Date: Mon, 7 Feb 2011 11:03:30 -

Author: ---

Subject: FW: my projector screen destroys circular polarization

Post:

Dick,

Let me guess: you missed Avatar.

Michael Thomason, Director of Physics Learning Laboratories
University of Colorado Boulder Department of Physics
303-492-7117
thomason@colorado.edu
http://physicslearning.colorado.edu


-----Original Message-----
From: Michael Thomason [mailto:thomason@colorado.edu]
Sent: Monday, February 07, 2011 10:59 AM
To: 'tap-l@lists.ncsu.edu'
Subject: RE: [tap-l] my projector screen destroys circular polarization

Dick,

The commercial circular polarization systems allow you to see 3d even when
you tilt you head at large angles. The glasses lenses are oppositely
circularly polarized and the projector flashes alternating circularly
polarized frames for each eye. This system is being used for new 3d hdtvs,

Michael Thomason, Director of Physics Learning Laboratories
University of Colorado Boulder Department of Physics
303-492-7117
thomason@colorado.edu
http://physicslearning.colorado.edu


-----Original Message-----
From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Richard Berg
Sent: Monday, February 07, 2011 9:33 AM
To: tap-l@lists.ncsu.edu
Cc: Paul Nord
Subject: Re: [tap-l] my projector screen destroys circular polarization

Folks,

Pardon me for asking a really silly question: Why do you need circularly
polarized light to do this demonstration?

We have been doing this sort of 3D demonstration for decades using
linearly polarized light and 3D glasses, polarized at +/- 45degrees, like
those used in lots of three dimensional movies (at least at the time,
over twenty y ears ago). We purchased the glasses from the people who
distribute them for use in movie theaters.

http://www.physics.umd.edu/lecdem/services/demos/demoso4/o4-52.htm

My recollection is that this technique was used at theaters in
Disneyland and other large amusement parks, at least partly because the
movies could be produced using full color, unlike the "red-blue" three
dimensional technique (anaglyph).

http://www.physics.umd.edu/lecdem/services/demos/demoso4/o4-51.htm

The screen must be a smooth conducting surface, like a thin aluminum
sheet, which, according to Maxwell, does not change the polarization when
it reflects the light.

http://www.physics.umd.edu/lecdem/services/demos/demosm7/m7-17.htm

Dick

On Mon, 7 Feb 2011, Paul Nord wrote:

> 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? 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?
>
> 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 Zani
> Demonstration Manager
> Physics
> Brown University
> (401) 863-3964
>
>
>
>

***********************************************************************
Dr. Richard E. Berg, Professor of the Practice, Retired
Physics Lecture-Demonstration Facility
U.S. mail address:
Department of Physics
University of Maryland
College Park, MD 20742-4111
Phone: (301) 405-5994
FAX: (301) 314-9525
e-mail reberg@umd.edu
www.physics.umd.edu/lecdem
***********************************************************************



From tap-l-owner@lists.ncsu.edu Mon Feb 7 13:19:11 2011

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