Patent ID: 8797659

Claim:
A macro lens comprising, in the order from an object side to an image side: a first lens group; a second lens group having a positive refractive power as a whole; and a third lens group, wherein the first lens group includes a plane S1 and a plane S2 having curvature radii of a same sign and defined by the following conditional expressions (1) through (3), and focusing is performed by fixing the first lens group and the third lens group, and by moving the second lens group on an optical axis in focusing from an infinite object to a close distance object, 0.6< M 2/ f 2<1 (1) (φinf−φnear) f 2<−0.0002 (2) e 0/ f 2<0.15 (3) where M2: a moving amount of the second lens group from an infinite distance to a closest distance, f2: a focal length of the second lens group, e0: an air equivalent distance between the plane S1 and the plane S2 on the optical axis, φinf: a combined optical power of the plane S1 and the plane S2 in a direction parallel to the optical axis, and an optical power to be defined by the following conditional expression (4A), assuming that Yinf is a height of a light ray of a light flux from the optical axis, the light ray passing a center of an aperture stop and intersecting the plane S1, the light flux forming an image having a maximum image height at a time of forming an infinite object, φinf=(φ1( Y inf)+φ2( Y inf)−φ1( Y inf)φ2( Y inf) e ( Y inf))/ n 3 (4A) assuming that n1 is a refractive index of an object-side medium of the plane S1 for a d-line, n2 is a refractive index of a medium between the plane S1 and the plane S2 for the d-line, n3 is a refractive index of an image-side medium of the plane S2 for the d-line, C1(Y) is a curvature of the plane S1 at a height Y, C2(Y) is a curvature of the plane S2 at the height Y, and e(Y) is an air equivalent distance (air equivalent plane interval) between the plane S1 and the plane S2 in the direction parallel to the optical axis with respect to the height Y, φ1(Y) is an optical power of the plane S1 at the height Y from the optical axis, and is an optical power to be defined by the following conditional expression (5), and φ2(Y) is an optical power of the plane S2 at the height Y from the optical axis, and is an optical power to be defined by the following conditional expression (6), φ1( Y )=( n 2− n 1) C 1( Y ) (5) φ2( Y )=( n 3− n 2) C 2( Y ) (6) where φnear: a combined optical power of the plane S1 and the plane S2 in the direction parallel to the optical axis, and an optical power to be defined by the following conditional expression (4B), assuming that Ynear is a height of a light ray of a light flux from the optical axis, the light ray passing a center of an aperture stop and intersecting the plane S1, the light flux forming an image having a maximum image height at a time of forming a closest distance object, φnear=(φ1( Y near)+φ2( Y near)−φ1( Y near)φ2( Y near) e ( Y near))/ n 3 (4B).