New parabolic lens for motion picture projection: New development broadens application of incandescent lamp projection in moving picture theaters

For many years condenser lenses have been made in either of two ways: Molded as is the prismatic lens used in motion picture projection and in railway signal lamps, or ground with plane or spherical surfaces as are the plano-convex lenses, regularly used with arc lamp projectors. For some time it has been know that accurately ground surfaces of other than plane or spherical contour (aspheric surfaces) would permit much better control of the light, but early lenses of this design were so costly that they were not practicable for motion picture condensers.