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Figure 2-10 Spread roller system
The basic theory of the lm processing method
remains unchanged from previous Polaroid
system. That is , the developping chemistry is
encapsuled in a pod on each sheet of lm and,
as the sheet is passed between rollers, the
pod is burst and the chemical spread evenly
between the negative and the mylar protective
cover. Except for this characteristics, no direct
similarities exist. The SX-70 camera employs a
unique process which totally eliminates the «throw
array» negative. The print is drawn through the
spread rolls by the motor drive system so that
no action need be taken by the operator. See
Figure2-10. Development takes place outside
of the camera and unaffected by ambient light
conditions. Since the end result is determined
when the picture emerges from the camera, no
time measurement si necessary. (Additional lm
information is available on page 60 and 61 of
«The world of SX-70»)
The operator pushes S1, applying full power to
solenoid #1, which closes the shutter blades,
and pushed solenoid #1 against S4, changing it
from CA to CB. Closing CB cuts solenoid #1’s
power from high to low; low is enough to hold the
blades closed. Closing CB also signals the ECM
to start the motor. The motor starts the gear train
moving. The movement of a cam on cam on the
gear train releases the recock ram and, through
G. FILM PROCESSING COMPONENTS
H. SEQUENCE OF OPERATIONS
spring action, raises the Fresnel carrier. When
the recock rammoves, it opens S5 and then S3
at certain Fresnel carrier angles. Opening S5
stops the motor after it has made only a brief jog.
Opening S3 starts the «Y» delay : 40 milliseconds
delay which allows the Fresnel carrier to come
to rest after its travel. (This eliminates bouncing
caused by the sudden stop of the carrier on the
mirror cover.)
At the end of the «Y» delay, power is removed
from solenoid #1, allowing the spring to open the
shutter for exposure, and moving S4 from CB to
CA position. When the proper exposure level is
reached, the photocell trips the Schmitt Trigger
(S/T) in the ECM which sends full power to
solenoid #1. This closes the blades and tranfers
S4 from CA to CB. As before, closing CB cuts
solenoid #1’s power from full to low, sufcient to
hold the blades closed; closing CB also signals
the electronics to start the motor.
The motor starts the gear train again, and this
time the cams cause a series of actions at
different position of gear train movement :
- it starts the pick which pulls the lm into the
rollers (one of which is attached to gear train it
is this powered roller rotation that pulls the lm
through and out of the camera);
- it stops the pick;
- it pulls down the Fresnel carrier, which in turn,
moves the counter to the next number;
- it moves the recock ram, closing S3 (resetting it
for the next cycle);
- it retruns the pick;
- it seats the Fresnel carrier so it is ready for the
next cycle;
- it moves the recock ram, closing S5, which
stops the motor;
- and it stops the spred action.
When S5 closes, it cuts power to the solenoid #1;
the spring opens the shutter blades, and S4 is
pushed from CB to CA. (The blades open only
if the operator releases the red button.) The
system is ready for a new exposure cycle.
Springs are used in three of the operations
discussed above : holds the shutter blades open,
lps the Fresnel carrier up, and holds the pick at
the rest position.
As indicated, inserting a lm pack causes
automatic action. This could, of course, be a