Dry objective
A dry objective includes: first lens group that includes a plurality of meniscus lens components and has a positive power; a second lens group that includes a cemented lens, turns a pencil of diverging light from the first lens group into a pencil of converging light, and has a positive power; and a third lens group that includes a front group and a rear group and has a negative power, the front and rear groups having concave surfaces adjacent to and facing each other. The dry objective satisfies the following conditional expression: 0.43≤( hg 2 −hg 1 )/ gt 1 ≤0.9 (1) where gt 1 indicates a thickness that a lens component of the rear group that is the closest to the object has on an optical axis; hg 1 and hg 2 , the heights of an axial marginal light ray at the lens surface of the lens component that is the closest to the object and an image.
1. A dry objective comprising:
a first lens group that includes a plurality of meniscus lens components and has a positive refractive power;
a second lens group that includes a cemented lens, turns a pencil of diverging light from the first lens group into a pencil of converging light, and has a positive refractive power; and
a third lens group that includes a front group and a rear group and has a negative refractive power, the front and rear groups having concave surfaces adjacent to and facing each other,
wherein:
an object, the first lens group, the second lens group, and the third lens group are arranged in this order,
the dry objective has a 30-fold magnification or lower and a numerical aperture of 0.75 or higher, and
the dry objective satisfies the following conditional expression:
0.43≤( hg 2 −hg 1 )/ gt 1 ≤0.9 (1)
where
gt 1 indicates a thickness on an optical axis of a first lens component, the first lens component being a lens component of the rear group that is closest to the object,
hg 1 indicates a height of an axial marginal light ray at a lens surface of the first lens component that is closest to the object, and
hg 2 indicates a height of the axial marginal light ray at a lens surface of the first lens component that is closest to an image.
2. The dry objective of claim 1 , wherein:
each of the plurality of meniscus lens components comprises a single lens, and
the dry objective satisfies the following conditional expression:
| d 1 −d 2 |/F≤ 0.2 (2)
where
d 1 indicates a thickness on the optical axis of a first meniscus lens component, the first meniscus lens component being a meniscus lens component that is closest to the object from among the plurality of meniscus lens components included in the first lens group,
d 2 indicates a thickness on the optical axis of a second meniscus lens component, the second meniscus lens component being a meniscus lens component that is second closest to the object from among the plurality of meniscus lens components included in the first lens group, and
F indicates a focal length of the dry objective.
3. The dry objective of claim 2 , wherein the dry objective satisfies the following conditional expression:
1.3≤| rg 2 /d 2 |≤2.4 (3)
where rg 2 indicates a radius of curvature of a lens surface of the second meniscus lens component on an image side.
4. The dry objective of claim 1 , wherein:
the rear group includes at least two lens components, and
the dry objective satisfies the following conditional expression:
0.6≤ Lf/Lb≤ 1.6 (4)
where Lf indicates a total length of the front group, and Lb indicates a total length of the rear group.
5. The dry objective of claim 2 , wherein:
the rear group includes at least two lens components, and
the dry objective satisfies the following conditional expression:
0.6≤ Lf/Lb≤ 1.6 (4)
where Lf indicates a total length of the front group, and Lb indicates a total length of the rear group.
6. The dry objective of claim 3 , wherein:
the rear group includes at least two lens components, and the dry objective satisfies the following conditional expression:
0.6≤ Lf/Lb≤ 1.6 (4)
where Lf indicates a total length of the front group, and Lb indicates a total length of the rear group.
7. The dry objective of claim 1 , wherein:
the second lens group includes a cemented triplet lens consisting of a positive lens, a negative lens, and a positive lens, and the object, the positive lens, the negative lens, and the positive lens are arranged in this order.
8. The dry objective of claim 2 , wherein:
the second lens group includes a cemented triplet lens consisting of a positive lens, a negative lens, and a positive lens, and
the object, the positive lens, the negative lens, and the positive lens are arranged in this order.
9. The dry objective of claim 3 , wherein:
the second lens group includes a cemented triplet lens consisting of a positive lens, a negative lens, and a positive lens, and
the object, the positive lens, the negative lens, and the positive lens are arranged in this order.
10. The dry objective of claim 4 , wherein:
the second lens group includes a cemented triplet lens consisting of a positive lens, a negative lens, and a positive lens, and
the object, the positive lens, the negative lens, and the positive lens are arranged in this order.
11. The dry objective of claim 5 , wherein:
the second lens group includes a cemented triplet lens consisting of a positive lens, a negative lens, and a positive lens, and
the object, the positive lens, the negative lens, and the positive lens are arranged in this order.
12. The dry objective of claim 6 , wherein:
the second lens group includes a cemented triplet lens consisting of a positive lens, a negative lens, and a positive lens, and
the object, the positive lens, the negative lens, and the positive lens are arranged in this order.
13. The dry objective of claim 1 , wherein the third lens group includes a Double Gauss.
14. The dry objective of claim 2 , wherein the third lens group includes a Double Gauss.
15. The dry objective of claim 3 , wherein the third lens group includes a Double Gauss.
16. The dry objective of claim 4 , wherein the third lens group includes a Double Gauss.
17. The dry objective of claim 1 , wherein the dry objective satisfies the following conditional expression:
57.6≤ν d 1 ≤87.3 (5)
where vd 1 indicates an Abbe number that a lens of the dry objective that is closest to the object has for a d line.
18. The dry objective of claim 1 , wherein the dry objective satisfies the following conditional expression:
0.440≤Δ hg≤ 0.453 (6)
where Δhg indicates a partial dispersion ratio that a lens of the dry objective that is closest to the object has for an h line.
19. A dry objective with a 30-fold magnification or lower and a numerical aperture of 0.75 or higher, the dry objective comprising:
a first lens group that includes a plurality of meniscus lens components and has a positive refractive power;
a second lens group that includes a cemented lens, turns a pencil of diverging light from the first lens group into a pencil of converging light, and has a positive refractive power; and
a third lens group that includes a front group and a rear group and has a negative refractive power, the front and rear groups having concave surfaces adjacent to and facing each other,
wherein:
an object, the first lens group, the second lens group, and the third lens group are arranged in this order, and
the dry objective satisfies the following conditional expression:
57.6≤ν d 1 ≤87.3 (5)
where vd 1 indicates an Abbe number that a lens of the dry objective that is closest to the object has for a d line.
20. The dry objective of claim 19 , wherein the dry objective satisfies the following conditional expression:
0.440≤Δ hg≤ 0.453 (6)
where Δhg indicates a partial dispersion ratio that a lens of the dry objective that is closest to the object has for an h line.