November 5, 2011

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Fill Flash Balances Foreground with Backdrop

By Alex Wild

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This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

Here's a simple image of a bug on a branch:

Appearances aside, producing this image was technically more challenging than my usual fare. Both the sky and the insect are properly exposed, meaning I essentially had to plan and meter for two photographs in one exposure.

Consider the scene with only natural sunlight and the camera metered for the sky:

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To correct for the dark, underexposed bug I added foreground light in the form of a diffused radio-triggered flash. Thus, the full process behind the top photo was as follows:

  1. Set bug on a stick with an off-camera strobe positioned nearby (just off-frame to the top-left).

  2. Arrange orientation so that sunlight backlights the bug, highlighting its outline.

  3. Set aperture for desired depth-of-field (f/16).

  4. Metering on sky, adjust ISO (200) and shutter speed (1/200 sec) to expose backdrop for the desired shade of blue.

  5. Manually adjust fill flash until the bug is properly exposed (Canon 55o EX strobe at 1/32 power).

Although these mixed ambient/strobe shots take additional preparation, they result in photographs that show both the insect and its environment.

 

Alex Wild is Curator of Entomology at the University of Texas at Austin, where he studies the evolutionary history of ants. In 2003 he founded a photography business as an aesthetic complement to his scientific work, and his natural history photographs appear in numerous museums, books and media outlets.

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