VARIABLE FOCAL LENGTH PROJECTION LENS FOR USE ON OVERHEAD PROJECTORS

摘要

254,947 CAN/JCB Variable Focal Length Projection Lens For Use on Overhead Projectors A variable focal length overhead projector lens having four elements positioned in a projection head with two elements on either side of a folding mirror and having a single movable negative lens element closest to the screen being movable to vary the focal length and magnification at a fixed object-to-image distance to fill the screen.