Immersion objective optical system
View Patent ↗An objective optical system whose outer diameter is reduced, whose overall length is increased, in which chromatic aberrations are well corrected, and which is suitable for in-vivo examination with a high numerical aperture is realized. There is provided an immersion objective optical system comprising, in order from an object side: a first group having positive power; a second group having positive power; a third group having negative power; a fourth group having positive power; and a fifth group having positive power, wherein the first group includes a plano-convex lens L 1 whose convex surface faces an image-plane side, and a surface at the extreme object side is a substantially flat surface; the second group includes a lens L 2 in which a surface at the extreme object side of the second group is a convex surface facing the object side and a lens L 3 in which a surface at the extreme image-plane side of the second group is a concave surface facing the image-plane side; the third group includes a compound lens in which a biconvex lens L 4 and a biconcave lens L 5 , from the object side, are joined; the fourth group includes a positive lens L 6 whose convex surface faces the object side; and the fifth group includes at least one compound lens.
1. An immersion objective optical system comprising, in order from an object side: a first group having positive power; a second group having positive power; a third group having negative power; a fourth group having positive power; and a fifth group having positive power,
wherein the first group includes a plano-convex lens L 1 whose convex surface faces an image-plane side, and a surface at the extreme object side is a substantially flat surface;
the second group includes a lens L 2 in which a surface at the extreme object side of the second group is a convex surface facing the object side and a lens L 3 in which a surface at the extreme image-plane side of the second group is a concave surface facing the image-plane side;
the third group includes a compound lens in which a biconvex lens L 4 and a biconcave lens L 5 , from the object side, are joined;
the fourth group includes a positive lens L 6 whose convex surface faces the object side; and
the fifth group includes at least one compound lens.
2. An immersion objective optical system according to claim 1 , wherein conditional expression (1) below is satisfied:
0.03<| F 12 /F 3 |<0.13 (1)
where
F 3 is the focal length of the third group; and
F 12 is the combined focal length from the first group to the second group.
3. An immersion objective optical system according to claim 2 , wherein conditional expression (2) below is satisfied:
0.8<|β F 14 /F 5 |<1.2 (2)
where
β is the magnification of the immersion objective optical system;
F 14 is the combined focal length from the first group to the fourth group; and
F 5 is the focal length of the fifth group.
4. An immersion objective optical system according to claim 3 , wherein conditional expressions (3), (4), and (5) below are satisfied:
ν 4 −ν 5 >40 (3)
0.12 <n 6 −n 4 <0.22 (4)
1.4<| R 40 /R 45 |<1.9 (5)
where
ν 4 and ν 5 are Abbe numbers, at the d-line, of the biconvex lens L 4 and the biconcave lens L 5 , respectively;
n 4 and n 5 are refractive indexes, at the d-line, of the biconvex lens L 4 and the biconcave lens L 5 , respectively; and
R 40 and R 45 are radii of curvature at the object side of the biconvex lens L 4 and a joining face of the biconvex lens L 4 and the biconcave lens L 5 , respectively.
5. An immersion objective optical system according to claim 4 , wherein conditional expressions (6), (7), and (8) below are satisfied:
n 3 <1.65 (6)
ν 3 <50 (7)
3< |R 3I /F 12 |<5 (8)
where
n 3 is a refractive index, at the d-line, of the lens L 3 ;
ν 3 is an Abbe number, at the d-line, of the lens L 3 ;
R 3 I is a radius of curvature at the image-plane side of the lens L 3 ; and
F 12 is the combined focal length of the first group and the second group.
6. An immersion objective optical system according to claim 5 , wherein the lens at the extreme object side in the fifth group is compound lens in which a negative lens L 7 and a positive lens L 8 are joined, and conditional expression (9) below is satisfied:
0.2 <F 14 2 ·{( n 5 −1)/ R 5I 2 +( n 7 −n 8 )/ R 78 2 }<0.4 (9)
where
F 14 is the combined focal length from the first group to the fourth group;
n 5 , n 7 , and n 8 are refractive indexes, at the d-line, of the lens L 5 , the lens L 7 , and the lens L 8 , respectively; and
R 5 I and R 78 are a radius of curvature at the image-plane side of the lens L 5 and radius of curvature of a joining face of the lens L 7 and the lens L 8 .
7. An immersion objective optical system according to claim 6 , wherein the fifth group includes, from the object side, the compound lens in which the negative lens L 7 at the extreme object side and the positive lens L 8 are joined; a positive lens L 9 ; and a compound lens in which a positive lens L 10 and a negative lens L 11 whose concave surface faces the image-plane side are joined.
8. An immersion objective optical system according to claim 1 , wherein conditional expression (2) below is satisfied:
0.8<|β F 14 /F 5 |<1.2 (2)
where
β is a magnification of the immersion objective optical system;
F 14 is a combined focal length from the first group to the fourth group; and
F 5 is a focal length of the fifth group.
9. An immersion objective optical system according to claim 8 , wherein conditional expressions (3), (4), and (5) below are satisfied:
ν 4 −ν 5 >40 (3)
0.12 <n 6 −n 4 <0.22 (4)
1.4<| R 40 /R 45 |<1.9 (5)
where
ν 4 and ν 5 are Abbe numbers, at the d-line, of the biconvex lens L 4 and the biconcave lens L 5 , respectively;
n 4 and n 5 are refractive indexes, at the d-line, of the biconvex lens L 4 and the biconcave lens L 5 , respectively; and
R 40 and R 45 are radii of curvature at the object side of the biconvex lens L 4 and a joining face of the biconvex lens L 4 and the biconcave lens L 5 , respectively.
10. An immersion objective optical system according to claim 9 , wherein conditional expressions (6), (7), and (8) below are satisfied:
n 3 <1.65 (6)
ν 3 <50 (7)
3< |R 3I /F 12 |<5 (8)
where
n 3 is a refractive index, at the d-line, of the lens L 3 ;
ν 3 is an Abbe number, at the d-line, of the lens L 3 ;
R 3 I is a radius of curvature at the image-plane side of the lens L 3 ; and
F 12 is a combined focal length of the first group and the second group.
11. An immersion objective optical system according to claim 10 , wherein the lens at the extreme object side in the fifth group is a compound lens in which a negative lens L 7 and a positive lens L 8 are joined, and conditional expression (9) below is satisfied:
0.2 <F 14 2 ·{( n 5 −1)/ R 5I 2 +( n 7 −n 8 )/ R 78 2 }<0.4 (9)
where
F 14 is the combined focal length from the first group to the fourth group;
n 5 , n 7 , and n 8 are refractive indexes, at the d-line, of the lens L 5 , the lens L 7 , and the lens L 8 , respectively; and
R 5 I and R 78 are a radius of curvature at the image-plane side of the lens L 5 and a radius of curvature of a joining face of the lens L 7 and the lens L 8 .
12. An immersion objective optical system according to claim 11 , wherein the fifth group includes, from the extreme object side, the compound lens in which the negative lens L 7 and the positive lens L 8 are joined; a positive lens L 9 ; and a compound lens in which a positive lens L 10 and a negative length L 11 whose concave surface faces the image-plane side are joined.
13. An immersion objective optical system according to claim 1 , wherein conditional expressions (3), (4), and (5) below are satisfied:
ν 4 −ν 5 >40 (3)
0.12 <n 6 −n 4 <0.22 (4)
1.4<| R 40 /R 45 |<1.9 (5)
where
ν 4 and ν 5 are Abbe numbers, at the d-line, of the biconvex lens L 4 and the biconcave lens L 5 , respectively;
n 4 and n 5 are refractive indexes, at the d-line, of the biconvex lens L 4 and the biconcave lens L 5 , respectively; and
R 40 and R 45 are radii of curvature at the object side of the biconvex lens L 4 and the joining surface of the biconvex lens L 4 and the biconcave lens L 5 , respectively.
14. An immersion objective optical system according to claim 13 , wherein conditional expressions (6), (7), and (8) below are satisfied:
n 3 <1.65 (6)
ν 3 <50 (7)
3< |R 3I /F 12 |<5 (8)
where
n 3 is a refractive index, at the d-line, of the lens L 3 ;
ν 3 is an Abbe number, at the d-line, of the lens L 3 ;
R 3 I is a radius of curvature at the image-plane side of the lens L 3 ; and
F 12 is a combined focal length of the first group and the second group.
15. An immersion objective optical system according to claim 14 , wherein the lens at the extreme object side in the fifth group is a compound lens in which a negative lens L 7 and a positive lens L 8 are joined, and conditional expression (9) below is satisfied:
0.2 <F 14 2 ·{( n 5 −1)/ R 5I 2 +( n 7 −n 8 )/ R 78 2 }<0.4 (9)
where
F 14 is a combined focal length from the first group to the fourth group;
n 5 , n 7 , and n 8 are refractive indexes, at the d-line, of the lens L 5 , the lens L 7 , and the lens L 8 , respectively; and
R 5 I and R 78 are a radius of curvature at the image-plane side of the lens L 5 and a radius of curvature of a joining surface of the lens L 7 and the lens L 8 .
16. An immersion objective optical system according to claim 15 , wherein the fifth group includes, from the object side, the compound lens in which the lens L 7 at the extreme object side and the lens L 8 are joined; a positive lens L 9 ; and a compound lens in which a positive lens L 10 and a negative lens L 11 whose concave surface faces the image-plane side are joined.
17. An immersion objective optical system according to claim 1 , wherein conditional expressions (6), (7), and (8) below are satisfied:
n 3 <1.65 (6)
ν 3 <50 (7)
3< |R 3I /F 12 |<5 (8)
where
n 3 is a refractive index, at the d-line, of the lens L 3 ;
ν 3 is an Abbe number, at the d-line, of the lens L 3 ;
R 3 I is a radius of curvature at the image-plane side of the lens L 3 ; and
F 12 is a combine focal length of the first group and the second group.
18. An immersion objective optical system according to claim 17 , wherein the lens at the extreme object side in the fifth group is a compound lens in which a negative lens L 7 and a positive lens L 8 are joined, and conditional expression (9) below is satisfied:
0.2 <F 14 2 ·{( n 5 −1)/ R 5I 2 +( n 7 −n 8 )/ R 78 2 }<0.4 (9)
where
F 14 is a combine focal length from the first group to the fourth group;
n 5 , n 7 , and n 8 are refractive indexes, at the d-line, of the lens L 5 , the lens L 7 , and the lens L 8 , respectively; and
R 5 I and R 78 are a radius of curvature at the image-plane side of the lens L 5 and a radius of curvature of a joining face of the lens L 7 and the lens L 8 .
19. An immersion objective optical system according to claim 18 , wherein the fifth group includes, from the object side, the compound lens in which the negative lens L 7 , at the extreme object side, and the positive lens L 8 are joined; a positive lens L 9 ; and a compound lens in which a positive lens L 10 and a negative lens L 11 whose concave surface faces the image-plane side are combined.
20. An immersion objective optical system according to claim 19 , wherein the lens at the extreme object side in the fifth group is the compound lens in which the negative lens L 7 and the positive lens L 8 are joined, and conditional expression (9) below is satisfied:
0.2 <F 14 2 ·{( n 5 −1)/ R 5I 2 +( n 7 −n 8 )/ R 78 2 }<0.4 (9)
where F 14 is the combined focal length from the first group to the fourth group:
n 5 , n 7 , and n 8 are refractive indexes, at the d-line, of the lens L 5 , the lens L 7 , and the lens L 8 , respectively; and
R 5 I and R 78 are a radius of curvature at the image-plane side of the lens L 5 and a radius of curvature of a joining face of the lens L 7 and the lens L 8 .