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Tuesday, June 19, 2012

Cross With Purpose

Reflecting On Reflections • The Triggertrap App • Stacked Converters • Autofocus At F/8

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Cross-polarization improves the rendition of this lustrous piece of petrified wood by removing reflections that mask true color and detail. In the first image [above], captured with two flashes and a 100mm macro lens, glare hides the complexity of color in the wood. In the second image [below right], cross-polarization of the light sources and lens reveals color and detail. No Photoshop enhancement was used. Canon EOS 5D Mark III and two Canon Speedlite 580EX flashes.

Reflecting On Reflections
Many exciting nature subjects come with a built-in photographic challenge: reflections that mask color and detail. It's a particular problem with minerals, shiny flower and leaf surfaces, or anything that's wet or moist, such as tide pool denizens. In the studio, controlling reflections is a factor when photographing jewelry, coins and crystals. No, you can't just fix it in Photoshop—at least, not yet. But there's an excellent solution to the problem: cross-polarization.

A single polarizing filter is a common photographic tool used to darken skies, improve color saturation and eliminate reflections when photographing through glass or plastic. More control is gained when the light source and lens are cross-polarized; that is, polarizing material is placed over the light source(s) and a polarizing filter is placed over the lens and aligned in such a way that nearly all divergent light rays from the subject and the light source are kept from entering the lens. The technique doesn't get every reflection on a multifaceted subject because to do that would be to cut out all light from every direction. But cross-polarization does eliminate nearly all reflections and enhances the discernable colors and detail in the subject.

I first used this technique years ago when I was involved with art conservation photography. I was shooting large-format images of art for museums, either to document them or for use in exhibition catalogs. Oil paintings with lots of varnish have reflections that are normally impossible to eliminate with standard lighting. I used two large studio flashes covered with polarizing material along with a polarizer over the camera lens; the combination amazingly cut through the glare, revealing all the color and none of the brushstroke reflections. I then applied the technique to nature subjects, such as wet specimens, minerals like quartz and shiny black beetles.
Place the polarizer on the lens, and look through the camera into a mirror. While looking through the viewfinder, rotate the lens polarizer until you see the flash polarizers go black. Mark that position on the lens polarizer so the next time the setup will be easier to adjust for maximum cross-polarization without the need for a mirror.
You'll need two (one will work, but not as well) electronic flashes (a large hot-shoe type is adequate), a circular polarizer for the lens and polarized material in sheets, available from www.Polarization.com and Edmund Optics at www.edmundoptics.com/optics/polarizers/linear-polarizers/visible-linear-polarizing-laminated-film/1912.


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