Patent ID: 7675690

Claim:
A zoom lens system comprising: in order from an object side, a first lens unit having a positive refractive power, wherein the total number of lenses of the first lens unit is two or less; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a refractive power, during zooming from a wide-angle end to a telephoto end, a space between the first lens unit and the second lens unit, a space between the second lens unit and the third lens unit and a space between the third lens unit and the fourth lens unit being changed, the second lens unit including two lenses of a negative lens and a positive lens in order from the object side, wherein the positive lens of the second lens unit is a meniscus lens having a convex shape which faces the object side and wherein the total number of lenses of the second lens unit is two; the zoom lens system further comprises an aperture stop; during the zooming from the wide-angle end to the telephoto end, the first, second, third and fourth lens units being moved so that the space between the first lens unit and the second lens unit enlarges, the space between the second lens unit and the third lens unit narrows and the space between the third lens unit and the fourth lens unit enlarges, the aperture stop being moved together with the third lens unit in an optical axis direction, and the following conditions being satisfied: 1.88<n d2p <2.20 (1A); 13.0<v d2p <3.00 (2A); and −5.0<SF 2p <−1.0 (3A), in which n d2p is a refractive index of the positive lens of the second lens unit for the d-line, v d2p is the Abbe number of the positive lens of the second lens unit, and SF 2p is defined by SF 2p =(R 2pf +R 2pr )/(R 2pf −R 2pr ), wherein R 2pf is a paraxial radius of curvature of an object-side surface of the positive lens of the second lens unit, and R 2pr is a paraxial radius of curvature of an image-side surface of the positive lens of the second lens unit.