Canon EOS 7D Mark II (G) Instruction Manual page 269

Shutter synchronization
If [Second-curtain synchronization] is set, the flash will fire right
before the shutter closes. When this is combined with a slow shutter
speed, you can create a trail of light such as from car headlights at night
with a more natural feel. With second-curtain synchronization, two
flashes will be fired: once when you press the shutter button completely,
and once immediately before the exposure ends.
If [High-speed synchronization] is set, the flash can be used at all
shutter speeds. This is especially effective for portraits using fill flash
when you want to give priority to the aperture setting.
Flash exposure compensation
Flash exposure bracketing
Normally, set this to [First-curtain
synchronization] so that the flash fires
immediately after the exposure starts.
You can set flash exposure
compensation up to ±3 stops in 1/3-stop
increments.
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 equipped with
flash exposure bracketing.
3 Setting the FlashN
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