Patent ID: 7227693

Claim:
A zoom lens comprised of, in order from the enlarging side, as follows: a first lens group having negative refractive power, that is movable for focusing, and that is stationary during zooming; a second lens group having positive refractive power; a third lens group; a fourth lens group; a fifth lens group having positive refractive power, that consists of a single lens element, and that is stationary during zooming; wherein said second lens group, said third lens group, and said fourth lens group move relative to said first lens group and said fifth lens group during zooming; and the follow conditions are satisfied: F NO <2.0 F NO ·( LL/Bf )<5.25 f 2 /f 3<1.0 0.8 <f 23 /fw <1.4 4.5 <|f 4 /fw| 1.6 <f 5 /fw <2.8 where F NO is the f-number of the zoom lens at the wide-angle end; Bf is the air-equivalent back focus distance of the zoom lens at the wide-angle end; LL is the overall length of the zoom lens; f2 is the focal length of said second lens group; f3 is the focal length of said third lens group; f23 is the focal length of the combination of said second lens group and said third lens group at the wide-angle end; fw is the focal length of the zoom lens at the wide-angle end; f4 is the focal length of said fourth lens group; and f5 is the focal length of said fifth lens group.