Patent ID: 7580194

Claim:
A projection lens with a variable effective focal length comprising, in this order from the screen-side thereof, a negative lens group having negative refraction of power, comprising, in this order form the screen-side of the projection lens, a first lens having positive refraction of power, a second lens having negative refraction of power, a third lens having negative refraction of power, and a fourth lens having positive refraction of power; and a positive lens group having positive refraction of power, the positive lens group comprising, in this order from the screen-side of the projection lens, a first lens having positive refraction of power, a second lens having positive refraction of power, a third lens having negative refraction of power, a fourth lens having positive refraction of power, and a fifth lens having positive refraction of power, wherein the projection lens satisfies the formulas of: −2<F1/Fw<−1.6; 1.2<F2/Fw<1.4; and Vg2>56, where F1, and F2 respectively represent the effective focal lengths of the negative lens group and the positive lens group, Fw is the shortest effective focal lengths of the projection lens, and Vg2 is the average of the Abbe numbers of the lenses having positive refraction of power in the positive lens group.