P3D Re: Polarizing Lenses

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

>1. What, if any, is the advantage of polarizing at the "last optical step"
>(instead of typically before or after the slide, but before the lens, at any
>rate)?  Seem a whole lot easier to put polarizers on the end of the lens.

Polarizer location    Advantage   
------------------    --------------------------------------------------------
Before slide          Cuts off radiation from reaching slide (2 stops of light)
                      Assuming that polarization remains unaffected by what
                      happens after the slide, it makes sense to cut off the
                      radiation and protect the slide if this radiation will
                      be lost anyway.

After slide/lens      Minimizes ghosting.  Some films depolarize light.  In
                      addition to the known films that do depolarize the light,
                      I have noticed that older Kodachrome (ca. 60s) also
                      depolarizes to some degree.  This loss of polarization
                      manifests itself as "ghosting".

George Themelis


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