Canon A-1 - Manual (Page 61)

Stopped-down AE Photography
There are basically two cases which require
stopped-down AE photography (unless you
wish to operate in manual override). It is
necessary when you use any lens which is
not FD, such as FL or R lenses or the Reflex
Lens 500mm f/8. With the exceptions
of the FD-U extension tubes or Extenders,
it is also necessary whenever any accessory
is inserted between the camera and any lens
for increasing the lens' focal length or for
increasing lens extension for higher magni-
fications in close-ups or photomacrography.
It is, of course, also necessary in photo-
micrography. It is possible, but not neces-
sary, to use the stopped-down AE mode
when an FD lens is mounted directly onto
the camera with no accessory in-between.
In the stopped-down AE mode, exposure
metering will be done not at full aperture as
usual but, rather, at the same aperture that
the picture will actually be taken.
To set the camera in the stopped-down AE
mode when using a non-FD lens, simply fold
and push in the A-1's stop-down lever.
When using an FD lens, first advance the
film and then disengage the lens aperture
ring from the “A” mark before you push
in the stop-down lever. If the film is not
advanced before turning the aperture ring
from the “A” mark, the lens will stop down
only as far as the aperture set for the
previous exposure. It is impossible to push in
the stop-down lever when an FD lens is set
at “A”.
When in the stopped-down AE mode, it does
not matter whether the AE mode selector is
set to TV or Av. The camera will behave as
if it was in the aperture priority AE mode.
You must select the aperture by turning the
lens aperture ring while the camera will auto-
matically select a shutter speed. When you
preview the exposure, only the shutter speed
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