Film-Tech Forum ARCHIVE: What Screen to Go? Silver or white 1.1Gain

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Posted by Peter Das (Member # 4690) on 04-14-2008, 09:23 AM:

I have a small theater in India and need a new screen. Its 38ft Wide and using a super Lumex 2500w Bulb. So What Screen I should go. Silver or White 1.1gain. Thank you in advance

Posted by Mitchell Dvoskin (Member # 751) on 04-14-2008, 10:01 AM:

If your auditorium is not much wider than the screen, go Silver. The problem with silver screens is that they reflect most of the light back the way it came, so that brightness drops off fairly quickly for those seats that are left or right of the screen.

Posted by Peter Das (Member # 4690) on 04-14-2008, 11:06 AM:

HI
The Theater is wide 42ft and screen is 38ft wide.

Posted by Darryl Spicer (Member # 711) on 04-14-2008, 11:58 AM:

I wouldn't do silver unless I was planning on doing the RealD 3-D process. I would go a high gain screen like 1.8 if I was planning on using Dolby 3-D. I would put a standard screen if not planning any 3-D.

Posted by Marco Giustini (Member # 4544) on 04-14-2008, 02:00 PM:

I have a question on high gain screens (not silver, just 1.4 Perlux for example).

Every installation I saw with perlux screens has a bad hot spot in the center. It's obvious on flat frame (I think perlux should not be installed on flat frames, isn't it? [Smile]

), 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!

My question is: is there a way to install a Perlux (read: high gain) screen without hot spotting it? Perhaps the curvature of the frames I saw was not enough?

Marco

Posted by Gordon McLeod (Member # 33) on 04-14-2008, 02:47 PM:

The higher the gain (directivity) the more of a hot spot there will be Proper curving the screen will lessen it but not usually get rid of it

Posted by Marco Giustini (Member # 4544) on 04-14-2008, 02:56 PM:

If the hot spot cannot be removed... then I prefer lower gain!

Ciao
Marco

Posted by Paul Mayer (Member # 355) on 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 ]

Posted by Mark Gulbrandsen (Member # 72) on 04-14-2008, 08:13 PM:

I would get 1 sq. meter samples of both 1.1 and 1.4 gain surfaces from MDI and Harkness because they are somewhat different... nothing over 1.4 gain in your case because of the width and I assume its a flat screen. You didn't mention any radius of a curve in the frame or the throw distance and lens specs. Place both samples as close to the present screen as you can get them and run some test previews or reels of film then pick the one you like. I find the higher gain screens offer a somewhat more pleasing contrast and a bit more snap to the image... people seem to prefer this. The 1.4 gain screen would be pushing this gain in a flat frame a bit and it will hot spot somewhat. Measurements and calculations here really don't matter unless you're being ultra critical and or are willing to alter the frame's curve. Some technicians tend to get totally carried away in locations that actually should be kept to a few sensical simple choices of what surface you like.

Mark

Posted by Frank Angel (Member # 248) on 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.

Posted by John Walsh (Member # 168) on 04-15-2008, 07:45 PM:

Is there any data about changes in color temperature with a silver screen vs. a regular matte?

Posted by Frank Angel (Member # 248) on 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 ]

Posted by Peter Das (Member # 4690) on 04-17-2008, 10:43 AM:

Frank
So in my case for 38ft wide screen and 42ft wide theater, I should I go with Silver screen?.
I am burning Super Lumex 2000W. Straight screen.

Posted by Frank Angel (Member # 248) on 04-19-2008, 06:32 PM:

Peter, I would advise you to talk to a few screen manufactures --talk to MDI and perhaps Harkness and get input from them. As has been said on these posts, using silver screens for standard 2D projection often results in hotspotting. It will only work will under certain ideal conditions such as a narrow room (yours does seem to fit that) but also the projection angle and other factors that you could avoid dealing with if you went with a standard screen, taking the hotspot issue out of the equation.

I would give all the parameter of the theatre to the screen manufacture and let them tell you that their silver screen will work well in your theatre. As I said, MDI claimed that their silver screen minimizes hotspotting.