Canon A-1 - Manual (Page 43)

Selecting an Aperture
A discussion of how to select an appropriate
aperture boils down to an explanation of
depth of field. When your subject is in focus,
there is only a limited range in the fore-
ground and background of the subject which
is also in focus. This zone of sharpness is
called depth of field.
Depth of field is governed by three factors:
aperture, lens focal length and shooting
distance. Remember the following relation-
ships:
(1) The smaller the aperture, the deeper the
depth of field (the other two factors
remaining the same).
For example, if the lens focal length
and the shooting distance stay the same,
the depth of field is much deeper at f/16
than at f/1.4.
(2)The shorter the lens focal length, the
deeper the depth of field (the other two
factors remaining the same).
For example, comparing a 28mm lens
with a 50mm lens at the same aperture
and shooting distance, depth of field is
deeper with the 28mm lens.
(3) The greater the shooting distance, the
deeper the depth of field (the other two
factors remaining the same).
For example, if the subject is photo-
graphed from three and then from seven
meters away, the zone of sharpness in
the foreground and background is great-
er at seven meters.
Another characteristic of depth of field
is that it is generally deeper in the back-
ground than in the foreground.
When depth of field is important in your
picture, it is best to control the aperture
directly using the aperture priority AE
mode. Using a small aperture is great for
getting sharp overall focus in a landscape or
any other type of subject, but shallow depth
of field also has its merits. Using a relatively
large aperture will make your subject stand
out against its surroundings by blurring the
background. This is an especially successful
technique in portraiture and special effects.
There are ways to check the extent of depth
of field. For this information, please refer
to page 76.
Not For Resale – Free Download at http://www.joe-chan.com/manuals
S Aperture priority AE
FD 300mm f/2.8 S.S.C. FLUORITE, f/2.8 ASA 125 –43–