DISTORTION CORRECTION FOR AN OVERHEAD PROJECTOR SYSTEM

摘要

An overhead projector is provided which is able to project a uniformly focused image of a transparency onto a vertical surface at an oblique angle above the horizontal plane without introducing keystone distortion by offsetting a projection lens and its associated mirror from the center of a transparency stage of the projector in the direction of projection and directing light through the transparency and to the projection lens 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 by offsetting the upper lens of a two-element circular Fresnel condensing lens system in the direction of displacement of the projection lens.