T3D Re: T3D polarization & rear projection?

[bercov@xxxxxxxxxxx (John Bercovitz)]

Jim C. writes:
> I'm sure this has come up before, but I just can't remember.  Is it
> possible to maintain polarization using a rear-projection screen?
 
That was actually a fairly recent topic on P3D.  I've seen the screen
of which Andrew speaks and it is excellent.
 
John B
 
> Date: Wed, 14 Jan 1998 13:29:14 +0800 (WST)
> From: Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>
> To: photo-3d@xxxxxxxxxxxxxxxxx
> Subject: P3D Re: Consumer Electronic Show report... AND MORE!
> Message-ID: <199801140529.NAA17279@xxxxxxxxxxxxxxxxxxxxx>
> 
> MarkKernes <MarkKernes@xxxxxxx> wrote:
> > However, at the Consumer Electronic Show last week, I saw a display at the QD
> > Technology booth that may bear on this question. The 3D image in question,
> > measuring about 6"x8", was mounted in a light box, and while the 3D didn't
> > show much depth, it was the smoothest 3D I've ever seen in what I assumed was
> > lenticular format. There were NO "lens" lines that one always sees with
> > lenticulars, and the guy running the booth, Brad (?) Nelson, denied that the
> > photo was lenticular; said it was some other process.
> 
> I believe the image is a parallax barrier type 3D image.
> 
> > But much as I was impressed by the lent, I was even more impressed by his big-
> > screen TV which was displaying a real-time 3D video image viewable with simple
> > polarized glasses - not an LCD shutter unit in sight. He was using one of the
> > old Toshiba 3D cameras and handing glasses to passersby so they could see
> > themselves in 3D. I interviewed the guy briefly, and when I type it up
> > sometime later this week, I'll make it available to anyone who wants it. I
> > will also be writing a piece on the technology (as fars as I can make head or
> > tail of it) for Adult Video News - after all, the guy was selling it in the
> > adult section. For those who can't wait, QD Technology is located at 536 N.
> > Santa Cruz Blvd., #201, Los Gatos, CA 95030; phone (408) 354-0650.
> 
> This display premiered at last year's Stereoscopic Displays and Applications
> conference.  You can see a picture of it at:
>   http://info.curtin.edu.au/~iwoodsa/spie97/sd97phde.html
> It's the eighth set of images down the page.
> 
> The display makes use of the "3D Black Screen" material developed at QD
> which allows polarised 3D rear projection to work extremely well.  
> In the box I believe are two video projectors (one for each eye) - each
> with a circular polariser in front.
> 
> A larger version of this was used as the main 3D display for the 1997
> conference - this used two 3 gun CRT projectors.  Impressive stuff.
> You can see an image of this at: 
>   http://info.curtin.edu.au/~iwoodsa/spie97/sd97phco.html
> 
> Andrew Woods
> 
> 
> 
> 12 days to go to the Stereoscopic Displays and Applications conference
>          http://info.curtin.edu.au/~iwoodsa/stereoscopic
> 
> ===============================================================
> 
> Date: Tue, 13 Jan 1998 20:15:49 EST
> From: WDuggan3D <WDuggan3D@xxxxxxx>
> To: photo-3d@xxxxxxxxxxxxxxxxx
> Cc: bd3d@xxxxxxxxxxxxx, Michael.Amundson@xxxxxxx
> Subject: P3D Re: P3d 3D Projection Screens, Rear, & Polarizers
> Message-ID: <69f7a83b.34bc11c8@xxxxxxx>
> 
> In response to a number of Photo-3d inquiries about 3D projection
> screens,  rear projection screens, and polarizers:
> 
> Neither the PSSP nor I have tested the Harkness spectral 2000
> screens, possibly used in the ISU World Congresses in the UK 
> and Netherlands.  Will someone from the UK and someone from
> the Netherlands please report what screen sizes and what screen 
> material, and what manufacturer was used at these two ISU World
> Congresses so we can have the facts?  Also, I would appreciate
> receiving information, literature, price lists, and screen samples 
> from the manufacturer, and the address and phone number of the 
> new factory in Virginia.
> 
> At the ISU in the UK I noted a reasonably bright image, but with 
> some ghosting, when I sat in the center section of the theater, but
> when I moved across the aisle to either the right section or the left
> section, I noted a dropoff in brightness.  Unfortunately, I could not 
> afford the expense to travel to the Netherlands for the ISU World 
> Congress held there, and thus I did not see that screen.
> 
> As reported earlier, PSSP testing included the DA-LITE made 
> "SPECTRA" pearl gray material made for video projection, which 
> can be made up to any size without the seams showing, but which 
> ghosts slightly and, like flat silver screens, had brightness to about 
> 15 degrees from the center axis of projection, for a total coverage 
> of about 30 degrees of brightness. From our testing, any flat silver 
> screen  material would be better for 3D slide projection.  As this was
> some years ago, perhaps DA-LITE now has a new and improved 
> Spectra material, as DA-LITE is always testing, experimenting, and
> trying to improve their products.  Over the years I have noted frequent 
> changes in the backing of DA-LITE Wonder-Lite and Super-Wonder-Lite
> silver lenticular screens, sometimes woven material, sometimes plastic,
> and varying in color:  white, black, gray, ivory, maroon, etc.   I am under
> the impression that silver leaf is fastened to the backing and then run 
> through a roller machine that creates the lenticular ribs, sometimes 
> perpendicular to the length of the rolls for seamless wide screens, but 
> now apparently only parallel with the length of the rolls so that they can't
> make up a screen wider than the 6' width of the roll. As the coefficient 
> of expansion of the silver surface is not the same as the coefficient of 
> expansion of the backing, the silver can separate from the backing if
> stored or transported at temperatures higher or lower than normal room
> temperatures, which is why I can't recommend shipping by any carrier.
> 
> Several companies in the US can make flat silver screens in large
> sizes without seams showing.  I have for sale a Hurley Screen 
> Company made "Silver GLOW" flat screen 8' high by 12' wide 
> which fits a DA-LITE 8' x 12' FAST-FOLD Frame.
> 
> I have six rigid dark plastic rear projection screens 5' x 7' which are 
> very directional, and a friend has a rigid, transparent (with silver 
> specks imbedded in the plastic) rear 40" x 40"  projection screen, 
> which is very bright but also very directional.   All flexible, roll-up, 
> plastic rear projection material that I have been able to test 
> depolarizes light, and is therefore unsuitable for 3D projection,
> except for the material used at the 1987 ISU World Congress in 
> Interlaken, Switzerland.  Can someone in Europe tell us the name 
> and manufacturer of that material, and whether it is now available 
> wider than the meter-wide strips used there??  The approximately
> meter-wide strips were weighted at the bottom and hung from a pole
> beside each other, with no seams, but sometimes with gaps between
>  the strips so that direct projector light came through between the
> strips into the eyes of some viewers. Another problem with rear 
> projection is that the slides must be reversed, in which case the 
> black side of GEPE mounts would face the projector lamps,
> causing heat build-up that might damage the film chips, unless
> special 90 degree projector lenses with front surface mirrors are
>  used, and these would slightly degrade the sharpness of the images 
> and also be very difficult to align without keystoning.
> 
> Raven Screen Corp., Spring Street, Monroe, NY, has just acquired 
> some flexible, roll-up, rear screen material, but it has not yet been 
> tested for depolarization, is very expensive, is very fragile, and cannot 
> have grommet rings installed along the borders, and thus requires a 
> special frame.
> 
> If anyone knows of any suitable for 3D projection material that I have 
> not covered, please send information and samples to:
> 
>      William A. DUGGAN, APSA
>      NSA Projection Consultant
>      NSA Program Coordinator for Richmond
>      P. O. Box 805
>      McLean, VA 22101-0805
>      Phone:  (703) 849-0961
>      E-Mail:  Wduggan3d@xxxxxxx
> 
> As to polarizers, I do not feel qualified to add any information, except 
> that I have been satisfied to use TDC and VM and 4" x 4" polarizers 
> sold by Reel 3-D.  When hung on the projection lenses, polarizers can
> collect lint from the air in the room and slightly degrade images.  They
> must be cleaned frequently with soap and water and rubbed only by 
> your fingers under running water.  There is an invisible focal point of 
> heat in front of all lenses, and on two occasions I have burned up the 
> center of polarizers hung over the lenses.  
> 
> The BRACKETT  polarizers which clip onto the condensing lens inside 
> KODAK EKTAGRAPHIC projectors do not degrade the sharpness of 
> images, block about one third of the heat from reaching the film, remain
> cool and clean because of the blower in the projector, but cannot be used 
> if the film base depolarizes light or if kodalith film is used as a mask or
> sandwiched in to make a title slide.  Mylar based film depolarizes light.
> 
> White subject matter, including ice and white statues and the Washington
>  Monument and waterfalls and white clothing, can "ghost" (depolarize)  to 
> some extent, in which case the projectionist must merge the white objects 
> to eliminate the ghosting.
> 
> Perhaps Robert Brackett, David Starkman, Susan Pinsky, Paul Wing, 
> Ron Labbe,  Jon Golden, or someone from Polaroid can advise us on 
> the various grades of polarizing material for projectors and glasses.  . 
> 
> ========================================================
> 
> Date: Sun, 11 Jan 1998 18:23:46 -0500
> From: Bill Davis <bd3d@xxxxxxxxxxxxx>
> To: photo-3d@xxxxxxxxxxxxxxxxx
> Subject: P3D Best Polarizing Material?
> Message-ID: <3.0.1.32.19980111182346.006a0568@xxxxxxxxxxxxxxx>
> 
> Greetings.
> 
> Time for me to pick the collective brains of Photo-3D again.
> 
> As some of you know, an ongoing project of mine for the past year or so has
> been trying to find the best screen material for rear-projection stereo.
> The main criterium is non-depolarization of the light, with secondary
> criteria being minimal hot-spotting and minimal grain.
> 
> My method for testing non-depolarization has been projecting only one side
> of a stereo pair onto the test screen and  viewing it through the opposite
> lens of my glasses, basically seeing how much cross-imaging is visible. I
> use a variety of slides, one of the toughest being an image of a floodlit
> Chicago building against a night sky. With test materials set up in an
> array, I can look from one to the other and select the best. My test
> standard has been a Da-Lite V.I.P. silver lenticular screen.  When I find a
> likely prospect, I switch on the other lamp and check the stereo image for
> ghosting.
> 
> I found a material recently that looks promising, with apparently equal
> performance to the silver screen, but now I want to know which is *better*.
>  To really compare the two I need to eliminate as many losses as possible.
> I should be using the best possible polarizers in the projector *and* in my
> glasses.  For purposes of my testing, maximum polarization and minimal
> scattered light would my main concerns.  The amount of light lost wouldn't
> strictly be a concern for this testing, 'though I would probably leave the
> good stuff in afterwards.     
> 
> I've got new Reel-3D material in my projector now, and have a variety of
> glasses.  The projector material is better than that in the glasses, I can
> tell.  Holding a peice in front of my eye and rotating it for maximum
> extinction shows less ghosting than any of my glasses.
> 
> So..... what's the *absolute best* material to use for projection
> polarizers? There has been talk over the years about the different options,
> including Reel-3D, Edmunds and various camera polarizing filters, but has
> anyone ever done a head to head test with names and numbers?  Bill Duggan,
> maybe?
> 
> Someone (DrT?) had once talked about getting both grades of polarizing
> material (Commercial grade w/25% transmission and Tech Spec w/38%
> transmission) from Edmund Scientific and testing.  I don't recall reading
> how that came out.
> 
> 
> Best regards,
> Bill Davis
> mailto:bd3d@xxxxxxxxxxxxx
 
 


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