My DIY attempt at building a passive projection rig

[Tril]

Almost year ago, I tried to make my own screen for passive projection. I built a frame and stretched fabric on it. I tested many samples of paint and painted the screen. The tests of the samples consisted of painting small canvas of 10x8 inches with different paint and seeing with a projector, a polarizing filter and polarized glasses if the paint preserved the polarization and how dark the light got. That testing went well but I messed up when the time came to do it full scale on my screen. My first try was with paint in cans and it left visible streaks marks. My second attempt was with rolling and it left too much texture and I messed up the paint choice. I tried to mix white paint that ghosted with grey paint that did not ghost to try to get a less dark color. This mix did not preserve polarization properly.

I also made my own projectors holder. It's made of basic stuff. Some wood, steel threaded rods, nuts, some steel stuff to hold the filters and some screws. I use the nuts to adjust the distance between the projectors and to adjust the angle. It's an ugly design but it works.

Projectors holder

I made the screen out of wood. I cut the wood planks at 45 degrees and assembled them with steel angled thing (don't know how it's called). I made two frames that I screwed together. The back frame is bigger than the front frame and has a black velvet fabric on it. It gives the screen a black frame around the picture. The front frame has the fabric for the screen on it. A problem with this design is that the wood of the front frame is slightly visible through the screen fabric. Also, the fabric is not quite tight enough on the frame. I took some pictures. There's masking tape on the back frame so it appears black on the picture. I removed some of the tape to show how it's supposed to look.

Screen - Front
Screen - Front - close-up
Screen - Back

I'm now going to give a report on the paints I've tried. First I'll show the paints that preserve polarization. They are ordered by the brightness of the screen when the linear polarizing filters are crossed. Darker is better, lighter is worse. Except that it's not entirely true. Some of those paints where darker than others so they appeared very dark with crossed filters but that was not all a result of better extinction, it was also because of the color. It wold have been better to measure the brightness with the filter in both positions for all the paints but I did not do it. A brightness of 1 is very bright (potentially, it might ghost) and 10 is very dark (almost invisible). Some of the paints tried are rust paint and can easily be bought in large quantities, some other paints are available in cans and require a few cans to paint a screen and others are only available in very small quantities and are made to be used by artists.

Paints that preserve at least a little polarization

Liquitex iridescent stainless steel/metallic stainless steel
10

Armor Coat rust paint aluminium
7
Smells strong for a long time

Tremclad aluminium antirust paint
7
Smells strong for a long time

Motomaster near match radiant silver
6
Too shiny

DecorArt Dazzling metallics shimmering silver
5
Hard to spread

Krylon int/ext aluminium mat
5

Liquitex iridescent silver/metallic silver
5

Dupli-Color high performance wheel coating silver
3
Shiny

Pébéo iridescent silver
3

Krylon original chrome
3

Krylon Fusion 42521 Graphite
Forgot to write the brightness
Too shiny


Paints that don't preserve polarization

Rust-Oleum white
Dupli-Color Truck, Van & SUV T346 BR white
Dupli-Color high performance white
Motomaster near match mmm universal white
Krylon H2O Gulf Gray
Liquitex iridescent white

I think the best results might come from spraying the paint with a good spray gun.

Last year, I wrote a post about my dual projector setup but I never posted it. I'm going to post it in the next post. It's not up to date anymore but it might be interesting for information purposes.

[Tril]

This is a post I wrote last year but never posted. It talks about my setup at the time. It's not up to date so some stuff might not apply now.

My passive setup is not finished yet but I decided to share my work.


Requirements for a passive 3D setup with dual projectors :

2 Projectors
1 projectors holder with 2 filters holders
1 Silverscreen
2 Filters
2 Cables
pc with NVIDIA dual output video card
NVIDIA Stereo Drivers


Optionnal :

Stereoscopic Player from 3dtv.at



2 Projectors :

I bought the cheapest 1024x768 projectors I could find. I would have prefered to buy two 1080p projectors but they are 5 times more expensive and that was too much for me. I bought two recertified Optoma EP739 for 600 canadians dollars each at Tigerdirect.ca. I'm using their DVI connectors and I'm using economy mode to increase bulb life.

My projectors are made to be mounted upside down on a ceiling or on their feet on a table. Since I'm placed them close to the ceiling, they are sitting upside down in the holder.

One feature that is handy to have that I don't have on my projectors is called "lens shift". This allows you to adjust the height at which the picture is projected without adding keystone distortion. With this feature, you don't need to tilt the two projectors to align them with each other.


1 projector holder with 2 filters holders :

I made a projector holder myself with common hardare you can find at the hardware store. It's not totally perfect but it's good enough. It's made out of four threaded rods, two wood boards, some wood pieces to keep the prohjectors from falling out of it, many nuts and four rubber feets.

The holders are made out of wood. They have one of the rod pass through them. The nuts are tightened to keep the holders from rotating. Each filter is held in place by four metal pieces.

The nuts supporting the filter holders are used to adjust the height of the holders.

The nuts suppporting the wood boards are used to adjust the height of the four corners of the two wood boards to align the pictures.


1 Silverscreen :

I don't have one yet. I do have samples I requested from many different companies.

I have samples of :
Silver 3-D from Stewart
Silver Vision from Da-Lite
Silver Matte from Da-Lite
SilverFabric Silver 3D from silverfabric.com
ST-Power-Screen-3D from Screen-Tech

They all have their strong and their weak points. I'm not sure which is better because it's hard to tell.

I'll try to comment on all of them. Keek in mind that what follows is my opinion and you may have a different opinion. If you are seriously considering buying a screen, I suggest that you ask for a sample by email and judge by yourself. Most companies will send them by mail for free.

The samples all reflect polarized light about the same amount.

Silver 3-D from Stewart
Its texture is not really noticeable on the picture.
I asked for a screen sample by email and they sent me one for free.

Silver Vision from Da-Lite
It's very stretchy so it absolutely needs a screen that will pull on it on all sides.
It's a darker grey than the other samples and its gain is 1.5 (specification from Da-Lite).
It sparkles a lot. What I mean by that is that if you project a white picture and you move your head around, you'll see lots of sparkling dots of all colors moving on the screen. For that reason, I would not choose it for a 2D screen. However, when used with dark moving picture like those of a game, the noticeable sparkle is minimal.
Its texture is not really noticeable on the picture.
I asked for a screen sample by email and they sent me one for free.

Silver Matte from Da-Lite
It does not need to be stretched like the other Da-Lite screen.
It's a lighter grey than the Silver Vision and its gain is 1.3 (specification from Da-Lite).
Sparkles a lot less than the Silver Vision.
From close up, you can clearly see a pattern in its texture but from a normal viewing it's not really noticeable on the projection.
I asked for a screen sample by email and they sent me one for free.

SilverFabric Silver 3D from silverfabric.com
From close up, you can clearly see a pattern of parallel lines on all the screen but from a normal viewing it's not really noticeable on the projection.
I asked for a screen sample by email and they sent me one for free.

ST-Power-Screen-3D from Screen-Tech
It's made out of one piece of acrylic glass.
This screen sample is the one out of the five that sparkles the least.
It's also the screen that produces a picture that's closest to what is projected. If I get close to the screen, I can clearly seen the individual pixels of my projectors. The other samples tend to slightly blur the picture and to somewhat blend the pixels together. For this reason, I would choose this screen if I planned to use the screen for uses other than S-3D projection.
Gain : 2.8 (specification from Screen-Tech)
Viewing angle : > 120 degrees (specification from Screen-Tech)
Half Viewing angle : +- 32 degrees (specification from Screen-Tech)
What that means is that it's very bright. It's indeed the brightest of the samples. However, it also means that this screen might give you a picture that's brighter in the middle than the corners.
I like this sample a lot. I would probably buy it and risk having some hotspotting if I had the sufficients funds.
The company is based in Germany and this screen material is not flexible and it may be a bit fragile. For these reasons, this screen is costly to ship. It's expensive but it's not that bad. I was quoted 156 euro to ship to the province of Quebec in Canada.


I haven't decided what to do yet. I think that the cheapest screen is the Silver Matte from Da-Lite with a Versatol tripod and I may go with that.

It's possible to make a frame yourself, stretch a screen on it and paint it with silver paint. The two pics below are from one I made. I used a type of cloth that has a cloh side and a plastic side. I could not get a result as good as the professional screens. I was able to find many paint that retained polarization. The problem (at least to me) is mainly applying the paint perfectly. I tried to spray and to roll paint.

When I first sprayed, I did it on the cloth side. This affected the quality of the picture badly. There were lots of fibers of the cloth sticking out if it and when projecting on that, it produced black dots (they were shadows) everywhere on the screen.

I spayed paint again on the other side. The result was uneven at many places and it affected the picture. When looking at a S-3D projection, it looked as looking through some mist located at screen depth.

When I rolled the paint, I left roller marks and the paint got a texture because of the roller. The paint I tried this time also did not retain polarization enough.

It's possible to successfully paint a screen by spraying or by rolling but it's hard to get perfect. Don't try it if you're not ready to try a few times and waste paint. Later, I'll make a list of all the paint (between 10 and 25) I tried and I'll tell if they retained polarization and if they looked like a good choice to make a silver screen.


2 Filters :

There are a few places where you can get them.
I bought a sheet of polarizer at Edmund Optics. It's product number NT45-668. I made some mistakes when cutting it and I ended up with many small part, tool small to fit in my holders so I bought some more from another place.
I bought a sheet of polarizer that has a thickness of 3 mils at Polarization.com.
The sheets of Edmund Optics and polarization.com look like they are of the same material. They have the same color, the same thickness, the same protective plastic and they seem to polarize the same amount.
I also bought a polarizer from 3dlens.com. It's much less thick than the two previous polarizers so it's harder to mount.
I decided to try a higher quality polarizer and bought one from American Polarizers. It's made of a polarizer sandwiched between two glass sheets that have an anti-reflection coating. This is a lot more costly than the other polarizers.

In the end, I decided to cut the filters sheet from polarization.com to shape and use them. The filters from American Polarizers are probably better but the difference in quality is small, they polarize the same amount and I would need to change my holders to use them. I'm also worried about breaking them. If I improve my setup in a few years and use better projectors, I'll get them out of storage and I'll use them.

It's easy to touch the filters with your fingers by mistake and leave finger marks. It's also possible to burn the filters so that they don't polarize light annymore. For these reasons, I prefer to use cheap filters that can be cleaned without worrying about scratching them and that can be replaced for cheap.


2 Cables :

I bought two DVI SonicWave 7.0m cables from DirectDial.com. These cables are expensive but they are also sturdy and long enough for my needs. They come with a lifetime warranty.


pc with NVIDIA dual output video card :

Any pc will do. I use a NVIDIA 7900 GT video card. I'm using the two DVI connectors of the card. I chose an NVIDIA card because of the NVIDIA stereo drivers.



NVIDIA Stereo Drivers :

You need to install the NVIDIa Drivers and the NVIDIA Stereo Drivers.
In the configuration of the Stereo Drivers, you need to choose the Dual ouput option.
When you connect two projectors to the card, a menu gets added in the NVIDIA Drivers. It lets you choose which projector is the projector 1 and which is the projector 2. You can use that to reverse the left and right eyes if they are reversed (instead of swapping the two DVI cables).
On my system, I found out that I needed to put the two projectors in clone mode to get stereo to work properly. DualView was causing problems with the display of textures in Stereo mode (some textures replaced by random black and white pixels).

At the time of the writing of this post, the NVIDIA Stereo Drivers don't support Vista x86, Vista x64, post-processing effects and the series 8xxx NVIDIA video cards.


Stereoscopic Player from 3dtv.at :

This is optionnal. It's a good player for stereo content and new versions with improvements often come out. You can watch S-3D videos with it. There are some video samples at 3dtv.at website.

While on the topic, I bought two S-3D movies. They are not great movies in themselves but I wanted to buy some S-3D movies and there's not much choice so far. They are :
Spy Kids 3-D Game Over (HQFS)
The Adventures of SharkBoy and LavaGirl in 3-D (HQFS)

HQFS means high quality field sequential. I can watch them with the two projectors and Stereoscopic Player. I only watched a few minutes of each of them. This made me notice a disadvantage of a passive dual projectors system for movies such as these. The movies are not always in S-3D. Some scenes are 2D. The picture is blurry during 2D scenes because the same picture is projected on the screen by the two projectors that are not perfectly aligned.


Alignment :

The two projectors need to be aligned to closest to perfectly to get a good picture. It more important to get vertical alignment perfect than to get horizontal perfect. If it's incorrectly aligned vertically, you will notice it a lot with the glasses on.
If it's incorrectly aligned horizontally, you will only notice an incorrect depth with the glasses on. For example, if you're watching your desktop and there's incorrect horizontal alignment, you'll still see the icon text clearly but it will look like it's a bit in or out of the screen.

Below is a picture of my current alignment. I could not get the whole screen to be perfect so I tried my best to get the center of the screen perfect.

[ignatius]

Hey Tril,

Fantastic job and thanks for sharing all your hard work. This will definitely help a lot of people out there build their own 3D passive projection setup.

Looking at your polarizer filter holder gave me a lot of ideas, can't wait to make it.

I'm also gonna have to find one of those paints you used, "
Liquitex iridescent stainless steel/metallic stainless steel" that you rated as a 10 for darkness. Do you remember how good or bad the image quality looked? The colors, brightness, etc?

Thanks for the great post.
-Varinder

[Tril]

It's not that good, I think. It's a very dark grey paint. That's probably why I though the extinction was good. It comes in very small bottles for artistic work. It would not really be affordable to make a screen. I think I bought that at Walmart.

[Likay]

There's a lot of useful info there Tril! Great effort!

[hksdrager]

hey there can you tell me which exact filter you ordered from polarization.com I order some the other day but i looks like its the wrong kind. Having tough time finding the right one

[ignatius]

I've been using 3D glasses like the ones you wear at IMAX as my polarizing filter ever since I built my 3D theatre. I was always planning to buy better ones but, never found the time yet. Surprisingly the IMAX polarizing glasses give off impressive results, no ghosting at all. I guess what the other polarizing filters would do is allow for more light to shine through for a brighter image.

But for now, if your waiting on getting a more premium polarizing filter, just use your 3D glasses for now.

[PalmerTech]

Great guide, will be very useful for me!

I love Krylon products, I use Krylon Fusion for pretty much all my DIY projects. The Krylon Chrome appears to do pretty well? Could I just get a smooth piece of wood, glass, metal, etc, and paint it with that and get good results?

[hksdrager]

are you telling me that you just took apart some imax glasses and used those for filters for your projector?? can you post a pic of your setup? thanks

[Likay]

I'm quoting in with the answer from your question in the other thread:

You got the ones without adhesive coating right?
Besides if i'm not wrong the filters might be covered with a transparent protection layer. You need to peel that off before the polarizer work as it should.
If you got a purple tint (i assume you're using lcd-projectors) you most probably need to rotate the filter 45°. If you got circular filters then also make sure that the right side is facing the projectorlense!

You should try this first before doing something else.
If you have the same purple tint as in this vid then just rotate 45° and you'll be fine.

[ignatius]

Hey hksdrager,

I posted up a 'how-to' guide on how i made my setup. You can check it out here:
http://www.mtbs3d.com/phpBB/viewtopic.p ... 9&start=15" onclick="window.open(this.href);return false;

Just scroll down a bit on the second page and you'll see some pic's of my setup. Works like a charm.

[hksdrager]

omg you are the man!!! that setup is freaking brilliant. you man the whole thing so simple when all i have seen were complex setups. hey on the silver paint are you suggesting that the krylon number 3 is the best to go with?