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An overhead projector works on the same principle as a slide projector, in which a focusing lens projects light from an illuminated slide onto a projection screen where a real image is formed. However some differences are necessitated by the much larger size of the transparencies used (generally the size of a printed page), and the requirement ...
Many overhead projectors are used with a flat-panel LCD which, when used this way, is referred to as a spatial light modulator or SLM. Data projectors are often based on some form of SLM in a projection path. An LCD is a transmissive SLM, whereas other technologies such as Texas Instrument's DLP are reflective SLMs. Not all projectors use SLMs ...
Overhead projector and slide projector: Video projector: Primarily for continued use of older materials. Some teachers find the overhead projector more convenient for lectures depending on their teaching style. Phonograph and phonograph record: Audio cassette, 8 track tape, CD, digital audio: Used to play older or archived recordings.
As a subsidiary of Mast Development Company, Keystone produced telebinoculars, eye training products and overhead projectors. In 1972 Gifford Mast closed down the Meadville manufacturing site, although the name of Keystone View Company continues to be used on eye training equipment.
The mobile era, however, signaled the end for the old-fashioned landline. In 2017, lawmakers in Illinois finally voted to allow AT&T to stop serving the state's 1.2 million remaining landline ...
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 ...
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