DIY Dual Projector 3D Display

I recently went to see James Cameron's Avatar, in 3D at the theater. In fact, I've now seen it 4 times 6 7 times. See my short review here: http://www.kaelhankins.com/home/2009/12/27/avatar-review.html I was so inspired by this use of 3D that I am going to attempt to replicate something close to it.

I have done a good deal of research now on the workings of the RealD(tm) technology that the film uses so well. I intend to use two projectors, a pair of opposite cirular polarization filters and a suport structure of some sort to keep it all together to produce reasnoble quality stereo 3D, visuals that do not suffer from viewing angle issues as with traditional, horizontal/vertical polarized 3D. Sound ambitious enough? The video source will be my computer, running the iZ3D drivers for dual VGA output of the left and right viewpoints.

I really have no idea if I can pull this off but I intend to find out.

Goals:

• Provide a realistic 3D experience for movie content as well as real-time rendered 3D games.
• Use circular polarization to avoid crosstalk issues with viewing angle change.
• Build a support structure for the projectors to be stacked vertically and aligned precisely with each other. This structure should also hold the polarization filters.
• Provide a screen that does not change the polarization of the light as it is reflected back, or at least changes it uniformly.

Possible problems and concerns:

• Since the projectors will be in a slightly different position vertically, the keystone settings will be slightly different, will this affect perfect alignment of the two images?
• Coming up with a suitable display surface may be difficult.
• My inexact understanding of the optics involved will be a hindrance.
• Finding suitable filters may be difficult.
• Filters may melt from proximity to projectors and/or prolonged use.
  • Dedicated cooling fans may help with this.
• If projectors are not started at the exact same time will the difference in refresh timing hinder quality?

Found polarization filters?

After a bit of searching I was able to find what I think is exactly what I am looking for at a website called, suprise, polarization.com.  I believe that these are exacty the ticket: http://www.polarization.com/polarshop/product_info.php?cPath=22&products_id=34

The website says that these filters are "Made by gluing a linear polarizer to a high-performance quarter wave retarder sheet." Which according to my wikipedia research is exactly what I am looking for. See the article in the references section of this post.

Polarized 3D and Projection Surfaces

As mentioned in my introductory post, one of my concerns is the scattering of the polarized light that will occur with any normal screen. The solution used in theaters is a silver screen, a return to the original silver surfaced screens used in the early days of cinema. These screens reflect more light, useful if a single projector is used for both eyes, and preserve the polarization of the light when it is reflected back. As it turns out, modern silver screens are rather expensive and seem to cater more to cinemas than home setups (go figure).

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.

First surface trial and test

As I mentioned in the last post I decided to try simple spray paint before looking at a more complicated (expensive) projection surface. The goal is to get a surface that maintains the polarity of the light as it is reflected back to the viewer. See the last post for links to a few commercial products. 

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.



Surface Test #2

After disapointing results from my first surface test, I decided to try again with a smoother finish silver paint.

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.

Surface Test 3

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 Test 3 (Continued) Filter Problems?

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

Dual Projector Stand

Just a quick update, I've nearly finished the dual projector stand, I just need to get the proper sized bolts so that I can fine tune the throw angle on the projectors to match exactly.

 

First 3D Test Successful!

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.

Bigger, Better Screen!

Unpainted Poster BoardSilver paintedI decided that my screen may be playing a part in the ghosting issue I saw in the last test. I am also having some issues with the really short throw distances required by the small size screen. In order to tackle both of these issues at once I made a much larger screen using a 40" x 60" piece of poster board and most of my remaining Rust-oleum "Metallica" paint. As you can see from the pictures, the results are looking very good, the finish is much smoother then any of my previous prototypes. Hopefully I can now concentrate on getting my filters working better.

Ghosting issues resolved!

After a suggestion from Kim Zhou via facebook I decided to revisit my screen. Kim suggested that my polarization preservation issues might arise from some of the light from the projectors making it through the reflective paint layer and to be reflected back from the white surface of the poster board. He suggested using a black poster board as the base for the screen so that light making it through the paint layer would be absorbed rather then reflected back to the viewer.

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

Project on hold until I can get better projectors.