Pentax 645 - Page 55

Programmed AE Diagram
The Pentax 645's shutter/aperture combination in
the Programmed AE mode is shown in the chart.
The green line represents the variation of shutter
speed and aperture combination with the standard
75mm f/2.8 lens (w/ISO 100 film). Note that only
the shutter speed slows down after the lens reaches
its limit of f/2.8 in combination with a speed of
approx. 1/60 sec. Using a lens with a different
maximum aperture, the exposure program varies
the aperture and the shutter speed in combination
until reaching the maximum aperture of the lens in
use. For example, with an f/4 lens the program
adjusts the combination as shown by the green
dotted line. When using a lens with a different
maximum/minimum aperture, or film with a
different ISO film speed, refer to the fine green and
dotted green lines seen in the Programmed AE
diagram. The limit of the meter coupling range will
vary if a lens other than the 75mm f/2.8 standard
lens is utilized.
Meter Coupling and Shutter/Aperture Coupling
Range
Meter coupling range indicates the range of subject
luminance within which the built-in exposure meter
functions to control exposure.
The shutter/aperture coupling range is that part of
the meter coupling range within which the shutter
speed and f/stop can be combined for proper
exposure control.
With the 75mm f/2.8 standard lens and ISO 100 film,
the meter coupling range extends from EV 3
{f/2.8,1 sec) to EV19 [f/22,1/1000]. In the
diagram at the left, the diagonal lines from the left
top to lower right will move in parallel depending on
the ISO rating.
The diagram within the frame illustrates the meter
coupling and shutter/aperture coupling ranges.
EV (Exposure Value)
EV represents the amount of exposure by a
combination of the shutter speed and lens aperture,
determined by the film speed and the brightness of
the subject.
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