Patent ID: 7012764

Claim:
A projection lens, for enlarging and projecting a picture formed on a flat fluorescent plate of a CRT projection tube, comprising: a first lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being convex to the screen side at a central portion including an optical axis thereof; a second lens unit of a minus lens, having aspheric surfaces on both surfaces thereof, being concave to the screen side at a central portion including an optical axis thereof; a third lens unit of a plus lens, having spherical surfaces on both surfaces thereof, being convex on both sides; a fourth lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being curved in concave-like to the screen side, on a peripheral portion far from the optical axis into a radial direction thereof; and a fifth lens unit of a minus lens, being made up with a transparent liquid, commonly serving a faceplate of said CRT projection tube and a cooling, and a meniscus lens, having a thickness being nearly equal to and at least an aspheric surface directing a concave surface thereof to the screen side, being disposed successively from a screen side to said CRT projection tube, wherein the following conditions (1) to (5) are satisfied: (1) 0.1<f 0 /f 1 <0.3; (2) −0.15<f 0 /f 2 <−0.01; (3) 0.7<f 0 /f 3 <0.9; (4) 0.15<f 0 /f 4 <0.35; (5) −1.3<f 0 /f 5 <−0.9; where, f 0 is a focal distance of a total system; f 1 is a focal distance of said first lens unit; f 2 is a focal distance of said second lens unit; f 3 is a focal distance of said third lens unit; f 4 is a focal distance of said fourth lens unit; and f 5 is a focal distance of said fifth lens unit.