[photo-3d] Re: stereo projection dome

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

John A. Rupklavis wrote

>That project involved stereoscopic projection of stereo slides on a 70 foot
>diameter spherical screen.  This screen was actually a balloon...
 
There is a group in the UK which tours schools with an arrangement
like this and we once had them at the university where I work. It
is not stereo projection however but is a portable planetarium with
a centraly placed projector consisting of a drum and disc with holes
for the stars around a bicycle halogen lamp, there is no lens and the
drum can rotate to produce the apparent movement of the stars. I think
the material was an aluminised plastic so stereo projection might be
possible apart from the problems you mention below.

>Although the plastic that the balloon was made of was non-depolarizing on
>axis, it tended to depolarize at an angle.  Although I experimented with
>polarizers, I ended up using anaglyph projection, so that a large area of
>the surface could be covered using Ektagraphics fitted with extreme wide
>angle projection lenses

Unless the material diffuses the light it wont "Depolarise" it but
some plastics do convert to other polarisations such as circular or
elliptical. As yours did not "depolarise" on axis I dont think it
actualy "depolarised" at all but the stong curvature of the dome
and your extreme wide angle lenses would have twisted the plane of
the plane polarised light. I believe this is why Omnimax uses LCD
shutter glasses for stereo projection as you mention below and I
replied to this effect directly to the original post about dome
projection as they suggested but did not keep a copy. P.J.Homer