Patent ID: 7319562

Claim:
A zoom lens system comprising, in order from an object side to an image side: a first lens unit of positive refractive power; a second lens unit of negative refractive power; a third lens unit of positive refractive power; and a fourth lens unit of positive refractive power, wherein the first lens unit is positioned closer to the object side at a telephoto end than at a wide-angle end; a distance between the first lens unit and the second lens unit is larger at the telephoto end than at the wide-angle end; a distance between the second lens unit and the third lens unit is smaller at the telephoto end than at the wide-angle end; a distance between the third lens unit and the fourth lens unit is larger at the telephoto end than at the wide-angle end; the first lens unit consists of a negative lens element and a positive lens element; the second lens unit consists of a negative lens element and a positive lens element in this order from the object side to the image side; and the following conditions are satisfied: −2.0 <f 2 /fw <−1.1 4.5 <ft/fw <7.5 −1.2 <f 2 lgn/fw <−0.6 where f 2 lgn is the focal length of the negative lens element in the second lens unit; f 2 is the focal length of the second lens unit; and fw and ft are the focal lengths of the entire lens system at the wide-angle end and the telephoto end, respectively.