Polaroid ProCam Repair Manual page 18

At the start of the exposure cycle, when Solenoid 1 is energized, the Walking
Beam releases the Quintic Kick Spring. This Spring strikes the Quintic sector
causing it to start its arc through the optical path; obviously, the Shutter Blades are
still closed during the movement of the Quintic sector.
Along the edge of the Quintic sector is a series of teeth and cutouts in the plastic
frame. On one side of the plastic frame is a LED and on the other side is a photo-
transistor which detects light from the LED. These two devices are part of the
encoder circuit. As the cutouts in the frame pass between these two devices, the
encoder circuit counts the pulses resulting from the interruptions of the light beam
between LED and photo-transistor. (The first pulse is the First Light Detect which
is the starting marker for all exposure calculations.) These pulses correspond to
the ten focus zones created by the interaction of the aspheric lenses.
CATCH PAWL
SOLENOID 1
DRIVE LINK
Figure 1-9. Quintic Lens System Starting Conditions
DRIVE
LINK
WALKING
BEAM
Figure 1-10. Kick Spring Starts Quintic Lens Motion
WALKING BEAM
KICK
SPRING
1 - 12
MOVING QUINTIC LENS
ENCODER LED
INERTIA
SOLENOID 1
ENERGIZED