Patent ID: 7310188

Claim:
A projection lens comprising, in order from a magnification side: a first lens group; a second lens group; and a third lens group, wherein: the first lens group comprises, in order from the magnification side: a negative lens whose lens made of a non-resin; a plastic lens at least one surface of which is aspheric; and a positive lens, the second lens group comprises: a plastic lens at least one surface of which is aspheric; a positive lens; and a negative lens, the third lens group comprises a positive lens, and the following conditional expressions (1), (2a) and (3a) are satisfied; 1.0 <Bf/f≦ 1.8 (1) 2.0 <f 1/ f (2a) 2.0 <f 2 /f (3a) where Bf denotes a air-conversion back focus of the entire system, f denotes a focal length of the entire system, f1 denotes a focal length of the first lens group and f2 denotes a focal length of the second lens group.