Sony SLT-A77VM - Manual (Page 48)

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Using the flash
(Flash Off) Does not fire even the built-in flash pops up.
• You cannot select this item when the mode dial is set to P,
A, S, or M. However, the flash will not be fired if it is not
pulled up.
(Autoflash) Fires if it is dark or against light.
(Fill-flash) Fires every time you trigger the shutter.
(Rear Sync.) Fires right before the exposure is completed every time you
trigger the shutter.
(Wireless) Fires an external flash (sold separately) that is off the camera
and away from it (Wireless flash shooting).