Preflashes

Discussion in 'Photography' started by Gary Morrison, Aug 14, 2003.

  1. On my Nikon D100, and I suspect this applies to at least some Nikon film
    cameras as well, the built-in flash performs a virtually imperceptably fast
    series of preflashes in order to gauge how brightly to fire the flash. I
    confess that I didn't quite completely follow all of the description in the
    book, in part because it references single-letter lens types I'm not
    immediately familiar with, but I'm wondering one thing: can this feature
    be disabled entirely?

    I ask because my brother, a freelance photographer, has a "classic"
    portrait-oriented, optically-fired slave flash unit, and the preflashes
    appear to be firing off that unit prematurely.

    This gismology is, although very welcome, still a little foreign to me.
    Until I got the D100 a couple weeks ago, the only SLR I've really worked
    with had been with an aaaaaaaancient purely-mechanical Pentax, back from
    the Pentax line's earliest times in America when Honeywell was importing
    them and stamping their name on them.
     
    Gary Morrison, Aug 14, 2003
    #1
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  2. Gary Morrison

    Ender W. Guest

    Some cameras will disable the first flash if the camera is put into
    manual mode.
     
    Ender W., Aug 14, 2003
    #2
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  3. Gary Morrison

    Brian Guest

    I had a Canon EOS 300 which would fire a series of short flash blasts if
    flash was required, it was linked to the auto focus mechanism, to enable it
    to operate in low light situations, it also used it as a red-eye reduction
    feature, apparently to narrow the pupil of the "victim" shortly before the
    "real " flash fired, there by reducing the pupil size and cutting down the
    amount of light hitting the retina and in turn the amount of red-eye
    bouncing back from the eye.
    Both features could be disabled, the red-eye, through the function buttons,
    and the auto focus part could be disabled by using manual focus, or ensuring
    that the flash didn't pop up during auto focus, or by using manual settings.

    Brian..........................
     
    Brian, Aug 14, 2003
    #3
  4. Gary Morrison

    dave Guest

    my dimage 5 *always* fires a preflash when the internal flash is used.
    i can work around this (well, sort of) by attaching an external flash. in my
    case a jessops unit, that ignores the preflash. obviously when doing this,
    you need to set the camera settings manually based on the exposure table
    printed on the back of the flash. the downside is, there is now a delay of
    about 0.4s between pressing the release button and the flash actually firing
    (the camera thinks it's doing a preflash, but isn't). this is fine if you're
    doing static shoots, but for moving objects (motorsport photography etc)
    it's fatal.

    not sure if the d100 will work the same, but may be worth a go.
     
    dave, Aug 14, 2003
    #4
  5. i can work around this (well, sort of) by attaching an external flash.

    Thanks for the replies, folks!

    My brother was able to get around this using his Vivitar flash unit on the
    D100's hot shoe. He pointed out though that the Vivitar unit has strictly two
    contacts, whereas the hot shoe itself has ... I think a total of 5. He
    suspects that, if a flash unit with all five contacts were connected, it would
    play the same tricks as the built-in flash and thus, once again, not work with
    his slave flash unit. Any thoughts on that?
     
    Gary Morrison, Aug 14, 2003
    #5
  6. Gary Morrison

    Chris Hoopes Guest

    By default, the D100 is set to D-TTL mode, which fires off the pre-flashes.
    You can disable this in the menu by setting the flash mode to Manual.
    Depending on the flash you are using, it will fire at full power when the
    camera is set to Manual mode.
     
    Chris Hoopes, Aug 14, 2003
    #6
  7. Gary Morrison

    Tom Thackrey Guest

    From the D100 manual: Custom setting 23 if set to 'manual' will stop the
    preflashes.
     
    Tom Thackrey, Aug 14, 2003
    #7
  8. Gary Morrison

    Frederick Guest

    Gary,

    are you sure this is for judging the amount of light? Some built in
    flashes omit a series of pre-fire flashes as a red-eye reduction. This
    helps adjust the subjects eye to the bright light coming and helps to
    reduce the amount of red-eye you will get.

    If this is the feature you are experencing, then yes it can be turned
    off.
     
    Frederick, Aug 14, 2003
    #8
  9. Gary Morrison

    Charlie D Guest

    Just trying to help you in future communication.
    For the second word of the second sentence you should have said Emit,
    not Omit. They have essentially the opposite meaning in this context.
     
    Charlie D, Aug 14, 2003
    #9
  10. Gary Morrison

    Todd Walker Guest

    Everytime a thread is started here about preflashes, someone says that
    it's the redeye reduction. NO, it isn't.

    From www.srelectronics.com:

    "Most popular digital camera lines have inadequate flash systems and
    lack a connector for use with an external flash. Ordinary slave units
    will not work with most digital cameras because these cameras use a very
    rapid series of pre-flashes (we're not talking about red-eye reduction).
    The pre-flashes are used to set the white balance of the camera's image
    sensor chip - not the exposure. A typical slave unit will fire on the
    pre-flash it senses while the digital camera captures the image on the
    last flash. Thus, the extra light from the slave does not show up in the
    digital camera photo."

    --
    ________________________________
    Todd Walker
    http://twalker.d2g.com
    Canon 10D:
    http://twalker.d2g.com/canon10d
    My Digital Photography Weblog:
    http://twalker.d2g.com/dpblog.htm
    _________________________________
     
    Todd Walker, Aug 14, 2003
    #10
  11. Yes, this is definitely not red-eye reduction, according to the manual. I'm familiar with what
    that looks like, and the D100 has a different light for that purpose - the same one it uses for
    auto-focus illumination. Also, these preflashes take an almost completely imperceptible fraction
    of a second to happen.

    That much I have read in the manual, but apparently I haven't yet gotten to the part where it says
    that you can turn off the preflashes by setting the flash to manual mode.
     
    Gary Morrison, Aug 14, 2003
    #11
  12. Gary Morrison

    Les Marquart Guest

    Don't know about the D100 but the Oly cameras I have use this
    imperceptible flash for white balance reading. It cannot be turned off
    in any mode if flash will be used. You can buy slaves that ignore the
    first flash - Digislave for one.
    Les
     
    Les Marquart, Aug 14, 2003
    #12
  13. Gary Morrison

    Paul Brecht Guest

    That is correct...

    The "D" function of lenses & flash is designated because it is for distance
    encoding. (not meaning for digital)

    With the distance encoding, the flash does not use TTL metering during
    exposure, but rather calculates distance from the distance encoding chip in
    the matching lens. Thus, the flash is set automatically to produce a
    specific GN power. Once the shutter is released, the flash fires a
    "pre-flash" to make sure it's being recorded & the exposure, based on GN
    calculations produces correct exposure...

    Well... Theoretically that's the way it's supposed to work. I don't really
    think it's all that because you can't use it with diffusers or bounced
    flash. I really don't find direct flash (spotlight in your eyes) very
    flattering. Another flaw I find is that if you're more than 15 feet away,
    the pre-flash weakens the actual burst firing during exposure causing
    under-exposure in a lot of cases...

    You can disable the pre-flesh & "D" encoding in a custom function in the
    camera. If you are firing studio strobes, you should be using "M" mode and
    not using TTL or D encoding anyway.

    You should have everything set to manual. Aim the flash away from the
    subject (bounce it off the ceiling or wall) & have it turned down to the
    minimum power that will be able to trigger the slaves in the monolights.
    Have your shutter speed slower than 1/60 & your f-stop will determine your
    exposure...

    Paul
    ////////////////
     
    Paul Brecht, Aug 15, 2003
    #13
  14. The C-5050Z at least has a mode to turn off the pre-flash. Earlier C-* cameras
    did not have this option (dunno about the E10/E20). I would imagine the
    C-750UZ might also have it, since it was made after the C-5050Z, assuming that
    they reuse the firmware between models.
     
    Michael Meissner, Aug 16, 2003
    #14
  15. As another replier (if that's a word) pointed out, that is also available on the
    D100 through custom setting #23 (I think that's the number), flash mode of manual.
    I independently verified that by picking up a flash unit that can act as a slave
    flash, and it does indeed work as such now.
     
    Gary Morrison, Aug 16, 2003
    #15
  16. Gary Morrison

    Terry Smith Guest

    G'Day Gary,

    I use a NIKON CP880. I just constructed for myself a project that appeared
    in the July issue of "Silicon Chip Magazine". This device is programmable
    and be me set to fire any flash with between 1-31 pre-flashes coming from
    the host. Works GREAT! Cost AUD$27 (in kit form).


    Terry.

    p.s. IKELITE makes a "Smart" flash that ignores the pre-flash.
     
    Terry Smith, Aug 16, 2003
    #16
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