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HELPFUL INFORMATION ABOUT PROJECTION & SCREENS:
Projection Parameters
Viewing Angle
The maximum acceptable viewing angle is 45 degrees. Beyond that characters and image elements become undecipherable. Ideally, all viewers should be seated within 30° of the projection axis, and never more than 45° off axis.
Screen center should be no more than 20° above the eye level of any viewer.
Diagonal Screen Size
Because the aspect ratio for video is 4:3, the diagonal produced from those numbers turns out to form a perfect integer relationship: 3 - 4 - 5.
For instance: How large is a 100 inch (diagonal) video screen?
Dividing 100 by 5 equals 20. This multiplied by 3 equals the height of the screen = 60 inch.
Multiply the same 20 by 4 and we get the screen width = 80 inch.
ANSI
Acronym for American National Standards Institute, ANSI has established the standards for measuring lumen brightness of projectors.
The ANSI lumen standards ANSI/NAPM IT7.228-1997 and ANSI/PIMA IT7.227-1998 actually were retired on July 25, 2003.
The IEC lumen standard for projectors equals the ANSI standard, but manufacturer hesitate to use a different term than ANSI. The parameter ANSI lumen became too important and the term 'IEC lumen' would confuse the entire projection business. Probably something like "ANSI/IEC lumens" will emerge during the next few years (ANSI and IEC suggest referring to the IEC standards for testing from now on) ...
The IEC lumen standards are IEC 61947-1 and IEC 61947-2, the testing procedures are basically the same as under ANSI: An IEC lumen is the same as an ANSI lumen!
Lumen is the unit of illumination on a surface. One lumen is the light of one candle power on each square foot of a surface of a sphere at a radius of one foot from the light source.
ANSI or IEC Lumens are not comparable to 'lumens' expressed in general lighting terms!
Aspect Ratio
The ratio of width to height of a frame or screen. The most common aspect ratios for projectors are 4:3 and 16:9.
Contrast Ratio
The ratio of the maximum white to the minimum black level possible for a particular spot on the image without background light.
