TM 11-6720-242-35
tour of the cam is such that the lens assembly is moved
network applies a proportionately smaller portion of the
forward and backward at rates which conform to the
aec output voltage to the chopper amplifier.
angle of the prism position. The dragbrake exerts a
(4) For all light conditions, the chopper amplifier
drag torque of 1.0 + 0.5 ounce-inches on the shaft
compares the aec output voltage, from the photocell,
rotation. The counterweights, which oscillate about the
with the feedback voltage (dc) from the aec feedback
pivot arms, counteract the force created by the moving
potentiometer R1. If these two de voltages are not
mount, lens, and aperture.
equal, the chopper amplifier converts the difference to
b. The electrical circuits which control the action of
an ac signal voltage and applies it to the input of the aec
the imc mechanism are illustrated in figure 2-3.
servo amplifier. The amplifier ac output voltage of the
Regulated +22vdc is applied to the winding of solenoid
aec servo amplifier is applied to the aec motor B1 as an
L1. The other end of the solenoid winding is connected
excitation voltage.
to the collector of driver transistor Q4. Regulated +
(5) Increasing the light intensity to the photocell
22vdc is applied to the base of Q4 and when Q4
causes aec motor B1 to close the slit and mechanically
conducts, the circuit through the solenoid is closed and
reposition the arm of the aec feedback potentiometer,
by the resulting magnetic action the lever slides the
thus changing the magnitude of the feedback voltage to
coupling into engagement with the rotating gear.
the chopper amplifier. When the feedback voltage is
c. The regulated +22vdc is applied to the base of
equal in magnitude to the aec output voltage applied to
transistor Q4 through mode relay K3, operate relay K2,
the chopper amplifier, the ac output voltage of the
and CAMERA SEL switch S4 when the camera is
chopper amplifier is at a very low magnitude. This
operating in the autocycle mode. Relay K3 is energized
causes the aec motor B1 operation to stop, holding the
when the v/h input level governing the mode of
slit at an opening proportional to the amount of light and
operation sets the camera for autocycle operation.
the v/h command voltage. When the slit reaches its
When the v/h input drops below the gradient of
minimum opening; the mechanical linkage starts to
autocycle operation, mode relay K3 is deenergized and
close the aperture. If the light intensity level is high and
imc automatically ceases.
starts decreasing, the aperture opens until it reaches its
maximum limit (f/2.8). When the aperture reaches its
2-9. Functioning of Drive Mechanism
maximum limit the mechanical linkage opens the slit.
2-8. Functioning of Image Motion
a. Body Drive Mechanism. The drive mechanism,
Compensation
transports film, rotates the prism, and maintains timing
The camera contains an image motion compensation
relationships, is housed in the body and the magazine.
(imc) mechanism which permits the lens to move across
Excitation voltage from the scan drive circuits (para 2-
the focal plane, as a function of scan rate, to eliminate
10) causes the scan motor B1 (1) to rotate. The scan
image motion during exposure. Imc functions only in a
motor gear (2) drives the tach gear (3) causing the
vertically mounted camera and while the camera is
tachometer (4) to rotate and generate a voltage applied
operating in the autocycle mode.
to the chopper amplifier (fig. 6-16) which is proportional
a. The imc mechanism (fig. 24) consists of a shaft
to the speed of the scan motor shaft. The pinion (5) of
assembly and a solenoid and lever assembly. The shaft
the scan motor gear drives an idler gear (6). The pinion
assembly includes an imc cam, a dragbrake, a coupling,
(7) of the idler gear (6) meshes with gear (8). Pulley (9)
a gear, and a shoulder shaft. The cam is pinned to the
drives pulley (10) via a belt (11). The linkage gear (12)
end of the shaft and it inserts into a cam follower on the
delivers mechanical power to the magazine input gear
carriage which supports the lens assembly. The gear is
(13). The pinion (7) of idler gear (6) also meshes with
freewheeling and it rotates continuously in a gear train
the idler gear (14). The rear pinion (16) of idler gear
that is driven by scan motor B1. A solenoid is mounted
(14) meshes with gear (17) which, when the solenoid
below the shaft with the yoke of the associated lever
(18) is energized, engages and rotates the imc cam (19)
engaged in coupling. When the solenoid is actuated,
causing the lens assembly (20) to perform imc
the lever causes the coupling to mesh with the rotating
gear. The con
2-8
