Patent ID: 7133084
Filing Date: 2006-11-07
Classification: G02B,H04N

Abstract:
1. A projection lens system for use in a projection television which has a screen and a first cathode ray tube which produces light of primarily a first color, a second cathode ray tube which produces light of primarily a second color, and a third cathode ray tube which produces light of primarily a third color, said projection lens system comprising three projection lenses, one projection lens being associated with each of the cathode ray tubes during use of the system for forming an image of the light produced by that tube on the screen, each projection lens consisting of: (A) a first lens unit on the long conjugate side of the lens, said first lens unit having a positive power; and (B) a second lens unit which (i) is associated with a cathode ray tube during use of the lens, (ii) has a strong negative power when so associated, and (iii) provides most of the correction of the lens' field curvature; wherein: (a) the first color is green and the second color is red; (b) the first lens units of the first and second projection lenses are identical to within manufacturing tolerances; (c) the second lens unit of the second projection lens differs from the second lens unit of the first projection lens in at least one optical property, said difference being based on said first and second colors; and (d) the MTF/OTF performance of the second projection lens is improved compared to the MTF/OTF performance of the first projection lens refocused for use with red light.