Nissin i400 TTL Flash for Cameras - Manual (Page 16)

Following functions are available on Nikon cameras. Refer to
camera owner's manual for details.
The flash is controlled at a slow shutter speed to the correct
exposure for both the main subject and back ground in low
light conditions or at night.
For Nikon Version only
Slow shutter synchronization
To prevent the subject's eyes from appearing red, i400
fires three controlled flashes just before the picture is
taken. Red-eye reduction can be combined with slow
sync.
Red-eye reduction
In rear-curtain sync., the flash fires just before the rear
curtain closes. By using this function at slow shutter
speeds, a moving subject will appear with such moving
marks behind.
Rear curtain synchronization
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