Locking-in an exposure reading, Basic operation – Canon EF User Manual
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BASIC OPERATION
I
Locking-In an Exposure Reading
In the majoritv of cases, Canon EF's Central
Emphasis Metering system will give correct exposure
readings in AE photography. However, occasionally
you will encounter picture-taking situations which
require a departure from normal AE operation. For
example;
(1)
Your subject is strongly backlighted or con
trasts sharply with the background and will not
appear in the center of the picture.
(2)
The entire scene is either extremely light, such
as a light colored subject in snow; or it is very dark,
such as a dark colored subject in deep shade or
against a dark background.
In the above cases, it is necessary to modify the
automatic exposure reading which the camera nor
mally sets by itself. The Canon EF provides a
convenient way to do this by incorporating an AE
memory lock button on the left side of the camera
between the pentaprism and the ASA ring. By
holding in this button, you can lock the meter
needle of the camera at a particular f/stop while you
change the position of the camera (and hence the
view in the viewfinder). To produce a good exposure
in the first situation (1) described above, focus on
your main subject and center it in the viewfinder. If
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