Single-focus optical system and optical apparatus using the same

1. A single-focus optical system forms a conjugate relationship between a conjugate point on an enlargement side at a long distance and a conjugate point on a reduction side at a short distance, the single-focus optical system comprising in order from the enlargement side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power; and

a third lens unit having a positive refractive power, wherein:

a lens component is one of a single lens and a cemented lens, and

the first lens unit consists of, in order from the enlargement side, either a first sub-unit, a second sub-unit, and a third sub-unit, or the first sub-unit, one positive lens component, the second sub-unit, and the third sub-unit, and

the first sub-unit consists of one negative lens component or a plurality of negative lens components that are continuous, and

the second sub-unit consists of two meniscus lens components having respective concave surfaces thereof facing mutually, and

the third sub-unit consists of a plurality of positive lens components, and

the second lens unit consists of only one kind of lens component which is a negative lens component, and

the third lens unit consists of, in order from the enlargement side, a front side sub-unit and a rear side sub-unit, and

the front side sub-unit includes a positive lens component nearest to the enlargement side, and

at the time of focusing, the first lens unit is fixed, at least the front side sub-unit is movable, and the rear side sub-unit is fixed, and

at least a distance between the second lens unit and the front side sub-unit and a distance between the front side sub-unit and the rear side sub-unit are variable, and

a distance between two lens surfaces in the first lens unit, the second lens unit, the front side sub-unit, and the rear side sub-unit is constant.

2. The single-focus optical system according to claim 1 , wherein the second lens unit consists of one negative lens component.

3. The single-focus optical system according to claim 2 , wherein:

a reduction-side surface of the negative lens component in the second lens unit is a concave surface, and

an absolute value of curvature of the reduction-side surface of the negative lens component in the second lens unit is higher than an absolute value of curvature of an enlargement-side surface of the negative lens component in the second lens unit.

4. The single-focus optical system according to claim 2 , wherein the negative lens component in the second lens unit satisfies the following conditional expression (5):

0<SF 21 <5.0  (5)

where,

SF 21 =( R F21 +R R21 )/( R F21 −R R21 ), and here

R F21 denotes a radius of curvature of a surface nearest to the enlargement side of the negative lens component in the second lens unit, and

R R21 denotes a radius of curvature of a surface nearest to the reduction side of the negative lens component in the second lens unit.

5. The single-focus optical system according to claim 1 , wherein the rear side sub-unit includes a positive lens and a negative lens.

6. The single-focus optical system according to claim 1 , wherein a lens disposed nearest to the reduction side in the rear side sub-unit has a positive refractive power.

7. The single-focus optical system according to claim 1 , wherein the rear side sub-unit consists of, in order from the enlargement side, a negative lens and a positive lens, or a negative lens, a positive lens, and a positive lens, or a positive lens, a negative lens, and a positive lens.

8. The single-focus optical system according to claim 1 , wherein:

the rear side sub-unit consists of one positive lens and one negative lens, and

at the time of focusing, the second lens unit and the front side sub-unit are moved while changing a distance between the second lens unit and the front side sub-unit.

9. The single-focus optical system according to claim 1 , wherein:

the rear side sub-unit consists of two positive lenses and one negative lens, and

at the time of focusing, the front side sub-unit is moved while changing a distance between the second lens unit and the front side sub-unit.

10. The single-focus optical system according to claim 1 , wherein the front side sub-unit consists of a positive single lens.

11. The single-focus optical system according to claim 1 , wherein the first lens unit includes a reduction-side positive lens component closest to the reduction side.

12. The single-focus optical system according to claim 1 , wherein:

the second sub-unit includes a cemented lens having a concave surface directed toward the enlargement side,

one of the two meniscus lens components is the cemented lens in the second sub-unit, and

the cemented lens in the second sub-unit consists of, in order from the enlargement side, a negative lens and a positive lens.

13. The single-focus optical system according to claim 1 , wherein:

the second sub-unit includes a cemented lens having a concave surface directed toward the enlargement side and a reduction-side lens component,

one of the two meniscus lens components is the cemented lens in the second sub-unit, and the other of the two meniscus lens components is the reduction-side lens component,

the cemented lens in the second sub-unit consists of, in order from the enlargement side, a negative lens and a positive lens,

the reduction-side lens component is disposed on the enlargement side of the cemented lens in the second sub-unit, adjacent to the cemented lens in the second sub-unit, and

a shape of the reduction-side lens component is a meniscus shape having a convex surface directed toward the enlargement side.

14. The single-focus optical system according to claim 1 , wherein a lens unit disposed on the reduction side of the second lens unit is only the third lens unit.

15. The single-focus optical system according to claim 1 , wherein:

the first lens unit includes an enlargement-side lens component closest to the enlargement side, and

the following conditional expression (1) is satisfied:

065<SF 11 <3.5  (1)

where,

SF 11 =( R F11 +R R11 )/( R F11 −R R11 ), and here

R F11 denotes a radius of curvature of a surface nearest to the enlargement side in the enlargement-side lens component, and

R R11 denotes a radius of curvature of a surface nearest to the reduction side in the enlargement-side lens component.

16. The single-focus optical system according to claim 1 , wherein:

the second sub-unit includes a reduction-side lens component,

the reduction-side lens component is a meniscus lens component positioned on the enlargement side of the two meniscus lens components, and

the following conditional expression (2) is satisfied

1.1<SF 12 <15  (2)

where,

SF 12 =( R F12 +R R12 )/( R F12 −R R12 ), and here

R F12 denotes a radius of curvature of a surface nearest to the enlargement side in the reduction-side lens component, and

R R12 denotes a radius of curvature of a surface nearest to the reduction side in the reduction-side lens component.

17. The single-focus optical system according to claim 1 , wherein:

the second sub-unit includes a cemented lens,

the cemented lens in the second sub-unit is a meniscus lens component positioned on the reduction side of the two meniscus lens components, and

the following conditional expression (3) is satisfied:

−12<SF 13 <−1.0  (3)

where,

SF 13 =( R F13 +R R13 )/( R F13 −R R13 ), and here

R F13 denotes a radius of curvature of a surface nearest to the enlargement side in the cemented lens of the second sub-unit, and

R R13 denotes a radius of curvature of a surface nearest to the reduction side in the cemented lens of the second sub-unit.

18. The single-focus optical system according to claim 1 , wherein:

the plurality of positive lens components in the third sub-unit includes a front-side positive lens component which is positioned closest to the enlargement side, and a rear-side positive lens component which is positioned closest to the reduction side, and

the following conditional expression (4) is satisfied:

−2.0<SF 14 −SF 15 <6.0  (4)

where,

SF 14 =( R F14 +R R14 )/( R F14 −R R14 ), and

SF 15 =( R F15 +R R15 )/( R F15 −R R15 ), and here

R F14 denotes a radius of curvature of a surface nearest to the enlargement side in the front-side positive lens component,

R R14 denotes a radius of curvature of a surface nearest to the reduction side in the front-side positive lens component,

R F15 denotes a radius of curvature of a surface nearest to the enlargement side in the rear-side positive lens component, and

R R15 denotes a radius of curvature of a surface nearest to the reduction side in the rear-side positive lens component.

19. The single-focus optical system according to claim 1 , wherein the following conditional expression (6) is satisfied:

−2.5<SF 31 <1.0  (6)

where,

SF 31 =( R F31 +R R31 )/( R F31 −R R31 ), and here

R F31 denotes a radius of curvature of a surface nearest to the enlargement side in the positive lens component of the front side sub-unit, and

R R31 denotes a radius of curvature of a surface nearest to the reduction side in the positive lens component of the front side sub-unit.

20. The single-focus optical system according to claim 1 , wherein:

the first lens unit includes a reduction-side positive lens component closest to the reduction side,

the reduction-side positive lens component is a single lens, and

in a rectangular coordinate system in which a horizontal axis is let to be Nd 1PR and a vertical axis is let to be vd 1PR , when a straight line represented by Nd 1PR =α×vd 1PR +β 1PR , where, α=−0.01, is set, Nd 1PR and vd 1PR for the reduction-side positive lens component are included in both of an area determined by a straight line when a lower limit value of a range of the following conditional expression (11) is β 1PR =2.25, and an area determined by the following conditional expressions (12) and (13):

2.25≤β 1PR   (11),

1.40< Nd 1PR   (12), and

35< vd 1PR   (13)

where,

Nd 1PR denotes a refractive index of the reduction-side positive lens component, and

vd 1PR denotes Abbe number for the reduction-side positive lens component.

21. The single-focus optical system according to claim 1 , wherein:

the front side sub-unit consists of one positive lens component,

the positive lens component in the front side sub-unit is a single lens, and

in a rectangular coordinate system in which a horizontal axis is let to be Nd 3PF and a vertical axis is let to be vd 3PF , when a straight line represented by Nd 3PF =α□vd 3PF +β 3PF , where α=−0.01, is set, Nd 3PF and vd 3PF for the positive lens component in the front side sub-unit are included in both of an area determined by a straight line when a lower limit value β 3PF of a range of the following conditional expression (14) is β 3PF =2.15 and an area determined by the following conditional expressions (15) and (16):

2.15≤β 3PF   (14),

1.45< ND 3PF   (15), and

25< vd 3PF   (16)

where,

ND 3PF denotes a refractive index of the positive lens component in the front side sub-unit, and

vd 3PF denotes Abbe number for the positive lens component in the front side sub-unit.

22. The single-focus optical system according to claim 1 , wherein:

the first lens unit includes an enlargement-side lens component closest to the enlargement side, and

the following conditional expression (A) is satisfied:

0< f/e N1F <2  (A)

where,

f denotes a focal length of the overall single-focus optical system at the time of focusing to an object at infinity, and

e N1F denotes a maximum effective aperture of the enlargement-side lens component in the first lens unit.

23. The single-focus optical system according to claim 1 , further comprising:

an aperture stop, wherein the following conditional expression (B) is satisfied:

0<( f/e AS )/ F no<2  (B)

where,

f denotes a focal length of the overall single-focus optical system at the time of focusing to an object at infinity,

e AS denotes a maximum diameter of the aperture stop, and

Fno denotes an F-number for the overall single-focus optical system at the time of focusing to an object at infinity.

24. The single-focus optical system according to claim 1 , wherein the following conditional expression (C) is satisfied:

0< T air_max /Σd≤ 0.3  (C)

where,

T air_max is a largest axial air space in the range from a surface positioned closest to the enlargement side to a surface positioned closest to the reduction side in the single-focus optical system, and

Σd is an axial distance from the surface positioned closest to the enlargement side to the surface positioned closest to the reduction side in the single-focus optical system.

25. An optical apparatus comprising:

an optical system; and

an image pickup element which is disposed on a reduction side, wherein:

the image pickup element has an image pickup surface, and converts an image formed on the image pickup surface by the optical system to an electric signal, and

the optical system is the single-focus optical system according to claim 1 .

26. An optical apparatus comprising:

an optical system; and

a display element which is disposed on a reduction side, wherein:

the display element has a display surface,

an image displayed on the display surface is projected on the enlargement side by the optical system, and

the optical system is the single-focus optical system according to claim 1 .