Canon A-1 Instructions Manual page 43

Selecting an Aperture .
A discussion of how t o select an appropriate
aperture boils down to an
c;xpl~n~tion
of
depth of field.
Wh~n
your subJec.t 1s
m
focus,
there is onlv a limited range m the fore-
ground and background of the subject
whic~1
is also in focus. This zone of sharpness 1s
called depth of field.
Depth of field is governed by three
fact~rs:
aperture, lens focal length ai;d
shoo~mg
distance. Remember the followmg relation-
ships:
(1) The smaller the aperture, t:he deeper the
d epth of field (the other two factors
remaining
t he 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
~ Aperture
priority
AE
FD 300mm f/2.8 S.S.C. FLUORITE, f/2.8 ASA 125
-43-
(3)
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.
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-
f,'l·aphed from three and then from seven
meters a way, the zone of sharpness in
t he foreground and backgro und 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
th~ ~perturc
directly using Lhe aperture pnonty AE
mode. Using a small aperture
is
1,>reat for
getting sh<lrp overall focus in a landscape or
any other type of subject, but shallow d.epth
of
field also has its merits. Using a relat1vcly
large aperture will make you r
subjec~
stand
o ut 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.