Canon EOS 30D - Manual (Page 75)

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f Selecting the AF ModeN
Pressing the shutter button
halfway activates the autofocus
and achieves focus once.
X The AF point which achieves focus flashes
briefly. At the same time, the focus confirmation
light in the viewfinder is displayed.
X With evaluative metering, the exposure setting
(shutter speed and aperture) will be set when
focus is achieved. The exposure setting and
focus will be locked as long as the shutter
button is pressed halfway. (p.79) You can then
recompose the shot while retaining the
exposure setting and point of focus.
While you press the shutter
button halfway, the camera
focuses continuously.
This AF mode is for moving subjects when
the focusing distance keeps changing.
X With predictive AF (p.76), the camera can
also focus track a subject which steadily
approaches or retreats from the camera.
X The exposure is set at the moment
the picture is taken.
One-Shot AF for Still Subjects
AF point Focus confirmation
light
AI Servo AF for Moving Subjects
If focus cannot be achieved, the focus confirmation light in the
viewfinder will blink. If this occurs, a picture cannot be taken even if the
shutter button is pressed completely. Recompose the picture and try to
focus again. Or see “When Autofocus Fails (Manual Focusing)” (p.80).
In a Creative Zone mode (except <8>), the beeper will not sound even when focus
is achieved. Also, the focus confirmation light in the viewfinder will not light.