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Author
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Topic: Xenon color temp question
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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 01-23-2002 12:58 PM
If you have too much screen luminance, you can reduce light level by reducing current, defocusing the lamp, or perhaps using a three-blade shutter. Reducing current slightly (but staying within the operational current range specified for the lamp) shouldn't significantly change color temperature. Going too low may cause premature blackening of the envelope (running too cool) or arc instability. Defocusing will tend to improve light uniformity, but may shift color slightly. Backing off focus too far might produce a "doughnut" light distribution, where the screen edges are brighter than the center. A three blade shutter will halve the light level compared to an equivalent two blade shutter, but will greatly reduce flicker perception. Increasing the shutter blade angle is also an option to reduce light. If you have light "to burn", I favor consideration of the three blade shutter.Don't forget that SMPTE 196M allows theatres to be as high as 22 footlamberts. Some feel that pictures actually look better at higher luminance, but the aim is 16 footlamberts: http://www.kodak.com/US/en/motion/newsletters/reel/spring98/pointers.shtml ------------------ John P. Pytlak, Senior Technical Specialist Worldwide Technical Services, Entertainment Imaging Research Labs, Building 69, Room 7525A Rochester, New York, 14650-1922 USA Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243 E-Mail: john.pytlak@kodak.com Web site: http://www.kodak.com/go/motion
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