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06-10-09, 02:36 PM
Join Date: Sep 2009
Exactly how many flash pulses there are, I'm not sure.
There are, as far as I can tell,two groups of flashes.
There's the pre-flash, before the shutter opens. iTTL flash depends on the return from the first sequence of pre-flashes (before the shutter opens) to determine the flash power to use during the exposure. If you set the AF-L/AE-L button to FV Lock, pressing that button will get the pre-flash over & done with, the camera will decide how much flash power to use in subsequent shots (until you do it again, or change shooting mode, or stuff like that), and you won't get the pre-flash, just the flash on the exposure.
In commander mode, the pop-up flash might give a total of 12 pulses in the pre-flash sequence, with 2 flashes from each of the remote groups. The pulses from the pop-up are probably too close together to see.
If you go to manual flash mode rather than TTL, the pre-flash isn't needed at all.
After the shutter opens, probably when the flash is required (so it may be long after the shutter opens if we're talking rear sync) the flash delivers a quick pulse and then fires at the required power. I'm not sure if that quick pulse happens if the flash is not in commander mode.
Hope this helps
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