Microscope objective lens

1. A microscope objective lens, comprising in order starting from an object side:

a first lens group having positive power;

a second lens group having positive power;

a third lens group having negative power; and

a fourth lens group having positive power, wherein:

the second lens group is configured to move in an optical axis direction between the first lens group and the third lens group so as to correct a variation in an aberration caused by a thickness of a cover glass; and

the following conditions are satisfied:

0.65<NA<1; and

1< f 1 /F< 2, where:

NA is a numerical aperture of the microscope objective lens, F is a focal length of the microscope objective lens, and f 1 is a focal length of the first lens group.

2. The microscope objective lens according to claim 1 , wherein:

the following conditions are satisfied:

1< f 2/ F< 3; and

1<| f 3/ F |<2.4, where:

f 2 is a focal length of the second lens group, and f 3 is a focal length of the third lens group.

3. The microscope objective lens according to claim 2 , wherein:

the first lens group includes three single lenses;

the second lens group includes, in order starting from an object side, a cemented lens having a negative lens and a positive lens, and a biconvex lens;

the third lens group includes a cemented lens that has a meniscus shape having a convex surface on an object side, and that has a positive lens and a negative lens;

the fourth lens group includes a cemented lens located at a position closest to an object side;

at least two of the single lenses on an object side are meniscus lenses each having a concave surface on an object side; and

the following condition is satisfied:

5<| f 2CE/ F |<15, where:

f 2 CE is a focal length of the cemented lens included in the second lens group.

4. A microscope objective lens according to claim 3 , wherein:

the following condition is satisfied:

0.1< Δd/F< 0.3, where:

Δd is a maximum movement distance of the second lens group in the optical axis direction.