Overhead projector with achromatic Fresnel lens

Details Overhead projector with achromatic Fresnel lens Overhead projector with achromatic Fresnel lens

1994-03-29

1995-09-26

Sugerman, Scott J.

Optical: systems and elements

Lens

With multipart element

359726, G02B 308, G02B 1700

Patent

active

054538807

ABSTRACT:
A low-profile, transmissive overhead projector (OHP) employs a novel condensing lens system having a catadioptric Fresnel lens and a dioptric Fresnel lens. Each of the lenses exhibits chromatic aberration, but the dispersion of one lens is selected to cancel out the dispersion of the other, e.g., if the catadioptric lens has negative dispersion then the dioptric lens is selected to have positive dispersion. The mutual cancellation of the dispersion of each lens practically eliminates longitudinal chromatic aberration through the lens system. The lens system provides a fast condensing system which allows collimation, dispersion or concentration of light striking the lens at a high angle of incidence. This characteristic is particularly suited for a low-profile OHP as it allows the light source to be placed directly under, but very close to, the stage area.

REFERENCES:
patent: 4108540 (1978-08-01), Anderson et al.
patent: 5317349 (1994-05-01), Vanderwerf

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