Soft focus optical system, soft focus adapter, soft focus lens, and image pickup apparatus

1. A soft focus optical system configured to be arranged on an image side of an image pickup optical system, the soft focus optical system consisting of:

a negative lens; and

a positive lens,

wherein a conditional expression

0.950< B< 1.050,

is satisfied, where B is a magnification of the soft focus optical system, and

wherein a conditional expression

|(2 Y ) 2 /( fn×fp )|≤0.005

is satisfied or conditional expressions

0.005<|(2 Y ) 2 /( fn×fp )|; and

fn/fp<− 0.750,

are satisfied, where fn is a focal length of the negative lens, fp is a focal length of the positive lens, and Y is a maximum image height of the image pickup lens.

2. The soft focus optical system according to claim 1 , wherein a conditional expression

|SA|/(2 Y× Fno)<4.000×10 −3 ,

is satisfied, where SA is a spherical aberration amount of the image pickup optical system at 100 percent of ray height with respect to a d-line in an in-focus state at an infinite object distance, and Fno is an F-number of the image pickup lens.

3. The soft focus optical system according to claim 1 , wherein the image pickup lens is a fixed focal length lens.

4. The soft focus optical system according to claim 1 , wherein in a case where a conditional expression

|(2 Y ) 2 /( fn×fp )|≤0.005,

is satisfied, conditional expressions

2.5<| SFn |; and

2.5<| SFp|,

are satisfied, where SFn and SFp are defined by expressions

SFn =( rn 1+ rn 2)/( rn 1− rn 2); and

SFp =( rp 1+ rp 2)/( rp 1− rp 2),

where rp1 is a curvature radius of a surface on an object side of the positive lens, rp2 is a curvature radius of a surface on the image side of the positive lens, ml is a curvature radius of a surface on the object side of the negative lens, and rn2 is a curvature radius of a surface on the image side of the negative lens.

5. The soft focus optical system according to claim 1 , wherein in a case where a conditional expression of 0.005<|(2Y) 2 /(fn×fp)| is satisfied, a surface on an object side of one, disposed on the object side, of the positive lens and the negative lens is convex toward the object side, a surface on the image side of the other, disposed on the image side, of the positive lens and the negative lens is convex toward the object side, and conditional expression

6.5<| SFnp|

is satisfied, here SFnp is defined by an expression

SFnp =( r 1+ r 4)/( r 1− r 4),

where r1 is a curvature radius of the surface on the object side of the one, and r4 is a curvature radius of the surface on the image side of the other.

6. The soft focus optical system according to claim 1 , wherein a conditional expression

0.740< Nn/Np< 1.350,

is satisfied, where Nn is a refractive index of a material of the negative lens with respect to a d-line, and Np is a refractive index of a material of the positive lens with respect to the d-line.

7. The soft focus optical system according to claim 1 , wherein the negative lens and the positive lens are constituents of a cemented lens.

8. The soft focus optical system according to claim 1 , wherein conditional expression

−7.000×10 −3 <(SAs−SA)/(2 Y× Fno)<−0.800×10 −3 ,

is satisfied, where SA is a spherical aberration amount of the image pickup optical system at 100 percent of ray height with respect to a d-line in an in-focus state at an infinite object distance, SAs is a spherical aberration amount of integration of the image pickup optical system and the soft focus optical system at 100 percent of ray height with respect to the d-line in an in-focus state at the infinite object distance.

9. A soft focus lens comprising in order from an object side to an image side:

an image pickup optical system; and

a soft focus optical system,

wherein the soft focus optical system consists of:

a negative lens; and

a positive lens,

wherein a conditional expression

0.950< B< 1.050,

is satisfied, where B is a magnification of the soft focus optical system, and

wherein a conditional expression

|(2 Y ) 2 /( fn×fp )|≤0.005

is satisfied or conditional expressions

0.005<|(2 Y ) 2 /( fn×fp )|; and

fn/fp<− 0.750,

are satisfied, where fn is a focal length of the negative lens, fp is a focal length of the positive lens, and Y is a maximum image height of the image pickup lens.

10. The soft focus lens according to claim 9 , wherein a conditional expression

0.000< L 1/ L 1 d< 0.500,

is satisfied, where L1 is a distance from a surface closest to the image side of the image pickup optical system to a surface closest to the object side of the soft focus optical system, and L1d is a distance from the surface closest to the image side of the image pickup optical system to an image plane.

11. The soft focus lens according to claim 10 , wherein a conditional expression

−0.033<1/ Tk 1<−0.009,

is satisfied, where Tk1 is a distance from an exit pupil of a lens apparatus consisting of the image pickup optical system to the image plane.

12. A soft focus adapter comprising:

a soft focus optical system; and

a structure attachable to and detachable from an image pickup apparatus at an image side of the image pickup apparatus,

wherein the soft focus optical system consists of:

a negative lens; and

a positive lens,

wherein a conditional expression

0.950< B< 1.050,

is satisfied, where B is a magnification of the soft focus optical system, and

wherein a conditional expression

|(2 Y ) 2 /( fn×fp )|≤0.005

is satisfied or conditional expressions

0.005<|(2 Y ) 2 /( fn×fp )|; and

fn/fp<− 0.750,

are satisfied, where fn is a focal length of the negative lens, fp is a focal length of the positive lens, and Y is a maximum image height of the image pickup lens.

13. An image pickup apparatus comprising:

a soft focus lens defined in claim 9 ; and

an image pickup element arranged on an image plane of the soft focus lens.