FUTURE DEVELOPMENTS IN APPARATUS AND METHODS
Prophecy is an undertaking that always involves risk. The prophet's
guess of what the future will bring forth is based only on the
tendencies of the past, the most urgent needs of the present, and the
activity of his imagination. He may easily—and he usually does—entirely
overlook certain possibilities which may arise apparently from nowhere
and which profoundly affect the whole trend of development. Conditions
which dominate at the present time—such as military necessity—may
happily drop into the background and free the science from some of its
severest restrictions. With this caution, some future possibilities in
apparatus and methods may be presented along the lines already used in
discussing the present status of aerial photography.
=Lenses.=—From the military standpoint the next steps in lens design
would be toward telephoto lenses on the one hand, and on the other
toward lenses of short focus and wide angle. The telephoto lenses used
for spotting would be of long equivalent focus—a meter and more—but of
handy size, that is, not more than 50 centimeters over all working
distance. The wide angle short focus lenses would be designed for low
flying reconnaissance or quick mapping work. They would also be demanded
for peace-time mapping projects, where the largest possible amount of
territory should be covered in a single flight. Both types of lens
should be pushed to the extreme in aperture, for short exposures and the
maximum of working days will always be demanded.
=Cameras.=—Peace-times will give the necessary opportunity to develop
self-contained and therefore simply installed cameras. They will at the
same time be made very completely automatic but simple to operate in
spite of their complexity. Such cameras have, during the war, been the
ideal of all aerial photographers, but the time has been too short since
the necessary conditions have been understood for that lengthy
development work and those complete service tests which are so necessary
to develop all automatic apparatus. Several designs which are now being
perfected may be counted on to take us a long way toward this ideal.
On the other hand, that military ideal which leaves the camera operator
the greatest possible freedom for other activities, is apt to be
entirely reversed in peace. The camera operator can now be required to
be an expert, who will be free to change plates or filters and to
estimate exposures, instead of giving his best efforts to the problem of
defence. For him a simple and reliable hand-operated or semi-automatic
camera is entirely satisfactory, and the great expense of complicated
automatic apparatus has no longer its former justification.
=Camera Suspension.=—Perhaps the most pleasing prospect before the
aerial photographer as he turns from war to peace work is that of having
planes built for and dedicated primarily to photography. Instead of his
camera being relegated to an inaccessible position, picked after the
plane design has been officially “locked;” instead of yielding first
place to controls, machine gun and ammunition; instead of being
jealously criticised for the space and weight it takes up, the camera
can now claim space, weight, and location suitable for any likely aerial
photographic need. High speed no longer will be vital, and slower
planes, permitting longer exposures in inverse ratio to their speed,
will be chosen for photographic purposes.
A development which is sure to intrigue many investigators is the
gyroscopically controlled camera. This has its chief _raison d'être_ in
precision mapping, whose possibilities from the air will undoubtedly be
intensively studied at once. With the automatically leveled camera will
come renewed attention to indicators of time, altitude, and direction,
with the ultimate goal of producing aerial negatives that show upon
their face the exact printing and arranging directions necessary to put
together an accurate map.
=Sensitive Materials.=—Manufacturers of plates and films will direct
efforts toward producing emulsions of good contrast, high color
sensitiveness and high effective speed, especially when used in
conjunction with the filters necessary for haze penetration. Exposure
data will be accumulated and exposure meters appropriate for aerial work
will be developed.
=Color Photography.=—Color photography from the air by any of the
screen-plate or film-pack methods is probably out of the question
because of the long exposures required. The screen-plates are unsuitable
also because of the relatively large size of their grain compared to the
detail of the aerial photograph. Ordinary three-color photography, using
three separate negatives, is always subject on the earth's surface to
the difficulty that the three negatives must be exposed from the same
point of view, either in succession or by means of some optical
arrangement which is costly from the standpoint of light. In
photographing from the air this difficulty of securing a single point of
view for the three photographs is absent. Three matched cameras, side by
side in the fuselage, have identical points of view as far as objects on
the earth below are in question. Consequently, three-color negatives are
entirely possible, and indeed will be simple to make as soon as plates
of adequate color sensitiveness and speed are available. Probably the
new Ilford panchromatic plate has the necessary qualities.
=Night Photography.=—The searching eye of photography was so omnipresent
in the later stages of the Great War that extensive troop movements and
other preparations had to be carried out either in photographically
impossible weather or else at night. The natural reply to the
utilization of the cover of night is to “turn night into day” by proper
artificial illumination. At first thought it might well appear that the
task of illuminating a whole landscape adequately for airplane
photography is well-nigh hopeless by any artificial means. On one hand
we have the very short exposures alone permissible; on the other the
fact that the intensity of daylight illumination is overwhelmingly
greater than those common in the most extravagant forms of artificial
illumination.
Toward the close of the war, however, actual experiments made with
instantaneous flashes of several million candlepower showed that if
proper means were provided to insure the flash going off near the
ground, and if its duration were made no longer than about 1/50 second,
interpretable photographs were obtainable on the fastest plates. It
appears, therefore, merely a matter of manufacturers perfecting the
technique of flash production, and of inventors providing the launching
and igniting devices to push this kind of photography to the practical
stage. The achievement of night photography cannot fail to have an
enormous effect on future tactics.
The technique of night photography may take either of two directions. On
one hand we may develop flashes of the requisite intensity to give all
their light in 1/100 second; on the other hand, it may prove more
feasible to use flashes of longer duration and to arrange for the camera
shutter (of the between-the-lens type) to be exposed synchronously with
the middle of the flash. One way, frequently suggested, to use these
longer flashes would be to trail the charge on a long wire, through
which the ignition is effected electrically. This is not likely to be
satisfactory, however, for the resistance of a wire is so great that
when the plane flies at any practical height, the trailed flash, if it
reaches near the ground, will be forced to a very great distance behind.
Probably the best solution will involve accurate synchronizing of the
fuse in the freely dropped sack of flash powder with the exposing
mechanism in the camera.