Canon EOS 5D MARK IV Instruction Manual page 506

7 Custom ControlsN
: Direct AF area selection
If the metering timer is active, you can press the <p> (AF area
selection) button to directly select an AF area selection mode without
pressing the <S> button.
: Pause Movie Servo AF
When Movie Servo AF is active, you can pause the AF by pressing the
Depth-of-field preview button or <0>. Press the button again to
resume Movie Servo AF.
Exposure
: Metering start
When you press the shutter button halfway, exposure metering is
performed (AF is not performed).
: AE lock
When you press the button assigned to this function, you can lock the
exposure (AE lock) while the metering timer is active. Useful when you
want to focus and meter the shot separately.
: AE lock (while button pressed)
The exposure will be locked (AE lock) while you hold down 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)].
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