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Compound Eye

Compound Eye

The many facets of science photography

A more realistic focus-stack

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Eupholus weevil

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 groups devoted to the technique.

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:

f/14, strobes at high power, lens focused to bottom of planned focus stack. Note the top of the insect is out of focus.

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 background of the top image is a capture at f/14 and high-power flash. The bottom image shows a regular focus-stack at f/8 without a separate small-aperture image included.

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

To purchase a print of the weevil: http://bit.ly/WrVlmp


postscript: for those interested in gear, the images here were taken with a Canon 7D camera and MP-E 65mm macro lens mounted on a vertical macro rail. Lighting was provided by 3 flashes and diffused by a plastic cone around the subject. The yellow background is construction paper. Images were stacked in Combine ZP and cleaned in Adobe Photoshop.

The views expressed are those of the author and are not necessarily those of Scientific American.

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