Patent ID: 7755848

Claim:
A zoom lens system comprising in order from an object side thereof: a first lens unit having a positive refracting power; a second lens unit having a negative refracting power; a rear lens group having a positive refracting power which includes a third lens unit having a positive refracting power; and an aperture stop which is disposed between the second lens unit and the third lens unit, wherein at a time of zooming from a wide angle end to a telephoto end, when focused on an object at a longest distance, each of the first lens unit, the second lens unit, and the third lens unit moves such that a distance between the first lens unit and the second lens unit is increased and a distance between the second lens unit and the third lens unit is decreased, and the aperture stop moves such that a distance of the aperture stop from the second lens unit is decreased, and the second lens unit comprises in order from the object side, a first negative lens L 2n1 , a positive lens L 2p , and a second negative lens L 2n2 , wherein the positive lens L 2p is a biconvex lens, and the total number of lenses in the second lens unit is three, and satisfies the following conditional expressions −0.28 <f 2 /f t <−0.07 (1) −0.38 <f 2n2 /f t <−0.14 (2) where, f 2 denotes a focal length of the second lens unit, f 2n2 denotes a focal length of the second negative lens L 2n2 in the second lens unit, and f t denotes a focal length of the entire zoom lens system, at the telephoto end, and wherein a material of the positive lens in the second lens unit satisfies the following conditional expressions 1.84<n d2p <2.20 (9) 13<ν d2p <30 (10) where, n d2p denotes a refractive index for a d-line, of the positive lens L 2p in the second lens unit, and ν d2p denotes an Abbe's number for the positive lens L 2p the second lens unit.