Optical system, optical apparatus, and method for manufacturing the optical system

1. A fixed focal length optical system, comprising a continuous series of six lenses consisting of, in order from an object, consecutively:

a first lens having negative refractive power;

a second lens having positive refractive power;

a third lens having positive refractive power;

a fourth lens having negative refractive power;

a fifth lens having negative refractive power; and

a sixth lens having positive refractive power, and

the following conditional expression being satisfied:

0.88 <L 4 R 2 /f

where L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens, and f denotes a focal length of the total lens system, and

wherein

the following conditional expression is satisfied:

−1.000<( L 5 R 1+L4 R 2)/( L 5 R 1 −L 4 R 2)<−0.310

where L 5 R 1 denotes a radius of curvature of an object side surface of the fifth lens,

wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image, and wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series.

2. The fixed focal length optical system according to claim 1 , wherein

the following conditional expression is satisfied:

L 3 f/f< 0.56

where L 3 f denotes a focal length of the third lens.

3. The fixed focal length optical system according to claim 1 , wherein

the first lens is a negative meniscus lens having a concave surface facing the image.

4. The fixed focal length optical system according to claim 1 , wherein

an image side surface of the lens located closest to the image is aspherical.

5. An optical apparatus including the fixed focal length optical system according to claim 1 .

6. The fixed focal length optical system according to claim 1 , wherein

the following conditional expressions are satisfied:

1.820 ≤L 3 R 1 /f 3

where L 3 R 1 denotes a radius of curvature of an object side lens surface of the third lens, and f3 denotes a focal length of the third lens

0.10 <n 3 −n 4<0.30

where n 3 denotes a refractive index of a material of the third lens at the d-line, and n 4 denotes a refractive index of a material of the fourth lens at the d-line

1.00 <Σd/f< 1.30

where Σd denotes a distance on the optical axis from a lens surface closest to the object to a lens surface closest to the image in the optical system, and f denotes a focal length of the total lens system

or

the following conditional expressions are satisfied:

0.88 <L 4 R 2 /f

where L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens, and f denotes a focal length of the total lens system

−1.000<( L 5 R 1 +L 4 R 2)/( L 5 R 1 −L 4 R 2)<−0.310

where L 5 R 1 denotes a radius of curvature of an object side surface of the fifth lens

L 3 f/f< 0.56

where L 3 f denotes a focal length of the third lens.

7. The fixed focal length optical system according to claim 1 , wherein

the fifth lens is a concave lens or a negative meniscus lens having a concave surface facing the object.

8. A method for manufacturing a fixed focal length optical system including a continuous series of six lenses consisting of, in order from an object, consecutively, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,

the method comprising assembling each lens in a lens barrel so as to satisfy the following conditional expression:

0.88< L 4 R 2/ f

where L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens, and f denotes a focal length of the total lens system,

wherein

the following conditional expression is satisfied:

−1.000 <( L 5 R 1+ L 4 R 2)/( L 5 R 1− L 4 R 2)<−0.310

where L 5 R 1 denotes a radius of curvature of an object side surface of the fifth lens, and

wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image, and wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series.

9. A fixed focal length optical system, comprising a continuous series of six lenses consisting of, in order from an object, consecutively:

a first lens having negative refractive power;

a second lens having positive refractive power;

a third lens having positive refractive power;

a fourth lens having negative refractive power;

a fifth lens having negative refractive power; and

a sixth lens having positive refractive power, and

the following conditional expressions being satisfied:

1.52< L 3 R 1/ f 3

−1.000 <( L 5 R 1+ L 4 R 2)/( L 5 R 1− L 4 R 2)<−0.310

where L 3 R 1 denotes a radius of curvature of an object side lens surface of the third lens,

f 3 denotes a focal length of the third lens, and

L 5 R 1 denotes a radius of curvature of an object side surface of the fifth lens, and

L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens,

wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,

wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and

wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.

10. The fixed focal length optical system according to claim 9 , wherein

the third lens and the fourth lens constitute a cemented lens, and satisfy the following conditional expression:

0.10< n 3− n 4<0.30

where n 3 denotes a refractive index of a material of the third lens at the d-line, and n 4 denotes a refractive index of a material of the fourth lens at the d-line.

11. The fixed focal length optical system according to claim 9 , wherein

the second lens is a positive meniscus lens having a convex surface facing the object.

12. The fixed focal length optical system according to claim 9 , wherein

the following conditional expression is satisfied:

1.00<Σ d/f< 1.30

where Σd denotes a distance on the optical axis from a lens surface closest to the object to a lens surface closest to the image in the optical system, and f denotes a focal length of the total lens system.

13. The fixed focal length optical system according to claim 9 , wherein

a lens surface closest to the image is aspherical.

14. An optical apparatus including the fixed focal length optical system according to claim 9 .

15. A method for manufacturing a fixed focal length optical system including a continuous series of six lenses consisting of, in order from an object, consecutively, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,

the method comprising assembling each lens in a lens barrel so as to satisfy the following conditional expressions:

1.52< L 3 R 1/ f 3

−1.000 <( L 5 R 1+ L 4 R 2)/( L 5 R 1− L 4 R 2)<−0.310

where L 3 R 1 denotes a radius of curvature of an object side lens surface of the third lens,

f 3 denotes a focal length of the third lens,

L 5 R 1 denotes a radius of curvature of an object side surface of the fifth lens, and

L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens,

wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,

wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and

wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.

16. A fixed focal length optical system, comprising a continuous series of six lenses consisting of, in order from an object, consecutively:

a first lens having negative refractive power;

a second lens having positive refractive power;

a third lens having positive refractive power;

a fourth lens having negative refractive power;

a fifth lens having negative refractive power; and

a sixth lens having positive refractive power, and

the following conditional expressions being satisfied:

1.52< L 3 R 1/ f 3

0.88< L 4 R 2/ f

where L 3 R 1 denotes a radius of curvature of an object side lens surface of the third lens,

f 3 denotes a focal length of the third lens,

L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens, and

f denotes a focal length of the total lens system,

wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,

wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and

wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.

17. The fixed focal length optical system according to claim 16 , wherein

the third lens and the fourth lens constitute a cemented lens, and satisfy the following conditional expression:

0.10< n 3− n 4<0.30

where n 3 denotes a refractive index of a material of the third lens at the d-line, and n 4 denotes a refractive index of a material of the fourth lens at the d-line.

18. The fixed focal length optical system according to claim 16 , wherein

the second lens is a positive meniscus lens having a convex surface facing the object.

19. The fixed focal length optical system according to claim 16 , wherein

the following conditional expression is satisfied:

1.00<Σ d/f< 1.30

where Σd denotes a distance on the optical axis from a lens surface closest to the object to a lens surface closest to the image in the optical system, and f denotes the focal length of the total lens system.

20. The fixed focal length optical system according to claim 16 , wherein

a lens surface closest to the image is aspherical.

21. An optical apparatus including the fixed focal length optical system according to claim 16 .

22. A method for manufacturing a fixed focal length optical system including a continuous series of six lenses consisting of, in order from an object, consecutively, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,

the method comprising assembling each lens in a lens barrel so as to satisfy the following conditional expressions:

1.52< L 3 R 1/ f 3

0.88< L 4 R 2/ f

where L 3 R 1 denotes a radius of curvature of an object side lens surface of the third lens,

f 3 denotes a focal length of the third lens,

L 4 R 2 denotes a radius of curvature of an image side surface of the fourth lens, and

f denotes a focal length of the total lens system,

wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,

wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and

wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.