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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 ...
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 ...
In the GDR, it was mainly known for producing overhead projectors, called Polylux. The company was founded in 1870 as Reißzeugrichter and manufactured drawing table tools. In 1874 the founder Emil Oskar Richter invented the bow compass. After switching its focus to overhead projectors in the late 1960s, it was renamed to VEB Polytechnik.
The Polylux was an overhead projector produced in the German Democratic Republic (GDR). It also functioned as a generic name for overhead projectors in the GDR. The Polylux was produced in the VEB ( Volkseigener Betrieb : people’s enterprise) Phylatex-Physikgeräte DDR, in Frankenberg near Chemnitz (then known as Karl-Marx-Stadt ).
Overhead projector in operation, with a transparency being flashed. A transparency, also known variously as a viewfoil or foil (from the French word "feuille" or sheet), or viewgraph, is a thin sheet of transparent flexible material, typically polyester (historically cellulose acetate), onto which figures can be drawn.
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Different markets exist for screens targeted for use with digital projectors, movie projectors, overhead projectors and slide projectors, although the basic idea for each of them is very much the same: front projection screens work on diffusely reflecting the light projected on to them, whereas back-projection screens work by diffusely ...
Shows could be as simple as a single operator and two or three modified slideprojectors or overhead projectors and a couple of color wheels or as complex as shows with ten or more operators, 70 plus projectors (including liquid slide, liquid overhead, movie and still image models plus a vast array of highly advanced (for the time) special ...