Date: Mon, 07 Feb 2011 16:47:28

Author: ---

Subject: Re: my projector screen destroys circular polarization

Post:

There are now many 3D formats being used for projection and home TV's,
each with slightly different physics. Linear polarization, as Dick
described,
uses "silver" (metallic) screen and preserves linear polarization.

Circular polarization. The RealD movie system uses a single projector with
a electronically switchable Phase Plate in front, so the circular
polarization
is changed sequentially from right to left handed as the right and left
views
are displayed. This can also be done with two projectors and fixed
circular polarizers. Circular polarization is NOT preserved on
reflection from
the silver screen, it is inverted, so left hand becomes right hand
polarization.
Try this with your RealD glasses and a mirror, and compare to linear glasses
and a mirror. (notice which eye is blacked out on reflection).

The first modern HD TVs using shutter glasses were DLP projectors
(Samsung and
Mitsubishi) which put up the right and left views in a checkerboard
pattern. The
current generation of sets alternate the "whole" left and right views at
120 Hz and
can be dlp, plasma or LED. The passive circular polarization sets are
coming next.

There are now TV's and laptop screens which use circular polarization.
These
are passive screens, with every other row or column covered with fixed
circular
polarizer. Here is one laptop with a circular polarized screen
http://www.amazon.com/Lenovo-Ideapad-0646-2KU-15-6-Inch-Laptop/dp/B003N2OVTI
So far, large passive circular polarized TV's are much more expensive
than active
shutter glass systems, but that may be changing. Here are JVC 3D TVs
using circ pol.
http://pro.jvc.com/pro/microsite/3d/technology/xpol.html
This technique cuts the vertical resolution in half.

The holy grail is glassless viewing, which can be done with barrier screens,
directed light source backlighting, lenticular and holographic screens.
Many
TV manufacturers have shown prototype sets for many years but few have
come to market because of inherent limitations, such as limited sweet spots,
limited depth and resolution. I have a small 3.5 inch glassless 3D
(autostereoscopic) screen on the back of my 3D Fuji W3 camera.
http://www.amazon.com/Fujifilm-FinePix-Real-3D-W3/dp/B003ZHV70M

Marty







On 2/7/2011 11:29 AM, Michael Thomason wrote:
> This is a new Samsung Real 3d system for hdtvs. They might not be available
> yet,
>
> 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 Sam Sampere
> Sent: Monday, February 07, 2011 11:19 AM
> To: 'tap-l@lists.ncsu.edu'
> Subject: Re: [tap-l] my projector screen destroys circular polarization
>
> Areyou sure the 3d HDTVs are polarized?? There are two pixels for every
> element, one for each polarization? How do you polarize the light from an
> LED without using polarizers? I thought the glasses were shuttered, and
> that's why they were so expensive. One eye sees one frame, the other eye
> sees the other frame.
>
> Sam
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
> Behalf Of Michael Thomason
> Sent: Monday, February 07, 2011 12:59 PM
> 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 20:05:59 2011

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