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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 ...
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.
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.
At a more advanced level, flip charts, slide projectors, and overhead projectors can be used for displaying prepared content. The use of prepared material often results in a neater and more accessible presentation. Laser pointers or sticks are often used to highlight a particular point of interest within a slide or image. Many manufacturers ...
It works with an overhead projector. The panel consists of a translucent LCD, and a fan to keep it cool. The projection panel sits on the bed of the overhead projector, and acts like a piece of transparency. The panels have a VGA input, and sometimes Composite (RCA) and S-Video input. Later models have remotes, with functions such as 'freeze ...
As copying technology advanced, Thermofax machines were subsequently marketed as a method of producing transparencies (viewgraphs) for overhead projector presentations. A sheet of heat-sensitive clear stock was placed on top of the original, and passed through a ThermoFax, producing a black image on the clear stock.
A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens , but some newer types of projectors can project the image directly, by using lasers .
The Keystone View Company was a major distributor of stereographic images, and was located in Meadville, Pennsylvania. From 1892 through 1963 Keystone produced and distributed both educational and comic/sentimental stereoviews, and stereoscopes. By 1905 it was the world's largest stereographic company. In 1963 Department A (stereoviews sold to ...