B. E, ST
OF THE SOCIETY OF
MOTION PICTURE ENGINEERS
Volume XXXVII July, 1941
Twenty-Fifth Anniversary of the Society of Motion Picture En-
Salute to the SMPE WILL H. HAYS 5
Another Milestone. . EMERY HUSE 7
Twenty-Five Years of Service F. H. RICHARDSON 9
Recent Advances in the Theory of the Photographic Process . .
C. E. K. MEES 10
Recommended Procedure and Equipment Specifications for
Educational 16-Mm Projection A Report of the Commit-
tee on Non-Theatrical Equipment
Part I. General ^Recommendations 22
Part II. The Optical Properties of Commercially Available
Screens for 16-Mm Projection 47
Part III. Performance Specifications for 16-Mm Projection
Equipment for Educational Service 57
Supplement. Resolution Tests on 16-Mm Projection Lenses 70
Report of the Standards Committee 76
Report of the Theater Engineering Committee 78
Television Report, Order, Rules, and Regulations of the Federal
Communications Commission 87
Characteristics of Intermittent Carbon Arcs
F. T. BOWDITCH, R. B. DULL, AND H. G. MACPHERSON 98
Development and Current Uses of the Acoustic Envelope
H. BURRIS-MEYER 109
Current Literature 115
1941 Fall Convention at New York, October 20th-23rd 117
OF THE SOCIETY OF
MOTION PICTURE ENGINEERS
SYLVAN HARRIS, EDITOR
BOARD OF EDITORS
A C. DOWNES, Chairman
I I CRABTUB A. N. GOLDSMITH E. W. KELLOGG
H K A. M. GUNDELFINGER C. R. SAWYER
A. C. HARDY
Sub*rriptkm to non-members, $8.00 per annum ; to members, $5.00 per annum,
! E tfc
thru annual membership dues; single copies, $1.00. A discount
oa MibKriptton or single copies of 15 per cent is allowed to accredited agencies.
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton
4Jton. Pm.. or Hotel Pennsylvania, New York, N. Y.
t*ubit*bed monthly at Easton, Pa., by the Society of Motion Picture Engineers.
Publication Office, 20th & Northampton Sts., Easton, Pa.
General and Editorial Office, Hotel Pennsylvania, New York, N. Y.
West Coast Office. Suite 226. Equitable Bldg., Hollywood, Calif.
Entered a* second class matter January 15, 1930, at the Post Office at Easton,
Pa . under the Act of March 3, 1879. Copyrighted, 1941, by the Society of
Motion Picture Engineers, Inc.
OFFICERS OF THE SOCIETY
EMERY HUSB, 6706 Santa Monica Blvd., Hollywood, Calif.
fut: E. ALLAN WILLIFORD, 30 East 42nd St., New York, N. Y.
Yut-Presidcnt: HERBERT GRIFFIN, 90 Gold St., New York, N. Y.
/.*Cirs c Vic*-President: D. E. HYNDMAN, 350 Madison Ave., New York
Vic*-Prtsidenl: ARTHUR C. DOWNES, Box 6087, Cleveland, Ohio.
esident: A. S. DICKINSON, 28 W. 44th St., New York, N. Y.
resident: W. C. KUNZMANN, Box 6087, Cleveland, Ohio
r: PAUL J. LARSBN. 44 Beverly Rd., Summit, N. J.
Trmimrtr: GBORGB FRIEDL, JR.. 90 Gold St., New York, N. Y.
BATSBL. 501 N. LaSalle St.. Indianapolis, Ind.
DUWUY. 1801 Larchmont Ave., Chicago, 111.
Jon* C. FRAYNB. 6601 Romaine St., Hollywood, Calif.
GOLDSMITH. 680 Fifth Ave., New York, N. Y.
L HARDY. Massachusetts Institute of Technology, Cambridge. Mass.
RTMR. 5451 Marathon St., Hollywood. Calif
195 Broadway. New York. N Y
Snoot. 35-11 35th St., Astoria, L. L, N. Y.
Term expire* December 31. 1941.
*Ttm eipire* December 31. 1942.
SOCIETY OF MOTION PICTURE ENGINEERS
Incorporated at Washington, D. C.
July 24. 1916
C. FRANCIS JENKINS
DONALD J. BELL
PAUL H. CROMELIN
C. A. WILLATT
FRANCIS B. CANNOCK
W. BURTON WESTCOTT
E. KENDALL GILLETT
J. P. LYONS
Washington, D. C.
New York, N. Y.
New York, N. Y.
Washington, D. C.
New York, N. Y.
New York, N. Y.
The object of the Society shall be ... Advancement in the theory
and practice of motion picture engineering and the allied arts and sciences,
the standardization of the mechanisms and practices employed therein,
and the maintenance of a high professional standing among its members.
Membership of the Society
The membership of the Society at the first meeting, held at the
Hotel Astor, New York, N. Y., October 2-3, 1916, numbered twenty-
six persons, as follows :
C. FRANCIS JENKINS CARL E. AKELEY M. D. COPPLE
DONALD J. BELL H. T. WILKINS F. H. RICHARDSON
PAUL H. CROMELIN R. G. HASTINGS H. T. EDWARDS
C. A. WILLAT H. B. COLES MAX MAYER
FRANCIS B. CANNOCK HARVEY M. WIBLE WM. C. KUNZMANN
W. BURTON WESCOTT H. A. CAMPE A. S. VICTOR
PAUL BROCKETT R. E. VOM SAAL E. M. PORTER
E. KENDALL GILLETT BARTON A. PROCTOR N. I. BROWN
HERBERT MILES HERMANN KELLNER
From this modest beginning the Society has grown to nearly 1300
members distributed all over the world, a tribute to its success in
fulfilling the object stated on the previous page. Every branch of
the motion picture industry, including both the artistic and the
scientific aspects of photography, processing, distribution and pro-
jection is well represented in the Society, not only by those directly
engaged in these professions but by chemists, engineers, and research
workers interested in perfecting the apparatus and materials involved.
Presidents of the Society
C. FRANCIS JENKINS 1916-1918
H. A. CAMPE 1919-1921
LAWRENCE C. PORTER 1922-1923
LOYD A. JONES 1924-1925
WILLARD B. COOK 1926-1928
LAWRENCE C. PORTER 1929-1930
JOHN I. CRABTREE 1930-1931
ALFRED N. GOLDSMITH 1932-1934
HOMER G. TASKER 1935-1936
S. K. WOLF 1937-1938
E. ALLAN WILLIFORD 1939-1940
EMERY HUSE 1941-
SALUTE TO THE SMPE
WILL H. HAYS
When your Society was founded twenty-five years ago, the mo-
tion picture, with slow and faltering steps, was just beginning to
grope its way into the hearts and affections of the public. The
pioneers of that seemingly far away period had enthusiastic confi-
dence in this youngster among the arts, but the world at large too often
looked down its nose at the "movies." The child grew and devel-
oped, soon was taking prodigious strides, until today the motion pic-
ture is the most democratic of the arts of our century, and the uni-
versal entertainment of all the people everywhere.
Of the past, with its heartaches and its exhilarations, with its de-
feats and its unparalleled triumphs, we can be justly proud, but it
is the present and the future that now concern us most.
6 SALUTE TO THE SMPE
If we are going to develop this art-industry to its fullest poten-
tialities, as I know we are, then the work in no small measure will have
to be done by the technicians and engineers of your group. In a basic
sense, the motion picture is a mechanical art, the product of technical
wizardry. During my long years of association with the industry, I
have never ceased to have a feeling of awe on learning of each fabulous
scientific advance that has come from the laboratories and workshops,
from the minds of men seeking constantly to improve the art. How
many times have the unknowing said, "Well, this is it .... nothing more
is possible!" And then some Aladdin among you has rubbed a magic
lamp and brought forth a new wonder to dazzle and stun the imagina-
You have given the screen voice, color, undreamed-of realism.
Knowing what you have done, what you are capable of, I won't
even hazard a guess what the motion pictures will be twenty-five
years from now when the Society of Motion Picture Engineers cele-
brates its Golden Jubilee. But I do know this: whatever the future
holds you will contribute greatly to its course.
The motion picture is a collaborative art, requiring many minds
and many hands. Some 275 arts and crafts and professions partici-
pate in the making of a single film in our studios. It is this coopera-
tion of talents, harmoniously integrated, which has made the screen
one of the greatest constructive forces of modern times. Our industry
must always combine depth of human interest and human under-
standing with foresight, tenacity, sound judgment, and unswerving
devotion to the public welfare.
The entire industry rejoices to extend greetings and best wishes on
this occasion of your Society's 25th Anniversary.
WILL H. HAYS,
President, Motion Picture Producers
and Distributors of America,
July 24, 1941, marks the Twenty- Fifth Anniversary of the Society
of Motion Picture Engineers. In 1916 when a group of twenty-six
technical men, headed by Mr. C. Francis Jenkins of Washington,
D. C., met with the idea of formulating a motion picture engineering
society, little did they realize what might come of their idea. The
Society as a mere infant passed through the First World War with
only a few scars. As the years passed the Society grew in member-
ship and in strength until it eventually became a nationwide organi-
zation. Some years after its inception it began to reach out into the
world for membershfp and as a result of its far-reaching activities it
has become without question the outstanding motion picture engi-
neering society in the world today.
Some idea of the growth of the Society, particularly during the past
ten or twelve years, can be had if one knows that in 1928, at the time
the Pacific Coast Section of the Society was organized, the total mem-
bership of the national organization was less than the current mem-
bership of the Pacific Coast Section alone. The Society is now made
up of two Sections in addition to that on the Pacific Coast the Mid-
West Section, located in Chicago, and the East Coast Section, with
headquarters in New York. The East Coast Section is fundamen-
tally the parent body of the Society. From the standpoint of mem-
bership from all over the world, the Society now boasts of approxi-
mately thirteen hundred motion picture engineers.
It is most unfortunate for the affairs of men that the world today is
in such a state of turmoil, but it is the purpose of the Society of Mo-
tion Picture Engineers during these trying times to maintain its nor-
mal activities as far as it is possible to do so. It is firmly believed
that in times of war, peacetime activities and efforts must go on and
the Society must remain a worthy outlet for the accumulated knowl-
edge in the minds of men doing peacetime work, or even war work,
provided the latter is connected with motion picture engineering. If
8 ANOTHER MILESTONE
we are able to live up to these worthy desires it seems certain that
when this period of emergency is over the importance and prestige of
the Society will be maintained, and we believe we will have laid a firm
foundation upon which a better peacetime program in the field of
motion picture engineering may be built.
This issue of the JOURNAL of the Society of Motion Picture Engi-
neers, which is dedicated to the Twenty-Fifth Anniversary of the
Society, marks a definite milestone in the accomplishments of the
Society. It must be proved that these accomplishments have not
been made in vain, and it is up to each and every member of the
Society to dedicate himself to the perpetuation of the ideals of this
Society. This can be done best by looking ahead to the Fiftieth
Semi- Annual Convention of the Society which will take place in New
York City, October 20 to 23, 1941. We must all put our shoulders to
the wheel and see to it that this Convention is the most outstanding
ever held by our Society.
TWENTY-FIVE YEARS OF SERVICE
F. H. RICHARDSON
Historically speaking, twenty-five years is an infinitesimal portion
of time, but in relation to the motion picture industry, twenty-five
years covers almost the entire period of birth, growth, and adolescence
of the industry. Twenty-five years ago I sat at a meeting with
twenty-five other men who had somehow chosen "moving pictures"
as their interest and livelihood, and we put this Society to work for us.
We had no idea the Society was going to last for twenty-five years
or that it would grow to the technical importance it now holds for the
entire industry. We had a job to do, and we set about to do it, and
the formation of the Society was one means of helping us to do it.
The Society grew slowly at first, because the industry was flounder-
ing about, trying to find itself ; but soon it grew more rapidly as the
movies began to expand into the enormous industry we have today;
and when sound came into the picture .... It is needless to go into
details. Today the Society's influence encompasses the entire world;
it has members in all important countries of the world; and consti-
tutes the most important source of information on the up-to-date prog-
ress and technical developments of motion picture engineering.
I am proud to have been one of the founders of the Society, and all
through the years I have tried to contribute whatever I could to the
betterment of the industry and of the Society. Projection has been
my principal interest, because I started as a projectionist or "opera-
tor," in those days and I am indeed happy in the fact that, with the
aid of a few others, I have been helpful in arousing the interest of the
Society in the humble art of "operating moving picture machines."
I trust and feel confident that the Society will continue successfully
this work begun so many years ago, and I can but repeat that I am
proud to have had a part in all this work. May the Society prosper
and find success in all its endeavors.
RECENT ADVANCES IN THE THEORY OF THE
C. E. KENNETH MEES**
Summary. A photographic film consists of a layer of gelatin coated on cellulose
base in which are dispersed a great number of very small siher bromide crystals.
When exposed to light, electrons are liberated in the crystals and these collect at certain
Points, where they are neutralized by silver ions which deposit atoms of metallic siher.
This metallic silver deposited in definite specks forms what is known as the latent
image, which makes possible the development of the crystal. The surface of each
silver bromide crystal in the gelatin layer of an emulsion immersed in the developer is
protected by charged layers of bromide and potassium ions. The development of the
grain is initiated by the break in this charged layer caused by the presence of the silver
latent image. When the developer acts on the silver bromide crystal, metallic silver
is produced in a ribbon-like form, a tangled mass of which forms the developed silver
Behind all our technology there lies the basic theory of the photo-
graphic process the chemistry and physics of the formation and
structure of the photographic material, its reaction to light, its be-
havior in the developer when the image is produced, and the prop-
erties of that image.
The science of photography is founded on the two great sister
sciences, chemistry and physics, and it was only as our knowledge of
these grew that progress could be made on the problems of photo-
graphic science. Until recently, photographic science tended to con-
sist of a chaos of observations, some of them of real value and others
of very doubtful value, with little in the way of theories to connect
them properly. It is only within the last few years that fact after
fact has been falling into place in an ordered network. At the present
time we can say that while much remains to be done, we have a very
clear and definite science of photography something which can be
written out and generalized upon and to which the missing parts can
be added as more work is done.
* Presented at the 1941 Spring Meeting at Rochester, N. Y.; received May 6,
** Kodak Research Laboratories, Rochester, N. Y.
<> The Society is not responsible for statements by authors <>
ADVANCES IN PHOTOGRAPHIC PROCESSES 1 1
Strictly speaking, many light-sensitive substances could be used
for making photographic images, and the science of photography
should be co-extensive with photochemistry itself; that is, with the
chemistry and physics of light-sensitive substances. But in practice,
this is not the case, and the art of photography is almost entirely con-
fined to the use of silver salts, so that the science of photography is
necessarily preoccupied with the very complex system of silver halide
crystals dispersed in gelatin. Information as to the reactions which
go on in the simpler systems used in photochemical investigations
throws little light on the photographic process.
If we enlarge a photographic film under a microscope to about the
limit of resolution of the microscope ; that is, to some 2500 diameters,
we shall find that it consists of a very complex system. On the base,
which is cellulose nitrate or acetate, there is coated a layer of gelatin
containing silver halide crystals. These silver halide crystals are
composed of silver bromide containing a small amount of silver io-
dide, and they may be dyed to sensitize them to the longer wave-
lengths of light. The crystals vary considerably in size but are of
the same general shape. They are triangles and hexagons, which are
the natural forms of silver bromide, and they are held in photographic
gelatin (Fig. 1). Analysis would show that the film also contains a
number of materials glycerine, hardeners, and other things adapted
to control its properties. When this film is exposed to light, the
silver bromide crystals are affected in some way by an extraordi-
narily small amount of light, and they suffer some change. That
change must take place in two steps and not quite instantaneously,
although it occurs in a very short fraction of a second. The reason
for this conclusion is that the amount of change produced depends
somewhat upon the rate at which the light is supplied. This is
what is known as the ''reciprocity effect." If the light is supplied
rapidly, somewhat more effect is produced than if the light is ap-
plied very slowly as if, for instance, a faucet were running into a
bucket and the bucket had a small hole in it. But the analogy is not
good because when the exposure is over, the change that has occurred
is permanent; the image will keep for long periods. When Andre's
photographs were found at the Pole thirty years after his balloon
fell on the ice and were developed, they were quite satisfactory, the
latent image having been preserved by the cold in spite of immersion
in sea water.
The silver bromide crystals in the emulsion depend for their sensi-
12 C. E. K. MEES [J. S. M. P. E
tivity upon the gelatin in which they are suspended. Emulsion
makers have known for many years that some gelatins were active
and would give sensitive emulsions and that others were inactive.
In an arduous research, this was traced by Sheppard to the presence
in the gelatin of traces of free sulfur compounds, which are presum-
ably derived from the plants which the calves and their mothers ate.
When gelatin is made from little animals, like rabbits, which avoid
the hot-tasting plants, such as mustard, which contain sulfur, the
gelatin does not contain these sulfur compounds, so that it was not
. v ^ P-
FIG. 1. Silver bromide grains in a photographic emulsion.
improper to state that "if cows didn't like mustard we wouldn't
have any movies!" The sulfur compounds in the gelatin react with
the silver bromide and produce specks of silver sulfide. These specks
of silver sulfide in some way increase the sensitivity of the silver
bromide crystal to light.
Recently, a thoroughly consistent theory of the effect of light upon
the silver bromide grains has come out of the work of our laboratories
and from Professors Gurney and Mott of Bristol, England. In the
first place, if we consider the energy diagram (Fig. 2) of a silver bro-
mide crystal, we shall find that we have two energy levels, the 5 and
July, 1941] ADVANCES IN PHOTOGRAPHIC PROCESSES 13
P levels, in which the electrons may be situated. The S band is
normally empty and is referred to as a "conduction band." The P
band is normally completely filled with the electrons. Upon ex-
posure of a silver bromide crystal to light which is absorbed in the
long-wavelength end of the characteristic absorption band, the elec-
trons are transferred from the lower P band to the 5 band, and the
crystal becomes conducting. This property is well known in other
materials, as well as in silver bromide, as "photo-conductance," and
the silver bromide crystal exposed to light may be imagined to be
filled with a sort of gas of conducting electrons. Also, when light is
absorbed by the silver bromide, electrons are released. This is the
primary photographic process the thing that happens instantly
when light falls on the crystal. The electrons move about with
great speed inside the crystal and will very frequently reach the
ZERO POTENTIAL ENERGV
BC AqS, AqBP ^ ^ ^ ^ ^
FIG. 2. Energy diagram of the silver bromide crystal.
boundaries of the crystal, but when they reach a sensitivity speck,
they will be trapped by it and the sensitivity speck will become nega-
tively charged by the electrons that it has absorbed. Naturally,
the sensitivity specks will themselves be giving out electrons slowly
if they are at normal temperatures, just as does any other solid body.
During an ordinary exposure, the amount of electrons given out by
the sensitivity specks will be very small; while those which will be
absorbed from the electrons freed by light will be very great. After
the formation of the free electrons by light, therefore, the sensitivity
specks acquire a negative charge by the absorption of these free elec-
In a crystal, there is always available, of course, a certain amount
of silver ions which are formed inside the lattice. As soon as the
sensitivity specks acquire negative charges, these silver ions are at-
tracted to the specks, each negative charge neutralizes one silver ion
and produces a deposit of a silver atom at the sensitivity speck, so
14 C. E. K. MEES [J. S. M. P. E.
that every electron freed by the original light exposure is eventually
transformed into a silver atom deposited on a sensitivity speck.
This theory of the effect of exposure was suggested by Sheppard
and Trivelli of our laboratory over ten years ago under the title of
"the concentration speck theory," but they were unable to give a
satisfactory mechanism for the formation of the concentration speck
although they saw that in some way the effect of light must be to
produce a silver deposit at the sensitivity specks. The new theory
of Webb and Gurney and Mott shows that the effect occurs in two
stages: first, the release of free electrons, which occurs instantane-
ously ; and then the transformation of the free electrons by neutraliza-
tion through the silver ions into silver atoms at the sensitivity specks.
This accounts for the reciprocity effect. When the light acts, free
electrons are formed and go to the sensitivity specks, but the sensi-
tivity specks are continually losing electrons and, consequently, if
the light is weak, there will not be as many silver atoms deposited at
the sensitivity specks as there should be. A certain minimum con-
centration of electrons must be built up in the crystal before the elec-
trons begin to be trapped by the sensitivity specks. This explana-
tion is shown to fit the facts because, when the loss of electrons from
the sensitivity specks is reduced by greatly lowering the temperature,
the rate at which the light is supplied no longer affects the resulting
The action of light, then, on the silver halide crystals is, first, to
produce instantaneously a charge of free electrons. Then these elec-
trons are attracted to the sensitivity specks, and their charge is
neutralized by silver ions, with the result that metallic silver is de-
posited around each sensitivity speck and forms the permanent
nucleus which we call the "latent image."
The great efficiency of the photographic process is due to the very
small amount of work which is done by light in forming an image and
the very large amount of work which is done by the chemical de-
A photographic developer is a reducing agent; that is, it is a sub-
stance which is itself oxidized by silver bromide and, in being oxi-
dized, reduces the silver bromide to metallic silver. The matter is,
however, very complicated, and we are only beginning to understand
the behavior of photographic development. In the first place, not
all reducing agents, by any means, are photographic developers.
If the reducing agents are too strong, they reduce the unexposed
July, 1941] ADVANCES IN PHOTOGRAPHIC PROCESSES 1.-,