Immersion microscope objective and microscope using the same

1. A microscope objective 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 includes a first cemented lens, and at least one positive single lens,

the second lens group includes a second cemented lens, and changes a divergent bundle of rays to a convergent bundle of rays,

the third lens group includes in order from the object side, a first lens component and a second lens component,

a positive lens and a meniscus lens are cemented in the first cemented lens,

a surface nearest to an image side of the first lens component is a concave surface directed toward the image side,

a surface nearest to the object side of the second lens component is a concave surface directed toward the object side,

the first lens component and the second lens component are disposed such that the concave surface of the first lens component and the concave surface of the second lens component are face-to-face, and

the following conditional expression (1) is satisfied;

0.5<( n 0 /n 1o )/ NA ob <0.65  (1)

where,

NA ob denotes an object-side numerical aperture of the microscope objective,

n 0 denotes a refractive index for a d-line of a medium on the object side of the positive lens, and

n 1o denotes a refractive index for a d-line of the positive lens.

2. The microscope objective according to claim 1 , wherein the first lens group includes a plurality of positive single lenses, and

the following conditional expression (2) is satisfied;

1 <r 1c /r 1i <2  (2)

where,

r 1c denotes a radius of curvature of a cemented surface of the first cemented lens, and

r 1i denotes a radius of curvature of an image-side surface of the first cemented lens.

3. The microscope objective according to claim 2 , wherein the following conditional expression (5) is satisfied;

0.2< n 1H −n 1L <<0.6  (5)

where,

n 1H denotes a highest refractive index for a d-line of one of the plurality of positive single lenses, and

n 1L denotes a lowest refractive index for a d-line of another one of the plurality of positive single lenses.

4. The microscope objective according to claim 1 , wherein the following conditional expression (3) is satisfied;

0.2<( d 1o ×n 1o )/( d 1i ×n 1i )<1  (3)

where,

d 1o denotes an optical axial thickness of the positive lens,

n 1o denotes the refractive index for the d-line of the positive lens,

d 1i denotes an optical axial thickness of the meniscus lens, and

n 1i denotes a refractive index for a d-line of the meniscus lens.

5. The microscope objective according to claim 1 , wherein the following conditional expression (4) is satisfied;

0.2< f 1 /d 1 <0.45  (4)

where,

f 1 denotes a focal length of the first lens group, and

d 1 denotes an overall length of the first lens group.

6. The microscope objective according to claim 1 , wherein

the second lens component includes an object-side lens and a third cemented lens, and

a height of an axial marginal ray is the maximum at the third cemented lens of the second lens component, and is the minimum at a surface nearest to the object side of the second lens component, and

the following conditional expression (6) is satisfied;

0< f 32o /f 32 <0.45  (6)

where,

f 32o denotes a focal length of the object-side lens, and

f 32 denotes a focal length of the second lens component.

7. The microscope objective according to claim 1 , wherein one of the first lens group, the second lens group, and the third lens group moves along an optical axis.

8. A microscope comprising:

a light source;

an illumination optical system;

a main-body section;

an observation optical system; and

the microscope objective according to claim 1 .

9. The microscope objective according to claim 1 , wherein the following conditional expression (3′) is satisfied;

0.25<( d 1o ×n 1o )/( d 1i ×n 1i )<0.4  (3′)

where,

d 1o denotes an optical axial thickness of the positive lens,

n 1o denotes the refractive index for the d-line of the positive lens,

d 1i denotes an optical axial thickness of the meniscus lens, and

n 1i denotes a refractive index for a d-line of the meniscus lens.