Thought of the Day with Unwanted Ambient Light in Flash Photography

Discussion in 'Digital SLR' started by C J Southern, Jan 4, 2006.

  1. C J Southern

    C J Southern Guest

    The other day we were discussing (in part) the subject of ambient /modelling
    light - and the effect it might have on a photo that's (it's desired to
    have) exposed with flash/strobes only.

    Thinking about it last night - if I want to see how much ambient or unwanted
    light is sneaking in, is it a valid technique to simply fire off a shot at
    my intended aperture & shutter speed with the flashes turned off, and "see
    what develops" - with a black or hopelessly underexposed image indicating
    that the ambient light is playing an insignificant part of the exposure?


    C J Southern, Jan 4, 2006
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  2. C J Southern

    eawckyegcy Guest

    Most people just look at the exposure meter: if it's indicating a -2
    or more under-exposure, the flash will be the dominant source of light.
    eawckyegcy, Jan 4, 2006
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  3. In many (most?) circumstance that will not indicate much, though
    it tells more than looking at an exposure meter.

    Specifically, "at my intended aperture" is only easy if you are
    using everything in manual. That is unlikely these days, though
    possible. The results from any form of automatic control will
    of course cause what you see in the no-flash image to be a poor
    representation of the light from flash as compared to ambient.

    But even in manual, the only time it has much significance is
    when the no-flash exposure is nearly *all* black. Just being
    "hopelessly underexposed" is not good enough because for any
    place that has *any* significant light, you do not know if the
    flash will provide half that much, the same, or twice as much.

    Hence the only proof positive way, is a test exposure, either to
    the camera or to an exposure meter (which can measure
    flash). The next best thing is experience that develops enough
    skill at judging lighting setups to be able to make a good
    estimate. Even then it usually just means you can get very
    close on the first guess.
    Floyd Davidson, Jan 4, 2006
  4. Yes, basically, that's a valid test.

    And generally you'll find that's what you get.
    David Dyer-Bennet, Jan 4, 2006
  5. C J Southern

    G- Blank Guest

    Typically ambient light won't sneak in unless your using a
    1/15th or slower shutter speed. For certain types of photo's it can be a

    "To announce that there must be no criticism of the President,
    or that we are to stand by the President, right or wrong,
    is not only unpatriotic and servile, but is morally treasonable
    to the American public."--Theodore Roosevelt, May 7, 1918

    G- Blank, Jan 5, 2006
  6. C J Southern

    C J Southern Guest

    Perhaps I'm wrong, but I would have thought that shooting manual would be
    the norm for studio strobes (as opposed to E-TTL II compatible flashes), and
    anything with flash that's over X-Sync speed?
    C J Southern, Jan 5, 2006
  7. C J Southern

    zeitgeist Guest

    Should not have any effect. Most of you shoot a monolight with a couple
    hundred watt seconds of light, maybe even 5 or 600 worth.

    A 'watt second' is the equivalent of a light bulb burning for one full
    second. So a 100 watts second flash is about what a 100 watt bulb would
    give if you used a one second exposure. you would need 2 bulbs to get a
    half second, 4 to get a 1/4 second, 8 to shoot at one eighth. and 16, well
    you get the idea. So what is the wattage of your modeling light? 100,
    150, 250? Lets say 250, how many stops would it underexpose if your flash
    failed to fire? If its more than 3 stops then you won't have much of an
    image, 2.5 stops was the max you could print with a storm of grain and color

    This reply is echoed to the z-prophoto mailing list at
    zeitgeist, Jan 5, 2006
  8. Sure, but the opening sentence in the OP's query was:

    "The other day we were discussing (in part) the subject of
    ambient /modelling light - and the effect it might have on a
    photo that's (it's desired to have) exposed with
    flash/strobes only."

    And the rest of his discussion mentioned only "ambient" and
    "flash", hence it is doubtful that his question was about studio
    work (which is precisely the "though possible" in my response),
    as opposed to recognition that it would be a similar problem.
    Floyd Davidson, Jan 5, 2006
  9. That is true, and a good discussion. But it needs to be clear
    that it discusses a *modelling light* (co-located with the
    strobe) only. Other ambient light, coming from light source in
    different directions than the strobe, cannot be evaluated in the
    same way because the intensity will vary in a different manner
    (e.g., shadows will be in different locations) than the strobe.

    And example would be bright sunlight coming through a window to
    the left of a posed subject, with for example two
    strobe/modelling lights providing the main illumination from the
    front and right of the subject. (Or replace the "sunlight" with
    a relatively bright flourescent fixture with four or more tubes
    in it, to get a really disgusting variation! :)
    Floyd Davidson, Jan 5, 2006
  10. C J Southern

    C J Southern Guest

    The OP was me - and I was thinking of indoor work at the time. You're
    right - I did leave a few too many doors open in asking the question.


    C J Southern, Jan 5, 2006
  11. That's not a problem... as long as the reply covers all the bases;
    and you can then filter out the part you don't need.
    Floyd Davidson, Jan 5, 2006
  12. C J Southern

    Hunt Guest

    Depending on the amount and things like spectals, that is why I often darken
    the studio completely, and turn the modeling lights off. If one doesn't have
    Broncolor, or similar strobes, the modeling light beam will be different than
    the flash tube's light beam. A mini-Maglite with the little mouth grip works
    great to keep the photographer from tripping over the set, the tripod legs, or
    wires. Just don't let the Maglite's beam fall on the subject, if the shutter
    speed is very slow. Had a problem with an Ampex video switcher once, and kept
    getting a reflection, that moved from sheet to sheet! After about an hour, my
    assistant, pointed out that I'd place the flashlight into my back pocket, turn
    around to the camera, and that the flashlight's beam would reflect off of the
    set and onto the product!!!!!!! Lot of wasted 8x10 Ektachrome that day, but I

    Hunt, Jan 6, 2006
  13. C J Southern

    Hunt Guest

    And, along those lines, try to shoot electronic gear in a plant, with "
    emergency" flourescent fixtures, that cannot be turned off, AND you need to do
    a "double-burn" for gauges, LED's, etc. I've had to build a black tent over
    such products, even with 20,000 WS of strobe power, because I needed to get
    some semblance of glow from the dials, or CRT's.

    Hunt, Jan 6, 2006
  14. C J Southern

    C J Southern Guest

    Did you fire than "damned" assistant for not spotting it sooner? ;)
    C J Southern, Jan 6, 2006
  15. C J Southern

    Hunt Guest

    No, she got a bonus, as I'd probably STILL be working that shot! Along the
    same lines, I learned to have assistants dress in black, when doing night time
    interiors, so they would not show up in some window, off to the side. By the
    '80s, it seemed that they all work black anyway - same for the youthful art

    Hunt, Jan 6, 2006
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