Objective and method of assembling objective

1 . A method of assembling an objective, the objective comprising: an objective barrel; a plurality of lens sub-assemblies stacked in an optical axis direction of the objective in the objective barrel, each of the plurality of lens sub-assemblies including a lens and a lens frame holding the lens; and a screw member screwed into the objective barrel, the screw member having an annular shape, the screw member pressing the plurality of lens sub-assemblies against the objective barrel along the optical axis direction of the objective, the screw member having six or more concave portions into which a jig is fitted when the screw member is screwed into the objective barrel, a number of the six or more concave portions being a multiple of three, and the six or more concave portions being provided at equal intervals in a circumferential direction of the screw member, and the method comprising:

(a) selecting a set of three concave portions into which three protrusions of a jig are fitted, from the six or more concave portions provided at equal intervals in the screw member included in the objective;

(b) screwing the screw member into the objective barrel included in the objective by the jig in which the three protrusions are fitted into the set of three concave portions selected in (a);

(c) measuring an optical performance of the objective after (b);

(d) repeating (a) through (c) at least once;

(e) determining one set from a plurality of sets, each set being a set of the three concave portions selected in (a), based on the optical performance measured in (c) performed at least twice; and

(f) screwing the screw member into the objective barrel by the jig in which the three protrusions are fitted into the three concave portions included in the one set determined in (e).

2 . The method according to claim 1 , wherein at least one lens frame of a plurality of lens frames included in the plurality of lens sub-assemblies has:

an annular shape; and

three protrusions provided, on an end surface in contact with another lens frame or the screw member, at equal intervals in a circumferential direction of the at least one lens frame.

3 . The method according to claim 1 , wherein a plurality of lenses included in the plurality of lens sub-assemblies includes at least one single lens that satisfies a following conditional expression:

0

<

t

min

/

φ

<

0.08

where t min is a thickness of a thinnest portion of the at least one single lens in the optical axis direction, and φ is an outer diameter of the at least one single lens, and

the single lens is disposed in an optical system without being cemented to another lens.

4 . The method according to claim 1 , wherein

the objective is for a microscope, and

the plurality of lens sub-assemblies include at least one cemented lens.

5 . A method of assembling an objective, the objective comprising: an objective barrel; a plurality of lens sub-assemblies stacked in an optical axis direction of the objective in the objective barrel, each of the plurality of lens sub-assemblies including a lens and a lens frame holding the lens; and a screw member screwed into the objective barrel, the screw member having an annular shape, the screw member pressing the plurality of lens sub-assemblies against the objective barrel along the optical axis direction of the objective, the screw member having four or more concave portions into which a jig is fitted when the screw member is screwed into the objective barrel, and the four or more concave portions including four or more even-numbered concave portions provided at equal intervals in a circumferential direction of the screw member, and the method comprising:

(a) selecting a set of two concave portions into which two protrusions of a jig are fitted, from the four or more even-numbered concave portions provided at equal intervals in the screw member included in the objective;

(b) screwing the screw member into the objective barrel included in the objective by the jig in which the two protrusions are fitted into the set of the two concave portions selected in (a);

(c) measuring an optical performance of the objective after (b);

(d) repeating (a) through (c) at least once;

(e) determining one set from a plurality of sets, each set being a set of the two concave portions selected in (a), based on the optical performance measured in (c) performed at least twice; and

(f) screwing the screw member into the objective barrel by the jig in which the two protrusions are fitted into the two concave portions included in the one set determined in (e).

6 . The method according to claim 5 , wherein at least one lens frame of a plurality of lens frames included in the plurality of lens sub-assemblies has:

an annular shape; and

two protrusions provided, on an end surface in contact with another lens frame or the screw member, at equal intervals in a circumferential direction of the at least one lens frame.

7 . The method according to claim 5 , wherein a plurality of lenses included in the plurality of lens sub-assemblies includes at least one single lens that satisfies a following conditional expression:

0

<

t

min

/

φ

<

0.08

where t min is a thickness of a thinnest portion of the at least one single lens in the optical axis direction, and φ is an outer diameter of the at least one single lens, and

the single lens is disposed in an optical system without being cemented to another lens.

8 . The method according to claim 5 , wherein

the objective is for a microscope, and

the plurality of lens sub-assemblies include at least one cemented lens.

9 . A method of assembling an objective, the objective comprising: an objective barrel; a plurality of lens sub-assemblies stacked in an optical axis direction of the objective in the objective barrel, each of the plurality of lens sub-assemblies including a lens and a lens frame holding the lens; and a screw member screwed into the objective barrel, the screw member having an annular shape, the screw member pressing the plurality of lens sub-assemblies against the objective barrel along the optical axis direction of the objective, the screw member having six or more concave portions into which a jig is fitted when the screw member is screwed into the objective barrel, a number of the six or more concave portions being a multiple of three, and the six or more concave portions being provided at equal intervals in a circumferential direction of the screw member, and the method comprising:

(a) selecting a set of three concave portions into which three protrusions of a jig are fitted, from the six or more concave portions provided at equal intervals in the screw member included in the objective;

(b) screwing the screw member into the objective barrel included in the objective by the jig in which the three protrusions are fitted into the set of three concave portions selected in (a);

(c) measuring an optical performance of the objective after (b);

(d) determining, based on the optical performance measured in (c), whether the objective satisfies a predetermined optical performance; and

(e) if it is determined that the predetermined optical performance is not satisfied in (d), selecting a set of three concave portions different from the set of three concave portions and repeating (b), (c), and (d).

10 . The method according to claim 9 , wherein at least one lens frame of a plurality of lens frames included in the plurality of lens sub-assemblies has:

an annular shape; and

three protrusions provided, on an end surface in contact with another lens frame or the screw member, at equal intervals in a circumferential direction of the at least one lens frame.

11 . The method according to claim 9 , wherein a plurality of lenses included in the plurality of lens sub-assemblies includes at least one single lens that satisfies a following conditional expression:

0

<

t

min

/

φ

<

0.08

where t min is a thickness of a thinnest portion of the at least one single lens in the optical axis direction, and φ is an outer diameter of the at least one single lens, and

the single lens is disposed in an optical system without being cemented to another lens.

12 . The method according to claim 9 , wherein

the objective is for a microscope, and

the plurality of lens sub-assemblies include at least one cemented lens.

13 . A method of assembling an objective, the objective comprising: an objective barrel; a plurality of lens sub-assemblies stacked in an optical axis direction of the objective in the objective barrel, each of the plurality of lens sub-assemblies including a lens and a lens frame holding the lens; and a screw member screwed into the objective barrel, the screw member having an annular shape, the screw member pressing the plurality of lens sub-assemblies against the objective barrel along the optical axis direction of the objective, the screw member having four or more concave portions into which a jig is fitted when the screw member is screwed into the objective barrel, and the four or more concave portions including four or more even-numbered concave portions provided at equal intervals in a circumferential direction of the screw member, and the method comprising:

(a) selecting a set of two concave portions into which two protrusions of a jig are fitted, from the four or more even-numbered concave portions provided at equal intervals in the screw member included in the objective;

(b) screwing the screw member into the objective barrel included in the objective by the jig in which the two protrusions are fitted into the set of the two concave portions selected in (a);

(c) measuring an optical performance of the objective after (b);

(d) determining, based on the optical performance measured in (c), whether the objective satisfies a predetermined optical performance; and

(e) if it is determined that the predetermined optical performance is not satisfied in (d), selecting a set of two concave portions different from the set of two concave portions and repeating (b), (c), and (d).

14 . The method according to claim 13 , wherein at least one lens frame of a plurality of lens frames included in the plurality of lens sub-assemblies has:

an annular shape; and

two protrusions provided, on an end surface in contact with another lens frame or the screw member, at equal intervals in a circumferential direction of the at least one lens frame.

15 . The method according to claim 13 , wherein a plurality of lenses included in the plurality of lens sub-assemblies includes at least one single lens that satisfies a following conditional expression:

0

<

t

min

/

φ

<

0.08

where t min is a thickness of a thinnest portion of the at least one single lens in the optical axis direction, and φ is an outer diameter of the at least one single lens, and

the single lens is disposed in an optical system without being cemented to another lens.

16 . The method according to claim 13 , wherein

the objective is for a microscope, and

the plurality of lens sub-assemblies include at least one cemented lens.