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Thread: Theoretical question: No-motion long exp. - is flash timing important?

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    Theoretical question: No-motion long exp. - is flash timing important?

    Say you're taking a 20 - 30 second exposure photo in a dark (but not completely black) environment and using flash.

    If there is a moving object (say a car going past), I understand the different effects that would occur if the flash is fired at the beginning of the exposure, or at the end of the exposure.

    But what if the object is stationary?
    Two photos, identical in every respect, except one had the flash fire just after the beginning of the exposure, and the other had the flash fire just before the end of the exposure. Is there any difference between the resulting images?
    Nikon D70s / Nikkor 18-70mm / Nikkor 12-24mm / Tamron 90mm macro / SB600

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    No difference.

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    In Training MarkChap's Avatar
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    Would be an interesting experiment.

    I am thinking that although there really shouldn't be any difference, maybe the second curtain sync may give a slightly more pleasing image as the camera would be thinking it has done the exposure and spit out a bit less light from the flash ???
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    There is no difference at all.
    I do it all the time.

    JJ

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    If the flash output is the same there shouldn't be any difference. Not exactly hard to test either. Just try both.
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    Dave



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    Thanks all.

    I'm doing a lot of thinking at the moment (while stuck at work) and am trying to get some of the theory firmly in my head, so I have more time for thinking about the pic I'm trying to take instead of the theory stuff.

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    As others said: no difference in the end result.

    However... (yeah, there's always a 'but' ). Your image will consist of two exposures, one lit by flash, the other lit by available light. If you use sync on second curtain, the mirror slaps a long time before the flash fires. If you sync on first, camera shake due to the mirror slap happens in the time the flash fires. Since the flash is very short you might not notice this but theoretically you could see a difference there. Especially if you have exposures of 1/2 or 1 second, camera shake will be big in the beginning and almost nul in the end. Now, flash usually is short enough not to show camera shake (and flash shake maybe?), but in theory it could make a difference.
    Last edited by jev; 26-05-2009 at 4:02pm.
    Ciao, Joost

    All feedback is highly appreciated!

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