Wednesday, April 20, 2016

Polarized light photography for absolute beginners

kw: photography, photographs, polarized light, polarizers

Many years ago I had a film SLR camera, and a rotating polarizer that I could fit to the main lens. If you have a digital SLR or other camera with removable lenses, and the front of the lens is bigger than about an inch or so in diameter, the method described below won't work with that camera. But read on anyway if you like, particularly if you also have a point-and-shoot or even a superzoom camera with a smallish lens.

When light scatters it gets partially polarized. Our eyes do not distinguish polarization so we don't see these effects without a special filter. One kind of scattering is off a shiny, or somewhat shiny, surface. This causes glare if the surface is not metallic; polished metal reflects light without affecting its polarization.

Light striking asphalt, for example, is polarized almost completely when the angle of the light from the vertical is about 50-55°. Light reflecting off auto paint is also polarized, not quite so much, and at slightly larger angles. This is why polarized sunglasses help you see to drive safely in sunny conditions. When you are driving into the sun, much of the light reflected off the road and your car, and other cars, is polarized horizontally, so such sunglasses have vertical polarization and block the horizontally polarized glare.

Light scattered by air molecules is also polarized. Not completely, but about 80% as these pictures show. The greatest polarization is at 90° from the sun, which is about perfect for photos like these. Instead of a special-purpose polarizer I used my polarized sunglasses. The camera can focus right through the lens.

With the sun behind and above me I could shoot at a high angle into the Dogwood tree. The upper photo was  taken without the polarizer and shows the relative brightness of the flowers and the sky to ordinary vision. The second was taken with crossed polarization, so most of the light was blocked. This makes the sky look quite a bit darker. The third was taken with the polarization direction of the sunglass lens parallel to the sky light's direction, and shows the sky looking brighter than in the first picture. This is because the polarizer blocks half the light from the flowers, but lets most of the vertically polarized sky light through.

This trio of pictures, in the same order, shows apple blossoms and young leaves against a similar patch of sky. It produces quite lovely effects, and gives you flexibility to adjust the relative contrast of foreground objects and the sky.

A polarizer can make a partly cloudy sky look lots more dramatic, by darkening the sky around the clouds. A deeper blue sky just looks better for many kinds of landscape photography, and also for some kinds of portrait photography.

The tricky part about using this technique is to hold the camera and press the shutter with the right hand while holding the sunglasses with the other. This is why folks with a DSLR or other camera with a lens that accepts filters will spend $30-$70 for a rotating polarizing filter.

This is more of a "life hack" method for cheapskates like me! And it is a way to learn how polarization works before shelling out for a special filter.

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