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This topic comprises 2 pages: 1 2
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Author
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Topic: 10-12 footlamberts
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John Pytlak
Film God
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Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 11-12-1999 06:57 AM
Standard SMPTE 196M specifies an aim of 16 footlamberts, with an allowed range of 12 to 22 footlamberts for theatres. Almost all prints are timed by the laboratory in accordance with this standard, and should ideally be projected at 16 footlamberts. The contrast aims of the film stocks are based on prints being shown at the 16 footlambert aim.If the distributor timed the prints lighter in hopes of compensating for theatres that had dim screens, they compromised the overall quality of the image. Making a print lighter will tend to compress the highlight detail, wash out the flesh tones, and make the blacks more "smoky". But since they accepted the "look" of the prints that way, and are recommending a lower luminance for showing them, I would comply with their request. But be sure to return to the standard 16fL luminance after the run. To show why this philosophy is flawed, imagine taking the practice to the extreme. If theatres have dim screens, why not make the prints REALLY light? If you do, the film will be clear and have no image! ![](http://www.film-tech.com/ubb/smile.gif) ------------------ John Pytlak, Senior Technical Specialist Worldwide Technical Services, Professional Motion Imaging Research Labs, Building 69, Room 7419 Eastman Kodak Company Rochester, NY 14650-1922 USA Tel: 716-477-5325 Fax: 716-722-7243
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John Walsh
Film God
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Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 11-12-1999 10:50 AM
I really hate to sound like a cynic (and maybe like a pain in the ass, too) but I just can't see 99% of theaters adjusting the lamp to match the recommened fL for one film. IMSO (in my sarcastic opinion) most theaters can't even get 10fL if they wanted to. Sorry to rant, but not only do I feel this is the most prevalent single problem in theaters, but is ignored by owners and equipment installers.Theater owner: I need 20 consoles for my new theater complex. I want the best light on the screen I can get. All of them are 18ft x 45ft. Equipment supplier: "Well, our "BlastLight 5000W" seems about right. That'll be $1800 each." Theater owner: "At DarkStar supply, they told me that the Cataract 2000W's would work. It's $750 cheaper. See ya later....." Equipment supplier: "Wait! I can supply the TotalEclipse 2000W's," (sigh) "for the same price." Theater owner: "How good are they?" Equipment supplier: "Well, they aren't as bright as....." Theater owner: "Well, if they're no good..." (starts dialing cell phone.) Equipment supplier: "I meant, uhm.. ah.. the PAINT on the outside is not as bright, yeah, that's what I meant..." Theater owner: (Hangs up cell phone, but doesn't put it away.) "So I really don't need 5000 watts?" Equipment supplier: (Eyes are on phone) "No, you don't really need it." Theater owner: "OK then." (puts phone in pocket.) "Trying to up sell me, eh? Ha-ha, well, I'm an expert at that. So how good are these lamps?" Equipment supplier: (Sighs) "Very good." (theater owner reaches towards pocket) "I meant to say, 'the best you can get.'" Theater owner: "Good, that's what I want to brag to other owners at NATO. Give me some free logo T-shirts and baseball caps, too. Those consoles come with the bulbs, right?" It also doesn't help that you need a $2200 meter to read brightness. When you can't get your boss to buy good quality splicing tape, how are you going to get a meter? Unless someone comes up with a cheaper way of mesuring reflected light, few people will even know how bad off they are. SO THERE! .....i feel better now.....
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John Pytlak
Film God
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Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 11-23-1999 10:32 AM
Based on Strong's "Lens Selector and Picture Size Computer", figure about 5 watts per square foot of screen area (2.39:1 scope format) to adequately light a 1.0 gain matte white screen. So a 1000 square-foot matte screen will need at least 5000 watts.With a 1.5 gain curved screen, figure about 4 watts per square foot. And about 3 watts per square foot for a 1.7 gain curved screen. Obviously this assumes normal efficiencies for the lamphouse, shutter and optics. Any misalignment, dirty screen, three-blade shutter, etc. will require much more power. The effective f/stop of the projection lens is also an important factor, with a wider lens opening offering greater light efficiency, at the expense of depth of focus. BTW, a 1000-square foot screen is 20.5 X 49 feet for the 2.39:1 scope format. ------------------ John Pytlak, Senior Technical Specialist Worldwide Technical Services, Professional Motion Imaging Research Labs, Building 69, Room 7419 Eastman Kodak Company Rochester, NY 14650-1922 USA Tel: 716-477-5325 Fax: 716-722-7243
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John Pytlak
Film God
![](http://www.film-tech.com/ubbmembers/331cap.gif)
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 11-23-1999 10:53 AM
Just an addendum for our friends outside of the USA that use the metric system:For a 1.0 gain matte white screen, figure about 54 watts per square metre of screen area. So a 100 square metre (6.5 X 15.5 metres) matte white screen needs at least 5400 watts, so a 6000-watt xenon bulb is the smallest that will do the job. Use at least 43 watts per square metre for a 1.5 gain curved screen. Use at least 34 watts per square metre for a 1.7 gain curved screen. Again, these "rules of thumb" are based on the Strong/IscoOptic "Lens Selector and Picture Size Comparator". ------------------ John Pytlak, Senior Technical Specialist Worldwide Technical Services, Professional Motion Imaging Research Labs, Building 69, Room 7419 Eastman Kodak Company Rochester, NY 14650-1922 USA Tel: 716-477-5325 Fax: 716-722-7243
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John Walsh
Film God
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Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 11-23-1999 02:31 PM
I always used:Height of screen squared, times 12 exp: 20.5 ft screen sq = 420.25 times 12 = 5049 watts Which is the same, but JP's formula is better, because you can account for gain screens (which our theater company dislikes, so we don't have to worry about it.)
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