Canon EOS 6D Instruction Manual page 177

Flash Custom Function Settings
For details on the Speedlite's Custom Functions, refer to the Speedlite's
instruction manual.
Clear Settings
With an EX-series Speedlite, if the [Flash metering mode] Custom
Function is set to [TTL] (autoflash), the Speedlite will always fire at full
output.
The Speedlite's Personal Functions (P.Fn) cannot be set or canceled with
the camera's [External Speedlite control] screen. Set it with the Speedlite.
1
Select [Flash C.Fn settings].
Select [Flash C.Fn settings], then
press <0>.
2
Set the functions.
Press the <U> key to select the
number, then press <0>.
Select the setting, then press <0>.
1
Select [Clear settings].
Under the [z2: External Speedlite
control] tab, select [Clear settings],
then press <0>.
2 Select the settings to be cleared.
Select either [Clear flash settings] or
[Clear all Speedlite C.Fn's], then
press <0>.
When you select [OK], the respective
flash settings will be cleared.
3 Setting the FlashN
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