SU-800 and pre-flashes

Discussion in 'General flash photography, lighting, and technique' started by Philippe Roger, May 20, 2007.

  1. So, the SU-800 sitting on top of a camera sends IR signals to the remote flashes, such as SB-800, SB-600. My question is: do those remote flashes still emit pre-flashes, so that the SU-800 can measure their contribution and adjust their output, just as would happen if a Commander/Master flash was sitting on top of the camera instead?

    The reason I ask is twofold:

    1. I have heard mention (by Uncle Frank amongst others) that one of the benefit of the SU-800 is to eliminate pre-flashes, but I am afraid that this only applies to the on-camera flash (replaced by the SU-800)

    2. If indeed, there is no pre-flashes emitted by the remotes, they can in turn be used to trigger optically any other flashes. While they won't be part of the CLS magic, they could be set manually and trigger at the right time, not being confused by the pre-flash sequence

    ... or, am I only dreaming?

    Thanks!
     
  2. Philipe
    I believe statement number one is accurate.
     
  3. I_media

    I_media

    112
    May 16, 2007
    Norway
    If you want to use TTL, the remotes has to emit pre-flashes (but obviously you won't see the communication from the SU-800 to the remotes). If used in full manual, or FV-lock, there shouldn't be any need for pre-flashes. If I got things right.
     
  4. Thank you guys.

    This really makes it crystal clear for me now: I hope this helps others who might have been a bit confused :confused: as well! :smile:
     
  5. Your first statement is accurate Philippe. The elimination of pre-flashes from your on camera flash is one of the benefits of the SU800 in my opinion. If your subject has sensitive eyes the SU800 will go a long way towards eliminating the blinking problem.
     
  6. Taylor

    Taylor

    May 21, 2007
    Toronto, ON
    You can cover up your pop-up flash with some cardboard or other material, and it will still fire your SB-800.

    I tried it with my D200's popup in commander mode and a handheld SB-800.

    Results are no blinding pre-flashes from your camera, and only one from the SB-800 (provided you turned off modeling flash)
     
  7. I_media

    I_media

    112
    May 16, 2007
    Norway
    Hm, there seem to be a confusion about what is a "pre-flash".

    According to the Magic Lantern Guide - Nikon AF Speedlight Flash System book, the signal to the remotes are not pre-flashes, but tells the remotes to initiate their pre-flash system, which then (the remotes) emits one or two pulses of light, the pre-flash(es). The light from these pre-flashes is bounced back from the scene, through the lens and into the iTTL sensor in the camera. After analyzing the camera sends another signal to the remotes to initiate the main flash discharge, which is quenched the instant the amount of light pre-determined from the pre-flashes has been emitted.

    To cover up the pop-up flash, I usually use my hand or something if needed, but there is also this device (SG-3IR):

    nikon_sg3ir_m.
     
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