Canon EOS-1D Mark IV - Manual (Page 225)

Custom Function Settings
C.rn III ‘13 AF point display during focus
0: On
1:Off
The AF point will not light in red other than during AF point selection.
2: On (when focus achieved)
During AF, the manually-selected AF point will no longer light faintly.
After AF starts, the AF point will light only when it achieves focus.
C.Fn ill *14 AF point brightness
0: Normal
1: Brighter
Makes the AF point light up brighter in red.
Cxn III ‘15 AF-asslst beam firing
Enables or disables the EOS-dedicated Speedlite's AF-assist beam.
0: Enable
The external Speedlite will emit the AF-assist beam when necessary.
1: Disable
2: IR AF assist beam only
Among external Speedlites, only those which have an infrared AF-assist
beam will be able to emit the beam. Set this if you do not want the AF
assist to be emitted as small flashes.
1^ The external Speedlite's Custom Function [AF-assist beam firing] set to
[Disabled] will override this Custom Function's 0 and 2 settings. The AF-
asslst beam will not be emitted.
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