PLATE-HOLDERS AND MAGAZINES
In the earlier days of airplane photography the ordinary plate-holder or
double dark slide was used to some extent, but it is ill-suited to the
purpose because of the considerable time and attention required for its
operation. It has nevertheless the merit of adding little to the length
of the camera, and it works in any position. For these reasons it has
remained in occasional use for the taking of oblique views with long
focus cameras in a cramped fuselage.
Next in order of progress rank the simple box magazines, for holding a
dozen, eighteen or twenty-four plates, as used in the English C, E, and
L type cameras. These are little more than boxes with sliding lids which
when open permit the introduction or removal of the plates. Figs. 45 and
46 illustrate the magazine of this type as made for the English C and E
cameras. It is constructed of wood, grooved to fit tracks on the camera,
and is furnished with a sliding door or lid hinged in the middle to fold
down out of the way when open. The eighteen plates are carried in metal
sheaths, both to provide opaque screens between them, and to protect
them from injury in the mechanism of the camera. Fig. 27 shows the
all-metal magazine made for the American model L camera. This differs
from the English in material of construction, plate capacity (24 instead
of 18) and manner of operating the slide, which is built up of three
thicknesses of phosphor bronze and draws out through metal guides bent
into semicircular form. A snap catch holds this slide at either end of
its travel. The leather strap introduced in the American model for
carrying and handling is a distinct improvement. These magazines contain
no springs or other mechanism, as the cameras with which they are used
depend upon the action of gravity for emptying the upper (feeding)
magazine, and filling the lower (receiving) one.
[Illustration:
FIG. 31.—Aerial hand camera (U. S. type A-2).]
Next in order of complexity may be ranked the _bag magazine_ (Figs. 31
and 44). In this the exposed plate is pulled out of the magazine proper
by a metal slide or rod into a leather bag. The rod is then pushed back,
the plate in its metal sheath is grasped through the leather bag, lifted
to the back of the magazine, and forced in behind the other plates. The
number of plates exposed is indicated either by numbers on the backs of
the sheaths, visible through a red glazed opening in the back, or else
by a counter actuated by the metal slide rod. Usually twelve are carried
in a magazine. For aerial work the common design of this magazine as
used for ground work must be modified by providing extra large easily
grasped hooks both on the draw rod and on the dark slide, which must be
drawn before making the first exposure and replaced after the last. The
small rings and grips of the standard commercial magazine are almost
impossible to handle through heavy gloves.
The next type of magazine is represented by three designs, the _Gaumont_
and _deMaria_, used very generally by the French during the war, and the
_Ernemann_, used almost universally in the German air service (Figs. 32,
40 and 42). In all of these the operation of plate changing is the same:
the end of the magazine is pulled out and thrust back, a more simple
operation than the bag manipulation just described. The internal
workings are different according to size. In the smaller French
magazines (13 × 18 cm.) the camera is first pointed upward, all the
plates are drawn out except the one to be changed, and this, with the
aid of springs, drops to the bottom, after which the other plates push
back over it. The plates pull out in the direction of their long
dimension. In the larger French magazine (18 × 24 cm.) only the exposed
plate pulls out. The pull is in the direction of the shorter dimension
of the plate, which is lifted up by heavy springs and slides back over
the top of the pile. In the Ernemann magazine only six plates are
carried, which there is good reason to believe represent the maximum
feasible number, judging by the reports of jambs and breakages in the
twelve-plate French magazines. In all of these magazines laminated wood
slides pull out and in at each operation, and while satisfactory if made
and operated in one climate, experience indicates that if made in
America and sent abroad swelling of the wood may be expected to prevent
their successful operation.
[Illustration:
FIG. 32.—Various plate magazines used on aerial cameras.]
Alternative forms of magazine, somewhat more practical from the
standpoint of manufacture and export, are several designs embodying _two
compartments_ (Fig. 32). In the most simple of these the plates are
moved, immediately before or after exposing, from the unexposed to the
exposed side. Illustrative of this type are the Folmer designs, in which
the to-and-fro motion is imparted by a rack geared to a pinion actuated
either by a lever, in the hand camera, or by the power drive, in the
automatic design (Figs. 33 and 53). Another illustration is afforded by
the Piserini and Mondini magazine, in which the operation of changing is
performed by a back-and-forth motion of a hand-grip, which also sets the
camera shutter (Fig. 47).
[Illustration:
FIG. 33.—U. S. Air Service hand camera, with two-compartment magazine.]
[Illustration:
FIG. 34.—Film type hand camera.]
In these magazines the center of gravity changes as the exposed plates
are moved over, and only half the inside space is occupied with plates.
These objections are overcome in the Chassel form, where both
compartments are always full. Transfer of the bottom exposed plate from
one compartment to the other is compensated for by the simultaneous
shift of the top plate in the receiving compartment, to the feeding
side. In a modification of this idea by Ruttan the exposing position is
when the plates are half-way through the shifting process, whereby the
magazine may be symmetrically mounted on the camera body.
[Illustration:
FIG. 35.—Apparatus for straightening plate sheaths.]
Other more complicated magazines have been designed, some of which are
shown in the diagrammatic _ensembles_ of Figs. 32 and 48. In the
Jacquelin, the main body of plates is raised while the bottom (exposed)
plate is folded against the side. The main body of plates then drops
back to place, the exposed plate is carried on upward and folds down on
the back of the pile. The Bellieni magazine system uses three, a central
feeding one and two below for receiving, one on each side of the camera
body. These were made solely for attachment to captured German cameras.
In the Fournieux magazine the plates are carried in an interior rotating
box. The plate to be exposed is dropped off the front of the pile, down
to the focal plane, and after exposure is picked up and placed at the
back of the pile, which has turned over in the meanwhile. The deRam
rotating magazine is described in connection with the camera of which it
is an essential part (Fig. 52).
[Illustration:
FIG. 36.—Training plane equipped for photography, showing “L” camera
in floor mount and magazine rack forward of the observer.]
For the protection of the plates during their manipulation, and in the
camera, all plate magazines thus far developed carry them in thin _metal
sheaths_. These add greatly both to the weight and to the time necessary
to handle the plates, but no means have as yet been found for dispensing
with them. Fig. 35 shows a representative sheath or septum, as used in
the L camera. On three sides the edge is bent up and turned over,
forming a ledge for the plate to press against. The fourth side is left
open for inserting the plate, which is then held in by a small upward
projecting lip, and kept close against the ledges by narrow springs at
the sides. To insert or remove the plate the projecting lip is
depressed, either by springing the sheath by pressure from the sides or
by using an appropriate tool.
_Care of sheaths._ Unless systematically taken care of, plate sheaths
become bent or dented. They are then a menace to camera operation,
catching or jamming in the plate changing process, breaking plates and
damaging camera mechanisms. In order to maintain them flat and true,
steel forms are necessary on which the sheaths may be hammered to shape
with a mallet (Fig. 35).
_Magazine racks._ Reconnaissance and mapping call for a number of
exposures much greater than the capacity of one 12, 18, or 24 plate
magazine. Additional magazines must therefore be carried. These should
be in racks convenient to the observer (Fig. 36), securely held yet
capable of quick removal and insertion. In the rack designed to carry
two of the metal magazines for the American L Camera, the magazines
slide into loose grooves formed by a metal lip. They are prevented from
slipping out by a spring catch, past which they slide when inserted but
which is instantly thrown aside by pressure of the thumb as the hand
grasps the magazine handle for removal.