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P3D Re: Projection problems


  • From: Paul Talbot <ptww@xxxxxxxxx>
  • Subject: P3D Re: Projection problems
  • Date: Tue, 24 Aug 1999 01:07:45 -0500

Dr. George A. Themelis quoted and wrote:
 
> >I'm getting such extreme ghosting that the images are
> >effectively unviewable.  The problem seems to be lack of
> >(or insufficient) extinction in the right-eye view.

> It is hard to think of way that the screen will selectively
> depolarize one image.

It might be a "brain interpretation" effect.  With a slide
in the projector, I see double images when I close my left
eye.  I don't see them when I close my right eye.  It is
odd because when viewing projection I have never before
seen ghosting in the right eye image.  When I see ghosting
in normal stereo projection, I only see it in the left eye
image.  I would think ghosting must BE in both images, but
I never see it like that.

So I suppose it is possible both sides are depolarizing.
I can't see any difference between left and right sides
when I test without trying to view a slide in 3D.

> >But when I place a pair of polarized glasses in
> >front of the projector lenses, the screen goes completely
> >dark.  This suggests the polarizers in the projector must
> >be OK, right?
> 
> To simplify things, pull out the polarizer assembly
> (very easy: remove top, grab assembly with both hands
> and pull straight up) and test each filter with one
> side of the glasses.  Look at a bright light source
> and see how much goes through.

I did that already, sort of.  But I just looked out a
window.  There was darkening, but not as much as I had
expected.  There was *much* more darkening with two pair
of glasses.

> >I find that if I project
> >one side at a time, the image on the screen is mostly still
> >viewable with either eye, though one side is slightly dimmer
> >than the other.
> 
> Seems that you need new polarizers!

But the glasses placed in front of the lenses block out almost
100% of the light from the projector.  (And block out almost
none if I flip the glasses upside down.)  So the light must
be getting polarized in the projector, right?

I also tried viewing the images with a pair of glasses in
front of the projector.  I figured that would simulate the
effect of replacing the polarizers.  There was no improvement
in viewing the images.

Paul Talbot


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End of PHOTO-3D Digest 3463
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