Film-based depolarization and ghosting

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

I am concerned about the film as a source of ghosting in polarized stereo
projection.  Last night I noticed that the projected images (all Kodachrome
pictures taken in the 50s and 60s) showed considerable ghosting (more than
I am used to seeing with my "fresh" Fuji pictures).  I have also noticed
significant ghosting in older Ted Lambert's slides.  One source of ghosting
can be the milky layer that develops in glass-mounted slides with time or
abrasion in non glass-protected slides.  But how about the film material
itself?  I know there are films that depolarize light by nature and there
was a talk about "defective" films that depolarize light while they
shouldn't.  But how about regular every day stuff?

Question #1:  Does the film tend to depolarize light as it ages? 

Question #2:  Is there a difference between different films (Kodachrome,
E6s, etc.) in terms of depolarization of light when fresh or as they age?

To eliminate film-based ghosting, one can place the polarizing filters
after the slide (as in the Compco projectors) and not before as it is done
in the TDC projectors, but if there is no film-induced ghosting I'd rather
have the filters before the slide to offer extra radiation protection.

-- George Themelis


------------------------------