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A more realistic focus-stack

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


Why is this beetle so crisp?

The clarity results from the image being not a single photograph but a composite. I took 50 exposures at different focal depths and merged them in a file sharp enough to cut diamonds.

This extra-clean look is increasingly common, and for a reason. Digital cameras and focus-stacking software are now affordable enough that "stacking" as a genre is positively thriving. Check out Flickr's many groupsdevoted tothe technique.


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Since the method creates optically impossible images- no lens can produce a sharp image over an extended focal plane- stacks exude a surreal quality. An experienced eye can pick them, as most stacks transition from sharply focused to completely blurry with little subtlety. The in-focus bits are insanely crisp, and the out-of-focus bits are butter creamy.

I have been experimenting with disguising the telltale focus boundary. Since the point of stacking is to increase sharpness, blurring over the stack's focused parts would be counterproductive. Instead, I settled on boosting background detail the old-fashioned way.

Once I had taken all the exposures to be included in the regular stack, without moving the camera or the beetle, I stopped the lens down, boosted flash power to compensate, and took one more photograph. This final capture left a similar but softer exposure with more native depth of field:

When the high DOF image is added to the stack as background, the image acquires a more realistic aspect while retaining its Whiz-Bang stack sharpness. Compare a stack with an additional small-aperture background file (top) to a stack without one (bottom):

The improved image is still the result of severe digital manipulation, but it doesn't look as much like it.

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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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