Passive 3D projection with 2 Pico Projectors?

[ShawmK]

I wonder if anyone can help with this; I'm thinking of trying to set up a portable(ish) 3D projection system using 2 matching pico projectors with polarised filters.

My idea is to run them off a laptop using Stereoscopic Player in its "Dual Screen" mode. With a couple of filters over the lenses, people would be able to watch using passive glasses, and the whole kit should be (in theory!) relatively easy to set up and dismantle.

Has anyone actually tried this with pico projectors? If so, I would love to hear how well it worked.

My main question is about which projectors might be best suited to this project. I'm going to need two of them running off the same laptop and I would really like a model that can connect to a USB port, rather than a VGA port.

I've been doing some reading online, and I'm looking seriously at the Acer C20.
http://www.acer.co.uk/ac/en/GB/content/ ... .JBT01.001

Does anyone know for sure if this projector can function as an external monitor via a USB cable? The manual mentions USB connection, but it's a little vague.

I'd be grateful for any advice or suggestions!

[AntiCatalyst]

I'll try to help you
My first concern is about light. In pico projectors, there's not much of it to start with, and most 3d methods remove at least half of it.

If you're set on using polarized glasses you should look for projectors that output uniformly polarized light, because then you could alter the polarization(to match your glasses) with clear retarder films in front of the projector. This keeps all the light, as opposed to regular polarizers that cut 50% off the already low light output.

Secondly, the laptop should support AMD EyeFinity, because otherwise Windows' desktop manager won't bother keeping the two projectors synced. This means that one projector will lag behind the other, which ruins the experience for both movies and games.


You'll also need a portable silver screen. I think i remember cybereality here talked about making a semi-portable screen some time ago, but i'm not sure.

[ShawmK]

Thanks for the response; you raise some good points!

Pico projectors don't output very much light, but I was hoping that would be compensated by the fact that there will be two projectors working together (producing more light than you would get from a single projector with active shutter glasses). I also wasn't thinking about projecting a huge image - about 20 inches at most - so I shouldn't be pushing the limits of the projectors too much.

It's a good suggestion to look at projectors that that can output uniformly polarised light; I hadn't thought about that. Am I correct in thinking that limits it to LCD projectors? I understand that the light from a DLP projector is unpolarised, but what about these new laser pico projectors? I can't find any information about the light they produce.

I'm trying to set up a passive projection system because I want something I can use with a group of people. I hate anaglyph, and I can't afford a whole box-full of active shutter glasses...

Do you think the synch will be a big problem? I wouldn't be using the set-up for games; it will simply be for photo slideshows and video clips - both of which can be done by Stereoscopic Player in "Dual Screen" mode.

The silver screen is actually the easy part - I have a collapsable screen designed for use with pico projectors:



It wasn't advertised as silver, but it turned out to be; I did a very rough test (using filters from a pair of RealD glasses) and it worked pretty well.

I'll keep doing research to see what options I have!

[AntiCatalyst]

yeah DLPs are out, since they're unpolarized. LCDs are a bit of a letdown, since they have red and blue at the same polarization, and then green is shifted 90 degrees. There's really no way around this, so that leaves LCOS and laser. I think most of them are uniformly polarized, but you'd have to confirm this somehow for the projector you decide on.

I'm not sure btw if pico LCDs are single-chip to save space? because then it'd work, it's the internal beam-splitting in regular 3-LCD projectors that messes up polarization.


You are right, dual projection means you are outputting twice as much light, but you can't really count that since you only see one projector's image with each eye. So, even in a perfect world, a "lossless" wave retarder setup only ends up as bright in 3d as a single identical projector outputting regular 2d. A regular polarizer setup will at most look half as bright as a single one.

But then again, if it would(hypothetically) come down to either a polarized projector with 25 lumen or a DLP with 50, you should of course get the DLP, since you'll have better 2d brightness at the same 3d brightness. In a way, polarized projectors also waste half the light. the difference is that it happens by design, inside the projector, so the designers can compensate by using a more powerful light source.


Photos will look great on that setup, since they're not moving. Video i'm not sure. I have an nvidia card for my dual DLP home theater, and the eye lag is really frustrating at times. It works pretty well in 60Hz refresh ratio(so it'll probably work out for you), but 24Hz-native playback is impossible. The worst part is that it comes and goes, and there's nothing you can do about it.

[ShawmK]

LCDs are a bit of a letdown, since they have red and blue at the same polarization, and then green is shifted 90 degrees.

Doesn't the "StereoBright" format try to take advantage of this? I've never seen it in action, so I have no idea how well it works, but it certainly sounds ingenious!

I think I need to do some more research into the technology involved in these little projectors; I'll see how suited they are to my needs.

I'm very surprised to hear about the eye-lag problem; I would never have expected that from an NVidia card. I know how annoying it is if the images are out of synch, though - that's pretty much what killed dual-projector 3D in the 1950s!

Thanks again for your thoughts; I'll post updates as I make progress!

[ERP]

I've tried this with 2 3M pico projectors and to me the light output was unacceptably low even in my media room but YMMV.

[cybereality]

I am looking at doing this with an OPTOMA PK201. They are 854x480, but can accept up to 1280x800 source signal, 20 lumens. Only $200. Very affordable for a wide-screen pico projector. DLP is the best since it is not polarized. I know from PalmerTech that the ShowWX laser projector has strange polarization so it is useless for passive rig. A lot of LCDs are also like this I believe. So DLP is best bet.

[AntiCatalyst]

Doesn't the "StereoBright" format try to take advantage of this? I've never seen it in action, so I have no idea how well it works, but it certainly sounds ingenious!

Yes, it'll work. Just be sure to check the polarization angles before purchasing the projectors. If you can't check, get a DLP instead.

I'm very surprised to hear about the eye-lag problem; I would never have expected that from an NVidia card.

It's not just nvidia cards that have this issue, it'd happen on an AMD too if you'd use the regular dual screen mode. The difference is that AMD cards have a workaround in their Eyefinity mode. It can do any configuration of monitors(two in this case), and works with a single card, while nvidias Surround only works on an SLI rig with 3 monitors because they're(and this is not an opinion, it's a fact that they've proven many times) heartless sons of bitches who just want to sell more cards. >.<

[tritosine5G]

There's really no way around this, so that leaves LCOS and laser.

hey I found a pdf about this, "3LCD" (lol) can be physically corrected and a foreign prof did it , you can find it I think. But I'll look if you can't . ***

On a different note, Ihave my eye on my new CRT It s beatiful.

So I ve been thinking about the old time parallel & sequential debate gain.

How about this theoretical display:

CRT alike , with phosphor screen, two beams for excitation ( can be 2x pico projector, using its blue laser), and short burn RGB phosphor , itd burn for several hundred microseconds.

Shutterglasses would be better than LC , with microsecond switching times. And it could be so close to parallel, it would be only microseconds apart. Also wouldnt rely on polarization, but advanced cloaking technology. Then turn it up to 240hz, I think this would be great.

Maybe the blue laser of picoprojectors can be used directly

*
**
http://read.pudn.com/downloads156/ebook ... System.pdf" onclick="window.open(this.href);return false;

[ShawmK]

I've written to Acer with a couple of questions about their projector. They haven't answered yet, but if I get some good news I think I'll give it a go. This projector is going for a good price at the moment

[Likay]

I tried stereobright with my own projectors (3-lcd's). It works well with a very high lumen output (even higher than the spars i have actually). The easyness of making the filters is definitely a plus (only a quarterwave retarderfilm is needed) to create native circular polarization (works using standard passive real-d cinemaglasses).
Kinda fun reading of stereobright when knowing this...

However it's my experience that the backsides of stereobright outmoves the advantages because:
For the right eye the red and blue portion is sent from one projector while the green portion is sent from the other. This means you need special software for this. I used the stereoscopic player for movies but for gaming stereobright is no go.
Since one eye image is composed by the light from two projectors it also means that alignment is very critical to avoid fuzziness. When using standard dual projection this isn't an issue at all, at least not in 3d (while the doubling if any is disturbing in 2d).
I also had more ghosting when using stereobright, even compared to using standard circular polarization filters. The best result is achieved using linear polarizers with linear polarized glasses (least ghosting).
If you're using lcd-projectors it seems that all 3-lcd's (lcos probably another polarization) have 0/90° polarization so using filters with angles 45/135° will work nicely (damps all colors equally) with lcd's. This will of course also work using dlp's.
Nice find of silverscreen btw. A lot of metallic paints seems to work well using dual projection too.

[tritosine5G]

theres a patent how to combine 2x DLP light engines for dual linear polarized and zero brightness loss, bet you can find it if you really want

[Likay]

Dlp light engines? Arent they the same as for other beamers?

[tritosine5G]

well , not exactly, if you think about it 3LCD were always feature laden compared to DLP, thats not exactly because DLP manufacturers are cheap, rather because 3LCD is easier to add features.

Also its reflective like LCOS rather than transmissive. Oh I also found how they boost lumen output on LCOS , they use expensive micro polarizers instead of standard polarizer, and lumen output just goes up! It should be possible to build a micropolarized light source for DLP, but so far they did without it just fine.

[ShawmK]

Update:

The project so far:



The whole project turned out to be far more straightforward than I had expected. I used a pair of the Acer C20 DLP projectors (chosen mostly because I was able to get them cheap ) plugged into my laptop. The laptop isn't even that powerful - it's a netbook, but it can run Stereoscopic Player without any difficulty.

The polarising filters I'm using at the moment are simply taken from a pair of RealD glasses (the kind given out in Cinemas). I've ordered a set of proper projection polarisers but they haven't arrived yet, and the temporary lenses are working surprisingly well.



Because these projectors are small, they don't get very hot (they don't even require cooling fans) otherwise these lenses would probably melt . The only serious difficulty I encountered was in plugging both projectors into the laptop simultaneously. The laptop only has one VGA port, so I had to buy a VGA-to-USB adaptor (that blue gizmo in the photo). Once installed, I was able to connect both projectors, and the computer accepted them as two separate displays. The synch seems to be absolutely fine; I was especially worried because of the USB adaptor - I thought there might be a lag - but they remain very nicely together.
When projecting onto this 22-inch screen, the image is nice and bright and the contrast is very good. I wouldn't try to project a larger image, but since I don't have a larger silver screen, that isn't an issue anyway. This is obviously purely for photos and movies (not games) but it uses passive glasses - so many people can watch together - and it can be set up anywhere (although the assembly is a bit fiddly).

Now I'm looking forward to receiving the proper filters, but I'm really pleased with the results so far!

[AntiCatalyst]

Update:

The project so far:

https://lh3.googleusercontent.com/-aFdF ... 020045.JPG" onclick="window.open(this.href);return false;

The whole project turned out to be far more straightforward than I had expected. I used a pair of the Acer C20 DLP projectors (chosen mostly because I was able to get them cheap ) plugged into my laptop. The laptop isn't even that powerful - it's a netbook, but it can run Stereoscopic Player without any difficulty.

The polarising filters I'm using at the moment are simply taken from a pair of RealD glasses (the kind given out in Cinemas). I've ordered a set of proper projection polarisers but they haven't arrived yet, and the temporary lenses are working surprisingly well.

https://lh5.googleusercontent.com/-eut1 ... 020046.JPG" onclick="window.open(this.href);return false;

Because these projectors are small, they don't get very hot (they don't even require cooling fans) otherwise these lenses would probably melt . The only serious difficulty I encountered was in plugging both projectors into the laptop simultaneously. The laptop only has one VGA port, so I had to buy a VGA-to-USB adaptor (that blue gizmo in the photo). Once installed, I was able to connect both projectors, and the computer accepted them as two separate displays. The synch seems to be absolutely fine; I was especially worried because of the USB adaptor - I thought there might be a lag - but they remain very nicely together.
When projecting onto this 22-inch screen, the image is nice and bright and the contrast is very good. I wouldn't try to project a larger image, but since I don't have a larger silver screen, that isn't an issue anyway. This is obviously purely for photos and movies (not games) but it uses passive glasses - so many people can watch together - and it can be set up anywhere (although the assembly is a bit fiddly).

Now I'm looking forward to receiving the proper filters, but I'm really pleased with the results so far!

nice! but from the looks of it, you have the filters aligned wrong way - they should be rotated 90° from the glasses for best extinction.

Those RealD filters work just as well as regular projection polarizers, the only difference between them and the "real" glass filters are the amount of light they can polarize without melting. I'm using realD lenses on my 1200 lumen HT setup, so yours will be just fine.



BTW, couldn't you fit all that in a neat little DIY projector box? Just put the projectors on top of each other, separated by half an inch or something, and then fit a PC case fan and make air holes on the sides for cooling.

[Likay]

Cool and it looks good!
If you're pleased with the circular polarization, then linear will give even better performance (twice the ghosting rejection and reduced "washed out" image).
This kind of rig would be quite feasible with polpreserving rearprojectionmaterial like the dalite virtual black.
Do you have any unnecessary keystone problems since the projectors are so far from each other?

[ShawmK]

AntiCatalyst, thanks for the tip about rotating the polarisers; I hadn't realised that applied to circular polarisers. I've done that now and there is much less ghosting.

Likay, I was expecting keystoning to be a big issue, but it turns out these projectors are designed to throw the image upwards - presumably so they can be used sitting on a desk without a tripod. By turning one of them upside down, they throw nicely complimentary images:

[Likay]

Pretty clever. I didn't realize.

[LeonZA]

Will this also work with two AAXA M2 projectors? I see they are going cheap and are 1024x768 and 110 lumen.

[ShawmK]

In theory they should work fine.

I would just test one with a polarising filter, if possible; they look like they are LCoS, and the light they give off may already be polarised.