The Ultimate 3D projection system: A Practical Discussion Thread - Page 8

so I am understanding correctly, I can get 2 3dxl and 2 1080p non 3d projectors (Mitsubishi 3080) to achieve 3d 1080p? can u mount the projectors side by side or should they be on top of each other.

yea u can align them by the ddd pc 3d program, but the question is that, the 3d glasses do they sync with the 3d-xl or with 3d projector, if they sync with projector then the nvidia 3d vision kit is the solution.

rdjam,

Are you considering trying the Dolby glasses using the Infitec system?

Thanks,
Darin

Not my thread but I am sure rdjam don't mind. :-) I am setting up a dual Dolby 3D solution and the 3DXL's are the only things missing. I'll post a report with pictures when I got it up in a week. Will be PS3 source only.

rdjam,

How effective do you think your strategy would work with DLP? Do you have an idea of how much light loss would occur? Do you think it would work well?

Thanks

A little review and info:

Projector output filtering requirements differ depending on the projector. If their output beams are polarized, you need phase retarder plates to convert the beams to circular polarized. One needs to be a quarter-wave and the other, a three-quarter wave plate (for clockwise and counter-clockwise polarization). Retarder plates transmit upwards of 90 percent of the input light, so very little light loss here. You don't have any choices in this case other than circular polarized (can't change the polarization angle of linear polarized light).

If the projector output is non-polarized, you have two options. You can use linear polarizers, one at 45 degrees and the other at 135 degrees in front of each projector to get a linear polarized system. Conventional linear polarized glasses work with this system.

Alternately, you can use two circular polarized filters, one clockwise and the other counter-cockwise, to get a circular polarized system.

The latter is preferred since RealD uses that method and theater glasses work quite well with a homebrew circular polarized system. Also, head tilt has little effect on the crosstalk (ghosting) in a circular polarized arrangement.

Either polarizer method will soak up about 30 percent of the input light so there is some sacrifice in brightness with these systems. Also, a special screen is required ("silver" screen which has a metallic coating) which doesn't change the polarization of the returned light.

To check your projector for polarization, just place a linear polarizer in front and rotate it. If the light intensity or color change, the beam is polarized. If not, it's either not polarized or it's circular polarized (the latter is most unlikely). It might be advantageous to start a list somewhere of the polarization of known projectors for a reference to be used in this work.



The other method mentioned (Dolby) uses differing light frequencies (colors or wavelengths), requires special filters on the projectors which as, rdjam mentioned, are pretty pricey, and requires color correction. Even the glasses are quite expensive compared to polarized versions. This method should work with any projector although the dichroic projector filters characteristics are affected by polarization to some extent so a non-polarized projector would be preferable. There is also substantial light loss with this method. The advantage is no special screen is required which can be used to partially compensate for the light lost (high gain screen).



In my experimental setup, I'm using Panasonic AE2000 projectors, which have non-polarized outputs, so I'm pairing them up with circular polarizing filters and RealD glasses. Unfortunately, I don't have a budget for the 3D-XL boxes yet, so I'm waiting (with a prayer) for a Chinese demultiplexer dongle to become available in the near future that does the same thing as the two 3D-XL boxes, in a more compact form (this is wishful thinking - no I don't have a source). I'll be most interested to hear rdjam's results with his 3D-XL boxes when he gets it all up and going (pretty soon now from what it looks like).

Radjam, can you give us a breakdown of the cost for your 2 projector system? Just guessing, but I suspect we're talking about $12,000 to $18,000 including the filters, two converter boxes, two projectors and screen. You will have two lamps to replace instead of one for those projectors. I have two almost identical Epson 1080p LCD projectors (with an extra lamp for each), but I don't think LCD will work nor will my HP screen. If I could get away with $3 to $4K I'd give it a shot. Using a passive system the DI for each projector could remain active and the black level would be awesome. The best black level I've seen from any digital was when I put my Epson 9500 into dynamic mode, DI on and lamp on normal mode (as opposed to economy) and watched the crummy 3D with the cardboard glasses - full fade to blacks!

RDJAM,
RealD glasses have a "sweet spot" as I found a color cast that disappears when the circular polarizers are rotated 90 degrees. I can do this on my projector polarizers but it sounds like you're stuck with it due to the JVC output (too bad you can't rotate their linear outputs). The film in the glasses is the same type as that I sourced some posts back, although it will be flipped around backwards in the glasses relative to the projectors. You might be able to fashion some of this material into glasses with the proper orientation (check by testing with your actual system).

http://www.polarization.com/polarsho...products_id=34

Also, here are some manufactures that you might approach. Don't know what they can provide, but they might have something. Really interesting sites anyway.

http://www.3dglassesonline.com/our-products/polarized

and

http://www.3dstereo.com/viewmaster/glp.html

and

http://www.berezin.com/3D/3dglasses.htm#Circular

The latter also has glass mounted projector filters $$$$$$

I wonder how much difference that would make in reality compared to using the lenses out of the glasses. I was able to get glasses for under $20 per pair, but don't have anything to drive 3D for this kind of system.

It is kind of fun for running a dual player videogame with 2 PS3s and 2 projectors where each player basically sees their own image at full screen size and full resolution (although with bad ghosting if one player goes in the dark while another is in the light) though.

--Darin

RDJAM,
Circular polarizers are a sandwich of a linear polarizer and a retarder sheet. That's why you had very little light loss. Your projector's linear output went through the linear layer without much attenuation, having the same polarization as that layer. Afterwards the retarder converts it to circular without much more loss. If you're using the circular filters stand-alone, it's important to get the right side towards the source you're trying to circularly polarize. If an unpolarized beam goes through the retarder first and then the polarizer, it comes out linearly polarized (you really don't have much more than a linear polarizer). The light needs to go through the polarizer layer first (linear polarized) and then the retarder layer which converts it to circular.

The same applies to the glasses only in reverse. Light from the screen needs to go through the retarder first which converts it back to linear and then through the polarizer layer which either passes or blocks it.

Retarders aren't perfect so the light is usually what they call elliptically polarized. It behaves almost the same way as circular, but one filter axis is better than another. That's why rotating the circular polarizer on the glasses end gives better results one way (90 degrees) than another (0 degrees). The last isn't really important unless you want the best performance (which we do). You're right about the RealD system. It's aligned to give the best results with the glasses in the normal position (side-by-side). In your case, you'd have to tweak the direction of the linear polarization going into the retarder, which you can't because it's set by the projector. That's a problem I'm sure you'll overcome. If you have non-polarized sources, the angle of the projector filter determines the linear polarization angle (prior to entering the retarder), so it can be adjusted to match the glasses.

Projector filters made from glasses will work, but the problem is usually that they aren't large enough to cover the projector beam fully. Also, be sure they are used in reverse (light from the projector going in the eye side) as explained above.

rdjam, when using the htpc to play a bluray 3D movie you still need to nVidia's hotkey to turn 3D on (Ctrl-T by default,) even if you aren't using nVidia's glasses. You also need nVidia's emitter hooked up, again, even if you aren't using it. They want their money. Of course the seperate player is a much better solution.

Deja vu, you could do this cheaper.
If you have a PS3 already it would help.
PS3 free (otherwise 180 for a BR3D player.)
Benq W1000 x 2 : 1000x2 = 2000
Optoma 3DXL x 2 : 400x 2 = 800
HDMI Splitter (3D support) = 40
Berezin cheap liner filters and glasses = 40
Harkness 120" 3D screen material (make your own frame) = 360

so $3240. total if you have the ps3, otherwise $3420.

These cheap DLP projectors don't have lens shift so one will have to be a little above center and one a little below, but it will be good enough, and pretty amazing, I am sure.

If you are on a tight budget though, it is well worth trying out an Acer 5360 or Optoma HD66 with a single 3DXL box and be in only a grand. It really is amazing what those projectors can do.
Warren.

Did you come up with a solution for color correction, or will you be working within the confines of the projectors' color adjustments?

Since i don't yet have the 3DXL's (store just changed the date to feb 17 sigh) I have played left eye from one ps3 and right eye from another PS3 of a certain demuxed movie I stumbled upon on the net in full HD (which I also own on bluray 3D btw) to try my setup without demuxer(s). I am doing the color correction with the projectors built-in adjustments and cms and I think I got really good results. I use lenses from the glasses as filters and it works really well I think. I only watch movies in complete darkness so lightloss although quite large doesn't bother me.

If you go to a Dolby 3D cinema with expensive infitec color correction and shut one eye you still see the greenish and reddish differences but your brain compensate since the difference is so small. In my experience I have almost as good color correction as my local cinema. The 3D image i am getting is fantastic. I for one think this system has the advantage.

horizone & RBTO

forgive me... i'm trying to understand...

horizone, i notice you used the redish lense on one pj and the blueish on the other pj. since one ps3 is playing the left eye and the other ps3 is playing the right eye... would it be more correct to use a similiar circular polarizer lense (such as can be purchased for SLR AF camera) on each pj while wearing the real3D glasses?

also, how do you sync the signals from the two separate PS3's.

...

RTBO, on a standard SLR AF circular polarizer, if i wanted the light to go through the polarizer layer first... i am assuming the threaded side would be toward the pj lense... similiar to screwing the polarizer into the camera lense?

so if i went the really cheap route using 1080p DLP projectors with non-polarized light output... i would outfit each pj exactly the same with a circular polarizer on each and the threaded side towards the pj... correct?

then again,
you also mentioned having one circular filter clockwise and the other counter clockwise... if so, then could you explain how i might do that using SLR AF circular polarizers on each PJ.

-thanx

If you are going cheap just use linear polarizers. They are much easier to use and generally perform better.

If you by circular are not referring to the polarisation but the shape of the lenses then yes it would be easier if they were circular in shape but those cost thousands of dollars for dolby 3d/infitec while these taken from the glasses are $20 or something.

I don't sync it yet, I just press play on two remotes simultaneously (which is a lottery) but this is only for testing before the final pieces of the puzzle arrive. The 3DXL's.

I want to try polarisation too, I would be really interesting to really see the difference between homebrew Dolby 3D and homebrew RealD.

Anyone know if my two Panasonic AE3000 is polarisation friendly? Can I use glasses as filters in RealD too? The real problem is needing silver screen though... Hm.

They Panny projectors have a microlens that really reduces screen door effect nicely. It also seems to de-polarize the image somewhat. I got some of the fancy german passive polarizers for lcd projectors and they didn't work at all with my panny ae-2000. I didn't do a lot of testing though, so it might be something you just have to try.
Warren.