Polaroid SX70 manual

mechanical coupling device set the exposure counter to the position just before the first exposure and closed S8, but since S7 has removed all battery power no action occurs).

d- The operators closes and latches the front cover. S7 closes, power is apllied and the camera eject the dark slide.

NOTE : During this action (and in certain other operations) other switches actuate and functions occur but, unless they contribute to the paticular camera function being described, they are omitted from the discussion).

The counter indicates exposures #10 (and opens S8) thereby showing that the camera is ready to take first picture.

e- The operators aims, focuses the lens, and presses the red shutter release button (S1). The ECM actuates solenoid #1 which closes the shutter blades. Solenoid #1 transfers the S4 contacts from CA to CB, which in turn, switches the circuit from full solenoid power to holding current (power-down). Closing contacts CB of switch S4 also starts the drive motor. Opening S4 (CA) removes power from the FFA.

f- As the gear train runs, it mechanically releases the spring-loaded Fresnel carrier so that it leaves the film plane and rises to its exposure position. This is accomplished by the mirror release cam of the recock gear. the recock ram falls off the recock cam, allowing the ram to snap forward. This allows the drive spring to raise the Fresnel assembly to the exposure mode. The ram also moves away from S5 allowing S5 to open. This action causes the ECM to dynamically brake the motor which will remain at the rest throughout the exposure segment of the cycle. The S5 switch action also programs the ECM to complete the cycle even though the operator has released the exposure button after S5 is open.

NOTE : there would appear to be a contradiction between this step and the step j-10 below wherein closing of S5 performs the identical function, i.e, stops the motor and applies braking. S5 is able to perform in this manner, however, because the circuit (gate) to which it is connected is in a different condition during each of the steps.

g- While the Fresnel carrier was moving up prior to motor shutdown, the recock ram opens switch S3. When S3 opens, it signals the ECM to initiate a 40 millisecond delay in the sequence. This amount of time prevents a picture from being

taken until mirror bounce has subsided.

h- At the end of the 40 millisecond delay period, the ECM removes power from solenoid #1 and the shutter opens. Simultaneously, the circuit starts timing the exposure (integration). The integration components of the ECm are controlled by the amount of light received by the photocell. At this time, the flash delay section of the ECM is made ready but will not function unless a flashbar has been plugged in, to close switch S2.

i- When power is removed from solenoid #1 (and the shutter begins opening), the actuator on the plunger returns switch S4 to its original condition (CA closed); When the exposure timing cycle is complete, power is returned to solenoid #1 and the shutter closes, opening CA, closing CB, placing solenoid #1 again in the power down condition and starting the motor to eject the exposed film.

NOTE : the lenght of, the timing cycle is determined in amount of the light reaching the photocell. If there is insufficient light to correctly operate the integration circuits, the system will automaticall terminate the exposure within 14 to 30 seconds.

j- When, in the previous step, the solenoid closes the shutter blades and drive motor is energized, the gear train resumes its sequence with the following results :

1.The film pick feeds the exposed film to the spread rolls.

2.At the end of its travel the pick uis held in its forward position by the pick latch.

3.Film moves through the spread system.

4.The recock gear cam proceeds to retrun the recock ran which, through the bell crank, moves the Fresnel carrier down.

5.The recock ram closes switch S3 to prepare for another exposure.

6.The light stop opens the optical path to the viewfinder.

7.The film completes its passage through the spread rollers. The front cover idler gear meshing with the gear train powers the top roller which drives the film through the exit slot.

8.The Fresnel carrier when fully scated is held by the recock ram.

9.The pick latch releases the pick and the pick returns to its starting position.

10.The recock ram closes S5 to cause the ECM to shut off and dynamically brake the drive motor.