Overhead projector with catadioptric fresnel lens

Optical: systems and elements – Lens – With multipart element

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G02B 308

Patent

active

055683240

ABSTRACT:
A low-profile transmissive overhead projector employs a folded optical path and an off-axis Fresnel lens condensing system which includes a catadioptric lens element. This lens provides a fast condensing system which allows collimation, dispersion, or concentration of light striking the lens at a high angle of incidence, with efficient transmission to the far edge of the lens. This also enables additional reduction in the OHP base height by allowing the single mirror to be mounted at a flatter angle, with the light source still maintained at a position below (and adjacent) the stage. A novel catadioptric lens design further imparts achromaticity to the element, so that it may be constructed of any material, regardless of its index of refraction. The condensing system may have a single or doublet catadioptric lens.

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SPIE Brochure-"Nonimaaging Optics: Maximun Efficiency Light Transfer"- vol. 1528, Copyright 1991 by the Society of Photo-Optical Instrumentation Engineers.

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