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This topic comprises 2 pages: 1 2
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Topic: 16 ft lamberts...
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Dave Bird
Jedi Master Film Handler
Posts: 777
From: Perth, Ontario, Canada
Registered: Jun 2000
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posted 07-09-2001 08:16 AM
Steve, your point about larger screens underluminated looking OK is right on from a layman's point-of-view. We camped over the weekend and visited a drive-in I nearly bought one time. It had been closed, 3-phase power disconnected. Typical bureaucratic BS meant that upon re-opening, and despite the fact that the MAIN POWER LINES cut 30 feet behind the booth, the utility INSISTED he run brand-new poles and lines 2 miles from the main highway if he wanted to be reconnected in 3-phase. (Even though the school next door and boat locks downline are still okay). So he connected single-phase (from same "bad" lines), and ran 3K to an 80-foot screen! Using John's 5W per sq. ft. "rule", I can't imagine he's getting much over 4ft lmbt's.
But with NO outside light, it was really quite good, didn't have any
problems at all seeing, so I believe the eyes really do compensate for lower light when such a large screen is present. The screen is cement-block that's been stuccoed which I'd never seen. This means of course that it is NOT tilted to the field either, though projection is from 2nd storey, so that may help......
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Jerry Chase
Phenomenal Film Handler
Posts: 1068
From: Margate, FL, USA
Registered: Nov 2000
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posted 07-09-2001 10:23 AM
Brad, I was responding to a comment, so I don't have first hand knowledge of that screen. A normal screen loses about 5% of the light to the perforations. The difference of 5% is less than one fL variation at most illumination levels, and we all know that many auditoriums don't come near to achieving this flatness. If the screen was microperfed, the density of perf is less than 1/2 that, and would be less objectionable than seeing the rows of perfs in a very small auditorium. While the variation in seeing perfed areas and non-perfed areas might seem objectionable, if the speaker perfs were located below the centerline of the screen, they would be covered with textured images the bulk of the time and lost in the visual "noise."Ideally, NO screen should have perf holes in it. What I find strange is that for years no company or sound technician has figured out that by limiting the thickness of the screen in small circles - say an inch in diameter or so - tweeter drivers could be glued to the back of the screen in these areas and provide a better sound than those trying to push sound through the screen. Digital cinema in small auditoriums probably has it's own set of problems with perfs. If the lines of perfs don't exactly match the lines of the pixels a disturbing pattern might appear. If blended colors aren't used and a set of perfs happens to nearly match the pitch of the pixels, color shifts could occur.
Perhaps someone else knows if the AMC sucker screens used perfs only over the speakers?
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Adam Martin
I'm not even gonna point out the irony.
Posts: 3686
From: Dallas, TX
Registered: Nov 2000
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posted 07-09-2001 10:53 AM
Regarding the perfs only in front of the speakers at the Starworld 20 in Bixby, OK, and at the Northrock 14 in Wichita, KS, the light output on these screens was crap, so you never noticed anyway. In fact, the throw was so short for such a large screen, the flat image actually vignetted on a couple of them. The screen was overwhelming on the floor and the balcony seating was just too far away. The sweet spot was taken up by the architect's retarded placement of the booth. (Note the 6-foot window in the middle of the room for sound and light to bounce off of.) Oh, and did I mention the vertical masking?  
 As for the Torus screens at AMC, all of the ones I saw had the speakers mounted above and below the screen.
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Will Kutler
Phenomenal Film Handler
Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001
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posted 07-09-2001 12:02 PM
Other things to consider when adjusting for screen brightness.If the screen, audience and projector are not in alignment, it may be difficult to obtain 16fl w/even screen brightness. We had a few screens at my old theater where this was true. I had to compromise because of this. 16 fl w/o even screen brightness, or 12fl with even brightness. I was not authorized to realign lamphouse and cut new plates. All I could do was report the problem. Even then, part of the problem was theater design architecture, and correcting that part of the problem was impossible. Also keep in mind that if you bring the bulb too far forward in the lamphouse to increase screen brightness, then you can risk overheating and damaging the film and reflector mirror. Some people also think that adjusting the current tap switch on the Christie SLC consoles will increase screen brightness. Not true. Forward and aft bulb adjustments for screen brightness only. Currrent tap switch used to ensure proper bulb current and to stabalize bulb as it ages. Remember that on the SLC lamphouses, that you cannot rotate bulb. Also, when making up, down, left and right adjustments on the Christie, then these adjustments will be the same for both flat and scope.
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Will Kutler
Phenomenal Film Handler
Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001
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posted 07-09-2001 03:54 PM
GordonThe information in my last post was given to me by Devon at Christie, as well as our Area Tech. I did not notice any increase or decrease in screen brightness using the current tap switch on the Christie SLC. Our Area Tech also informed me that bulb rotation on the Christie SLC console is not possible due to its design. I was also informed about problems with Christies current tap switch, that the contacts are prone to burning/melting, and that the tap-switch was being set at the factory at the highest possible level, and being left alone. I was told that the bad tap switch design is another problem that Christie is looking into.
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