Polaroid Joshua Captiva, Service Manual

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Unique Microprocessor-Controlled Exposure System (Figure 1-5)
Significant improvement in exposure accuracy and picture sharpness, under virtually every conceivable
picture-taking condition, has been achieved in the Joshua. The Camera uses entirely new methods of
measuring and controlling the ambient and strobe contributions to exposure, and optimizing the shutter
aperture at which the exposure is made. Advances in integrated circuit technology permit measuring and
combining, in microseconds, the IR and visible ambient photometer readings. Ambient brightness is also
measured prior to exposure.
To predict the optimum aperture at which to fire the strobe, and secondarily to determine whether the
subject is near or far from the Camera, Joshua employs a strobe wink system. This involves firing
approximately one-tenth of the strobe energy prior to exposure and measuring its reflected IR value.
Using these ambient (visible) and IR measurements, a micro- processor then selects the optimum strobe fire
aperture and total exposure value from a lookup table. This table contains stored values for the best
aperture, percent strobe and percent ambient to use, for thousands of photo situations.
In addition, a highly-developed encoder system provides precise shutter blade position information,
allowing the strobe to be fired at the correct aperture. This system is not dependent on blade speed, as in
the past; consequently, the Camera needs no proJoshua for adjusting shutter blade speed.
Figure 1-5. Microprocessor Control of Exposure