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DataRay Inc. - ISO 11146-Compliant Laser Beam Profilers
Photonics Dictionary

overhead projector

A projector used to project transparencies. A horizontal 8 x 10-in. stage for writing or laying down preformed transparencies is provided with either an elliptical mirror or a plastic Fresnel lens below the stage to form an image of a lamp filament in the projection lens situated above the stage. A 45° mirror above or below the lens turns the vertical beam into a horizontal direction toward the screen behind the lecturer's head. The imagery is such that when the speaker is facing the audience, his normal writing on the stage appears erect and correct on the screen.
 
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