Can TTL be used with bounce flash?

Discussion in 'Digital Cameras' started by David Arnstein, Feb 8, 2006.

  1. I have access to two flashes that have a TTL mode: the Metz Mecablitz
    54 MZ-4 and the Sony HVLF32X. I am trying to understand what TTL is,
    and in particular if I can use it when bouncing the flash light off a
    ceiling.

    I *think* that TTL means that the camera determines how much light is
    needed, and then signals the flash unit to emit that much light.

    If my understanding is correct, then TTL cannot be used when performing
    "bounce flash." This, because the camera does not know how reflective
    the ceiling is. Therefore, its determination of needed light is not
    possible.

    Am I understanding this correctly? Both of these flash units will do
    bounce flash in TTL mode, without complaining. So I suspect that my
    understanding is faulty.

    These two flash units also offer another automatic mode, wherein the
    camera signals the flash gun what aperture, shutter speed, and ISO
    sensitivity it is using. The flash unit then measures the output of its
    own flash light hitting a sensor on the flash unit itself. The flash
    unit cuts power to its flash tube when its sensor has absorbed the proper
    amount of light for the signalled aperture, shutter speed, and ISO
    sensitivity.

    Right?

    To me, this second mode seems suitable for use with bounce flash.
    Neither the camera nor the flash unit need to know about the optical
    properties of the ceiling. The flash unit uses the good old empirical
    method, measuring light returning from one, two, or more reflective
    surfaces.

    I'd appreciate any corrections to my (very weak) understanding.
     
    David Arnstein, Feb 8, 2006
    #1
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  2. Exactly how TTL flash metering works depends as much on the camera as it
    does on the flash, but usually it means it meters the light coming back
    from the subject through the lens, so it will take the reflectivity of
    the bounce screen into account. Depending on the camera, this metering
    can be achieved during the actual exposure itself or based on a lower
    power test flash emitted either when the shutter release is half pressed
    or immediately before the shutter opens.
     
    Kennedy McEwen, Feb 8, 2006
    #2
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  3. David Arnstein

    secheese Guest

    TTL flash works great with bounced light.
     
    secheese, Feb 8, 2006
    #3
  4. TTL = "thru the lens". The expression came into common parlance when
    light-metering was changed from external, hand-held light meters to built-in
    meters at or near the film plane. Judging by the current demand for old
    Weston Master light meters on E-Bay, it would seem the photographic world is
    going into reverse.

    I can imagine a whole gaggle of digital photographers waving their old Westo
    n Masters around, not believing the aperture/shutter info on the digital
    screen, and going to full manual set-up for each shot.

    Progress? Don't make me laugh!

    Dennis.
     
    Dennis Pogson, Feb 8, 2006
    #4
  5. My Olympus C310ZOOM uses preflashes to measure the exposure in the same way
    the iTTL and dTTL modes do on Nikon DSLRs.

    Ronnie
     
    Ronnie Sellar, Feb 8, 2006
    #5
  6. Not surprising really. Olympus pioneered TTL flash metering 30 years
    ago when they introduced the OTF metering OM-2 and the QA-310 flash
    unit.
     
    Kennedy McEwen, Feb 8, 2006
    #6
  7. So what's the problem? Obviously if you use a slave that doesn't expect
    a pre-flash you know it won't work. Get the right tools for the job.
     
    Kennedy McEwen, Feb 9, 2006
    #7
  8. David Arnstein

    ASAAR Guest

    Bull! You wrote it because you're a trekkie, Cap'n Kirk. <g>

    BTW, the Canon S10/S20 in no way has "close temporal proximity"
    between pre-flash and the main flash. It's impossible to avoid
    noticing both flashes. But as they're fairly old digital cameras
    now (even though I occasionally use the S20) they can be excused.
     
    ASAAR, Feb 9, 2006
    #8
  9. NO! It's because the two flashes fire so close together that you can't
    see it....






    <s>




    That *was* a nice lot of words you put together, tho.

    I am perplexed as to why there's no distance in my EXIF data, either.
    Often I know, but the camera should be able to record precisely what
    it's focussed on....in my case a 20 D with a 50mm Canon lens, for example.
     
    John McWilliams, Feb 10, 2006
    #9
  10. In that particular case, the camera certainly doesn't know what distance
    it is focussed on. Only certain lenses in the Canon range return
    distance data to the camera, and none of the 50mm lenses are included.

    A reasonably up-to-date list of lenses with and without distance
    encoders is at:
    http://photonotes.org/articles/eos-flash/#distancedata
     
    Kennedy McEwen, Feb 10, 2006
    #10
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