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SB800 remote operation question

Discussion in 'General Technical Discussion' started by RonS, Nov 9, 2005.

  1. I have been using two SB800's with a D2x, and they work quite well. Being curious (one of the problems of being an engineer), I was wondering if anyone can explain the details on how they operate.

    Typical setup: Master on the D2x, remote 45 degrees to the right, same distance to the subject.

    Both set to TTL, master -.7, remote at 0.

    Camera A priority, usually f5.6, 1/60 sec. Sometimes 1/30 and/or f8 to f11.

    Now the questions...
    The master flashes two times. I assume the first flash transmits the setup data to the remote, then they both flash simultaneous.

    Does the master pre-flash so the camera can calculate the exposure to control the flash duration?

    Does the remote pre-flash? If so how does this work with the camera for the calculations?

    If only the master pre-flashes, how does this work with the remote adding in additional light during the exposure?

    How does the camera turn off the remote to control its light output?

    Or am I way off base with how I think all this works?

  2. marc

    marc Guest

    as an engineer, you probably are looking for something that may not exist

    the master and remote communicate thru IR

    this is why you need line of sight

    yed there are preflashes and yes they do communicate this way.

    that is all my understanding

    no radio control, just IR
  3. I don't know how it all works but I think your presumption that your getting two flashes is wrong, it may look like two flashes but there is a preflash for metering then there are communication flashes then the main flash, the communication flashes happen very quickly and all the information for remotes is transmitted this way.

  4. Thanks Martin.

    What I do notice is that when using only one flash, I cannot see a flash through the viewfinder as I open the shutter. The preflashes must be the invisible (very short) ones.

    When using multiple flashes I do see a bright flash just before the mirror blocks the light, but the remote only flashes one time. The master flashed two times, the first just as the mirror is going up.

    Conjecture on my part, this is why I am asking.
  5. MontyDog


    Jan 30, 2005
    #1064 - You have an error in your SQL syntax;
  6. TheKO


    May 3, 2005
    Tampa, FL
    May be in left field but...

    Not an engineer either nor am I the duty expert but...

    I think there is a setting to accomplish red-eye reduction that sets the flash off before the exposure. This is done to reduce the size of the eye retina and thereby reduces the red eye effect. This pre-flash does not provide inter-flash communications.

    You might want to check your flash setting on the master.
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