Polaroid ProCam Repair Manual page 35

With the Shutter Blades opened to the proper aperture, strobe firing now occurs.
(If the Strobe is turned off, exposure will be determined by light integration or a
maximum time-out of 2.8 seconds). Strobe fire duration is dependent on the
integration of the Transducer camera-to- subject distance information and light
measurement information. If the subject is more than 14 feet away, the Strobe
may be fully discharged.
As previously mentioned, ProCam exposure measurements are a combination of
the best features of the Spectra system. The dual-cell photodiode measures all
visible white light which is the primary contributor to ambient exposure
calculations. It also measures the infrared component of the reflected strobe light
which is the primary contributor to strobe exposures (Figure 1-32). Electronic
mixing of the proper amount of each of these light sources provides optimum film
exposure by precisely determining when to fire the Strobe, when to turn it off, and
when to close the Shutter Blades.
DUAL CELL
PHOTODIODE
Figure 1-32. Measurement of Visible Light and Infrared Light
When the light measurement determines that the Strobe should be shut down, a
pair of series thyristors in the Strobe circuit acts to save any unused energy remain-
ing in the flash capacitor. This departure from previous Polaroid strobes results in
a shorter recharge time for the succeeding exposure.
When the exposure cycle is completed, the logic circuits again energize Solenoid 1
(Figure 1-35).
LIGHT MEASUREMENT
CIRCUIT
1 - 29
PHOTODIODE
FILTER