Canon EOS 3 - Manual (Page 36)

AF Mode Selection
A!
Servo AF
for
Moving
Subjects
While you press the shutter button
halfway, the camera focuses
continuously. This AF mode suits
moving subjects. With predictive AF,
the camera can also focus track a
subject which steadily approaches or
retreats from the camera. The
exposure setting are set immediately
before the picture is taken.
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In the Al Servo AF mode, the viewfinder’s in-focus indicator does not light and the
beeper does not sound even when focus is achieved.
If the viewfinder’s in-focus indicator blinks, focus cannot be achieved.
The focus cannot be locked (except when Custom Function CF-4 is set to 2.)
* About Predictive AF
If the subject approaches or retreats from the camera at a constant rate,
the camera tracks the subject and predicts the focusing distance
immediately before the picture is taken. This is for obtaining correct focus
at the moment of exposure.
When focusing point selection is automatic, the camera first uses the
center focusing point to focus. If the subject later moves away from the
center focusing point, focus tracking continues as long as the subject is
covered by another focusing point in the area AF ellipse. The active
focusing point does not light.
With Custom Function CF-4, you can lock the focus momentarily by pressing the
<*> button even while the Al Servo AF is active. See page 108.
Custom Function CF-11 enables you turn the <0> dial to change the focusing
point to track the subject in the Al Servo AF mode. See page 116.
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