I knew light was making it through but I hadn't considered using a black base to solve the problem, rather I simply tried more coats of silver which improved but in no way eliminated the issue. I was not able to find black posted board in a suitable size so sanded down the paint a bit on my existing screen, coated is with flat black paint and then with two coats of silver. The results speak for themselves the ghosting I had seen before is now nearly imperceptible even when using a test image I specifically designed to show ghosting. In fact I suspect this this level of ghosting rivals purpose built theater screens. Now if I can get a hold of some better projectors, ones that can keystone, I will be all set.

Checkout the images below, my camera does not like the polarized light so the images come out red shifted.

The left and right images that I use to test the ghosting are avaliable here in the files section.

View without filter glassesView through left eye filterView through right eyefilter

I decided to try a test before I had the stand properly working. This of course made holding the filters in place and getting the projectors properly aligned quite a task. I was able to overcome this difficulty in part by inventing the new state of the art

alignment system you see in the pictures :)  Once I had everything aligned I realized that my old projectors lack a keystone function, meaning that a good alignment at any angle will be pretty much impossible. However, for testing I'm working with a really short throw distance so I aligned the projectors as best I could and then chose a black and white test image (actually the logo for a lan party I help host) so that I could better see any ghosting. Anyway, after offsetting the images, I got the filters aligned and donned my glasses.

There was a 3D image! Ghosting still seems to be a bit of a problem and I will need to do some more test to figure out if the problem is my screen or my filters but indications are pretty positive at this point.

Primer coated 20 guage vinyl

I finally got around to actually testing the new screen surface and it looks better then the drywal. The new surface has been coated with a single coat of Rust-oleum (tm) flat white primer and a single coat of Krylon (tm) brilliant metallic silver paint.

The difference in light levels from left to right eye is about the same as the difference as you simply look through the filter however this is still about a 65% difference only. This is not really sufficient for a 3D setup so I think I will have to look for a better polarization filter.

Silver Coated

20 guage Clear Vinal

The rough surface of the gypsum board I have been using in previous tests seemed to be limiting the ability of the surface to preserve the polarization of the projected light. For my next test I decided to use a much smoother surface and one more suitable for an actual screen so for this test I will try applying the silver paint to 20 gauge clear plastic vinyl. I will also be using a better quality primer getting the paint to adhere properly to the vinyl may be difficult.

To begin I cut an 18" x 24" sample from a larger piece of vinyl.

The top and bottom are sandwiched with 1x2 pine.  I roughed up the mating surface on both sides of the vinyl to improve adhesion with the epoxy.

After mating the vinyl and wood with epoxy I used 3/4 inch 18 gauge brad nails to finish the edges and distribute the weight of the sheet. Eyelets were attached to the wood edges so that the vinyl sheet can be easily hung. I also added eyelets to the bottom of the sheet so that I can stretch it to help remove slight wrinkles.

Lightly sanded edges to improve adhesion with epoxy

Weighted to help stretch out wrinkles when heat is applied

Surface 2: Cleaned surface 1 and re-coated with a single coat of Krylon (tm) Brilliant Silver paint, the can states "Exceptionally Smooth Finish" so hopefully this will work out better.

Test 2: Same setup as test 1; Old 3-lcd projector > circular polarization filter > Screen surface 2 > reald(tm) glasses > eyes.

Results: The brightness diffence from left to right eye was far more apparent than with the Rust-oleum(tm) paint but still amounted only about a 50% difference.

Conslusion: I am going to go ahead and try again with a second and third coat of the Krylon (tm) sliver but give the general roughness of the gypsum board 50% may be the best I can get without moving to asmoother surface.

For my test surface I am using a 24" x 24" piece of gypsum board, the surface of which is probably too rough for real use but hopefully will make a reasonable test surface.

Surface 1: Cleaned surface followed by two coats of white spray paint to insure that the gray gypsum board color does not interfere. The final later is two coats of Silver Rust-oleum (tm) Brilliant Metal Finish spray paint.

It's worth noting that the metal flakes in this paint are very prominent, much more so then I thought when I bought it. this makes for a fairly rough finish that I do not think will work very well.

Test 1: Despite my misgivings about the surface I decided to go ahead and test the surface anyway. My test consisted of a single old 3-LCD projector, projecting through the circular polarization filter onto the surface. I simply put on a pair of RealD (tm) 3d glasses left over from a recent Avatar showing and subjectively compared the image brightness reflected to each eye.

Results: There was an apparent difference in brightness, indicating that the surface is not entirely eliminating the polarization. However, the difference was only about 10% overall brightness.

Conclusion: I am confident that the polarization filter is working properly but the surface is changing the polarity too much. I think this is due in part to the roughness of the surface but also due to the large metallic flecks in the paint. I will try a similar paint with a smoother finish and then look into a smoother base surface.



So, instead of looking for a suitable screen to buy, I will try for a DIY solution first. My first try will probably be a paint on screen with a smooth masonite or metal background. I have found a couple of promising compounds like 3D HD Silver available here: https://www.paintonscreen.com/cgi-bin/store/store.pl and Silver 3D Screen Goo available here: http://www.theaterthings.com/store/projector-screen-paint-ultra-silver-3d,Category.asp. However even these solutions are rather on the expensive side at $250 and $189 per quart respectively so I will likely try simple silver paint first. Check back for the results.