Canon EOS Rebel T1i Instruction Manual page 116

Using AF to FocusN
Quick Mode: f
The dedicated AF sensor is used to focus in the One-Shot AF mode
(p.64), using the same AF method as with viewfinder shooting.
Although you can focus the target area quickly, the Live View image
will be interrupted momentarily during the AF operation.
AF point
Magnifying frame
116
Display the Live View image.
1
Press the <A> button.
The Live View image will appear on
the LCD monitor.
The small boxes on the screen are
the AF points, and the larger box is
the magnifying frame.
Select the AF point.
2
When you press <0>, the Quick
Control screen will appear.
The current settable function will be
highlighted in blue.
Press the <U> key to make the AF
point selectable.
Turn the <6> dial to select the AF
point.