2-1. Functioning of Camera
this signal as the cycling rate must be proportion to the
height above the terrain to photograph the entire line of
flight with a 60-percent overlap. In autocycle mode the
a. General. The function of the camera is to take
cycling rates start above 1 cycle per second and are
photographs from high
continuously variable to 8.5 cycles per second. In the
speed, low flying aircraft. The camera may be mounted
pulse mode the camera operates 1 cycle every 4.5
in an aircraft with the lens positioned to face either
seconds up to 1 cycle per second above which it
vertically downward or in a forward oblique direction at a
automatically switches into the autocycle mode.
20-degree angle of depression. In either mounting, the
ground beneath the aircraft is photographed sequentially
rotating the double-dove prism in front of the lens and
from horizon to horizon, with a 60-percent overlap.
by simultaneously advancing the film past the slit
Image motion compensation (imc) is provided to offset
(shutter) in the focal plate. The film advance and the
the blurring effects of the aircraft flight. Correct film
prism rotation are synchronized to paint the image on
exposure is maintained by an automatic exposure
the film as the prism scans a 90-degree angle from
control (aec) circuit.
The operational modes are
horizon to horizon.
autocycle and pulse. The changeover to either mode of
(1) The mirror effect of the prism's
operation is determined by an E V/H voltage (the ratio of
doubledove is an angular displacement which produces
ground speed (V) and altitude (H) to voltage (E))
an optical scan angle of 180 degrees. Before starting a
generated by the aircraft equipment.
90-degree photographic scan the prism rotates through
b. Major Photographic Components (fig. 214).
The optical system includes the following components:
degree photographic scan the prism then rotates
(1) A 3 inch, 75mm, f/'2.8 lens assembly.
through a 45-degree deceleration angle. In one cycle
(2) A double-dove prism which rotates in front
the prism and a lift cam both rotate 180 degrees.
of the lens on an axis parallel to the direction of flight.
(2) A continuously rotating rubber covered
(3) A focal plate having an exposure slit
cylinder (puck) advances the film past the slit in the
which is automatically adjusted via the shutter blade, to
focal plate coordinately with the 90-degree scan angle of
vary the slit width.
the prism by the operation of a pressure roller which is
(4) A variable aperture which operates in
actuated by the lift cam which is rotating in synchronism
association with the shutter blade.
with the prism. Immediately following the 45-degree
(5) An automatic exposure control (aec). (A
servo system which positions the shutter blade and the
made to press the film into frictional contact with the
puck by the lift cam. Upon completion of the 90-degree
(6) Image motion compensation (imc). (A
scan angle of the prism, the pressure roller is no longer
device which moves the lens back and forth parallel to
actuated by the lift cam and film advance ceases. Film
the exposure slit. The action is limited to vertically
velocity at the focal plate is 19 inches per second at 1
mounted cameras and to the autocycle mode of
cycle per second. The velocity is a product of scan rate
and focal length. Photography is continuous until the
c. Camera Operation. The autocycle or pulse
end of film is reached, the film breaks, or the equipment
mode of operation is determined by an E V/H signal
is turned off. However, single pictures may be taken
voltage which is generated by the aircraft equipment.
between pulses with the OPERATE switch set to OFF, if
Optical scan rates are derived from
the camera is oper-