Fresnel type lenses of high precision and excellent surface quality have been made in thin sheet plastic materials. The prismatic elements are very fine—about 0.003″ to 0.005″—and are not visible to the average unaided eye. A high degree of correction for spherical aberration has been achieved. Molded from high precision molds, lenses have been made in diameters of two to fifteen inches and focal lengths of to inches. Relative apertures in excess of f/1.0 have been made. These lenses have found many applications as light collecting elements where weight and space are limited. Such applications include uses for large condensers, large field lenses in finders, camera viewing screens, and translucent screens for projection.
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