Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 267)

267
3 Setting the Flash Function
Shutter synchronization
Normally, set this to [ First-curtain
synchronization ] so that the flash fires
immediately after the exposure starts.
If [ Second-curtain synchronization ] is set, the flash will be fired 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. When second-curtain synchronization is set
together with [
ETTL II ], the flash will be fired twice in a row: once when
you press the shutter button completely and once right before the end
of the exposure.
If [
High-speed synchronization ] is set, the flash can be used at all
shutter speeds. This is effective when you want to shoot with
background blur (open aperture) in locations such as outdoors in
daylight.
Flash exposure compensation
You can set flash exposure
compensation up to ±3 stops in 1/3-stop
increments.
For details, refer to the Speedlite’s
Instruction Manual.
Flash exposure bracketing
While changing the flash output
automatically, three shots will be taken.
For details, refer to the Instruction
Manual of a Speedlite equipped with
flash exposure bracketing.