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Topic: What Screen to Go? Silver or white 1.1Gain
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Paul Mayer
Oh get out of it Melvin, before it pulls you under!
Posts: 3836
From: Albuquerque, NM
Registered: Feb 2000
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posted 04-14-2008 02:59 PM
Anytime one uses a gain surface it must be curved properly to avoid hotspots. As mentioned in the quote below by the late great John Pytlak, the curve should be determined by ray tracing to put the light into the center of the seating area. The quote comes from this thread referencing SMPTE RP95 and other good info and posts about curved screens:
Curved Screens vs Flat Screens
quote:
Harkness Hall ran a fairly comprehensive study of screen gain and curvature a few years ago, and presented a report at the ITEA Seminar in Los Angeles. Participants included Schneider Optics, Kodak, Lucasfilm, and Famous Players theatres.
SMPTE Recommended Practice RP 95 specifies "Installation of Gain Screens".
The optimal way to determine the proper curve is by ray tracing. The idea is to curve a gain screen such that the projected light is reflected back to the center of the prime seating area.
Very high gain "silver" screens are VERY directional, and as you note, sensitive to handprints, showing seams, etc. Their primary application is polarized 3D projection, which requires a screen that maintains polarization of the reflected light.
For moderate (15 x 35 foot) sized screens, a matte or slight gain surface is the best choice, since getting enough light is usually not an issue.
Here are some links to information:
Link
Linkety
Linky
Link
Link
[ 04-14-2008, 09:09 PM: Message edited by: Adam Martin ]
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Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 04-14-2008 10:18 PM
MDI has a silver screen with a lenticular surface which is their special process; they claim that it eliminates hot spotting if used on a curved frame.
I recall reading that the original Fox spec for CinemaScope called for their "Miracle Mirror" (or some such name) silver screen which they needed to compensate for the loss of light to the extra width (and the anamorphic lenses as well, I am sure). Their silver screen had a lenticular surface which supposedly did prevent hot spotting. Problem is that they stopped making lenticular silver screens and they haven't been available for years until MDI.
You might check with them about this; I never saw any third party evaluation, just what their salesman told me. Also, I am not really sure whether or not the leticular surface still holds the polarization. It may be silver, but not be any good for 3D. Check with MDI.
I once walked into a theatre and was immediately impressed with the screen image. It was sunshine bright and very good contrast and a unique quality, Mark describes it best as a "snap" that made me take a really good look. This probably was about a 40-45ft width. When I went up to the booth, I asked the projectionist if he was buring 4500w or even higher to get such a beautifully bright picture, but no, he said he was buring 1600w; my jaw dropped. But he added that it was a silver screen. I went back down and walked around and I am telling you, with the image on the screen, there was no VISIBLE hot spot. Sure, it probably would would be evident with no film in the gate, and you probably could read fall-off, but as far as the movie-goer is concerned, it was undescernable. I will add that it was curved and the width of the room was no more than a few seats wider than the screen. But it completely sold me on the possibility of silver screens working if installed properly.
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Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 04-15-2008 10:06 PM
Lab people and techies make a big deal about color temperature, but in the trenches, it's not nearly as critical. The eye and brain are constantly working to white-balance everything. That's why a white piece of paper under an 60w incandescent (heavily yellow) looks white, but take it outside in the sunlight (lots of blue) and it will still look white after only a few minutes. Take it under flourescent light (mostly some puke-ish green), and it will STILL look white.
You want to see how dramatically your eyes & brain can color-correct? Look at any well lit room. Now cover one eye with your hand making sure you block all light (don't just close your eyelid). Keep the eye covered for a full minute and a half. Now with your eye still covered, focus on some item in the room, prefereably something with lots of a primary color -- try to find green. Now take your hand way from your eye and just using your eyelids open one eye and shut the other, back and forth repeatedly. You will see a very dramatic color shift between your eyes until the covered eye does it's balancing thing and finally matches the other eye.
The eyes really couldn't care less about slight shifts in color temp....they will work to resolve so that white looks white. That's not to say we shouldn't have strick objective standards, of course, but when it comes to color and the eyes, there is a very wide latititude.
[ 04-16-2008, 04:49 AM: Message edited by: Frank Angel ]
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), but I saw curved screens too and there is hot spot at the center of the screen, even if the curvature of the screen makes the hot spot larger. I'm sure that is not lamp alignment issue. The hot spot follow you depending where you seat!
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