Patent ID: 7477455
Filing Date: 2009-01-13
Classification: G02B

Abstract:
1. A zoom lens system comprising, in order from an object 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 refractive power, wherein during magnification change 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 change, the second lens unit has a double-concave negative lens closest to the object side, and includes two or less negative lenses and one positive lens as a whole, and the total number of the lenses of the second lens unit is two or three, and the following conditions are satisfied: in which SF 2n1 is defined by SF 2n1 =(R 2n1f +R 2n1r )/(R 2n1f −R 2n1r ), R 2n1f is a paraxial radius of curvature of an object-side surface of the negative lens of the second lens unit closest to the object side, R 2n1r is a paraxial radius of curvature of an image-side surface of the negative lens of the second lens unit closest to the object side, f w is a focal length of the zoom lens system in the wide-angle end, and f t is a focal length of the zoom lens system in the telephoto end.