Canon EOS 6D Mark II Instruction Manual page 480

3 Custom Function SettingsN
C.Fn II-6
Enables or disables the EOS-dedicated external Speedlite's AF-assist
beam.
0: Enable
The external Speedlite emits the AF-assist beam when necessary.
1: Disable
The external Speedlite will not emit the AF-assist beam. This
prevents the AF-assist beam from disturbing others.
2: IR AF assist beam only
When an external Speedlite is attached, only the infrared AF-assist
beam will be emitted. Useful when you do not want to fire a series
of small flashes as the AF-assist light (Intermittent flash method).
With an EX-series Speedlite equipped with an LED light, the LED
light will not automatically turn on as the AF-assist beam.
If an external Speedlite's [AF-assist beam firing] Custom Function is set to
[Disable], this function's setting will be overridden and the AF-assist beam
will not be emitted.
480
AF-assist beam firing