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The top half of the photodiode measures all visible light, while the bottom half
measures the infrared portion of the spectrum. By utilizing a dual photodiode
system, light measurements are more precise than previous cameras. These
measurements determine whether the strobe is to fire at full output or if there is to
be a partial strobe output (quenching).
ProCam System Autofocus
The transducer (Figure 1-16) provides subject distance information to the encoder
circuit. The distance information determines when the moving Quintic lens should
be stopped by the catch pawl for proper focus. It also provides information to
determine when to stop the shutter blades for the appropriate aperture. When the
autofocus system is turned off, the blades open fully and the hyperfocal (infinity)
lens position is chosen.
Figure 1-16. ProCam System Transducer
Electronic Trim
In previous camera models, trim has been achieved by sliding a shaded wedge over
the photocell to fool it into causing longer or shorter exposures. In the ProCam
system, trim is achieved electronically. Moving the Lighten/Darken Switch on the
Control Panel affects the electronic circuit of the ProCam, causing exposure times
to be increased or decreased by 0.65 +/- 0.25 stop. There are no gradations
between fully lighten or fully darken. The change in exposure value is 0.65 +/- 0.25
stop from nominal in either direction.
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