No Subject

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

ROdiger Pein wrote

>Also he showed me a special silver screen without any surface protection
>and said that other screens would depolarize some of the light.
>This special screen was about $150 per m^2 and every contact with it
>destroyed parts of the surface. Not very nice...
>Does anyone have other, cheaper, more tricky solutions?
>And if I understood the polarizer discussion correctly: Can I only use
>linear polarizers for my projectors, can I also use circular ones, or
>can I use circular ones only in one direction?

White screens certainly depolarise light the transparent protective layer
on some silver screens actualy is more likely to act as a retarder and
convert it to some other polarisation form but the effect is the same it
screws up your projection . Circular polarisation has been used for stereo
projection but not often it has only one advantage that I know of you dont
see double images if you tilt your head. For a long time certainly up to
1964 it was not possible to produce achromatic circular polarisers  apart
from bulky prism type devices but it seems it can now be done judjing from
the camera and computer screen polarisers available. There have been posts
from other people in this group who have had experience using circular
polarisation who could advise you  I believe one of them mentioned that
there was an even greater light loss than with linear. I am not shure what
you mean by  "can I use circular ones  only in one direction?" but you will
need both directions of rotation for stereo projection.
 The only sources of the material I can think of are the computer and
camera filters both expensive but you get quite large sheets with the
computer filters but I dont know if you could get both rotations this way.
P.J.Homer



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