Patent ID: 9001433
Filing Date: 2015-04-07
Classification: G02B

Abstract:
1. A zoom lens, substantially consisting of: a first lens group having a positive refractive power, which is fixed while changing magnification; a second lens group having a negative refractive power, which moves from an object side to an image side while changing magnification from a wide angle end to a telephoto end; a third lens group having a negative refractive power, which corrects movement of an imaging surface while changing magnification; and a fourth lens group having a positive refractive power, which is fixed while changing magnification, provided in this order from the object side; the first lens group substantially consisting of: a first lens subgroup having a negative refractive power, which is fixed during focusing operations; a second lens subgroup having a positive refractive power, which moves during focusing operations; and a third lens subgroup having a positive refractive power, which is fixed during focusing operations, provided in this order from the object side; the second lens subgroup substantially consisting of: a positive lens having a surface having a radius of curvature with a smaller absolute value toward the image side; and a cemented lens constituted by a negative lens toward the object side and a positive lens toward the image side, cemented together at a joint surface having a convex surface toward the object side, provided in this order from the magnification side; the second lens subgroup satisfying the following conditional formula: wherein f12 is the focal length of the second lens subgroup, and fw is the focal length of the entire system at the wide angle end.