Bracketing for HDR by Changing Flash Intensity vs. Exposure

Discussion in 'HDR Discussions' started by William Steinmetz, Apr 1, 2016.

  1. William Steinmetz

    William Steinmetz TPF Noob!

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    Who can help me solve this riddle? I recently shot an HDR table-top sequence by stepping my flash intensity through 5 increments from -2 to +2. The illuminated foreground changed as expected, BUT so did the distant sun-lit background even though the exposure was constant through the sequence at 1/125 at f 2.4. Why would the background exposure change too?


     
  2. KmH

    KmH In memoriam Supporting Member

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    What camera make/model?
    What focal length lens?
    What flash unit, what focal length was the flash unit set to?
     
  3. john.margetts

    john.margetts No longer a newbie, moving up!

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    If shutter and aperture were constant, the only way the background exposure could change is if you had ISO set to Auto.
     
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  4. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    The camera adjusted the exposure based on the changes made to the output of the speedlight. Doing so caused the unchanging natural-light background to be rendered different according to the changing exposures.

    Same reason you can easily be blinded by a match in a dark room, but you may not even see it in direct sunlight. The match isn't any darker.... your eyes just adjusted from the dark room to the bright sunlit area.
     
  5. William Steinmetz

    William Steinmetz TPF Noob!

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    I was fooled; the background IS the same in the attached comparison shots from the ends of the HDR range. I was visually tricked by not isolating the background in my comparison, but viewing the whole image.

    Camera: Olympus C8080WZ, 1/125 @ F2.4, ISO 50, internal flash, 31 mm focus
     

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