Patent ID: 6509937
Filing Date: 2003-01-21
Classification: G02B,H04N

Abstract:
A projection lens system for use with a cathode ray tube (CRT) which in combination with the CRT has a focal length f0 and which from its long conjugate to its short conjugate consists of:(a) a first lens element which has (i) a weak optical power and (ii) at least one aspherical surface; (b) a second lens element which (i) has a positive focal length f2 and (ii) provides most of the optical power of the lens system, the ratio of f0 to f2 being at least about 0.89; (c) a third lens element which has (i) a positive focal length f3 and (ii) at least one aspherical surface; and (d) a fourth lens unit which, during use of the lens system, (i) consists of a lens element, coupling fluid, and the faceplate of the CRT, (ii) has a strong negative optical power, and (ii) provides most of the correction of the field curvature of the lens system; and which further consists of:(e) a corrector lens element which is located adjacent to the second lens element and has (i) a weak optical power and (ii) at least one aspherical surface; wherein:2<f3/f2<4, |fc/f3|>3, and max|z|/rca<0.15 where fc is the focal length of the corrector lens element, max|z| is the maximum sag of the two surfaces of the corrector lens element, and rca is the clear aperture radius of the surface having the maximum sag.