Using Focus Lock - Canon EOS 30D Instruction Manual

Using Focus Lock

After achieving focus, you can lock the focus on a subject and
recompose the shot. This is called "focus lock." Focus lock works only
in the One-Shot AF mode.
If the AF mode is AI Servo AF (or AI Focus AF set to Servo mode), focus
lock will not work.
Focus lock is also possible in Basic Zone modes (except <5>). In this
case, start from step 3.
Set the Mode Dial to a Creative
1
Zone mode.
Select the desired AF point.
2
Focus the subject.
3
Move the AF point over the subject
and press the shutter button halfway.
Keep pressing the shutter button
4
halfway and recompose the
picture as desired.
Take the picture.
5
(p.77)
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