Canon A-1 - Manual (Page 97)

flashes showing the lens maximum aperture
to
indicate underexposure. At very low
shutter speeds, it is possible for a different
exposure, turn the AT dial to as lower shut­
ter speed,
speed.
Overexposure
Whenever any aperture smaller than f/16
(that is, 19 to 32) appears in the readout, it
will always be flashing on and off. Whether
or not this indicates overexposure depends
on the lens minimum aperture. If the
minimum aperture of the lens is equal to or
smaller than the flashing aperture, exposure
will
be correct. If the lens minimum
aperture is larger than the flashing aperture,
increase the shutter speed for correct ex­
posure.
There is one exception to the above which
occurs when the minimum aperture of the
lens is f/32. Since f/32 is the smallest
aperture which can appear in the readout,
it is not immediately apparent whether ex­
posure is correct or not. To find out,
increase the shutter speed until the readout
shows a flashing f/22. At that point, you
may reduce the shutter speed one step for
correct exposure at f/32.
There is a rare case where f/16 may flash on
and off in the viewfinder. If you are using a
lens with an f/16 minimum aperture, the
image may be overexposed, so increase the
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