Canon AT 1 - Manual (Page 78)

the moving main subject in the viewfinder.
You then release the shutter while still twist­
ing. When you use this technique, the main
subject should be sharp even at slow shutter
speeds and the image of the background is
blurred according to the speed of the panning
movement. This hightens the feeling of
motion in the picture.
Effects of Changing the Aperture
The lens aperture does not only control
exposure but it also has an effect on the
photograph as follows:
In example C, the aperture was set at
f/5.6 with the shutter speed dial adjusted
before shooting. In example D, a f/16 setting
was used to clearly demonstrate the diffe­
rence. In C, the miniature cars in the back and
front are blurred and only the miniature cars
in the central area are in focus. In D, most of
the miniature cars are sharp and clear. Thus,
the lens aperture has a marked effect on how
much of the picture is reproduced sharply.