Date: Mon, 7 Feb 2011 08:41:17 -

Author: --- Paul

Subject: Re: my projector screen destroys circular polarization

Post:


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Ah, thank you. That makes sense. We were puzzled about movie screens. =
It shouldn't be surprising that a 3D movie requires a special screen.

Can I throw one more subtlety out for the wisdom of tap-l?
When aligning the polarizer and quarter-wave films in front of =
the projector, I found that I needed a specific alignment of the =
polarizer for the effect to work best. Not only did the fast axis of =
the quarter-wave film need a specific alignment relative to the =
polarizer, but the entire polarizer worked best if it too was at a =
particular alignment. If I, wearing Real-D glasses, turned my head too =
far sideways, the effect was lost. But I had to turn my head more than =
45=BA to see this effect.
Is it just that the glasses and my filter setup are not purely =
circular polarizers? Is there still some combination of linear and =
circular polarization going on?

Paul

On Feb 7, 2011, at 5:51 AM, Zani, Gerald wrote:

> A change in the polarization by the reflection from the screen and the =
paint surfaces?
>=20
> No change in polarization by reflection from the black board, the =
original polarization is preserved.
>=20
> Some initial thoughts early Monday morn after cup-o-joe. - J
>=20
> On Mon, Feb 7, 2011 at 5:02 AM, William Beaty =
wrote:
> On Sun, 6 Feb 2011, Paul Nord wrote:
>=20
> When you hold an object (buckeyball model) in the path, you get a pair =
of shadows cast on the far wall. If you wear REAL-D glasses each eye =
only sees one of the shadows. And you will see a 3-D image from the =
shadows.
>=20
> Back in the old days, if you wanted to do a 3D stereo slideshow with =
two projectors and polarizers, either you had to buy an expensive =
polarization-preserving metallized screen, or you could use brushed =
sheet metal or the matte side of aluminum foil. I think "rear =
projection" type screens also might have worked too.
>=20
> I suspect that the problem comes from multiple scatterings. Wouldn't =
incoming light remain polarized if it was reflected from just one =
surface, rather than bouncing around inside transparent particles inside =
"white" paint?
>=20
>=20
> (((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
> William J. Beaty http://staff.washington.edu/wbeaty/
> beaty, chem washington edu Research Engineer
> billb, amasci com UW Chem Dept, Bagley Hall RM74
> 206-543-6195 Box 351700, Seattle, WA 98195-1700
>=20
>=20
>=20
> --=20
> Gerald Zani
> Demonstration Manager
> Physics
> Brown University
> (401) 863-3964
>=20


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When aligning the polarizer and =
quarter-wave films in front of the projector, I found that I needed a =
specific alignment of the polarizer for the effect to work best. =
Not only did the fast axis of the quarter-wave film need a =
specific alignment relative to the polarizer, but the entire polarizer =
worked best if it too was at a particular alignment. If I, wearing =
Real-D glasses, turned my head too far sideways, the effect was lost. =
But I had to turn my head more than 45=BA to see this =
effect. Is it just that the glasses and =
my filter setup are not purely circular polarizers? Is there still =
some combination of linear and circular polarization going =
on?PaulOn Feb 7, =
2011, at 5:51 AM, Zani, Gerald wrote:A change =
in the polarization by the reflection from the screen and the paint =
surfaces?No change in polarization by reflection from the black =
board, the original polarization is preserved.Some initial =
thoughts early Monday morn after cup-o-joe. - J

On Mon, Feb 7, 2011 at 5:02 AM, William =
Beaty =
wrote:

On Sun, 6 Feb 2011, Paul Nord wrote:


When you hold an object (buckeyball model) in the path, you get a pair =
of shadows cast on the far wall. If you wear REAL-D glasses each =
eye only sees one of the shadows. And you will see a 3-D image =
from the shadows.




Back in the old days, if you wanted to do a 3D stereo slideshow with two =
projectors and polarizers, either you had to buy an expensive =
polarization-preserving metallized screen, or you could use brushed =
sheet metal or the matte side of aluminum foil. I think "rear =
projection" type screens also might have worked too.



I suspect that the problem comes from multiple scatterings. =
Wouldn't incoming light remain polarized if it was reflected from =
just one surface, rather than bouncing around inside transparent =
particles inside "white" paint?




(((((((((((((((((( ( ( ( ( (O) ) =
) ) ) )))))))))))))))))))
William J. Beaty =
http://staff.washington.edu/wbeaty/
beaty, chem washington edu Research Engineer
billb, amasci com UW =
Chem Dept, Bagley Hall RM74
206-543-6195 =
Box 351700, Seattle, WA 98195-1700
-- Gerald =
ZaniDemonstration ManagerPhysicsBrown University(401) =
863-3964
=

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