Re: [photo-3d] Re: Estar Depolarizes

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

> Greg Dinkins told me that the projector he and Sheldon were using (I
> think it was a TDC-116) did have the polarizers in front of the slides
> and the Dale labs film still wouldn't polarize properly.

All TDC stereo projectors have the polarizing filters behind
the slide carrier.  So, unless he has done something special
to the projector, the polarizers are behind the slide.

Why do stereo projectors have these filters behind the film
and not in front?  To protect the film.  The polarizers cut
off a good part of the radiation which damages the film.  T
his reduction in radiation will take place anyway, so why 
not take place before the film?  If the film does not 
depolarize the light then having the polarizing filters 
between the film and the light source is the best configuration.  
If the film depolarizes the light then there is no choice.

While on this subject, I have noticed that older Kodachrome
slides partially depolarize light.  This manifests itself as
"ghosting". Ghosting shows up in high contrast scenes
where bright parts of the scene show up (with reduced
intensity i.e. as ghosts) in the wrong eye side (e.g. left
instead of only right).  This ghosting or cross-talk
is an inherent problem in polarized light projection.
Other factors that contribute to ghosting include
weak polarizing filters (these can be tested by
crossing them with your viewing glasses) or wrong
type of screen.

George Themelis