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

Okay, so what relevant wavelengths do the glasses not block that the other filters do? Maybe those people have it wrong on that one issue given that my actual measurements show that about 99.7% of even sunlight outside is getting blocked by using 2 lenses stacked according to a high end meter measuring off a white piece of paper. Or maybe the wavelengths they and you are talking about aren't even in the visible range, or are blocked by projectors with UHP lamps normally anyway (especially by LCD projectors using LCD lamps). From anybody who thinks the filters won't work strictly on the basis that "... the glasses are designed to allow, not block, certain light frequencies" (not the heat/too much light issue) I would love to hear what the specific wavelengths are that the glasses don't block, but are blocked by the other filters.

And I would like to hear why they would make the glasses let light through at wavelengths that the internal filters don't if somebody is claiming that the glasses have 3 bands that are wider than the internal filter bands.

Ghosting at .3% with 2 lens filters stacked could definitely be worse than with the other filters put inside, but I'm talking about the issue of it being a problem because, "... the glasses are designed to allow, not block, certain light frequencies."

For the record, my numbers measuring off the white piece of paper outside about half an hour ago using a Minolta LS-110 were (in cd/m2):

No filter: 17500
Green filter: 3600
Red filter: 8200
Both filters: 56

--Darin

I have a few unordered thoughts :

If it's black with both lens superposed, they obviously allow only the 3 narrow bands.

I think a 300:1 extinction ratio is better than probably any silver screens (haven't found anything significantly better than 200:1 on axis, including Stewart and Harkness), so this could still be a high quality alternative to passive polarizers.

Depending on how sensitive the angle is, it could be a problem with any projectors unless they are very long throw. Otherwise there would be a need for an (expensive) spherical filter, or putting the filters inside the projector. This is an even bigger problem because we want the shortest throw possible for the highest light output.

I don't know exactly how it works, but if the glasses are based on some form of waveplates, and other weird optics requiring precise thickness, the wavelength of those would probably shift based on the angle (thickness augments at an angle). The projector's filters would need to have narrower bands than the glasses, then the glasses would have some wiggle room to fit the narrow filters inside of their wider filters. That would improve the extinction ratio.

The 94% quoted loss could make sense, depending on how they calculated it:
- Darin's "red filter" measurements gets 7.4, on a total available light of 51.8
- I assume it would be less with the correct white point, let's say (this is completely arbitrary) it would be 6
- the other eye would need to perfectly match the white point, the brightness, and the gamut, so it can't possibly get more than 6, it needs to be exactly the same.
- Each eye see only one projector, the total effective brightness is 6, the total initial available light is 103.6. Calculating that way would give the 94% loss.
- Calculating the same way, a single DLP with those 6 different colors on the wheel (instead of the RGBRGB wheel) would get 3 of the 51.8 available light, so half the brightness of the dual projector setup, and also 94% effective loss.

This technology would be a revolution if we had those 6 wavelengths available in high-power leds or even laser, inside a single chip DLP projector.

If you really want to know - lend me a piece of glass from one of the glasses and I could do a wavelength scan in the spectrophotometer at work and we'll have in black and white the exact part of the spectrum that is blocked and how much is let through. (I'm a scientist in a biochemistry lab).

rdjam, how will you have a working system by adding circular polarizers, considering the projectors are already circular poalrized ?
How much light do you expect to have compared to a single rs40 with shutter glasses if you put a polarizer on each projector ?

We should keep in mind that the 300:1 isn't white to black since they also reduce the white level. Looks like closer to 100:1.

As I've mentioned, I don't have a way to drive 3D to them. Only experimented with simple test patterns and used the glasses to play a videogame full screen with 2 people getting their own image. Worked pretty well, but one image is very greenish and one very reddish.

No, as I pretty much mentioned earlier.
That isn't really the case because our eyes can adjust quite a bit with a little time, so you can't just go by what you see when just looking at the one image that should be black. Obviously if it is black then you are good to go, but it doesn't have to be that dark to human vision when looking at one to work without visible ghosting when looking at both images at the same time.

--Darin

Thanks. I could send you a pair of glasses or just the lenses out of them. Just let me know what you want and where I should send it.

--Darin

Got it Darin. The spirit CAN still be with you without you seeing any ghosts.

Yes, I understand you want to do what we assume LG did with the CF3D, but what you are trying to do won't work.

The main issue is that both of your projectors will be polarized the same way, you'll get either two left eyes or two right eyes. You don't need a polarizer if you already have polarized light. You have to reverse the polarization on one of the projectors, and you cannot do that with a polarizer, it would simply block the light.

I think the Runco system is using a glass that reverse the polarization with a current applied. That kind of assembly is possibly available from scientific optics suppliers. From what I understand of circular polarization, you'd need a half-wave plate.

(EDIT: I found some documentation, a half-wave plate works to reverse the circular polarization)
http://www.redoptronics.com/waveplate.html
It works for lasers, with a single wavelength, Not sure how much it will work on white light. Probably not well.

Something difficult to setup physically, but inexpensive and higher quality, would be to use a first-surface mirror at 45 degrees on one projector. You'd get 98% of one projector.
Mount one of them normally, and the other shooting at 90 degrees, very close to the lens of the other projector, with a mirror at 45 degrees as close as possible to the lens.

There are pictures at this link - real spectra and also the spectrum of the light being filtered by the two types of filter. There are also lasers available (at least in the physics world) to fit into each window and be super duper low crosstalk with the eixisting filters...

(I used to be a scientist in a biochemistry lab and spectroscopy was a specialty )

I finally read the last sentence at that link (I'm a glasses wearer)

Okay, wait a sec, is the output of the JVC linear or circular ? I only have an SXRD to test and it's already circular, are you saying the JVC is linear ?

Wire grid polarizers are linear polarizers, not circular. At least that is what I have read so far. Of course, I only understand a fraction of what I have read.

Oh wow, that's great, it's linear so it's full of options !
This makes me consider trying it, but I'm a chicken, so I'll wait for you to tell me if it works well

Good night all.

O.K. for those who have not already seen this thread - here it is, the most definitive dual projector passive setup thread I've seen. This forum member, who is using this system, supports Mark Haflich's claim that 2 projectors for 3D is considerably brighter than any single projector system. He's using 2 Epson LCD pjs with passive filters so apparently it does work! See posts 1305 and 1307 (Blackshark)

http://www.avsforum.com/avs-vb/showt...1#post19099091

EDIT: I don't think the Epson setup can take advantage of the polarization.
It remains to be seen how much light gets through, considering all 3 panels are not aligned the same way, and the solution was to put the polarizers at 45 degrees (cutting half the brightness in the process). I assume the JVC will probably be much less problematic and more efficient because all panels have the polarization aligned.

In light of rdjam's mention that the JVCs are linear polarized and aligned, I'm rewriting all my assumptions about the efficiency of different 3D systems right here. It all depends on how exact the numbers are and the reliability of the sources. For the record I think the realD glasses are more than 66% but it's the numbers from realD and other's claiming 60% to 70%. I am also beginning to doubt the 1300 versus 900 advantage. I also doubt the 17% from realD as they possibly don't account for blanking. Measurements will tell, so I keep those number until proven otherwise. All percentages are transmittance, not loss. The total is a percentage relative to a single projector's light output in 2D.

EDIT: I found some more detailed documentation from RealD, and glasses specs are 80%, not 66%. My guess is that the 66% was for the whole system, not just the glasses (80% * 80% = about 66%) So I changed all numbers.

Sony vw90es and other simple shutter systems, including single DLP:
17% shutters
total : 17%

JVC RS40 with (still unconfirmed) 1300 lumens in 3D compared to 900 in 2D at D65:
17% shutters
1300/900 gain in lumens
total : 24%

Dual LCD like the Epsons (unaligned panel polarization) :
80% polarizers
50% 45 degrees polarization angle
80% RealD glasses
Total = 32%

Dual DLP (not polarized):
40% polarizers
80% RealD glasses
Total = 32%

rdjam dream system above or other LCD or LCOS with all panels with a linear polarization aligned:
80% polarizers
80% RealD glasses
Total = 64%

LG with all panels circular polarization aligned (assumed):
80% RealD glasses
Total = 80% (of one light engine, this is 2 projectors in one case)

I am beginning to get a much better understanding of exactly why all dual projector setups at CEDIA were perceived A LOT brighter than the JVC.
- I previously calculated 24% vs 27% for a single RS40, versus dual 900 lumens projectors with realD polarizers.
- It is now 24% vs 32% because the realD glasses transmittance number was wrong.
- With the JVC being linear and aligned polarization it is possible to get 64%, similar to what the LG is doing (but we already knew that about the LG).
- DLP systems are still 32% with the numbers I used.

24 versus 32 is not significant enough, so my next hypothesis to test are :
- The 17% number is possibly wrong because it doesn't account for the blanking
- The 1300 lumens might not be at D65 through the glasses, it could be less than what the hype suggested (or 2D at D65 is more than 900)
- The expensive DLP systems might have a light source significantly above 200W, and they were calculating the light output AFTER polarization
- Those DLPs have a light source that is already polarized (a special kind of LED perhaps), DLP, being a mirror, would retain that polarization
- Things were lost in translation because I don't speak german

rdjam, I think you could get more than 80%, possibly near 100% by using a quarter wave plate at 45 degrees and 135 degrees instead of complete polarizers. A circular polarizer being a linear polarizer with a wave plate added, since your light is already linear polarized, you only need the wave plate. Less loss in the process. Maybe it's worth a try, you might get about the same efficiency as the LG. Of course it depends what the loss is on the polarizer part, and the waveplate part. Maybe it's all in the waveplate...

Another idea, you could also use an LCD plate to rotate one projector's polarization by 90 degrees (essentially an LCD shutter element without a polarizer), and use linear IMAX glasses, they have better extinction ratio than realD, and you'd also get possibly much more than 80% efficiency. The IMAX glasses are also 80% to 90% versus realD 80%. Those glasses don't have any of the purple ghosting that the realD glasses have. As long as you keep you head straight

I can lock my head in a vice for viewing. But when I try to understand all this, I definately can`t keep my head straight.

I just found a small problem that could prevent the system from working well. I was reading about wave-plates and I am now sure they don't work well with white light. The problem I found is that realD glasses are made with a wave plate.

The impact of this is that the realD glasses are NOT circular polarizers on all visible light, they are tuned on green, so they become a mix between linear and circular with red and blue, that is because the wave plate in it only works with green light.

You can test that problem by wearing a pair of realD glasses, and looking through a second pair level (with the branches away from you) toward a bright white wall. Closing one eye, the lens which you expect to be black is actually purple. To get a good black and white, you need to put the second pair vertical at 90 degrees, because red and blue are still linear polarization and are still dependent on the angle. This is a problem because it means you will need to have the projectors polarization aligned with the glasses, or you'll lose light and/or extinction ratio.

I thought of a test to verify if it will be a problem with a specific projector.
- Put some realD glasses on the projector (branches must be toward the projector, not toward you) and rotate it, looking at the effect the angle has on light output.
- There should be an angle with almost no loss of light, and it should be black exactly 90 degrees from that point.
- If the highest light output is with the glasses at 90 degrees vertical,the standard realD glasses will work. Otherwise they might cause a heavy purple ghosting.

Of course I can't do this test with my projector (sxrd), but I tried it with an LCD monitor which is linear polarized, and I need a 45 degrees angle to get the most light output, I don't know if it's the monitor that is at 45 degrees or the realD glasses. Please tell me if you test it with a JVC !

Agreed, the LG is 2 projectors in one case after all...