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<blockquote data-quote="WayneF" data-source="post: 236769" data-attributes="member: 12496">In TTL flash mode, there is always a preflash immediately before the shutter opens,&nbsp; and then the final flash when the shutter does open (maybe 100 msec separation).&nbsp; Normally, they are&nbsp; indistinguishable to humans, looks like one flash.&nbsp;(it is NOT&nbsp; related to Red eye, which delays about one second while flashing a&nbsp; couple of times, trying to reduce the diameter of the eye pupil - this is very distinguishable.)If you set the camera to rear curtain sync mode, then the final flash is&nbsp; at the tail end of the shutter duration.&nbsp; If a slow shutter speed, then&nbsp; this can make the two flashes appear more separate.&nbsp; You won't realize&nbsp; it for normal front curtain sync.Preflash is absolutely necessary for digital cameras..&nbsp;&nbsp; The preflash is what is metered, to set the final flash power level.&nbsp; All compact and DSLR cameras must do it (for automatic TTL flash).&nbsp;&nbsp; You probably only see it if Rear Curtain Sync mode.You can select Manual flash mode to eliminate the prefash.&nbsp; Then,&nbsp; instead of the TTL automation metering the preflash and setting the&nbsp; final flash level, then it is up to you to directly set the final flash&nbsp; level manually, yourself.</blockquote>

[QUOTE="WayneF, post: 236769, member: 12496"] In TTL flash mode, there is always a preflash immediately before the shutter opens, and then the final flash when the shutter does open (maybe 100 msec separation). Normally, they are indistinguishable to humans, looks like one flash. (it is NOT related to Red eye, which delays about one second while flashing a couple of times, trying to reduce the diameter of the eye pupil - this is very distinguishable.) If you set the camera to rear curtain sync mode, then the final flash is at the tail end of the shutter duration. If a slow shutter speed, then this can make the two flashes appear more separate. You won't realize it for normal front curtain sync. Preflash is absolutely necessary for digital cameras.. The preflash is what is metered, to set the final flash power level. All compact and DSLR cameras must do it (for automatic TTL flash). You probably only see it if Rear Curtain Sync mode. You can select Manual flash mode to eliminate the prefash. Then, instead of the TTL automation metering the preflash and setting the final flash level, then it is up to you to directly set the final flash level manually, yourself. [/QUOTE]

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