SIGMA DP3 Quattro - Manual (Page 89)

89
NORMAL FLASH
When you use the external flash, you can use your camera in this mode.

Please use this mode for ordinary photography.
RED-EYE REDUCTION FLASH (REDEYE)
When taking a picture with flash, sometimes the person’s eyes reflects the
flash light and the “redeye” phenomenon will appear in the picture. In order
to avoid this effect, the flash will blink several times, for about one second
before the picture is taken, in order to reduce the effect of this
phenomenon.

Depending on the lighting and subject conditions, the Redeye Reduction
flash may not completely eliminate the redeye in all cases.
/
SLOW SYNCHRO MODE
When using the flash with P / A mode, the shutter speed value is limited to
faster than 1/60. The slow synchro mode changes the shutter speed up to
30 second depending on light condition. This mode is suitable for a portrait
in a nightscape.
CAUTION!!

The Flash Mode can not be set if the flashgun is not attached to the
camera, or the flashgun is turned off.

It is not possible to use the Red-eye reduction flash when Manual Flash
mode is selected on the external flash unit.