Canon EOS 20D Instruction Manual page 69

Focusing an Off-Center Subject
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.
_ Set the Mode Dial to a Creative
Zone mode.
_, Select the desired AF point.
_, Focus the subject.
_ Move the AF point over the subject
and press the shutter button halfway.
4, Keep pressing the shutter button
halfway and recompose the
picture as desired.
_ Take the picture.
0 If the AF mode is AI Servo AF (or A! FocusAF set tOSery0 mode), focus
Focus lock is also possible in Basic Zone modes (except <_>). In this
case, start from step 3.
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