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Author
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Topic: Formula for Lumens vs. Screen Size?
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Frank Angel
Film God
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Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 06-22-2011 11:28 AM
Is there any general rule-of-thumb when sizing a video projector for a known screen size? For example, we have a 55ft scope screen, 0 gain -- we may need to rent a video projector. 10K lumens, 20K? Anyone have a chart to show that kind of size/light requirement?
We currently have dual Barcos R6+ Performers at 6,000 lumens each. Stacked, they were supposed to be adaquate for our screen, but the big hitch is that they are NOT stable enough to be aligned the night before a show and remain aligned (pixel for pixel) for the show the next night. Once they are turned off and cool down, you are screwed. Barco says you have to align them each time. Fine for indoors, but this is an outdoor venue and we don't have the luxury of aligning them before the show on the day-of because, well, it's out in daylight.
We have a scope picture that has to be shown and I fear using only the one Barco will not make it, thus the need to rent. I would GUESS, 12k -15k would be bright enough (remember, this is outdoors and there is more ambient light than in an indoor theatre), but was hoping there is some chart that gives real numbers.
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Robert Minichino
Master Film Handler
Posts: 350
From: Haskell, NJ, USA
Registered: Dec 2005
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posted 06-22-2011 09:37 PM
It depends on the format and the target brightness. Since the Barcos are 4:3, projecting scope only uses half of the imager (assuming no anamorphic), so you only get 3000 lumens out of them, and that's before color calibration which eats a little light.
I'm assuming your screen is 1 gain and not actually zero , and it's 23x55, that's 1,265 ft^2. To get 14 fL from a 1.0 gain screen, you'd need 1,265*14=17,710 lumens. Your two 3000 lumen projectors get you 6000 lumens total, or 4.7 fL. That's pretty dim, but it might be acceptable if you don't have much ambient light on the screen.
I'd rent something brighter, preferably with a 16:9 imager to get more light efficiency. A 20k lumen projector would be ideal, but even 10k would be way better than what you've got.
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