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Author Topic: Spot cleaning screens Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-18-2003 06:25 AM                        quote: A high gain screen must be properly curved, or you will have non-uniform illumination. Really high gain (3D silver) screens have a relatively narrow optimum viewing angle, even if curved. Please explain further!  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 07-18-2003 08:20 AM                        SMPTE Recommended Practice RP 95 specifies "Installation of Gain Screens". A low gain "matte" surface reflects light nearly equally in all directions --- it is a "lambertian reflector". Matte surface screens should be installed flat to minimize contrast-reducing cross-reflections. Gain screens have a surface that has a higher reflectance in one direction, much like a mirror (angle of reflection = angle of incidence). If you do a "ray trace", you will see that a gain screen needs to be curved to reflect the projector's light back to the center of the audience, especially in wider auditoriums. Kodak's "Film Notes for Reel People" Fall 1997 issue (publication H-50-44) had an article by Glenn Berggren and Gerald Nash about screen curvature and its effect on illumination uniformity: http://www.film-tech.com/manuals/H5044.pdf Although their high-gain compound curve design "Torus" screen had issues for sound (could not be perforated, tended to focus sound reflections), it certainly delivered good illumination uniformity with high gain, based on good engineering principles. Lambertian Reflector Lambertian Source  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-18-2003 03:12 PM                        Thanks!  |  IP: Logged

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