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Author
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Topic: Replaced the bulb but screen still dark
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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 05-21-2004 08:44 AM
Basic things:
1.The optical path is in perfect alignment from the reflector, to the lamp, to the film aperture, through the lens, to the center of the screen image (string or laser alignment).
2. The distance from the reflector to the film aperture is set to specification.
3. The lamp is mounted correctly, with the proper spacers or adapters if needed.
4. The reflector is in good condition and clean.
5. The lamp is operating at the correct current (check ammeter calibration).
6. Do the "bullseye" alignment without the lens, adjusting the position and focus of the lamp (x-y-z position)
7. Tweek position and focus to obtain optimum uniformity of illumination with "open gate white light" projected on the screen (be careful not to overheat the lens) -- meeting standard SMPTE 196M:
quote: 5.3 Theater luminance limits Theater screen luminance at the screen center shall be between 41 cd/m2 (12 fL) and 75 cd/m2 (22 fL). Luminance at the screen sides shall be 75% to 90% of the screen center luminance, but not less than 34 cd/m2 (10 fL).
quote: 6 Luminance distribution The screen luminance shall be symmetrically distributed about the geometric center of the screen. The luminance of any point on the screen between the center and the edges, as measured from any seat in the middle row, shall not exceed the screen center reading (see annex A.2). For screens with a gain factor of 1.1 or more, the screen shall be curved for light uniformity as described in SMPTE RP 95. A more complete measurement of screen luminance distribution is described in SMPTE RP 98 and is recommended for new or revised installations.
Remember, ALWAYS use the proper safety gear when handling xenon lamps, or that exploding lamp may be the last thing you ever see!
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