Canon A-1 - Manual (Page 110)

2-
light reaching the film plane is greatly
reduced due to attached accessories, the A-1
is capable of metering as low a light level aS
EV-2 (with ASA 100 film) in the stopped-
down AE mode. Furthermore, since the A-1
employs a through-the-lens meter, no expo­
sure correction is necessary when accessori­
es are inserted between camera and lens.
When you are finished operating in the
stopped-down AE mode, unfold and press
down on the stop-down lever. It will pop out
and the camera will be reset for full aper­
ture metering. With an FD lens, you can
now return the lens aperture ring to the “A”
mark if you wish to use the A-1 in a full
aperture metering AE mode,
if you return the aperture ring to “A” but
leave the stop-down lever pushed in, the
camera will remain in the stopped-down AE
mode and all subsequent exposures will be
made at the lens minimum aperture. Though
exposure will be correct, this situation se­
verely strains camera mechanisms and is not
recommended.
When performing stopped-down metering,
you also have the advantage of being able to
confirm depth of field directly in the view­
finder.See Checking the Depth of Field.
It is not possible to shoot sequentially with
the Power Winder A or Motor Drive MA
when in the stopped-down AE mode using
an FD lens. In this situation, only single­
frame power winding is possible.