Canon AE-1 Instructions Manual page 50

"A" mark.
This i s because the aperture value
is
stored in the AEcircuit as a result of stopp-
ingdown the lens, and you will end up getting
incorrect automatic exposure for the next
shot, if you fail t o do that.
Generally, the depth-of-field will become
deeper as the aperture becomes smaller, and
shallower as the aperture becomes larger. A
shorter focal length as well as a greater subject
distance will also deepen the depth-of-field.
Comparing an interchangeable 28mm lens
with a standard 50mm lens set a t the same
50
flstop, the 28mm lens's depth-of-field will be
greater. And when the photographic distance
changes, the depth-of-field changes, too. For
example, i f the same subject is photographed
from three and then from seven meters away,
the foreground and background of the subject
will be deeper at the greater distance.
2
Depth-of-Field Scale on the Lens
A depth-of-field scale is engraved on the
lens barrel, shown as a series of flnumbers on
each side of the distance index mark opposite
the distance scale. Focusing and depth-of-field
are so closely interrelated that the depth-
of-field scale is engraved together with the
distance scale.
You can tell the extent of depth-of-field
from the distance scale. For example, if you
use the camera with a standard 50mm lens
that is focused on a subiect at medium dis-
tance, say 3m with the aperture set at f18,
the depth-of-field extends from 2.4m t o 4.5m.
This tells you that with the 50mm lens
focused at 3m and the subject between 2.4m
and 4.5m the film image will be reasonably
sharp.