Canon EOS 80D Instruction Manual page 241

Wireless functions / Flash ratio control
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Flash zoom (Flash coverage)
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Shutter synchronization
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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. When second-curtain synchronization is set together with [E-
TTL 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 useful when you want to shoot with background
blur (open aperture) in locations such as outdoors in daylight.
Wireless (multiple) flash shooting is
possible with radio or optical
transmission.
For details on wireless flash, refer to the
instruction manual of a Speedlite
compatible with wireless flash shooting.
With a macro flash (MR-14EX II, etc.)
compatible with flash function settings,
you can set the flash ratio between flash
tubes or flash heads A and B, or perform
wireless flash with additional slave units.
For details on flash ratio control, refer to
the macro flash's instruction manual.
With Speedlites having a zooming flash
head, you can set the flash coverage.
Normally, set this to [AUTO] so that the
camera will automatically set the flash
coverage to match the lens focal length.
Normally, set this to [First-curtain
synchronization] so that the flash fires
immediately after the exposure starts.
3 Setting the FlashN
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