2.6 FILM TRANSPORT 
Conventional mechanisms for film transport in metric cameras typically 
employ an assemblage of gears, cams, levers, solenoids and springs. By con- 
trast, the CRC-1 does away entirely with such complex mechanical assemblies 
and uses instead a modern digitally controlled, direct drive system. Film 
transport is actuated by a small, but powerful gearhead motor mounted in the 
magazine itself. The drive shaft of the motor is connected by a timing belt 
to the shaft of the film spindle. A rotary optical encoder coupled to the 
take-up film roller generates 1024 pulses per revolution of the film roller. 
These pulses are transmitted to a digital counter. Output from the counter 
controls the film transport motor in one of two optional modes. In the 
full-advance mode, the film-flattening vacuum is turned off and the drive 
motor is actuated until the film has moved 275 mm, a distance sufficient to 
assure that no film that had been resting on rollers is transferred to with- 
in the photographic format. Advance of a full frame takes two seconds. In 
the incremental-advance mode, the vacuum is turned off for an instant and, 
within a fraction of a second, the film is advanced 1.0 mm,. whereupon 
another exposure can be made on the same frame. This process of incremental 
advancing (which is normally exercised for multiple exposures of retroreflec- 
tive targets) can be continued indefinitely, the practical limits being set 
by the buildup in the exposure of the photographic background. Such buildup 
results from a combination of ambient light exposed with each opening of the 
shutter and the cumulative effect of flashes from the ring strobe. 
Power for the CRC-1 is provided by an external 12 volt, rechargeable 
gel-cell battery weighing three kilograms. When power is switched on, film 
is automatically advanced one frame, and the film-flattening vacuum is 
turned on. The vacuum pump is located inside the film magazine. All 
internal functional sequences are automatically controlled by an integrated 
circuit board in the magazine. The circuit board accepts operational 
commands from an external, hand-held control unit. With the switch set in 
the normal 'on' (or full-advance) mode, the following sequence of events 
occurs when the shutter is actuated by a cable release. 
(1) The shutter is opened. 
(2) A strobe light (if used) is flashed at full opening of the 
shutter. 
(3) The fiducials are exposed. 
(4) The electroluminescent panel in the platen is turned on 
for a sufficient time to expose the reseau images. 
(5) After the completion of (4) the vacuum pump is turned 
off and the film is advanced to the next frame. 
(6) The vacuum pump is turned on and remains on until either 
the power is turned off or the shutter is released, thus 
repeating the cycle. 
When the switch is set for the incremental advance (or jog) mode, steps 
(1) through (4) are executed as above, but in step (5) the advance is only 
a single step of 1.0 mm. Each time the shutter is released, an incremental 
advance occurs, and the fiducials are exposed. However, the reseau images 
are exposed automatically only upon the initial release of the shutter; 
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