DISTORTION CORRECTION FOR AN OVERHEAD PROJECTOR SYSTEM

摘要

Distortion Correction for an Overhead Projector System An overhead projector (27) is provided which is able to project a uniformly focused image (36) of a transparency onto a vertical surface (32) at an oblique angle above the horizontal plane without introducing keystone distortion by offsetting a projection lens (28) and its associated mirror (33) from the center of a transparency stage (30) of the projector (27) in the direction of projection and directing light through the transparency and to the projection lens (28) at an angle which is equal to the oblique angle above the horizontal plane at which the image is projected. Light is directed to the projection lens (28) by offsetting the upper lens (40) of a two-element circular Fresnel condensing lens system (40, 44) in the direction of displacement of the projection lens (28).