P3D Polarizing Lenses

[Michael Georgoff <Michael_Georgoff@xxxxxxxxxxxxxx>]

I see that Ron Labbe had posted to S3D that he has polarizing filters
available for projectors.  These are, per his web page, 67mm Vivitar glass
polarizing filters which are added  to the front of the projector lenses for
stereo projection. Two questions:

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.

3. How might light transmission of a Vivitar filter compare to, say, a set
of plastic filters, as typically available from Reel 3D or Dalia?  Might a
Vivitar polarizer be "more efficient," meaning more light transmitted??

For some reason I never equated projection polarizers with photographic
polarizers.  I guess they're both linear polarizers...

Michael Georgoff
San Jose, CA 


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