GB666222A - Improvements in or relating to optical lenses - Google Patents

Abstract

666,222. Lenses; projection screens. ELECTRIC & MUSICAL INDUSTRIES, Ltd. July 30, 1949 [July 31, 1948], No. 20417/48. Class 97 (i). Rectilinear prismatic elements are formed on both sides of a light-transmitting sheet, the elements on one side being at right-angles to those on the other, the angles of the elements increasing towards the perimeter of the sheet so as to form a Fresnel lens. The lens may be associated with a projection screen comprising a light-transmitting sheet having parallel cylindrical lenses on one surface and other parallel cylindrical lenses on the other surface at right angles to those on the first. Fig. 1 shows a cross-section, in one direction, of a combination of lens and screen, Fig. 2 being a section in a perpendicular direction. The screen 1 has semi-cylindrical elements 2 on one face and arcuate cylindrical elements 3 on the other face which may be silvered if a reflecting screen is required. The lens 6 has prismatic elements 7, on one face, of the same pitch as the screen elements 2. Similar prismatic elements 8 on the opposite face of the lens correspond to the screen elements 3. The centre of the lens may be left plane.