Patent ID: 8169710

Claim:
A zoom lens comprising, in order from the object side: a first lens group with a negative focal length; a second lens group with a positive focal length; a third lens group with a negative focal length; and a fourth lens group with a positive focal length, wherein during zooming from a wide-angle end to a telephoto end, the first lens group moves along a locus having a convex shape toward an image side while decreasing an air space between the first and second lens groups, and the second and third lens groups move toward the object side while increasing an air space therebetween, wherein a surface closest to the object side in the second lens group is convex toward the object side and is aspheric, and the second lens group includes a cemented lens formed of a negative meniscus lens convex toward the object side and a positive lens, wherein the cemented lens of the second lens group satisfies the following conditional expression (1): 0.3 <R CL /f 2<1.0, (1) where R CL is a radius of curvature of a cemented surface of the cemented lens constituting the second lens group, and f 2 is a focal length of the second lens group, and wherein two lenses constituting the first lens group satisfy the following conditional expressions (2) and (3): 0.3<( R 21 −R 12)/( R 12 +R 21)<0.5, and (2) 0.1<(| Sg 21 |+|Sg 12|)/| f 1|<0.3, (3) where R 21 is a paraxial radius of curvature of an object side surface of a positive lens in the first lens group, R 12 is a paraxial radius of curvature of an image side surface of a negative lens in the first lens group, f 1 is a focal length of the first lens group, f(Δsag) value is a value obtained by subtracting a sag amount of an aspheric shape from a sag amount of a paraxial radius of curvature, Sg 21 is an f(Δsag) value at an effective diameter position on the object side surface of the positive lens in the first lens group, and Sg 12 is an f(Δsag) value at an effective diameter position on the image side surface of the negative lens in the first lens group, or is an f(Δsag) value at a position radially spaced at a distance (corresponding to R 12 ) from an optical axis when the effective diameter position on the image side surface of the negative lens in the first lens group is larger than R 12 .