A2 49mm-62mm adapter

Started Mar 5, 2004 | Discussions thread
PeteGanzel
PeteGanzel Senior Member • Posts: 1,417
Birefringence

Hi Jens:

Thanks for creating this informative site.

This property of birefringence is very interesting to me. Many materials are birefrinent, in fact a piece of cellophane can substitute as a "retarder" converting a linear polarizer to a circular one. The thickness determines the amount of the retardation. I'm not sure a quarter wave exactly is necessary, just that some retardation is necessary for focusing to work correctly in an SLR. Also, the birefringent material in a circular polarizer will prevent two polarizers together going to extinction if the birefringent side is between the two polarizers.

Here's a photo with two linear polarizers with a birefringent plastic ruler between them.

The ruler is in effect the "retarder" of a circular polarizer, only this one is not flat.

The rainbow effect is caused by the difference in thickness in the beveled edges of the ruler, effectively going through several rainbow "rotations" of the polarized plane.

Birefringence is the basis of polarized light photography, allowing beautiful renditions of normally colorless materials, especially crystals.

I've got a couple of galleries devoted to this if you're interested;

http://www.pbase.com/pganzel/through_the_microscope

http://www.pbase.com/pganzel/polarizers

Thanks again,

Pete

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