阅读说明：本技术 物镜、光学系统及显微镜 (Objective lens, optical system and microscope ) 是由 渡边胜也 野中杏菜 于 2018-05-09 设计创作，主要内容包括：物镜(OL)具有从物体侧依次排列的正透镜(L11)、与正透镜(L11)接合并使凹面朝向物体侧的负凹凸透镜(L12)和使凹面朝向物体侧的正凹凸透镜(L13),其满足以下条件式：2.03≤n1m≤2.30且20≤ν1m,其中,n1m表示负凹凸透镜(L12)的相对于d线的折射率,ν1m表示负凹凸透镜(L12)的阿贝数。(The Objective Lens (OL) has a positive lens (L11), a negative meniscus lens (L12) joined to the positive lens (L11) and having a concave surface facing the object side, and a positive meniscus lens (L13) having a concave surface facing the object side, arranged in this order from the object side, and satisfies the following conditional expressions: 2.03. ltoreq. n1 m. ltoreq.2.30 and 20. ltoreq. v 1m, where n1m denotes a refractive index of the negative meniscus lens (L12) with respect to the d-line, and v 1m denotes an Abbe number of the negative meniscus lens (L12).)

1. An objective lens characterized in that an objective lens is provided,

comprising a positive lens, a negative meniscus lens having a concave surface facing the object side and a positive meniscus lens having a concave surface facing the object side, which are arranged in this order from the object side,

the objective lens satisfies the following conditional expression:

2.03≤n1m≤2.30

20≤ν1m

wherein the content of the first and second substances,

n1m represents the refractive index of the negative meniscus lens with respect to the d-line,

ν 1m denotes an abbe number of the negative meniscus lens.

2. The objective of claim 1,

the following conditional expressions are satisfied:

20≤ν1m≤40。

3. the objective of claim 1 or 2,

the following conditional expressions are satisfied:

1.40≤n1p≤1.60

where n1p denotes the refractive index of the positive lens with respect to the d-line.

4. The objective of any one of claims 1 to 3,

the following conditional expressions are satisfied:

0.3＜(d0+d1p)/(-r1c)＜1.8

0.8＜(-r1m)/d1m＜1.7

wherein the content of the first and second substances,

d0 represents the distance on the optical axis from the object to the lens surface on the object side of the positive lens,

d1p denotes the thickness of the positive lens on the optical axis,

d1m represents the thickness of the negative meniscus lens on the optical axis,

r1c represents the radius of curvature of the joint surface where the positive lens and the negative meniscus lens are joined with the case of bulging to the object side being positive,

r1m represents a curvature radius of the lens surface on the image side of the negative meniscus lens when bulging to the object side is positive.

5. The objective of any one of claims 1 to 4,

the following conditional expressions are satisfied:

4.0＜NA×f＜15.0

0.03＜d0/f＜0.20

wherein the content of the first and second substances,

f denotes a focal distance of the objective lens,

NA represents the object-side numerical aperture of the objective lens,

d0 represents the distance on the optical axis from the object to the lens surface on the object side of the positive lens.

6. The objective of any one of claims 1 to 5,

the objective lens is composed of a 1 st lens group having positive refractive power, a 2 nd lens group having positive refractive power, and a 3 rd lens group having negative refractive power, which are arranged in this order from the object side,

the 1 st lens group is composed of the positive lens, the negative meniscus lens and the positive meniscus lens arranged in this order from the object side,

the 2 nd lens group has at least two cemented lenses,

the 3 rd lens group includes a 1 st opposing negative lens having an image side lens surface with a concave surface facing the image side, and a 2 nd opposing negative lens disposed opposite to the 1 st opposing negative lens on the image side and having an object side lens surface with a concave surface facing the object side.

7. The objective of claim 6,

the 3 rd lens group includes a 2 nd opposing positive lens joined to the 2 nd opposing negative lens and having a concave surface facing the object side on a lens surface on the image side,

the objective lens satisfies the following conditional expression:

1.70≤n3p≤2.00

25≤ν3p≤45

wherein the content of the first and second substances,

n3p represents the refractive index of the 2 nd opposed positive lens with respect to the d-line,

ν 3p denotes an abbe number of the 2 nd opposed positive lens.

8. The objective of claim 6 or 7,

the 3 rd lens group is composed of a 1 st cemented lens, a 2 nd cemented lens and a 3 rd cemented lens arranged in this order from the object side,

the 2 nd cemented lens is composed of the 1 st opposing negative lens and a 1 st opposing positive lens cemented to the object side of the 1 st opposing negative lens,

the 3 rd cemented lens is composed of the 2 nd opposing negative lens and a 2 nd opposing positive lens cemented to the image side of the 2 nd opposing negative lens.

9. The objective of any one of claims 6 to 8,

the interval between the 2 nd lens group and the 3 rd lens group varies according to the thickness of the cover glass.

10. An optical system, characterized in that,

having an objective lens and an imaging lens as claimed in any of claims 1 to 9.

11. A microscope, characterized in that,

having an objective lens as claimed in any of claims 1 to 9.

Technical Field

The invention relates to an objective lens, an optical system and a microscope.

Background

In addition to the observation of a so-called fixed specimen in which conventional cells, tissue sections, or the like are chemically treated with formaldehyde or the like, the importance of observation of a biological sample in which changes in the morphology or behavior of cells in a living state are captured has recently increased as an application to an optical microscope in the biological field. In the observation of a biological sample, a wide field of view, a high numerical aperture, and a sufficiently long operating distance are desired, and a liquid immersion microscope objective lens satisfying these needs has been proposed (for example, see patent document 1).

Disclosure of Invention

The objective lens according to claim 1 has, arranged in order from an object side, a positive lens, a negative meniscus lens joined to the positive lens and having a concave surface facing the object side, and a positive meniscus lens having a concave surface facing the object side, and satisfies the following conditional expressions:

2.03≤n1m≤2.30

20≤ν1m

wherein the content of the first and second substances,

n1m represents the refractive index of the negative meniscus lens with respect to the d-line,

ν 1m denotes an abbe number of the negative meniscus lens.

The optical system of claim 2 includes the objective lens and the imaging lens of claim 1.

The microscope of claim 3 has the objective lens of claim 1.

Drawings

Fig. 1 is a sectional view showing the configuration of an objective lens of a liquid immersion microscope according to embodiment 1.

Fig. 2 is an aberration diagram of the objective lens of the immersion microscope of example 1.

Fig. 3 is a sectional view showing the configuration of the objective lens of the immersion microscope of embodiment 2.

Fig. 4 is an aberration diagram of the objective lens of the immersion microscope of example 2.

Fig. 5 is a sectional view showing the configuration of the objective lens of the immersion microscope of embodiment 3.

Fig. 6 is an aberration diagram of the objective lens of the immersion microscope of example 3.

Fig. 7 is a sectional view showing the configuration of the objective lens of the immersion microscope according to example 4.

Fig. 8 is an aberration diagram of the objective lens of the immersion microscope according to example 4.

Fig. 9 is a sectional view showing the configuration of the imaging lens.

Fig. 10 is a schematic diagram of essential parts of a microscope having a liquid immersion microscope objective lens.

Detailed Description

The objective lens and microscope of the immersion microscope according to the present embodiment will be described below with reference to the drawings. In this embodiment, a description will be given of a liquid immersion microscope objective lens which can obtain good optical performance up to the periphery of a field of view while maintaining a high numerical aperture, having a wide field of view, and a sufficient operating distance.

As an example of the immersion microscope objective lens OL of the present embodiment, the immersion microscope objective lens OL (1) shown in fig. 1 is configured to have a plano-convex shape or a positive lens L11 with a small curvature (close to a plane) on the object side, a negative meniscus lens L12 with a concave surface facing the object side and a positive meniscus lens L13 with a concave surface facing the object side, which are joined to a positive lens L11, in this order from the object side. The immersion microscope objective lens OL according to the present embodiment may be the immersion microscope objective lens OL (2) shown in fig. 3, the immersion microscope objective lens OL (3) shown in fig. 5, or the immersion microscope objective lens OL (4) shown in fig. 7. The respective lenses of the immersion microscope objective lenses OL (2) to OL (4) shown in fig. 3, 5, and 7 are configured in the same manner as the immersion microscope objective lens OL (1) shown in fig. 1.

In general, in a dry high NA objective lens, a lens closest to an object side is often composed of a single lens having a concave-convex shape in which a concave surface having a small radius of curvature is directed to the object side. Thus, the incidence angle of a large-angle light flux spreading from the object surface when entering the lens closest to the object side is reduced, and the occurrence of aberration such as spherical aberration is suppressed. In addition, the concave surface of the lens closest to the object side reduces the petzval sum, thereby contributing to correction of field curvature.

On the other hand, in a liquid immersion type objective lens, a lens surface closest to the object side is often formed of a flat surface or a gently curved surface in order to facilitate cleaning of a tip end portion and to prevent bubbles from entering the immersion liquid. When only the lens closest to the object side is formed into a substantially plano-convex shape, the petzval and the element of the reduced negative refractive power are eliminated. In this regard, a method of joining a positive lens of a substantially plano-convex shape having a relatively low refractive index with a negative meniscus lens having a relatively high refractive index to secure negative power at the joining surface thereof is considered. This enables correction of field curvature. As shown in this embodiment, in order to increase the working distance while increasing the field of view, the effective diameter of the positive lens closest to the object side becomes large, and therefore it is difficult to sufficiently reduce the radius of curvature of the joint surface. The lens surface refractive power is determined by the front-back refractive index difference of the lens surface and the radius of curvature of the lens surface. If the refractive index difference between the positive lens and the negative meniscus lens is increased, the amount of increase in the radius of curvature of the joint surface can be offset. Since the conventional glass has a refractive index of about 2.0 at the highest, there is a limit to increase the refractive index difference between the positive lens and the negative meniscus lens.

By a new glass production method called a suspension melting method, vitrification can be achieved even with an unstable composition that has been difficult to vitrify until now. Accordingly, there is a development that glass having a high refractive index, small dispersion, and high transmittance even at short wavelengths can be produced. When such a glass having a high refractive index is used for the negative meniscus lens, the difference in refractive index between the positive lens and the negative meniscus lens becomes large, and the increase in the radius of curvature of the joining surface can be cancelled out, so that the petzval sum can be reduced.

In the objective lens OL for an immersion microscope according to the present embodiment, a divergent light flux emitted from an object passes through the positive meniscus lens L11 and the negative meniscus lens L12 and is bent toward the converging side by the positive meniscus lens L13. The positive meniscus lens L13 has a large refractive power to suppress beam divergence, and therefore, it is preferable to have a concave-convex shape with a concave surface facing the object side so as not to generate large aberrations.

In the above configuration, the immersion microscope objective lens OL of the present embodiment satisfies the following conditional expressions (1) to (2).

2.03≤n1m≤2.30…(1)

20≤ν1m…(2)

Wherein the content of the first and second substances,

n1 m: the refractive index of the negative meniscus lens L12 with respect to the d-line,

v 1 m: the abbe number of the negative meniscus L12.

The conditional expression (1) is a conditional expression for specifying an appropriate refractive index of the nitro material used for the negative meniscus lens L12. If the corresponding value of conditional expression (1) is lower than the lower limit, sufficient negative refractive power cannot be obtained at the joint surface where positive lens L11 and negative meniscus lens L12, which contact the lens surface on the object side with the immersion liquid, are joined. As a result, the petzval sum cannot be sufficiently reduced, and the flatness of the image plane is undesirably reduced. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (1) may preferably be set to 2.05.

If the corresponding value of conditional expression (1) exceeds the upper limit value, the positive refractive power of the lens surface on the image side of the negative meniscus lens L12 becomes too strong, and the negative refractive power of the joint surface where the positive lens L11 and the negative meniscus lens L12 are joined is cancelled. As a result, the petzval sum reduction effect is reduced, and the flatness of the image plane is lowered, which is not preferable. In order to reliably achieve the effect of the present embodiment, it is preferable that the upper limit value of the conditional expression (1) is 2.20.

The conditional expression (2) is a conditional expression for specifying an appropriate abbe number of the nitro material used for the negative meniscus L12. If the corresponding value of conditional expression (2) is lower than the lower limit value, the dispersion is too large, and the difference in color due to field curvature or coma aberration becomes large. Therefore, it is difficult to correct the field curvature or coma aberration by the negative meniscus lens L12 and subsequent lenses. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (2) may preferably be set to 25.

The immersion microscope objective lens OL according to the present embodiment may satisfy the following conditional expression (2A) instead of the conditional expression (2).

20≤ν1m≤40…(2A)

The conditional expression (2A) is also a conditional expression for specifying an appropriate abbe number of the nitro material used for the negative meniscus L12. If the corresponding value of conditional expression (2A) is lower than the lower limit value, the dispersion is too large, and the difference in color due to field curvature or coma aberration becomes large. Therefore, it is difficult to correct the field curvature or coma aberration by the negative meniscus lens L12 and subsequent lenses. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (2A) may preferably be set to 25.

If the value of the conditional expression (2A) exceeds the upper limit, the nitro material as the negative meniscus L12 is hardly vitrified, and it is difficult to ensure stable quality. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (2A) may preferably be set to 35.

The immersion microscope objective lens OL according to the present embodiment may satisfy the following conditional expression (3).

1.40≤n1p≤1.60…(3)

Wherein, n1 p: the refractive index of the positive lens L11 with respect to the d-line.

The conditional expression (3) is a conditional expression for specifying an appropriate refractive index of the nitro material used for the positive lens L11. If the corresponding value of conditional expression (3) exceeds the upper limit value, a sufficient negative refractive power cannot be obtained at the joint surface where the positive lens L11 and the negative meniscus lens L12 are joined. As a result, the petzval sum cannot be sufficiently reduced, and the flatness of the image plane is undesirably reduced. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (3) may be preferably 1.55, and more preferably 1.52.

If the corresponding value of conditional expression (3) is less than the lower limit value, the refractive index difference with the immersion liquid becomes large, and high-order spherical aberration and coma aberration are likely to occur due to the influence of refraction at the interface with the immersion liquid. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (3) may preferably be set to 1.45.

The liquid immersion microscope objective lens OL according to the present embodiment may satisfy the following conditional expressions (4) to (5).

0.3＜(d0+d1p)/(-r1c)＜1.8…(4)

0.8＜(-r1m)/d1m＜1.7…(5)

Wherein the content of the first and second substances,

d 0: the distance on the optical axis from the object to the object-side lens surface of the positive lens L11,

d1 p: the thickness on the optical axis of the positive lens L11,

d1 m: the thickness on the optical axis of the negative meniscus lens L12,

r1 c: the radius of curvature of the joint surface where the positive lens L11 and the negative meniscus lens L12 are joined when bulging to the object side,

r1 m: the radius of curvature of the lens surface on the image side of the negative meniscus lens L12 when bulging to the object side is positive.

The conditional expression (4) is a conditional expression for specifying an appropriate ratio of the radius of curvature of the joint surface where the positive lens L11 and the negative meniscus lens L12 are joined to the distance from the object to the joint surface. If the corresponding value of the conditional expression (4) exceeds the upper limit value, the radius of curvature of the joint surface of the positive lens L11 and the negative meniscus lens L12 becomes too small to satisfy the effective diameter of the off-axis light flux in the wide field of view, and a shadow around the field of view is formed. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (4) may preferably be set to 1.3.

If the corresponding value of conditional expression (4) is less than the lower limit, the radius of curvature of the joint surface where the positive lens L11 and the negative meniscus lens L12 are joined is too large, and petzval sum cannot be sufficiently reduced, which makes it difficult to correct curvature of field or astigmatism. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (4) may preferably be set to 0.4.

The conditional expression (5) is a conditional expression for defining an appropriate ratio of the radius of curvature of the lens surface on the image side of the negative meniscus lens L12 to the thickness of the negative meniscus lens L12 on the optical axis. When the corresponding value of the conditional expression (5) exceeds the upper limit value, the curvature radius of the lens surface on the image side of the negative meniscus lens L12 becomes large, and the light flux from the object is excessively diffused. In order to suppress the spread of the light flux, the radius of curvature of each lens surface of the positive meniscus lens L13 needs to be small, and it becomes difficult to manufacture the positive meniscus lens L13. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (5) may preferably be set to 1.5.

If the corresponding value of conditional expression (5) is lower than the lower limit, the radius of curvature of the lens surface on the image side of the negative meniscus lens L12 becomes too small, and it becomes difficult to correct coma aberration, particularly the higher-order component, and it becomes difficult to enlarge the field of view. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (5) may preferably be set to 0.9.

The liquid immersion microscope objective lens OL according to the present embodiment may satisfy the following conditional expressions (6) to (7).

4.0＜NA×f＜15.0…(6)

0.03＜d0/f＜0.20…(7)

Wherein the content of the first and second substances,

f: the focal distance of the objective lens OL of the immersion microscope,

NA: the object side numerical aperture of the objective lens OL of the immersion microscope,

d 0: distance on the optical axis from the object to the object-side lens surface of the positive lens L11.

The conditional expression (6) is a conditional expression relating to the field of view that can be observed with a microscope and the brightness of an image. If the corresponding value of conditional expression (6) is less than the lower limit value, the magnification of the objective lens of the immersion microscope inevitably increases, and the field of view that can be observed becomes narrow. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (6) may be preferably 5.0, and more preferably 6.0.

If the corresponding value of conditional expression (6) exceeds the upper limit value, a wider field of view and a bright image can be obtained, but the liquid immersion microscope objective lens becomes large and it is difficult to maintain the same focal distance as the other liquid immersion objective lenses. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (6) may be set to preferably 12.0, and more preferably 10.0.

The conditional expression (7) is a conditional expression for specifying an appropriate operating distance. If the corresponding value of conditional expression (7) is lower than the lower limit value, a sufficient movement distance for observing the inside of the sample having a thickness cannot be obtained. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (7) may be preferably 0.05, and more preferably 0.06.

If the corresponding value of conditional expression (7) exceeds the upper limit value, it becomes difficult to hold the immersion liquid when the objective lens of the immersion microscope is used for an inverted microscope or the like, and the usability is deteriorated particularly when the stage is moved greatly. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (7) may be preferably 0.15, and more preferably 0.13.

The immersion microscope objective lens OL according to the present embodiment may be composed of a 1 st lens group G1 having positive refractive power, a 2 nd lens group G2 having positive refractive power, and a 3 rd lens group G3 having negative refractive power, which are arranged in this order from the object side. The 1 st lens group G1 is composed of the aforementioned positive lens L11, the aforementioned negative meniscus lens L12, and the aforementioned positive meniscus lens L13, which are arranged in this order from the object side.

The 2 nd lens group G2 has a role of gradually converting into a converging light beam while aberration-correcting the light beam from the 1 st lens group G1 still in a divergent state. The 2 nd lens group G2 is configured to have at least two sets of cemented lenses. In the 1 st lens group G1, since various aberrations such as spherical aberration and chromatic aberration still exist, these aberrations are mainly corrected by the cemented lens after the 2 nd lens group G2.

Further, regarding chromatic aberration, not only chromatic aberration correction using two wavelengths is performed, but also occurrence of a second-order spectrum must be suppressed as much as possible. Therefore, it is desirable that the positive lens and the negative lens constituting the cemented lens of the 2 nd lens group G2 be together composed of a nitro material having anomalous dispersibility. However, the nitro material of the negative lens having the abnormal dispersibility mostly does not have a material having a large dispersibility. Therefore, the 2 nd lens group G2 also requires a plurality of cemented lenses for first-order chromatic aberration correction. Further, the cemented lens of the 2 nd lens group G2 is not limited to two cemented lenses, and it is also effective to use three cemented lenses.

The 3 rd lens group G3 has a function of converting the converged light flux from the 2 nd lens group G2 into a parallel light flux and guiding the parallel light flux to an imaging lens described later. The 3 rd lens group G3 is configured as a 1 st opposing negative lens L34 whose lens surface on the image side has a concave surface facing the image side and a 2 nd opposing negative lens L35 which is disposed opposite to the 1 st opposing negative lens L34 on the image side and whose lens surface on the object side has a concave surface facing the object side. In the 3 rd lens group G3, a so-called gaussian lens (the 1 st opposing negative lens L34 and the 2 nd opposing negative lens L35) in which concave surfaces having strong refractive powers are opposed is disposed, whereby petzval sum can be reduced by complementing the 1 st lens group G1.

In the immersion microscope objective lens OL according to the present embodiment, the 3 rd lens group G3 may include the 2 nd opposing positive lens L36 joined to the 2 nd opposing negative lens L35 on the image side with the concave surface of the lens surface on the image side facing the object side, and may satisfy the following conditional expressions (8) to (9).

1.70≤n3p≤2.00…(8)

25≤ν3p≤45…(9)

Wherein the content of the first and second substances,

n3 p: the refractive index of the 2 nd opposed positive lens L36 with respect to the d-line,

v 3 p: abbe number of the 2 nd opposed positive lens L36.

The conditional expression (8) is a conditional expression for defining an appropriate refractive index of the nitro material used for the 2 nd opposing positive lens L36 disposed closest to the image side in the 3 rd lens group G3. Under the condition that the corresponding value of the conditional expression (8) is lower than the lower limit value, the radius of curvature of the 2 nd opposed positive lens L36 needs to be decreased in order to maintain the same refractive power. As a result, coma aberration is likely to occur, and it is difficult to reduce the petzval sum by the 1 st opposing negative lens L34 and the 2 nd opposing negative lens L35. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (8) may be set to 1.80.

If the value of conditional expression (8) exceeds the upper limit value, transmittance of light on the short wavelength side is decreased, which is not preferable. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (8) may be preferably 1.96, and more preferably 1.92.

The conditional expression (9) is a conditional expression for defining an appropriate abbe number of the nitro material used for the 2 nd opposed positive lens L36. If the corresponding value of conditional expression (9) exceeds the upper limit value, it is difficult to correct chromatic aberration of magnification. In order to reliably achieve the effect of the present embodiment, the upper limit value of conditional expression (9) may be set to 40.

If the corresponding value of conditional expression (9) is lower than the lower limit, it is difficult to suppress the second-order spectrum of chromatic aberration of magnification. In order to reliably achieve the effect of the present embodiment, the lower limit of conditional expression (9) may be set to 30.

In the immersion microscope objective lens OL according to the present embodiment, the 3 rd lens group G3 may be composed of a 1 st cemented lens, a 2 nd cemented lens, and a 3 rd cemented lens arranged in this order from the object side, the 2 nd cemented lens may be composed of a 1 st opposing negative lens L34 and a 1 st opposing positive lens L33 cemented to the object side of the 1 st opposing negative lens L34, and the 3 rd cemented lens may be composed of a 2 nd opposing negative lens L35 and a 2 nd opposing positive lens L36 cemented to the image side of the 2 nd opposing negative lens L35. In the 3 rd lens group G3, the 1 st opposed negative lens L34 and the 2 nd opposed negative lens L35, in which concave surfaces having strong refractive powers are opposed, are disposed at portions where light fluxes are converged by the front and rear 1 st opposed positive lens L33 and 2 nd opposed positive lens L36, so that petzval sum can be reduced by supplementing the 1 st lens group G1.

In the immersion microscope objective lens OL of the present embodiment, the interval between the 2 nd lens group G2 and the 3 rd lens group G3 may be changed according to the thickness of the cover glass C. The light flux converged by the 2 nd lens group G2 has a relatively large difference in height between the 2 nd lens group G2 and the 3 rd lens group G3 in the air space. By changing the air gap between the 2 nd lens group G2 and the 3 rd lens group G3, the lens functions as a so-called correction ring, and spherical aberration which changes according to the thickness of the cover glass C can be corrected. As described above, in the 3 rd lens group G3, the 1 st cemented lens may be disposed between the cemented lens (the 2 nd cemented lens and the 3 rd cemented lens) including the 1 st opposing negative lens L34 and the 2 nd opposing negative lens L35 and the 2 nd lens group G2. Accordingly, the incident height of the light beam incident on the 3 rd lens group G3 does not become too low, and spherical aberration can be corrected favorably when the air gap between the 2 nd lens group G2 and the 3 rd lens group G3 is changed.

In the objective lens OL for an immersion microscope of the present embodiment, the nitro material of the negative meniscus lens L12 (hereinafter referred to as glass for lens L12 for convenience of explanation) contains B as a cation component³⁺、La³⁺And optionally Nb⁵⁺The optical glass of (1). For example, the lens L12 of the present embodiment contains B in a glass in a proportion of 10 cat% to 50 cat% based on the total cationic component (in terms of cation%) contained in the glass³⁺. Glass for lens L12Nb is contained in a proportion of 0 to 40 cat% based on the whole cationic component contained in the glass⁵⁺. Glass for lens L12 containing Nb⁵⁺In the case of (3), La as a rare earth ion is contained in a proportion of 40 to 65 cat% based on the whole cationic component contained in the glass³⁺The content is preferably 50 to 65 cat%, more preferably 54 to 65 cat%. On the other hand, the glass for lens L12 does not contain Nb⁵⁺In the case (2), La is contained in a proportion of 40 to 63 cat%³⁺The content of the organic solvent is preferably 50 to 63 cat%. The lens L12 is made of glass B in a ratio based on the whole cationic component contained in the glass³⁺、La³⁺And Nb₅The total ratio of (A) is 80 to 100 cat%.

Furthermore, the cation% (cat%) is B in%³⁺Number of (La)³⁺Number of (2), Nb⁵⁺The number of cations in the cation group is a ratio of the number of cations to the total number of the cations. For example, only B is contained as a cationic component³⁺、La³⁺And Nb⁵⁺La in the case of³⁺Cation% of (A) is La³⁺Relative to the number of B³⁺Number of (La)³⁺Number of (2) and Nb⁵⁺The ratio of the total number of (a) to (b). The raw material for such optical glass can be selected from, for example, B according to the production conditions of the glass₂O₃、La₂O₃、Nb₂O₅And the like, and known materials such as oxides, hydroxides, carbonates, nitrates, sulfates, and the like containing the above-mentioned cationic component. Such an optical glass can be produced by a suspension melting method (see, for example, japanese unexamined patent publication No. 2014-196236). Specifically, the sample can be produced by irradiating the sample with a laser beam such as carbonic acid gas in a laser floating furnace to dissolve the sample, floating the dissolved substance with a fluid of a suspension gas discharged from a nozzle, and then cooling and solidifying the substance. The suspension gas may be any gas capable of floating the sample, and depending on the application, an inert gas such as air, nitrogen, oxygen, or argon is used as the inert gasIn addition to the above, the solvent can be appropriately selected from dry air and the like. The suspension melting method is also called a containerless solidification method, and is a method of obtaining glass by heating and dissolving a material without using a container such as a Pt alloy (Pt or platinum alloy, for example, Pt — Au — Rh, or the like) and then cooling and solidifying the material. Such optical glass can be produced not only by the suspension melting method but also in a state free from gravity.

Specific examples of the glass for lens L12 include glass B³⁺Set at 10 cat% and La³⁺Set to 60 cat%, Nb⁵⁺When the concentration is 30 cat%, a glass for lens L12 having n1m of 2.12040 and ν 1m of 26.12 can be obtained by the above-described suspension melting method. In the process of mixing B³⁺Set at 20 cat% and La³⁺Set to 40 cat%, Nb⁵⁺When the cat% is 40%, a glass for lens L12 having n1m of 2.17005 and ν 1m of 21.73 can be obtained by the above-described suspension melting method. In the process of mixing B³⁺Set at 20 cat% and La³⁺Set to 60 cat%, Nb⁵⁺When the cat% is 20%, a glass for lens L12 having n1m of 2.05013 and ν 1m of 30.25 can be obtained by the above-described suspension melting method. As described above, B is appropriately adjusted within the above range of the ratio to the whole cationic component contained in the glass³⁺、La³⁺And Nb⁵⁺And the glass for lens L12 having a high refractive index as exemplified in examples 1 to 4 described later can be obtained at the same ratio.

The microscope of the present embodiment is configured to have the immersion microscope objective lens OL configured as described above. As a specific example thereof, a microscope (liquid immersion microscope) having the liquid immersion microscope objective lens OL according to the present embodiment will be described with reference to fig. 10. The microscope 100 includes a stage frame 101, a stage 111 attached to a base portion 102 of the stage frame 101, a lens barrel 121 attached to an arm portion 103 of the stage frame 101, and an imaging unit 131 connected to the lens barrel 121. An observation object (biological sample or the like), not shown, held between the slide glass B and the cover glass C (reference numeral omitted in fig. 10) is placed on the stage 111. A condenser lens 117 constituting a transmission illumination device 116 is mounted on the lower side of the stage 111. Further, the above-described transmission illumination device 116, transmission illumination light source 118, and the like are mounted on base portion 102 of stage frame 101 in addition to stage 111.

The objective lens 122 is mounted on a converter 126 disposed below the lens barrel 121. The immersion liquid is filled between the tip end portion of the objective lens 122 and the cover glass C. The immersion microscope objective lens OL of the present embodiment is used as the objective lens 122 attached below the lens barrel 121. An imaging lens 123 and a prism 124 are provided on the lens barrel 121. An imaging lens IL described later is used as the imaging lens 123 provided in the lens barrel 121. Further, an epi-fluorescence device 127, an epi-fluorescence light source 128, an eyepiece 129, and the like are attached to the lens barrel 121. The image pickup unit 131 is provided with an image pickup device 132.

In the microscope 100, light from an observation object passes through the cover glass C and the immersion liquid, the objective lens 122, the imaging lens 123, and the prism 124, and reaches the image pickup device 132. An image of the observation object is formed on the imaging surface of the imaging element 132 by the imaging lens 123, and the image of the observation object is captured by the imaging element 132. An image of the observation object captured by the imaging element 132 is displayed on the monitor MT via an external computer PC. The external computer PC can perform various image processing on the image data of the observation object captured by the image pickup device 132. With such a configuration, by mounting the liquid immersion microscope objective lens OL according to the above-described embodiment, a microscope having a wide field of view and a sufficient operating distance and having good optical performance even in the peripheral portion of the field of view can be obtained. The microscope 100 may be an upright microscope or an inverted microscope.