Macro lens and imaging apparatus

1. 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).

2. The macro lens according to claim 1 , wherein

the macro lens satisfies the following conditional expression (7)

−0.1< f 2/ f 1<0.2  (7)

where

f1: a focal length of the first lens group.

3. The macro lens according to claim 1 , wherein

the first lens group includes at least one positive lens element and at least one negative lens element.

4. The macro lens according to claim 3 , wherein

the S1 plane is an object-side plane in a space disposed between the positive lens element and the negative lens element,

the S2 plane is an image-side plane in the space, and

the macro lens satisfies the following conditional expression (8)

3<|( r 1+ r 2)/( r 1− r 2)|  (8)

where

r1: a curvature radius of the plane S1, and

r2: a curvature radius of the plane S2.

5. The macro lens according to claim 1 , wherein

the first lens group includes at least one aspherical surface, and

the aspherical surface corresponds to one of the S1 plane and the S2 plane.

6. The macro lens according to claim 1 , wherein

the macro lens satisfies the following conditional expression (9)

−0.6< f 2/ f 3<0.1  (9)

where

f3: a focal length of the third lens group.

7. The macro lens according to claim 1 , wherein

the third lens group includes at least one positive lens element and at least one negative lens element.

8. The macro lens according to claim 1 , wherein

the second lens group includes at least one aspherical surface.

9. The macro lens according to claim 1 , wherein

vibration control is performed by moving a part of lens elements of the third lens group in a direction perpendicular to the optical axis, the part of the lens elements of the third lens group serving as a vibration control lens group.

10. The macro lens according to claim 9 , wherein

the vibration control lens group to be moved for the vibration control is a lens group disposed on the object side than a positive lens element disposed at a position closest to the image side in the third lens group, and

the macro lens satisfies the following conditional expression (10)

2<βν<9  (10)

where

βν; a paraxial lateral magnification of the vibration control lens group in focusing an infinite object.

11. The macro lens according to claim 1 , wherein

the first lens group has a positive refractive power as a whole, and

the third lens group has a negative refractive power as a whole.

12. The macro lens according to claim 1 , wherein

the first lens group has a negative refractive power as a whole, and

the third lens group has a positive refractive power as a whole.

13. An imaging apparatus, comprising:

the macro lens of claim 1 ; and

an imaging element which converts an optical image into an electrical signal, wherein

the macro lens is configured to form an optical image of an object on a light receiving surface of the imaging element.