posted 12-02-2005 11:11 AM                       

Standard SMPTE 243M specifies "35- and 70-mm Projection Lenses and Mounts". Table 2 lists the threads as 36tpi (0.706 mm pitch).

All MODERN lenses should be made to this standard. If you are using a ancient lens with a different thread (e.g., the Snaplites), it is likely unworthy of use in a modern theatre.

Old lens designs are significant "contrast killers", not to mention usually having poor sharpness and focus uniformity:

Kodak "Contrast Killer" Article

quote:

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Contrast Killer 3: Lens Flare
The projector lens itself can be a significant contrast killer. Modern projection
lenses feature efficient multi-layer anti-reflection coatings on each glass
element, and careful design to absorb internal reflections. They also eliminate
old-fashioned cemented elements that separated, crazed or yellowed with age
and the intense heat of the projector's light. "Hand-me-down" used lenses are
false economy, as they severely compromise the quality of the projected
image. Lenses over 15 years old are better used as paperweights or museum
pieces, as they rarely match the resolution, field flatness, and contrast of
modern lenses.
Even modern lenses can be contrast killers. Improper cleaning can scratch or
damage the surfaces of the glass, or introduce moisture into the lens. Loose
dust should be carefully brushed away with a soft camels-hair lens brush.
Cleaning should never be done with a dry cloth or tissue that can scratch the
lens surface. Liquid lens cleaner should be used with great care not to get
moisture into the lens. Look down the barrel of the lens as it is projecting an
image — it should be scratch-free, without any significant haze. The lens
should be sent for cleaning and evaluation if there is significant internal haze,
scratched elements, loose elements, or any other defect.

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