Canon A-1 - Manual (Page 113)

Warnings of Incorrect Operation in
Stopped-down Photography
Two problems can arise if you use the
camera incorrectly in the stopped-down
mode. The first problem occurs if the
stop-down lever of the camera is locked in
before you mount the lens. If you e.xpose a
frame in thi.s situation, it will be incorrectly
exposed due to incorrect coupling of the
ajjerture ring. To prevent this, before you
mount a lens, make sure there is no red dot
beside the stop-down coupling lever inside
the camera body. The red dot is very con­
spicuous and appears only when the stop-
down lever is pushed in.
The second problem arises if you push in the
camera’s stop-down lever and, before taking
a shot, release the stop-down lever and
return the lens aperture ring to the “A”
mark. If you then try to press the shutter
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