an illuminated object is
reflecting light rays in many directions and the func –
tion of the pinhole is merely to limit the number of
these that fall on the image screen so that they will
be distinguishable as an image of the object. The image
is inverted because the ray through the pinhole from the
top of the object falls on the bottom of the screen
While one from the bottom of the object can only trav-
erse the pinhole to reach the image screen near the top.
Any light tight box having some means of fastening a
film at one end may be used as a pinhole camera. At
the opposite end of the box an exceedingly smooth,
round pinhole should be made, preferably in a thin
sheet of metal mounted there. A cardboard flap so
º
.
PHOTOGRAPHIC OPTICS 121
mounted that it can cover the pinhole and be removed at
will can serve as a shutter. Apart from their the O-
retical interest, pinhole cameras have value Whenever
it is desired to photograph objects at various dis -
tances with approximately equal sharpnes S. They are
also capable of including a very large angle of View .
Their limitations are that they cannot give the Sharp-
ness of definition of a fine lens and that the exposures
are very long, usually from thirty seconds to several
minutes in Sunlight.
Experiment: Using the same equipment as in the
previous experiment, take another cardboard screen and
make an aperture of the correct size to project the image
of the filament on the screen. Note the changes produced
in image size and brightness as the pinhole is moved near-
er or farther from the screen.
A very useful geometrical principle is illus –
trated here. Whenever images are formed either by pin-
holes or by lenses, rays drawn from the extremities of
the object through the aperture to the extremities of
the image form With the object and image respectively
tWO triangles, one in object and one in image space,
that are geometrically similar. Corresponding sides
are therefore proportional. From this it follows that
Height image Distance image Hi Di
Height object Distanceobject Ho Do
Experiment: Punch holes in the cardboard so that
eight or ten images can be seen on the image screen. Next,
take an ordinary reading glass and cover all the pinholes
with it. Move the image screen back and forth until the
image is as sharp as possible. It will be found that the
multiple images formed by the separate pinholes have now
become one by Superposition that has a brightness equal
to the sum of the separate brightnesses. For best results,
the distance from the light to the image screen should be
a little more than four times the focal length of the lens.

122 FIRST COLLEGE COURSE IN PHOTOGRAPHY
O
|
|
|
|
|
|
|
|
>k
B. Do
Figure 23. Object—image size relation. In the
above drawing, KB represents the object and LP, the image.
The two triangles, KOB in object space and LOP in image
space, are similar because they are equiangular. The
ratio, Di/Do, represents the scale of reduction or magni-
fication of the image in comparison to the Object.
The Lens Formula. It Will be realized fºr Om the
foregoing experiment that a lens can collect light over
a much larger area than can a pinhole and form a sharp
image. It thus produces a brighter image that makes
possible a great reduction in exposure. The disadvan-
tage is that focusing is now necessary for, in general,
there are but two positions of the lens for a given
separation of object and image screen where the image
Will be sharp. As a matter of fact, no real image can
be formed if the separation of image plane and object is
less than four times the focal length of the lens.
The formula that expresses the space requirement
for exact focusing is one of the most all-inclusive gen-
eralizations in optics and may be stated as follows:
l + l l
Object distance image distance T focal length
or l/Do + 1/Di = 1/f"
l. A geometrical derivation of this formula may be found in Black's
Introductory Course in College Physics, page 617; an analytical
derivation, in Robertson's Introduction to Physical Optics,
pages 81–5, Second Edition.

PHOTOGRAPHIC OPTICS 123
It will be instructive to investigate where the image
will be formed for various object distances as this
will tell us which cases of image formation are of
practical value in photography.
Case I. If Do is very great, l/Do approaches
zero as a limit and the lens formula becomes
l/Di = 1/f or Di = f'
This enables us to define the focal length of a lens as
the image distance when the object is at infinity. It
also shows us where the image Will be formed When We
focus upon remote objects such as a distant mountain,
the sun or the moon. As a matter of fact, the focal
length is the minimum distance from the image at Which
it is possible to place the lens. The foregoing also
suggests a simple way of making an approximate determi-
nation of the focal length of a lens. All that is nec –
essary is to focus the image of the sun on a card With
such a lens and the distance between the lens and the
card is the focal length.
It should be mentioned that the lens formula as
given here applies strictly only to infinitely thin
single lenses while photographic objectives are com-
pound, thick lenses. Quantitative work in the Way of
lens measurements must take into account the so-called
nodal points of a lens system and deal With the con-
siderably more complicated formulas of thick lens op-
tics. For a photographer, however, the simple thin
lens formula is usually sufficient as he uses it merely
to gain a general idea of the order of magnitude of the
Quantities involved and for such purposes the l’efine-
ments and difficulties of thick lens Optics Would sub-
stitute laborious processes for very simple ones merely
to contribute a degree of accuracy that is not ordinari-
ly required.
Let us imagine that We are Watching the image
on the ground glass of a distant locomotive as it trav-
els toward us. This image Will be sharply focused When
the ground glass is at a distance equal to the focal
length from the lens. As the locomotive approaches,


12}} FIRST coLLEGE courSE IN PHOTOGRAPHY
the ground glass must be slowly moved back and the
image grows larger. In fact, the image Will become so
large by the time the locomotive is about twenty feet
from the camera that it, Will be Well to substitute a
toy locomotive for the real one. By the time this is
twice the focal length of the lens from it, the image
will be formed at the same distance from the lens on
the other side and the image is the exact size of the
object. In other Words, while the object has moved all
the way from infinity to a point twice the focal length
of the lens from it, the image has moved back only from
the focus to a distance equal to twice the focal length
On the Other side. Case I represents
the camera as it is ordinarily used to produce images
that are reduced in size in comparison to the object.
Next, consider the use of
the camera for exact size copying. In this instance
DL and Do are both equal to twice the focal length of
the lens. In the case of the toy locomotive, the image
would be the same size as the object. If it continued
to move in toward the lens, the ground glass Would need
to be moved farther away from the lens and an enlarged
image would result. This is Case III - Of
image formation and is represented by the enlarging
camera and the projection lantern. Case IV, which rep-
resents the object at the focus and the image at in-
finity, has little practical significance for photog-
raphers. * A spotlight adjusted to give a parallel beam
Would represent this case but a camera obviously never .
attempts to cope with an image that is formed at in-
finity. Finally, when the object approaches nearer the
lens than the focus, the image is on the same side of
the lens as the object. This is Case V, -
and represents an image that cannot be of value in a
camera. An example of this is the use of a reading
glass as a simple magnifier.
Applications of the Lens Formula. The follow-
ing problems illustrate types containing information of
2. In spectrographs, light passing through the slit may be made
parallel in this way before dispersion.
ſº
#
PHOTOGRAPHIC OPTICS 125
value to photographers for which approximate answers
are available by use of the simple lens formula.
l. In photographing the moon, show that Di is equal to
the focal length.
Here, Do = co
Substituting in the lens formula, we have
++ + = + + = 0
CO Di T f co T
l l
F- = F and D = f°.
Di F Il f
2. Find Di When a lens having a focal length of 2 inch-
es is focused upon an object 3-1/2 feet distant.
Here, Do = H2 inches.
Substituting in the lens formula, we have
+++ - + + – 4 + – £9.
IE * B = a B = 2 - ||a = Tº
42
2O = 2. l inches.
D
3. How would the size of the image compare with that of
the object in the above case ? -
D4 2. l l
e e = ++ — - - -
- Ratio of reduction Do 112 2O
The dimensions of the image will be 1/20 the dimen—
sions of the object.
H. What bellows length will be required in order to
photograph a beetle four times its natural size with
a six inch lens 2
Here, f = ′ 6 inches and Di = 1; Do
Substituting in the lens formula,
++ l = + Multiply by 12D
Do 4Do 6 ll lp Lyſ y - O
l2 + 5 = 2Do 2Do = 15 in. Do = 7# in.
4Do = 3O in.
The bellows length should be 30 inches.

126 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Spherical and Chromatic Aberration. While
images are easily formed With Single lenses that are
recognizable, a critical examination of them will showſ
that they are actually unsharp and have colored edges.
Two very serious defects inevitably exist in such
lenses, spherical and chromatic aberration. The first
arises from the fact that the Outer Zones of a lens do
not bring the light to the same focus as the inner -
zones. While this has sometimes been minimized by a
change in the curvature of the outer part of the lens,
this is difficult and expensive as the processes in-
volved in lens making lend themselves best to the pro-
duction of spherical curves. The simplest Way to re-
duce spherical aberration is by cutting off the outer #Tº
zones by means of a diaphragm. This has the disadvan- §
tage of cutting down the amount of light transmitted by *
the lens : - ~
Experiment. (a) Take an ordinary convex lens such
as a reading glass and project the image of the filament
of a clear glass electric light bulb on a screen. Note . . . .
that the image formed is somewhat unsharp and has colored - #
edges. Compare the image obtained in this way with one * . . .
formed by a fine photographic lens. (b) Form an image º
with a reading glass as before and note how this improves * T
in sharpness when a cardboard diaphragm is placed over the T
lens that permits light to pass through only the central T.
portion. -----------
>
Figure 24. Spherical aberration. Note that the Fº
Outer Zones bring the light to a focus at points closer *-
to the lens than the inner zones.


PHOTOGRAPHIC OPTICS 127
We have already seen that light of different
colors is refracted by different amounts in passing
through a prism or lens made of a single kind of glass.
In the case of a lens, this would mean that the image
would show a color fringe and Would not be sharp. In
fact, no less a pers on than Newton became so thoroughly
convinced that this color fringe was inherent in the
nature of lenses that he turned his attention to the
development of concave mirrors for image formation. In
these chromatic aberration is not present as the mirror
reflects all colors in the same directions and no re-
fraction of light is involved.
%
White \
ar
Figure 2.5. Chromatic aberration by a simple lens.
Note the following.
l. The light is not refracted at the boundary at which it
enters the glass because it is travelling normal to the
Surface.
2. Blue light is refracted more than red light so that it
comes to a focus farther in.
The exact amount of deviation produced by a lens
or prism depends partly upon the kind of glass of which
it is made and partly upon the curvature of the lens
Surface or the refracting angle of the prism. Moreover,
Various kinds of glass differ considerably in the devia–
tion and dispersion that they produce. As a result, it
is possible to construct a prism or a lens out of two
kinds of glass that Will deviate the light and form a
much sharper image with practically uncolored edges.



128 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Experiment. Pairs of prisms of crown and flint
glass are obtainable that have their refracting angles
matched so that the two can produce deviation of light
without dispersion into the separate colors. Allow a
loeam of light from a projection lantern to pass through
a narrow slit and then through one of the prisms. The
light will be deviated and spread out into a spectrum
that may be seen on the wall if the room is darkened.
Either prism alone deviates and disperses the light.
Note, however, that while the dispersion of the two sep-
arate prisms is the same, the deviation is quite differ-
ent. Now place both in the beam of light together so
that their refracting angles face in opposite directions.
Since each is attempting to disperse the light in a di-
rection opposite to that of the other and their disper-
Sion, for two colors is the same, the net result is that
these colors are not dispersed. The beam is deviated,
however, because the two deviations are not identical and
we see a deviated beam of white light probably slightly
colored at the edges as perfect achromatism for all
colors is not possible with only two kinds of glass.
By taking a convex lens of crown glass and a
concave of flint having just the right curvatures to
compensate each other, it is possible to produce a lens
that Will bring light of two colors such as blue and
green to the same focus. Before photographic materials
Were sensitive to red light, this Was all that was nec –
essary to secure a sharp image. Today, very fine
lenses are corrected for three colors, blue, green and
red, by the use of three kinds of glass of suitable
curvature. Such lenses are likely to be remarkably
free from chromatic aberration, It is interesting to
note that very old photographic lenses may not be suit —
able for use with red sensitive film if they were made
before the use of panchromatic emulsions because it was
then unnecessary to design lenses that would make the
image formed by red light coincide With the green and
blue images as the red image did not affect the emul—
Sion.
The Ideal Photographic Objective. The simple
lenses that We have been discussing up to this point
produce images that are far from sharp. The focal
§
º
PHOTOGRAPHIC OPTICS 129
surface, instead of being a plane, is saucer-shaped and
there is a very considerable amount of distortion of
the image particularly in those portions that are far-
thest from the center. That it has been found possible
to develop lenses that combine exquisite definition,
large aperture, flatness of field and freedom from dis-
tortion to the extent that this is done today seems
little short of miraculous. In fact, it is probably
not an over-statement to claim that the computation of
an exceptionally fine objective requires inspiration
little short of genius. Many mutually contradictory
factors are involved and an alteration that may produce
a desirable effect in one respect may upset something
else. It has been stated that the computation of the
Zeiss Tessar consumed two or three years. Photographic
objectives present one complication not found in as –
tronomical objectives because of their large angle of
view. Oblique pencils of light are therefore important
and these present serious complications. An ideal Ob-
jective might be defined as one that would give exact
point for point correspondence between a plane in Ob-
ject space and one in image space. This Would imply
precise definition, flatness of field and congruence
|between object and image space. Below are listed the
more common aberrations that interfere With the reali-
Zation of this.
l. Spherical aberration. We have already noted that
the outer zones of a simple lens do not bring the
light to the same focus as the inner zones.
2. Chromatic aberration. This arises because light of
different colors is not brought to the same focus by
a simple lens.
5. Flatness of field. It is very essential that the
image surface shall be a plane in order to prevent
a falling off in sharpness toward the edges of a
picture.
!. Astigmatism. With a simple lens, oblique pencils of
light form images of points in object space that are
quite unlike these points in form.


130 FIRST COLLEGE COURSE IN PHOTOGRAPHY
5. Distortion. It is an extremely difficult problem to
produce a lens that can photograph a subject such as
a piece of cross section paper so that the lines in
image space are all straight, rendered in the proper
relative position, and With equal sharpness.
Finally, owing to the Wave nature of light, a point in
object space is inevitably rendered as a minute area in
image space With a somewhat unsharp edge. In fact, the
image of a brightly illuminated pinhole made With a
very fine lens at a distance and highly magnified Will
show One or tWO C Oncentric circles of illumination
around the central disk.
The student is urged to give very careful
thought to the contents of this chapter. While it is
unlikely that most of us will ever need to concern our-
selves with lens computations, some appreciation of the
complexity of the problems involved cannot but add to
an understanding of What a marvelous thing a fine objec-
tive really is and what a privilege We enjoy in having
them at our disposal. In addition, the fundamental
theory presented here has very extensive implications
that give adequate answers to innumerable questions as
they arise but only if it has been comprehended.
QUESTIONS
l. State the reflect iOn laws.
2. Explain why broad light sources are desirable in
photography.
3. HOW may specular reflection be avoided in photo-
graphing a person Wearing glasses 2 What causes it 2
4. Locate the image of an object reflected in a plane
mirror. Trace the actual and the apparent paths
from the object to the eye of the observer.
5. As you Walk away from a plane mirror, does your
image diminish in size 2 Explain.
6. The following question, While not particularly
closely related to photography, is a very good test
of your understanding of the reflection laws.
What is the minimum length of perpendicular,
plane mirror in which you can just see yourself full
º
PHOTOGRAPHIC OPTICS 151
lO.
ll.
l2.
13.
l!.
l6.
l'7.
18.
l9.
20.
length? Check your conclusions with a mirror.
. Why does the pinhole camera produce an inverted
image 2
Measure the angles With a protract Or and determine
the index of refraction from the denser to the less
dense medium in Figure 2. Do the same from the
less dense to the denser medium.
Draw Figure 11 from memory. Which color is refract –
ed most 2
Describe the image in each of the following cases
of image formation by a lens.
(a) Object at infinity.
(b) Object between 2f and infinity.
(c) Object at 2f.
(d) Object between 2f and f.
(e) Object inside f.
Make drawings to show cases I, II, III and V of
image formation by a convex lens.
What is spherical aberration and how can it be mini-
mized With a simple lens 2
Make a drawing to show chromatic aberration. Which
Color has the greatest deviation?
Describe the experiment. With the achromatic prisms.
Find the critical angle for Water if the index of
refraction, Water-air, is .75.
From the above data, compare the velocities of
light in Water and in air. -
In Figure 8 what color would the image have at the
edges if the focal plane were placed at B2 At R2
EXplain.
An enlarger having a lens with a focal length of 4
inches is to be constructed to make 2X to 5X en-
largements.
(a) Find Di and Do for the limiting cases.
(b) Draw a diagram.
(c) What bellows extension will be required?
What bellows length will be required to photograph
an insect lo times its size with a 2-inch lens?
A Telyt lens for a Leica has a focal length of 8
inches. The minimum distance at which it can be
focused Without the use of extension tubes is 9
feet, .
(a) Find Di.
(b) Find the ratio of reduction.
(c) Find the angle of view if the negatives are
l x li inches.

Chapter | X
MO RE PHOTO GRAPH | C OPT | CS
Stops and Stops Numbers. It has always been
customary to build photographic shutters with some
means of varying the size of the lens opening. This
serves two important purposes, first, to control tile
amount of light that falls upon the film and, second,
to make possible a variation in the depth of field
Within which a reasonably sharp image is secured. A
convenient Way to designate the various stop openings
Would be by numbers preferably so chosen that a given
number Would indicate that same relative exposure With
all lenses regardless of differences in design or focal
length. Stop numbers are therefore defined as follows.
focal length
diameter of entrance pupil
Stop number =
As the entrance pupil in photographic lenses is defined
by the diaphragm, the stop number tells us the number
by which we must multiply the effective opening to Ob-
tain the focal length of the lens.
The light admitted by each opening, however, is
proportional not to the stop number but to the square
of this number as this is a function not of the diam-
eter but of the area of the opening. The diagrams be-
low show the exact size of the effective stop openings
f/8 F/4 7/2
Figure 26. A comparison of different apertures
for a 2-inch lens.

132
MORE PHOTOGRAPHIC OPTICS 133
&º
* - --
FºL
º
at the stops indicated for a lens having a focal length
of two inches. We can express this relation in general
terms by stating that the light admitted by different
stops is inversely proportional to the squares of the
stop number’s .
Li/L2 = (S2)*/(S1)*
Example: Compare the speeds of two lenses whose maximum stops
are f/2 and f/8.
La - 82 - 64 – 16
Here, I.- - -2 = T = i
The f/2 lens admits 16 times as much light as the f/8
lens.
Often, what interests us is the relative expos –
ures when We use the same lens at different St Op Open-
ings. Here, since the smaller stop number is associat-
ed with the larger opening and, therefore, With the
shorter exposure, we have a case of direct proportion
which may be expressed as follows.
E1/E2 = (S1)*/(S2)*
Example: If l second is the correct exposure at f/8, what is the
correct exposure at f/16?
E1 = l sec.
8 2
163 =
6,
256
:
6Hz = 256 x = | seconds
The following table shows the stop numbers or –
dinarily marked on lens barrels to indicate the higher
stop numbers. -
Stop (f) 8 ll 16 22 32
f
lſº
2 6l. 121 256 l;8l. 102h. 2025
It, Will be noticed that the f values have been so chosen
that their squares double as We pass from one to the
next higher which means that the equivalent exposures
bear the same relation to each other. Thus, if the cor-
rect exposure is known för one stop, simple multiplica-
tion or division by powers of 2 will indicate the ex-
posure at any other stop.



l3 || FIRST COLLEGE COURSE IN PHOTOGRAPHY
Example: If l/25 second is the correct exposure at f 8, what is
the correct exposure at stop lºº
Since this stop is 5 stop numbers to the right, the ex-
posure will be 25 or 52 times as great.
For the smaller stop numbers on faster lenses,
no such simple relationship exists probably because
they came into use one at a time and indicated the max-
imum stop openings available at the moment. With im–
proved lens design. In the table below, it will be
noted that several are about double other stops in the
series but there are many exceptions.
Stop (f) 1.5 2 2.5 2.8 3.2 3.5 lº.5 6.3
f* 2.25 l; 6.25 7.8l. 10.2), 12.25 20.25 ko.25
In such cases, the exposure ratio can always be obtained
by squaring the stop numbers.
In general, it will be evident that exposures
may be altered by varying either the stop or the shutter
speed. Which is more desirable depends upon circum-
stances. A large stop admits maximum light but gives
little depth of field . While this would be undesirable
in making a picture that sought to show maximum detail
at various distances from the camera, it might be very
desirable When one Wishes to subdue an undesirable back-
ground. A large stop is also desirable when one wishes
to stop fast action under adverse light conditions. As
the stop is made smaller, there is a gradual increase
in depth of focus.
It is not safe to assume that an extremely fast
lens stopped down considerably gives as great critical
definition as a slower lens at the same stop. The dif-
ficulties inherent in computing very fast lenses demand
certain compromises that may make it necessary to im-
pair performance slightly at smaller stop openings. On
this account, ultra-fast lenses are to be regarded as
Special purpose equipment rather than standard and are
not used. When a slower lens Will suffice.
In motion picture cameras, exposure is usually
regulated by adjusting the stop rather than the shutter
Speed. Such cameras have rotary shutters and shutter:
i.
f
MORE PHOTOGRAPHIC OPTICS 135
speeds are changed by changing the rate of rotation,
normally sixteen revolutions per second, to some other
rate between eight and one hundred twenty-eight. While
this effectively changes the shutter speed, it also
changes the number of pictures taken per second by the
camera and so produces a very marked change in the
tempo of the action when it is run through a project Or
at normal speed. Hence, exposures are usually regulat-
ed by a change in stop except when a change in tempo
is desired.
In general, the exposure is inversely propor-
tional to the brightness of the subject, directly pro-
portional to the square of the stop number and inde –
pendent of the distance of the subject. That exposure
is independent of the distance of the subject is sub-
ject to the qualification that it must be sufficiently
distant so that the image formed is considerably re-
duced in size. A photograph of a person ten feet from
the camera Will require the same exposure as one twenty
feet distant. While it is true that the light reflect –
ed by the person obeys the inverse square law and so
Would represent four times as great intensity at ten
feet as at twenty, it is also true that this light
energy is forming an image having four times the area
so identical exposures yield the same average light per
unit, area. On the film. In both cases the distance fºr Om
the lens to the film, Di, does not differ much from the
focal length of the lens so the stop used actually has
a value not far from what it would be for an object at
infinity. §
If the bellows is extended, however, to focus
upon a near object the actual stop number may be so
much greater than that indicated on the lens barrel
that serious under exposure Will result. Strictly
Speaking, the actual stop is not the focal length di-
vided by the diameter of the diaphragm opening but,
rather, the image distance, Di, divided by this quan-
tity. As a result, in the case of exact size copying,
Di is twice the focal length of the lens so the actual
Stop number is twice that indicated on the lens barrel
and the exposure at that stop is only one quarter as
great. This means that the stop number should be

136 FIRST COLLEGE COURSE IN PHOTOGRAPHY
multiplied by a correction factor in all cases for
Which Di assumes values that differ greatly from the
focal length. This correction factor is Di/f and has
Values that are by no means negligible in certain cases,
as shown in the following table.
Di/Do Or Di (from lens Multiply stop
D# /f
magnification formula) 1/ number by
l 2f 2 2
2 5f 3 3
l; 5f 5 5
LO Llf ll ll
The Circle of Confusion. While We have previ-
Ously dealt with rays in considering the formation of
images by lenses because these most clearly indicate
Specific directions, it will now be desirable to con–
sider another aspect of image formation. Actually, a
point on an object may be thought of as reflecting di-
vergent light in many directions . . That portion will be
effective in forming an image that falls upon the effec –
tive area of the lens where it will be made convergent
and brought to a focus on the film. Thus, we may pic –
ture a cone of light having its vertex at a point on
the object and its base, the effective lens area as the
light energy that is effective in producing an Image of
the point. -
Lens
Figure 27. Light from a point effective in pro-
ducing photographic image.
In the above diagram we note that the beam in image
Space becomes divergent after it passes through the for
cal point and that the effect of stopping down the lens
}:

MORE PHOTOGRAPHIC OPTICS 137
is to reduce the area of the base of the cone of light
and also the vertex angle as shown by the dotted lines.
Only one plane in object space can be in sharp-
est focus. In general, with a three-dimensional sub-
ject, we must arbitrarily choose this plane by select-
ing that one in which the most important portions of
the scene lie and focusing sharply there. The images
of portions either nearer or farther away Will be pro-
jected onto this plane more or less unsharp depending
upon their distance from the principal object.
A
F
C
#
º
Yº-
—
Figure 28. Circles of confusion.
In the figure above, it is assumed that the
principal object forms an image at F While an object
farther away forms one at A and one nearer, at C. Light
converging either to A or C will form a circle of sen-
sible size on the film at F. These circles are known
as circles of confusion. The image of a scene is a
composite of such points representing objects at vari-
ous distances. Some are very minute and others are
disks of increasing size as the objects rendered lie
farther and farther from the principal object. To the
eye, all Will look equally sharp if their circles of
confusion are less than .1 millimeter in diameter and
the picture is viewed at a distance of ten inches. If
the negative is to be enlarged, the permissible circle
of confusion should be smaller but need never be small-
er than . 025 millimeter as this value approaches the
diameter of the grain clumps of which the image is com—
posed.







138 FIRST COLLEGE COURSE IN PHOTOGRAPHY
It is an exercise in simple plane geometry in-
volving similar triangles to discover where the planes
A and C lie for a given value of the circle of confu-
sion. This gives us the depth of focus in image space.
Then, applications of the lens formula Will enable us
to compute the values of Do corresponding to image
planes at F and C.
In Figure 10, triangles DXL and KOL are similar.
DX = radius of effective aperture of lens.
XL = Di.
KO = radius of permissible circle of confu-
Sion.
OL = distance from focal plane to image
plane that gives circle of confusion
KO. -
DX KO
Then, XI. = OL
Exerything is known except OL which can therefore
be computed. The information more useful to the photog-
rapher is the corresponding distance in object space. For
this, XO equals Di, the focal length of the lens was giv-
en, and Do can be computed from the lens formula,
l/Do + 1/Di = 1/f. This value would represent the maxi-
mum distance at which an object could lie and be in sat-
isfactorily sharp focus when the focal plane was at F.
By a similar computation, the nearer point in object space
could be found that would form a sharp image at C.
All such computations, though capable of abridg-
ment by the use of formulas that do not bring out the
fundamental geometry so clearly, are admittedly laborious
and the photographer ordinarily obtains such information
from tables such as that following.
Such tables are applicable only to lenses of the focal
length for which they have been computed and should
specify the circle of confusion used. They are most
useful in connection. With cameras that do not permit
direct focusing, particularly when these are to be used
at very short distances where depth of field is so
limited that the use of too large a stop might result
in failure to get everything desired into sharp focus
at the same time.
H
MORE PHOTOGRAPHIC OPTICS 139
DEPTH OF FIELDS OF 50 MM FOCUS LENS
3-4/2 3-10/8 4-9/8 5-8 6-6 7-5 9- |0-8 || 3 | 6-8 23 33-2 49-7 98 ft. & in.
f:2.5 3.5 4 5 6 7 8 |0 |2 |5 20 30 50 |00 CO {+.
3-71%, 4-2 5-3 a 6-5 7-7 8-9 1-2 13-8 17-8 25- 43-2 102 OO ° ft. & in.
3-4 3-9/2 4-8 5-6 6-4 7-2 8-9 || 0-3 || 2–4 ||5-7 2 | 29 4 | 70 ft. & in.
f:3.5 3.5 4 5 6 7 8 |0 |2 | 5 20 30 50 |00 CO #.
3-8/2 4-3 5-5 6-7 7-9 9-0 | 1-8 (4-6 19-1 28 50 °o oo oo ft. & in.
3-3/2 3-8%. 4.7 5-5 6-2 7-0 8-5 9-10 || |-9 |4-8 [9-4 26-2 35-5 55 ft. & in.
f:4.5 3.5 4 5 6 7 8 |O |2 15 20 30 50 |00 CO {+.
3-9 4-4 5-6 6-9 8-0 9-4 12-3 ||5-5 20-8 3|-7 66 CO CO * #. & in.
3-2)/2 3-7/2 4-5 5-2 5-1 || 6-7 7-1 || 9-2 10-10 13-3 17 22 28 39 ft. & in.
f:6.3 3. 4 5 6 7 8 |0 |2 |5 20 30 50 |00 CO #.
3-10 4-5/2 5-9 7-1 8-6 IO- 13-5 17-4 24-4 4| | 29 CO od ° ft. & in.
3- || 3–6 4-3 4-1 || 5-7 6-2 7-4 8-4 9-8 1-7 4-4 (7-8 21-6 27 ft. & in.
#:9 3.5 4 5 6 7 8 |0 |2 15 20 30 50 100 CO {+.
4-0 4-8 6- . 7-8 9-5 ||-4 ||5-9 2 |-5 33-3 75 CO &O CO °o H. & in.
3-0 3-4 4-0 4–7, 5-2 5-8 6-8 7-5 8-6 9-1 | | |-| | |4-2 || 6-5 20 ft. & in.
f: [2.5 3.5 4 5 6 7 8 |0 |2 15 20 30 50 |00 CO #.
4-3 5-0 6-8 8-8 10-10 || 3–6 20-4 30-9 63 OO CO CO CO °o #. & in.
2-9/2 3-I 3-8 4-2 4-8 5-0 5-9 6-5 7-2 8-| 9-5 |0-9 |2 |4 ft. & in.
#: | 8 3.5 4 5 6 7 8 |0 |2 |5 20 30 50 |00 CO #.
4-8/2 5-8 7-1 | 10-8 4-4 19-3 37-3 98 CO CO CO CO CO ° H. & in.
Teica Data Book
It should now be apparent Why stopping down a
lens increases its depth of focus. Since this makes
the vertex angle of the cone of light smaller, (Fig-
ure 27) planes A and C can move farther from the focal
plane F (Figure 28) before light from point sources
focused here Will produce images on F larger than the
permissible circles of confusion. On this account, it
is common practice to reduce the size of the effective
aperture whenever necessary in order to bring objects
at different distances into sharp focus. This can
scarcely be overdone with ordinary photographic sub-
jects as the observer gains an impression of increased
sharpness as more and more of distance and foreground
are brought into focus. Actually, however, with any
lens there is an optimum stop that produces the utmost
in the Way of critical definition in the sharply for
cused image plane. See Plate VII, Certainly, it would
be very desirable to know which stop this is in the
case of an enlarger lens.
While depth of field increases as the lens is
stopped down, resolving power decreases under these
conditions. Thus, one factor that contributes to the
highest critical definition is opposed to the other


ll. O FIRST COLLEGE COURSE IN PHOTOGRAPHY
and it is therefore necessary to arrive at the best
practical compromise by using one of the intermediate
stops. See Plate VII.
The Eye as a Camera. In some respects the eye
is very like a camera but in others, it shows distinct
differences that need to be recognized if one is to
understand clearly the psychological interpretation of
the photographic image by the observer. The eye has a
lens which focuses by changing its curvature. The eye –
ball is the camera and the retina corresponds to the
film. The retina, however, is a curved rather than a
plane surface and only a very tiny area corresponding
to not more than three or four square millimeters at a
distance of ten inches in object space is in the region
of sharpest vision. Surrounding this is a larger re-
gion of relatively sharp vision which comprises a vis-
ual angle of a few degrees. By the use of the muscles
of the eyes it is possible to include about forty-five
degrees in the region of satisfactorily sharp vision
Without moving the head which may be the reas on Why this
angle of view seems most natural to us in photographs.
Most astonishing of all, our angle of vision comprises
more than one hundred and eighty degrees if we include
not only the space in which We can distinguish detail
but also that outlying region in Which vision tells us
little except that an object is present or absent.
Experiment. (a) Make a small dot on a piece of
paper and focus your eyes on it sharply. Place another
dot where you can see it with equal sharpness while con-
tinuing to look at the first. These are not likely to be
more than 2 millimeters apart and indicate the approximate
limits of the region of sharpest Vision.
(b) Determine the number of letters on a printed
page that can be seen clearly enough to recognize them
Without moving the eyes. At 10 inches, this is likely to
be a group half ºr three quarters of an inch in length.
(c) Determine the angle within which you can see
clearly by moving the eyes while keeping the head still.
(d) Stand before a mirror and note the position of
a Small object as you bring it forward past your ear until
you can just recognize that something is there.
3.
MORE PHOTOGRAPHIC OPTICS ll. 1
From the foregoing, it will be realized that the term,
visual angle, is a very indefinite one that is almost
meaningless unless We define the degree of visual acui-
ty with which we are concerned.
The eye also represents refraction quite differ –
ent from that of an ordinary camera. The cornea, eye
lens, vitreous and aqueous humors all have indices of
refraction not far from that of Water so the refracting
system acts more like air-Water-Water than air-glass –
air. Curiously enough, most of the refraction takes
place at the outer surface of the cornea and Only a
small part in the eye lens itself. This is the reason
that it is impossible to focus objects sharply. When our
heads are under water. Under these conditions, the re-
fraction at the cornea which is surrounded by Water is
so reduced that the eye cannot form sharp retinal images.
Moreover, after satisfactory retinal images are formed,
some very interesting psychological feats have to be
performed before the brain has finished interpreting
What the eye has seen. It must first interpret invert –
ed images as a World that is right side up. Next, the
two slightly dissimilar retinal images constitute a
stereoscopic pair Which the brain interprets as a sin–
gle three-dimensional object. The brain also shows a
marked tendency to be ultra-conservative and exhibits a
marked tendency to interpret all retinal images in the
light of those to Which it is most accustomed. As We
look out upon the World, we see a visual field of fair
distinctness subtending about forty-five degrees and
long familiarity. With this visual angle causes us to
try to interpret all photographs as if they must have
been made With this angle of view. Ordinarily they are
because this seems most "natural" but when they are not,
our minds sometimes fall into strange errors of inter-
pretation as We shall show later. -
Perspective. By perspective we refer to the
projection of a three-dimensional scene on a surface,
Which is Ordinarily plane and perpendicular. Let us as –
Sume that We have projected such a scene on a film in a
pinhole camera with the image plane ten inches from the
pinhole. If We later take the developed negative and

ll;2 FIRST COLLEGE COURSE IN PHOTOGRAPHY
look at the scene through it with the eye at the posi-
tion of the pinhole, We shall find that our image Will
cover the scene point, for point and line for line. This
Would also be true and perspective would be geometrical-
ly correct if the image plane had been tilted but habit
and convention cause us to regard such projection upon
any surface except a perpendicular plane as unpleasant-
ly dist Orted. What our pinhole camera produced Was the
single point perspective of the artist with the vanish-
ing point at the pinhole through which all the rays had
to pass in order to reach the image plane.
We must next consider What factors cause a
photograph to look "natural" Quite obviously, the
perspective rendered in the photograph must be at least
quite similar to that rendered by the eye although it
is apparent that it cannot be identical because of the
different media involved in refraction, the curved
retinal surface, the ability of the eye lens to scan a
scene part by part by movement of the eye and un-
certainties about the precise meaning of the angle of
view. In addition, our brains tend to conventionalize
What a photograph should be and make a determined effort
to interpret all of them as if they had been made on a
perpendicular image plane and With an angle of view of
about forty-five degrees. If they were not made thus,
our minds tend to consider them distorted. Thus, a
photograph made With a camera lying on its back With
the lens pointed straight up in the midst of tall build-
ings looks quite like what we should see if we lay on
the Walk and looked up also. The point is, however,
that We do this so rarely that our minds have not
learned to appreciate such views and rather object to
them as grotesque. Whether it would be well to culti-
vate the "worm's eye" viewpoint is debatable and it is
surely more practical merely to remember this tendency
of the human mind to interpret all photographs as if
they had been made on a perpendicular plane With an
angle of view of about forty-five degrees and to give
especially careful thought to what we are doing when we
decide to violate these conditions.
Everyone has seen straight walks exhibit wide
curves in photographs made With a panoramic camera.
j
..
º-º-º:
PLATE X | | |
Effect of a Wide Angle Lens.
Both views were made with a wide angle lens and are
identical except that the lower view has been trimmed
to make it subtend the normal viewing angle of forty
five degrees. Note how this shortens the street and
removes the slanting perpendiculars.


l!!!! FIRST COLLEGE COURSE IN PHOTOGRAPHY
Here, too, there is nothing Wrong with the lens image.
The result looks strange because it was made on a cyl-
indrical focal surface and is viewed spread out in a
plane. Such a photograph enlarged sufficiently so that
the retinal images of the observer would be about the
size they would have been if he had stood at the camera
viewpoint and mounted on the inside of a cylindrical
surface so that the observer could view it. While stand-
ing at the center Would look perfectly normal.
Another case of perspective that looks wrong is
shown on Plate XIII of one of the extremely short and
narrow streets in Old Quebec taken with a wide angle
lens. The upper print, shows the entire picture and
represents an angle of view of about seventy-five de –
grees. As We look at it, We first mentally move the
foreground back until it subtends about forty-five de-
grees. The perspective, however, is that belonging to
a nearer viewpoint and the vertical elements recede in
size so rapidly that it makes the street seem abnormal-
ly long. In addition, the tops of the buildings and
the telephone poles lean in unpleasantly. If the angle
of view were smaller, they would not do that and they
look strange because the eye has no precedent for inter-
preting the Wide angle view since it cannot achieve it
With distinct vision to the boundaries. That the dis —
tortion is due to the Wide angle of view is shown by
the lower print which is identical With the upper except
that the outer margins have been cut away to give a more
normal angle of view. In this Way We have removed the
unpleasantly distorted vertical lines and shortened the
street. With a wide angle lens it is perfectly possible
to make a cramped steamship stateroom look positively
commodious. Such lenses almost inevitably produce false
impressions and should be used only when it is impossi-
ble to get sufficiently far away to use a lens of longer
focus. -
With the telephoto lens, on the other hand, We
must exercise care in planning Our pictures because the
angle of view is much less than the normal angle. As a
result, the observer tends to bring the scene toward him
and to interpret its perspective as if it had been made
from a shorter distance. This does not necessarily give
.
º
> *º
-º
Fi
--
t
Fº
---. .
#, sº
J
||f||1}
a s , /*
ſi. . , ºt !!! # ,,”, | |
PLATE X | W
º, Perspective Produced by Normal and Telephoto Lenses.
Upper view traced from an enlargement of a
negative made by a 2" lens on a Leica.
Lower view traced from an enlargement from a
nagative made by a 6" lens at about three times the
distance.



l!6 FIRST COLLEGE COURSE IN PHOTOGRAPHY
a false impression. Very excellent portraits, for in-
stance, can be made with the Tely t eight-inch lens on a
Leica. At a distance of nine feet, this lens Will just
include a person's head and shoulders in the image area
and the angle of view is about twelve degrees, one-
fourth of What it, Would be With the normal two-inch lens.
When we view such an image, and metally move it nearer,
the perspective does not appear faulty because a very
large part of our experience in looking at people takes
place at about that distance. It is possible, however,
to make portraits with a lens of greater focal length
from a greater distance that will cause the face to look
flat.
As an example of how a telephoto lens may give a
Wholly false impression, We shall next examine Plate
XIV . This shows tracings from photographs of a large
Colonial house, the upper taken from a distance of about
sixty feet With a two-inch lens and the lower, With a
six-inch lens at a distance of one hundred and eighty
feet. Between the two camera positions Was a row of
rather tall shrubbery which was behind the photographer
in the upper picture while directly before the house
Were some low stone Walls and a formal garden. Which Were
behind the shrubbery in the distant view. With the two-
inch lens and an angle of view approximating the normal
Visual angle, the house appears as it really is , a large
two-story house. With the six-inch lens, it has become
a small cottage. The shrubs far out in front of the
house cover the first story and sunroom completely and
are projected into the image plane to give the impres–
sion of low shrubs planted directly in front of the cot–
tage. The complete change in the impression of size
arises both from the hiding of the lower story and from
the tendency of the observer to interpret it as if it
had been made from one-third the distance and with three
times the angle of view, thus reducing its dimensions to
one-third what they really were . In general, when using
lenses that include an angle of view that is much less
or greater than the normal viewing angle, it is neces –
sary to analyse the scene rather carefully to discover
Whether this Will lead to an erroneous interpretation.
If such an interpretation is feared, a change in
MORE PHOTOGRAPHIC OPTICS 1||7
viewpoint Will often help matters and, if this is not
possible, the best solution may be not to take the pic-
ture at all.
The normal lens on a motion picture camera has
about half the angle of view of that on a still camera
primarily because it is impractical to have the screen
on which the pictures are projected subtend an angle
greater than this from the audience viewpoint. For com—
plete naturalness, the taking and the viewing angles
should be quite similar. Because of this narrow angle
of view, it is possible to include a Wide vista only
by "panoramming" or by taking a series of separate ad-
jacent views. Both methods leave much to be desired
from the standpoint of naturalness. When our eyes scan
such a scene we turn both our eyes and our heads, Our
eyes examine one part for a few seconds, then shift
abruptly to another part back and forth so that Our
minds gain an impression of the scene in its entirety.
We most emphatically do not view it by turning Our
heads slowly and steadily as if our necks were operated
by some sort of Worm gear, which is all that the camera
can do. On the other hand, the difficulty with taking
a series of separate views is that , unlike the eye
images, they are completely cut off from one another and
it is often difficult to sense their relation to each
other and grasp the scene in its entirety. Probably the
best solution for this problem is to recognize that the
motion picture camera is at its best. When subjects are
relatively near and adapted to a narrow angle of view.
"Panoramming" should be resorted to only when absolute-
ly necessary and should not be overdone.
Reason for Unsatisfactory Perspective When the
Lens Distance is Very Short. When a three-dimensional
subject is photographed from a position very near the
lens, portions at different distances are frequently
projected into the image plane so that their relative
size relation is quite Wrong. Thus, a portrait might
show a person. With an abnormally large nose and small
ears. Plate XV applies this to the case of a man
seated. On a table With his foot, extended. The camera
shown is an enormous pinhole camera. Which was used for



`ss CASE I |B = IMAGE OF BODY
*S `ss, |F = IMAGE OF FOOT
3 ~ G B A RATIO
- - - - -3'- # st-H F001/BODY = 1/3
`ss; CASE I F/E-2/3
---. is . CASE II F /s- 2/5
I HEIGHT OF BODY - 3.
HEIGHT OF FOOT - |
-------_ --- CASE II
> -------_
Cº) TT - - - -
3| ,------- T- T - - -
co º ă. `------------------_____ " " - T T - - - G B A
––– -3- - - -ti-j< — — — — — — — — — 5-------------------------------- i...; º:#;
---|-3-4---
|
A STUDY IN PERSPECTIVE
PLATE XV


MORE PHOTOGRAPHIC OPTICS l!9
no reason except that this made it possible to represent
image space on a scale that could be read from the draw-
ing. In Case I, the foot is only three feet from the
pinhole and is rendered exact size on image plane A.
The man's body, however, is half size because it is
twice as far away as the foot. The result is that the
image shows a man with a foot two-thirds as long as his
body. The mind of the observer simply cannot cope with
the interpretation of this satisfactorily for he can
only conclude either that his foot is two-thirds as
long as his body by leaving him where he is or that his
leg is several times as long as it really is if he moves
the whole thing farther back and interprets the existing
perspective from the new position. In Case II, the
camera is fifteen feet from the man's extended foot and
eighteen feet from his body. Under these conditions,
the image of his foot is two-fifths the height of the
image of his body, a ratio that is much nearer the
actual ratio of foot to body. One other thing should
be noted on these drawings. If the image planes had
been moved to B or C in either case, it would have had
no effect upon the relative proportions of the similar
triangles involved. This is equivalent to saying that
all images formed at the same viewpoint. Whether by pin-
holes or lenses will represent practically the same
perspective regardless of the distance of the image
plane. The only reas on that longer focus lenses can
give better perspective is that they make it possible
to form an image of the same size at a greater distance
from the subject, thus avoiding the unpleasant perspec-
tive that they, too, would have to produce if they were
to be used at the shorter distance.
The Perspective Produced by Lenses of Different
Focal Lengths. The above statement is, however, subject
to certain qualifications. In the first place, depth of
field diminishes with increase in focal length. With a
lens of longer focal length, near and distant objects
Will be less sharp when the middle distance is in sharp
focus than with a short focus lens If one were to
make two photographs identical in every way except
that one was made with a miniature camera having a
2 inch lens and the other with a view camera and an






150 FIRST COLLEGE COURSE IN PHOTOGRAPHY
*S..s
8 inch lens, it would be likely that the effect pro-
duced would be quite different. This would be true
even when both were enlarged to the same size because
of the difference in depth of field of the two lenses
at the same stop. It should be mentioned that
sharpness of all the planes in object space is not
necessarily desirable as it deprives the photographer
of his chief means of emphasis, namely by a subordina-
tion of those planes that do not contain the principal
objects.
Different lenses also produce slight differences
in effect because of variations inherent in their de-
sign. A very highly corrected lens will produce images
that fall off in sharpness more noticeably in depicting
objects outside the focal plane than Will an inferior
lens . This is due to the fact, that comparis Ons are
relative and in the former case our standard is a very
fine image and in the other, one that is not so good.
Slight differences due to variation in design contribute
something to that intangible element in a photograph
that we call atmosphere. Lenses exhibit individual dif-
ferences in performance that are learned only by long
association with them so that there is a certain amount
of logic behind the conviction expressed by photog-
raphers of long experience that they can do more with
their pet lenses than with any others. Probably, of
course, their deep inner conviction that this is the
case contributes somewhat to successful results.
The Stereoscopic Principle. It is a matter of
common information that the two retinal images formed by
our two eyes are not identical because of the fact that
they occupy viewpoints about two and a half inches -
apart, a difference that is appreciable in viewing ob-
jects at ordinary distances. As a result, the merging
of these two images as interpreted by the brain gives
an impression of slightly more of the objects than is
comprised in the direct front view. As a result, we
obtain a three-dimensional effect that makes vision
much more satisfactory than would otherwise be the case.
By using cameras that have two lenses mounted
side by side at a distance from each other equal to the
B.
.§
... -- ~3:
º
--
MORE PHOTOGRAPHIC OPTICS 151
separation of our two eyes and With coupled shutters
operated by the same cable release, it is possible to
produce two negatives simultaneously that bear the same
general relationship to each other as the retinal images
formed by our two eyes. If prints made from these are
mounted in transposed positions so that the one that Was
taken with the left-hand lens is on the right and that
taken with the right-hand lens on the left, they will
produce a three dimensional effect. When examined With a
stereoscope. What the stereoscope does is to make it
possible for one eye to see one picture and the other
eye, the other of a stereoscopic pair just as truly as
if the eyes were forming the stereoscopic pair directly
by looking at the scene. The brain merges one about as
readily as the other to give the three-dimensional im–
pression.
Experiment. Such a pair of pictures of a still
subject can be made with an ordinary box camera. After
one picture is taken, the camera should be moved to a po-
sition accurately parallel to the first with the lens
about two and one-half inches from the first position and
another picture taken. If prints from these negatives
are mounted in the transposed position in accurate hori-
zontal alignment with corresponding points 2-1/2 inches
apart, they will give the illusion of the third of dimen-
sion with a stereoscope. It is also possible to see this
without a stereoscope by focusing the eyes on a distant
object and then bringing the stereoscopic pair into the
line of sight.
With such pictures, the most natural effect is
secured when the subject is about fifteen feet from the
lens. When the subject is very close, distances are
exaggerated as With a Wide angle lens. For distant ob-
jects this effect is not obtained because the two views
are too nearly alike. In airplane photography, stereo-
Scopic photographs are produced that give a normal or
even an abnormally great stereoscopic perspective by al-
lowing the airplane to fly a sufficient distance between
the two exposures so that the angle of view changes by
the amount required for a stereoscopic effect. This may
be as much as a mile :


lº;2 FIRST COLLEGE COURSE IN PHOTOGRAPHY
QUESTIONS
l. For a pinhole camera having the pinhole 6 inches
lC).
ll.
from the image plane, the optimum diameter of the
pinhole for a reasonably distant object is . 02 inch.
Find the f/ratio.
. What is the distinction between depth of focus and
depth of field?
If l second is the correct exposure at stop 5 for a
camera with a lens, what exposure should be given
in the case of the above pinhole camera?
Summarize the advantages and disadvantages of pin-
hole cameras.
. What is the angle of view of a lö millimeter motion
picture camera if the diagonal of the frame is l/2
inch and the focal length of the normal lens,
l inch? -
Compare the angles of view obtained with that in
the above case if we substitute lenses having the
following focal lengths: 3/5 inch, 2 inches, 3
inches, H inches and 6 inches."
. A Leica camera has a minimum focal distance of
3-l/2 feet with the 2-inch lens. ' The picture size
is l x 1-1/2 inches.
(a) Compute Di for this distance.
(b) What is the angle of view?
(c) About what fraction of the Whole figure could
be shown of a man 6 feet tall at this distance?
. Why would it be inadvisable to put an extension
tube on the camera to increase Di in the above case
in order to photograph only his head and shoulders ?
The difficulty does not lie in the necessity of
gues sing at the focus as attachments are available
for ground-glass focusing.
ShoW that depth of field increases as the lens is
St. Opped down. -
Show that depth of field lessens as the focal length
increases.
Show that depth of field diminishes as Do becomes
Smaller. -
1. In problems 5 and 6, students who have not studied trigonometry
should make scale drawings and measure the angles with a pro-
tractor. * -
º
E. : :
tº... .
| ||
MORE PHOTOGRAPHIC OPTICS 153
12.
13.
l!.
lº.
16.
17.
18.
19.
20.
2l.
22.
23.
2}.
25.
Show that the ratio of the height of the man's body
to his foot is 2/3 in Case I and 2/5 in Case II on
Plate XV . *
Show that the exposure is inversely proportional to
the brightness of the subject.
Show that the exposure is independent of the dis —
tance as long as the image is considerably reduced
in size in comparis on to the object. Why is this
no longer the case When the image approaches the
size of the object or is magnified?
How many times as fast is an f/2 lens as one whose
maximum effective aperture is f/6.3%
Determine the angle of sharpest vision for your
eyes.
Determine the angle of sufficiently sharp vision so
that you are able to read type.
Show that negatives made With short focus lenses
have greater depth of field than those made with
long focus lenses even when the circles of confusion
produced by the former are magnified to produce
images of the same size as the latter.
Show that depth of focus is proportional to the
st Op used.
Discuss stereoscopic photography.
Discuss Plate XIII,
Discuss Plate XIV .
Why does one experience the illusion that he is
looking at the subject full size when looking
through a stereoscope at a stereoscopic photograph?
Compare the perspective produced by the different
lenses mentioned in problem 6 for the same Do.
Explain the optical principles involved in the fol-
lowing classes of camera finders.
(a) The finder on a box camera.
(b) The brilliant finder on folding cameras.
(c) The direct vision finder.
(l) Wire frame type.
(2) Concave lens type.
(d) The telescopic finder on miniature cameras.


Chapter X
THE REND E R | N G 0 F COL 0 R J N M 0N 0 CHROME
As one gains experience in the handling of
photographic materials, he becomes aware that the pre-
cise way that the indefinitely large number of colors
in the average subject is translated into monochrome is
both interesting and intricate. Usually We Want this
translation to reproduce the tone values of the subject
as nearly as possible as they appear visually. Immedi-
ately we are in trouble because most photographic mate –
rial has a color sensitivity quite different from that
of the eye. The rendering of various colors by differ —
ent kinds of film on Plate III should be examined again.
We note that process film is sensitive mainly
to blue, Orthochromatic, to blue and green and panchro-
matic, to all colors. Even panchromatic films, however,
do not necessarily render all colors as the eye sees
them. Often these films are rather too sensitive to
red and as a result, make the red elements such as the
lips in a portrait appear too light. HollyWood uses
make-up having brown rather than red tones on this ac-
count. Visually, the effect is quite unnatural but it
photographs to give a representation similar to What the
eye sees under normal circumstances. -
Another reason why this matter of representing
colored objects is complicated arises from the fact that
the light reflected from the subject depends not only
upon the reflecting power of the subject but also upon
the Spectral quality of the light for, quite obviously,
no color can be reflected by the subject that is not
present in the incident light.
Experiment. In a dark room, note the appearance
of a person illuminated only by a sodium light. Such a
light may be made by holding a piece of asbestos that has
been soaked in sodium chloride solution in a non-luminous
*
|\ \
.*
3.
（
15||
THE RENDERING OF COLOR IN MONOCHROME 155
gas flame. It contains practically nothing except yellow.
As a result, the red tones of a person's lips and cheeks
cannot be reflected and these appear dark.
Artificial light sources differ noticeably from one an–
other and all differ from daylight. In fact, daylight
itself is not constant in spectral quality and contains
much more yellow in the early morning and late afternoon
than at noon.
The Eye as a Color Analyser. A comparis On Of
the color sensitivity of the eye and of various films
is shown on Plate XVI. These are all schematic dia–
grams based upon spectrograms made With the wedge spec –
trograph. The wave lengths are represented by a scale
of equal parts along the axis of absciss as and the sen-
sitivities by a logarithmic scale along the axis of or—
dinates. The greater the ordinates, the greater the
transmission. In each case the region of transmission
is represented by the White area. Note that the eye is
most sensitive to green and sensitivity diminishes
gradually both toward the red and toward the blue.
Experiment. Which traffic light can be seen at
the greater distance down the street, red or green? Note
that this would depend not only upon the color sensitivi-
ty of the eye but also upon the percentage of light trans-
mitted by the colored glass.
Light having wave lengths below l;000 A.U. is invisible
and we note that all three classes of film are sensi-
tive to this ultra-violet light that the eye does not
See Which is an additional complicating factor in ren-
dering objects as the eye sees them. An examination of
Plate XVI shows that all the films are about equally
sensitive to blue but orthochromatic film also possesses
sensitivity to green and panchromatic, to green and red.
The panchromatic film shown is more sensitive to red
than the eye. Thus, these diagrams indicate that the
best we can do in rendering all colors without filters
is to obtain a panchromatic film that is sensitive to
Some light that does not affect the eye at all, is
rather less sensitive to green and more sensitive to
red and blue than the eye. With all three classes of


156 FIRST COLLEGE COURSE IN PHOTOGRAPHY
film, We are attempting to make a medium that is most
sensitive to blue represent the tones of colored objects
&B, S they appear to the eye Which is most sensitive to
green and yellow. The eye can tell us in a general Way
Whether reds and browns predominate, which would make
panchromatic film desirable, but, as a matter of fact,
it is not at all trustworthy as a color analyser. While
it is very sensitive in recognizing differences in
brightness and quite sensitive in recognizing color dif-
ferences, it is totally unable to determine the exact
colors that are actually present. While the ear of a
trained musician can pick out the individual tones in a
chord and is certain that one and only one combination
of frequencies will produce it, the eye has no such ca-
pacity. Rather, the eye has only a limited number of
different color receptors each of which may be stimulat-
ed by many frequencies so that the brain may experience
the same color sensation in a variety of Ways. If the
visible spectrum could be represented by a range of fre-
quencies similar to a piano keyboard, We might think of
the sensitivity of the eye as such that all the fre-
quencies of the lowest, octaves could stimulate one set
of color receptors on the retina, the middle octaves,
the second, and the upper octaves, the third.
Helmholtz showed many years ago that various
pairs of monochromatic Wave lengths could be recognized
by the observer as white. In every case, they were
complementary colors, i.e., colors Which When mixed ad-
ditively produce the sensation of White. As White
light is a mixture of all the Wave lengths of the visi-
ble spectrum to the physicist, the fact that an ob-
server can experience the same sensation from a single
pair of selected wave lengths as from heterogeneous
White light containing an indefinitely large number of
wave lengths must lie in his power to perceive rather
than in the light itself. This simply serves to em-
phasize that the brain may interpret as identical color
stimuli that are quite different. In addition, the ob-
server is Wholly unable to identify individual light
frequencies and, more than that, he may not even be
aware of the presence of a Whole band of color if it is
mixed with much more light energy of another color that
masks it.
#.
É
|
#
;
THE RENDERING OF COLOR IN MONOCHROME 157
Experiment. Certain filters that appear blue
transmit both blue and red light. If an ordinary Orange
is examined by the light transmitted by such a filter,
it will appear as red as a bright red apple. By white
light it is orange because it reflects so much more
orange light than red that the observer is not aware of
the latter. The filter reveals the red color of the
orange by transmitting red light and absorbing the Orange
light that would have been reflected predominantly if it
had been present
The Young-Helmholtz Theory of Color Vision. Ac –
cording to the Young–Helmholtz theory of color vision,
there are three sets of receptors on the retina, red
sensitive, green sensitive and blue sensitive. When
light falls on the retina, these are stimulated singly,
two together, or all three at a time according to the
color of the incident light. The brain interprets
these stimuli as shown in the following table.
Color of light Color perceived by observer
Red Red
Green Green
Blue Blue
Red + Green Yellow
Red + Blue Magenta
Green + Blue . Blue Green
Red + Green, excess of Red Orange
Red + Blue, excess of Blue Purple
Red + Blue + Green White
It Will be noted that every color of the spectrum is in-
cluded here.
That this theory is much more than a piece of
pure speculation is shown by the fact that we can ac-
tually produce this whole array of colors by mixing red,
blue and green in proper proportions. We must, however,
miX colored lights rather than pigments because the
separate colors must all reach the eye of the observer
Without absorption and can do so provided We project
them all as lights on a non-selective White screen.
Then, each color is reflected just as it would be if

MINUS BLUE
RED+GREEN -
YELLOW
MINUS GREEN
RED + BLUE -
MAGENTA
MINUS RED
BLUE + GREEN-
BLUE GREEN
Additive primaries- large circles.
Subtractive primaries — portions of circles
where two additive primaries are superimposed.
White - portion of circles where all three ad-
ditive primaries are superimposed.
Each additive primary is complementary to the
subtractive primary that lies opposite, i.e.
it is complementary to the subtractive primary
formed by the other two additive primaries.
Each pair of subtractive primaries combined sub-
tractively as by mixing pigments yields the ad-
ditive primary included between them.
Consider the following.
1. What colors should we get if we combine the
subtractive primaries in pairs additively by
mixing lights 2 Explain.
2. What color should we get if we combine all
three additive primaries as pigments 2 Explain.
3. What color should we get if we combine all
three subtractive primaries as lights projected
on a white screen? Explain.
PLATE XVI Additive Color Mixing.














THE RENDERING OF COLOR IN MONOCHROME 159
the other's Were not there and no absorption takes place
between them." -
Experiment. Project circular spots of light on
a white screen through Projection Red, Projection Green
and Projection Blue Wratten filters by means of a tri-
ple lantern or three ordinary projection lanterns. Al-
low the colors to overlap as shown on Plate XVI and the
colors indicated there will be obtained. If it is possi-
ble to change the relative intensities of the lights,
orange and purple can also be obtained.
That we can produce all these colors With only three
lights makes the Young-Helmholtz theory appear extreme –
ly plausible. Later theories of color vision differ
slightly in the number of different color receptors to
be found on the retina but all agree that they are
limited in number and can be stimulated in a great
variety of Ways.
Experiment. Additional evidence that an observer
can experience the sensation of yellow by the combined
effect of red and green is shown by an examination with a
microscope of a Lumière color plate showing a yellow ob-
ject. Under magnification this is shown to consist of
nothing except an aggregate of red and green dots.
1. Additive color mixing must be carefully distinguished from the
|better known subtractive color mixing familiar to everybody
from experience with paints or dyes. A transparent object ap-
pears colored when white light falls upon it because it trans-
mits only part of the colors that are actually present in the
white light and absorbs the rest. When we superimpose two dif-
ferent colored filters only those colors will reach the eye of
the observer as he looks through it that are not absorbed by
either filter. If, however, we place the two filters in sepa-
rate projection lanterns and superimpose their projected images
on a white screen, all of the colors that are transmitted by
both filters will be reflected back to the observer. Thus,
- yellow and blue filters when superimposed and projected on a
white screen by a single lantern produce green by subtractive
§. color mixing while the same filters placed in separate lanterns
i. produce an approximate white by additive color mixing. In the
|- latter case, the blue filter transmits about one-third of the
º spectrum and the yellow, the remainder so the observer inter-
º prets the combination as white.


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THE RENDERING OF COLOR IN MONOCHROME l61
The Wedge Spectrograph. (Plate XVII ) Since
the eye is so unreliable as a color analyser, it is
very fortunate that We have at our disposal in the
spectroscope and spectrograph instruments that are very
precise. Here, an illuminated slit acts as a very nar-
row source and the light is made parallel by a lens
that is so placed that the slit is at its focus. (Case
IV of image formation.) This light is then dispersed by
a prism or a diffraction grating. * The dispersed light
is examined visually With a telescope in the spectro-
scope and is allowed to form a permanent image on a
photographic plate in the spectrograph. Diffraction
gratings are preferable to prisms in these instruments
as they produce spectra in which the red, green and
blue portions are of about the same length and propor-
tional to the Wave length ranges involved While prisms
produce spectra in which the red portion is much short –
er than the blue. Plate XVI shows the essential
parts of one form of Wedge spectrograph.
Experiment. Examine a narrow light source by
looking through a transparent grating.
(a) Compare the dispersions of gratings having
different numbers of lines per inch.
(b) Which color is deviated least? How does
this compare with prism spectra?
If We Wish to know only in a general Way What
the sensitivity of a given plate or film is to light of
different colors, it is only necessary to insert it in
the spectrograph, illuminate the slit. With White light,
Open the shutter for the necessary length of time to
make an exposure, and develop the plate. Upon develop-
ment, regions representing colors to which the material
is very sensitive appear strongly while regions of
Smaller sensitivity come out partially or not at all.
It should be realized, however, that sensitivity to
light of a given color is a relative rather than an ab–
Solute thing so When We say, for instance, that a given
film is insensitive to red light, What we really mean
2. A discussion of the construction, use and theory of diffraction
gratings will be found in any general physics text.

| I ! |
SENSITIVITY
OF THE EYE T. |
Blue" of EEN' RED
4OO 5OO 6 OO 7OO
NON-COLOR-SENSITIZED
U.V. BLUE GREEN RED
SAFELIGHT SERIES I
ORTHOCHROMATIC
SAFELIGHT SERIES 2
PANCHROMATIC
SAFELIGHT SERIES 3
i DARK
| GREEN
SAFELIGHT COLOR AND
NEGATIVE SENSITIVITY
Eastman Kodak Co.
PLATE XVIII
§:º H
#3-ſº
l. 3;-
Rš.



THE RENDERING OF COLOR IN MONOCHROME 163
#
--
i
º
-
#3.
is that the red light did not produce a developable
image under the prescribed conditions of exposure. Had
the exposure been longer, this might not have been the
case. Thus, a red safelight Will not fog an Orthochro-
matic film because it transmits only those Wave lengths
to which the film is relatively insensitive provided it
is not too close, the light bulb is not too large, Or
the sensitive material exposed to it for an unduly long
time. If, however, the exposure is excessive for any
of the above reasons, the plate Will be fogged.
In general, a safelight must be selected that
transmits as little light as possible to which the film
or paper is sensitive. Below each film shown on Plate
XVIII is a diagram showing the transmission of the safe-
light designed for use with it. The bright red Series l
is suitable for non-color -sensitized films because the
transmission band for this safelight is far from the
band to Which such films are sensitive. It Would not
be advisable, however, to use this with an orthochro-
matic film. Here, the much deeper red Series 2 should
be used. With panchromatic films which are sensitive
to all colors, it is not possible to find a safelight
that has a transmission band outside the region to which
the film is sensitive. A green safelight is therefore
Selected Whose transmission is so low that the film can
be exposed to it for brief intervals without damage and
the image can be seen better by such faint light because
the visual acuity of the eye to green is exceptionally
high. In any case, not much can be seen and, With ultra-
fast, panchromatic films in use today, it is not permissi-
ble to use any light during development. It should per-
haps be mentioned that all photographic materials are
much less sensitive to light. When Wet so that a brief
examination is possible after development has proceeded
for a minute or two by a safelight that would have
fogged the dry film. Present tendencies, however, seem
to be toward the use of methods that make it unnecessary
to examine film at all during development.
It Often happens that it is necessary to know
quantitatively how the light affects the photographic
plate. In Such cases, a tiny black glass Wedge may be
put over the slit so that the light that falls upon the

l6|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
photographic plate must pass through it. The light
will therefore be absorbed according to the thickness
of the wedge. In this way it is possible to vary the
intensity of the light uniformly from the top to the
bottom of the slit. Often the wedges are constructed
with an angle such that the density varies uniformly
from 0 to l; which means that the transmission is com—
plete at one end and only l/10000 as great at the other.
The wedge is so tiny that the whole region of transmis-
sion represents a length just sufficient to cover the
spectrograph slit and if this is placed over the slit,
the light that falls upon the photographic plate varies
uniformly in intensity from 10000 to l so that the bot-
tom of the spectral area is receiving loC)00 times as
much light as the top. The photographed spectrum is
therefore of variable height, being highest in those re-
gions to which the plate is most sensitive. Just how
high this maximum part will be depends upon the expos –
ure given and relative sensitivity in the other parts
can be obtained by a comparison of the ordinates repre-
senting the different parts of the photographed spec-
trum. These computations are greatly simplified if an
exposure is given that makes the maximum ordinate fall
on the plate at a height represented by a density of 2
on the Wedge. Then, the minimum amount of light that
produces a developable image is l/loo of the maximum
which provides a scale that is readily translated into
percentages representing relative sensitivity. It must
not be forgotten, however, that these Ordinates are
logarithmic so an ordinate half as high represents a
sensitivity not of fifty per cent but of only ten per
cent. Plate XXIII shows spectrograms made With a
wedge spectrograph through different colored filters.
Filters. It is frequently impossible to find a
film that has the precise color sensitivity desired for
a given subject. In such cases it is often desirable
to place a suitably colored filter either over the lens
or over the light to absorb more or less of the color
that affects the plate too strongly. Such colored fil-
ters are selective absorbers and show a much more marked
tendency to absorb certain parts of the spectrum than
others. As a result, the light that passes through one
Ex-
| il.
PLATE X | X
Rendering of the Cubes by the Light Transmitted
by Different Colored Filters on Panchromatic Film.
Top . Wr at ten K-2 .
Center . Omag green.
Bottom. Omag orange.
(The color of each cube is indicated by the
initial letter on its face . )



l66 FIRST COLLEGE COURSE IN PHOTOGRAPHY
of these before reaching the film shows a distinctly
different spectral distribution or intensity in differ –
ent portions and some regions are likely to disappear
entirely.
Experiment. Project a spectrum on a screen and
insert various filters in the path of the beam, such as
the Wratten A (red), B (green), Cs (blue), K-2 (yellow),
and Kodachrome (pink). Note that these do not change the
color of any part of the spectrum that they transmit but
simply cut off portions. Filters transmit strongly the
color that they appear to be by transmitted light but
frequently transmit much more.
Filters are used for a great variety of different pur-
poses which we shall now consider briefly.
l. Filters are used to render the tones of
colored objects as the eye sees them. Since all ordi-
nary films are very sensitive to blue light, the blue
portions of a picture are apt to be represented by such
great densities on the negative that they are too light
on the print. As a result, White clouds in a blue sky
show much less than the visual contrast, a blue dress
, may appear white or a copy of an architect 's blueprint
may be rendered as light gray lines against a drab back-
ground in the prints. We can, however, cut off part of
the blue light by a suitable choice of filter selecting
one that transmits only part of the blue light. Usual-
ly such filters are various shades of yellow, depending
upon the amount of blue that it is desired to cut off.
By their use, the blue portions in the picture will be
represented by lower densities on the negative and Will
therefore print darker than they would if no filter had
been used. Study carefully the rendering of the cubes
on Plate XIX by green, yellow and Orange filters.
2. We also use filter’s When We Wish to increase
contrast. As was mentioned above, a photograph of the
White lines and blue background of an ordinary blue-
print without a filter is so low in contrast that a
print cannot be made from it that Will make the lines
stand out against the background as they do visually.
The reas on for this is that the blue and White portions
both reflect about equal amounts of actinic light. The
THE RENDERING OF COLOR IN MONOCHROME 167
densities produced are therefore so similar that the
lines do not stand out satisfactorily by contrast. We
have already seen that a yellow filter will increase
this contrast by absorbing more of the light from the
blue background than from the White lines so that the
resulting print Will show White lines against a medium
gray background. If we wished to produce a print show-
ing White lines against a black background, this could
be done by exposing the negative through a red A filter.
An examination of its spectrogram on Plate XXI Will
show that this filter transmits no blue light. The blue
background reflects little else while the White lines
reflect all colors. A negative made through the red
filter will therefore show the image of the lines as
dense black against a transparent background and the
print will give the impression that the subject was
black and White instead of blue and White.
Photographic copies of faded ancient manuscripts
have been made that were actually easier to read than
the originals by the use of contrast filters. The rule
is that a filter should be selected that absorbs strong—
ly the predominating color from one portion while trans –
mitting that from the other that is to stand out by con–
trast . Often, a visual examination of the subject by
looking at the subject through the filter will indicate
Whether it will have the desired effect. Those parts
that are reflecting only colors that the filter absorbs
Will appear black while parts reflecting colors trans –
mitted will appear light. These will therefore stand
out by contrast. This test, however, should be regard—
ed as only approximate as it makes no allowance for the
differences in the sensitivity of films and of the eye.
3. Still another use of filters is to eliminate
undesired portions in the photographic copy or to select
those parts that are capable of reflecting light of a
particular color. If a copy of a photograph showing a
yellow stain was desired, one could be made through a
suitable yellow filter that would produce a print entirely
free from all evidence of the Stain. In Order to do this
as perfectly as possible, it would be necessary to select
a yellow filter that was capable of transmitting light of
the spectral quality of that reflected by the stain and


168 FIRST COLLEGE COURSE IN PHOTOGRAPHY
of absorbing the blue light reflected from the White
parts of the photograph. The White parts and the yel-
low stain would thus be reflecting predominantly yellow
to the film and would therefore produce so nearly the
same densities that the stain could not be distinguished
from the White paper. A copy of a manuscript written
With black ink on white paper with corrections in red
ink can be made with the corrections omitted by using a
red filter and panchromatic film. Since both the White
paper and the red ink reflect about the same amounts of
the red, yellow and orange light transmitted by the fil-
ter, they Will produce the same densities and a print
can be made in which the red ink cannot be distinguished.
Color prints of colored subjects are frequently
obtained by making a set of separation negatives through
red, green and blue filters. In this Way negatives are
made by the light of a little more than one-third of the
spectrum in each case. If prints are made from each in
the complementary color and carefully superposed, a
colored replica of the original will be obtained. The
precise details and theory embodied here Will be con-
sidered later. It Will be sufficient for the moment to
recognize that these processes represent an important
development of photography in which filters are used to
make the photograph in the band of colors desired and
to reject the rest. - -
- lſ. Filters are frequently used in photomicrogra-
phy because sharper photographs can be obtained with
many microscope objectives by using a single relatively
narrow color band rather than all the colors in White
light. Because of the high magnification involved here,
defects of achromatism in the objective too minute to
be noticeable in ordinary photography become serious.
While such defects are corrected in apochromatic objec-
tives, these are very expensive and it is usually suffi-
cient to use an ordinary achromatic objective and pre-
vent the unsharpness of multicolored images by selecting
a filter that permits only one color to fall upon the
film. A filter over the light source is used in prefer-
ence to one close to the objective to avoid impairment
of the image under the high magnification utilized.
Allº r
Lº
º,
THE RENDERING OF COLOR IN MONOCHROME 169
Many other cases exist in which filters are used
over the light source itself to change its spectral
quality. Artificial light sources are frequently cor-
rected in this Way to approximate daylight. Whether the
filter should be used over the lens or over the light
depends upon circumstances. Where practicable, it is
probably better to put the filter over the light source
as there is inevitably a slight impairment of the image
when a filter is used over the lens. This is often im-
possible, however, and the impairment due to a filter
over the lens can be reduced to a minimum by using a
high quality filter with accurately ground plane paral-
lel sides, having it scrupulously clean and placing it
perpendicular to the optical axis. Focusing should be
done with the filter in position if possible although
some filters transmit so little light that it is diffi-
cult to see the image clearly through them.
The Filter Used with Kodachrome. An interesting
application of the use of filters is to be found in
color photography with Kodachrome. Since artificial
light is deficient in blue, the film is manufactured in
two grades, Regular, for daylight, and A, for artificial
light. The latter has an emulsion that is extra sensi-
tive to blue light to make up for the fact that arti-
ficial illumination is deficient in it. This film gives
satisfactory color rendering with Photofloods but if
used in daylight makes the blues much too deep. A blue
sky in daytime, for instance, appears rather like a
night sky. By using a pinkish filter supplied by the
manufacturer, part of the blue in daylight is filtered
out and the film then gives a very satisfactory render-
ing of colored objects in daylight. It occasionally
happens that one may Wish to make an indoor photograph
Where daylight cannot be excluded and yet is insuffi-
cient without some artificial light. If daylight and
Ordinary Photofloods are used together, the color ren-
dering Will be false. It is immaterial whether the
light has daylight quality or Photoflood quality provid-
ed the proper kind of Kodachrome is used but it is in-
advisable to mix the two. Methods are available, how –
ever, for meeting this difficulty. In the first place,
We may use Kodachrome Regular and blue Photofloods to


17O FIRST COLLEGE COURSE IN PHOTOGRAPHY
augment the daylight. The blue bulbs act as a filter
to cut off some of the yellow light and thus give a bal-
ance that approximates daylight. In the second place,
We can use Kodachrome A, ordinary Photofloods and cover
the Windows With pink Cellophane to make the daylight
approximate the spectral quality of the Photofloods.
Filter Factors. As filters inevitably absorb
part of the incident light, it is usually necessary to
take this into account and compensate for it by a cor-
responding increase in exposure. As a result, it is
necessary to know the filter factor of a given filter
in order to use it intelligently. Filters are there —
fore designated by the manufacturer as 1-1/2 X, 2X,
3X etc. , the number in each case indicating that by
Which the exposure Without a filter should be multi-
plied. When the filter is used. These factors are ordi-
narily sufficient as the latitude of film is so great
that some variation in relative exposures Will not seri-
ously affect the result. It will be realized, however,
that in very precise work the filter factor is a func-
tion not only of the light transmitted by the filter but
also of the color sensitivity of the film with which it
is to be used. In making color separation negatives,
for instance, the latter variable must be taken into ac –
count. This can be done by photographing a gray scale
Without a filter and With each filter to be used. These
must all be developed under identical conditions and re-
peated trials made until exposures are secured that re-
produce the same densities for corresponding steps
throughout the entire range of the gray scale. This
match may be made visually Or, much more accurately,
With a densit Ometer.
Certain haze filters designed to cut off ultra-
violet light in photographing distant objects require
no increase in exposure. This merely indicates that the
amount of light that they cut off is so small that it
is unnecessary to compensate for it. Quite obviously,
a filter that really cut off no light would be useless.
Polarizing Filters . Polarizing filters serve
several very useful purposes in photography. Light may
ºft
T;
--
º
Fºl
E.ſº
º
THE RENDERING OF COLOR IN MONOCHROME 171
be defined as a transverse vibration that travels With
extremely high velocity. The term, transverse, means
that the vibrations are at right angles to the direction
of propagation. A little thought will show that there
is actually an indefinitely large number of directions
that are at right angles to this.
H F D
A
B
C E G
Figure 29, Possible Directions of Transverse Wibrations.
In the above figure, the direction of propagation of the
light, is perpendicular to the plane of the paper and AB,
CD, EF, GH represent a few of the indefinitely large
number of possible directions of vibration that are at
right angles to this. Ordinary heterogeneous light is
thought of as consisting of a mixture of all possible
Vibration planes. When such light falls upon a reflect –
ing surface, a very curious modification occurs and the
light reflected is found to be more or less plane polar-
ized. Instead of representing a great variety of orien—
tations of the vibration plane, the plane polarized por—
tion of the light is all found to be vibrating in a
plane parallel to the plane of the reflecting surface.
This makes no difference in its spectral quality or in
any other respect that the eye can detect directly. If,
however, one looks at such light through a polarizing
filter, it Will be transmitted with maximum intensity in
two positions of the filter and will gradually change in
intensity as this is rotated before the eye. The light
decreases gradually in intensity without change in color
until the transmitted light is practically extinguished
When it reaches points that are ninety degrees from the
positions for maximum intensity. In other words, cer–
tain crystalline materials possess the ability to absorb
or to transmit plane polarized light according to the


l'72 FIRST COLLEGE COURSE IN PHOTOGRAPHY
orientation of the crystal with respect to the vibration
plane of the polarized light. These materials provide
a means of changing the intensity of plane polarized
light without alteration in its spectral quality.
A polarizing filter is a layer of such crystal-
line material held in position between two pieces of
plane glass. The remarkable thing about these screens
is that the crystals are of microscopic size and yet
methods have been devised to cause them to Orient, them-
selves so that the incident light travels through all
of them in essentially the same direction. This, it
will be realized, is necessary if they are to produce
an appreciable effect upon the incident light. In Or-
der to be effective, it is essential that the light pass
through the crystals in a particular direction and this
would be possible for only a small fraction if they were
Oriented at random. -
These screens have many important applications
that need not be mentioned here. A few, however, are
of importance to photographers. It has already been
mentioned that light from reflecting surfaces is partly
polarized and it is also true that this light may be
producing unpleasant reflections. If we wished to make
a photograph through a shop Window or of a living room
containing furniture With glass doors, it is quite like-
ly that We should see reflected images in the glass
that could not be avoided by a change of camera view-
point. Since this light that is producing undesirable
reflections is plane polarized, it can be absorbed by a
polarizing filter placed before the camera lens. It
must, however, be oriented so that it will produce maxi-
mum absorption of this light. In order to discover the
correct position, all that is necessary is to hold the
filter before the eye, rotate it until the reflections
disappear and then slip it over the camera lens in
exactly that position. Unpolarized light Will be trans-
mitted by the filter and will form an image in the usual
Way but Without the reflections. The exact filter fac-
tors are variable as it is, in general, not possible to
know What fraction of the light is polarized and ab-
sorbed but it. Will usually be found satisfactory to dou-
ble the exposure.
º
:
-5.º
3.
ſº
jº
THE RENDERING OF COLOR IN MONOCHROME 173
Experiment. Take a position from which it is pos-
sible to see a bright object such as a window reflected
obliquely from a pane of glass such as the glass in a book-
case or apparatus case. Hold a polarizing screen before
the eye and rotate it. Note that two positions can be
found at which the reflections are greatly subdued or en-
tirely disappear.
Polarizing filters are often helpful in photo-
graphing distant views such as the Grand Canyon from
the Rim. Under certain atmospheric conditions the
colors appear rather dull and the distance is indistinct
because of scattered light less far away. This scat —
tered light is reflected and polarized so that it can
be cut off by a polarizing screen by following the same
procedure as in the last paragraph. It is really re-
markable What an improvement can be made in the Clear –
ness with which distant objects can be rendered in this
Way.
Experiment. Hold a polarizing screen before the
eye when looking at a distant landscape. Rotate it slow-
ly and note the improvement in the brilliancy of coloring
of distant parts for two positions of the screen.
Sky light is partly polarized so that skies taken on
color film through a polarizing screen set at the posi-
tion for maximum absorption show extremely blue skies
Which are sometimes liked for a certain dramatic effect
even though they are not entirely natural. The reason
for this is that an appreciable fraction of the sky
light does not traverse the filter and fall upon the
film so the sky receives a lower exposure than would be
the case without a filter. With color film, a moderate –
ly reduced exposure alwāys results in brighter colors.
Experiment. Examine a rainbow through a polariz-
ing screen. Two positions will be found at which it dis–
appears almost entirely. What does this indicate?
The selection of the correct filter for a given
purpose is often rather complicated because of the fact
that a variety of colors is involved and the correct
filter to help one may at the same time produce an ad-
verse effect upon another. A knowledge of the


17|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
Sensitivities Of films and the transmissions of differ —
ent filter’s should make it, possible to select the one
that Will be the best practical compromise in every
case. It should be realized, however, that no filter
is a general panacea that can be applied With benefi-
cial results to any subject whatsoever and that is is
essential to do everything possible by a proper choice
of film and careful lighting as well if results are to
be satisfactory.
The Analglyph. A very curious and interesting
application of color filters is to be found in the
analglyph, a method of rendering a stereoscopic pair of
photographs to show their three-dimensional quality
Without a stereoscope. Instead of presenting separate
pictures to the two eyes by placing them side by side
and viewing them. With a stereoscope, the analglyph shows
the two separate pictures superposed with corresponding
points separated by only a fraction of an inch. With-
out the viewer, the overlapping images appear decidedly
confused. One of these images is printed in blue or
green and the other, in red. The viewer consists of a
simple cardboard frame resembling a pair of spectacles
With one eyepiece covered with a red gelatine and the
Other With blue or green to match the colors used in
making the prints. When this is held before the eyes,
the red eyepiece transmits the light reflected from the
red image about as well as the light reflected from the
White background so this image does not stand out by
contrast and is practically invisible to this eye. The
green or blue image, on the other hand, appears black
against a light background because it is incapable of
reflecting light of a color that this filter can trans —
mit. In the same way the filter before the other eye
causes the red image to stand out strongly and appear
dark While the blue or green image disappears. Thus,
each eye is seeing only one image of a stereoscopic pair
and the brain fuses these to produce the stereoscopic
illusion just as it would if each eye had received its
separate image by means of the stereoscope.
The main advantages possessed by the analglyph
over the ordinary stereoscopic view are that the
º
º
t
º
º,
:
º*º:º
|
&
; :
º
- * .
º
º
|
ſ
- | .
H.T.
ſº
THE RENDERING OF COLOR IN MONOCHROME 175
pictures are not limited in size as they are with the
Stereoscope and can be viewed by numbers of people at
the same time. In fact, , three-dimensional motion pic –
tures based upon this principle have occasionally been
shown in the theatres. As it is necessary to supply
each person in the audience with a viewer, the results,
While interesting, are not likely to be adopted gen–
erally. The customary magnification of a single image
produces a reasonably satisfactory spatial illusion and
the complications involved in taking double pictures
and supplying everyone in the audience with viewers are
serious. The greater usefulness of the analglyph would
appear to lie in depicting three-dimensional spatial re-
lations in scientific or mathematical material that are
not readily grasped from ordinary two-dimensional draw —
ings.
QUESTIONS
l. Compare the abilities of the eye and the ear to
recognize individual frequencies.
2. Show that all the colors of the spectrum may be ob-
tained by suitable mixtures of red, green and blue.
5. Why is a diffraction grating used in preference to
a prism in the Wedge spectrograph?
. What is the Young–Helmholtz theory of color vision?
. What does it signify about the nature of color per-
ception that an observer will recognize certain
pairs of monochromatic wave lengths as white 2
6. Describe what you observed in looking through a dif-
fraction grating at a narrow light source.
7. What is a filter ? What is the difference between
selective and non-selective filters 2 Give examples
of the use of each.
8. What are filter factors ? Upon what do they depend?
How could you determine the factor for a filter
whose factor you did not know?
9. Study Plate XIX carefully and compare the rendering
of the various colors by the different filters.
Which two are most alike 2
lC). Which light bulb will give the greatest amount of
illumination, a 100 Watt clear bulb or a loC) Watt,
daylight blue? Explain.
:


176
FIRST COLLEGE COURSE IN PHOTOGRAPHY
ll.
l2.
l3.
l!.
lp.
l6.
17.
18.
l9.
20.
2l.
22.
23.
2}.
25.
Why does a photograph of a blueprint made through a
red filter have excessive contrast 2
What would be the result of using a red A filter
with an Orthochromatic film?
Give examples of subjects that would require the
use of filters for the following purposes. State
Which filter should be used in each case.
(a) To render the subject as the eye sees it.
(b) To increase contrast.
(c) To eliminate a portion of the subject.
(d) To select a portion.
(e) To eliminate all possible traces of chromatic
aberration.
(f) To cut out haze.
Describe a wedge spectrograph. For What purposes
is it used? &
What range of transmission is represented by a
wedge whose density range is from 0 to 5?
Draw the color diagram on Plate XVIII from memory.
Discuss the color sensitivity of Kodachrome.
What effect has the pink Kodachrome filter 2
What filter should be used to eliminate a yellow
stain from a photograph? If the stain still showed
faintly on the negative, should the print be made
on hard or on soft paper ?
Quartz lenses have sometimes been recommended for
portraits because they transmit ultra-violet light
absorbed by glass lenses as well as the visible
light and thus shorten the exposure. Would this
shorten the exposure ? Is it desirable 3
Is there any objection to the use of mercury vapor
lights that are high in ultra-violet radiation for
portraiture?
Under what circumstances would you use a red filter
in photographing clouds 2 -
What is polarized light 2 Under What conditions
that are of interest to photographers does light
become polarized? -
What is a polarizing filter? Describe its use in
eliminating undesirable reflections. What effect
would it have upon unpolarized light 2 What filter
factor should be used?
Explain why a polarizing filter is useful in elimi-
nating the effect of haze in taking distant views.
i
º
s
THE RENDERING OF COLOR IN MONOCHROME 177
26.
27.
28.
29.
30.
How is the proper orientation of a polarizing fil—
ter, determined ?
Why would it be inadvisable to attempt to use a
lens from a larger camera having a focal length of
6 inches as a telephoto lens on a motion picture
Camera 2
Describe the analglyph. What is the color of the
image seen through the viewer? What would be the
effect of reversing the viewer so that each gela—
tine covered the opposite eye?
What happens to the energy of light that is ab-
sorbed by a colored filter? By the law of the con–
servation of energy, it cannot be destroyed.
Discuss the different effects observed when yellow
and blue filters are used to produce additive and
subtractive color mixing.


Chapter X |
| N T R O DU C T ORY CONS | DE RAT | ONS RE GARD | N G
COL 0 R P HO TO GRAPHY
The sudden increase in interest in color photog-
raphy Within the past few years is really astonishing
although practical color processes are not matters of
Such recent development as is generally supposed. As
far back as lSO7 the Royal Photographic Society be –
St OWed its medal for distinguished photographic achieve –
ment upon the manufacturers of the Lumiere color plate.
Since the beginning of the century this process has
produced color Work of really excuisite beauty in ex-
pert hands but exposures have always been critical and,
until the development of the photoelectric exposure
meter, so much experience Was necessary that few had
both the time and the inclination to master this ad—
mittedly expensive process. Photoflood lights have
probably had much to do With the increase in popular in-
terest by making it possible for the photographer to get
all the light he needs exactly where he wants it without
elaborate equipment. The third factor is the great re-
duction in technical skill demanded when processing is
done for the amateur in professional laboratories.
As a result, color has come to stay but it would
be too much to claim for it that it has really gained
complete acceptance by all photographers. Moreover, it
should not be forgotten that many Who hesitate to accept
it are among those who, far from lacking artistic per-
ception or technical skill, are among Our most skillful
exponents in black and White. Admittedly, the tech-
nique is quite different and it is easy to understand
Why great proficiency in the One form may make a person
hesitant about embracing the other. Moreover, from the
very fact that ordinary photography lacks color, it as —
sumes a certain abstract quality that is very attractive
to many people. Then, unquestionably We are creatures
|
§
#
178
considERATIONS REGARDING COLOR PHOTOGRAPHY 179
of habit and have learned to enjoy Our photographs un-
colored just as We usually do Our etchings. On the
other hand, an oil painting Without color Would be dis-
appointing. As a further example of the extent to
which custom affects our criteria of taste , we might re-
mind ourselves that the Greeks applied color to their
statues and yet how bizarre it Would seem to us today
to attempt to restore it.
It should not be forgotten that color is a
means, not an end in itself and must contribute to the
Whole rather than dominate it. The day. When one could
collect all the varicolored objects that happened to be
lying around and incorporate them in a color photograph
to make the World marvel is definitely past. With cer–
tain subjects, however, whose charm lies primarily in
color rather than in form, it is difficult to believe
that a color photograph is not to be preferred to one
in black and White. In a sunset or a distant view
across the Grand Canyon, for instance, color can con-
tribute something that is almost equivalent to another
dimension and make it intelligible as it would never be
in black and White. But, this is subject to the proviso
that the colors must be reasonably close approximations
of the originals or, instead of contributing to the
Whole, they may be definitely distracting. For in-
stance, by under-exposing a brilliant sunset containing
rather heavy clouds, it is possible to produce a con-
glomeration of jet blacks, deep purples and brick reds
that have never been known to appear in any sky and
While the undiscriminating observer may exclaim over
this in admiration, it Will be apparent to those With
more Cultivated taste that it. Would have been better if
this had never been made.
Certainly some of the lack of interest in color
photography is due to such demonstrations of What it
should not be. Another difficulty lies in the limited
latitude of color film which makes it necessary to keep
the light values to be rendered fairly close together or
else bald uncolored highlights and blocked shadows will
result. Still another difficulty arises from the fact
that We all tend to conventionalize color and may easily
reject as unnatural a rendering that is correct simply

18O FIRST COLLEGE COURSE IN PHOTOGRAPHY
because it does not conform to our pre conceived idea of
what the colors should be. To many who have not given
thought to the matter, the green of foliage is the green
of grass in spring and no departure from this seems en-
tirely "natural" All that can be said to such as these
is to go out and look. Certainly an interest in color
photography stimulates an interest in color as such and
vastly increases our power to sense subtle differences.
In fact, if it did nothing more than to contribute this
increased perception of the beauty inherent in the
realm of nature, it is difficult to see how the time
could have been more profitably employed.
Granting that color photography is far from
perfect, the facination of it lies, perhaps, not so
much in what it is as in what it may become. To many
there is a challenge and an inspiration in color that,
Will not be denied. It may be that the attitude of the
individual is primarily a matter of emphasis. One Who
is Willing to dwell upon What a remarkable achievement
it is will find himself deeply interested in its present
status and future potentialities While another Who
thinks more particularly of its limitations will prefer
to turn his attention to something else. Meanwhile, a
person Who is able to combine the color sense of the
artist with the scientific ability of the skilled tech-
nologist need not hesitate to explore the more compli-
cated color processes. In these he is likely to find
much inner satisfaction and a possible profession. Where
his talents may be rewarded because the combination is
not very frequently found.
Newton's Contribution to Color Theory. Previous
to the time of Newton, White light had been regarded as
the simplest kind of visible light rather than the most
complex. By allowing a beam of sunlight admitted
through a narrow opening into a darkened room to pass
through a prism and fall on a White screen, Newton was
able to show that the light is spread out into a col-
ored band. This did not make it absolutely conclusive
that White light is actually an aggregate of all the
colors for there was a possibility that the light might
have been changed in essential character in passing
§. Aº.EºsLºmi.ſº[ _ſºfºu

ſ:
º
w
#
.
CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY 181
through the glass. Experimenting further, he placed an–
other prism in the path of the beam dispersed by the
first, but so turned that its refracting edge would dis —
perse the light in a direction opposite to that of the
first prism. The result, Was that the colored band Was
recombined into a spot of White light. This proved
that White light is actually a very complex aggregate
of all the spectral colors that are merely separated by
a prism as is indicated by the fact that another prism
can be used to recombine them into White light. *
Coupler Developers. When certain photographic
developers undergo oxidation in reducing silver bromide,
they either result directly in the formation of an oxi-
dation product that is a colored dye or that is capable
of uniting with something else in the solution to pro-
duce such a dye. To be of value in color photography,
such dyes should represent the primary colors; they
must be formed in the emulsion precisely where the sil-
ver bromide is being reduced and they must be insoluble
in the developing solution so that they will not diffuse
into the adjacent gelatine and make the image unsharp.
Under these circumstances we may picture the film after
development as consisting of the usual silver image
mingled With an identical image in a colored dye, which
Will be masked more or less by the black silver image.
Oxidizing agents exist, however, that Will destroy the
silver image without destroying the dye image thus leav-
ing a final image in a colored dye.
We may distinguish two classes of such develop-
ers. In the first, the dye is the direct product of the
l. This was Newton's first published work. The experiment was per-
formed in 1666 and communicated to the Royal Society in 1671. In
another part of the same communication he showed that it is im–
|possible to change the color of light by either reflection or
transmission and that all colors are refracted by different
amounts. The last fact caused Newton to conclude that it would
be impossible to make a lens form a sharp image and doubtless
had much to do with his decision to abandon lens design and
turn his attention to the development of the reflecting tele-
Scope. Here, since the light is reflected and not refracted,
there is no difficulty about chromatic aberration.


182 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Oxidation of the developeſ. These are known as primary
developers and were first investigated by Lie sang in
l896. In the second class, the oxidation product unites
With something else that is present in the developer to
form a dye. Such developers are known as secondary de-
velopers and were first discussed in the literature by
Siegrist and Fischer in l914. The dyes that they con-
sidered, however, were soluble under the conditions of
their experiments and so unsuitable for photographic
purposes. Suitable insoluble dyes have since been dis –
covered and put to very excellent use. f
Another process involving the use of dyes in de-
velopment consists in incorporating dyes of the required
colors in the emulsion itself that remain stable during
development and fixing. After these processes are com—
pleted, the negative is treated with certain agents that
do not attack the dyes except in the presence of finely
divided silver. In this way the dye is destroyed where
the silver image had been and remains elsewhere, thus
leaving a dye image that is a positive. These are known
as silver dye-bleaching methods and have found applica-
tion. On a C Ommercial scale in the Gaspar process.
Photographic Reversal. Photographic reversal
may be defined as any process in which the light sensi-
tive material originally exposed in the camera is so
treated that the final result, is a positive rather than
a negative. This is a very fundamental part of such
color processes as Lumière, Agfa, Dufaycolor, and Koda-
chrome but it will be simpler to consider first in some
detail how it is applied to ordinary film before taking
up the additional intricacies involved. When the final
image is to be in color.
The reversal process is used almost invariably
in non-professional motion pictures as these are not
2. Students of Organic chemistry will find much interesting mate-
rial about the dye processes of color photography in the follow-
ing journals:
American Photography, 5l: lil-6–8, 1957
17 11 31:585-6, 1937
11 11 31:892–5, 1937
Photographic Journal 76:218, 1936
º
#
º
º
CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY 183
usually duplicated, and there is a distinct saving in
the cost of material if the film that Went into the
camera can be made into a positive so that it is unne C –
essary to use another film to make a print from it. An-
other advantage is that positive films made by photo-
graphic reversal have exceptional fineness of grain for
reasons that Will be considered after the process has
been discussed.
Suppose We make a print on paper from a negative
showing a black cross on a White ground. If exposure
and development have been satisfactory, We find on the
paper a black background, in Which the original light –
sensitive emulsion has been completely converted into
metallic silver, and a White cross Where the paper is
still coated With the original light-sensitive emulsion
that was not affected by the printing light, because it
was shielded by the black cross on the negative. If
now, instead of dissolving away the unused silver bro-
mide or chloride in the fixing bath to make the image
permanent, it is desired to reverse the print, it may
be immersed in the following solution:
Water - 1 liter.
Potassium dichromate 5 grams.
Sulphuric acid 5 cc.
This solution rapidly dissolves the black de-
posit of metallic silver but leaves the light-sensitive
silver salts covering the White cross unchanged. The
Solution should be allowed to act, until the black de –
posit of metallic silver has completely disappeared.
The paper then retains a cream white cross of light —
Sensitive silver salts on a background of White paper.
After Washing for a minute or two in clear water the
print should again be exposed to a strong printing light
and developed once more. Since there is no unexposed
Silver salt on the background, this remains white. The
cream-colored cross, however, undergoes the latent –
image change and is reduced to black metallic silver by
the second development so the final result is a positive
like the original negative —-a black cross on a White
background. Moreover, the image is now permanent since
the light-sensitive salts have all been reduced and


18|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
nothing remains on the paper except an image in metallic
silver.
If this same process is carried out. With an or –
dinary negative containing a variety of halftones, the
first exposure is likely to expose only part of the sil-
ver salt in any given area. Thus, only part Will be de-
veloped the first time and the rest, Will remain un-
changed on the paper until the second exposure and de –
velopment. It then becomes visible, as a shade of gray
Whose depth Will depend upon the amount of silver salt
that remained until the second development. The print,
made in this Way Will be recognizable as a positive but
Will probably have a muddy appearance as traces of
light-sensitive silver salts will have been left over
the entire print, to be reduced by the second develop-
ment. In order to avoid this, films intended for photo-
graphic reversal have the emulsion coating made somewhat
thinner than usual With the results that the first de –
velopment goes completely through the emulsion in those
parts representing the brightest light and leaves no
residue of silver bromide there to veil the highlights
on second development. The thinner emulsion coating re-
sults in some loss of latitude but not, however, enough
to be seriously detrimental when photographing any or—
dinary subject.
Moreover, there is a very important compensat-
ing advantage in reversal film in that the final image
is more fine grained than one made by printing from the
negative in the ordinary way. This is true because the
first exposure exercises a selective action on the sil-
ver bromide grains and is most likely to produce the
latent image change in those that are most sensitive to
light. These are the coarser grains which undergo de-
velopment the first time and are dissolved away in the
acid dichromate solution. The slower, finer grains re-
main to be developed by the second development.
A summary of the steps involved in making a
positive by reversal follows.
l. Develop the negative in the usual Way, preferably
With a high contrast developer.
#
Rºmº#

CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY 185
Tº "
s
2. Dissolve away the negative image With a reducing so-
lution.
5. Expose to light until all the silver salt remaining
has undergone the latent image change and develop
completely. -
Thorough Washing is essential between all operations.
Control of density is indirect here as the density of
the final image depends upon the relative amount of the
silver salts that remain after the first development.
As a result, under-exposure tends to produce too dense
results as insufficient, silver salts are used in the
first development, and too much therefore remains for
the second. Over. exposure, on the other hand, utilizes
too much of the available silver bromide for the first
development, and too little remains for the second de –
velopment. The resulting image is therefore weak and
thin.
The reversal process can also be utilized to
make an enlarged negative from a miniature with a single
Operation instead of by making first a positive and then
another negative. Where large numbers are to be made,
the saving in time would be very great. Without a very
considerable amount of experience, however, such a proc-
ess is likely to prove difficult as the density and con-
trast obtained after the second development is very
largely dependent upon the precise treatment given dur-
ing the first development. Learning What exposure and
development, should be used the first time in order to
leave just the right amount of silver bromide for the
Second development is not easy and one who has only a
few enlarged negatives to make Will probably save time
by making them in two operations as a separate positives
and negatives and secure better quality by so doing.
The Special thin emulsions designed for reversal proc-
esses are considerably easier to handle by reversal
than the regular negative materials, apparently, be —
Cause the latter provide so much silver bromide that
Considerable experience is required before one is able
to produce a final result without excessive density.
186 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Three Color Printing. The best known method of
reproducing an object in its original colors is by
three color printing. Printers have long been accus –
tomed to do this by first preparing separate plates
carrying the blue green, magenta and yellow portions of
the subject. When these Were inked with the appropriate
colored inks and the impressions accurately superimposed,
the object could be reproduced in colors closely approx–
imating those of the original. The rules of color mix-
ing that apply here are subtractive and the results ob-
tained by superimposing transparent colored images are
the same as those With Which the artist is familiar
When he mixes colors on his palate. The following ta-
ble is a summary of the results obtained.
Table 1
Subtractive Color Mixing
Primaries = blue-green, yellow and magenta
Blue green + yellow = green
Blue green + magenta = violet
Yellow + magenta = red
White = unprinted white paper
Black = blue green + yellow + magenta
By varying the proportions of the primaries, it is
possible to produce practically any color desired.
While theoretically three printings should be
sufficient, printers sometimes resort to as many as ten
or twelve superimposed impressions to get the effect
they want. The reason for this is that it has never
been possible to get precisely the correct spectral
quality in printing inks° to represent the subtractive
primaries perfectly and the printer can often effect the
best practical compromise by using additional colored
inks where they are required.
When the photographer wishes to utilize three
color printing, he must first produce a set of separation
3. The dyes, pigments and chemical toning processes of the photog-
rapher all present Similar difficulties regarding the spectral
quality of the available colors. -

CoLoR PRINT
ſº ſa ſa ºn ſa ſa ſa ſa ſa ： " （ ， ， ， ， ， ， ， ， ,
PLATE XX


IX-X GILVT-I
>{2eIq pºus Aq ºulouqpepox

is :* -*ºm-s
...sº
** *
tºe
lº
º:
hº
,
º
º
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º
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.*.
A
: §
º,
:
§
r
;
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§- -W.
CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY 189
negatives that represent the blue green, yellow and
magent a portions of the subject. This is accomplished
by making the three exposures through the red, blue and
green tricolor filters, that is, through filters that
are complementary to the colors of the prints. Exactly
why the negatives are made through filters that are
complementary to the colors in which they Will ultimate -
ly be printed will become apparent if we consider the
nature of the negative. Since the latter renders the
light that the filter transmits as black silver upon de-
velopment, it has blocked it out and the print result –
ing Will show strongly the detail that Was transparent
on the film, that is, those portions that appeared in
colors that the filter did not transmit. Thus, the neg—
ative made through a red filter produces a print that is
minus red and so should be printed not in red but in the
remainder of the spectrum, blue green. - -
Before proceeding farther, let us assume that we
wish to make a color print of a very simple subject, a
red cross on a black background, and apply the foregoing
principle regarding the use of the complementary colors.
The red filter negative will show a black cross and a
transparent background as everything that was red in the
original has been rendered in black. A print from this
negative records everything that was not red and if
printed in red would give us a red background and a
White cross, certainly a considerable departure from
the subject which was a black background and red cross.
A more detailed analysis of the results through
all the filters Will reveal how We obtain a print in
the correct color. The following table summarizes the
results obtained with both negatives and prints. We
note that the colors of the original have been restored.
The explanation has , however, been somewhat oversimpli–
fied. Actually, the colors by reflected light are nev-
er pure. An opaque object invariably reflects more
or less light of other colors beside that which pre-
dominates so that each one of a set of separation neg—
atives often shows all the details though they will dif-
fer considerably in the values assigned to the various
predominating colors. As a matter of fact, it is of—
ten. So difficult to be certain Which filter made each



190 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Table 2
Filter Negative
Red I. Transparent ground, black cross.
Green II. Transparent ground and cross.
Blue III. Transparent ground and cross.
Color of print. Result.
Negative I. Blue green Blue green background, white
Cr’OSS ,
Negative II. Magenta Magenta background and cross.
Negative III. Yellow Yellow background and cross.
Final result, when these prints are superimposed.
Background – Blue green + magenta + yellow = black.
Cross Magenta + yellow = red.
negative that it is customary to photograph a small col-
ored test object in the corner of each consisting of
colors that can be positively identified. At this point
it Will be Well to make a careful comparative study of
the black and White prints on Plate XXII I rom the
negatives of the cubes made through red, green and blue
filters. Much can be learned by a careful comparison of
of the rendering of the different colors. The original
color of each cube is indicated by the initial on its face.
It Will be realized that the development of the
proper filters to make a set of separation negatives
must be based upon a careful spectroscopic study by the
manufacturer. One Way of doing this is with the wedge
Spectrograph which yields a set of spectrograms as shown
on Plate XXIII. The spectral range transmitted by each is
represented by the light portion and can be translated
into colors by interpreting the superimposed Wave length
Scale.
Table 3
Approximate Median Wave Length for Light of
Different Colors
Centimeters Angstrom Units |1|1 |l
Red .OOOO68 68OO 68O .68
Yellow .OOOO68 58OO 580 .58
Green .OOOO52 52OO 52O .52
Blue .OOOO!6 H6OO l:60 ...h6
Wiolet .000Ol;2 l;200 l;20 .l;2
-~-•-----------T--
PLATE XX || ||
Rendering of the Cubes by the Light Transmitted
by the Tricolor Filters.
Top . Wratten A (red).
Center. Wratten B (green).
Bottom. Wratten C5 (blue).
(The color of each cube is indicated by the
initial letter on its face.)


192 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Note on Plate XXII that there is a certain amount of
over-lapping of spectral regions so that the subtractive
primaries blue green and yellow are transmitted by two
of the filters and absorbed completely by only one.
Thus, yellow, (580 pp.), is transmitted by both the A
and B filters and blue green, (490 p.p.), by the B and C
filt, erºs .
Wedge spectrograms such as the fore going serve
to give a graphic picture of the transmissions of fil-
ters but their small size and indistinct edges make it
difficult to read them with any accuracy. By use of
more laborious methods, it is possible to determine the
percentage transmitted by a filter for as many individ-
ual wave lengths as may be desired and these can then be
plotted by means of schematic diagrams such as those
shown on Plate XXIII. As before, the light portion indi-
cates transmission. Note that these are plotted to
give the densities as an arithmetic scale so the corre –
sponding transparencies would be logarithmic. The per-
centages to indicate transmission are also in logarith-
mic proportion so that care is necessary in order to -
interpret these properly. In Table H is given the per-
centage transmission of the Wratten A, B and Cs tri-
color filter's in still more detailed form.
Exercise of a much higher degree of technical
skill is necessary in making a really satisfactory set
of separation negatives than in making a single negative
for black and White printing because they must be care —
fully matched to each other. In order to obtain a prop-
er color balance in the final print, the three nega-
tives must be developed to the same gamma as it would
OtherWise be impossible to make the light and dark tones
of a given color both contain the correct amounts of the
required primaries to yield the desired result. For the
same reason, it is very desirable that the character—
istic curves represented by the three negatives shall be
as nearly identical as possible. This sometimes neces –
sitates the use of different negative material with one
of the filters because light of different colors does
not invariably yield identical characteristic curves on
the same film. It is also a great convenience to have
negatives of comparable density so that the same exposure
:
*
ſº

- -- ºr. - -. 3.- ºr-->x. xzºº º **...*.*... sº tº :* -: *.*.*.*.*.*.*. *"...*** : * > . - " - - - ‘. . . . . . . “. . . . . . ... sº ºf . ‘. . . . * *E. -- i. * . * . . . .-- • * 3. . . . . .--" **:: , , ; ,” .
ſººº: , tº tº- ſº-- | - j * - i - tº - ". .. tº ... tº * . . . " ".: # , ſº • , tº - [*j ; , , ... * º **::::...
Aſſº
No. 49. (’4 - C (Tricolor Blue)
º
B (Tricolor Green)
No. 58. B2 º-º-º:
-Yº fº = ... : º
º . - $ - t
A (Tricolor Red)
PLATE XX | | |
No. 25. A Tricºlor ite!
Eastman Kodak Co.





1911 FIRST COLLEGE COURSE IN PHOTOGRAPHY
Table l; (Eastman Kodak Co.)
Percentage Transmission of the Tricolor Filters
Filter Blue #19 Green #58 Red #25
HOO 5.76
LO 7.21;
2O 9.75
3O 12.8
|O 2O.O
5O 26.2
6O 26.2
7O 20. O
8O 10.1; l.97
90 3.17 ll. H6
5OO .19 30.23
LO 50.1
2O 60.2
30 51.7
HO 39.0
50 30.2
6O 25.1
70 17.0
8O 10. O . 16
90 5.5 10.2
6OO 2.8 50.1
1O l. 3 61.6
2O .57 72. H.
30 .2l 71.0
|O 76.O
50 77.7
6O 79.11
70 79.l.
8O 79.l.
90 . 10 79.l.
7OO - 1.97 79.l.
can be given to each of the prints. All of this is most
conveniently realized by photographing a gray step scale
in the corner of each negative. Measurement of the
densities of the various steps With a densit ometer Will
quickly reveal whether the negatives are matched. If
they are not, it is time wasted to attempt to make a
color print from them. Comparatively little of the film
CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY 195
area needs to be used for the gray scale as densitom-
eters are Obtainable that can measure densities over an
area having a diameter of no more than 1/50 inch.
The precise details involved in making prints
by photographic methods from a matched set of separa-
tion negatives Will be discussed in a later chapter.
In the meanwhile, the student is advised to examine
Plates XIX and XX rather carefully and to note the
color effects secured by the various ways in which the
color prints from the separation negatives can be com—
|bined.
Dichromated Gelatine. Essentially quite differ —
ent from the methods considered previously for the pro-
duction of a photographic image is the use of dichromat –
ed gelatine. A mixture of potassium dichromate and
gelatine is coated upon a support and allowed to dry.
If this is then exposed to a strong light through a neg—
ative, the gelatine is rendered more or less insoluble
according to the intensity of the light that reaches it.
The precise nature of the process is somewhat obscure
but it seems plausible that the light exerts a reducing
action upon the dichromate reducing it to chromate which
insolubilizes the gelatine. By printing through the
back of a transparent support, the insoluble gelatine
Will be formed adjacent to the support and the gelatine
that is still soluble can then be washed away by care-
fully flowing warm water over the image. The image will
finally be left in low relief on the support and can be
seen faintly by oblique light.
In order to adapt this nearly invisible image
for use in making prints, it is possible to secure a
gelatine coated paper that has finely powdered pigment
incorporated in the gelatine on the paper support.
Usually such paper is sensitized by coating it with the
dichromate solution just before use. After it has been
allowed to dry a negative is used to print it in the
usual Way except that a strong light such as sunlight
or a carbon arc must be used. Then, since the image
lies on the surface of the coating it would be Washed
away if an attempt were made to develop it on the origi-
nal Support. As a result, it is necessary to soak the

196 FIRST COLLEGE COURSE IN PHOTOGRAPHY
sheet in water, roll this into close contact with a
piece of moist transfer paper allowing the Whole to re-
main under pressure for several minutes. Then, the
combination is placed in Warm Water which soon causes
the soluble gelatine to melt and begin to ooze out at
the edges. When this occurs the original support and
the transfer paper can be pulled apart, the image re-
maining on the transfer paper. At this point it will
be found that the support is covered with a smudge of
pigment and soluble gelatine in Which the image is in-
distinguishable. Careful Washing with Warm Water grad-
ually removes the surplus gelatine and pigment and
should be continued until the image is completely freed
from this covering layer. This is the process known as
carbon printing and has the following advantages.
l. Since the print consists of nothing except pigment
imbedded in gelatine, it is absolutely permanent.
2. The colors that can be obtained are numerous.
Such paper can reproduce the entire scale of a nega-
tive with remarkable fidelity.
l!. Local modification is possible by using water at a
higher temperature on portions that it is desired to
lighten.
5. Extremely rich deep tones are obtainable.
6. Carbon tissues are obtainable that yield prints in
the colors of the subtractive primaries so that three
of these made from a set of suitable separation nega-
tives and superimposed can be used to make a color
print.
The main disadvantages are the inconvenience of having
to use such a strong light that enlargements are im–
practical and the fact that the wet image is extremely
delicate and liable to damage.
Wash-Off Relief Film. Wash-Off Relief film is a
special film in which a yellow dye is incorporated dur-
ing manufacture that carries the emulsion in unusually
soluble gelatine. The image is printed through the back
of the film in order to produce the insolubilized image
!.
- º
[" | {{
ſ
[... i !:
ſº
#
|...,
L. is 5
[. f
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i

CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY lo'7
in close proximity to the film base. Development is
accomplished by means of an Ordinary positive developer
or by special developers that assist in insolubilizing
the gelatine by a tanning action of their own. After a
brief Wash the film is next placed in an acid bichromate
solution which dissolves the silver image and at the
same time insolubilizes the gelatine in Which the silver
image is imbedded. The next operation consists in flow-
ing warm water over the film which rapidly removes the
portion of the gelatine that is still soluble and
leaves the image in relief in practically colorless
gelatine. Washing should continue until the Wash Water
loses all milky appearance due to the presence of Solu-
ble gelatine and the image is then fixed briefly in a
non-hardening fixing bath, rinsed and dried.
After drying, the image can be seen in low re-
lief by oblique light. Such an image has the power to
absorb dye yielding a depth of color that depends upon
the thickness of the gelatine. Such an image might be
dried and bound as a transparency. A more usual pro-
cedure, however, consists in rolling the dyed matrix
into contact with a piece of mordanted transfer paper.
The purpose of the mordant is to convert, the dye into
an insoluble form on the paper so that it Will not Wash
out or run. Here, in a period varying from a few min-
utes to half or three quarters of an hour, the dye
transfers completely from the matrix to the paper. The
matrix can then be lifted off and it will be found that
the result obtained is a paper print carrying an image
that consists entirely of dye. The matrix can be re-
dyed and used to make such images a large number of
times if carefully handled. The main apºgºn Of
this is in making color prints. The-Faeºspièce W8, S
made by transferring the three prints shown on Plate
## in the order Tägenta\ yellow and blue green. The
details will be discussed more fully in Chapter XIII.
Requirements of a Satisfactory Color Process.
Before leaving this chapter that is intended to lay a
foundation for a more explicit consideration of the
color processes that are in use today, it Will be Well
to consider precisely what the factors are that should

l98 FIRST COLLEGE COURSE IN PHOTOGRAPHY
be included in an accurate appraisal of the usefulness
of these . Without a doubt, the first and most important
is the accuracy of color rendering for while it is true
that a color process might have value that was deficient,
it could not compete against one that was definitely su-
perior in this respect. It is also of the first impor’—
tance that the photographer shall be able to reproduce
his results, that is , he must have reasonable assurance
that when he has once learned how to produce a satis –
factory color picture an application of the same tech-
nique again Will also produce a satisfactory result.
This is equivalent to saying that the material must be
standardized in manufacture so that its characteristics
vary little from one batch to the next. It also means
that the process of development should not be so compli-
cated as to make it unduly difficult to reproduce re-
Sults. For another thing, the dyes should be permanent.
A conspicuous defect evident in many of the early color
processes lies in the fact, that this Was not the case.
Lumiere plates Will fade if exposed for any length of
time to strong light and even when not exposed to light
many color photographs have lost their color after a
time because of the instability of the dyes used. Pres —
ent indications are that the dyes are now much more
stable than formerly. For certain kinds of commercial
Work it might be argued that it is immaterial whether
the color photograph will last for years but aside from
commercial Work that is done, used and discarded, it is
usually of the utmost importance that the result remain
unimpaired as long as possible. Next, the possibility
of making duplicates is very important for many pur-
poses. This has proved to be a very difficult problem
for the color deficiencies inherent in the original are
multiplied in the duplicate in any of the reversal proc-
esses so that it is far better to make duplicates by
making additional exposures with the camera rather than
to attempt to make copies of the original. In printing
processes using negatives, however, as many prints can
be made as may be desired. Another important considera–
tion is the amount of magnification that color photo-
graphs can stand Without becoming unsharp or displaying
a screen pattern of some kind. They should also be as
transparent as possible if they are to be projected as a

CONSIDERATIONS REGARDING COLOR PHOTOGRAPHY 199
color slide that absorbs an undue amount of light either
produces a dull screen image or else makes it necessary
to use such a powerful projection light that there is
danger of damageing the slide by overheating. Finally,
there is a very great demand for paper prints in prefer –
ence to transparencies arising doubtless from the fact
that a projector is necessary if one Wishes to do jus-
tice to a transparency. Larger paper prints are more
easily obtained than equally large transparencies and
they are more readily worked over if they need to be
modified in any way. On the other hand, no print can
ever reveal the brilliancy, delicate gradation and
luminosity that can be imparted to a fine slide by
skilled projection so that it is a little puzzling to
discover why slides are not more generally appreciated.
This, however, appears to be a condition that is remedy-
ing itself now that projectors are appearing that are
excellent optically, less cumbersome and relatively in-
expensive.
QUESTIONS
l. Discuss the reasons why some photographers of much
skill and experience are not interested in color
photography.
2. Why must the range of light values represented by
the subject be rather short for satisfactory render-
ing by the reversal processes of color photography?
3. What are coupler developers? Describe the essential
characteristics of a dye coupler that will be satis –
factory for color photography. -
4. Precisely what did Newton prove by his famous prism
experiment? -
5. Consider a subject consisting of a white circle, a
gray background and a black border. Describe the
process of reproducing it by photographic reversal.
Make drawings to show the appearance of the film
after the first development, after the reduction of
this silver image and after the second development.
6. Why do reversal negatives have particularly fine
grain?
7. Why are positives made by reversal too dense if they
have been under-exposed?

2 OO
FIRST COLLEGE COURSE IN PHOTOGRAPHY
8.
9.
lC).
ll.
l2.
l3.
l!.
lº.
16.
17.
Describe the reversal process.
Consider a subject consisting of a green cross, a
blue background and a yellow border and assume that
this is to be reproduced cutting the appropriate
linoleum blocks and superimposing three printings
in magenta, blue green and yellow, respectively.
Make drawings to indicate the pattern to be cut in
each block and state the color in which each is to
be printed. . -
Make drawings of the three negatives that will re-
sult if the above subject is photographed through
the A (red), B (green) and Cs (blue) filters. As –
Sume that the color's are pure.
Show that the colors of the originals can be re-
stored by superimposing prints from the above nega-
tives in colors complementary to those of the taking
filter’s . .
Describe the desirable and undesirable character—
istics of carbon prints. .*
What is Wash-Off Relief film? Describe its process –
ing.
A colored test chart consisting of a green R, a
blue Y and a red B on a background was photographed
in the corner of each of a set of separation nega-
tives. Describe its appearance in each negative.
Explain how this identifies the taking filter in
each case and the color in Which it should be print –
ed.
What is bichromated gelatine? Describe two ways in
which gelatine can be insolubilized to form an image
in low relief.
Describe two ways in which such images can be
utilized to form satisfactory visible images.
Describe the requirements of a satisfactory color
process.

Chapter X | |
THE ADD | T | WE PRO C ESSES OF COLOR PHOTOGRAPHY
Additive and Subtractive Color Processes Dis–
tinguished. One distinguishing feature of the additive
processes of color photography lies in the fact that
all utilize a screen to supply color ele-
ments so small that the eye does not resolve them. In
every case, the light must pass through this screen be –
fore reaching the panchromatic emulsion and the color
elements act, as microscopic filters that transmit or a b-
sorb the light. The emulsion behind the grains that are
the proper color to transmit the incident light undergo
the latent image change While that behind grains that
absorb the light will be unaffected. The process of de-
velopment is merely the reversal process and serves to
reveal the colored grains that made the picture and to
mask those that did not contribute to it. It Will be
realized that such plates inevitably have limited trans-
parency because the screen plate itself cuts off much
light and because the grains that are not used must be –
come masked With silver during development.
- In the additive processes, the colors are placed
on the plate sor on a separate color screen that must be
in close contact with the emulsion during exposure, as
discrete areas so small that the eye does not resolve
them and development serves to reveal the photograph in
color by masking With black silver all the color ele-
ments that did not transmit the light that made it. In
subtractive processes, on the other hand, color is pro-
duced where it is wanted during processing so the color
image lies either on a White paper or transparent film
and no black is present except. Where it was actually
present in the subject. The additive processes use the
primaries red, green and blue and obtain the other
Colors by presenting these to the observer under condi-
tions that produce retinal stimulation by two or more
2Ol

2O2 FIRST COLLEGE COURSE IN PHOTOGRAPHY
of these simultaneously. The subtractive processes use
the primaries blue green, yellow and magenta and obtain
the other colors by Superimposing these so that the
color that reaches the observer represents only the
light that did not undergo absorption by any constituent
Of the mixture.
Methods of Producing Additive Color Mixing. We
shall next consider the ways in which it is possible to
mix colors that, Will permit each to reach the observer
in its entirety regardless of what other colors may be
present. This can be done in at least three Ways.
First, we may accomplish this by projecting colored
lights upon a White screen, Plate XVIII. Since the
screen is white, each color will be reflected in its
entirety and the stimulus that reaches the observer Will
consist of the sum of all the colors that are present in
any of the lights. The response by his brain is closely
allied With the nature of color vision. Should all the
Color receptors on the retina be stimulated simultane-
ously, he will see white, red and green only produce
yellow, and red and blue, magenta as discussed previous –
ly. With the primaries, red, blue and green, it is pos –
sible to produce all the colors of the spectrum With ex-
ceptional brilliancy by mixing lights. Additive color
mixing is applied extensively today in stage lighting by
floodlighting the stage from the front with lights of
appropriate colors and Superimposing these as desired.
Second, additive color mixing may be accom—
plished by building up an image of colored dots so
minute that the eye does not resolve them. Curiously
enough, if these dots should be red and green, the brain
of the observer Will interpret, the combined stimulus as
yellow. Evidently, the stimulus on the retina produced
by tiny adjacent images affects the brain in the same
way as would lights of the same two colors if superim-
posed. In either case, it appears to amount to the
simultaneous stimulation of the red and green color re-
ceptors on the retina. We shall consider later how this
kind of color mixing is utilized in the screen processes
of color photography. Certain artists have also ob-
tained additive color mixing With their pigments by


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filling in areas with tiny dots of colors whose additive
mixing would produce the color desired. Such work,
viewed from a sufficient distance so that the dots are
not resolved, gives the same impression as the sum of
the separate colors.
- Third, the color top first devised by Clerk Max-
well, represents additive color mixing. This is an or-
dinary top so constructed that sectors of differently
colored papers can be placed on it and Will rotate With
the top. By placing sectors of different colors on the
spinning top, the observer sees each portion of the
image alternately in the different colors. These
change so rapidly, however, that the image of one re-
mains on the retina because of persistence of vision,
until the other arrives so, again, the retina is stimu-
lated simultaneously by two or more colors and the brain
interprets the result, as their sum.
Experiment. Prepare sectors of colored paper that
can be rotated together either on a laboratory rotator or
a top. Experiment with as many different combinations as
possible and note the effects of varying the proportions of
the different colors. These colors are never as vivid as
those secured by mixing lights because reflected colors
are never pure under ordinary illumination. Examination of
the light reflected by any colored object with a spectro-
scope is likely to show that all colors are present to some
extent.
Yellow and blue produce a degraded white rather than
green. Since the mixing is additive, this should not
be considered surprising. Yellow, we have already seen
stimulates the red and green color receptors in the eye
and if the blue are also stimulated, the observer will
see white as this is the way in which the brain inter-
prets the simultaneous stimulation of all the color re-
ceptors on the retina however produced.
The Additive Color Mixer. While the projection
of colored lights as shown on Plate XVII gives some
idea of additive color mixing, it is impossible to ap-
preciate fully the variety and beauty of the colors that
can be produced without having some means of altering






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THE ADDITIVE PROCESSES OF COLOR PHOTOGRAPHY 2O5
the relative intensities of the different primaries.
This may be done very satisfactorily and simply by the
color mixer shown on Plate XXIII. With this, using auto-
mobile headlight bulbs as light sources, it is possible
to display the color pattern in a totally darkened room
on a scale that Will make it possible for thirty or
forty people to see it at the same time.
The lights consist of automobile headlight bulbs
each connected in series with a variable rheostat of
from 6 to 10 ohms resistance. Each light is mounted as
a separate unit so that it can be moved about independ-
ently of the others. Beakers having a capacity of about
1100 cubic centimeters are inverted over the lights to
serve as lamp houses to direct the beam of colored light.
The beakers have been silvered on the outside and paint –
ed With opaque paint except for a circular area about
tWO inches in diameter on the side of each beaker that,
serves as a Window. Over these Windows are red, green
and blue gelatines. The Wratten Projection Red, Projec –
tion Green and Projection Blue have been found very sat -
isfactory. After the lights are arranged on a table be –
fore a non-selective White screen so that they illumi-
nate the screen with red, green and blue light, the rel-
ative amounts of each color may be varied with the
rheostats. This, of course, changes somewhat the Spec –
tral quality of the emitted light, but not so seriously
as to interfere with a purely qualitative demonstration.
By trial and error the intensities of the three colored
lights should be adjusted until the area in which their
illumination is superimposed appears White. Next, a
cone about 10 inches in height should be placed before
the lights so that they Will cast its shadow on the
screen. When the distances are correct, three large
Over-lapping triangular shadows of the cone will be
shown on the screen as indicated in Plate XXIV. If the
lights are tilted slightly and the cone is placed a
little higher than the lights, the shadow pattern on
the screen Will be produced at such a height that it
can be seen by a large number of people at the same
time. The color array seems really astonishing the
first time one sees it and can be varied within very
Wide limits by manipulating the rheostats connected to

2O6 FIRST COLLEGE COURSE IN PHOTOGRAPHY
each light. A lºC Watt laboratory transformer Will be
found satisfactory as a source of power.
It will clarify thinking about this color pat-
tern to locate first the shadow cast by each light.
With the arrangement of colors shown on Plate XLVI, the
shadow cast by the blue light or the region. Within -
Which blue does not fall is represented by the triangle
farthest to the left. This is therefore minus blue.
Similarly, the green light casts the middle triangle
and so this region is minus green and the red light
casts the right-hand triangle which is therefore minus
red. The minus blue triangle, however, is receiving
light from both the red and green sources and so ap-
pears to be yellow to the observer. The minus green
middle triangle is receiving light from the red and blue
so it appears to be magenta and the minus red triangle
is receiving light from the blue and green so it ap-
pears to be blue green.
Let us next consider the areas in Which the tri-
angles overlap. The area in which the minus blue and
minus green triangles overlap lacks both these colors,
receives light only from the red source and is therefore
red. In the same way, the other over-lapping triangle
is minus red and green and is therefore blue. It is
also possible to place a box under the cone with open-
ings that allow the green to illuminate an area on the
screen that the other lights do not reach.
To sum up, we find that the background is White
because all three of the lights fall upon it in proper
proportions. It will be recalled that this is true be —
cause the intensities of the three colors were adjusted
to produce this effect. The three large triangles dis —
play the three subtractive primaries, magenta, blue
green and yellow. The over-lapping triangles and the
area illuminated by the box under the cone display the
additive primaries. Black could be produced by putting
up some sort of obstacle that cast over-lapping shadows
from all three sources on the screen. Most interesting
of all is the great variety of effects that can be pro-
duced by varying the intensities of one or more of the
lights. The variety and beauty of the colors that can
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lbe produced in this Way are really amazing. Even dark
shades such as midnight blue or maroon can be produced.
Actually these are contrast phenomena and largely in
the brain of the observer but it is none the less
strange to produce colors on the screen that appear to
|be much darker than the colors of the primary sources.
It is next important to recognize that the in-
terpretation of color is actually very complicated and
from a failure to recognize and accept this complexity,
much misunderstanding and argument results. To the
chemist, a color may be a dye ; to a physicist, a Wave
length; to a physiologist, a complicated matter involv-
ing such things as the retina and optic nerve; to the
psychologist, a stimulus to the brain. We know, too,
that the color of an object depends upon circumstances
and is really threefold in character because it depends
partly upon the object itself, partly upon the light by
which it is viewed and partly upon the interpretation
made by the brain of the observer.
Experiment. Examine a bunch of yellow and red
artificial masturtiums by each of the three lights of
the color mixer. Any will appear black when viewed by
light of a color for which they have no reflecting power
thus showing that the light by which they are viewed has
a very important bearing upon their color. Note, also,
that they can appear almost white when illuminated by
light for which they have very high reflecting power.
This is partly psychological for the brain is accustomed
to interpret as white anything that has very high re-
flecting power.
Experiment. Examine a yellow object such as a
daffodil on a Lumière color plate with a microscope. Note
that it is actually an aggregate of dots predominantly
red and green and that no yellow is to be observed on the
plate.
Quite evidently this is a psychological yellow in con-
trast to the physical yellow of the sodium light.
It is by no means certain, even in the case of
people with normal color vision, that we all see the
same color When we look at the same object. Another way


2O8 FIRST COLLEGE COURSE IN PHOTOGRAPHY
of realizing the great complexity of this subject is to
consider the number of Sciences that must contribute in
one way or another to a complete understanding of the
result, . To the extent, that color phenomena deal With
the objective World, they are in the domain of physics,
but the instant that color is recognized by an observer,
it becomes a very intricate matter in the domain of
physiology and psychology. Thus, it is not surprising
that a completely consistent, theory of color on which
the physicist, the physiologist, and the psychologist
can agree has not yet arrived. In photography, though
our interest is both in color in the objective World and
in its psychological interpretation, We need not par-
ticularly concern ourselves With the precise mechanism
by which these external stimuli make an impression on
the brain of the observer. At least additive color mix-
ing of the primaries, red, green and blue makes the
Young–Helmholtz theory of color vision seem very plausi-
ble . . That We can produce any color desired by suitable
mixtures of red, green and blue makes it seem very rea-
sonable that color receptors sensitive to these three
could account for the complexities of color vision. It
must be acknowledged, however, that no one has ever been
able to demonstrate the existence of the mechanism by
Which this could take place. It seems quite possible
that this theory is too simple to account completely for
the complexities of color vision. It is interesting to
note, however, that no later theory has been able to
supplant this. Rather, the newer theories merely make a
place for themselves beside the old Which is probably
evidence that much more remains to be learned. Mean-
While, this theory throws much light upon those aspects
of color that are of interest to the photographer and he
is wise to accept it for what it is worth remembering
always that part of the story remains to be told.
Screen Plate Transparencies. The earliest of
the successful processes of color photography and in ad-
dition one capable of producing very beautiful results
is the Autochrome manufactured in France by Lumiere. We
shall consider this in considerable detail, as it is
typical of all the so-called screen plate processes, and
then discuss briefly the respects in which certain


THE ADDITIVE PROCESSES OF COLOR PHOTOGRAPHY 209
.
º
other's differ from it. Many technical problems had to
be solved and that this was done With very considerable
success is apparent from the beauty of the results ob-
tained. Today, it seems probable that these screen -
plate processes are due to fall into disuse as certain
subtractive processes have definite advantages but a
study of them is still of value both for its intrinsic
interest and for the light it throws on the nature of
color and of color vision.
The original process involved the use of a glass
plate which was coated with a tacky substance and then
dusted with starch grains that had been dyed the colors
of the additive primaries, red, green and blue mixed in
the proper proportion to make white. Those that came
in contact. With the tacky substance Would adhere to the
plate, While the surplus could be removed, possibly
With an air blast, so that a layer of grains covered
the plate. It was essential that there should be no
over-lapping of grains as this would produce subtractive
color mixing and some degradation of color. At this
stage, there would be open spaces between grains through
which White light could pass, producing a reduction in
the brightness of the colors. The next step consisted
dusting finely divided carbon into these open spaces and
then rolling the grains out flat, under considerable
pressure Which Would cause them to spread out to fill in
the interstices if any remained uncovered that had previ-
ously permitted White light to pass through. Such a
plate, When viewed by transmitted light, Would appear
light gray, Which is actually White under low illumina–
tion, as all the color receptors on the retina would be
stimulated simultaneously.
The plate had next to be coated with a water-
proof coating to protect the color screen from the solu-
tions used in development and was finally coated With a
very sensitive panchromatic emulsion. The fact that the
emulsion could not be coated directly on the glass plate
resulted in its adhering much less tenaciously than in
the case of an Ordinary plate. As a result, extremely
careful handling Was necessary during development. In
case the Waterproof protective coating Over the color
screen was damaged, the developing solutions would get


2l O FIRST COLLEGE COURSE IN PHOTOGRAPHY
l
into the starch layer at that point, and produce a bright
green spot.
All screen plates have to be loaded into the
camera with the emulsion side away from the lens so that
the light will traverse the screen before reaching the
emulsion. The screen may therefore be thought of as a
aggregate of innumerable minute colored filters too
small to be resolved yet exercising precisely the same
selective transmission that We have already considered
With filter’s that, COver the Whole lens. Before C On-
sidering how these plates render all colors simultane-
ously, it Will be Well to carry the process through
With only one. Let us assume, therefore, that an Auto-
chrome plate has been given a correct exposure by a pure
green light which has had to pass through the back of
the plate and through the color screen before reaching
the emulsion. The image formed will be transmitted by
green grains in the screen and Will cause areas on the
emulsion behind these grains to undergo the latent image
change. At the same time adjacent grains colored blue
or red will absorb this light so that it does not reach
the emulsion behind these.
Development consists of the reversal process
that has already been discussed. After the first de-
velopment, the plate will appear uniformly gray because
the screen elements are so Small. Actually, however,
the only portions that will have been developed will be
the tiny areas behind the green grains and as a result
these Will be completely masked by the developed silver.
Those areas that were cut off from the incident green
light by red or blue grains did not undergo the latent
image change and so remain as silver bromide. The de –
veloped image therefore consists of a random distribu-
tion of dots of developed silver under each of which is
a green starch grain distributed over an area that still
has all the red and blue grains covered with the Origi-
nal silver bromide emulsion. At this point in the de –
veloping process, no green would be visible by trans-
mitted light as all the green grains are masked by de-
veloped silver. The red and blue grains are still cov-
ered by translucent silver bromide so that the plate
Would be colored faintly magent a by the simultaneous




THE ADDITIVE PROCESSES OF COLOR PHOTOGRAPHY 211
transmission of red and blue. The next Step consists in
dissolving completely the developed image without alter-
ing the silver bromide. This may be accomplished by a wa-
ter Solution of potassium permanganate or potassium di-
chromate acidified with sulphuric acid. The plate would
then appear green by transmitted Light because the green
grains are no longer masked in any Way but the green
Would appear rather light because the adjacent red and
blue grains that are still masked with yellowish yellow
bromide transmit additional light which gives the ob-
server the sensation of White mixed With the predominat -
ing green. To make the green really brilliant, it is
necessary to mask these red and blue grains with black
metallic silver which is accomplished by the final step
in the reversal process, namely, by exposing the plate
to White light for a sufficient length of time to cause
all the remaining silver bromide to undergo the latent
image change and developing it fully. After a brief
Washing the plate can be dried. On looking through it
one will see a true green undiluted by any other color
because all the light that is now transmitted is first
passing through green starch grains since both other
colors are completely masked with silver . It Will also
become apparent now why these plates are inevitably
lacking in transparency because a considerable fraction
of any area representing anything but white is covered
With the silver deposit that masks the grains that do
not represent, the color required for this portion. A
similar process by which the colored grains are selec –
tively masked or revealed Will produce the other colors
as shown in the following table.
Color Color Elements Revealed Color Elements Masked
Wiolet, Blue and red, blue in excess Green
Magenta Blue and red, red in excess Green
Blue Blue Green and red
Green Green Blue and red
Yellow Green and red . IBlue
Orange Green and red, red in excess |Blue
Red Red Green and blue
White Red, green and blue None
Black None Red, green, blue


212 FIRST COLLEGE COURSE IN PHOTOGRAPHY
We shall next, consider the result, obtained if
We photograph a red barn, yellow straw stack, green
trees, White clouds, blue sky and a bed of Orange
flowers on an Autochrome plate. To simplify the dis –
cussion, We shall again assume that the colors are pure .
Then, the light coming through the lens from the red
barºn Will be red and it, Will therefore be transmitted
by the red grains and Will reach the emulsion to pro-
duce the latent image change over the areas that are
covered by the red grains. Similarly, the light from
the straw stack Will be transmitted by red and green
grains and the yellow image will be formed behind these
grains. The green image of the grass and trees will be
formed behind the green grains, the blue sky behind blue
grains, the White clouds behind red, green and blue
grains and the orange flowers behind red and green
grains With the red predominating. The first develop-
ment will therefore mask all the grains that transmit –
ted the light to form the entire image. Reduction. With
acid permanganate or dichromate Will dissolve this neg-
ative image completely and reveal the grains behind it
and, finally, exposure to light and a second development,
Will reduce all the remaining silver bromide to silver
thus masking all the color elements that were not re-
quired to make the picture. If exposure has been cor-
rect, the image reproduces the object brilliantly in
its original colors. The following table summarizes
the color’s obtained.
Transmitted by Color to Observer
Barn Red grains Red
Stack Red and green grains Yellow
Tree and grass Green Green
Clouds Red, green and blue White
Sky Elue - Blue
Flowers Red and green, red in excess Orange
Black outlining None Black
Fixing is unnecessary, as there is no silver bromide re-
maining to remove and as there is thus no hypo to Wash
out , Washing need take only a few minutes. Drying
should be hastened by placing the plates in a good.

THE ADDITIVE PROCESSES OF COLOR PHOTOGRAPHY 213
circulation of air but heating is inadvisable as it is
apt to cause the emulsion to separate from the plate
around the edges. The final step consists in varnish-
ing the plates with a varnish consisting of gum dammar
dissolved in benzene to make the color's more brilliant .
After this has dried, binding the transparency with a
cover glass is highly desirable.
Autochrome transparencies should not be exposed
unnecessarily to strong daylight as this Will fade the
colors but if protected from daylight. When not being
viewed, the colors Will last for many years. Results
can be obtained by this process that are very beautiful,
the color rendering can be very lovely, and with a very
intense light source, projection up to full theater size
is satisfactory. Such a lantern, however, presents
problems in the way of filtering out the heat radiation
before the light is transmitted through the plate, for
a high temperature Would quickly impair the colors as
the color elements are organic material that Will turn
brown if heated much. Water cells placed between the
condensers and the plate have been used but the problem
of satisfactory projection has always involved difficul-
ties because of the limited light transmission of the
transparencies that is inherent in the nature of the
process. Another serious limitation arises from the
fact that the emulsion is extremely liable to damage
during processing. Still another was that these plates
were very slow requiring from sixty to one hundred times
the exposure of a reasonably fast ordinary plate. This
was largely due to the fact that the light intensity was
cut down greatly both by the yellow filter" that had to
be used to cut off some of the incident blue light and
by the absorption in the color screen itself.
Lumière et Cie. now make a color film called
Filmcolor that uses a film as support instead of a glass
plate and is considerably faster than the original
plates.
Several other similar processes have been com—
mercially successful. First of these to appear after
l. This yellow filter was necessary as the panchromatic emulsion
was so sensitive to blue that a color photograph without it
would have shown a predominantly bluish cast.

21 l; FIRST COLLEGE COURSE IN PHOTOGRAPHY
the Lumière plate was the Agfa plate which is similar
to it except that the dyed color elements in the screen
are resin particles. Later these Were marketed on a
film support. Both Lumière and Agfa plates represent a
completely random distribution of the color elements
which are much too small to be seen under magnification
With anything less than a microscope. Unfortunately,
grains of the same color show considerable tendency to
clump so that, as many as six or eight of the same color
may be found side by side. These aggregates are visi-
ble under low magnification which rather limits the use –
fulness of these plates for projection by giving the
color pictures a rather granular effect if the magnifi.
cation is too great or the audience too near.
The Finlay process makes use of a color screen
consisting of a geometrical array of color elements
distributed in a symmetrical pattern over a glass plate.
Plate VII is an enlarged photograph of such a plate.
The fact that, these plates have a repetitive color
screen means that the screen can be manufactured sepa –
ºrate from the emulsion. The two are loaded into a spe –
cial plate holder that holds them in close contact dur-
ing the exposure so that the color elements on the
screen act as tiny filters as with the Lumière and Agfa
plates.
After exposure, the film is removed from the
holder, separated from the color screen, and developed
as a negative in the usual Way. The finished negative
appears like any other Without magnification but actual-
ly consists of tiny areas identical in pattern With the
taking screen. From this, black and White positives are
made in the usual way which will, of course, reproduce
this same pattern. Usually registry marks are made on
the negative and positive to assist in assembling the
positive with a viewing screen. This viewing screen
carries the same array of color elements in the same or –
der as the taking screen and it is not very difficult
to superimpose the positive correctly by looking through
the two toward a light. When registry is not quite cor-
rect, a complicated moire pattern can be seen which dis —
appears When the pattern of the positive and the view -
ing screen are exactly superimposed.

THE ADDITIVE PROCESSES OF COLOR PHOTOGRAPHY 215
The Finlay process offers two important ad-
vantages. First, there is a considerable saving in
cost. The most expensive element in manufacture of any
of these materials is the color screen Which is lost
Whenever an exposure is spoiled in the other screen
plate processes. Here, however, nothing is Wasted ex-
cept the panchromatic film, as the taking screen is
separate and can be used over and over . Viewing Screens
must , of course, be bound in contact With the good color
positives, but no screens are Wasted on those that are
not good. The other advantage is the ease of duplica-
tion. In order to make any number of color duplicates
from one negative, all that is necessary is to make the
required number of positives on ordinary films or plates
and bind each to a viewing screen with lantern slide
binding.
The Dufay process also makes use of a color
screen providing a geometrical array of color elements
on the film under the emulsion. The special feature of
these is the extreme minuteness of these elements which
are ruled on film with a ruling engine and colored inks.
That this is a very remarkable achievement will be evi-
dent. When one realizes that there are approximately a
thousand color elements per linear inch Or a million
per square inch. Lumiere plates carry starch grains
only one two-thousandth of an inch in diameter, but the
color elements appear larger because of the occasional
clumping of several of the same color together. Finlay
plates have about one hundred and seventy-five color ele-
ments per linear inch. One advantage of Dufay film is
that it. Will stand considerably more handling during de –
Velopment than Will the earlier materials which have the
emulsion coated over starch or resin color screens.
Duplication of Screen Transparencies. In all of
these except the Finlay, duplication is rather complicat-
ed. In order to print a color plate from a color plante,
it is necessary to cause the colored light transmitted
by the Original transparency to traverse the screen of
the second before reaching its emulsion. This makes it
impossible to place the emülsions in contact. Rather,
they must be separated by the thickness of the glass or

216 FIRST COLLEGE COURSE IN PHOTOGRAPHY
film support and screen Which must result in a deteri-
oration in definition in the duplicate. To avoid this,
projection printing is sometimes resorted to by pro-
jecting the image of the first color plate through the
back of a second plate that is placed in the focal
plane. Duplicates Of color transparencies on film
would show less tendency to be unsharp if printed by
contact because of the reduced thickness of the support
but, at best , are scarcely satisfactory. Color render-
ing in the duplicate is invariably inferior to that of
the original both because the printing light is rarely
identical in quality. With the light used in taking the
original and because dyes have not yet been discovered
that have exactly the transmissive and absorptive char –
acteristics required. While the discrepancy is not very
noticeable in the original, it must be multiplied in the
duplicate which will therefore be less satisfactory. As
a general thing it will be found best to make the dupli-
cates required by making successive exposures of the
subject. With the camera. Whenever possible as this is far
simpler and gives better quality.
While the presence of the color screen is a
detriment in all of these processes by limiting the de-
gree of magnification that is possible without reveal–
ing the screen pattern and by an inevitable lack of
transparency, all of them have one advantage over the
subtractive processes to be discussed in the next chap —
ter. This arises from the fact that processing is sim—
ple and can be carried out With ordinary equipment. FOrº
certain sorts of scientific record photography in which
it is impossible to keep the subject in the desired
state for more than a brief period or in Which it is de –
sirable to record a sequence of changes, it is of enor –
Inous value to be able to develop the exposure immediate —
ly so that it can be retaken if the result desired has
not been obtained. With any of the additive processes
this is perfectly practical as the equipment required
is only that used in ordinary photography and processing
is not difficult. It Will be found that the subtractive
processes to be considered next involve much more com—
plicated processing and more elaborate equipment.

i
tº.
º
THE ADDITIVE PROCESSES OF COLOR PHOTOGRAPHY 217
lC).
QUESTIONS
Complete the following table of subtractive color
mixing.
Magenta + yellow (magenta predominaving).
Magenta + yellow (yellow predominating).
Magenta + blue green (blue green predominat -
ing).
Magenta + blue green (magenta predominating).
Yellow + blue green (yellow predominating).
Yellow + blue green (blue green predominating).
Complete the following table of additive color mix-
ing.
Red + blue (red predominating).
Red + blue (blue predominating).
Red + green (red predominating).
Red + green (green predominating).
Blue + green (green predominating).
Blue + green (blue predominating).
. Describe briefly three ways in which additive color
mixing may be demonstrated.
Describe the color mixer.
. Make a drawing of the array of colors on the screen
if the lights of the color mixer are placed in the
Order blue, red, green.
Describe experiments that show that color is de-
termined partly by the object, partly by the light
by which it is viewed and partly by the brain of
the observer.
. Assume that red light is allowed to fall upon the
back of a Lumière color plate. Describe the process
of development and the color that is visible by
transmitted light at each stage of development.
. Make a table showing the color of the starch grains
that transmit the light through a Lumière plate for
each portion of a colored subject consisting of an
American flag supported on a yellow staff and stand-
ing On green grass.
. Why must screen plates be loaded into the camera
With the emulsion away from the lens 2
Why are the colors on a Lumière transparency de-
graded with gray when one looks obliquely through it 2

218 FIRST COLLEGE COURSE IN PHOTOGRAPHY
ll. Why does over-exposure produce weak, faded colors
on a screen plate? -
l2. What is meant by the "clumping" of the color ele-
ments on a Lumière or Agfa plate? In what respect
is this detrimental? * *
15. Why do some screen plates require a yellow filter
Over the lens 2
l!. Describe the Finlay process. What are its ad-
vantages and disadvantages? -
lB. Why are all screen plates difficult to project for
a large audience?
l6. Describe Dufay film.
iT . Compare the size of the color elements on the dif–
ferent screen plates.
l8. Describe the effect produced by projecting the
shadow pattern of the cone With the color mixer us –
ing the subtractive primaries, magenta, blue green
and yellow, to cover the lights.
19. Describe the effect produced by using the A (red),
B (green), and Cs (blue) filters used in making
separation negatives to cover the lights of the
Color mixer . - -
20. What is the precise significance of the fact that a
certain monochromatic yellow and a certain monochro-
matic blue Will cause the observer to experience
the Sensation of White?
2l. Discuss the problems involved in duplicating color
transparencies.

\
Ea
in
chapter X | 1 |
THE SUB TRACT | WE PROCESSES OF COLOR PHOTOGRAPHY
Experiment. Prepare solutions of magenta, blue
green and yellow dyes such as the Eastman Wash-off Re-
lief dyes and note the results of mixing them.
When we mix equal volumes of the yellow and the
blue green dyes, we note that the mixture becomes a
clear green. Without the slightest suggestion of either
yellow or blue. In general, anything is the color of
the predominating light that it reflects or transmits
so We may conclude that in this case this light is
green. The question then arises regarding what has hap-
pened to the yellow and blue constituents of the dyes
and precisely where the green came from. Examination
With a spectroscope Will show that the yellow dye trans-
mits both yellow and green light and appears yellow be -
cause this color predominates. Similarly, the blue
green dye transmits both blue and green with the blue
predominating. When we mix the dyes, however, they act
upon each other in such a Way that the blue green dye
absorbs the yellow light transmitted by the yellow dye
and the latter absorbs the blue transmitted by the blue
green dye. As a result, the only color that gets to
the eye of the observer is green which is transmitted
by both constituents of the mixture. It is readily ap-
parent therefore, why this should be called subtractive
color mixing for in each case the color observed is that
which is not removed by absorption by any of the dyes in
the mixture. All ordinary color mixing, whether of dyes,
pigments or paints, falls into this class and all can be
accounted for by absorption. A summary of the results
observed When we mix about equal amounts of the indicat-
ed colors follows. -
I. Blue Green + Yellow = Green.
Blue green reflects blue and green, absorbs yel-
low. Yellow reflects yellow and green, absorbs blue.
219




22O FIRST COLLEGE COURSE IN PHOTOGRAPHY
:
Therefore, yellow absorbs blue and blue absorbs
yellow so the predominating color to reach the observer
is green. |
II. Magenta + Yellow = Red.
Magent a reflects magenta and red, absorbs yel-
low. -
Yeliow reflects yellow and red, absorbs magenta.
Since yellow absorbs magenta and magenta ab-
sorbs yellow, the predominating color to reach the ob-
Server is red.
III. Magenta + Blue Green = Blue.
Magent a reflects magenta and blue , absorbs blue
green. - -
Blue green reflects blue green and blue, absorbs
magenta.
Since magenta absorbs blue green and blue green
absorbs magenta, the predominating color to reach the
Observer is blue. -
When all three of the subtractive primaries,
blue green, yellow and magenta, are mixed the result, is
an indeterminate brown or black because all the colors
present are being absorbed by one or another component
of the mixture and so that small amount of light to be
reflected or transmitted has no definite color.
It Will be realized, of course, that an indefinitely
large number of subtractive colors can be obtained by
varying the proportions of any of the components of a
mixture. Thus, a mixture of magenta and yellow Will
produce Orange if considerable yellow is present, While
a mixture of magenta with less yellow will be red. As
a matter of fact, it is difficult not to over-simplify
in listing the colors at all and it Will be well to
study carefully the color separations on Plate XXIII
in order to appreciate the range and complexity of the
colors obtained. .
One Shot Cameras . We have already considered
the production of separation negatives by making the
successive exposures one after another through the proper

f
º
|
!
|
t -
º
|
.
E.I.
THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 221
filters With an ordinary camera. Quite obviously, this
method is limited to subjects that will remain still
for an appreciable fraction of a minute. For subjects
in motion, the separation negatives must either be made
simultaneously or not at all. Cameras are available,
however, that are actually able to make the three nega-
tives in this way and give each the correct, exposure
through the proper filter. This is done by the use
of some device that divides the light forming the image
after it passes through the lens into two parts that
then come to a focus in two different focal planes form-
ing two images of the subject. One of these parts may
be divided again by a similar device so that three
images can be formed. Such cameras are really marvels
of mechanical ingenuity for the problems that must be
solved in the design of a camera that forms three images
of identical size and equivalent exposure through three
different filters are both numerous and complicated.
The division of the light beam is accomplished
by some sort of beam splitting device. Light falling
upon a plane surface is inevitably reflected to some ex-
tent and if this surface is covered with a thin layer of
some metal, preferably One such as gold or platinum that
is not tarnished by the atmosphere, the fraction of the
light reflected may be any portion desired by varying
the thickness of the metallic layer. Such thin films
of metal deposited on the surface of a transparent solid
placed at an angle of 15 degrees will thus reflect part
of the light to form an image at one side and Will trans-
mit part to form another image in the usual direction.
The following diagram shows how the light from an object
point is brought to a focus by the lens in two different
focal planes When it is partly transmitted and partly
reflected by a mirror carrying a semi-transparent metal-
lic deposit.
. Various methods are available for depositing
metallic films in this Way. Certain metals can be de-
posited by chemical reduction of solutions of their
salts. This is the usual method for silvering mirrors.
An electrical method is also available known as sputter —
ing. Last, metals of sufficiently low melting points
can be evaporated in a vacuum and allowed to condense

222 FIRST COLLEGE COURSE IN PHOTOGRAPHY
INCIDENT LIGHT
FROM POINT ON
OBJECT
== HIMAGE
BEAM SPLITTER
Figure 30.
upon the surface to be covered. All metallic films are
semi-transparent if they are sufficiently thin and the
opaque characteristics With Which people are much more
familiar are merely due to an increased thickness of
the layer.
The Color Scout . The Color Scout, is an inter” –
esting example of a one shot camera that is manufactured
for amateur use. A careful study of Plate XXV Will
reveal much more about its construction than a mere de-
Scription Will. It Will be noted that it uses three
film packs to record the three images. The upper view
shows that two mirrors are used to split the image
formed by the lens into three parts. The mirror near-
est, the lens deflects part of the light upward where it
traverses a red filter and forms the red filter image
On the film pack placed in that focal plane. At the
second mirror, part of the light that traversed the
first is reflected downward, passes through a blue vio-
let filter and records the blue violet image on the film
pack there. The rest of the light goes on through the
second mirror and a yellow green filter to form the
green image on the third film pack. Such a camera must
be built. With great precision and rigidity, the lens
must be capable of forming images identical in size in
the three focal planes with light of different colors,
there must be no distortion or impairment of image by
the mirrors and these must reflect and transmit exactly
the correct amounts of light to give the proper expos –
ures through the various filters. In this camera the
-.”".# a •- --


Optical Chassis
- a one-piece
rigid aluminum
casting Completely baſ-
fled to prevent
flare or “light-
--
Yellow-Graan
Fiſher
Ys Rigid. Iight-
- --ight brace-
hold mirror-
against vibration
Exclusive
-URTIs
DLArom
Mirrors
The weak spot in
...! -º-º-º-
- - mad-strong in
Blue-Violai Filiar º:
COLOR-scout
through special
"closed fruis"
design
- –
-º-º: -L-5E-
Tauss
X - RAY V |EW OF THE COLOR - SCOUT
Green Filter
Record – Re-
p a c → d by
- | locks preven
- accid-ni- with- -
- - - ra-I - ciº-r- -
- - - - ange Finder
Lenn Shade – - optional
standard equip- -
ment N. - -
º - -
Perfected Film-pack
adaptation permits 12
3-color loads in
All-Metal construchen
enuine pin-seal leather
Chromium, and etched
duraluminum finish
SALIENT FEATURES OF THE COLOR-SCOUT
Thomas S. Curtis Laboratories
PLATE XXV
One Shot Color Camera.






22 || FIRST COLLEGE COURSE IN PHOTOGRAPHY
mirrors are made of extremely thin organic material
known as Diafon Which Will last indefinitely unless
they should be punctured in some Way When the camera is
opened. It is surprising that the surfaces should be
sufficiently plane to leave the reflected images unim-
paired. Their thinness is, of course, a great advan-
tage in eliminating additional refraction at the sur-
faces of the transmitted light. By using the films rec —
ommended by the manufacturer it is possible to secure
very accurate balancing of the exposures as the metallic
coatings on the mirrors supplied can be balanced not
only for the light and filter but also for the color
sensitivity of the films.
In the larger professional sizes where sacrifice
of a little of the film area is permissible, it is cus –
tomary to place a step scale of neutral grays either be —
side the subject or in contact with the films so that
it Will be recorded on each negative. Needless to say
in the latter case it should be made as a transparency
so that the light would be transmitted through it.
After processing it is possible to measure these steps
one by One With a densit ometer on each negative. If the
densities of corresponding steps match throughout on all
three negatives, it is proof that the negatives are bal-
anced. If this turns out not to be the case, much time
can be saved by discarding the set and making it over
for a really satisfactory color balance is scarcely
possible under these circumstances. Moreover, much loss
of time and discouragement is avoided by not attempting
the color transfers until assured that the separation
negatives are really satisfactory.
Wash-Off Relief. One of the most satisfactory
processes for making color prints is the dye imbibition
process known as Wash-Off Relief. * The process of
l. It is not the purpose of this discussion to supply the very
numerous details that are essential for carrying out this and
the other color processes. Booklets can be obtained from the
manufacturers of the material that describe the successive
steps very minutely and should be obtained and studied care-
fully before attempting any one of them.

THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 225
º:
making the matrix positives from the three separation
negatives has already been described. Gelatine relief
negatives like these Will vary somewhat in the amount
of gelatine left on the support according to the tem-
perature of the Wash Water and the precise amount of
Washing received. Moreover, the amount of dye they will
later absorb and transfer depends upon the amount of
gelatine that makes up the relief. As a result, it is
advisable to process all three prints from the separa-
tion negatives at the same time taking care that all
are given identical treatment throughout. In this way
the color balance Will be preserved. While the relief
is being developed with Warm water, the image is ex-
tremely delicate and should not be touched. After dry-
ing, however, the image becomes so tough that any ordi-
nary handling Will not damage it. When it is moistened
again in one of the dye baths.
Baths of the dyes required should be carefully
prepared according to the manufacturer's directions.
The exact acidity is important as this determines the
amount of dye that each matrix will take up and trans-
fer to the final print. Mordanted paper is needed for
the print and is prepared by soaking gelatine coated
paper for five minutes first in a solution of aluminum
sulphate and sodium carbonate and then in a solution of
sodium acetate. The purpose of a dye mordant is to con-
vert the Water soluble dye into a form on the paper
that Will be fast so that the image will not become un-
sharp by slight diffusion or be washed away during sub-
sequent Operations.
Before beginning the actual transfer, it is very
desirable to be sure that the color balance is satisfac –
tory as some modification is possible by changing the
acidity of the different dyes, an increase in acidity
resulting in stronger color. By first placing a sheet
of thin celluloid over the mordanted paper, the dyed
matrices can be superimposed in order to be sure that
the color balance is satisfactory. If it is decided
that any one of the three matrices contains too much
dye, the dye may all be removed by washing in water and
the matrix re-dyed in the same dye bath as before except
that the acidity has been reduced by the addition of a


226 FIRST COLLEGE COURSE IN PHOTOGRAPHY
small amount of dilute ammonium hydroxide. Should one
color be too Weak, that dye bath should be made more
acid. With dilute acetic acid and the matrix returned to
it for a few minutes. As it is essential to know the
exact acidity of the baths at all times, burettes will
|be found very convenient for measuring the acetic acid
and ammonium hydroxide that may need to be added and an
accurate record should be kept of the acetic acid or
ammonium hydroxide used.
After the color balance is judged correct, trans-
ferring should begin. The yellow and blue green matri-
ces’ should be stored in separate trays of dilute acetic
acid until needed and the magent a matrix should be
placed face down on the mordanted paper and squeegeed
into close contact. After a period consisting of from
five minutes to half an hour or more, it will be found
on carefully lifting one corner of the matrix that the
dye has all been transferred to the paper. It should
then be lifted off and placed in a tray of clear water
or returned to the dye bath if other transfers are to be
made. The image should next be protected by a sheet of
thin celluloid and the yellow matrix placed over it.
This may be moved about freely until it is accurately
superimposed over the magenta image because of the pro-
tecting celluloid which is then slipped out and the yel-
low matrix squeegeed into close contact. With the mor-
danted paper. After the yellow image is transferred,
the blue green matrix is treated in the same way. The
entire process of transferring the dyes after everything
is prepared may require from twenty minutes to two hours
depending upon the dyes used, the depth of the dye
images, the temperature, etc.
The following summary of the steps involved may
be helpful. -
1. Print positives from the three separation negatives through the
loack of Wash-Off Relief film.
2. Develop in a developer that reduces the latent image to silver.
3. Dissolve the silver image. -
2. The exact order in which the colors are transferred varies some-
what with different dyes. In general, the least transparent
should be applied first.
º
º-#.

#
# * *
THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 227
li. Develop the gelatine relief image by washing away all gelatine
that is still soluble with warm water.
5. Fix to remove all traces of silver bromide.
6. Wash and dry.
7. Soak the gelatine reliefs in the appropriate dye baths.
8. Superimpose the three on a piece of celluloid lying on a white
surface to judge color balance.
9. Correct if necessary by altering slightly the acidity of the
dye baths.
10. Transfer the magenta image.
ll. Superimpose the yellow image and transfer.
12. Superimpose the blue green image and transfer.
lj. Wash briefly and dry.
Technicolor. It Will be realized from the fore —
going discussion that all of the methods involving
three color transfer are time consuming and demand a
very considerable amount of technical skill. That it
has been found possible to adapt a dye imbibition proc-
ess to motion pictures, notwithstanding the large number
of separate pictures required and the high degree of mag-
nification on the screen, must be regarded as a very re-
markable achievement. Needless to say, this is a strict-
ly professional enterprise that is practicable at pres–
ent only when the picture is of such importance that a
very large expenditure is possible in making it. With the
expectation that the return will be proportionate.
Technicolor uses a special one shot camera that
contains a beam splitting device consisting of an Opti-
cal cube. Actually this is made of two right-angled
prisms having a partially transmitting layer of gold de-
posited on the interface before the diagonal surfaces
are fitted together. The light through the lens passes
into this cube and is partly reflected by the gold film
in a direction at right angles to the optical axis of
the lens and forms its image in a focal plane that lies
close to this side of the cube. Here, both the blue and
red images are formed by placing a double film known as
a bipack in this focal plane. The blue image is formed
on the front film and a suitably colored layer allows
only red light to fall upon the rear film forming the
red filter image there. The rear image is inevitably.




228 FIRST COLLEGE COURSE IN PHOTOGRAPHY
unsharp largely because of scattering effects produced
in the light in traversing the first film but since the
final image consists of three sharp images and one un-
Sharp, the impairment is not serious. Meanwhile, the
transmitted portion of the light that traversed the
gold film is utilized to form the green filter image di-
rectly behind the cube. That a camera that can produce
three sets of motion pictures simultaneously at the rate
Of possibly twenty four per second must have involved
serious and intricate mechanical problems goes without
Saying. -
After development as negatives, the three films
are used to make positives on gelatine relief film.
These are then dyed in baths representing the colors
complementary to the taking filters and transferred to
a lightly printed black positive. All of this literal-
ly represents the three color transfer process by the
mile and individual pictures by the thousand so it does
not seem an over-statement to say that the success
achieved is really amazing. Modification of the color
balance is possible in dyeing the gelatine reliefs and
duplicates can be made in any desired quantity, both of
Which are attributes that are essential in commercial
production for the motion picture theatres.
Chromatone. Here, an emulsion similar to that
of bromide paper is provided on a thin collodion film
that can be readily stripped from its paper support.
Three prints are made from the three negatives by ordi-
nary development and fixing. They are then treated
chemically to convert the black silver into magenta,
yellow and blue green compounds respectively. The three
collodion films carrying their colored images are then
Superimposed on a paper support. One outstanding ad-
vantage of the process is that the collodion films are
remarkably tough and Will stand a surprising amount of
handling without damage. Disadvantages are that altera-
tion of the color balance is possible only by substitut-
ing another toned collodion print for one that is unsat-
isfactory in color. The image is carried on three
Collodion films Which makes it somewhat difficult to
keep the finished print from curling.
º
º

THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 229
º
sº
Three Color Carbon. Carbon tissue can be Ob-
tained carrying magenta, blue green and yellow pigment
in the gelatine. After sensitizing such paper with po-
tassium dichromate solution and drying it, the gelatine
image can be insolubilized by printing the separation
negatives on it. With a very strong light. When the
gelatine relief images are developed in Warm Water,
magenta, yellow and blue green prints result as the in-
soluble gelatine image retains the pigment mixed With
it. These images are first developed on a temporary
support and are then transferred to the final support
Where they are superimposed to make the color print. It
has been claimed that this process offers the most
beautiful color prints. Certainly the gradation and
the surface texture of carbon prints is very lovely but
it should be emphasized that the difficulties are con–
siderable. The images are very delicate and easily dam-
aged and the use of double transfer means that not three
but six successful transfer operations must be completed
for a single print.
In Carbro, the operations are very similar ex-
cept that the bichromated gelatine is insolubilized by
contact. With an ordinary bromide print. In this case
the bichromate oxidizes the silver image producing a
yellowish silver compound While the chromate is reduced
and the gelatine adjacent to the silver is insolubilized.
The subsequent treatment is practically identical With
carbon and Carbro except that Carbro prints are some —
times developed directly on the bromide print which pro-
duced the insolubilization of the gelatine. The result
of this is to produce an image in pigment superimposed
on the nearly colorless image that remains after the
Oxidation of the silver thus producing an image with
the beauty, gradation, color and texture of a carbon
print without any troublesome transfer process. More
frequently, however, the wet bromide print and dichromat -
ed carbon tissue are rolled into close contact and al-
lowed to remain for several minutes. The tissue is then
stripped from the print and transferred to another
support and developed with Warm Water. Double trans-
fer is unnecessary here as the image is not perverted.
The main advantage of Carbro over carbon printing is


23O FIRST COLLEGE COURSE IN PHOTOGRAPHY [.
ſº
that it does not require an arc light or sunlight. En- [i.
larged prints may also be made With Carbro. * g.
Kodachrome. While Technicolor is capable of *
producing very satisfactory results in the hands of ex- ~!
perts possessing very expensive and complicated equip- º
ment, in Kodachrome We have a process that makes it pos – f : . .
sible to obtain remarkably satisfactory results with or – º
dinary equipment used in the ordinary Way. It was de –
veloped by Mannes and Godowsky,” two young men Who com- ãº,
bine a singularly effective combination of artistic º
background and scientific training. After carrying the º
investigation as far as their individual resources Would
permit, they offered the results to the Eastman Kodak
Company who immediately recognized the value of it, took º “Tº
the two into their employ, and threw the full resources }:
of their research laboratory into the further develop-
ment of the process.
That the problems to be solved have been both
numerous and intricate goes without saying and When We
stress the simplicity of manipulation as far as the
camera user is concerned, it should not be forgotten
that this simplicity is more apparent than real and that
it follows as a result, of a really amazing development
of manufacture and processing. In fact, When one is
first introduced to the explanation of what is occurring,
it seems almost necessary to postulate the existence of
Maxwell's daemon endowed with power to tell the mole-
cules Where to go and what to do.
The film is a monopack, that is , a single film
carrying three separate emulsions. The top one is non-
Orthochromatic ; the second, orthochromatic ; and the
bottom, panchromatic. This is equivalent to saying that
the top layer is sensitive only to the portion of the
visible spectrum transmitted by the blue filter used in
making separation negatives; the middle layer is sensi- =l-
tive to light transmitted by both the blue and green -
filters ; while the bottom layer is sensitive to that w
transmitted by all three, blue, green and red. In order =|
5. Mannes, L.D. and L. Godowsky, Jr., The Kodachrome Process for -
Amateur Cinematography. J. Soc. Motion Picture Engrs. , 25, al-
65 (1935). -
THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 231
rºl
; FA
-º
to obtain separation negatives, it is therefore neces —
sary to prevent the blue light from contributing to
image formation except in the top layer and the green
from contributing in the bottom layer. This is accom—
plished by incorporating a yellow dye to absorb blue
light either in the top emulsion or immediately below
it and a filter absorbing green between the Orthochro-
matic and panchromatic emulsions. Thus, the blue por’—
tion of the spectrum is permitted to leave its image
only in the top layer, the green in the middle layer
Which is not red-sensitive, and the red in the bottom
layer.
Separating the emulsions in a Kodachrome film
are layers through which the solutions used in process –
ing penetrate rather slowly which makes it possible to
permit a reaction to go to completion in one layer and
terminate it before the solutions penetrate to the One
below. “ There is an interval of possibly thirty seconds
between the completion of a given process in one layer
and its start in the one below. Quite obviously, all
processing must, proceed from the top layer downward
Which means that it is not possible to use a blue green
coupler developer and produce an image of this color in
the bottom layer without previously producing it in the
upper layers as well. As a result, it is necessary to
destroy the dye and reconvert the silver into silver
bromide in the upper layers so that they may be de-
veloped with the coupler developers that yield images
in magenta and yellow. Controlled depth penetration
makes this possible. By very accurate control of the
concentration of solutions, time, temperature, and other
physical constants, dye destruction and the oxidation
of the developed silver to silver bromide can be pro-
duced in those upper layers where dye of a particular
color is not Wanted While leaving it unchanged below.
Development, takes place by the usual reversal
process except that the developers used for the second
development are coupler developers, one producing a blue
green dye, one a magenta, and one a yellow. The follow-
ing outline showing the successive steps may serve to
make clear how a triplicate emulsion, photographic re-
versal, coupler developers, delayed depth penetration,
h. This has reference to the original process. A discussion of
recent modifications follows.



232 FIRST COLLEGE COURSE IN PHOTOGRAPHY
and chemical destruction of dyes Where they are not
Wanted make possible the remarkably satisfactory re-
Sults obtainable With Kodachrome.
Let us assume that the colored object to be
photographed consists of an area having the left hand
third red, the center third, yellow and the right hand
third, green. When this is photographed on Kodachrome
film, latent images will be formed as follows.
Red light...... . . . . . . . . . . . . . Bottom layer.
Yellow light . . . . . . . . . . . . . . . .middle and bottom layers.
Green light . . . . . . . . & G & º ºs e º O & middle layer.
The following legend will be used to indicate the
changes produced in the different layers of film at each
step in the processing. In each diagram the horizontal
lines indicate the boundaries of the areas represented
by the different layers of film. It will be recalled
that these are coated on the film base in the order
panchromatic, orthochromatic and ordinary so that they
occur in this order on the diagrams reading from the
bottom up.
Legend
E. Silver Bromide Silver
| | Clear Film Dye and Silver
Color of dye is indicated by initial letter.
RED YELLOW GREEN
N \ y \, , , , , )
Step I. Develop exposed film in an ordinary developer.
Figure 3 | O O o O O O O O O O O O O O
O O O O O O O || O © O O O O O
Note that the top layer is unaffected as there
is no blue light, that the yellow light affects both the
orthochromatic and panchromatic layers, and that the red
light affects the panchromatic only. Consider carefully
the exact location of those regions that still remain as

THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 233
㺧§º
ºf
the original silver bromide because the light that was
transmitted through them was a color to which they were
not sensitive.
Step II. Dissolve the silver image in a reducing solu-
tion.
Figure 32
The previously developed silver image is removed
completely leaving transparent film While the undeveloped
silver bromide is unchanged. -
Step III. Expose to light and develop with a blue green
coupler developer.
© O BG O O o O BG o o o o BG O O
figure 33 |o o BG o o
o o BG o o
All the silver bromide remaining on the film is
converted into metallic silver intermingled With a blue
green dye in all layers.
Step IV. By controlled depth penetration, destroy the
blue green dye in the two top layers and con-
vert the silver there back into silver bromide. Stop
the process before it penetrates into the bottom layer
leaving the dye and silver image there.
Figure 3 ||
o o BG o o
Step W. Expose to light again and develop with a magenta
coupler developer. This Will leave a combined
magenta dye and silver image wherever there wes silver
bromide. At this point nothing occurs in the bottom
layer because there is no longer any silver bromide
there to reduce.
9 o M o o |o o M O O o o M Q @
Figure 35 o o M O O
FBGE


23|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
Step VI. By controlled depth penetration, destroy the
magent a dye in the top layer and convert the
silver there into silver bromide.
Figure 36 |eo o Moo
o o BG oo
Step VII. Expose to light and develcp the silver bromide
in a yellow coupler developer.
O © y ooloo Y © O || O © Y O O
Figure 37 |o o M oo
o o BG o o
Step VIII. In order to reveal the dye images unmasked by
silver, the silver images in all three layers
must be removed by a reducing solution that will not af-
fect the dyes.
Y Y Y
Figure 38 M
BG
Step IX. Dry and view by transmitted light. The dye
images combine subtractively as follows.
Magenta + Yellow = Red.
Yellow alone gives Yellow.
Yellow + Blue Green = Green.
Figure 39 TREDTTYELLOWTIGREENT
Note that the final image is rendered in the
colors of the light that was originally incident on the
film. , -
The foregoing discussion applies to the method
of processing used when Kodachrome was first brought out
in 1935. Controlled depth penetration for the destruc-
tion of the coupler dyes in the layers in which they
were not wanted was always difficult and involved drying
ºf .
#.

THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 235
the film three times during processing. It has now
(1940) been found possible to develop a method by which
each coupler dye forms its image only in the layer in
which it is desired by exposing the film to colored
printing lights before the second development. The first
development is carried out as usual in reversal methods
using a developer that does not alter the color sensi-
tivity of the three emulsions by affecting their dye
sensitizers. After destruction of this negative image,
the film still carries unexposed silver bromide that is
blue sensitive in the top layer, blue and green sensi-
tive in the second layer and red, blue and green sensi–
tive in the bottom layer. As the film moves along
through the processing machine, it is first exposed to
red light through the back which causes all of the pan-
chromatic emulsion in the bottom layer to undergo the
latent image change and leaves the two top layers unaf-
fected. As a result, development in a blue green coup-
ler developer produces the blue green image only in the
bottom layer where it is wanted. The film next travels
past a blue light which exposes all the silver bromide
in the top layer but does not affect the green sensitive
middle layer because the yellow filter that is still
present prevents passage of blue light into this. The
next step consists in developing the top layer in a
yellow coupler developer after which the middle ortho-
chromatic layer is exposed to white light and developed
in a magenta coupler developer. The final operation
consists in the removal of the silver images in all
three layers without destroying the dyes as in the ori-
ginal proces S.
Presumably, this represents a marked improvement
in the process both from the point of view of time ex-
pended in processing and certainty of results for the
production of the dye images only where they are desired
has much to commend it as compared to producing them in-
cidentally in the other layers and later destroying them.
It is also interesting as an example of how a very sim–
ple idea, though doubtless accompanied by very consider-
able experimental difficulties, Will accomplish a de—
sired result, .
It will be realized from the foregoing that no
modification of color is possible during processing and
that it is therefore most important to give the correct

|RED EYELLow I GREEN
º ! W J W W
O © O O O C O O G) O O O O O
O O O O O O O O O O O G O O
2. DISSOLVE SILVER IMAGE.
3. EXPOSE TO RED LIGHT AND DEVELOP
WITH BLUE GREEN COUPLER DEVELOPER.
o o oBGo o o
4. EXPOSE TO BLUE LIGHT AND DEVELOP
WITH YELLOW COUPLER DEVELOPER.
o o o Yo o o o o o Y o o o o o o Y o o o
o o ob Go o o
5. EXPOSE TO WHITE LIGHT AND DEVELOP
WITH MAGENTA COUPLER DEVELOPER.
o o o Yo o o o o o Yo o o o o o Y o o o
o o o Mo o o
o o ob Go o o
6. DISSOLVE SILVER IMAGE.
W. W. W W. W. W. W. W. W.
RED YELLOW GREEN
PLATE XXVI
INForm Arion Just RELEAs ED BY THE EASTMAN KODAK CoMPANY INDICATES THAT
STEP 2 is unnecessARY, Both THE NEGATIVE AND Positive silver IMAGEs ARE REe
Moved AT THE PolnT REPRESENTED BY STEP 6.
C. E. K.M EEs, AMERICAN PHOTOGRAPHY, MARCH, 1942.





THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 237
exposure. This clearly implies that the picture must
not contain light values so dissimilar that a correct
exposure is not possible for all its important elements.
A bed of crocuses, for instance, may make a charming
color subject provided it is entirely in the shade or
entirely in the sun but is likely to be disappointing
in color rendering if an attempt is made to render it
With half in the shade and the rest in the sun. In the
latter case, the light values are so dissimilar that
the crocuses in the sun must either be too light, from
over-exposure if those in the shade are correct or those
in the shade must be too dark from under-exposure if the
more brightly lighted ones are correct. In general,
much care can be advantageously employed in planning
color photographs in Kodachrome to keep the light values
Within the capacity of the film, thus avoiding Washed -
out highlights and black shadows. In landscapes, much
can be gained by a careful choice of the hour of the day
and in portraiture, by a judicious use of reflectors or
additional light. The advice that is frequently given
to rely upon a flat front lighting with Kodachrome mere —
ly takes cognizance of the fact that the light values
must not be too dissimilar and indicates the simplest
Way to attain this. Actually, however, far more beauti-
ful results are obtainable as in black and White photog-
raphy by oblique light but only on condition that the
attempt is not made to photograph bright highlights and
deep shadows at the same time. Very pleasing results
have frequently been obtained in the shade or on dull
days. While these present the complication of an ap- .
preciable alteration in the spectroscopic quality of the
light, they also yield even lighting and a softness of
coloring that may be very attractive.
It is frequently stated that exposure is very
critical With Kodachrome. Certainly, correct exposure
is the key to satisfactory color rendering and a photo-
electric exposure meter is very desirable but it need
not be assumed that there is no latitude of exposure at
all. As a matter of fact, With the average subject ex-
posures of half and double the correct exposure are both
likely to produce results that will be sufficiently good
so that their deficiencies will not be apparent unless a
correct exposure is available for comparison. As with
any other medium of artistic expression, one Will succeed






238 FIRST COLLEGE COURSE IN PHOTOGRAPHY
º
best if he comprehends the limitations and potentiali–
ties of his medium and, thus guided, applies all the
artistry at his command. A color photograph executed
superlatively of something that is well Within the range
of the medium is likely to be very satisfying aestheti-
Cally.
Furthermore, making such a photograph offers
scope for ability of a very high order. As time goes on
We may expect to see a sharper line drawn between those
who are Working with competent mastery in color and
those who remain satisfied with aimless trying. Ap-
preciation for color merely as color arises from its
novelty today but we may soon expect to see in its place
a far more discriminating sense of what should be done
With it. Meanwhile, it is Well to remember that the
statement that anyone can make a color photograph bears
the same relation to creative expression in this realm
as it Would in another to say that anyone can Write Who
can use a typewriter. .
QUESTIONS
l. Why are correctly exposed transparencies made by
subtractive processes more transparent than those
made by additive processes 2
2. Indicate how all the colors of the spectrum are ob-
tained by subtractive color mixing.
3. Describe the Color Scout camera.
!. Compare the methods used to produce the three images
in the Color Scout, and in the Technic Olor camera.
5. Explain why it is desirable to photograph a neutral
gray scale in making separation negatives.
6. Describe the making of a set of matrix positives on
Wash—Off Relief film.
7. Describe the making of a color print from these by a
dye imbibition process.
8. How is the color balance altered in the above proc-
ess 2 -
9. Describe the making of color motion pictures in
Technic Olor.
l0. Describe the Chromat. One process.
º
º
º w
|
--
-. - -***º--
f||i

THE SUBTRACTIVE PROCESSES OF COLOR PHOTOGRAPHY 239
ll.
l2.
l3.
ll.
lº).
16.
l'7.
18.
l9.
20.
21.
22.
23.
24.
25.
Describe the making of a color print by the carbon
pr’OC ess.
Describe the Carbro process.
Explain Why double transfer of the image is usually
resorted to in making a carbon print containing
printed matter. .
Is there any other way of attaining the same result 2
Can more than one print be made from the same bro —
mide by the Carbro process 2
Compare the advantages and disadvantages of the dye
imbibition processes, Chromatone, carbon and Carbro.
Describe Kodachrome film.
Write out a summary of the successive steps in
Kodachrome processing.
Explain the use of controlled depth penetration in
processing Kodachrome.
Draw diagrams to show What occurs at each step in
processing a Kodachrome film that has been used to
photograph an area that is one-third blue, one –
third magenta and one-third black.
What precautions should be taken regarding lighting
With Color film?
Discuss the latitude of color film.
Make a list of the research problems that must have
been considered in developing Kodachrome.
Have Kodachromes less graininess than black and
White films ? Explain.
Explain how black and White prints can be made from
|Kodachrome transparencies.
Chapter X | W
PHOTOGRAPHY AND CREAT | WE EXPRESS | 0N
By the time the student has reached this last
chapter it is to be hoped that his knowledge of the un-
derlying theory and his experience in the laboratory
have been sufficient to cause him to feel reasonably cer–
tain that he can make the photographic medium do what he
wishes. The problem of determining the correct exposure,
for ordinary subjects at least, should no longer be par-
ticularly troublesome. The day is past when he withdraws
the slide on the wrong side of the film holder, forgets
to draw it at all, or does it twice. He can now take it
for granted that he can focus and develop with the nec–
essary skill. He no longer experiences a peculiar com—
bination of pride and thanksgiving when a snapshot pro-
duce S a recognizable picture of the person portrayed but,
rather, takes it for granted that the prescribed sequence
of operations Will produce this effect. Perhaps he has
also passed through the stage when he felt an undue urge
to make trick shots with reeling perspective. Or, it
may have captured his fancy to attempt to photograph un-
der strange and difficult conditions. A rendering of
the cat down cellar at midnight by the light of one
match is calculated to make others marvel not because it
has been well done but merely because it has been pos-
sible to do it at all. Almost certainly, if he has a
miniature camera, the student Will have passed through
a stage when he has been obsessed with an urge in the
direction of quantity production and has aimlessly made
dozens of photographs whose principal claim to distinc-
tion is that they are numerous. Candid photography, by
which most people mean an enthusiastic quest for portray–
als of others that shall be as ridiculous as possible,
usually claims the attention of the novice for a time.
Finally, after experiencing these normal prelim-
inary stages in the development of a photographer and

2||O
PHOTOGRAPHY AND CREATIVE EXPRESSION 21:1
gaining reasonable proficiency in the exercise of the
craft, it becomes pertinent to inquire what lies ahead
and to attempt to gain a more adequate idea of what one
may hope to make of photography as a medium of expres–
Sion. The great variety of its applications makes pos-
sible a hundred different answers, and it is most fit-
ting that each student should seek the answer that is
most compatible With his own tastes and inclinations.
It is to be regretted that much effort in many other
fields beside photography makes little lasting impres–
sion upon students because the preliminary study from
day to day for class discussion, which is necessarily
fragmentary, is all it ever gets. It is as if a builder
should take the trouble to collect all the materials for
some structure and then, instead of building it, should
dump them somewhere and pay no further attention to them.
Quite obviously, the student must first collect consid—
erable factual information about any subject that inter-
ests him but the real measure of his accomplishment is to
be found not in this but in what he does with it, in his
ability to organize it, to comprehend its implications
and to fit it into place among the other things that he
knows so that it can offer its full quota to the breadth
of his interests and the effectiveness of his life. It
is the function of the teacher to do everything that is
humanly possible to light the torch of inspiration and
point the way. It is the function of the student to ac-
cept a very generous measure of personal responsibility
to travel along the way thus pointed out. The effective-
ness in both cases is measured by the extent to which the
individual concerned can penetrate below the surface of
purely factual relationships, grasp their underlying
meaning, and adapt them to his own purposes
It seems a fair statement that there are three
classes of first rate minds, those that can appreciate,
those that can interpret and those that can create.
Quite obviously, these three classes are not mutually
exclusive and minds differ rather in the emphasis they
tend to place upon each function than in the complete
possession or lack of it. Minds whose primary function
is to appreciate are to be found among those who have a
keen and sympathetic interest in various parts of the









21.2 FIRST COLLEGE COURSE IN PHOTOGRAPHY
field of human knowledge. Here, we find the "cultured
layman" whose appreciation, interest and understanding
serve both to enrich his own life and to inspire other's
in Whom the creative urge is more pronounced. It should
not be forgotten that the ages that have been distin-
guished for exceptional creative enterprise have invar-
iably been those that produced great numbers of people
who were competent to appraise distinguished achievement
and recognize it as good. Those with the interpretative
faculty must have , in addition, the power to formulate ,
analyse and express. It is well if the ministers, edi-
tor’S and teacher’s Of the World are found here. The ad–
ditional element present in the creative type of mind is
the ability to make a synthesis that is peculiarly one's
OWn. At times, this may partake of the nature of a glor-
ified form of interpretation; at others it will seem as
if the contribution is wholly new. In a sense, this is
interpretative but the distinction lies in the fact that
the predominantly interpretative mind bases its presen-
tation upon what has already been done by others while
the creative type blazes new trails and carries the sub-
ject where it has never been taken before.
Perhaps everyone possesses the creative urge to
some extent. Certainly, as We as cent the Scale of human
intelligence we find an increasing tendency to reflect
upon the essential meaning of things, to appreciate that
they are not as simple as they seem and to hunt for an
underlying order. The student is fortunate who learns
early that this reflective process is absolutely essen-
tial to the attainment of anything of real value While
in pursuit of an education. Whether he will find him—
self competent to do anything in the realm of pure cre-
ation depends largely upon the abilities with which he
has been born but in the realms Of appreciation and in-
terpretation, he can make his life immeasurably more ef-
fective if he has the necessary energy, initiative and
vision to rouse himself from aimlessness and do his OWn
thinking.
Photography becomes really significant only to
those who go on to utilize it for some purpose that will
add to their inner satisfaction and Who expend thought
upon their enterprises to raise them above the level of
I.


PHOTOGRAPHY AND CREATIVE EXPRESSION 213
the commonplace. Whether that purpose lies in landscape
photography, in portraiture, in Spectroscopy, photomi-
crography, or any number of other directions makes lit-
tle difference . It is immaterial. Whether it, bec Omes a
serious vocation or merely an avocation. The only thing
that is of importance if photography is to play any real
part in a person's development is that he bring to bear
upon its utilization all of the energy, thought and abil-
ity that he can.
- It has been said that photography is at the same
time a craft , a science and an art. That it is both a
craft, and a Science is undebatable but the claim that
photography is an art has aroused much discussion of a
highly controversial nature. Possessing as it does so
many purely utilitarian applications in the realm of
record making, it is not surprising that there are many
who question its right to be considered an art. More-
over , the fact that many of its applications demand noth—
ing except simple routine acts in the realm of exposure
and development causes many to regard it as a mere tech-
nique. It should be noted that the Word, demand, was
used advisedly in the last sentence as there is good
reason to believe that the most "practical" application
of photography may utilize, although it does not require,
originality and present problems that are a stimulating
challenge to the competent person that may easily carry
him over into the realm of creative enterprise .
Before we can suggest an answer to the question
Whether photography is an art, however, it will be well
to attempt to define this peculiarly elusive term. The
Word is derived from the Latin, ars, whose root, ar,
means to fit or put together. Very early the World was
thought of as consisting of two parts, art and nature ,
the first comprising all in which man acted as interme-
diary and the Second all that occurred quite independent–
ly of him. Here, we find in art the conception of man
as one who fashions or interprets. Later, the idea of
skill entered more definitely as is evidenced by such
terms as the arts of peace or of War. Finally the term
was limited in the fine arts to painting, sculpture,
architecture, music and poetry. Here, it should be
noted, the emphasis is put upon aesthetic appeal rather

2 || || FIRST COLLEGE COURSE IN PHOTOGRAPHY
than upon any utilitarian aspect . Even architecture 3.S
an art, put the emphasis upon Such things as balance,
symmetry and design rather than usefulness.
Thus, we see that the term has gradually become
more limited in its applications and more definite in
meaning. We may say, then, that man is always the inter-
mediary through whom art finds expression and tha & he is
seeking to make an interpretation. The value of this in-
terpretation is determined largely by the truth and uni-
versality of his concept and by his skill and originality
in its execution. But, curiously enough, when we get to
this point we discover that there is nothing in the above
statements that does not apply to creative science as
well as to art. Man surely is the intermediary when he
investigates such things as alternating currents; he
seeks to make an interpretation that frequently has no
utilitarian purpose. Certainly the investigations of
Clerk Maxwell in this field denote ability so superla-
tive as to indicate genius of the highest order, yet
this is not art, .
At first glance, the distinction between science
and art seems too obvious to require discussion, but a
closer examination indicates that they have much in com-
mon, so much that those with exceptional ability in art
or in science seem to dwell rather close to the boundary
between the two fields and to be able to pass at will
from one to the other. To such as these , the creative
urge that drives them represents more similarities than
differences.
Certainly, both seek truth. To the scientist,
beauty is incidental although anyone who has seen the
exquisite colors produced by the interference of plane
polarized light will probably be Willing to concede that
art has none to match them. Frequently, the utilitarian
urge is only incidental or Wholly absent in scientific
investigation as in art. Faraday, for instance, had no
idea that his inquiry into the effects of moving wires
in magnetic fields would lead to the motor and the
dynamo.
There is , however, a fundamental distinction in
the aspects of the subject chosen for investigation and
l. Today, there is a growing realization that architecture cannot
divorce itself from the usefulness of its creations without
losing much of its essential significance.

PHOTOGRAPHY AND CREATIVE EXPRESSION 215
ºrº
º::..
ka
treatment given them by an artist or a scientist that
leaves one in no doubt whatever regarding which has par-
ticipated in the result. There is no difficulty in dis-
tinguishing the work of a sculptor from that of a psy-
chologist as an interpretation of man. The graphical
record of the electrocardiograph has little in common
with the Sistine Madonna. In general, however, while
Some art concerns itself with nature apart from man,
far more deals with his joys, sorrows, accomplishments
and potentialities. The main emphasis in science, on
the other hand, is more frequently on nature.
The next fundamental distinction is in e.ttitude
of mind. In Science, emotions must not be allowed to
affect the result. In art, they occupy a transcendent
place. Thus, the scientist rules out his emotions as
completely as possible in drawing his conclusions. He
seeks to make his observations and their interpretations
as detached and objective as possible and disciplines
himself into keeping his emotional reactions so complete-
ly subordinated that they are eliminated from the result.
The artist, on the other hand, regards his emotions as
an important part of his stock in trade, so much so that
it is perhaps a fair statement to say that in the sci-
entist we have the output of mind dominant over the emo-
tions while in the artist we have mind dominated by them.
Possibly this is the reason that a peculiar basic
antagonism often exists between artists and scientists
causing the former to regard science as a drab, unimag-
inative form of task Work that has much in common With
hewing wood or drawing water. The latter, in his turn,
retaliates by accusing the artist of attaching altogether
too much importance to the precise way in which things
impress him and of sometimes reacting so violently emo-
tionally to things of little moment that it seems ra–
ther like much ado about nothing. Perhaps the artist
is sometimes tempted to justify in himself as evidence
of artistic temperament actions that a less sympathetic
observer would classify as temper tantrums. But, to
offset this, the scientist may easily be tempted to
overdo this matter of being objective and realistic to
such an extent that he may seem to others to be so

2 ||6 . FIRST COLLEGE COURSE IN PHOTOGRAPHY
engrossed in keeping his feet firmly planted on the
ground that he never looks overhead.
Actually, there is a very large measure of imag-
ination in anything that is either first rate science or
first rate art and one who fails to perceive its pres–
ence in the former Would be Well advised to ask himself
Whether the lack does not lie rather in his own powers
of perception rather than in science itself. And, an–
other who feels that art is too far removed from prac-
tical affairs to be of interest is equally well advised
to question a little his own powers of perception.
Another way in which the artist differs from the
scientist is in his attitude toward nature. To the sci-
entist, nature is orderly although she often conceals
her plans and laws so Well that even the initiated must
work long and patiently before making even a beginning
at understanding her mysteries. Moreover, one who
would discover her secrets must discipline himself until
he can rise superior to his own pre conceived ideas and
prejudices and draw his conclusions with complete de-
tachment. To the artist , nature is often fundamentally
erratic and disorderly and it is his function to select
and rearrange the material with which she presents him
as he sees fit. A very extreme example of this attitude
of mind was exemplified in a painting that appeared some
time ago in which the artist had not only depicted the
sun as shining from two different directions but also
vigorously defended his right to make the sun shine as
he pleased in order to express the idea that he had in
mind. Probably few artists would take a position as ex-
treme as this but, there can be little doubt, that Scien—
tists who make use of photography would be more inclined
to like it "straight" with a minimum of handwork, while
artists would be less hesitant about modifying the print
by after-treatment.
Wether or not one regards photography as an art
depends upon what it means to him. Certainly many of
its applications are not because they frankly aspire to
nothing more than to offer an accurate description of
the subject. The photographer makes these without the
slightest intention of attempting to do anything else.



PHOTOGRAPHY AND CREATIVE EXPRESSION 2||7
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But when he does strive to use photography for interpre-
tative pictorial purposes, it seems to indicate an undue
prejudice to dismiss the camera as an instrument, so me —
chanical and unresponsive to control that its results
are always mere records. In portraiture, in particular,
the camera is able to capture the momentary, passing ex-
pression in a way that is unsurpassed. Moreover, the
extent to which this capture may enter the realm of art
may be said to be limited only by the artistry in the
photographer. Similarly, with the other forms of pic–
torial photography, the Significant element is the per-
son who is using it rather than the instrument.
Actually, however, it would seem to make little
difference whether or not photography is granted a place
among the arts. Rather, it may be better to regard it
as a unique means of creative expression and to seek to
develop it in those directions in which it has no peer
Without either apology or argument. Certainly, no form
of graphic representation attains its own highest devel-
opment by producing results that seek to look like some–
thing else. The unitiated have no idea, how they make us
Writhe in Spirit when they tell us that our photographs
look like etchings or charcoal drawings. Rather, it
seems essential that photographers should retain the in-
dependence of outlook that will enable them to make the
most of those aspects in Which their medium is Supreme ,
rendering fine detail, its long scale of gradation, and
the capture of the fleeting moment. Whether those devo-
tees who venture into the realm of pictorial photography
achieve creditable results by a careful selection and
arrangement of their subject matter, which may be art,
or by patient Watchfulness and ability to act promptly
when nature produces the combination they seek, which
may be science, makes little difference. The results
may be superlative in either case but not too frequently
as the highest excellence here as elsewhere is not some-
thing that can be made to order or drawn on demand.
But, if one does wish to venture into the realm
of pictorial photography, he does well to familiarize
himself with the basic principles of composition that
have been derived from the study of the work of those
who have excelled in the different graphic arts. In

2 ||8 FIRST COLLEGE COURSE IN PHOTOGRAPHY
any supreme creative act is a very large measure of in-
tuition and the formulation of the rules that apply to
it follow rather than precede. As Sidney Lanier has
aptly put it,

"The poet, mad with heavenly fires
Flings men his song white hot, then back retires,
Cools heart, broods o'er the song again, inquires,
Why did I this, why that? and slowly draws
From Art's unconscious act Art's conscious laws." "
Nevertheless, just as one finds it advisable to learn
the accepted rules and forms of literary expression in
order to make his own writing effective, is he likely to
find it equally advisable to learn the accepted rules of
pictorial expression. While the latter are not nearly
as definite as the former and are frequently broken, vio-
lations that occur through ignorance produce a wholly
different impression from violations by design.
Since the lens depicts everything before it that
falls within its angle of view, the photographer must
resort to methods that are peculiarly his own to gain
the unity required if his work is to lay claim to artis-
tic merit, . While the artist. With his Sketch book can
sit comfortably on a hillside, include what he will of
the landscape before him, change relative positions if
it suits him, reject the irrelevant, the photographer
must resort, to other devices. The latter cannot induce
his lens to ignore the existence of those unwanted tele-
phone poles but he can do much to improve matters by a
careful selection of his point of view. Or, again, he
may use a lens of large aperture wide Open and so reduce
the depth of field that some of the irrelevant elements
sink into obscurity by being thrown out of focus. By
exercise of thought and by practice in these directions
it is surprising how much can be done that is not in the
least apparent to one who thinks that all One can do is
get directly in front of something and snap the shutter.
Last, by making an intermediate paper negative,
the photographer gains much of the artist's opportunity
2. Quoted by Henry Turner Bailey in the preface of his book, Photo-
graphy and Fine Art. This book is recommended as a sympathetic
and helpful interpretation of the role of the photographer by one
whose interests are primarily in art. |
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PHOTOGRAPHY AND CREATIVE EXPRESSION 21:9
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to eliminate or express as he chooses. Of course, one
With the necessary skill as a retoucher can do a great
deal With a retouching pencil and an etching knife on
the original negative. The difficulty here is that suf-
ficient skill to do this in any but the most rudimentary
Way can be acquired and retained only by constant daily
practice, making it available only to professionals. In
general, it demands much less dexterity to fill in a tone
that is too light. With a pencil than to remove portions
that are too dark With a knife. It is also much easier
to work on paper than on film and on full size negatives
rather than Smaller ones that are to be enlarged.
All of these facts have probably had much to do
with the development of the paper negative technique.
The process consists in first making a rather dense pos-
itive from the original negative. This may be either by
contact or projection and may be on paper or on film.
After any light spots that require darkening have been
attended to , a paper negative is made from the positive.
Work With a pencil or charcoal stump is done on this to
any extent desired from the slight softening of excessive
contrasts to the complete obliteration of parts that are
not desired. A final print is then made by contact.
While many examples of this process exhibit a
slightly mottled effect due to paper texture and some
loss of detail, it is by no means necessary that this
should be marked. True photographic quality can be re-
tained by making the intermediate positive on film ra—
ther than on paper. Next, on making the paper negative
from this, paper texture can be practically obliterated
without serious loss of sharpness by printing the nega-
tive by projection and placing the paper face down so
that the light must traverse the paper before it reaches
the emulsion. Papers are not uniformly translucent. An
inspection of almost any paper by transmitted light Will
reveal differences in opacity due to the methods used in
converting the paper pulp into a continuous sheet. In
spots where the paper is more translucent, more light
reaches the emulsion and makes a darker image While in
spots where the paper is denser, the same amount of
light produces a lighter image. As a result, the nega-
tive will appear badly mottled by reflected light after
development but will make a print by transmitted light
that is surprisingly free from paper texture. The hand

250 FIRST COLLEGE COURSE IN PHOTOGRAPHY
work on such a negative may be as much or as little as
one desires but it is probably well to place rather
strict restraints upon oneself or the result may lose
all photographic quality. In addition to what it tells
us regarding the repression and elimination of unwanted
elements, composition also offers a variety of more
positive suggestions regarding what should be included.
It may be stated at the outset that there must be an
idea that one wishes to express and this should be pon-
dered over and clarified in every possible way. While
it does occasionally happen that someone gets a remark–
able picture by a species of lucky accident, the chance
of doing so is vanishingly small and becomes smaller as
one learns enough to aspire to reach the standards of
really discriminating critics. Almost inevitably some-
thing Will be in the wrong place in the best of them and
the rest will surely confirm the conclusion that all of
us do better with any form of expression if our efforts
are not wholly extemporaneous. -
As examples of this the author recalls two pic-
tures depicting a man on a park bench. The first showed
a tramp asleep and, quite evidently, Snoring. There
were several irrelevant elements and the photograph sig–
nified nothing except that the photographer had caught
the tramp unawares and had thoughtlessly snapped the
picture in passing. The other had evidently been care-
fully planned. It showed an elderly man seated on a
bench, hands clasped on his cane, head bowed, Straggling
white hair, and shabby genteel clothing. Even a few
dried leaves on the sidewalk contributed to make the
whole an epitome of poverty-stricken old age. Whether
one was particularly interested in the conception or
not, he could not but sense that the picture represented
sympathetic comprehension of the subject and some care-
ful planning while the making of the first photograph
was a Wholly thoughtless act.
Next, while one idea is essential, unity demands
that a picture shall not have more than one. Any attempt
to intermingle two or more ideas in the same photograph
is likely to be as confusing as the attempt to listen to
two different conversations at the same time. Moreover,
even when this unity exists in the sense that there is a
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PHOTOGRAPHY AND CREATIVE EXPRESSION 25l.
Single idea and nothing irrelevant is included, there is
still much to be done to enhance this unity and make it
more satisfying aesthetically. A pile of building ma—
terials heaped upon the ground has unity of a sort but
this unity becomes much more apparent and interesting
When the materials are a SS embled int. O SOme Structure.
In the same way the elements of a picture give us a
greatly enhanced sense of unity and harmony if they are
grouped according to Some definite plan.
Artists frequently make use of one of the follow-
ing simple geometrical forms for this purpose, the tri-
angle, the circle, the cross, radial lines and the rect-
angle or L. On Plate XXVII are tracings from famous
paintings that have their principal elements grouped ac-
cording to one of these five forms.” It will be realized
that the photographer does not have the same opportunity
as the artist to compose his picture as he will. In
fact, neither invariably follows these forms but, at
least it may be said that they yield a peculiarly satis-
factory form of composition whenever it is practicable
to apply them. It Will be found instructive and inter-
esting to hunt through a collection of reproductions of
paintings or of photographs for other examples for if
One does not make himself thoroughly familiar with them
by the study of many pieces of work in which they ap-
pear, it is not likely that he would recognize an oppor—
tunity to apply them to his own work.
Another very important element in producing unity
and harmony in a picture is balance. Generally speaking,
a mass off to One Side of a picture needs to be balanced
by a mass on the other. Such balance, however, would
grow very artificial and monotonous if the balancing
masses did not possess definite visible differences, the
most obvious of which is size. All are familiar with
the fact that a relatively small Weight on the long arm
of a balance can be in equilibrium with a large weight
on the short arm. Frequently, careful study of a pic-
ture Will reveal the existence of a point in the picture
that may be regarded as a fulcrum about which the vari-
ous elements balance, a mass on the left against one on
2. Color prints of all of these may be found in Thomas Craven's
A Treasury of Art Masterpieces, Simon and Schuster, (1939).


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PHOTOGRAPHY AND CREATIVE EXPRESSION 253
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the right, one in the foreground against one in the dis–
tance, a cloud mass in the sky against Something on the
ground.
It will be realized that a certain subtlety must
enter into the application of these geometrical concepts
in composition. They must not be too obvious for the
state of mind into which geometrical propositions put
most people is not primarily aesthetic. A Suspension
bridge must be properly designed if it is to be an Ob-
ject of beauty but the stresses and strains of its
structural members are no part of the aesthetic appeal.
In any great art we find that our aesthetic re-
sponse is partly based upon what the Work depicts and
partly upon an overplus that it suggests only so that it
carries us in imagination far beyond the literal actual-
ity. It may be said without fear of contradiction that
great art must make this kind of imaginative appeal and
that it is part of the aesthetic response to see far
more than is portrayed. In fact, we demand of artistic
expression that it shall not be too obvious or We lose
interest in it. Composition that leads us into the
picture and then by a simple and logical route past the
main points of interest and finally off into the dis–
tance where we may let our fancy roam to suit ourselves
is likely to be very satisfying.
Curved lines are more interesting than straight
ones because it is so obvious where the latter are go-
ing. A square picture area makes less appeal than a
rectangle because its shape is both obvious and monoto-
nous. A horizon line or a main object that divides a
picture into two equal parts also lacks variety. The
so-called "line of beauty" which has the form of an
elongated letter, S, offers much of interest because
its shape can be altered almost without limit so it has
the imaginative appeal of the unpredictable and often
serves to lead the observer through the picture past
the principal objects of interest and on beyond.
Proportion is also important. A rectangular
picture area with a marked difference in the length
and width is more satisfactory than one that approaches
a square. Oval and circular pictures are generally to






25|| FIRST COLLEGE COURSE IN PHOTOGRAPHY
be avoided because their uniqueness gives such boundaries
an amount of attention that they do not deserve.
The study of what ratios constitute the most per-
fect proportion probably originated with the Greeks.
Certainly the division of a line in extreme and mean
ratio is to be found in Euclid. By this is meant the
division of a line into two parts such that the longer
Segment is a mean proportional between the whole line
and the shorter segment. Such a proportion is represent-
ed quite closely by the integers, 15, 8 and 5.
l3 : 8 = 8 : 5 -
A line lº units long can be divided into two parts of 8
and 5 units respectively. That the proportion is not
quite accurate can be shown by taking the product of the
means and the extremes which gives us the following.
6|| = 65
Artists have occasionally used this ratio, 8 : 5 both
for the dimensions of the picture rectangle and to di-
vide lines that fell within it as the ideal proportion.
This discussion suggests some of the rules that
artists ordinarily follow and the photographer does well
to know them and adapt them to his own purposes when he
can. In any field it is only the part of Wisdom to
profit by the accumulated experience of all who have un-
dertaken to do the same thing, or something similar, be-
fore. Actually, the rules may be regarded as clumsy half
truths that serve merely as guideposts to help the un-
initiated to gain some slight conception of what he
seeks. Once this has been accomplished, the way to learn
more is not by further study of anybody's exposition and
elaboration of the rules but , rather, by a thoughtful and
penetrating study of pictures themselves. Just as one
improves his own literary style by habitually reading
things that are well Written, can he improve as a pic–
torialist, by frequent study of great pictures. Such
study cannot be other than profitable because of what it
contributes to his knowledge and comprehension of pic-
tures .
Whether it can lead to adequate creative ex-
pression depends first , last and always upon whether he
has anything to say. All that the individual can do
about that is to keep his mind Working and to seek to
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PHOTOGRAPHY AND CREATIVE EXPRESSION 255
penetrate as far as possible into the meaning of things.
Next, with all the honesty and sincerity that he may, he
must try to express this meaning. Often that is much
more difficult than it sounds for all of us more or less
consciously travel with the herd. Not only do we tend
to become imitator's On that a.C. Count but also because
there is a strong temptation to repeat those effects
that have already been proved interesting to others. As
long as one is Willing to be an imitator, his work will
fall far short of genuine creation. Certainly there is
no harm in this if he frankly recognizes what he is do—
ing and makes no effort to pose as What he is not. But,
if, on the other hand, he wishes to make his medium do
something that is really original, he is still on the
horns of a dilemma. He must decide whether he will be
guided by the effort to please himself or to please oth—
ers . The latter is to be recommended if he wishes to be
paid for what he does. But the greatest inspiration and
development will come only if he follows strictly the
dictates of his own mind and heart wherever they may
lead quite unmoved by whether he manages to gain popular
acclaim or not. Probably the World will never particu-
larly concern itself with what he does but it is also
well within the realm of possibility that he might wake
up some day and find himself famous. But, even though
his name is never known by any except his personal ac-
quaintances, his reward Will come from the realization
that he has made no compromise With the truth as he saw
it. He will, however, rarely be satisfied with what he
has been able to do. In the creative act, the result of
having achieved what he has will cause his vision to
sweep on to greater heights. Thus, he sees more clearly
what he might have done and then there is tomorrow to
try again. But, if there is no rest to be found nor the
satisfaction of creating something that is as good as
the vision that prompted it, with Rabbi Ben Ezra let
him Say,
"All I had hoped to be and was not, comforts me."


256 FIRST COLLEGE COURSE IN PHOTOGRAPHY º
(U.
QUESTIONS
l. Discuss the uses and abuses of candid photography. - I
2. State your conception of the functions of a teacher [º
in college classes.
3. State your conception of the function of a student [º.
in Such Cla.S SeS
!. Do people with good minds usually have good memories? Tº
5. Show ways in which photography partakes of the na– ... - ---
ture of a science, a craft or an art. §:
6. Contrast the role of the emotions in science and in -
art. - re-
7. Discuss the quotation given in this chapter from - m
Sidney Lanier. - ~!
8. What are the five basic geometrical forms used in ram
composition? Find pictures that are examples of i.
each. ºr ,
9. A line lj inches long is to be divided into 2 parts
Such that the longer one shall be a mean proportion-
al between the whole line and the shorter segment. .
i.
Solve algebraically and determine the result to two Eº.
decimal places. What is the significance of the -
negative root ? # ,
lO. In your judgment, what qualifications does one need
to possess in order to qualify for creative Work? - r
ll. Do you consider that genius is "an infinite capacity "I
for taking pains"? Explain. - *
12. Is one more likely to develop while doing large |
amounts of Work at half pressure or half as much at
full pressure?
13. It is sometimes stated that the composition of a
picture together with its faults or virtues becomes
more apparent if we invert it. Is there any logic
to this 2 Explain.
l!. Explain carefully why printing a paper negative with
the emulsion away from the projector light minimizes
paper grain.
15. Has anyone ever received the Nobel prize for work
that would not have been possible. Without photogra-
phy? -
16. Mention several persons who have become famous for


PHOTOGRAPHY AND CREATIVE EXPRESSION 257
17.
l8.
l9.
20.
2l.
22.
23.
24.
applications of photography to science and describe
the general character of the work of each.
Is photography an art? If so, mention the work of
several photographers that substantiate your claim.
Write out your own conception of the distinction be-
tween science and art. -
Explain what is meant by "mistaking the will-o'-the-
wisp of eccentricity for the miracle working impulse
of genius."
Why is it likely to be objectionable to have a fence
extend directly across a picture in the foreground?
Why should we avoid placing a rapidly moving figure
close to the edge toward which he is moving of the
picture area.?
Discuss balance. Find a picture to illustrate What
you Say . .
Suggest reasons why the square does not have the
standing of the circle as one of the primary geo-
metrical forms of composition.
Analyse the pictures in some volume of reproductions
of famous paintings such as Thomas Craven's Treasury
of Art Masterpieces and list those whose composition
is based upon the circle, triangle, cross, radial
lines or L. Which do you find most frequently?

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LABORATORY MANUAL
Suggestions regarding laboratory work.
l. Work quietly. Few people are able to work with con-
centration while maintaining a steady flow of conversa-
tion on miscellaneous Subjects and anyone who can is a
nuisance in a group Such as this.
2. Mount an envelope on the back flyleaf of the text
and keep negatives in it.
35. Bring all finished material including negatives to
every laboratory period.
lº. Plan your work carefully to make every minute count.
The experiments must necessarily be performed a portion
at a time and considerable planning is necessary to get
them finished promptly.
5. As a rule, it will be found advisable to spend about
half the laboratory period making prints of the negative
of the previous week and the other half on a new nega-
tive. -
6. Finished work should be mounted in the text in the
spaces provided. If you are not satisfied with the re-
sult, mount it temporarily with gummed paper corners
and replace the print with a better one by repeating
the experiment when opportunity offers.
7. Make the negatives the proper size so that the
prints will look well in the spaces provided for them.
8. One really excellent piece of work will contribute
more to your ultimate salvation as a photographer than
a dozen poor ones.
259


260
LABORATORY MANUAL 2
Experiment I
M : X | N G PHOTOGRAPH | C SOLUT | ONS
Most photographic solutions will keep
for months in well-stoppered bottles that are
completely filled to exclude air. It will
therefore be convenient to make up a supply
of developer for paper, developer for film
and acid fixing bath sufficient for the semes-
ter. Each student should therefore mix these
Solutions according to Formulas l, 2, and 5
in the Formulary making up the amount indicat-
ed there in each case.
This acid fixing bath keeps well and
may be used over until it shows signs of dis-
coloration or a sludge in the bottom of the
bottle. Potassium alum is much more soluble
in hot water than in cold and much time may
be saved by dissolving this separately in a
Small amount of very hot water and pouring it
Slowly into the cold solution containing the
other constituents after those are completely
dissolved. A quantity of acid hardener will
have been made up in advance so students need
only prepare the water solution of hypo and
bring it to the assistant who will convert it
into an acid fixing bath by adding one part
of hardener made up according to Formula l;
for every eight parts of hypo solution.
After checking, the chemicals should
be dissolved in the order indicated in the
formula allowing each to dissolve completely
before adding the next.
The following rules regarding the use
of balances should always be followed. Ordi-
nary platform balances are sufficiently sensi-
tive for photographic purposes.
l. Be sure that the balance swings
freely and adjust the nut if equilibrium is
not satisfactory.
2. Never place chemicals directly on
the pans. Place papers of equal weight on
each and Weight materials on these.
5. Chemicals must be placed on the
left pan and weights on the right since the
rider on the beam represents additional weight
that is added to the weight on the right.
4. Balance is always determined while
the pans are swinging freely. .
5. Always be sure that the balance is
clean and the set of weights complete before
putting them away.
AS Soon as each solution is mixed it
should be brought to the assistant who will
Store it for future use .
Topics for Discussion
l. What would be the result of adding the car-
bonate before the sulphite in mixing de-
veloper?
2. What chemical or physical tests might be
used to distinguish the developer and the
fixing bath if one poured these into iden—
tical trays and forgot which was which?
5. Why do we use a distinctive tray, e.g.,
black rubber, for the acid fixing bath?
4. What would be the actual weight of the de-
veloper if we placed it by mistake on the
right-hand pan and found that it balanced
a lo-gram weight on the left pan and 2
grams on the beam?
5. What would happen if a liter of developer
Were poured by mistake into a liter of
acid-fixing bath?
Experiment 2
THE PR INT | N G CHARACTER | ST | CS OF
CONTACT PAPERS
A negative consisting of a series of
graduated grays will be supplied for each
printing box. These were made by giving the
Successive portions of the film a series of
exposures in geometrical progression such
that each exposure is equal to the preceding
one multiplied by V2. By adjusting the in-
tensity of the light, it is possible to make
the minimum exposure produce the faintest dis-
tinguishable gray and the successive exposures
will produce a series of increasing densities.
The advantage of having these in geometrical
progression lies in the fact that any series
of adjacent tones represents the same rela-
tive exposures as any other similar series
located elsewhere on the strip.
Procedure. Contact printing papers
representing the four most commonly used con-
trasts, ll (soft), 22 (normal), 35 (medium
hard), and 44 (hard) will be supplied. Con-
tinue to make prints with each grade until
one is obtained that prints the darkest tone
on the negative as the faintest distinguish–
able gray altering the printing time as seems
desirable. Develop for the exact amount of
time advised by the manufacturer of the paper
that is being used, rinse in water and fix in
an acid fixing bath for at least ten minutes.
Record the grade of paper and the printing
time on the back of each print.
Be sure that the glass in the print-
ing box is clean as spots on it are likely to
appear in the print. Developer for paper
which was made last time will be found on the
desk shelves. Dilute according to the direc-
tions on the bottle and provide three trays
in the following order, developer, water, fix-
ing bath. The fixing bath is used full
strength and is returned to the stock bottle
after using. The developer should be thrown
away.
Ordinarily, trial exposures are made
on pieces of paper so small that they cover
Only part of the negative to save material.
In this case, however, the negatives are so
Small that pieces the full size of the nega-
tive may be used. Negatives should be placed
on the glass of the printer dull or emulsion
Side up and the paper in contact. With it emul-
Sion side down. It is usually possible to de-
termine the sensitized side of the paper by
the sense of touch. If uncertain, it should

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T- 22 33 44
EXPOSURE TO PRODUCE
APER TIME (SE
22
33
44
SENSITOMETRIC STRIPS


262 LABORATORY
MANUAL l;
be remembered that the sensitive Side is
Slightly concave. .
After printing, develop for the exact
amount of time recommended by the manufactur-
er for the paper that is being used. While
experienced photographers vary the developing
time to some extent, it is inadvisable to do
this until the standard process has been thor-
oughly mastered and it will be much easier to
interpret the observed results in this experi-
ment if nothing is varied except the grade of
paper and the exposure time.
Prints and negatives should be left
in the washing tank and the assistant will
dry them after they have been washed for at
least an hour in running Water.
Prints will Stick fast if allowed to
dry face down on paper and should never be
spread out face up on newspapers as such pa–
per is likely to contain hypo which will be
absorbed by the wet prints. The curl may be
taken out of prints after drying by moisten-
ing the backs slightly and placing them in
magazines or between blotters of photographic
quality under moderate pressure.
Prints should be examined for the foll-
lowing defects and their causes should be
memorized.
l. Yellow brown stains. Too long development or old
developer.
2. Grayish whites. Over-exposure, too little
potassium bromide in develop-
er, too soft paper.
Greenish blacks. Old developer.
tassium bromide.
Too much po-
lº. Yellow stains or fad-
ing after the lapse
of months.
Insufficient washing.
Imperfect contact between
negative and print during
printing. In printers in
which the light comes on
automatically when the frame
is closed, it may come on too
soon. Negative wrong side up.
5. Unsharp prints.
Discussion of results. Be prepared
to discuss the following in class.
l. Compare the printing times necessary to
print the darkest gray on the negative so
that it gives the faintest distinguish-
able tone.
2. Compare the minimum printing times that
yield the deepest black on each paper
through the lightest gray on the negative.
Why should the minimum times be taken?
3. Do all the papers used yield equally black
maximum tones 7
Compare the numbers of distinguishable
tones obtained with the different papers.
Compare the best prints obtained with
each paper with the negative and deter-
mine which reproduce its scale most accu-
rately, which compress it and Which
5
Stretch it.
Does it seem paradoxical that hard papers
stretch the tone scale of the negative, yet
print a Smaller number of tones than softer
papers? Explain.
7. Under What conditions will the print yield
less tones than are on the negative 2
Can the print ever produce more ?
9. When do we use hard, normal or soft papers?
Select the print from each group that shows
best the characteristics of that paper and
mount the set on the following sheet.
6
Trimming end Mounting
Careful trimming and mounting add much
to the appearance of photographic prints.
Trimming boards are very convenient but should
be tested to make sure that the blade makes a
cut that is strictly at right angles to the
Scale on the board. Good boards provide means
for putting them into accurate adjustment if
this is not the case. For making a very nar-
row cut on a print or for working very accu-
rately to dimension, a Gem razor blade or a
Sharp Scalpel and a drawing triangle is to be
preferred. A sheet of zinc is excellent to
cut against as it will not dull the steel
blade. -
For mounting in cases where all possi-
ble strength and permanence are not required,
rubber cement is the most convenient mountant.
As it contains no Water, it shows no tendency
to make the paper stretch or buckle, it does
not dry out prematurely before the print is
in position and can be easily rubbed off the .
mount after the solvent has evaporated if it
appears where it is not wanted. Moreover,
its elastic nature enables it to show no ten-
dency to cause the mounts to warp with chang-
ing atmospheric conditions.
Dry mounting tissues are also avail—
able that consist of non-tacky sheets that
can be cut to the exact size of the prints.
After the print has been placed in position
on the mount, heat is applied by means of a
flatiron or regular mounting press. This
causes the tissue to melt and form a bond be-
tween the print and the mount when it cools.
Flattening the mounted prints by plac-
ing them under pressure for a few hours is
essential. In general, mounting should be -
kept simple as the purpose of the mount is to
emphasize the print by setting it off from
irrelevant surroundings and mounting that
tends to become unnecessarily elaborate de-
feats this purpose by drawing attention away
from the main object which is tho print.
Experiment 3
COPY OF A L | NE DRAW ING, EXACT S I ZE
A line drawing is easily focused and
is best done with process film, a clean-work-
ing, high contrast, slow film that permits
development by a relatively bright red light

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26||
LABORATORY
MANUAL 6
such as a Wratten, Series l.
Procedure. The drawing should be fas-
tened in the back of a light box having elec-
tric lights mounted in its interior so that
they illuminate the subject evently but do
not throw light directly on the lens. Focus
carefully and then measure corresponding
parts of image and object with a ruler or di-
viders. Probably several trials will be nec–
essary before the image and object are exact-
ly the same size.
A camera lens cannot form a real im—
age on the ground glass when the distance
from the object to the film is less than four
times the focal length of the lens which is
about 5l inches with our laboratory cameras.
The following table of the order of
Operations in taking a picture may be useful
until more experience has been gained with
the laboratory cameras.
(l) Set the shutter at T and open it.
(2) Focus with diaphragm wide open.
(3) Close shutter. This is very im–
portant. If step (li) is carried out without
step (3), the shutter may be damaged.
(4) Set shutter and diaphragm for ex-
posure required. -
(5) Insert plate holder.
(6) Withdraw dark slide.
(7) Expose.
(8) Insert slide. Push straight in.
If inserted cornerwise, light may be admitted
and part of the film fogged.
The exposure time is best determined
with a Weston meter. Ask for a reading when
ready. Note that the meter is held suffi-
ciently near to the subject to measure the
light reflected by the card alone yet not so
close that it cuts off the incident light.
A card carrying the name of the student mak-
ing the negative in letters about three-
eighths of an inch high should be placed in
the field of view close to the margin of the
picture area so that it will appear on the
negative for purposes of identification and
can be trimmed off the print.
Prepare trays of developer for film,
water and acid fixing bath and develop the
negative for 7 minutes under a Wratten Series
l safelight. Fixing should be continued for
about 5 minutes longer than is required to
remove all the yellow silver bromide from the
negative and if this requires more than lo
minutes, it would indicate an exhausted fix–
ing bath which would make it advisable to se–
cure a fresh fixing bath and place the nega-
tive in that for an additional five minutes.
The fixing bath should be returned to the
Shelf bottle and the developer discarded.
After removing the negative from the
fixing bath, suspend it by a cut film hanger
and place it in the washing tank for an hour.
The negative must then be dried in a place
free from dust and where neither side will
come in contact with anything while drying.
After the film is dry, the best print
possible should be made on paper selected in
the light of the experience gained in Experi-
ment l.
Topics for Discussion
l. Is the negative sharply focused in every
part 7
2. Has the print a clean white background and
clear black lines 2
5. Is it exactly the size of the original?
4. What might cause a negative such as this
to be unsharp at the edges?
5. What might cause the background to appear
gray rather than white in the print 7
Cautions: (1) Be sure that the nega-
tive is completely immersed in the developer
immediately or streaks may result.
(2) Always handle by edges.
(5) Do not remove from the developer
to inspect the progress of development by
holding it up to the dark room light. Little
can be seen and unnecessary handling may pro-
duce Scratches in the wet gelatine.
(#) Remember the gelatine on wet films
is very soft. The corner of one film may eas-
ily scratch another so care must be exercised
in placing them in the Washing tank that they
do not get scratched or damage those already
there .
Experiment l;
CONJUGATE FOC |
In general, if the object and the im-
age planes are at a fixed distance from each
other, there are two distinct points at which
the lens may be placed to form a sharp image.
These are known as the conjugate focal points.
As the object and image planes are moved
closer and closer together, these conjugate,
focal points also move toward each other until
they merge when the distance from the object
to the image is that required for exact size
copying. Usually the photographer concerns
himself with only one focal point, as both
are not usually found within the length of
the bellows.
Procedure. We may arrange to have
both images fall within the bellows length as
follows. Extend the camera bellows to the
limit which will place the lens as far from
the focal plane as it is possible to get it
with that particular camera. Direct the lens
toward a picture mounted in the light box and
without disturbing the lens move the camera
toward the light box until the image of the
drawing, or a part of it, is sharply focused
on the lower half of the ground glass. A
carboard shield should be placed in the slots
provided just inside the ground glass to cover
the upper half of the film. Make an exposure
on the lower half of the film according to
the Weston meter reading.
Next, use the rising front to transfer
*A subject with well-defined detail is most suitable here.
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266 LABORATORY
MANUAL 8
the
the
the
image of the card to the upper half of
film, and shift the cardboard to cover
lower half of the film. Without moving
the camera, move the lens toward the film un-
til the other sharp image is found. Photo-
graph on the upper half of the film using the
same exposure as before. After development
cut the negatives apart and print separately.
Save the negatives for the experiments on in-
tensification and reduction.
As it is somewhat difficult to judge
the sharpness of the larger image accurately,
it is a good plan to use a small magnifying
glass for focusing. Ordinarily, copying is
done with the lens stepped down considerably
to minimize slight errors in focusing by in-
creasing the depth of focus. Here, however,
use the lens at its largest effective aper-
ture as part of the purpose of the experiment
is to gain practice in accurate focusing. If
it is not possible to include the entire sub-
ject in the views care should be exercised to
select portions that will provide good compo-
sition.
Topics for Discussion
l. Why is the one image larger than the other?
2. Why is the smaller image denser than the
larger image 7
5. Why should the two exposures be cut apart
before printing? -
4. What is meant by depth of focus?
| Film | Weston | Exposure stop ||
| | | T
Ferrotyping
Prints may be given a very high gloss
by printing them on glossy paper and rolling
them into close contact. With a highly pol-
ished ferrotype plate for drying. The proc-
ess is desirable when the prints are to be
used for reproduction on a printing press or
when the maximum range of tone is desired
and all possible detail. From an artistic
standpoint, the high gloss is usually consid-
ered objectionable unless the prints are to
be exhibited behind glass. Glossy prints are
impractical for albums as the rubbing of the
leaves dulls their surfaces. A few rules
for success in ferrotyping are given below .
l. Use single weight paper unless a
wringer is available as it is almost impos-
sible to roll double weight paper into suffi-
ciently close contact to make the surface
uniformly glossy.
2. Certain papers when wet are some-
what pulpy so that it is safer to roll the
roller over them with moderate pressure Sev-
eral times. Excessive pressure may actually
increase the area of the print.
3. Care must be exercised to keep the
ferrotype plates clean and free from
scrat Che S.
l!. If they are in good condition,
waxing is not likely to be necessary.
- 5. If prints stick to the plate it is
likely to be due to a dirty ferrotype plate,
insufficient hardening of the gelatine because
of an exhausted fixing bath, or too high a
temperature in the solutions.
6. Waxing the plates with a small
amount of paraffine dissolved in carbon tetra-
chloride and then wiping them off as complete-
ly as possible with a cloth prevents sticking.
7. Too rapid drying causes excessive
curling of the prints.
Experiment 5
DEPTH OF F | ELD
When we focus on a given plane, objects
from a certain distance in front of this
plane to a certain distance behind it are sat-
isfactorily sharp. This is known as depth of
field and is dependent upon the aperture of
the lens, its focal length, the distance from
the object in the sharpest focus, and the pur-
pose for which the negative is to be used.
Satisfactory sharpness to a process engraver,
for instance, demands much higher definition
than would be necessary in ordinary camera
work. Negatives that are to be greatly mag-
nified must be much sharper than those that
are to be used only for contact printing.
Procedure. Arrange a set of seven or
eight alphabet blocks diagonally across the
top of a table so that the letters painted in
the same colors face the camera. The Se Will
photograph best if the colors used for the
letters and the background are two that show
good contrast on the film. This will mean
that two should be selected such that the
film is sensitive to one and not to the other,
Red letters against a yellow background, for
instance, do not show up well on panchromatic
film as this film is sensitive to both colors.
Both therefore appear dark on the negative
and light on the print resulting in a lack of
contrast between the letters and the back-
ground. Blue letters against an orange back-
ground, on the other hand, produce good con-
trast on Orthochromatic film as this is very
sensitive to blue and insensitive to orange.
As a result the blue photographs as a light
tone on the print and the Orange, as a dark
tone.
An Orthochromatic film should be used.
As this film is much more sensitive to light
than the process film used in the last two ex-
periments, greater care must be exercised to
prevent it from being fogged by the darkroom
light during development. It is a good plan
to cover the developing tray with a cardboard,
removing it at intervals to observe the prog-
ress of development. In fact, most films are
developed today in tanks without any inspec-
tion but Watching the process will be found
instructive during these first experiments.
Insert a cardboard in the back of the
camera to permit exposing half the film at a
time. Focus first on the lower half of the
film. Select a camera position that gives a
º
º
º
º
º
!,
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DEPTH OF FIELD





268
LABORATORY MANUAL l O
pleasing perspective and arrange the blocks
and the camera until the nearest and farthest
blocks are definitely out of focus when the
lens is focused on the middle block and is
used at maximum aperture. Daylight lighting
may be sufficient but if it seems rather dull,
a single Photoflood may be used. Note the
Shadows cast by this light and place it so
that these add interest to the composition.
It Will also be instructive to observe the
effects obtained with the camera on a level
With the table top and above it, selecting the
position that seems most pleasing. Note also
Whether the effect is better when the blocks
extend to the boundary of the picture area or
When they are moved closer together to leave
Space around them.
Determine the exposure at maximum
lens aperture with the Weston meter and make
this exposure on the lower half of the film.
Then raise the image to the upper half of the
film by means of the rising front and make
another exposure with the lens stopped down
as far as possible. The focus should remain
unchanged for the two exposures. Since expo-
Sures are directly proportional to the
squares of the stop numbers, the equivalent
exposure for the second negative may be com—
puted according toe the following formula.
(First Stop)*
second Exposure T (second stop):
Topics for Discussion
|First Exposure
l. Which seemed the more natural viewpoint
for the camera, above the table and tilted
downward or on a level with the table top
and horizontal? Explain.
2. How do you account for the fact that a
cardboard in the camera back can shield
half of the film that is not being exposed
even though light can pass around it?
Describe the effect that would be produced
by photographing red "letters against a
White background on process, orthochromat-
ic, and panchromatic films.
If an exposure of 2 seconds is correct at
stop f/1.5, what is the correct exposure
at stop f/16?
Lºïlm I Weston L. Exposurell
3
Stop |
Experiment 6
| NTENS F | CAT I 0N
(Experiments 6 and 8 should be per-
formed during the same laboratory period as
they require the same solutions.)
It occasionally happens that the neg-
ative image is too thin to print satisfacto-
rily because of under-exposure or under-
development. In such cases marked improve—
ment in printing quality may be obtained
either by producing an additional chemical
deposit superimposed on the original image
or by changing that image into a compound of
a different color that cuts off the transmit-
ted actinic light more effectively than did
the original silver image. The method that
we shall follow here consists in converting
the Silver image into brown silver sulphide
Which Will produce the desired effect because
an image of this color is more opaque to ac-
tinic light than the original gray image.
In general, it is well to realize
that intensification and reduction are pallia–
tives only that make the best of a bad situa-
tion but the quality will never be as good as
if the negative had been correctly made in
the first place. Gradation is likely to be
impaired and graininess may be more apparent.
As a result, whenever possible, it is better
to remake the negative but, as it occasionally
happens that this is impossible, it is well
to know what can be done to improve a defec-
tive negative.
By the process described here the im–
age is first converted into silver ferrocyan-
ide. As this is a light yellow compound that
is insoluble in water, the image gradually
turns yellow and the process should be con-
tinued until all black appearance has disap-
peared. After a brief rinse, the negative is
next transferred to a solution of silver sul-
phide in which the silver ferrocyanide image
is converted into brown silver sulphide.
Procedure. The thinner negative from
Experiment 4 should be used here. Cut the
film into two parts in such a direction that
each represents portions of comparable print-
ing quality. One part is to be left unchanged
and the other should be intensified.
Prepare the solutions given in Formu-
la 5 of the Formulary. t
Leave the negative in Solution l until
all the black Silver image is converted into
yellow Silver ferrocyanide. Rinse and trans-
fer to Solution 2 and allow to remain until
the image is converted into brown silver sul-
phide. Wash for at least one-half hour. At
a Subsequent laboratory period the two por-
.tions should be fitted together and a print
made giving the combination the exposure that
will best print the intensified portion. By
printing both parts at the same time it is
possible to discover exactly how much has
been accomplished by intensification.
Topics for Discussion
1. Compare the amount of time expended in in-
tensifying the negative with what would
have been required to repeat the exposure.
2. Has the photographer any control over the
depth of color obtained or must he simply
let the process go to completion? Explain.
For students of chemistry: -
3. Account for the formation of silver ferro-
cyanide by the interaction of potassium
ferricyanide and silver.
4. Write the equation for the interaction be-
tween the silver ferrocyanide and sodium
Sulphide.

REDUCTION
INTENSIFICATION


27O
LABORATORY MANUAL lz
Experiment 7
REDUCT | ON
It occasionally happens that a nega-
tive is so dense that it prints very slowly.
As a rule, this condition is due to over-
exposure which results in the production of
an extremely dense negative upon development.
It is therefore desirable to dissolve part of
the Silver image. Actually, the process is
one involving the oxidation of the silver im–
age as Silver with a valence of zero is con-
verted into a complex compound in which it
has valence of one. Photographers are there-
fore using the word reduction in a peculiar
sense all their own when they call this re-
duction.
By using dilute Solutions of potassi—
um ferricyanide and hypo, the silver is slow-
ly converted into silver ferrocyanide as in
the last experiment but in the presence of
hypo, this forms a complex soluble compound
that gradually dissolves away. Reduction is
most likely to prove useful in the case of
negatives that require an excessively long ex-
posure in the enlarging camera. Time spent
in reducing a negative so dense that it can-
not be printed satisfactorily by contact
would probably be wasted.
In many color processes, it is cus–
tomary to dissolve the first negative image
entirely. For this purpose Farmer's reducer
Would be too slow and, instead, a water solu-
tion of potassium dichromate acidified with
Sulphuric acid is used.
Procedure. Prepare the following so-
lution given in Formula 6 of the Formulary.
Cut the denser negative made in Ex-
periment l; into two parts as in the experi-
ment on intensification, reserve one for pur-
poses of comparison and place the other in
the Solution. Rock the tray and watch the
progress of reduction closely so that it will
be possible to remove the film before the
thinnest, detail that it is desired to retain
is removed entirely. Wash for an hour and
dry. During a subsequent laboratory period,
fit the reduced and unreduced negatives to—
gether and expose to make the best print pos–
sible of the reduced portion.
Topics for Discussion
l. Under what conditions is reduction useful?
2. Is Washing necessary before reduction?
5. Explain why reduction is a misleading
term to apply to this process.
For students of chemistry:
l!. Write out the equation for the reaction
petween Farmer 's reducer and Silver.
Experiment 8
SEP I A TON | NG
If a print is treated exactly as de-
scribed for the intensification of a negative
in Experiment 6, the image will be toned sepia.
It is essential to use a print of considerable
contrast and one that has been fully developed
if the result is to be satisfactory. Such
prints yield satisfactory chocolate browns
while a rather dull print or one that has not
been satisfactorily processed originally is
likely to yield yellow browns that are not
pleasing. It is also very essential to Wash
the print very thoroughly to remove all hypo
as hypo and potassium ferricyanide form Far-
mer's reducer. This would result in the
actual removal of some of the image during
toning and a loss in brilliancy.
In regions where the water contains
considerable amounts of iron, distilled water
must be used both for the solutions and for
the preliminary Washing. Ferricyanide in the
presence of ferric iron precipitates Prussian
blue which makes a blue deposit on the print
that will not wash out satisfactorily.
Procedure. Make a good print from a
rather contrasty negative such as that of Ex-
periment 5. Develop fully and wash very thor-
oughly after fixing. If necessary, it may be
dried and soaked in water again just before
toning. Carry out the processes of bleaching
and toning exactly as in Experiment 6. It is
advisable to keep all the solutions between
65° F and 70° F and to work rapidly as this
process has a marked tendency to soften the
gelatine. *
Topics for Discussion
l. Explain why it is essential to wash prints
or negatives very thoroughly that are to
be used for sepia toning.
2. What evidence have you that the gelatine
is softened considerably during this proc-
ess?
For students of chemistry.
3. Write out the equation for the reaction be-
tween ferric iron and potassium ferricya-
nide.
Experiment 9
REPRODUCT | 0N OF T0 NE WALUES
After we have gained sufficient prac-
tice in the mechanical routine of focusing,
exposing, developing, and printing, it becomes
possible to give attention to what we may
characterize as the more subtle aspects of
photography, aspects frequently ignored yet
most important if one aspires to be anything
more than a mere record maker. First of
these is the ability to visualize tones and
to picture how the bhree dimensional object

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SEPIA PRINT
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272
LABORATORY MANUAL ll;
will appear when translated into two dimen-
Sional space by the photographic medium.
Close observation and careful thought can pro-
vide much training in this respect and it is
highly desirable to train oneself to see the
final result by an inspection of the object
before the picture is taken. Thus, desirable
modifications may be made in advance with a
consequent Saving in time and material and a
distinct improvement in the general excellence
Of the result, .
The simplest case of tone representa-
tion is the one that we shall consider here,
the rendering of a white cube lighted so that
it shows a number of different shades of gray
by variations in the intensity of light fall-
ing on the different planes. Painted with the
White paint used for an undercoat before ap-
plying enamel, the cubes will have a white,
dull mat surface that is an excellent reflec-
tor of light with almost no tendency to pro-
duce specular reflection. If the cubes are
handled with tissue paper they will not be-
come finger marked, an important considera–
tion as this paint does not wash well.
Procedure. Place a cube on a piece
of White charcoal drawing paper or blotting
paper and use the same material as a back-
ground. Light With a single Photoflood and
make two negatives on the two halves of a
film. In both, adjust the light until six
different tones are visible, three on the ex-
posed sides of the cube, one on the horizon—
tal plane, one on the background, and one in
the cast shadow. For the first negative,
light the cube to show maximum contrast so
that the range of tones runs from dark gray
to white. Determine the exposures with an
exposure meter. Use Commercial Orthochromatic
film.
In the second negative, light again
to produce six different tones but reduce
contrasts so that the final print will be in
a high key, i.e., in six tones of light gray.
Both should be printed so that the lightest
tone shown is the faintest distinguishable
gray that the paper can produce. In general,
a print showing portions of any size repre-
sented by unprinted paper is likely to have
a bald, unfinished appearance and indicates
either that the printing time is too short or
the paper used, too hard. It will be instruc-
tive to make prints on several grades of pa-
per. Practice in lighting the cube so that
it shows a smaller number of tones than six
is also instructive but only the negatives
and prints already discussed need be made.
Topics for Discussion
l. How much of the total tone range of the
paper has been used in the print showing
maximum contrast 7 -
How much in the high key print, 7
3. How many distinguishable tones are found
in each?
Did the Weston reading give a satisfactory
2
l;

exposure value or is it desirable to modi-
fy it when photographing an extremely
light subject?
5. Which photograph gives the most satisfac-
tory impression of the white cube? Ex-
plain.
6. Can a photograph exaggerate contrast 7 Ex-
plain. º
7. What is specular reflection?
Film West. On Exposure Stop
Experiment 10
PROJECTION PR | NT | NG
While many consider the making of con-
tact prints a routine procedure that allows
little scope for individual expression or
artistry, it is generally conceded that the
making of prints by projection offers this to
an exceptional degree.
The enlarger should first be examined
for rigidity as the slightest vibration will
be made evident by a lack of sharpness in the
prints. Next, scrupulous care should be ex-
ercised to remove all dust from the film and
film carrier. In dry weather, this is compli-
cated by the fact that rubbing either film
or glass with a dry cloth is likely to impart
an electrostatic charge that will increase
their tendency to attract stray particles of .
foreign matter. Focusing is very important
and should always be done with the lens wide
open as with the camera. Various focusing
magnifiers have been made for use with en-
largers with the lens mounted obliquely so
that the image may be observed without getting
in the way of the project beam. A very sim-
ple way of focusing consists in putting a
distinct scratch on a spoiled negative. This
gives a much sharper and clearer image than
an ordinary negative so that the enlarger can
first be carefully focused with this in the
film carrier after which it is replaced by
the film desired. ' If the enlarger lens has
an iris diaphragm, best definition is usually
secured with a medium stop.
Auto-focus enlargers focus the lens
automatically as the enlarger moves up or
down on its track, a time saving convenience,
It is well, however, to check such enlargers
occasionally for accuracy of focus as they
sometimes get out of adjustment. -
The bromide or chloro-bromide papers
used in enlarging are much faster in printing
and slower in developing than the chloride
papers used in contact printing. Consequent-
ly, it is essential to use an orange or bright
red dark-room light. A Wratten Series OA
safelight is particularly satisfactory as its
greenish yellow color is safe and yet gives
an exceptionally accurate idea of how the
densities will appear by white light. Devel-
opment for at least a minute and a half is
advised with most papers of these types and
it cannot ordinarily be made shorter than the
manufacturer recommends Without marked im-
pairment of tone and contrast.
º#.



Éli
REPRODUCTION OF ToNES
27 l; LABORATORY
MANUAL 16
Procedure. Select a negative having
good definition and contrast. Place this in
the enlarger and focus carefully.
Determine the best exposure by making
a series of exposures on a test strip of nor-
mal paper. Develop fully, fix for a few sec-
onds and examine by white light. After the
correct exposure is determined, a print should
be made on normal paper.
Develop for the time recommended by
the manufacturer, fix for ten minutes and Wash
for an hour. Repeat the process with the same
negative using soft and hard papers. Mount
the best print.
Topics for Discussion
l. Which is the best of the three enlargements?
What does this indicate about the negative 2
2. In what respects are the poorer prints in-
ferior? Explain?
3. Are there noticeable differences in the
printing times of the various papers?
Experiment | |
PORTRA | TS
In portraiture we may recognize three
distinct aims which may or may not be sought
at the same time. The first aim is to produce
a likeness of the person portrayed though it
must be acknowledged that the frailties of hu-
man nature are such that those who expect to
be paid for their efforts do well to make it a
flattering one. A second possible aim is to
interpret character. A third aim may be to
delineate the mood of the moment. All of these
may be summarized by saying that a portrait
may tell us who it is, What manner of person
it is, or how he feels.
The accomplishment of these aims is
greatly aided by the possession of certain
qualities in the photographer himself. He
must first have the ability to make people
feel at ease. He needs to be a good judge of
human nature and to be able to interest people
so that they will forget themselves. Sympa-
thetic comprehension and genuine interest are
likely to cause people to drop their customary
conventional defences and reveal themselves as
they really are. Lacking those characteris-
tics, the photographer is apt to find himself
confronted by an inscrutable, awkward, morose,
or complacently conventional individual Whose
likeness will have little value except possib-
ly to paste on a passport.
It is frequently a good plan to take
the picture when the subject relaxes under the
impression that the photographer is occupied
with something else. One is often told not to
allow the subject to look directly at the
camera. This, it would seem, is open to argu-
ment. Rather, the point would appear to be
that the subject must look at something that
interests him. To an enthusiast in optics,
the sight of the lens might be the one thºng
needful to cause him to register interest and
animation. But, to others to whom a lens is
not an object of interest, it must be awakened
in some other way. The eyes are probably the
most expressive part of the face and when they
look directly from the picture at the observer,
they may contribute wonderfully in animation,
interest or character delineation.
Lighting is particularly important in
portraiture. The simplest is diffused outdoor
light. In fact, a very elaborate artificial
lighting frequently seeks to do little more
than produce under Studio conditions the kind
of lighting that we get naturally every time
we step outside in the daytime. For interior
portraiture, one does well to use only a small
number of lights and to master their potenti-
alities. Too many lights may multiply the
shadows or eliminate deisrable ones and, in
general, produce a state of complexity much
more difficult for the photographer to control
or interpret. A good general rule is to light
unequally from the two sides since shadows are
necessary to produce satisfactory modeling.
The larger the light source, the great-
er the probability that shadows will not be
harsh, making it desirable to use large re-
flectors. Diffusing screens of organdy or
thin muslin cut off a considerable percentage
of the incident light but soften the lighting
and improve modeling so much that their use is
highly desirable whenever possible. Much can
be learned by experimenting with lights and
observing closely the differences in the ef-
fects produced. Irrelevant cast shadows on
the background may often be thrown out of the
field of view by elevating lights or by in-
creasing the illumination there. Or again,
the subject may be moved farther from the
background to accomplish the same result. The
background itself should contain nothing that
Will attract attention to itself. If the sub-
ject wears glasses, it is essential to arrange
the lights or turn the head slightly so that
the glasses will not reflect light into the
camera lens.
In portraiture it is especially nec-
essary to avoid under-exposure as the skin
texture is then unsatisfactory. Expressions
indicating extreme animation on the part of
the subject should be avoided if time expo-
sures are to be made. Expressions normally
present only for an instant never appear natu-
ral when posed for a time exposure and if the
| lens and lighting equipment necessitate time
exposures, the photographer should confine his
efforts to delineating his subject in repose.
Procedure. Make photographs of the
same person on the two halves of a film. Give
one the exposure indicated by the Weston meter
and the other twice that exposure. Print
both and mount the better One.
Judge your portraits as follows:
l. Are focus and exposure correct 7
2. Is the skin texture satisfactory?
5. Are there any bad shadows?
!. Are there any bad high-lights?

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276 LABORATORY
MANUAL l8
5. Is the likeness satisfactory?
6. Has it interest as a character
study?
7. Does it express a definite mood?
Topic for Discussion
Summarize the good and bad points of
Film | Weston £xposure"
your portraits.
Stop |
|
| | |.
Experiment 12
TRANS PARENC ES
Most people do not fully appreciate
the beauty that is possible in the projected
image of a really good slide as most of those
ordinarily seen are made commercially and
seek to do little except to make a recogniz–
able image without even attempting to bring
out the long range of tone and delicate gra-
dations of which lantern slides are capable.
Actually, a really first rate slide of a
beautiful negative can be a revelation of un-
suspected potentialities in the photographic
medium. Transparencies possess a much great-
er range of tone than prints, they gain a
pseudostereoscopic effect when magnified, and
give a picture of exceptional luminosity and
fine detail.
One who can make really good trans-
parencies may feel justified in considering
that he is competent to master any ordinary
photographic process and the student is urged
to accept the challenge offered and demon-
strate his ability to succeed in this respect.
Here, we shall use pieces of 35 mm positive
film such as is used in making films for pro-
jection in the motion picture theatres as
Such film is cheap, has an emulsion slow
enough to print by contact in a printing box
and offers less difficulty in getting good
contact between the negative and positive ma—
terial for printing than plates. This is
rather difficult with an ordinary lantern
slide because of the rigidity of the glass
plate. In consequence, lantern slides are
often made by projection with an enlarging
camera. Such a method also offers the advan-
tages of making it possible to select only
part of a negative and of varying the size
of the part to fit the lantern slide.
Procedure. It is best to use a clean
working developer specially compounded for
lantern slides as the dark values must be
quite dense for satisfactory projection and
the Whites must be really transparent. De-
veloper is compounded according to Formula 7.
Use full strength and throw away after using.
Development is complete with this
developer in from l l/2 to 2 l/2 min. Slides
should be developed fully to build up the
density necessary so that they will not seem
weak when projected. A rule sometimes given
is to develop until the whites begin to be-
come slightly veiled from developer fog,
Cover the lights in the printing box
with enough pieces of yellow paper so that
the printing time for a correctly exposed
transparency is several Seconds. Make numer-
ous trials on pieces of positive film until a
Series is produced showing under-, over- and
normal exposure. Study carefully by white,
transmitted light after fixing in order to
select the best exposure for the full sized
transparency. Negatives made with a good
miniature camera are very satisfactory for
this experiment. After the transparency has
dried, it should be masked and mounted be-
tween 2" x 2" glass slides as a lantern slide.
Mark with thumb mark to assist in inserting
correctly in the project or and hand in in an
envelope.
A brief rinse in Farmer's reducer
after fixing is often given to lantern slides
to make the Whites as clear as possible. A
lantern Slide that has been somewhat over-
exposed may be fully developed, fixed, and
then reduced With Farmer 's reducer. With the
slow emulsion used here, a bright-red safe-
light such as Eastman photographic red cellu-
loid or a Wratten Series l is perfectly safe
and enough light should be used so that the
progress of development can be watched care-
fully.
Transparencies are best judged by
projection. Project your transparencies and
note whether they are critically sharp and
really satisfactory in contrast and gradation.
A few of the defects often found in
lantern slides and their causes are Summarized
below. n
Not sharp.
(l) With an automatic printer, the
light switch may operate before the cover is
down far enough to make good contrast between
the negatives and positive.
(2) The negative or positive film may
be wrong side up. Emulsions must be in con-
tact.
Whites not clear.
(l) Over-exposure.
(2) Old positive film.
(5) Two little potassium bromide in
the developer.
Blacks not dense enough.
(l) Under-exposure or under-develop-
ment. -
(2) Developer not adapted to making
transparencies.
Topics for Discussion
l. Is Washing necessary after fixing a trans-
parency before using Farmer's reducer?
Explain.
2. Suggest reasons why transparencies made by
reversal often show more detail than those
made from a negative. -
5. Why is a better result secured by develop-
ing an over-exposure fully and reducing

PORTRAIT



278
LABORATORY MANUAL 20
with Farmer's reducer than by under-
development 7
H. Give a rule for putting the thumb mark on
Slides.
5. When mats have one silvered side, which
way should it face in the projector? Why?
Exper i ment 3
EFFECT OF T | ME OF DEWELOPMENT UP 0N CONTRAST
If we make identical correct exposures
and develop them for different lengths of
time, we shall find that there are noticeable
differences not only in the printing times
but also in contrast. It is desirable to
study this point rather carefully. Negatives
of ordinary subjects are so complicated that
it will be well to simplify our problem by
making negatives that contain only a few
tones covering rather large areas. It will
then be possible to determine these densities
With the photometer to be described in the
next experiment and to gain a general idea of
the trend of the characteristic curve in each
case. It is essential to make the exposures
as accurate as possible as log E is one of
the variables to be plotted in Experiment ll!.
Procedure. Commercial Ortho film may
be used. Focus the camera on a white or buff
drawing paper and determine the Weston expo-
Sure. Our purpose is to make four different
exposure Strips about an inch wide on the
film. Insert the film holder and when all is
ready for exposure, withdraw the slide one
inch and give this portion twice the Weston
exposure. Withdraw the slide another inch
and expose again, giving the Weston exposure.
Repeat two more times withdrawing the slide
another inch before each exposure and make
the last two exposures one-half the West on
exposure. It is essential to make the expo-
sures as accurately as possible in order to
obtain Satisfactory graphs in the next ex-
periment.
Four different exposures covering
areas four by one inch now exist on the nega-
tive, giving total exposures as follows, W
indicates the Weston reading.
Part I. 2W + W + l/2 W + 1/2 W = 1; W
Part 2 W + 1/2 W + 1/2 W = 2 W
Part 3 l/2 W + l/2 W = W.
Part l; l/2 W
The illumination on the paper and the
stop used should be such that the Weston ex-
posure is at least two seconds.
In the darkroom, remove the film from
the holder and cut lengthwise into three
equal portions each of which should contain
all four exposures and an unexposed portion.
Develop all three in D-72 paper developer di-
luted with four parts of water to one part of
developer. Develop the strips for two, three
and six minutes respectively. Fix and wash
as usual. Prints need not be made but the
Strips should be handed in after Experiment
l! has been performed.
Topics for Discussion
l. Is it possible to see differences in the
densities on the films by visual examina-
tion?
2. Is it possible to be certain of differences
in contrast on the three films in this way?
5. Could this experiment be performed without
focusing the lens or without a lens in the
Shutter?
H. What would be the effect of allowing the
Strip that was developed for two minutes
to remain in Water for a minute or two in-
stead of transferring it promptly to the
acid fixing bath?
Exper I ment 14
THE CHARACTER IST : C C U RWE
The rather limited data obtainable
from the negatives of the last experiment may
be used to gain an approximate idea of their
characteristic curves. Since this involves
plotting the densities as ordinates against
the logarithms of the exposures as abscissas,
it is first necessary to determine the densi–
ties represented by the different film areas.
To do this We shall use a Weston meter sup-
ported in a frame that brings the window of
the Photronic cell in line with the lens of a
projector. A film holder is provided that
permits the light from the lantern to pass
through an area of the film about 3/16 inch
in diameter and fall upon the cell. Without
a film in position, the film holder should be
moved behind the cell until the light falls
on a particularly sensitive spot on the Pho-
tronic cell as indicated by the galvanometer
deflection. The light should then be adjust-
ed until the galv. Scale reads loC). The film
is then placed in position without changing
the other arrangements and the new galvanom-
eter reading noted. This must be lower be-
cause the film is absorbing part of the inci-
dent light. Let us assume that the new read-
ing is 50. Then, It /Io or the transparency
is 50/100 or 1/2 and the film at this point
transmits one-half of the incident light.
The opacity or Io/It is the reciprocal of 1/2
or 2 and the density is log 2 or .5.
In this way measure the densities for
the different portions of each negative and
plot on rectangular coordinate paper. Plot
the three graphs and compare their slopes and
the density ranges obtained with each. A
simple densitometer like this is not suffi-
ciently sensitive to measure high densities
and these may have to be rejected as too un-
certain to plot. Plot on page 285.
{{[{{
...i.ºi.
--
|t||
LABORATORY
MANUAL 21 279
d
º
§
º
Data ;
Trans- Den-
E| log E parency Opacity sity
Negative l -
Negative 2
Negative 3
Topics for Discussion
l. Why would it be inadvisable to use the
automatic shutter speeds in making the
negatives?
2. What effect has the density of the unex–
posed film upon the graphs 2
3. Do your graphs indicate that any of the
exposures gave densities lying on the toe
of the characteristic curve 2
l!. What does it signify if the higher densi-
ties have somewhat erratic values 2
Exper i ment 5
SEPARAT || 0 N N EGAT | WES
In many color processes, it is first
necessary to make a set of separation nega-
tives through the Wratten A (red), B (green),
and Cs (blue) filters or other filters simi-
lar to these. In this way the orange red,
yellow green, and blue violet portions of
the subject will be recorded on three sepa-
rate films. A fourth negative to be printed
in black for increase in contrast is fre-
quently included. Positives made in the col-
ors complementary to the taking filters are
then printed superposed either by purely pho-
tographic processes or in a printing press.
Here, we shall not attempt to carry
the process farther than the making of the
separation negatives but the following sum-
mary of the requirements that must be met by
such a set of negatives if they are to yield
a satisfactory color print may be useful.
l. The lens must be capable of form-
ing images by red, green or blue light that
are identical in size. Only exceptionally
fine lenses that have been achromat 1zed for
three colors Will do this.
2. The focus must not be changed be-
tween exposures.
3. No shifting of the camera or lens
or alteration of the image position between
exposures is permissible.
!. Satisfactory color balance is not
possible unless the negatives are developed
to the same gamma.
5. Negatives made by light of differ-
ent colors do not necessarily yield the same
gamma even when given identical development.
To compensate for this, some color workers
recommend giving the blue filter negative
about twenty per cent longer development than
the others.
6. Filter factors are only approximate
and must be corrected by trials with the film
to be used.
7. The sloppy, care less worker is
wasting his time in attempting color printing.
Procedure. The colored object con-
sists of a bunch of artificial flowers in a
neutral gray holder. If the correct expo-
sures are given, this support should be rep-
resented by the same density in all the nega-
tives. Photoflood illumination should be
used. Tri-X Panchromatic film is suitable
and the exposure factors used should be those
given on the printed card in the box of film
for this kind of light.
Provision is made in the camera back
for the insertion of two masks so that one
quarter of the film may be exposed at a time.
Make exposures through the A (red), B (green),
and Cs (blue) filters multiplying the Weston
exposure by the appropriate factor in each
case. The fourth exposure should be made
Without a filter.
Strictly speaking, these negatives
will not match perfectly because of the
change in perspective resulting from shifting
the position of the image between exposures.
If they were actually to be used for this
purpose, they would need to be made on sepa–
rate films So that this would not be necessa–
ry. It is essential to record which quarter
of the film has been used for each exposure
as all colors by reflected light are so com—
plex that the various portions of the subject
are usually recorded on all the negatives and
it is often rather difficult to identify them
after development.
&lrºë8.
LOWer le
left,
Ordinary black and white prints that
render the neutral gray support in the same
grays should be made and mounted on the plate
provided.









|
RED GREEN
BLUE NO FILTER
COLOR SEPARATION

LABORATORY
MANUAL 25 281
certain of their direction. Examine the im—
ages of some well-defined lines with a micro-
scope giving about 50X magnification and note
how much more clearly defined their boundaries
are when contrast is high.
Topics for Discussion
Explain how the McKay Photo Test
}hart might be used for the following pur-
poses:
l. Graininess of different films.
. Speed of different films.
. Color sensitivity of different films.
. Determination of filter factors.
. Testing different developers.
Testing lenses for spherical aberration.
Testing lenses for astigmatism.
i
# it… -
º: º ºr 1,
Topics for Discussion
l. How do you account for the fact that the
blue filter negative requires the longest
exposure in spite of the high actinic
power of blue light?
2. In making color prints, explain why the
positives must be made in colors comple -
mentary to those of the taking filters in
order to restore the original colors.
3. Why would it be inadvisable to light the
subject with ordinary low wattage Mazda
lights in this experiment 2
Experiment | 6
LENS TEST ING
Lenses differ greatly in the quality
of the images they form and a complete test
involves the use of special equipment to be
found only in an optical testing laboratory.
It is possible, however, to gain a good idea
of the general performance of a lens by means
of a test diagram consisting of geometrical
figures showing a gradually decreasing sepa-
ration of fine lines. Resolving power is
defined as the angular separation between two
objects that can just be distinguished as
separate and as any lens defect is likely to
impair definition, a test of resolving power
serves as an indirect test of general per-
formance. -
Procedure. A convenient diagram for
this purpose is the McKay Photo Test Chart
and it is suggested that the student will
find the experiment more interesting if he
performs it with a camera of his own rather
than With one of the laboratory cameras.
Place the camera exactly ll focal
lengths” from the camera or 10l focal lengths
if the camera does not permit focusing at this
closer distance, and focus the image carefully
With a magnifier or range finder. If the
latter is available, check the range finder
Setting, the focusing scale reading and the
measured distance with each other. In ground
glass focusing check the focus at all four
corners and focus with a magnifying glass.
Process film should be used and the image de-
veloped to high contrast. After the negative
is dry, it should be studied carefully with a
magnifier.
Various factors beside the quality of
the lens itself influence critical definition
so it is essential that the technique leaves
nothing to be desired as, otherwise, the test
may be without significance. The film used
affects the result. Correct exposure and de-
velopment are imperative and the negative
should be developed to high gamma. In general
lines are considered resolved if they are suf-
ficiently well defined so that one can be
Experiment 1 7
EXPOSURE METERS
Influencing every exposure are at least
seven independent variables, film, hour of day,
season, geographical latitude, stop, shutter
speed and subject. It is therefore understand-
able why many efforts should have been made to
invent optical or mechanical contrivances that
will assist the photographer in evaluating the
combined effect of all of these. Film latitude
is now so great that little more is demanded of
an exposure meter than a good approximation ex-
cept in color photography.
We may distinguish the following classes
of meters.
l. Slide rule type. These are the least
expensive meters and consist of one or two slides
that are free to move with respect to fixed
Scales.
2. Extinction type meter. Here a vari-
able density tint plate is rotated before ethe
eyepiece while the meter is directed toward the
scene to be photographed and a reading is taken
when the darkening of the field assumes the
state described in the instructions that accom—
pany the individual meter. Sometimes the actual
scene is viewed and, again, a series of numbers
is visible in the field. It will be readily
seen that the extent to which the tint plate can
be turned toward greater densities without total
loss of detail in either case is a measure of
the brightness of the light coming from the Sub-
ject. Then, a setting of the movable scale on
the meter in accordance with this determination
will make appropriate stops and exposure times
appear in juxtaposition. Considerable practice
with these meters is necessary before it is pos-
sible to repeat readings on the same subject
with much accuracy and the values obtained by
different people vary widely apparently because
their interpretation of the degree of extinction
required is not the same.
*The advantage of using these distances lies in the fact that the chart contains data regarding resolving power in
these terms.



282
LABORATORY MANUAL 21;
posite the light value given by the meter.
ll. Opposite the stop to be used read the
exposure time.
A thorough understanding of all the po-
tentialities of these photoelectric meters is
available only to those who study the instruc-
tion books that accompany them carefully, Wis-
dom gained in this way is unfortunately rare.
Procedure. A group of four or five stu-
dents should perform this experiment at the same
time. Each should make independent determina-
tions with each meter and then the results should
be compared to discover how well they agree.
Tabulate these below, making a check mark for
those cases in which it is impracticable to use
the meter in question.
Data
H
|
:
5. Actinometer type. Here, photosen-
sitive paper 1s darkened by light to match the
tint painted on an adjacent portion of the meter.
They are always slow and have now been almost en-
tirely supplanted by other types.
lſ. Photoelectric type. The two essen-
tial parts of these meters are a Photronic cell
that is capable of converting the light energy
that passes through the window of the meter into
electrical energy and a galvanometer whose de-
flection is a measure of the amount of electri-
cal energy obtained from the incident light.
Film-VALue scale
Shurten speed and (f) STOP -
. . . . . .
ºr
CALCULATOR Lock
Light-Value scALF.
SIMPLE INSTRUMENT scale
General Electric Co.
The scales on the photoelectric meter are an
elaboration of the simple slide rule type. Three
are provided, one carrying the light values in-
dicated by the meter, another, the time in sec-
onds and a third, the stops or f/ values. The
time scale can be rotated with respect to the
scale of light values so that the meter can be
pre-set for the speed of the film in use and a
catch is provided so that this setting will not
shift accidentally. Finally, the arrow on the
f/ scale is set opposite the light value read-
ing obtained when the meter is operated as indi-
cated below which makes appropriate stops and
times fall together. The following rules for
using photoelectric meters may be helpful.
1. Pre-set Film Value Scale for the
speed indicated by the manufacturer of the meter
for the film to be used.
2. Hold the meter with the window toward
the subject and read the galvanometer deflection
being careful not to include much sky. An al-
ternative method is to read the meter while hold-
ing it so that it receives the light reflected
by the palm of one is hand. In taking a reading
in this way, the hand should be held toward the
source of light and in the approximate position
of the subject. The meter should be held three
or four inches away and care should be exercised
that its shadow does not fall upon the hand.
- 5. Set the arrow on the rotating dial op-
Sunny outdoor scene
Shady outdoor scene
Person standing facing window
6 feet distant
Card in light box
Still life lighted by Photofloods
Topics for discussion
l. Which meters gave the best agreement?
2. Discuss the relative merits of the different
meters.
5. Consider whether the criticsm is valid that
one who acquired a photoelectric meter before
he had learned to make exposures without it
would find it a handicap.
!. Why are professional photographers usually of
the opinion that exposure meters are unneces-
sary and inconvenient except for color?
Experiment 18
GENERAL COMPETENCE WITH A CAMERA
The experiments previously performed il-
lustrate general principles and have a certain
basic generality that should be helpful in the
way of accumulated experience. The real test of
a person's competence with a camera, however,
consists not so much in doing a specific thing
when he has been told exactly what to do and how
to do it as in carrying out a general assignment
that leaves much to his judgment and ingenuity.
Photography demands technical skill, a very




LABORATORY MANUAL
283
considerable amount of capacity for taking pains,
and ability to remember a fairly large number of
things at the same time. All of these are neces-
sary to the good craftsman. In addition, one
who would use photography as a means of creative
expression must possess originality. His pic-
tures must show thought, a certain power of in-
terpretation and comprehension, and that inten- .
gible quality that makes his work peculiarly his
own. The distinction might be made that a good
technician will portray competently Whatever º
stands out in front of his camera. While an artist
will be able to select and emphasize the rele-
vant parts to express the idea that he has in
mind. Needless to say there must be an idea
that is worth expressing and a certain pleasing
facility in doing so if the effort is to rise
above the commonplace .
;
Procedure. Take a roll film camera,
load it with an eight-exposure roll of orthochro-
matic film and photograph the following subjects:
l. Portrait of a child.
2. Still life.
CHARACTERISTIC CURWEs
i
5. An architectural subject.
l!. A subject symbolizing "Spring" or "Win–
ter" according to the semester.
5. A landscape containing clouds.
Use the other exposures to make second exposures
of any of the subjects desired. Develop either
| by hand or in a tank and turn in the uncut roll
of film. Considerable dexterity is require to
load a film into a tank and it is advisable to
practice with a spoiled film until it can be
done with the eyes shut before attempting to do
it in the darkroom with a film one Wishes to
preserve. Handling roll film will be demon-
strated in the laboratory.
Topics ror discussion
l. Grade your negatives in regard to sharpness,
exposure, development and originality.
2. Work out your "batting average" on the basis
that eight printable negatives give a score
of loC)0.
3. Which contributes more to success in an as-
signment like this, an expensive camera or
skillful operator?
EXPERIMENT 14
LOG E.





FORMULARY
Formula 6. Farmer 's Reducer
Water - l25.0 cc.
Potassium ferricyanide . 2 gram
Hypo 5.0 grams
This solution is not atable and must be
used immediately.
Formula 7. Devel oper for Transpar encies
(Gevaert)
A special formula for transparencies
that yields results giving rather high con-
trast and freedom from developer fog will be
found more satisfactory than a paper develop-
er. For lower contrast, such developers may
be diluted with Water. -
Elon . 75 gram
Hydroquinone 3.0 grams
Sodium Sulphite 25.0 grams
Sodium Carbonate (mono.) 55.0 grams
Potassium Bromide 5 gram
Water to make 500.0 09: o
Develop from l; to 2% minutes at 65° F.
Formula 8. Fine Gra in Developer. (Eastman D-76)
Water, about 125° F.
Formula 1. Developer for Film. (Dupont)
Elon 2.5 grams
Sodium sulphite 75.0 grams
Hydroquinone 5.0 grams
Borax 5. O grams
Water l. O liter
Develop for 5–7 minutes at 68° F. This
developer is used without dilution and has
sufficiently good keeping qualities so that
it can be re-used. Students should discard it
in this laboratory after use to avoid all
chance of contaminating the stock solutions.
Formula 2. Developer for Paper. (Eastman D-72)
Water, about lz5° F. 500 cc.
Elon 3. l grams
Sodium sulphite, desiccated 115.0 grams
Hydroquinone - l2.0 grams
Sodium carbonate, desiccated 67.5 grams
Potassium bromide l.9 grams
Cold Water to make l. O liter
- Hot water is used to expedite getting the
sodium carbonate into solution. D-72 is a
standard developer for contact and projection
papers and for transparencies. It can also be
used when a vigorous developer is required for
films and plates.
Dilute as follows.
Contact paper
Projection paper
Transparencies
Films
l-2 parts water
2-ly parts water
2-l; parts water
l–6 parts water
Formula 3. Ac id Fixing Bath
Water 2.0 liters
Sodium thiosulphate (hypo) #80.0 grams
When dissolved, the following acid
hardener should be added.
Ac id Hardener
Water, about 125° F. 160 cc.
Sodium sulphite, disic cated 50.0 grams
Acetic acid (28%) 96.0 cc.
Potassium Alum 50.0 grams
If lump alum must be used, much time
will be saved by dissolving it in about 50 cc.
of boiling water. This should then be added
to the solution containing the acid and sul-
phite with constant stirring.
Formula iſ .
Formula 5. Sepia Toner and Intensifier
Solution l
Potassium ferricyanide 2.5 grams
Potassium bromide 2.5 grams
Water 60.0 cc.
Solution 2
Sodium sulphide (not sulphite), .5 gram
Water 0.0 cc.
Directions for use will be found in
Experiments 6 and 8.
750.0 cc.
Elon .0 grams
Sodium Sulphite, desiccated 100.0 grams
Hydroquinone 5.0 grams
Borax 2.0 grams
Water to make l. 0 lººter
Develop from 12 to 25 minutes at 65° F.
Can be re-used.
Formula 9. Fine Gra in Developer. (Sease #3)
Water, about 125° F. 750 CC s
Sodium Sulphite 90.0 grams
Paraphenylene Diamine 10.0 grams
Glycin .0 grams
Cold water to make l, 0 liter
Develop from 15 to 24 minutes at 68° F.
This developer is used without dilution and
can be re-used.
Formula 1 0. Preparation of 28% Acetic Acid
Water 8 parts by volume
Glacial Acetic Acid 3 parts by volume
The diluted acid is much safer to keep
in the darkroom than glacial acetic.
Formula | | . Acid Short Stop
Water l. 0 liter
Acetic acid (28%) l;8.0 cc.
Conversion Table (Approximate)
28 grams = l ounce avoirdupois
28 cc. = l ounce fluid measure
1,50 grams = 1 pound

s
PLATE XXW | |
tº is is is * * * * * tº ſº ſº.
FOUR-FIGURE LOGARITHMS
N | O I 2 3 4 || 5 6 || 7 8 9 | N | O I 2 3 4. 5 6 7 8 O I 2 3 4. 5 6 7 8 9
rol oooo |ooA3|oo86|or 28|or?olo212 o253 o294|og34|o374 ||40 | 6021 || 6031 6042 |6053 |6064|6075|6085|6096] 6107 8451 |8457|8463|847o | 8476|8482|8488|849.4|85ool 8506 f
11 o414 o453 o492 o531 o569 o607 |oé45|oč82 of 19 of 55 41 || 6128 6138|| 6149 616o 617of 6180 || 61.91 62or 6212 85.13 |8519 |8525 |8531 |8537 || 8543 |8549 |8555 |8561 |8567
12 oz.92 o828 o864|o899 og24 opó9 || Ioo4| Iog&| Ioz2| IIoô: |42 |6232 6243 || 6253 | 6263 |6274|6284|6294 | 63o4|6314 8573 || 8579 |8585 |8591 |8597 |8603 |8609 |8615 |8621 |8627
13||1139|| 1173 || 1206 | 1239 1271 || 1303 |1335||1367|1399 || 1430 ||43 |6335| 6345 6355 6365 6375 |6385|6395 6405 || 6415 8633 8639 |8645 8651 |8657 |8663 8669 |8675 |8681 | 8686
14|1461 1492 1523 1553| 1584|1614|1644|1673 1703|1732.44|6435|6444|6454|6464|6474|6484 |6493|6593 || 6513 8692 |8698 |8704|871o |8716|8722 |8727|8733|8739|8745|
15||1761 || 1790 | 1818, 1847 | 1875 | 1903 || 1931 1959- 1987 2014|45 || 6532 || 6542 || 6551 || 6561 |6571 |658o || 6590 6599 || 6609 8751 || 8756 |8762 |8768|8774 |8779 8785 879) |8797 || 8802 |
16| 2041 2068| 2005 || 2122 2148 || 2175 |22O1 2227 2253 2279. 46 | 6628 | 6637 | 6646 | 6656 | 6665 6675 | 6684|6693 || 6702 8808|8814|8820 |8825 | 8831 |8837 |8842'ſ 8848 8854 8859
17|2304 || 233o 2355 238o|2405 || 2430] 2455 248o 2504 || 2529 - 47 672 I 673o 6739| 6749 6758 6767 || 6776|| 6785| 6794 8865 |8871 |8876 8882 |8887 || 88.93|8899 || 8904 || 8910 | 891.5
18|2553 2577|2601 || 2625 2648 2672 2695 || 2718| 2742 2765, 48|6812 | 6821 | 6830 | 6839| 6848|6857 | 6866 | 6875 | 6884 892 I | 8927 | 8932 | 8938|8943 |8949 |8954 | 8960 | 8965 | 8971
19| 2788 2810 |2833 2856 2878|29ool 2923 || 2945 2967|2989 : 49 || 6902 || 6911 || 6920 | 6928|| 6937 |6946|6955 6964 6972 8976 |8982 | 8987 | 89.93|8998 good goog | 9or 5 9ozo go25-
Taolaoſo |3032 |3054|3075|3096 || 3118|3139|| 316o 3181 |320I so | 6990|6998|7oo7| 7oró|7024|7033 || 7042 |7oso | 7059 9031 9036 9042 | 9047 | 9053 || 9058|9063 9069 || 9074 9079
21 3222 || 3243 || 3263 || 3284 || 3304 || 3324|3345 || 3365 || 3385 3404 51 || 7076 7084| 7093 || 7 IoI | 71 Io 7118 || 7126 7135 | 7143 9085 | 9090 | 9096 || 9 IoI | 9106 || 9112 || 9,117 | 91.22 || 9,128| 91.33
22 |3424|3444|3464|3483 ||3502 |3522 |3541 || 3560 | 3579| 3598 52 716o 71.68|7177 7185 |7|193| 7202 || 72 Io 7218| 7226 9138|9143 || 9,149 | 91.54|9159 || 9,165 || 917ol 9175 || 9,180 91.86 |
23|3617|3636 3655 || 3674 3692 || 37II || 3729 || 3747 3766||3784. 53 | 7243 || 7251 | 7259 || 7267 | 7275 | 7284 || 7292 | 73ool 7308 9I9I 91.96 || 92OI 92O6 92 I2 | 92.17 | 9222 || 9227 9232 92.38
24 || 3802 || 3820 3838|3856|3874 || 3892 || 3909 || 3927 3945| 3962 54 | 7324 || 7332 | 734o 7348| 7356 | 7364 || 7372 | 738o | 7388 9243 |9248 || 9253 9258| 9263 9269 || 9274 92.79 || 9284|9289
25|3979| 3997.|4014|4031 |4048|4065|4082 |4099|41.16|4133; 55|7404|7412 |7419 |7427| 7435 | 7443 |7451 || 7459 |7466 9294 || 9299 || 9304 || 93C9 || 93 IS | 932O || 9325 || 933o 9335 Q34o
26|415ol 4166|.4183|420o |4216|4232 |4249|4265|4281 |4298; 56||7482 |7490 |7497 || 7505 || 7513 || 7520) 7528|7536||7543 9345 935o | 9355 | 9360 | 9365 | 93.70 || 93.75 938o | 9385 | 9396
27|4314|433ol. 4346|4362 |4378||4393 |4409|4425 |444o|4456; 57 || 7559| 7566||7574|7582 |7589 |7597 |7604 || 7612 |7616 9395 || 94oo 94O5 94Io 94I5 || 942O |9425 || 943O 9435 | 944O
28|4472 |4487 |4502 |4518|4533 |4548|4564 |4579 |4594 |4609 || 58|7634|7642 |7649 |7657 |7664 || 7672 || 7679 7686||7694 9445 945o 94.55 9460 9465 9469 || 9474 9479 |9484 || 9489
29 |4624|4639 |4654|4669 |4683 || 4698|4713|4728||4742 |4757 59 |77ool 77.16||7723 || 7731 || 7738|| 7745 || 7752 || 7760 |7767 9494 9499 || 95O4|9509 || 9513 || 9518 9523 || 9528 9533 9.538
30|4771 |4786|48ool.4814|4829 |4843 4857 |4871 || 4886|490o 6o |7782 |7789 |7796||78o3| 7810 || 7818| 7825 7832 7839 9542 9547 || 9552 95.57 9562 || 9566 || 957 I | 9576 | 9581 9586
31 || 4914|4928|4942 || 4955 4969 |4983 |4997 || 5or I 5024 5038||61||7853 |7860 |7868| 7875 |7882 |7889 |7896 || 7903 |791o 9590 9595 || 96oo 9605 || 9609 || 9614|9619 || 96.24 96.28|9633
32 5051 5065 5079 || 5092 || 51 oš 5II9 || 5132 || 5145 || 5159 || 5172 . 62 || 7924 7931 || 7938|| 7945 7952 7959 || 7966 7973 || 798o 9638 9643 |9647 9652 9657 || 9661 |9666 9671 96.75 968o.
33 || 5185| 5198| 5211 |5224| 5237 || 525ol 5263 |5276|5289 |5302 || 63 |7993 |8000 |8007 |8014 | 8021 |8028|8o35 |8041 |8048 9685 9689| 9694 | 9699 || 97.03 || 9708 || 9713 || 97.17 | 9722 || 97.27 l
34|| 5315|5328||534ol 5353 || 5366 5378||5391 || 5403 || 5416| 5428 || 64|8062 |8069|8075|| 8082 |8089 |8096 || 8102 || 8109|8116 973 I 97.36 || 974I | 9745 9750 | 97.54|| 97.59 || 9763 9768|9773
35 | 5441 5453 || 5465 5478 5490 || 5502 || 5514 5527| 5539||5551 "|| 65|8129 i 8136 8142 8149 || 8156|8162 |8169|8176|8182 97.77|| 9782 | 9786 97.91 || 97.95 || 98oo |9805 || 98og 9814 98.18
36|5563|5575|5587|5599 || 5611|5623|5635|5647 5658||567ol 66|8195|8202 |8209|8215|8222 8228 || 8235|8241 | 8248 9823 || 9827 | 9832 || 9836|984I | 9845||985o | 9854 |9859 |9863
37|5682 |5694 5705 || 5717 | 5729 || 5740 || 5752 |5763| 5775 5786, 67 |8261 | 8267 | 8274|828o |8287|8293 |8299|8306 |8312 9868 || 987.2 9877 | 9881 | 9886. 98.90 || 989.4|9899 || 99.03 99.08
38||5798 || 5809 || 5821 5832 || 5843 |5855 || 5866|5877 |5888||5899 || 68|8325|8331 |8338|8344|8351 |8357 || 8363|837o |8376 99.12 || 99.17 | 992 I | 9926|993ol. 9934 || 993.9 || 99.43 | 9948 9952
39||5911 |5922 || 5933 5944 |5955 |5966|5977| 5988||5999 || 6oro ||69|8388|8395 |84ol | 8407 | 8414|8420 |8426|8432 |8439|| 9956 | 996I | 9965 9969 || 9974 || 99.78|9983 || 9987 || 999 I | 99.96
The Macmillan
Company.


INDEX
Aberration
chromatic, l?7
spherical, lz6
Absorption of light, 81, 81,
Achromatism of prisms and lenses, 128
Agitation during development, 75
Ambrotype, lº
Cameras
box, 55
Exacta, 59
folding, 56
miniature, 60
reflex, 57
Speed Graphic, 58
twin lens, 60
view, 5l *
Characteristic curve, 86, 99, 278
graphs, 87, 94, l08, ll2, 285
Chromatone, 228
Circle of confusion, ljó
relation to depth of field, lj7
computation of, lj8
Color, wave length table, 190
Color mixer, 205, 201;
Color mixing, additive, 202, 21.l
Color mixing, subtractive, l86, l87, 190
Color processes,
additive and subtractive distinguished, 201
screen plate, 208
duplication, 215
limitations and advantages, 216
subtractive, 219
Color rendering of films, 54, 101, 165
Color Scout, 222, 223
Composition, principles of, 25l., 252
Condensers, use of, 105, l06
Conjugate foci, 264
Contrast of papers, 21, 22, llo
Copying, exact size, 264
Coupler developers, l8l
Critical definition, factors affecting, 66–70
Daguerreotype, 8, 15
Density, 21
Depth of field, lj9, 266
Development, theory of, 36
Developers, 44, 46, 284 sº
Developing solutions, 39, 284
Diffusion disks, 106, 107
Dispersion, ll&, ll.9
Enlarging, 10l., 105, l09, llo
Exposure meters, 281
Eye
as a cameral, l;0
as a color analyser, 155
Ferrotyping, 266
Film, manufacture of, 52
Fine grain development, 7l-76
286
Fine grain developers, 73, 74, 284
Focal plane shutter, 57
Formulary, 284
Gamma, 92, 95, 96, 97
Gelatine, 30, 195
Graininess, 71, 76
Graphs
characteristic curve, 87, 94
time-gamma, 94
time-temperature, 96
Intensification, 268, 284
Kodachrome, 250, 254, 256
Latent image, discovery, 5, 9
Latitude
film, 98
paper, l08, ll2
Lens formula, 122, 124
Miniature, negatives, contrast desirable, 78
Newton, contribution to color theory, 180
Opacity, 82, 85
Perspective, l'il
at short distances, ll:7, 148
effect of focal length, lºg
panoramic camera, lº2
telephoto lens, llllk, lºß
wide angle lens, lll, lº, lººk
Paper negatives, 248
Parallax, 59
Pinhole camera, ll.9, l2O
Portraits, 274
Projection printing, 102, 272
Reciprocity law, 86
Reduction, 270, 284
Reticulation, 250
Reversal, 182
Rising front, 55
Sensitometric tests of papers, 25
Separation negatives, 192, 281
Sepia toning, 270
Shutters
between lens, 63
focal plane, 57
Stops and stop numbers, 132, lj6
Swing back, 54
Technicolor, 227
Transparencies, 276, 284
Trimming and mounting, 262
Wash-off Relief process, 196, 224

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