Patent ID: 8218238

Claim:
A zoom lens system, comprising, in order from an object side to an image side: a first lens unit having a positive refractive power; 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 positive refractive power, the second lens unit and the fourth lens unit moving along an optical axis during zooming, wherein: the third lens unit comprises, in order from the object side to the image side: an aperture stop; a first lens subunit having a negative refractive power; and a second lens subunit having a positive refractive power which moves in a direction having a component in a direction perpendicular to the optical axis for moving an imaging position; the second lens subunit comprises a cemented lens in which a positive lens and a negative lens are joined together; and when curvature radii of surfaces of the cemented lens on the object side and the image side are R 3 A and R 3 B, respectively, a maximum aperture diameter of the aperture stop is Spa, a total thickness on the optical axis of the positive lenses configuring the second lens subunit is Dp, a total of lens thicknesses at a height from the optical axis of a half of the maximum aperture diameter of the negative lens that configures the second lens subunit at the wide angle end is Kn, a focal length of the third lens unit is f 3 , and focal lengths of an entire system at a wide angle end and a telephoto end are fw and ft, respectively, the following conditions are satisfied 5<|( R 3 A+R 3 B )/( R 3 A−R 3 B )|<30, 0.44<( Dp+Kn )/ Spa< 0.60, and 3.6 <f 3/√{square root over (( fw·ft ))}<6.2.