Canon EOS 6D Instruction Manual page 176

3 Setting the FlashN
Flash exposure compensation
Flash exposure bracketing
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 used 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 on the camera (with the flash function
settings). If it is set with both the camera and Speedlite, the Speedlite's
setting overrides the camera's.
176
The same setting as "Flash exposure
compensation" on page 170 can be set.
For details, refer to the Speedlite's
instruction manual.
While the flash output is changed
automatically, three shots are taken.
For details, refer to the instruction
manual of a Speedlite compatible with
flash exposure bracketing.