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AIRPLANE PHOTOGRAPHY
[Illustration]
AIRPLANE PHOTOGRAPHY
by
HERBERT E. IVES
Major, Aviation Section, Signal Officers Reserve Corps, United States
Army; Lately Officer in Charge of Experimental Department, Photographic
Branch, Air Service
208 ILLUSTRATIONS
[Illustration]
Philadelphia and London
J. B. Lippincott Company
Copyright, 1920, by J. B. Lippincott Company
Printed by J. B. Lippincott Company
at the Washington Square Press
Philadelphia, U. S. A.
TO MY WIFE
A HELPFUL CRITIC, EVEN THOUGH SHE NEITHER PHOTOGRAPHS NOR FLIES
PREFACE
Airplane photography had its birth, and passed through a period of
feverish development, in the Great War. Probably to many minds it
figures as a purely military activity. Such need not be the case, for
the application of aerial photography to mapping and other peace-time
problems promises soon to quite overshadow its military origin. It has
therefore been the writer's endeavor to treat the subject as far as
possible as a problem of scientific photography, emphasizing those
general principles which will apply no matter what may be the purpose of
making photographs from the air. It is of course inevitable that whoever
at the present time attempts a treatise on this newest kind of
photography must draw much of his material from war-time experience. If,
for this reason, the problems and illustrations of this book are
predominantly military, it may be remembered that the demands of war are
far more severe than those of peace; and hence the presumption is that
an account of how photography has been made successful in the military
plane will serve as an excellent guide to meeting the peace-time
problems of the near future.
It is assumed that the reader is already fairly conversant with ordinary
photography. Considerable space has indeed been devoted to a discussion
of the fundamentals of photography, and to scientific methods of study,
test, and specification. This has been done because aerial photography
strains to the utmost the capacity of the photographic process, and it
is necessary that the most advanced methods be understood by those who
would secure the best results or contribute to future progress. No
pretence is made that the book is an aerial photographic encyclopædia;
it is not a manual of instructions; nor is its appeal so popular as it
would be were the majority of the illustrations striking aerial
photographs of war subjects. It is hoped that the middle course steered
has produced a volume which will be informative and inspirational to
those who are seriously interested either in the practice of aerial
photography or in its development.
The writer is deeply in debt to many people, whose assistance of one
sort or another has made this book possible. First of all should be
mentioned those officers of the English, French and Italian armies
through whose courtesy it is that he can speak at first hand of the
photographic practices in these armies at the front. It is due to
Lieutenant Colonel R. A. Millikan that the experimental work of which
the writer has had charge was initiated in the United States Air
Service. To him and to Major C. E. Mendenhall, under whom the work was
organized in the Science and Research Division of the Signal Corps, are
owing the writer's thanks for the opportunities and support given by
them. A similar acknowledgment is made to Lieutenant Colonel J. S.
Sullivan, Chief of the Photographic Branch of the Army Air Service, for
his interest and encouragement in the compilation of this work, and for
the permission accorded to use the air service photographs and drawings
which form the majority of the illustrations.
The greatest debt of all, however, is to those officers who have formed
the staff of the Experimental Department. To mention them by name:
Captain C. A. Proctor, who was charged with our foreign liaison, and who
acted as deputy chief during the writer's absence overseas; Captain A.
K. Chapman, in charge of the work on optical parts, and later chief of
our Rochester Branch; Captain E. F. Kingsbury, who had immediate charge
of camera development; Lieutenant J. B. Brinsmade and Mr. R. P.
Wentworth, who handled the experimental work on camera mountings and
installation; Lieutenant A. H. Nietz, in charge of the Langley Field
Laboratory of the Experimental Department; Mr. R. B. Wilsey and
Lieutenant J. M. Hammond, who, with Lieutenant Nietz, carried on the
experimental work on sensitized materials. A large part of what is new
and what is ascribed in the following chapters to “The American Air
Service” is the work of this group of men. Were individual references
made, in place of this general and inclusive one, their names would
thickly sprinkle these pages. It has been a rare privilege to have
associates so able, enthusiastic, and loyal.
THE AUTHOR
NOVEMBER, 1919
CONTENTS
I. INTRODUCTORY
CHAPTER PAGE
1. GENERAL SURVEY 15
2. THE AIRPLANE CONSIDERED AS A CAMERA PLATFORM 20
II. THE AIRPLANE CAMERA
3. THE CAMERA—GENERAL CONSIDERATIONS 39
4. LENSES FOR AERIAL PHOTOGRAPHY 44
5. THE SHUTTER 68
6. PLATE-HOLDERS AND MAGAZINES 87
7. HAND-HELD CAMERAS FOR AERIAL WORK 95
8. NON-AUTOMATIC AERIAL PLATE CAMERAS 102
9. SEMI-AUTOMATIC AERIAL PLATE CAMERAS 116
10. AUTOMATIC AERIAL PLATE CAMERAS 124
11. AERIAL FILM CAMERAS 130
12. MOTIVE POWER FOR AERIAL CAMERAS 145
13. CAMERA AUXILIARIES 163
III. THE SUSPENSION AND INSTALLATION OF AIRPLANE CAMERAS
14. THEORY AND EXPERIMENTAL STUDY OF METHODS OF CAMERA SUSPENSION 179
15. PRACTICAL CAMERA MOUNTINGS 193
16. INSTALLATION OF CAMERAS AND MOUNTINGS IN PLANES 208
IV. SENSITIZED MATERIALS AND CHEMICALS
17. THE DISTRIBUTION OF LIGHT, SHADE AND COLOR IN THE AERIAL VIEW 221
18. CHARACTERISTICS OF PHOTOGRAPHIC EMULSIONS 227
19. FILTERS 239
20. EXPOSURE OF AERIAL NEGATIVES 247
21. PRINTING MEDIA 252
22. PHOTOGRAPHIC CHEMICALS 257
V. METHODS OF HANDLING PLATES, FILMS AND PAPERS
23. THE DEVELOPING AND DRYING OF PLATES AND FILMS 267
24. PRINTING AND ENLARGING 279
VI. PRACTICAL PROBLEMS AND DATA
25. SPOTTING 291
26. MAP MAKING 304
27. OBLIQUE AERIAL PHOTOGRAPHY 320
28. STEREOSCOPIC AERIAL PHOTOGRAPHY 329
29. THE INTERPRETATION OF AERIAL PHOTOGRAPHS 351
30. NAVAL AERIAL PHOTOGRAPHY 368
VII. THE FUTURE OF AERIAL PHOTOGRAPHY
31. FUTURE DEVELOPMENTS IN APPARATUS AND METHODS 383
32. TECHNICAL AND PICTORIAL USES 388
33. EXPLORATION AND MAPPING 401
I
INTRODUCTORY
AIRPLANE PHOTOGRAPHY
CHAPTER I
GENERAL SURVEY
=Aerial Photography from Balloons and Kites.=—Photography from the air
had been developed and used to a limited extent before the Great War,
but with very few exceptions the work was done from kites, from
balloons, and from dirigibles. Aerial photographs of European cities had
figured to a small extent in the illustration of guidebooks, and some
aerial photographic maps of cities had been made, notably by the Italian
dirigible balloon service. Kites had been employed with success to carry
cameras for photographing such objects as active volcanoes, whose
phenomena could be observed with unique advantage from the air, and
whose location was usually far from balloon or dirigible facilities.
As a result of this pre-war work we had achieved some knowledge of real
scientific value as to photographic conditions from the air. Notable
among these discoveries was the existence of a veil of haze over the
landscape when seen from high altitudes, and the consequent need for
sensitive emulsions of considerable contrast, and for color-sensitive
plates to be used with color filters.
The development of aerial photography would probably however have
advanced but little had it depended merely on the balloon or the kite.
As camera carriers their limitations are serious. The kite and the
captive balloon cannot navigate from place to place in such a way as to
permit the rapid or continuous photography of extended areas. The kite
suffers because the camera it supports must be manipulated either from
the ground or else by some elaborate mechanism, both for pointing and
for handling the exposing and plate changing devices. The free balloon
is at the mercy of the winds both as to its direction and its speed of
travel. The dirigible balloon, as it now exists after its development
during the war, is, it is true, not subject to the shortcomings just
mentioned. Indeed, in many ways it is perhaps superior to the airplane
for photographic purposes, since it affords more space for camera and
accessories, and is freer from vibration. It is capable also of much
slower motion, and can travel with less danger over forests and
inaccessible areas where engine failure would force a plane down to
probable disaster. But the smaller types as at present built are not
designed to fly so high as the airplane, and the dirigibles, both large
and small, are far more expensive in space and maintenance than the
plane. For this one reason especially they are not likely to be the most
used camera carriers of the aerial photographer of the future. Inasmuch
as the photographic problems of the plane are more difficult than those
of the dirigible and at the same time broader, the subject matter of
this book applies with equal force to photographic procedure for
dirigibles.
=Development of Airplane Photography in the Great War.=—The airplane has
totally changed the nature of warfare. It has almost eliminated the
element of surprise, by rendering impossible that secrecy which formerly
protected the accumulation of stores, or the gathering of forces for the
attack, a flanking movement or a “strategic retreat.” To the side having
command of the air the plans and activities of the enemy are an open
book. It is true that more is heard of combats between planes than of
the routine task of collecting information, and the public mind is more
apt to be impressed by the fighting and bombing aspects of aerial
warfare. Nevertheless, the fact remains that the chief use of the
airplane in war is _reconnaissance_. The airplane is “the eye of the
army.”
In the early days of the war, observation was visual. It was the task of
the observer in the plane to sketch the outlines of trenches, to count
the vehicles in a transport train, to estimate the numbers of marching
men, to record the guns in an artillery emplacement and to form an idea
of their size. But the capacity of the eye for including and studying
all the objects in a large area, particularly when moving at high speed,
was soon found to be quite too small to properly utilize the time and
opportunities available in the air. Moreover, the constant watching of
the sky for the “Hun in the sun” distracted the observer time and time
again from attention to the earth below. Very early in the war,
therefore, men's minds turned to photography. The all-seeing and
recording eye of the camera took the place of the observer in every kind
of work except artillery fire control and similar problems which require
immediate communication between plane and earth.
The volume of work done by the photographic sections of the military air
service steadily increased until toward the end of the war it became
truly enormous. The aerial negatives made per month in the British
service alone mounted into the scores of thousands, and the prints
distributed in the same period numbered in the neighborhood of a
million. The task of interpreting aerial photographs became a highly
specialized study. An entirely new activity—that of making photographic
mosaic maps and of maintaining them correct from day to day—usurped
first place among topographic problems. By the close of the war scarcely
a single military operation was undertaken without the preliminary of
aerial photographic information. Photography was depended on to discover
the objectives for artillery and bombing, and to record the results of
the subsequent “shoots” and bomb explosions. The exact configurations of
front, second, third line and communicating trenches, the machine gun
and mortar positions, the “pill boxes,” the organized shell holes, the
listening posts, and the barbed wire, were all revealed, studied and
attacked entirely on the evidence of the airplane camera. Toward the end
of the war important troop movements were possible only under the cover
of darkness, while the development of high intensity flashlights
threatened to expose even these to pitiless publicity.
=Limitations to Airplane Photography Set by War Conditions.=—The ability
of the pilot to take the modern high-powered plane over any chosen point
at any desired altitude in almost any condition of wind or weather gives
to the plane an essential advantage over the photographic kites and
balloons of pre-war days. There are, however, certain disadvantages in
the use of the plane which must be overcome in the design of the
photographic apparatus and in the method of its use. Some few of these
disadvantages are inherent in the plane itself; for instance, the
necessity for high speed in order to remain in the air, and the
vibration due to the constantly running engine. Others are peculiar to
war conditions, and their elimination in planes for peace-time
photography will give great opportunities for the development of aerial
photography as a science.
Chief among the war-time limitations is that of economy of space and
weight. A war plane must carry a certain equipment of guns,
radio-telegraphic apparatus and other instruments, all of which must be
readily accessible. Many planes have duplicate controls in the rear
cockpit to enable the observer to bring the plane to earth in case of
accident to the pilot. Armament and controls demand space which must be
subtracted from quarters already cramped, so that in most designs of
planes the photographic outfit must be accommodated in locations and
spaces wretchedly inadequate for it. Economy in weight is pushed to the
last extreme, for every ounce saved means increased ceiling and radius
of action, a greater bombing load, more ammunition, or fuel for a longer
flight. Hence comes the constant pressure to limit the weight of
photographic and other apparatus, even though the tasks required of the
camera constantly call for larger rather than smaller equipment.
To another military necessity is due in great measure the forced
development of aerial photographic apparatus in the direction of
automatic operation. The practice of entrusting the actual taking of the
pictures to observers with no photographic knowledge, whose function was
merely to “press the button” at the proper time, necessitated cameras as
simple in operation as possible. The multiplicity of tasks assigned to
the observer, and in particular the ever vital one of watching for enemy
aircraft, made the development of largely or wholly automatic cameras
the war-time ideal of all aerial photographic services. Whether the
freeing of the observer from other tasks will relegate the necessarily
complex and expensive automatic camera to strictly military use remains
to be seen.