Patent ID: 6452730
Filing Date: 2002-09-17
Classification: G02B

Abstract:
A zoom lens system comprising, in order from an object side:a first lens group having a negative refractive power; and a second lens group having a positive refractive power; wherein a zooming is performed by varying an air space between the first lens group and the second lens group; wherein the first lens group comprises, in order from the object side, a negative lens group consisting of one or two negative lens elements and a positive lens element having a convex surface facing to the object side; wherein all lens surfaces composing the first lens group are spherical or plane; and wherein the following conditional expressions (1) and (2) are satisfied; 1.4&lE;Nn&lE;1.621â€ƒâ€ƒ(1) 0.7&lE;|f1|/(fwÂ·ft)Â½&lE;1.15â€ƒâ€ƒ(2) where Nn denotes an average refractive index of the negative lens group within the first lens group for the d-line, f1 denotes the focal length of the first lens group, fw denotes the focal length of the zoom lens system in a wide-angle state, which gives the shortest focal length, and ft denotes the focal length of the zoom lens system in a telephoto state, which gives the longest focal length.