Dry-type microscope objective lens
View Patent ↗The present invention offers a dry-type microscope objective lens which has a high NA in the range from low magnification to middle magnification and is lightweight and by which a high-resolution image can be obtained without taking a user time and trouble in observation. A dry-type microscope objective lens according to the present invention comprises, in order from the object side, a first lens group, a second lens group, and a third lens group, the first lens group comprises a meniscus lens which is arranged on the most object side and which turns its concave surface to the object side and the first lens group has positive refracting power as a whole, the second lens group comprises plural cemented lens units and has positive refracting power as a whole, the third lens group comprises air contact surfaces which are concave surfaces adjoining each other and facing toward each other and the third lens group has negative refracting power as a whole, and the dry-type microscope objective lens satisfies the following conditions: 6≦ D/f ≦8 5≦f 0.8≦NA<1.0 where D is a distance from an object surface to the last surface of the objective lens, f is a focal length of the objective lens, and NA is an object-side numerical aperture.
1. A dry-type microscope objective lens comprising, in order from an object side, a first lens group, a second lens group, and a third lens group;
wherein the first lens group comprises a meniscus lens which is arranged on the most object side and which turns its concave surface to the object side and the first lens group has positive refracting power as a whole,
wherein the second lens group comprises plural cemented lens units and has positive refracting power as a whole,
wherein the third lens group comprises air contact surfaces which are concave surfaces adjoining each other and facing toward each other and the third lens group has negative refracting power as a whole, and
wherein the dry-type microscope objective lens satisfies the following conditions:
6≦ D/f≦ 8
5≦ f
0.8≦ NA< 1.0
4≦| f ( Lm )/f|≦15
0.3≦| Rm/f|≦ 1.0
where D is a distance from an object surface to the last surface of the objective lens, f is a focal length of the objective lens, NA is an object-side numerical aperture, f(Lm) is a focal length of the meniscus lens which is arranged on the most object side in the first lens group and which turns its concave surface to the object side, and Rm is an object-side radius of curvature of the meniscus lens.
2. The dry-type microscope objective lens according to claim 1 satisfying the following condition:
4.5≦| f ( Lm )/ f|≦ 10.
3. The dry-type microscope objective lens according to claim 1 satisfying the following condition:
0.5≦| Rm/f|≦ 0.8.
4. The dry-type microscope objective lens according to claim 1 satisfying the following condition:
0.7≦ H 3/ H 2≦1.2
where H 2 is the height of a marginal ray which is incident on the third lens group, and H 3 is the height of a marginal ray which emerges from the last surface of the objective lens.
5. The dry-type microscope objective lens according to claim 1 satisfying the following condition:
0.8≦ H 3/ H 2≦1.1
where H 2 is the height of a marginal ray which is incident on the third lens group, and H 3 is the height of a marginal ray which emerges from the last surface of the objective lens.
6. The dry-type microscope objective lens according to claim 1 satisfying the following condition:
−9≦ f ( G 3)/ f
where f(G 3 ) is a focal length of the third lens group, and f is a focal length of the objective lens.
7. The dry-type microscope objective lens according to claim 4 satisfying the following condition:
−9≦ f ( G 3)/ f
where f(G 3 ) is a focal length of the third lens group, and f is a focal length of the objective lens.