P3D Re: P3d 3D Projection Screens, Rear, & Polarizers

[WDuggan3D <WDuggan3D@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.  . 
f  



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