NON-AUTOMATIC AERIAL PLATE CAMERAS
The ideal of every military photographic service has been an automatic
or at least a semi-automatic camera, in order to reduce the observer's
work to a minimum. Yet as a matter of fact almost all the aerial
photography of the Great War was done with entirely hand-operated
cameras. The primary reason for this was that no entirely satisfactory
automatic cameras were developed, cameras at once simple to install and
reliable when operated. Even the propeller-drive semi-automatic L type
of the British Air Service was very commonly operated by hand, for many
of the pilots and observers regarded the propeller merely as another
part to go wrong.
Any automatic mechanism in the airplane must work well in spite of
vibration, three dimensional movements, and great range of temperature.
The requirements were well recognized when the war closed, but had not
yet been met. Careful study of the conditions and needs by competent
designers of automatic machinery may be expected to result at an early
date in reliable cameras of the automatic type, but the description
below of hand-operated cameras really covers practically all the cameras
found satisfactory in actual warfare.
=General Characteristics of Hand-operated Cameras.=—As distinguished
from the hand-held cameras the larger hand-operated cameras are
characterized by the greater focal length of their lenses, the size of
plate employed, and the manner of holding—by some form of anti-vibration
mounting attached directly to the fuselage.
Except for the early English C and E type cameras which called for 10
inch lenses and 4 × 5 inch plates, the general practice at the close of
the war by agreement between the French, English and American Air
Services, was for the use of 18 × 24 centimeter plates and for lenses
with focal lengths of approximately 25, 50 and 120 centimeters. The
English also made use of a 14 inch (35 centimeter) lens, and never made
a regular practice of anything larger than 50 centimeters. The Germans
and Italians restricted themselves to the 13 × 18 centimeter size of
plate, while a lens of 70 centimeters focal length was standardized with
the Germans, in addition to the 25, 50, and 120 centimeter.
The particular focal length was determined by the nature of the
photographic mission. Where large areas were to be covered at low
altitudes or without the demand for exquisite detail, the shorter focus
lenses suffice. The most commonly used lens in the French Service was
the 50 centimeter, while the 120 was employed when high flying was
necessary or when minute detail was required. As already mentioned, the
common practice was to keep cameras of all focal lengths available, but
the ideal at the close of the war was to have the camera nose and lens a
detachable unit, so that any focal length desired could be secured with
the same camera body.
_The standard French camera._ The hand-held form of French camera has
already been described. The cameras for larger plate sizes and longer
focus lenses differ only in the addition of a Bowden-wire distance
release for the shutter and in the use of the Gaumont magazine which
operates without the necessity of pointing the exposed side of the
magazine upward. Fig. 40 illustrates the 50 centimeter camera, and Fig.
41 the 120.
[Illustration:
FIG. 40.—50 centimeter deMaria hand operated camera on tennis ball
mounting.]
[Illustration:
FIG. 41.—120 centimeter deMaria camera.]
_The German Ica cameras._ These are larger editions of the light wood
hand camera already described, but with the addition of a Bowden-wire
shutter release. The body of the larger cameras carries a distinctive
feature in the distance control of the lens diafram, worked by means of
a lever which actuates racks, pinions and connecting rods leading to the
lens. On the side of the camera body a shallow box is provided for
carrying the color filter in its bayonet joint mount to fit on the lens
(Figs. 42 and 43).
[Illustration:
FIG. 42.—German aerial cameras.]
[Illustration:
FIG. 43.—Diagram of German 50 centimeter camera.]
[Illustration:
FIG. 44.—U. S. hand-operated aerial camera (type M) with 10 and 20
inch cones.]
_The hand-operated bag-magazine camera_ of the United States Air Service
(Type M) is similar to the small hand-held camera, but differs in three
respects: a removable shutter (of the variable-tension fixed-aperture
type) embodying an auxiliary curtain for capping during the setting
operation; a Bowden-wire shutter release; and the employment of a set of
standard interchangeable cones to hold lenses of several focal lengths.
The 20 inch and 10 inch cones are shown in Fig. 44. The operation of
this camera is similar to the French standard cameras, but not so simple
because of the number of motions required in manipulating the bag. Its
chief objection for war work lies in fact in the magazine, which should
be superseded by a two-compartment or other satisfactory type of plate
changing chamber. The camera alone, with 20 inch cone, weighs
approximately 40 pounds; the loaded magazine, with its plates in metal
sheaths, 15 pounds.
[Illustration:
FIG. 45.—English C type aerial camera.]
_The English C and E type cameras._ The C and E type cameras have now
chiefly an historic interest. They were the first used in the English
service, fixed to the fuselage, and were later used in training work in
England and in the United States. They were never built for plates
larger than 4 × 5 inch nor for lenses of more than 12 inch focus, a
limitation set by the lenses available at the time of their design.
[Illustration:
FIG. 46.—English type “E” hand-operated plate camera.]
In several respects the mode of operation of the two types is the same.
The unexposed plates are held in a magazine lying above the camera, in
the axis of the lens (Fig. 32). After exposure the bottom plate is
carried to one side and allowed to fall by the action of gravity into
the receiving magazine. In the C type (Fig. 45) an opaque slide is drawn
between the lens and the (variable-opening) shutter during the setting
operation. During the exposure period this slide projects into a
compartment on the opposite side of the camera from the receiving
magazine, thus making the camera mechanism three plates wide. In the E
type (Fig. 46), a flap over the lens makes it possible to dispense with
the sliding screen, and reduces the camera to about the width of two
plates. In the C type the plates are changed by a handle on top of the
camera; in the E type provision is made for distance control by cords,
and for shutter release by a Bowden wire. In both cameras the operation
of plate changing also sets the shutter, a definite advance over the two
preparatory motions in the French apparatus. The C type was constructed
of wood, the E of metal.
[Illustration:
FIG. 47.—Italian (Piserini and Mondini) two compartment magazine
hand-operated camera.]
_Italian two-compartment magazine camera._ A camera designed by Piserini
and Mondini was used to some extent by the Italian service toward the
close of the war (Fig. 47). This has the desirable feature just noted in
the C and E cameras: the operations of plate changing and shutter
setting are performed in a single motion. Unlike those cameras, however,
the plates are changed from one compartment to another of the magazine
already described, without dependence on gravity, by an entirely
positive shifting action. The setting of the self-capping focal-plane
shutter is accomplished by a projecting finger engaging the shutter
mechanism. Cameras of this general type, built for 18 by 24 centimeter
plates, with interchangeable lens cones, removable shutters, and
preferably magazines in which the center of gravity does not shift as
the plates are changed, represent the next step in advance of the French
practice, and may indeed prove all that is necessary or desirable in
camera complexity for peace-time photography from the air.
_The standard Italian camera and similar types._ The camera (Lamperti)
which the Italian Air Service used almost exclusively during the war
exemplifies a type quite different from anything as yet described (Figs.
48 and 49). Plates to the number of twenty-four (13 × 18 cm.) are loaded
into a chamber at the top of the camera. Each plate is held in a septum
furnished with projecting lugs at one end. A lever acting through a
Bowden wire, exposes the bottom plate, which then swings downward about
these lugs as pivots, and is forced by a pair of fingers into a
compartment at the side. The between-the-lens shutter has a single speed
of 1/150 second, and variation of exposure is achieved by altering the
lens aperture.
[Illustration:
FIG. 48.—Various plate changing devices.]
The great advantage of this camera is its simplicity, a single motion
performing all the operations. Its disadvantages are its dependence on
gravity for operation, its between-the-lens shutter, the limitation set
to the number of exposures, and the necessity for removing the whole
camera to take out the plates for developing. In actual practice the
camera has worked out well. The better light found in the Italian as
contrasted with the northern theatre of war makes the between-the-lens
shutter at high speed adequate, while the limitation to the number of
exposures has been met by carrying several complete cameras in each
plane. Because of the Bowden-wire operation these cameras need not be
accessible to the observer or pilot, so that the practice of carrying
them in single-seaters was common. Attempts at standardization of Allied
practice through the adoption of standard lens cones were, of course,
out of the question with this camera. With its limitations of shutter
efficiency and plate size it is doubtful whether it would have been
satisfactory outside the service for which it was developed.
[Illustration:
FIG. 49.—Italian (Lamperti) single-motion plate camera, on
anti-vibration tray.]
The limitations set by the between-the-lens shutter in this type have
been overcome in an experimental camera along similar lines made by the
Premo Works of the Eastman Kodak Company, and in the French Aubry model
(Fig. 48). These employ focal-plane shutters which swing out of the way
and are set as the exposed plate swings or drops to the receiving
chamber. The dependence on gravity in this type could doubtless be
avoided by positive finger mechanisms. If so, the resultant cameras, set
and exposed by a single motion, would acquire a highly desirable
simplicity of operation. They would have peculiar merit because of the
very short interval required between exposures—a characteristic needed
for making low stereo-oblique views. The cameras just mentioned have,
however, departed far in form from the lines of standardized practice
and have not been followed up.