Canon EOS Rebel SL1 18-55mm IS STM Lens Kit - Manual (Page 303)

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3 Custom Function SettingsN
C.Fn IV: Operation/Others
C.Fn-6 Shutter/AE lock button
0: AF/AE lock
1: AE lock/AF
This is convenient when you want to focus and meter separately.
Press the button to autofocus, and press the shutter button
halfway to apply AE lock.
2: AF/AF lock, no AE lock
In the AI Servo AF operation, you can press the button to
pause the AF operation momentarily. This prevents the AF from
being thrown off by any obstacle passing between the camera and
subject. The exposure is set at the moment the picture is taken.
3: AE/AF, no AE lock
This is useful for subjects that keep moving and stopping
repeatedly. During AI Servo AF, you can press the button to
start or stop the AI Servo AF operation. The exposure is set at the
moment the picture is taken. Thus, the optimum focusing and
exposure will always be achieved as you wait for the decisive
moment.
During Live View shooting or movie shooting
With setting 1 or 3, press the button for One-Shot AF. Also, using
the touch shutter will take a picture without autofocusing.
With setting 2, press the shutter button halfway for One-Shot AF.
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