Requesting advanced help! How to increase brightness of double-stacked projectors? Can curved high gain screen work with double-stack without homogeneity issues? "Prism" options?

I'm not sure what section of the forum is best to post this, this section or "Projectors and Screens," but I already have one topic on the front page in that section so I will try here. But if it's OK to have two in the same section at once then probably it would be better over there. Here is the section.

I am double-stacking projectors for passive 3D using a geobox etc. I want them to be much brighter. Their lenses are to be 18 feet from a 135 "(diagonal) 16: 9 screen. Seating will be 15 feet from the screen. Questions:

1. How high gain screen can I go, at this throw and seating distance, without hotspotting becoming noticeable?

Whatever the answer to that queston, which I am guessing is around 2 - 2.5 gain maybe 3 maximum, I am looking for ways to go higher if possible. 4 gain. 5 gain. This will create hospotting for sure on a flat screen, which brings me to questions 2 through 5.

2. Can curved screens be used with double-stacked projectors? There is curved screen made Germany that uses micro lenses in the screen material, that I have heard is excellent, called couchscreen. It don't think it comes in 135" 16:9 size anyway, but I was told even if it did, it would not work in this situation because it would cause homogeneity issues with double-stacked projectors. However, is this true for all curved gain screens, or only ones that use micro-lenses?

Maybe he meant with one projector stacked on top of another, the vertical angle is slightly different to the screen, so the high gain would make one appear brighter than another in the same spot from the same viewing angle. But shouldnt that be less of an issue with curved high gain screens than flat ones? So he must have meant something else.

3. If it's a problem with all curved high gain screens, not only ones with microlenses, then the only other way is to use an optical prism that combines the light of both projectors and projects them out from the same spot. Does anyone know where to find such a prism, and what it looks like, and how it works?

4. I have heard those prisms can reduce the contrast of the image. Does anyone know approximately how much contrast is lost? Are we talking 20% loss of on/off contrast and ANSI contrast, or 80% loss? Depending how bad it is, it could be or could not be an option.

5. To do passive 3D with double-stacked projectors, it requires different 3D filters placed in front of the lens of each projector to create stereoscopic separation for the viewer's right and left eyes. If you put the optical prism after each respective 3D filter and combine the light to the same point, will it maintain its distinct filtration? I assume it would with color bandpass filters, which is what I want to use, but Im not 100% sure. With polarization filters I have no idea, but it seems more dicey.

Thanks a lot for the help. This is only my fourth post since joining the forum so, you know, I wanted to start off with something simple and easy for everyone ...: D

Zitat von ((( atom )))

I wouldn't mind if your 5th post would tell us a little about yourself. ;)

Did you see my introduction post? In general though I am a pretty private person, maybe sometimes to my detriment. On one hand being private gets in the way of really becoming part of a community, but on the other hand, it could be anyone posting online. It also even restricts your ability to say things even if they are true if you put your name next to it. There are downsides to being private but also benefits, and you can't have both. I didn't really think of that until now though, it's just habit.

What do you want to know?

Zitat von JETS

ALso mein Englisch ist tatsächlich so schlecht, dass ich zwar fast alles lesen kann aber lieber deutsch antworte.

Ich glaube verstanden zu haben was Art möchte und versuche ein bisschen helfen zu können da ich schon über zehn Jahre doppelprojektor 3D Systeme einsetze.

Stacking ist nicht ganz easy, als erstes benötigt man eine steife aber einstellbare Verbindung beider Projektoren um zu stacken.

Hier hilft ein Rahmengestell aus Aluminium und Stahl, je dichter die Optiken beieinander sind desto leichter lässt sich das Ganze am Ende einstellen.

Bei manchen assymetrisch aufgebauten Projektoren hilft es einen davon auf den Kopf zu dehen und die Projektoren Rücken an Rücken zu montieren.

Stacking - egal ob aus helligkeits oder 3D Gründen - funktioniert auch auf gecurvten Leinwänden solange siese nur in einer Ebene eine Kurve haben.

Beim Gain kann man schon wieder etwas entspannter sein, da durch zwei Projektoren gleichzeitig auch eine gute Portion helligkeit hinzukommt.

Ich habe hier tatsächlich "nur" einen Gainfaktor bis maximal 1,5 eingesetzt und selbst bei diesem waren für mich die Nachteile schon überwiegend störend.

Lieber ein etwas nicht zu helles Bild riskieren als unhomogenitäten in Kauf zu nehmen. Das Auge gewöhnt sich eher an die Helligkeit als an ungleichmäßige Lichtverteilung.

Mit Anarmophoten oder Prismen habe ich es noch nicht ausprobiert, aber ich würde meinen dass zuerst die Optik, dann die Prismen und ganz zuletzt die Polarisationsfilter im Lichtweg sein sollten.

Das wichtigste Element ist hier tatsächlich die Leinwand, diese muss zwingend Polarisationserhaltend ausgeführt sein. Je mehr von der Polarisation erhalten bleibt, desto besser ist die Trennung rechts-links

und umso weniger Geisterbilder sind sichtbar. Außerdem darf sich auch die Leinwand nicht mehr bewegen können, eine zu locker gespannte oder gar eine Rollleinwand funktioniert hier nicht zufriedenstellend.

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No problem at all. I am the one who should be speaking German since this is a German forum. But I was using google translate to read the forum for weeks before I joined and incredibly it actually does almost a 99% perfect job, it seems.

Regarding your advice, does double stacking really increase brightness for passive 3D though? I know it does for active 3D, but with passive 3D, each eye is only seeing one projector so I have been told you are only getting the brightness of one projector. Maybe it is like if you close one eye while watching TV, the TV is just as bright to one eye. Then you open your second eye, and it is no brighter. Each eye is seeing x brightness but it does not double. With double stack projectors, yes its two different ones, not just one TV, but each eye is only seeing one, so it's like both are just looking at one display, I think.

Regarding the prism, apparently the way it works is that you put the 3D filters outside the lens of each projector in the stack, and then after that, you have two tubes or something, I have no idea, that funnel the light into a prism, and then the prism shoots the light out all together. The question is whether after the filtered light from each projector in the stack gets funneled into the prism, if it now loses its filtered status, in your case, its polarization.

I am curious what screen you found with 1.5 gain that has high polarization retention? When I researched that it seemed like the highest polarization screens were also tied to higher gain surfaces. More silver flakes in the screen material leads to more polarization retention ability of the screen, but also more gain, because the silver reflects more.

I would actually like to try Infitec or Omega filters, but these require even more brightness which makes it tough because I also want DLP projectors with no risk of rainbow effect, as well as frame interpolation. And minimum say 2,500 lumens calibrated or more. There seem to be very few options that fit all criteria. Oh, and bulb lightsource only, because only bulb lightsource seems to work well with Infitec and Omega filters (at least, the ones available to consumers. Infitec has a 6P systems for Barco and Christie cinema projectors but that's another story).

Do you know the names or categories for the curved screens that curve on multiple planes vs only one plane? If I find a curved screen that will work for me, how do I tell from the specifications if it is curved on multiple planes or not?

Zitat von JETS

As far as I know, you can no longer mix two light paths after the stereo filters and further process them optically while the polarization is completely preserved. So you need two separate light paths.

What about with color bandpass filters?

Either way, it sounds like I dont need any prism as long I get a curved screen that only curves horizontally, but not vertically? Correct?

If I get a horizontally curved screen with say 4 to 8 gain, will there be hotspotting? I am concerned not just about the center seat, but maybe 4 seats per row while will be about 90% as wide as the screen width. So no one will be sitting outside the right and left border of the curved screen, but some people will be more towards the left or right side.

Does curved screen eliminate hotspotting only for the center seat, or also for all the seats within its width?

Zitat von JETS

...you wont get an Hot-spot, you will get an Hot-line.

Zitat von FoLLgoTT

Ich empfehle hier meinen Hotspot-Simulator.

Zitat von ((( atom )))

Yeah, very good tool and yes, with some screens you get a hot-line and that is exactly what the simulator will show you. Tried it on my setup and the prediction was accurate. I use a retroflective screen and I have the lower area of the screen a bit brighter. Hotline is way better already than a hotspot.

Thank you very much everyone. I emailed the manufacturer of one curved screen and he told me that for double stacking projectors with a curved screen, the pixels from both projectors will be perfectly aligned in the center of the screen, but then they will start to go 1 pixel off on the corners because of the curve of the screen and the different angle of each projector to the screen, and he said this would look similar to increased crosstalk in 3D towards the sides of the screen.

True or false? I mean, true even on a curved screen that is curved horizontally only?

If it's true, is this something I can safely rely on a geobox g602 to correct? Or do I not want to buy and install a big screen with everything being dependent on a geobox's warping working perfectly?

Also, that hotspot simulator is so cool. I did not know that existed. However, I cannot get it to work. When I try to click it in winzip or winrar, it tells me it's not free, and after 40 days you need to buy it, but the only options it gives me are to "close" or buy it right away or "how to buy." No option to open it and use it for free for 40 days. Maybe the problem is I dont have excel on my computer, only in google sheets?