Lighting technique using polarizer?

Suhas Kulkarni , Mar 10, 2005; 05:27 a.m.

Some days back I read an article (in local magazine) on how to use circular polarizers with special lighting to create rainbow color effects in macro photography - particularly crystals or semi- precious stones or transparant plastic scales etc. The article contained some description like using a tungstan bulb light source to pass through circular polarizer and then come on the transparant subject which causes the color effects. The article also contained sample photographs which were quite impressive. I lost the copy of the magazine

Can someone point me to link of such technique, if it is there on internet? I tried to search, but what I got was only how to photograph snow / quartz crystals. But how the polarizer creates multiple colors is not shown anywhere

thanks in advance

regards, Suhas

Answers

Nikos Peri , Mar 10, 2005; 06:14 a.m.

You need to have a polarized light source. Put a polarizing gel on your light, AND a polarizing filter on your lens. Go nuts... it's fun.

Max Zomborszki , Mar 11, 2005; 02:55 a.m.

You can get this effect by placing a plastic object between two crossed sheets of polarizers. Engineers sometimes use this method to detect places of stress in constructions. They make a plastic replica and apply stress to it to see where it affects the construction. This method is called "photoelastic stress". Not many good pictures that I found but here are some sites that mention this:

http://www.physics.montana.edu/demonstrations/video/6_optics/demos/photoelasticstressfigures.html
http://www.brantacan.co.uk/polarizing.htm
http://hypertextbook.com/physics/waves/polarization/

Edward Ingold , Mar 11, 2005; 10:03 a.m.

Many crystals are birefringent, which means different polarization planes of light have different refractive indices, and the planes of polarization tend to rotate as they pass through the material. Since birefringence various with wavelength, different colors are affected differently, hence the rainbow effect.

To observe or photograph this effect, the subject is placed between two crossed (or partially crossed) polarizers. For photography, one polarizer is placed on the light source, which is passed through the subject, and the other on the camera.

Besides crystals, transparent plastic materials exhibit birefringence which varies with stress. Some stress is built-in, as in plexiglass windows or tempered glass, but can be seen to vary as you bend or stretch these or similar materials.

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