Canon EOS 5D Mark III Instruction Manual page 332

82: Custom Controls
: Switch to registered AF point
During metering, when you press the button assigned to this function,
the camera will switch to the AF point registered on page 330.
*3: In step 3 on page 327, when you press the <B> button, you can select [Switch
only when btn is held] or [Switch each time btn is pressed].
: AF point direct selection
During metering, you can select an AF point directly with the <5> dial or
<9> without pressing the <S> button. With the <5> dial, you can select a
left or right AF point. (With Zone AF, the selected zone will change in a loop.)
*4: If you use <9> and press the <B> button in step 3 on page 327, you can press
<9> straight down to select [Switch to center AF point] or [Switch to registered
AF point].
: Metering start
When you press the shutter button halfway, only exposure metering is
performed.
: AE lock
When you press the button assigned to this function, you can lock the
exposure (AE lock) during the metering. Convenient when you want to
focus and meter the shot at different areas or when you want to take
multiple shots at the same exposure setting.
: AE lock (while button pressed)
The exposure will be locked (AE lock) while you press the shutter
button.
If you assign [AE lock (while button pressed)] to the shutter button, any
buttons assigned to [AE lock] or [AE lock (hold)] will also work as [AE lock
(while button pressed)].
If you change the aperture in <a> mode when [AF point direct selection]
is set, turn the <6> dial while holding down the <
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> button.