Canon EOS REBEL XS EOS REBEL XS Instruction Manual page 103

You cannot take a picture during autofocusing. Take the picture only
while the Live View image is displayed.
You can move the focusing frame with the <S> keys. To magnify the
area within the focusing frame, press the <u> button.
Although you can set the AF mode to AI Servo AF or AI Focus AF, AF will
stop when the camera returns to the Live View image display (step 4), so
you cannot focus the moving subject.
If you want AF and AE lock to work separately, select the [7 Custom
Functions (C.Fn)] menu's [Shutter/AE lock button] (p.158) and set it to
[1: AE lock/AF].
AF is not possible with Remote Switch RS-60E3 (sold separately).
Focus the subject.
3
Aim the selected AF point over the
subject, and hold down the <A>
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
4
display and shoot.
When you let go of the <A> button,
the Live View image will reappear.
Check the focus and exposure, then
press the shutter button to take the
picture (p.99).
Using AF to FocusN
103