C silicon photocell, C. silicon photocell -14 – Canon EF User Manual

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Variable

Aperture

Control

Method

Commonly known as "shutter priority EE," the

Variable Aperture AE control method gives the

photographer absolute control over the shutter speed

to prevent camera shake. You select a shutter speed

appropriate to the action and/or the lens you are

using, and the camera automatically adjusts the

aperture of the lens to precisely the proper f/stop or
fraction thereof.

Silicon Photocell

The Silicon Photocell is a highly accurate and

extremely stable light measuring cell having a wider

range of sensitivity and much faster response to

rapidly changing light levels than the conventional

CdS cell. At ASA 100, the metering range of the

Silicon Photocell is from EV18 (1/1000 sec. atf/16)
down to EV —2 (8 sec. at f/1.4), which is five f/stops

more sensitive than the normal CdS cell. At ASA 25,
the range is from 1/1000 sec. at f/8 down to 30 sec.

at f/1.4. This increased sensitivity range is made

possible by the development of a special logarithmic
amplifier to intensify the low amount of current

generated by the photocell in very dim light

conditions.