Objective
An objective includes a first lens group that has a positive refractive power and a second lens group that has a negative refractive power. The objective includes a first negative lens and satisfies 0.005≤ d o1 /h o1 ≤0.1 (1) 0.005≤ h min /h l ≤0.72 (2) 10 mm≤ L ≤100 mm (3) 0.1≤ L/f ≤31 (4) when d o1 is a thickness of the first negative lens, h o1 is an axial marginal ray height on a lens surface on the object side of the first negative lens, h min is a minimum value of an axial marginal ray height in the second lens group, h l is a height of an axial marginal ray on a lens surface of the objective that is situated closest to the image side, L is a length of the objective, and f is a focal length of the objective.
1. An objective comprising:
a first lens group that has a positive refractive power and converts a divergent pencil of light from an object point into a convergent pencil of light; and
a second lens group that has a negative refractive power and is arranged closer to an image side than the first lens group,
wherein:
the objective includes a first negative lens, and
conditional expressions below
0.005 ≤d o1 /h o1 ≤0.1 (1)
0.01≤ h min /h l ≤0.70 (2-1)′
10 mm≤ L≤ 100 mm (3)
0.1≤ L/f≤ 31 (4)
are satisfied,
where d o1 is a thickness of the first negative lens on an optical axis, h o1 is a height of an axial marginal ray on a lens surface on an object side of the first negative lens, h min is a minimum value of a height of an axial marginal ray in the second lens group, h l is a height of an axial marginal ray on a lens surface of the objective that is situated closest to the image side, L is a length of the objective, and f is a focal length of the objective.
2. The objective according to claim 1 , wherein:
the objective includes a second negative lens that is different from the first negative lens, and
a conditional expression below
0.005≤ d o2 /h o2 ≤0.17 (5)
is satisfied,
where d o2 is a thickness of the second negative lens on the optical axis and h o2 is a height of an axial marginal ray on a lens surface on the object side of the second negative lens.
3. The objective according to claim 2 , wherein the first lens group includes a first achromatic lens component that includes a three-piece cemented lens.
4. The objective according to claim 3 , wherein:
the second lens group includes a second achromatic lens element that includes a three-piece cemented lens, and
a distance on the optical axis between a lens surface of the first lens group that is situated closest to the image side and a lens surface of the second achromatic lens component that is closest to the object side is less than a thickness of the second achromatic lens component on the optical axis.
5. The objective according to claim 2 , wherein:
the second lens group includes a second achromatic lens element that includes a three-piece cemented lens, and
a distance on the optical axis between a lens surface of the first lens group that is situated closest to the image side and a lens surface of the second achromatic lens component that is closest to the object side is less than a thickness of the second achromatic lens component on the optical axis.
6. The objective according to claim 2 , wherein:
the objective includes a meniscus lens that has a positive refractive power, and
a conditional expression below
0.02≤ d m1 /h m1 ≤0.45 (6)
is satisfied,
where d m1 is a thickness of the meniscus lens on the optical axis and h m1 is a height of an axial marginal ray on a lens surface on the object side of the meniscus lens.
7. The objective according to claim 1 , wherein the first lens group includes a first achromatic lens component that includes a three-piece cemented lens.
8. The objective according to claim 7 , wherein:
the second lens group includes a second achromatic lens element that includes a three-piece cemented lens, and
a distance on the optical axis between a lens surface of the first lens group that is situated closest to the image side and a lens surface of the second achromatic lens component that is closest to the object side is less than a thickness of the second achromatic lens component on the optical axis.
9. The objective according to claim 7 , wherein:
the objective includes a meniscus lens that has a positive refractive power, and
a conditional expression below
0.02≤ d m1 /h m1 ≤0.45 (6)
is satisfied,
where d m1 is a thickness of the meniscus lens on the optical axis and h m1 is a height of an axial marginal ray on a lens surface on the object side of the meniscus lens.
10. The objective according to claim 1 , wherein:
the second lens group includes a second achromatic lens element that includes a three-piece cemented lens, and
a distance on the optical axis between a lens surface of the first lens group that is situated closest to the image side and a lens surface of the second achromatic lens component that is closest to the object side is less than a thickness of the second achromatic lens component on the optical axis.
11. The objective according to claim 1 , wherein:
the objective includes a meniscus lens that has a positive refractive power, and
a conditional expression below
0.02≤ d m1 /h m1 ≤0.45 (6)
is satisfied,
where d m1 is a thickness of the meniscus lens on the optical axis and h m1 is a height of an axial marginal ray on a lens surface on the object side of the meniscus lens.
12. The objective according to claim 1 , wherein a conditional expression below
2.3≤( h max /f )×NA ob ≤6.5 (7)
is satisfied,
where h max is a maximum value of a height of an axial marginal ray in the objective and NA ob is a numerical aperture of the objective.
13. The objective according to claim 1 , wherein a conditional expression below
0.7≤(( h max −h min )/ f )×NA ob ≤3.6 (8)
is satisfied,
where h max is a maximum value of a height of an axial marginal ray in the objective and NA ob is a numerical aperture of the objective.
14. The objective according to claim 1 , wherein:
the first lens group includes a first lens component that is arranged closest to the object side and a second lens component that is arranged adjacent to the first lens component at the image side of the first lens group,
the first lens component includes a first meniscus lens that has a concave surface facing the object side, and
the second lens component includes a second meniscus lens that has a positive refractive power and has a concave surface facing the object side.
15. The objective according to claim 14 , wherein a conditional expression below
−3≤ R 21 /D o21 −0.8 (9)
is satisfied,
where R 21 is a radius of curvature of a lens surface on the object side of the second meniscus lens and D o21 is a distance on the optical axis from a focal plane of the objective to the lens surface on the object side of the second meniscus lens.
16. The objective according to claim 14 , wherein a conditional expression below
3.3≤( R 21 +R 22 )/( R 21 −R 22 )≤100 (10)
is satisfied,
where R 21 is a radius of curvature of the lens surface on the object side of the second meniscus lens and R 22 is a radius of curvature of a lens surface on the image side of the second meniscus lens.
17. The objective according to claim 14 , wherein a conditional expression below
1.75≤ n 1 ≤1.9 (11)
is satisfied,
where n 1 is a refractive index of the first meniscus lens.
18. The objective according to claim 14 , wherein a conditional expression below
0.88 ≤n 1 /n 2 ≤1.1 (12)
is satisfied,
where n 1 is a refractive index of the first meniscus lens and n 2 is a refractive index of the second meniscus lens.
19. An objective comprising:
a first lens group that has a positive refractive power, conducts a first conversion to convert a divergent pencil of light from an object into a convergent pencil of light, and emits the convergent pencil of light, the first conversion being a conversion that is conducted closest to an object among conversions from a divergent pencil of light into a convergent pencil of light; and
a second lens group that has a negative refractive power and is arranged closer to an image side than the first lens group,
wherein:
the first lens group includes a first achromatic lens component that includes a three-piece cemented lens,
the objective includes a first negative lens, and conditional expressions below
0.005≤ h min /h l ≤0.72 (2)
10 mm≤ L≤ 100 mm (3)
0.1≤ L/f≤ 31 (4)
are satisfied,
where h min is a minimum value of a height of an axial marginal ray in the second lens group, h l is a height of an axial marginal ray on a lens surface of the objective that is situated closest to the image side, L is a length of the objective, and f is a focal length of the objective.
20. An objective comprising:
a first lens group that has a positive refractive power, conducts a first conversion to convert a divergent pencil of light from an object into a convergent pencil of light, and emits the convergent pencil of light, the first conversion being a conversion that is conducted closest to an object among conversions from a divergent pencil of light into a convergent pencil of light; and
a second lens group that has a negative refractive power and is arranged closer to an image side than the first lens group,
wherein:
the second lens group includes a second achromatic lens element that includes a three-piece cemented lens,
the objective includes a first negative lens, and conditional expressions below
0.01≤ h min /h l ≤0.7 (2-1)
10 mm≤ L≤ 100 mm (3)
0.1≤ L/f≤ 31 (4)
are satisfied,
where h min is a minimum value of a height of an axial marginal ray in the second lens group, h l is a height of an axial marginal ray on a lens surface of the objective that is situated closest to the image side, L is a length of the objective, and f is a focal length of the objective.