Canon EOS 6D Instruction Manual page 309

C.Fn II -4
[Equal priority]
Equal priority is given to focusing and continuous shooting speed. In low light
or with low-contrast subjects, shooting speed may slow down.
[Shooting speed priority] (
Priority is given to the continuous shooting speed instead of achieving focus.
The continuous shooting speed does not slow down. Convenient when you
want to maintain the continuous shooting speed.
[Focus priority] (
Priority is given to achieving focus instead of the continuous shooting speed.
The picture is not taken until focus is achieved. Effective when you want to
achieve focus before capturing the shot.
C.Fn II -5
Enables or disables the EOS-dedicated Speedlite's AF-assist beam.
0: Enable
The Speedlite will emit the AF-assist beam when necessary.
1: Disable
The Speedlite will not emit the AF-assist beam. This prevents the AF-assist
beam from disturbing others.
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. This prevents the AF-assist light from firing as a
burst of small flashes.
With an EX-series Speedlite equipped with an LED light, the LED light will not
automatically turn on for AF-assist.
If the external Speedlite's Custom Function [AF-assist beam firing] is set
to [Disable], this function's setting will be overridden and the AF-assist
beam will not be emitted.
AI Servo 2nd image priority
You can set the AF operation characteristics and
shutter-release timing during continuous shooting
after the first shot with AI Servo AF.
)
)
AF-assist beam firing
3 Custom Function SettingsN
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