Why does my camera not see the slave flash?

Discussion in 'Digital Cameras' started by Henry Law, Jan 1, 2005.

  1. Henry Law

    Henry Law Guest

    Playing around with my new EOS 300D to see what my old equipment can
    do; flash this evening.

    I have a Vivitar 283 and an old Vivitar slave (the little cylindrical
    one); fitted them up on a tripod and put some tissues over the
    built-in flash so it was just bright enough to trigger the slave.

    Sometimes the shot doesn't show the flash (well not the main one),
    sometimes it does. Why would that be? I took a series of shots at
    1/60 f/5.6 (chosen by the camera on "P" setting) and 200ASA. If the
    slaved 283 is above the subject to my right, or at 90deg to the
    subject over to my left the shot comes out properly exposed, i.e. I
    can see the effects of the slave flash. But if the 283 is closer in
    to the line of shot (on a table down slightly to my left and in front
    of me, out of view) then the shot is dark, with just the effect of the
    built-in flash and the room lighting. Same exposure. And yes, I
    checked that the slave had fired: first I could see it out of the
    corner of my eye and also I could hear it re-charging.

    The only thing I can think of is a synch problem, but I can't imagine
    how it would happen. Light doesn't take an overly long time to get
    across my living room ...
     
    Henry Law, Jan 1, 2005
    #1
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  2. Henry Law

    Ken Weitzel Guest

    Hi Henry...

    I have (had) the same problem; gave up... :(

    Don't know your camera, but most fire a pre-flash;
    so close in time to the main flash that our eyes
    can't distinguish between the pre and main flash.

    This pre-flash is triggering your slave, so that the
    picture comes out much much worse than it would have
    had the slave not been used at all.

    Happy New Year

    Ken
     
    Ken Weitzel, Jan 1, 2005
    #2
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  3. Henry Law

    Edwin Bont Guest

    The 300D is fireing a preflash.
    If you hold the * button, he wil fire it only once.
    So when you press the shutter, he will fire one flash and the slaves will go
    off at the right time.
    Just hold the * button and you can take the next pictures whitout the
    preflash.

    That works very well, i use it with two flashes and a slavetrigger.
    You can test this by taking a picture of the slaveflash so you can see if it
    went off.

    Good luck,

    Edwin Bont, holland
     
    Edwin Bont, Jan 1, 2005
    #3
  4. I see that you have specific information for your camera...for others, and
    maybe you too, often the manual mode will not fire a pre-flash.
     
    Gene Palmiter, Jan 2, 2005
    #4
  5. Henry Law

    Bob Williams Guest

    Many digicams (Perhaps the 300D) give a preflash in addition to the main
    flash.
    Since you "desensitized" the slave, you may be firing on the Main flash
    when the slave is farther away or off to one side.
    When the slave is closer and in a more direct line with your camera, it
    is probably firing on the Preflash. :-(
    Put a few more thicknesses of tissue over the slave when it is up close
    or in a more direct line to the camera and see what happens
    Bob Williams
     
    Bob Williams, Jan 2, 2005
    #5
  6. Henry Law

    Henry Law Guest

    A good hypothesis which fits the facts observed to date. And now that
    various posts have suggested it I did some research: "The built-in
    pop-up flash unit uses Canon's E-TTL system to meter flash output. It
    does this by firing a low power pre-flash just milliseconds before the
    main flash." (From DPReview's evaluation of the 300D)

    I'll make some more careful tests and see what happens. Thanks!
     
    Henry Law, Jan 2, 2005
    #6
  7. Henry Law

    Cliff Hartle Guest

    There are digital slaves that fire with the main flash.
     
    Cliff Hartle, Jan 2, 2005
    #7
  8. Henry Law

    Peter Gordon Guest

    Try with the camera set to manual mode.
    I have a Canan G5 and this works.
    The Wein PN-XLD Ultra slave works reliably with the
    on-board flash or a Canon 420EX flash mounted on the
    camera. It does not work with the Wireless Emitter
    and the flash off the camera. However, it works in
    manual mode in the above conditions.

    Some of the electronics stores have kits for slaves
    which can count the pre-flashes. The number of
    pre-flashes can be set. I have not tried these.

    Good Luck.
     
    Peter Gordon, Jan 2, 2005
    #8
  9. This is from my experience with EOS300 (NOT D) but I assume that the
    in-built flashes work in the same way. If you use autofocus, the flash
    will fire at a lower power for focusing before it fires to take the
    picture. This focusing flash would often fire the slave. I avoided that by
    using manual focusing.
     
    Gautam Majumdar, Jan 2, 2005
    #9
  10. Henry Law

    Henry Law Guest

    OK, with all your help I've found a foolproof method for this. Manual
    mode was a good suggestion but actually doesn't work - the Canon EOS
    300D still fires the pre-flash (why, we might all ask, since it's not
    doing its own metering). Edwin Bont's suggestion of using the "*"
    button to fire the pre-flash on its own, leaving only the main flash
    is the key to this, but the problem with that is that you use two
    flashes - and two lots of charge-up time - for each shot.

    So now I use a modified version of Edwin's method: when I press the
    "*" button to fire the pre-flash I put my hand over the built-in flash
    and stop it triggering the slave, then take it away and press the
    button.

    I tried Bob Williams' suggestion - of tailoring the amount of
    attenuation of the built-in flash (read: kitchen paper folded over it)
    so that the pre-flash is too weak to fire the slave. It also works
    but needs to be re-done specially for each flash setup. OK for lots
    of shots the same.

    Thanks all. Though I will think about getting a slave unit that
    understands pre-flashes; it would be a lot more convenient. All that
    pressing and holding buttons with fingers and thumbs on the one hand,
    while waving the other one around, is tempting Murphy too much.
     
    Henry Law, Jan 2, 2005
    #10
  11. [re pre-flash triggering a slave]
    Most digicams only fire the pre-flash in program modes. If you use
    manual mode, you should be okay.

    -Joel
     
    Dr. Joel M. Hoffman, Mar 4, 2005
    #11
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