Using Af To Focus - Canon EOS 40D Instruction Manual

Live View ShootingN

Using AF to Focus

If the [8C.Fn III -6] (AF during Live View shooting) setting is set to
[Enable], you can focus with the <p> button.
Be sure to set the lens focus mode switch to <f>, set the AF
mode to <X>, and select the center AF point.
For very precise focusing, mount the camera on a tripod and magnify the
picture. Then focus manually. (p.110)
You can also use AI Servo AF or automatic/manual AF point selection.
However, if the AF point doesn't cover the subject, you might not obtain
the desired focusing result.
You cannot take a picture during autofocusing. Take the picture only
while the Live View image is displayed.
The exposure will be set with focusing frame-linked evaluative metering.
(The metering cannot be linked with an AF point.)
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Press <0> to the display Live
1
View image.
Focus the subject.
2
Cover the subject with the focusing
frame and press the <p> button.
The Live View image will turn off, the
reflex mirror will go back down, and
AF will be executed.
When focus is achieved, the beeper
will sound.
Return to the Live View image
3
display and shoot.
When you let go of the <p>
button, the Live View image will
return.
Check the focus and press the
shutter button to take the picture.