Patent ID: 7952811
Filing Date: 2011-05-31
Classification: G02B

Abstract:
1. A zoom lens formed by arranging a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from an object side to an image side, wherein at a time of varying power from a wide-angle end to a telephoto end, said first lens group is moved, and said second lens group is moved to the object side such that an air interval between said first lens group and said second lens group is decreased and such that an air interval between said second lens group and said third lens group is increased, and said first lens group is formed by arranging a first lens as a negative lens having both surfaces formed as aspheric surfaces and having a concave surface facing the image side and a second lens as a positive meniscus lens having both surfaces formed as aspheric surfaces and having a convex surface facing the object side in order from the object side to the image side, wherein the surface on the image side of said second lens is formed such that a negative refractive power is weakened as distance from an optical axis is increased, and said zoom lens is formed so as to satisfy a following conditional expression (1): where Sgf denotes a difference between an amount of sag of a paraxial radius of curvature of the surface on the object side in an effective diameter of the second lens and an amount of sag of an aspheric shape, and Sgr denotes a difference between an amount of sag of a paraxial radius of curvature of the surface on the image side in the effective diameter of the second lens and an amount of sag of an aspheric shape.