Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 268)

3 Setting the Flash Function
268
For details on the Speedlite’s Custom Functions, refer to the Speedlite’s
Instruction Manual.
1
Select [Flash C.Fn settings].
2
Set the desired functions.
Select the number, then press < 0 >.
Select the setting, then press < 0 >.
Flash Custom Function Settings
When using second-curtain synchronization, set the shutter speed to 1/25
sec. or slower. If the shutter speed is 1/30 sec. or faster, first-curtain
synchronization will be applied automatically even if [
Second-curtain
synchronization ] is set.
With an EX-series Speedlite not compatible with flash function settings,
you can only set the following: [
Flash firing ], [ E-TTL II meter. ], and
[ Flash exposure compensation ] under [ Flash function settings ].
([ Shutter synchronization ] can also be set with certain EX-series
Speedlites.)
If flash exposure compensation is set with the Speedlite, you cannot set
the flash exposure compensation with the camera. If it is set with both
the camera and Speedlite, the Speedlite’s setting overrides the camera’s.
With an EX-series Speedlite, the Speedlite will always fire at full output if the
[
Flash metering mode ] Custom Function is set to [ TTL flash metering ]
(autoflash).