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The opaque projector, or episcope is a device which displays opaque materials by shining a bright lamp onto the object from above. The episcope must be distinguished from the diascope , which is a projector used for projecting images of transparent objects (such as films), and from the epidiascope , which is capable of projecting images of both ...
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In the late 1950s and early 1960s, overhead projectors began to be widely used in schools and businesses. The first overhead projector was used for police identification work. [citation needed] It used a celluloid roll over a 9-inch stage allowing facial characteristics to be rolled across the stage. The United States military in 1940 was the ...
For classroom, businesses and houses of worship settings, 16:10 is the more commonly used projector screen aspect ratio because this matches the aspect ratio used by many modern computers. [ 5 ] Square-shaped screens used for overhead projectors sometimes double as projection screens for digital projectors in meeting rooms, where space is ...
A TELOP (TELevision OPtical Slide Projector) was the trademark name of a multifunction, four-channel "project-all" slide projector developed by the Gray Research & Development Company for television usage, introduced in 1949. [1] It was best remembered in the industry as an opaque slide projector for title cards.
In contrast, a modern LCD or DLP projector often uses an Ultra-high-performance lamp which has a higher luminous efficacy and lasts for thousands of hours. [5] A drawback of that technology is the warm up time required for such lamps. Older overhead projectors used a tubular quartz bulb which was mounted above a bowl-shaped polished reflector.