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Thread: Is the focal length multiplication factor considered in flash photography

  1. #1

    Default Is the focal length multiplication factor considered in flash photography

    Hi all,

    My apologies if this has already been answered here earlier.

    I am wondering if the zoom setting of the auxilliary flash takes into account the focal length multiplier in DSLRs (like D30, S2 Pro, etc.)

    For example, if I have a 50mm lens mounted on a D30 and with a 420 EX mounted on it, will the zoom setting on 420 EX be 50 mm or 80mm. (I believe if the setting is 80 mm the effective guide number will be higher).

    Thanks in advance.
    Rao

  2. #2
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    not sure for Canon, but for Nikons, it's a no. cos the FLM is just a crop of the 35mm image size and the focal length of the lens doesn't really change.

    so essentially you're flash-exposing for a lot more area than what your camera sensor actually captures.

  3. #3

    Default

    Thanks for the reply Larry.

    As the camera knows the focal length and also the multiplication factor, shouldn't the camera be reducing the angle of flash illumination resulting in higher GN.

    Regards.
    Rao

  4. #4
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    Originally posted by N V Rao
    As the camera knows the focal length and also the multiplication factor, shouldn't the camera be reducing the angle of flash illumination resulting in higher GN.
    i don't think the camera communicates the FLM values to the flash unit (despite the DX tag on the Nikon Speedlights). hence it has no way of knowing if it's a full frame cam (like the Kodak 14n) or the 1.5x FLM like the D1/100 cameras.

    Thom Hogan recommends manually zooming in the flash head to accomodate for this phenomenon, but in the field, if you're shooting and zooming your lens in and out qiuckly, that's too troublesome to bother with.

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