Inner focus lens
An inner focus lens includes sequentially from an object side, a first lens group having a positive refractive power; a second lens group having a negative refractive power; and a third lens group having a negative refractive power. The second lens group is moved along an optical axis, whereby focusing from a focus state for an object at infinity to a focus state for a minimum object distance is performed. A lens group configured by a lens other than a lens that is disposed farthest on the object side is moved in a direction orthogonal to the optical axis to shift an image. The inner focus lens satisfies a conditional expression (1) 0.15≦(1−βp)×βr≦4.50, where βp is transverse magnification of the orthogonally moved lens group and βr is composite transverse magnification of a lens group disposed farther on an image side than the orthogonally moved lens group.
1. An inner focus lens consisting of sequentially from an object side:
a first lens group having a positive refractive power;
a second lens group having a negative refractive power; and
a third lens group having a negative refractive power, and consisting of, sequentially from the object side:
a front sub-lens group having a positive refractive power, and
a rear sub-lens group having a negative refractive power; and
an axial air gap that is widest in the third lens group is formed between the front sub-lens group and the rear sub-lens group;
the second lens group is configured to move along an optical axis, whereby focusing from a focus state for an object at infinity to a focus state for a minimum object distance is performed,
a lens group configured by a lens other than a lens that is disposed farthest on the object side is moved in a direction orthogonal to the optical axis to shift an image, and
the inner focus lens satisfies a conditional expression (1) 0.15≦(1−βp)×βr≦4.50, where βp is transverse magnification of the lens group moved in a direction orthogonal to the optical axis and βr is composite transverse magnification of a lens group disposed farther on an image side than the lens group moved in a direction orthogonal to the optical axis.
2. The inner focus lens according to claim 1 , wherein
the inner focus lens satisfies a conditional expression (2) 0.18≦f1/f≦0.99, where f1 is a focal length of the first lens group at the focus state for an object at infinity and f is a focal length of the optical system overall of the inner focus lens at the focus state for an object at infinity.
3. The inner focus lens according to claim 1 , wherein
the inner focus lens satisfies a conditional expression (3) 0.51≦βinf/β mod≦2.07, where βinf is paraxial magnification of the second lens group at the focus state for an object at infinity and β mod is paraxial magnification of the second lens group at the focus state for the minimum object distance.
4. The inner focus lens according to claim 1 , wherein
the third lens group includes a simple lens element having a negative refractive power and disposed farthest on an image side, and
the inner focus lens satisfies a conditional expression (4) (R1+R2)/(R1−R2)≦0.0, where R1 is radius of curvature of a surface at an air interface on the object side of the simple lens element having a negative refractive power and R2 is radius of curvature of a surface at an air interface on the image side of the simple lens element having a negative refractive power.
5. The inner focus lens according to claim 4 , wherein
the simple lens element having a negative refractive power and disposed farthest on the image side of the third lens group is configured by a glass material, and
the inner focus lens satisfies a conditional expression (8) 30≦υen, where υen is an Abbe number for e-line of the simple lens element having a negative refractive power and disposed farthest on the image side of the third lens group.
6. The inner focus lens according to claim 1 , wherein
the inner focus lens satisfies a conditional expression (5) 0.01≦L1s/L≦0.53, where L1s is an axial distance from a surface farthest on the object side of the first lens group to an aperture stop and L is an overall optical system length of the inner focus lens.
7. The inner focus lens according to claim 6 , wherein the overall optical system length is an air-conversion optical path length from an apex of a lens surface farthest on the object side to an imaging plane.
8. The inner focus lens according to claim 1 , wherein
the second lens group is configured by a simple lens element having a negative refractive power.
9. The inner focus lens according to claim 1 , wherein
the inner focus lens satisfies a conditional expression (6) −2.12≦f2/f≦−0.18, where f2 is a focal length of the second lens group at the focus state for an object at infinity and f is the focal length of the optical system overall of the inner focus lens at the focus state for an object at infinity.
10. The inner focus lens according to claim 1 , wherein
the inner focus lens satisfies a conditional expression (7) −29.0≦f3/f≦−5.4, where f3 is a focal length of the third lens group at the focus state for an object at infinity and f is the focal length of the optical system overall of the inner focus lens at the focus state for an object at infinity.