Canon AE-1 PROGRAM - Film Plane Indicator

Film Plane Indicator
This mark, engraved on top of the camera body,
indicates the exact position
of the film plane. It is
useful for measuring the exact shooting distance
from
film to subject in close-up photography.
Distances on the
lens' distance scale are cali-
brated from this mark. It is not used in general
photography.
Note
The aperture ring of an FD lens must be removed
from " A" before you mount the lens on any of
these close-up accessories except for FD-U
Extension Tubes and Extenders
FD 2x and FD
1.4 x, which are designed for normal full-aperture
metering.
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