Silver Screen for Dual Projection?

[KrisRoberts]

When I have seen 3D movies recently in theaters it does not seem like they are using a silver screen.

The ones I have seen have been RealD-Coraline/UP and Imax3D-Avatar.

Everything I have read about passive projection says that you need to use a silver screen to maintain the polarization. But the commercial theaters dont seem to be doing that (or are they and I'm just confused).

Is there a way to use a white or matte screen?

[relaxman]

When I have seen 3D movies recently in theaters it does not seem like they are using a silver screen.

What kind of theaters? Dolby and Xpand doesnt need silver screen.

[KrisRoberts]

RealD-Coraline/UP and Imax3D-Avatar.
All using passive polarized glasses.
I'm pretty sure Coraline was with a film projector, but UP and Avatar were digital.

Walking up and looking at the screens after the shows they appeared to be white, not silver.

[Likay]

Reald uses circular polarization (all of their cinemas?) which requires a silverscreen. Silverscreens are also used in imax-theatre where they don't have shutterglasses but they use linear polarization.
Note: The silverscreen is probably called silverscreen because of the matte aluminium surface. You recognize it because it's more grey than white. It can actually be difficult to see the difference in a dimmed cinema and when the movie is rolling it's simply impossible.
An aluminiumbased screen is necessary to preserve the polarization. Using a standard screen will not give a stereoeffect. It's like trying to view without glasses or filters.

[KrisRoberts]

I guess in my heart I knew that was going to be the case, but was hoping there was some magic the commercial theaters were using to use a white screen.

My theater at home has a CRT projector as the main display device and a digital I use for games. My dream has been to build a passive 3D sytem with two digital projectors but I cant have a permanent silver screen for the CRT.

[Likay]

I use only one screen at home for both stereogaming and watching movies. A clear white one would most probably give a slight better image in 2d but now i'm cutting straws.

[KrisRoberts]

Well, for me the white is absolutely required for the CRT which would have terrible issues with color unifomity on a reflective screen.

As much as I would really prefer a passive system at home, I get the impression loud and clear that the best I'm likely to get in the near term is a 120hz single projector with active glasses.

[relaxman]

wtf?

[BlackShark]

I'm no projection specialist and I have a question I would like to ask.

I would like to know more about the relationships between brightness/colour uniformity, screen gain and the ability to maintain polarisation.
I've seen discussions on other threads about the Peroni superscreen material which has low gain but still maintains polarisation, so I got confused.

Is the screen uniformity problem tied to the gain or to the "silver" aspect of the screen, or have these factors become totally independent with modern screen materials ?

[Likay]

I'm no expert but i've tinkered with it practically:

Polarization ratio is obvious and important. Simply how much the screen depress ghosting: (should be as big as possible) mine has 80 and there's no visible ghosting (unless extremely high contrast situations) using linear polarization.

Gain~the glossiness: Is also important. A too high or too low gain is not good and i'll try with crap english to explain why. The silverscreen needs to reflect light but you also needs to see the image projected on it. If the screengain is too high it will act like a mirror and you'll simply see no image on it, only yourself but in 3d though. A lower gain means a darker, more pleasant image (less glare). Too low and the screen reflects no light at all.
My screen has gain 2.4 and there is a visible "mirrorglare" in the middle of the screen. I didn't noticed it until i took a picture of it with a camera though. So i guess a gain between 2 and 3 should be appropriate. Simply put: Higher gain: More brightness+glare - lower gain, less glare but darker image. As you can see this is also connected to viewing angles.

About colors: The silverscreen has a slight "grey" metallic tone which reflects the whole visible spectra. In my experience coloruniformity is not an issue using silverscreens, at least not with the one i have but other screens might do worse. It's not connected to the screengain. I do believe that screens especially made to have greater coloruniformity + better overall image quality easily outnumbers even a good silverscreen regarding those aspects though.

[Okta]

Hey Likay while we have you here i would like to try a little dual projector for fun with my 2 little gigawares before they move to other duties. My question is there any surface around the home i can use as a screen that will keep the polarization without resorting to buying something expensive or special plaint? Just a small area a foot squre to test with would be cool.

[Likay]

I've tried both duct tape (looks very similar to silverscreenmaterial) and aluminiumfoil but result with those is not worth mentioning. The "silverpaints" i've tried amazed me though (a spraycan of those costs about 6 euros). I'm preparing for a vid taken simultaneously of both silverfabric silverscreen + a painted screen but my camerabatteries went out. Being away this weekend so i get back with that next week probably.

[relaxman]

hi,
we ordered a 3,6x2,1m Spectral 240 screen from Harkness.
Just the material, with simple cut.
I can't wait for it to arrive

Has anybody a good idea how to make a lightweight, portable, easy assemle,
and yet solid frame? from what material, shape? etc.

thx!
Relax

[BlackShark]

How much did you pay for the simple Harkness screen ?

-> for your frame, how about wood ?
Have a look at the DIY projection screen section at avsforums for examples and guides about building your own screen.
http://www.avsforum.com/avs-vb/forumdisplay.php?f=110" onclick="window.open(this.href);return false;



the more I learn about projectors, the more I'm interested in going this way too.

[relaxman]

It was 550 Euro without shipping.
Hope we get it next week!
Thanks for the link.