Canon AE-1 - Manual (Page 75)

2 Effects of Changing the Aperture
Because this camera is an AE camera with
shutter speed priority, when you change the
shutter speed, the aperture will also change.
If you change the speed by one gradation, the
aperture also changes the equivalent of one
gradation. Aperture changes have an effect
on the photographic expression as follows:
In example C, the aperture was set at
f/1.8 with the shutter speed dial adjusted be­
fore shooting. In example D, a f/16 setting
was used to clearly demonstrate the dif­
ference. In C, the chesspieces in the back
and front are blurred and only the chesspiece
in the center is in focus. In D, most of the
chesspieces are sharp and clear and only
those in the back are blurred. Thus, the lens
aperture controls the zone of sharpness in
the subject field which is observed in the
viewfinder or recorded on the film.
Aperture Priority Photography
After having given careful thought to the
results of aperture adjustments, when the
f/stop has been determined before shooting,
press the exposure preview switch while
looking into the viewfinder. Then turn the