Canon EOS 600D Instruction Manual page 256

3 Custom Function SettingsN
C.Fn IV: Operation/Others
C.Fn-9
0: AF/AE lock
1: AE lock/AF
Convenient when you want to focus and meter separately. Press the <A>
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 mode, you can press the <A> button to stop 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 which keep moving and stopping repeatedly.
In the AI Servo AF mode, you can press the <A> 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.
C.Fn-10
You can assign a frequently-used function to <0>. Press <0> when the
camera is ready to shoot.
0: Normal (disabled)
1: Image quality
Press <0> to display the image-recording quality setting screen on the
LCD monitor. Select the desired image-recording quality, then press <0>.
2: Flash exposure compensation
When you press <0>, the flash exposure compensation setting screen
will appear. Set the flash exposure compensation, then press <0>.
3: LCD monitor On/Off
Assigns the same function as the <B> button.
4: Menu display
Press <0> to display the menu screen.
5: ISO speed
The ISO speed setting screen will appear. Press the <U> key or turn
the <6> dial to change the ISO speed. You can also refer to the
viewfinder to set the ISO speed.
256
Shutter/AE lock button
Assign SET button