Microscope objective lens, microscope optical system, and microscope device

Abstract

A microscope objective lens (OL) comprises, sequentially from the objective side along an optical axis, a first lens group (G1) and a second lens group (G2) having a negative refractivity. The second lens group (G2) has, sequentially from the objective side along the optical axis, a first cemented meniscus lens (CL21) that has a concave surface facing an image side and a second cemented meniscus lens (CL22) that has a concave surface facing the objective side. The first lens group (G1) has a prescribed positive lens that satisfies the following conditional expression.　0<θgFA+0.0015×νdA-0.6395, 1.60<ndA<1.85, 39.50<νdA<75.00, where ndA represents the refractive index with respect to d line of the prescribed positive lens, νdA represents the Abbe number of the prescribed positive lens, and θgFA represents the partial dispersion ratio of the prescribed positive lens

Description

Microscope objective lens, microscope optical system, and microscope device

[0001] The present invention relates to a microscope objective lens, a microscope optical system, and a microscope apparatus.

[0002] In recent years, various objective lenses for microscopes with high magnification and large numerical aperture have been proposed (see, for example, Patent Document 1). Such objective lenses are required to effectively correct chromatic aberration.

[0003] Japanese Patent Application Laid-Open No. 2019-191266

[0004] A first microscope objective lens according to the present invention comprises a first lens group and a second lens group having negative refractive power, arranged in order from the object side along the optical axis, the second lens group having a cemented meniscus lens with its concave surface facing the image side and a meniscus lens component with its concave surface facing the object side, arranged in order from the object side along the optical axis, and the first lens group having a predetermined positive lens that satisfies the following conditional expression: 0<θgFA+0.0015×νdA−0.6395 1.60<ndA<1.85 39.50<νdA<75.00 Where, ndA: refractive index of the predetermined positive lens for the d line νdA: Abbe number of the predetermined positive lens θgFA: partial dispersion ratio of the predetermined positive lens, which is defined by the following formula when the refractive index of the predetermined positive lens for the g line is ngA, the refractive index of the predetermined positive lens for the F line is nFA, and the refractive index of the predetermined positive lens for the C line is nCA: θgFA=(ngA−nFA) / (nFA−nCA)

[0005] A second microscope objective lens according to the present invention comprises a first lens group and a second lens group having negative refractive power, arranged in order from the object side along the optical axis, wherein the second lens group has a cemented meniscus lens with its concave surface facing the image side and a meniscus lens component with its concave surface facing the object side, arranged in order from the object side along the optical axis, and the first lens group has a predetermined positive lens that satisfies the following conditional expression: 0<θgFA+0.0016×νdA−0.6460 1.60<ndA<1.85 39.50<νdA<75.00 Where, ndA: refractive index of the predetermined positive lens for the d line νdA: Abbe number of the predetermined positive lens θgFA: partial dispersion ratio of the predetermined positive lens, which is defined by the following formula when the refractive index of the predetermined positive lens for the g line is ngA, the refractive index of the predetermined positive lens for the F line is nFA, and the refractive index of the predetermined positive lens for the C line is nCA: θgFA=(ngA−nFA) / (nFA−nCA)

[0006] A microscope optical system according to the present invention includes the above-described microscope objective lens and an imaging lens that forms an image using light from the microscope objective lens.

[0007] A microscope apparatus according to the present invention includes the microscope objective lens described above.

[0008] FIG. 1 is a cross-sectional view showing the configuration of a microscope objective lens according to Example 1. FIG. 2 is a diagram showing various aberrations of the microscope objective lens according to Example 1. FIG. 3 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to Example 1. FIG. 4 is a diagram showing coma aberration of the microscope objective lens according to Example 1. FIG. 5 is a cross-sectional view showing the configuration of a microscope objective lens according to Example 2. FIG. 6 is a diagram showing various aberrations of the microscope objective lens according to Example 2. FIG. 7 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to Example 2. FIG. 8 is a diagram showing coma aberration of the microscope objective lens according to Example 2. FIG. 9 is a cross-sectional view showing the configuration of a microscope objective lens according to Example 3. FIG. 10 is a diagram showing various aberrations of the microscope objective lens according to Example 3. FIG. 11 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to Example 3. FIG. 12 is a diagram showing coma aberration of the microscope objective lens according to Example 3. FIG. 13 is a cross-sectional view showing the configuration of a microscope objective lens according to Example 4. FIG. 14 is a diagram showing various aberrations of the microscope objective lens according to Example 4. FIG. 15 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to Example 4. FIG. 16 is a cross-sectional view showing the configuration of a microscope objective lens according to Example 5. FIG. 10 is a diagram showing various aberrations of the microscope objective lens according to Example 5. FIG. 11 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to Example 5. FIG. 12 is a diagram showing coma aberration of the microscope objective lens according to Example 5. FIG. 13 is a cross-sectional view showing the configuration of the microscope objective lens according to Example 6. FIG. 14 is a diagram showing various aberrations of the microscope objective lens according to Example 6. FIG. 15 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to Example 6. FIG. 16 is a cross-sectional view showing the configuration of an imaging lens. FIG. 17 is a schematic diagram showing the configuration of a confocal fluorescence microscope, which is an example of a microscope device.

[0009] Preferred embodiments of the present invention will be described below. First, a microscope optical system and a confocal fluorescence microscope (microscope device) equipped with a microscope objective lens according to each embodiment will be described with reference to Fig. 26. As shown in Fig. 26, a confocal fluorescence microscope 1 includes an excitation light introducing section 2 that guides illumination laser light from a light source unit 6 onto a sample SA, a scanning device 3 that deflects the laser light focused on the sample SA to scan the sample SA, a photodetector 5 that detects a light intensity signal from the sample SA, and a focusing optical system 4 that guides light from the sample SA to the photodetector 5.

[0010] The light source unit 6 may be provided in the confocal fluorescence microscope 1 or may be provided separately from the confocal fluorescence microscope 1. The light source unit 6 includes a laser light source (not shown), a beam diameter adjustment mechanism (not shown), etc. The light source unit 6 oscillates an illumination laser beam.

[0011] The excitation light introducing section 2 is configured with a collimator lens 21, a dichroic mirror 22, and a microscope optical system 25 having an imaging lens 23 and an objective lens 24. The collimator lens 21 and the dichroic mirror 22 are disposed inside the microscope housing 12 provided on the upper part of the lens barrel 11 of the microscope main body 10. The light source unit 6 and the microscope housing 12 are connected by an optical fiber 69 using connectors C3 and C4. The collimator lens 21 converts the laser light (light beam) emitted from the light source unit 6 into parallel light. The dichroic mirror 22 reflects the laser light from the collimator lens 21 toward the sample SA. The microscope optical system 25 focuses the laser light reflected by the dichroic mirror 22 onto the sample SA using the imaging lens 23 and the objective lens 24. The imaging lens 23 is disposed inside the lens barrel 11 of the microscope main body 10. The imaging lens 23 is also referred to as a second objective lens. The objective lens 24 is attached to the lower part of the lens barrel 11.

[0012] The scanning device 3 includes a scanning mechanism (scanner) 31 and a scanning optical system 32. The scanning device 3 is disposed inside the microscope housing 12 between the dichroic mirror 22 and the imaging lens 23. The scanning mechanism (scanner) 31 includes, for example, a galvanometer mirror (not shown) or a resonant mirror (not shown). The scanning mechanism (scanner) 31 deflects the incident laser light. That is, the scanning mechanism (scanner) 31 deflects the laser light focused on the sample SA to scan the sample SA. The scanning optical system 32 is an optical system provided between the scanning mechanism (scanner) 31 and the imaging lens 23. The scanning optical system 32 is an optical system in which the focal position of the scanning optical system 32 is located on an image plane 13 (also referred to as a primary image plane) conjugate with the sample SA (the scanning plane of the sample SA).

[0013] The focusing optical system 4 includes the objective lens 24 and the imaging lens 23, which constitute the microscope optical system 25, as well as a total reflection mirror 41 and a condenser lens 42. The objective lens 24 receives fluorescence generated by the sample SA and converts it into parallel light. The imaging lens 23 focuses the fluorescence (parallel light) emitted from the objective lens 24 onto the imaging plane 13 (primary image plane) to form an image. As a result, the fluorescence from the sample SA that passes through the objective lens 24 and the imaging lens 23 is focused onto the imaging plane 13, then passes through the scanning device 3 and the dichroic mirror 22 and reaches the total reflection mirror 41. The total reflection mirror 41 and the condenser lens 42 are disposed above the dichroic mirror 22 inside the microscope housing 12. The total reflection mirror 41 reflects the fluorescence from the sample SA that passes through the objective lens 24 and the imaging lens 23. The condenser lens 42 condenses the fluorescence reflected by the total reflection mirror 41 onto a light blocking plate 52 having a pinhole 51 (aperture).

[0014] The light detection device 5 is configured to include a light shielding plate 52 having a pinhole 51, an optical fiber 53, and a detection unit 55. The optical fiber 53 is connected to the microscope housing 12 and the detection unit 55 using connectors C1 and C2. Light (fluorescence) that has passed through the pinhole 51 is incident on the optical fiber 53. The detection unit 55 detects the light (fluorescence) that has passed through the pinhole 51 and the optical fiber 53. A processing unit 57 is electrically connected to the detection unit 55 via a cable 56. The processing unit 57 performs image processing (of the sample SA) based on the detection signal detected by the detection unit 55, and the observed image of the sample SA obtained by the image processing of the processing unit 57 is displayed on a monitor (not shown).

[0015] The laser light from the scanning device 3 is first focused on the image plane 13 (primary image plane) and then focused again on the sample SA by the imaging lens 23 and objective lens 24 of the microscope optical system 25. That is, the scanning surface of the sample SA, the image plane 13, and the pinhole 51 are conjugate with each other. Therefore, by focusing the light on the sample SA by the imaging lens 23 and the objective lens 24, it becomes possible for the fluorescence generated on the scanning surface of the sample SA, out of the light (fluorescence) from the sample SA, to pass through the pinhole 51.

[0016] Although the confocal fluorescence microscope 1 has been described as an example of a microscope apparatus according to this embodiment, the present invention is not limited to this. For example, the microscope apparatus according to this embodiment may be a multiphoton excitation microscope, a super-resolution microscope, or the like. Furthermore, the confocal fluorescence microscope 1 may be an upright microscope or an inverted microscope.

[0017] A microscope objective lens OL, which will be described later, can be used as the objective lens 24 of the microscope optical system 25 provided in such a confocal fluorescence microscope 1 (microscope device). Also, an imaging lens IL, which will be described later, can be used as the imaging lens 23 of the microscope optical system 25 provided in such a confocal fluorescence microscope 1. First, the microscope objective lens OL according to the first embodiment will be described.

[0018] As an example of the microscope objective lens OL according to the first embodiment, the microscope objective lens OL(1) shown in FIG. 1 includes a first lens group G1 and a second lens group G2 having negative refractive power, arranged in order from the object side along the optical axis. The second lens group G2 includes a cemented meniscus lens CL21 with its concave surface facing the image side and a meniscus lens component (CL22) with its concave surface facing the object side, arranged in order from the object side along the optical axis. Note that in each embodiment, the lens component refers to a single lens or a cemented lens. The meniscus lens component may also be a cemented meniscus lens formed by cementing multiple lenses together. Furthermore, the meniscus lens component is not limited to a cemented meniscus lens, and may also be a meniscus lens formed by a single lens.

[0019] With the above configuration, the first lens group G1 has a predetermined positive lens that satisfies the following conditional expressions (1) to (3): 0<θgFA+0.0015×νdA−0.6395 (1) 1.60<ndA<1.85 (2) 39.50<νdA<75.00 (3) where ndA: refractive index of the predetermined positive lens for the d-line νdA: Abbe number of the predetermined positive lens θgFA: partial dispersion ratio of the predetermined positive lens, which is defined by the following expression when the refractive index of the predetermined positive lens for the g-line is ngA, the refractive index of the predetermined positive lens for the F-line is nFA, and the refractive index of the predetermined positive lens for the C-line is nCA: θgFA=(ngA−nFA) / (nFA−nCA)

[0020] According to the first embodiment, it is possible to obtain a microscope objective lens in which various aberrations including chromatic aberration are well corrected, as well as a microscope optical system and a microscope apparatus including this microscope objective lens. The microscope objective lens OL according to the first embodiment may be the microscope objective lens OL(2) shown in Fig. 5, the microscope objective lens OL(3) shown in Fig. 9, the microscope objective lens OL(4) shown in Fig. 13, the microscope objective lens OL(5) shown in Fig. 17, or the microscope objective lens OL(6) shown in Fig. 21.

[0021] Conditional expression (1) defines an appropriate relationship between the Abbe number and partial dispersion ratio of a predetermined positive lens in the first lens group G1. By satisfying conditional expression (1), axial chromatic aberration and lateral chromatic aberration can be corrected well. Note that a predetermined positive lens satisfying conditional expressions (1) to (3) is formed using, for example, the optical glass disclosed in WO 2021 / 024366.

[0022] If the corresponding value of conditional expression (1) falls below the lower limit, it becomes difficult to correct the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration. By setting the lower limit of conditional expression (1) to 0.001, 0.002, or even 0.003, the effect of this embodiment can be more reliably achieved. Furthermore, the upper limit of conditional expression (1) may be set to 0.1, or even less than 0.05.

[0023] Conditional expression (2) defines an appropriate range for the refractive index of a predetermined positive lens in the first lens group G1. By satisfying conditional expression (2), it is possible to effectively correct off-axis coma while correcting field curvature.

[0024] If the corresponding value of conditional expression (2) exceeds the upper limit, the refractive index of the predetermined positive lens becomes high, making it difficult to reduce the Petzval sum and correct the curvature of field. By setting the upper limit of conditional expression (2) to 1.80, 1.75, or even 1.70, the effect of this embodiment can be made more certain.

[0025] If the corresponding value of conditional expression (2) is below the lower limit, the refractive index of the predetermined positive lens element becomes low, making it difficult to correct off-axis coma. By setting the lower limit of conditional expression (2) to 1.61 or even 1.62, the effect of this embodiment can be further ensured.

[0026] Conditional expression (3) defines an appropriate range for the Abbe number of a predetermined positive lens in the first lens group G1. By satisfying conditional expression (3), the first-order spectrum of axial chromatic aberration and the first-order spectrum of lateral chromatic aberration can be effectively corrected.

[0027] If the value corresponding to conditional expression (3) exceeds the upper limit, it becomes difficult to correct off-axial coma because an optical glass with a low refractive index must be used for the predetermined positive lens. By setting the upper limit of conditional expression (3) to 70.00, 68.00, 65.00, or even 63.00, the effect of this embodiment can be further ensured.

[0028] If the corresponding value of conditional expression (3) is below the lower limit, the dispersion of a given positive lens increases, making it difficult to correct the first-order spectrum of axial chromatic aberration and the first-order spectrum of lateral chromatic aberration. By setting the lower limit of conditional expression (3) to 40.00, 42.50, or even 45.00, the effects of this embodiment can be further ensured.

[0029] Next, a microscope objective lens according to a second embodiment will be described. The microscope objective lens according to the second embodiment has the same configuration as the microscope objective lens OL according to the first embodiment, and therefore will be described using the same reference numerals as in the first embodiment. As an example of the microscope objective lens OL according to the second embodiment, a microscope objective lens OL(1) shown in FIG. 1 is composed of, arranged in order from the object side along the optical axis, a first lens group G1 and a second lens group G2 having negative refractive power. The second lens group G2 has, arranged in order from the object side along the optical axis, a cemented meniscus lens CL21 with its concave surface facing the image side, and a meniscus lens component (CL22) with its concave surface facing the object side.

[0030] With the above configuration, the first lens group G1 has a predetermined positive lens that satisfies the following conditional expressions (4), (2), and (3): 0<θgFA+0.0016×νdA−0.6460 (4) 1.60<ndA<1.85 (2) 39.50<νdA<75.00 (3) where ndA: refractive index of the predetermined positive lens for the d-line νdA: Abbe number of the predetermined positive lens θgFA: partial dispersion ratio of the predetermined positive lens, which is defined by the following expression when the refractive index of the predetermined positive lens for the g-line is ngA, the refractive index of the predetermined positive lens for the F-line is nFA, and the refractive index of the predetermined positive lens for the C-line is nCA: θgFA=(ngA−nFA) / (nFA−nCA)

[0031] According to the second embodiment, it is possible to obtain a microscope objective lens in which various aberrations including chromatic aberration are well corrected, as well as a microscope optical system and a microscope apparatus including this microscope objective lens. The microscope objective lens OL according to the second embodiment may be the microscope objective lens OL(2) shown in Fig. 5, the microscope objective lens OL(3) shown in Fig. 9, the microscope objective lens OL(4) shown in Fig. 13, the microscope objective lens OL(5) shown in Fig. 17, or the microscope objective lens OL(6) shown in Fig. 21.

[0032] Conditional expression (4) defines an appropriate relationship between the Abbe number and partial dispersion ratio of a predetermined positive lens in the first lens group G1. By satisfying conditional expression (4), axial chromatic aberration and lateral chromatic aberration can be corrected well. Note that a predetermined positive lens satisfying conditional expressions (4), (2), and (3) is formed using, for example, the optical glass disclosed in International Publication No. 2021 / 024366.

[0033] If the corresponding value of conditional expression (4) falls below the lower limit, it becomes difficult to correct the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration. By setting the lower limit of conditional expression (4) to 0.0002, 0.0004, 0.001, 0.002, or even 0.0025, the effects of this embodiment can be further ensured. Furthermore, the upper limit of conditional expression (4) may be set to 0.1, or even less than 0.05.

[0034] As described above, conditional expression (2) defines an appropriate range for the refractive index of a predetermined positive lens in the first lens group G1. By satisfying conditional expression (2), it is possible to effectively correct off-axial coma while correcting field curvature. By setting the upper limit of conditional expression (2) to 1.80, 1.75, or even 1.70, the effects of this embodiment can be further ensured. Furthermore, by setting the lower limit of conditional expression (2) to 1.61, or even 1.62, the effects of this embodiment can be further ensured.

[0035] As described above, conditional expression (3) defines an appropriate range for the Abbe number of a predetermined positive lens in the first lens group G1. By satisfying conditional expression (3), the first-order spectrum of axial chromatic aberration and the first-order spectrum of lateral chromatic aberration can be effectively corrected. By setting the upper limit of conditional expression (3) to 70.00, 68.00, 65.00, or even 63.00, the effects of this embodiment can be further ensured. Furthermore, by setting the lower limit of conditional expression (3) to 40.00, 42.50, or even 45.00, the effects of this embodiment can be further ensured.

[0036] In the microscope objective lens OL according to the first and second embodiments, the predetermined positive lens may be a positive meniscus lens that satisfies the following conditional expression (5): −10<GAR1 / DGA1<1 (5) where GAR1 is the radius of curvature of the object-side lens surface of the positive meniscus lens, and DGA1 is the distance on the optical axis from the object-side lens surface of the positive meniscus lens to the object.

[0037] Conditional expression (5) defines an appropriate relationship between the radius of curvature of the object-side lens surface of a positive meniscus lens corresponding to a predetermined positive lens and the distance on the optical axis from the object-side lens surface of the positive meniscus lens to the object. Note that in each embodiment, the radius of curvature of the lens surface is set to a positive value when the lens surface is convex toward the object side. By satisfying conditional expression (5), it is possible to effectively correct off-axial coma while correcting field curvature.

[0038] If the value corresponding to conditional expression (5) falls outside the above range, the curvature of the object-side lens surface of the positive meniscus lens becomes small, making it difficult to correct off-axial coma while correcting field curvature. By setting the upper limit of conditional expression (5) to 0.5, or even 0.2, the effects of each embodiment can be made more certain. By setting the lower limit of conditional expression (5) to -8, or even -7, the effects of each embodiment can be made more certain.

[0039] In the microscope objective lens OL according to the first and second embodiments, the predetermined positive lens may be a positive meniscus lens that satisfies the following conditional expression (6): −10<GAR2 / DGA2<0 (6) where GAR2 is the radius of curvature of the image-side lens surface of the positive meniscus lens, and DGA2 is the distance on the optical axis from the image-side lens surface of the positive meniscus lens to the object.

[0040] Conditional expression (6) defines an appropriate relationship between the radius of curvature of the image-side lens surface of a positive meniscus lens corresponding to a predetermined positive lens and the distance on the optical axis from the image-side lens surface of the positive meniscus lens to an object. By satisfying conditional expression (6), it is possible to effectively correct off-axial coma while correcting field curvature.

[0041] If the corresponding value of conditional expression (6) falls outside the above range, the curvature of the image-side lens surface of the positive meniscus lens becomes small, making it difficult to correct off-axial coma while correcting field curvature. By setting the upper limit of conditional expression (6) to -0.2, or even -0.5, the effects of each embodiment can be made more certain. By setting the lower limit of conditional expression (6) to -5, or even -2, the effects of each embodiment can be made more certain.

[0042] In the microscope objective lens OL according to the first and second embodiments, the predetermined positive lens may be a positive meniscus lens that satisfies the following conditional expression (7): −0.3<(GAR2−GAR1+GAL) / TL<0.3 (7) where GAR1 is the radius of curvature of the lens surface on the object side of the positive meniscus lens, GAR2 is the radius of curvature of the lens surface on the image side of the positive meniscus lens, GAL is the length of the positive meniscus lens on the optical axis, and TL is the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the microscope objective lens OL.

[0043] In each embodiment, the difference between the radius of curvature of the image-side lens surface and the radius of curvature of the object-side lens surface of a meniscus lens plus the length of the meniscus lens on the optical axis represents the difference in spherical center positions between the image-side lens surface and the object-side lens surface of the meniscus lens. The difference in spherical center positions between the image-side lens surface and the object-side lens surface of a meniscus lens can also be said to be the difference between the position of the center of curvature of the image-side lens surface and the position of the center of curvature of the object-side lens surface of the meniscus lens. Conditional expression (7) defines an appropriate relationship between the difference in spherical center positions between the image-side lens surface and the object-side lens surface of a positive meniscus lens corresponding to a specified positive lens and the axial distance from the lens surface closest to the object to the lens surface closest to the image in the microscope objective lens OL. By satisfying conditional expression (7), the sine condition can be satisfied, enabling excellent correction of off-axis coma.

[0044] If the corresponding value of conditional expression (7) falls outside the above range, it becomes difficult to correct off-axial coma. By setting the upper limit of conditional expression (7) to 0.27, 0.25, 0.20, 0.19, 0.15, 0.10, or even 0.08, the effects of each embodiment can be more reliably achieved. By setting the lower limit of conditional expression (7) to -0.21, -0.20, -0.15, -0.10, or even 0.00, the effects of each embodiment can be more reliably achieved.

[0045] In the microscope objective lens OL according to the first and second embodiments, the positive meniscus lens may be disposed closest to the object in the first lens group G1. By disposing a positive meniscus lens, i.e., a predetermined positive lens, closest to the object in the first lens group G1, the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration can be effectively corrected. Furthermore, in a microscope objective lens in which the gap between the lens and the cover glass is filled with air, by disposing a positive meniscus lens (a predetermined positive lens) closest to the object in the first lens group G1, the difference in refractive index at the object-side lens surface of the positive meniscus lens becomes sufficiently large, and by satisfying conditional expression (2), the Petzval sum can be effectively reduced.

[0046] In the microscope objective lens OL according to the first and second embodiments, the first lens group G1 may have a subgroup G1a that is movable along the optical axis, whereby the subgroup G1a of the first lens group G1 functions as a so-called correction ring, and can effectively correct spherical aberration and axial chromatic aberration that change depending on the thickness of the cover glass CV.

[0047] In the microscope objective lens OL according to the first and second embodiments, the first lens group G1 may have an image-side lens having positive refractive power that is arranged closer to the image side than the above-mentioned positive meniscus lens, and the image-side lens may satisfy the following conditional expressions (8) and (9): 0<θgFB1+0.0015×νdB1−0.6395 (8) νdB1<40.00 (9) where νdB1 is the Abbe number of the image-side lens, and θgFB1 is the partial dispersion ratio of the image-side lens, which is defined by the following expression when the refractive index of the image-side lens for the g-line is ngB1, the refractive index of the image-side lens for the F-line is nFB1, and the refractive index of the image-side lens for the C-line is nCB1: θgFB1=(ngB1−nFB1) / (nFB1−nCB1)

[0048] Conditional expression (8) defines an appropriate relationship between the Abbe number and partial dispersion ratio of the image-side lens in the first lens group G1. Conditional expression (9) defines an appropriate range for the Abbe number of the image-side lens in the first lens group G1. By providing an image-side lens that satisfies conditional expressions (8) and (9) in addition to the positive meniscus lens (a predetermined positive lens) arranged closest to the object in the first lens group G1, it is possible to effectively correct not only the first-order spectrum of axial chromatic aberration but also the second-order spectrum of axial chromatic aberration. Note that the image-side lens that satisfies conditional expressions (8) and (9) is formed using, for example, the optical glass disclosed in International Publication No. WO 2019 / 082419.

[0049] If the corresponding value of conditional expression (8) falls below the lower limit, it becomes difficult to correct the secondary spectrum of axial chromatic aberration. By setting the lower limit of conditional expression (8) to 0.001, 0.002, or even 0.003, the effects of each embodiment can be more reliably achieved. Furthermore, the upper limit of conditional expression (8) may be set to 0.1, or even less than 0.05.

[0050] If the corresponding value of conditional expression (9) exceeds the upper limit, it becomes difficult to correct the secondary spectrum of axial chromatic aberration. By setting the upper limit of conditional expression (9) to 35.00, or even 33.00, the effects of each embodiment can be made more certain.

[0051] In the microscope objective lens OL according to the first and second embodiments, the first lens group G1 may include a lens component located closest to the object in the first lens group G1 with its flat surface facing the object side, and a positive meniscus lens may be located adjacent to the image side of the lens component. By arranging a positive meniscus lens, i.e., a predetermined positive lens, adjacent to the image side of the lens component located closest to the object in the first lens group G1, the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration can be effectively corrected. Furthermore, in a microscope objective lens in which the space between the lens and the cover glass is filled with immersion liquid, by arranging a positive meniscus lens (a predetermined positive lens) adjacent to the image side of the lens component located closest to the object in the first lens group G1, the longitudinal chromatic aberration and the lateral chromatic aberration can be effectively corrected. As described above, in each embodiment, the lens component refers to a single lens or a cemented lens. The lens component located closest to the object in the first lens group G1 may be a cemented lens including a plano-convex positive lens with its flat surface facing the object side. Furthermore, the lens component closest to the object side in the first lens group G1 is not limited to being a cemented lens, but may be a single lens.

[0052] In the microscope objective lens OL according to the first and second embodiments, the second lens group G2 is movable along the optical axis, and the first lens group G1 may have a subgroup that is movable along the optical axis together with the second lens group G2. This allows the subgroup of the first lens group G1 and the second lens group G2 to function as a so-called correction ring, and enables excellent correction of spherical aberration and axial chromatic aberration that change depending on the thickness of the cover glass CV.

[0053] In the microscope objective lens OL according to the first and second embodiments, the first lens group G1 has an image-side lens with positive refractive power that is arranged closer to the image side than the aforementioned positive meniscus lens, and the image-side lens may satisfy the following conditional expressions (10) to (12): 0<θgFB2+0.0015×νdB2−0.6395 (10) 1.60<ndB2<1.85 (11) 39.50<νdB2<75.00 (12) where ndB2: refractive index of the image-side lens for the d-line νdB2: Abbe number of the image-side lens θgFB2: partial dispersion ratio of the image-side lens, which is defined by the following equation when the refractive index of the image-side lens for the g-line is ngB2, the refractive index of the image-side lens for the F-line is nFB2, and the refractive index of the image-side lens for the C-line is nCB2: θgFB2=(ngB2−nFB2) / (nFB2−nCB2)

[0054] Conditional expression (10) prescribes an appropriate relationship between the Abbe number and partial dispersion ratio of the image-side lens in the first lens group G1. Conditional expression (11) prescribes an appropriate range for the refractive index of the image-side lens in the first lens group G1. Conditional expression (12) prescribes an appropriate range for the Abbe number of the image-side lens in the first lens group G1. By arranging a positive meniscus lens (a predetermined positive lens) next to the image side of the lens component closest to the object in the first lens group G1, and by arranging an image-side lens that satisfies conditional expressions (10) to (12), the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration can be well corrected. Furthermore, in a microscope objective lens of the type in which the space between the lens element and the cover glass is filled with an immersion liquid, a positive meniscus lens (a predetermined positive lens) is arranged next to the image side of the lens component closest to the object in the first lens group G1, and an image-side lens that satisfies conditional expressions (10) to (12) is also arranged, thereby making it possible to effectively correct axial chromatic aberration and chromatic aberration of magnification. Note that the image-side lens that satisfies conditional expressions (10) to (12) is formed using, for example, the optical glass disclosed in International Publication No. 2021 / 024366.

[0055] If the corresponding value of conditional expression (10) falls below the lower limit, it becomes difficult to correct the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration. By setting the lower limit of conditional expression (10) to 0.001, 0.002, or even 0.003, the effects of each embodiment can be more reliably achieved. Furthermore, the upper limit of conditional expression (10) may be set to 0.1, or even less than 0.05.

[0056] If the corresponding value of conditional expression (11) falls outside the above range, it becomes difficult to effectively correct axial chromatic aberration and lateral chromatic aberration. By setting the upper limit of conditional expression (11) to 1.80, 1.75, or even 1.70, the effects of each embodiment can be more reliably achieved. By setting the lower limit of conditional expression (11) to 1.61, or even 1.62, the effects of each embodiment can be more reliably achieved.

[0057] If the corresponding value of conditional expression (12) falls outside the above range, it becomes difficult to effectively correct axial chromatic aberration and lateral chromatic aberration. By setting the upper limit of conditional expression (12) to 70.00, 68.00, 65.00, or even 63.00, the effects of each embodiment can be more reliably achieved. By setting the lower limit of conditional expression (12) to 40.00, 42.50, or even 45.00, the effects of each embodiment can be more reliably achieved.

[0058] In the microscope objective lens OL according to the first and second embodiments, the first lens group G1 has an image-side lens with positive refractive power that is arranged closer to the image side than the aforementioned positive meniscus lens, and the image-side lens may satisfy the following conditional expressions (13), (11), and (12): 0<θgFB2+0.0016×νdB2−0.6460 (13) 1.60<ndB2<1.85 (11) 39.50<νdB2<75.00 (12) where ndB2: refractive index of the image-side lens for the d-line νdB2: Abbe number of the image-side lens θgFB2: partial dispersion ratio of the image-side lens, which is defined by the following equation when the refractive index of the image-side lens for the g-line is ngB2, the refractive index of the image-side lens for the F-line is nFB2, and the refractive index of the image-side lens for the C-line is nCB2: θgFB2=(ngB2−nFB2) / (nFB2−nCB2)

[0059] Conditional expression (13) defines an appropriate relationship between the Abbe number and partial dispersion ratio of the image-side lens in the first lens group G1. Conditional expression (11) defines an appropriate range for the refractive index of the image-side lens in the first lens group G1. Conditional expression (12) defines an appropriate range for the Abbe number of the image-side lens in the first lens group G1. By arranging a positive meniscus lens (a predetermined positive lens) next to the image side of the lens component closest to the object in the first lens group G1, and by arranging an image-side lens that satisfies conditional expressions (13), (11), and (12), the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration can be well corrected. Furthermore, in a microscope objective lens of the type in which the space between the cover glass and the objective lens is filled with an immersion liquid, a positive meniscus lens (a predetermined positive lens) is arranged next to the image side of the lens component closest to the object in the first lens group G1, and an image-side lens that satisfies conditional expressions (13), (11), and (12) is arranged, thereby making it possible to effectively correct axial chromatic aberration and chromatic aberration of magnification. Note that the image-side lens that satisfies conditional expressions (13), (11), and (12) is formed using, for example, the optical glass disclosed in International Publication No. 2021 / 024366.

[0060] If the corresponding value of conditional expression (13) falls below the lower limit, it becomes difficult to correct the secondary spectrum of axial chromatic aberration and the secondary spectrum of lateral chromatic aberration. By setting the lower limit of conditional expression (13) to 0.0002, 0.0004, 0.001, 0.002, or even 0.0025, the effects of each embodiment can be more reliably achieved. Furthermore, the upper limit of conditional expression (13) may be set to 0.1, or even less than 0.05.

[0061] If the corresponding value of conditional expression (11) falls outside the above range, it becomes difficult to effectively correct axial chromatic aberration and lateral chromatic aberration. By setting the upper limit of conditional expression (11) to 1.80, 1.75, or even 1.70, the effects of each embodiment can be more reliably achieved. By setting the lower limit of conditional expression (11) to 1.61, or even 1.62, the effects of each embodiment can be more reliably achieved.

[0062] If the corresponding value of conditional expression (12) falls outside the above range, it becomes difficult to effectively correct axial chromatic aberration and lateral chromatic aberration. By setting the upper limit of conditional expression (12) to 70.00, 68.00, 65.00, or even 63.00, the effects of each embodiment can be more reliably achieved. By setting the lower limit of conditional expression (12) to 40.00, 42.50, or even 45.00, the effects of each embodiment can be more reliably achieved.

[0063] Examples of the microscope objective lens OL according to each embodiment will be described below with reference to the drawings. FIGS. 1, 5, 9, 13, 17, and 21 are optical path diagrams showing the configurations of the microscope objective lenses OL (OL(1) to OL(6)) according to Examples 1 to 6. In FIGS. 1, 5, 9, 13, 17, and 21, each lens group is represented by a combination of the symbol G and a number (or alphabet), and each lens is represented by a combination of the symbol L and a number (or alphabet). In this case, to prevent the number and types of symbols and numbers from becoming too large and cumbersome, lenses, etc., are represented by separate combinations of symbols and numbers for each Example. Therefore, even if the same combinations of symbols and numbers are used between Examples, this does not necessarily mean that the structures are identical.

[0064] Tables 1 to 6 are shown below, with Table 1 showing data on the various specifications for Example 1, Table 2 for Example 2, Table 3 for Example 3, Table 4 for Example 4, Table 5 for Example 5, and Table 6 for Example 6. In each example, the d-line (wavelength λ=587.6 nm), C-line (wavelength λ=656.3 nm), and F-line (wavelength λ=486.1 nm) were selected as the targets for calculating aberration characteristics.

[0065] In the table of [Overall Specifications], β indicates the magnification of the microscope objective lens. f indicates the focal length of the microscope objective lens. φ indicates the pupil diameter of the microscope objective lens. NA indicates the numerical aperture of the microscope objective lens. TL indicates the total length of the microscope objective lens (the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the microscope objective lens).

[0066] In the "Lens Data" table, the surface numbers indicate the order of the lens surfaces from the object side, R indicates the radius of curvature corresponding to each surface number (positive values ​​are used for lens surfaces convex toward the object side), D indicates the axial lens thickness or air gap corresponding to each surface number, nd indicates the refractive index of the optical material corresponding to each surface number at the d-line (wavelength λ=587.6 nm), νd indicates the Abbe number of the optical material corresponding to each surface number with reference to the d-line, and θgF indicates the partial dispersion ratio of the material of the optical element corresponding to each surface number. The "∞" next to the radius of curvature indicates a flat surface or an aperture. The refractive index of air, nd=1.00000, is omitted.

[0067] Let ng be the refractive index of the material of the optical element with respect to the g-line (wavelength λ=435.8 nm), nF be the refractive index of the material of the optical element with respect to the F-line (wavelength λ=486.1 nm), and nC be the refractive index of the material of the optical element with respect to the C-line (wavelength λ=656.3 nm). In this case, the partial dispersion ratio θgF of the material of the optical element is defined by the following equation (A):

[0068] θgF=(ng-nF) / (nF-nC)...(A)

[0069] The [Variable Distance Data] table shows the surface spacing for surface number i, where the surface spacing in the [Lens Data] table is (Di). The [Variable Distance Data] table also shows surface spacing according to the thickness of the cover glass. In the [Variable Distance Data] table (and the [Lens Data] table), CG indicates the thickness of the cover glass. D0 indicates the distance between the cover glass and the lens surface closest to the object of the microscope objective lens.

[0070] The table of [Lens Group Data] shows the first surface (the surface closest to the object) and focal length of each lens group.

[0071] In the following, for all specifications, the focal length f, radius of curvature R, surface spacing D, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this because the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0072] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0073] First Example The first example will be described with reference to FIGS. 1 to 4 and Table 1. FIG. 1 is a cross-sectional view showing the configuration of a microscope objective lens according to the first example. The microscope objective lens OL(1) according to the first example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power. Air is filled between the tip of the microscope objective lens OL(1) according to the first example and a cover glass CV that covers the object. The refractive index of the cover glass CV for the d-line (wavelength λ=587.6 nm) is 1.5244.

[0074] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L101 with a concave surface facing the object side, a positive meniscus lens L102 with a concave surface facing the object side, a first cemented lens CL11 formed by cementing a biconcave negative lens L103 and a biconvex positive lens L104, a positive meniscus lens L105 with a concave surface facing the object side, a second cemented lens CL12 formed by cementing a negative meniscus lens L106 with a convex surface facing the object side and a biconvex positive lens L107, and a third cemented lens CL13 formed by cementing a biconvex positive lens L108 and a biconcave negative lens L109. The positive meniscus lens L101, which is arranged closest to the object side of the first lens group G1, corresponds to the aforementioned predetermined positive lens. The positive meniscus lens L105 in the first lens group G1 corresponds to the image-side lens that satisfies the above-mentioned conditional expressions (8) and (9).

[0075] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a first cemented meniscus lens CL21 formed by cementing a biconvex positive lens L201 and a biconcave negative lens L202 together, and a second cemented meniscus lens CL22 formed by cementing a negative meniscus lens L203 with its concave surface facing the object side and a positive meniscus lens L204 with its concave surface facing the object side. The first cemented meniscus lens CL21 is a cemented meniscus lens with its concave surface facing the image side. The second cemented meniscus lens CL22 is a cemented meniscus lens (meniscus lens component) with its concave surface facing the object side.

[0076] The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 are configured to be movable along the optical axis in accordance with the thickness of the cover glass CV. The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 constitute the sub-group G1a.

[0077] The following Table 1 shows the values ​​of the specifications of the microscope objective lens according to Example 1. Note that the first surface is the object surface.

[0078] (Table 1) [Overall specifications] β=40.0x f=5.000 φ=9.500 NA=0.950 TL=63.550 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.000 2 ∞ 0.170(CG) 1.5244 54.30 3 ∞ 0.540(D0) 4 -3.558 2.971 1.6285 59.17 0.5557 5 -3.040 2.893 6 -13.104 3.869 1.4978 82.57 7 -7.093 0.200 8 -24.625 0.700 1.6127 44.46 9 11.565 8.066 1.5932 67.90 10 -15.703 0.200 11 -54.760 2.097 1.7558 24.71 0.629 12 -28.966 (D12) 13 72.626 0.700 1.7340 51.51 14 13.128 7.604 1.4978 82.57 15 -17.619 0.200 16 29.449 4.349 1.4978 82.57 17 -18.677 3.490 1.6838 37.64 18 58.800 (D18) 19 9.615 4.304 1.4339 95.25 20 -49.045 9.500 1.7321 46.18 21 5.638 3.373 22 -5.119 0.735 1.8010 34.92 23 -9.287 5.198 1.7888 28.43 24 -7.981 140.000 [Variable interval data] CG 0.170 0.110 0.230 D0 0.540 0.547 0.531 D12 1.450 0.280 2.521 D18 1.650 2.820 0.579 [Lens group data] Group Initial surface Focal length G1 4 9.541 G2 19 -29.538

[0079] FIG. 2 shows various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to Example 1. FIG. 3 shows the lateral chromatic aberration of magnification of the microscope objective lens according to Example 1. FIG. 4 shows the coma aberrations (meridional coma and sagittal coma) of the microscope objective lens according to Example 1. Each aberration diagram shows various aberrations when the microscope objective lens is combined with an imaging lens. In each of the aberration diagrams shown in FIGS. 2 to 4, d indicates aberrations for the d-line (wavelength λ=587.6 nm), C indicates aberrations for the C-line (wavelength λ=656.3 nm), and F indicates aberrations for the F-line (wavelength λ=486.1 nm). In the spherical aberration diagrams, the vertical axis shows values ​​normalized with the maximum value of the entrance pupil radius set to 1, and the horizontal axis shows the aberration value [mm] for each light ray. In the aberration diagrams showing field curvature, the solid line indicates the meridional image plane for each wavelength, and the dashed line indicates the sagittal image plane for each wavelength. In the aberration diagrams showing field curvature, the vertical axis indicates image height [mm], and the horizontal axis indicates the aberration value [mm]. In the distortion diagrams, the vertical axis indicates image height [mm], and the horizontal axis indicates the aberration ratio as a percentage (% value). In the aberration diagrams showing lateral chromatic aberration, the vertical axis indicates image height [mm], and the horizontal axis indicates the aberration value [mm]. Each coma aberration diagram shows the aberration value when the image height ratio RFH (Relative Field Height) is 0.00 to 1.00. Note that the same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below, and redundant explanations will be omitted.

[0080] From each aberration diagram, it can be seen that the microscope objective lens according to Example 1 has excellent imaging performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0081] Second Example The second example will be described with reference to FIGS. 5 to 8 and Table 2. FIG. 5 is a cross-sectional view showing the configuration of the microscope objective lens according to the second example. The microscope objective lens OL(2) according to the second example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power. The space between the tip of the microscope objective lens OL(2) according to the second example and the cover glass CV that covers the object is filled with air. The refractive index of the cover glass CV for the d-line (wavelength λ=587.6 nm) is 1.5244.

[0082] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L101 with a concave surface facing the object side, a positive meniscus lens L102 with a concave surface facing the object side, a first cemented lens CL11 formed by cementing a biconcave negative lens L103 and a biconvex positive lens L104, a positive meniscus lens L105 with a concave surface facing the object side, a second cemented lens CL12 formed by cementing a biconcave negative lens L106 and a biconvex positive lens L107, and a third cemented lens CL13 formed by cementing a biconvex positive lens L108 and a negative meniscus lens L109 with a concave surface facing the object side. The positive meniscus lens L101, which is located closest to the object side of the first lens group G1, corresponds to the aforementioned predetermined positive lens. The positive meniscus lens L105 in the first lens group G1 corresponds to the image-side lens that satisfies the above-mentioned conditional expressions (8) and (9).

[0083] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a first cemented meniscus lens CL21 formed by cementing a biconvex positive lens L201 and a biconcave negative lens L202 together, and a second cemented meniscus lens CL22 formed by cementing a negative meniscus lens L203 with its concave surface facing the object side and a positive meniscus lens L204 with its concave surface facing the object side. The first cemented meniscus lens CL21 is a cemented meniscus lens with its concave surface facing the image side. The second cemented meniscus lens CL22 is a cemented meniscus lens (meniscus lens component) with its concave surface facing the object side.

[0084] The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 are configured to be movable along the optical axis in accordance with the thickness of the cover glass CV. The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 constitute the sub-group G1a.

[0085] The values ​​of the specifications of the microscope objective lens according to Example 2 are listed in Table 2 below. Note that the first surface is the object surface.

[0086] (Table 2) [Overall specifications] β = 30.0 times f = 6.667 φ = 12.267 NA = 0.920 TL = 63.540 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.000 2 ∞ 0.170(CG) 1.5244 54.30 3 ∞ 0.540(D0) 4 -3.380 4.171 1.6285 59.17 0.5557 5 -3.832 1.976 6 -25.062 6.388 1.4978 82.57 7 -9.189 0.250 8 -1171.983 0.700 1.6127 44.46 9 11.113 7.792 1.5932 67.90 10 -21.458 0.250 11 -35.057 1.752 1.7558 24.71 0.6290 12 -26.565 (D12) 13 -69.555 0.700 1.7340 51.51 14 13.763 7.271 1.4978 82.57 15 -17.046 0.250 16 39.282 4.014 1.4978 82.57 17 -22.052 0.700 1.6838 37.64 18 -157.531 (D18) 19 12.883 4.151 1.4339 95.25 20 -80.934 10.000 1.7321 46.18 21 8.209 4.041 22 -6.924 0.700 1.7550 52.34 23 -14.385 5.436 1.7380 32.33 24 -9.612 130.000 [Variable interval data] CG 0.170 0.110 0.230 D0 0.540 0.555 0.525 D12 1.500 1.099 1.896 D18 1.500 1.901 1.104 [Lens group data] Group Initial surface Focal length G1 4 9.981 G2 19 -37.435.

[0087] Fig. 6 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to Example 2. Fig. 7 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to Example 2. Fig. 8 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to Example 2. From each aberration diagram, it can be seen that the microscope objective lens according to Example 2 has excellent imaging performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0088] Third Example The third example will be described with reference to FIGS. 9 to 12 and Table 3. FIG. 9 is a cross-sectional view showing the configuration of the microscope objective lens according to the third example. The microscope objective lens OL(3) according to the third example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power. The space between the tip of the microscope objective lens OL(3) according to the third example and the cover glass CV covering the object is filled with an immersion liquid (water). The refractive index of the immersion liquid for the d-line (wavelength λ=587.6 nm) is 1.3326. The refractive index of the cover glass CV for the d-line is 1.5244.

[0089] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a first cemented lens CL11 formed by cementing together a plano-convex positive lens L101 with a flat surface facing the object side and a negative meniscus lens L102 with a concave surface facing the object side; a positive meniscus lens L103 with a concave surface facing the object side; a second cemented lens CL12 formed by cementing together a positive meniscus lens L104 with a concave surface facing the object side and a negative meniscus lens L105 with a concave surface facing the object side; a biconvex positive lens L106; a third cemented lens CL13 formed by cementing together a biconvex positive lens L108, a biconcave negative lens L108, and a biconvex positive lens L109; and a fourth cemented lens CL14 formed by cementing together a negative meniscus lens L110 with a convex surface facing the object side and a biconvex positive lens L111. The positive meniscus lens L103 arranged next to the first cemented lens CL11 on the image side in the first lens group G1 corresponds to the above-mentioned predetermined positive lens, and the positive meniscus lens L104 in the first lens group G1 corresponds to the image-side lens that satisfies the above-mentioned conditional expressions (10) to (13).

[0090] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a first cemented meniscus lens CL21 formed by cementing a positive meniscus lens L201 having a convex surface facing the object side with a negative meniscus lens L202 having a convex surface facing the object side, and a second cemented meniscus lens CL22 formed by cementing a negative meniscus lens L203 having a concave surface facing the object side with a positive meniscus lens L204 having a concave surface facing the object side. The first cemented meniscus lens CL21 is a cemented meniscus lens with a concave surface facing the image side. The second cemented meniscus lens CL22 is a cemented meniscus lens (meniscus lens component) with a concave surface facing the object side.

[0091] The fourth cemented lens CL14 of the first lens group G1 and the second lens group G2 are configured to be movable along the optical axis in accordance with the thickness of the cover glass CV. The fourth cemented lens CL14 of the first lens group G1 constitutes the subgroup G1a described above.

[0092] The values ​​of the specifications of the microscope objective lens according to Example 3 are listed in Table 3 below. Note that the first surface is the object surface.

[0093] (Table 3) [Overall specifications] β = 20.0 times f = 10.000 φ = 19.000 NA = 0.950 TL = 62.975 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.000 1.3326 55.89 2 ∞ 0.170(CG) 1.5244 54.28 3 ∞ 1.055(D0) 1.3326 55.89 4 ∞ 0.990 1.4585 67.85 5 -2.020 6.353 2.0509 26.94 6 -8.390 0.200 7 -21.531 2.929 1.6285 59.17 0.5557 8 -11.392 0.200 9 -85.912 4.693 1.6285 59.17 0.5557 10 -12.890 1.000 1.6127 44.46 11 -24.732 0.200 12 59.134 3.979 1.4560 91.37 13 -35.993 0.200 14 18.298 6.282 1.4343 94.77 15 -47.404 0.700 1.7340 51.47 16 17.642 7.033 1.4339 95.25 17 -32.322 (D17) 18 63.071 0.700 1.8340 37.16 19 12.507 5.653 1.4343 94.77 20 -43.873 0.200 21 13.290 3.308 1.5691 71.34 22 33.145 3.408 1.7321 46.18 23 11.362 6.367 24 -9.283 3.094 1.6393 44.87 25 -32.362 3.687 1.9037 31.34 26 -14.467 140.000 [Variable distance data] CG 0.170 0.110 0.230 D0 1.055 1.109 1.001 D17 1.800 1.717 1.879 [Lens group data] Group Initial surface Focal length G1 4 9.433 G2 21 -402.240

[0094] Fig. 10 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to Example 3. Fig. 11 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to Example 3. Fig. 12 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to Example 3. From each aberration diagram, it can be seen that the microscope objective lens according to Example 3 has excellent imaging performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0095] Fourth Example The fourth example will be described with reference to FIGS. 13 to 16 and Table 4. FIG. 13 is a cross-sectional view showing the configuration of the microscope objective lens according to the fourth example. The microscope objective lens OL(4) according to the fourth example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power. The space between the tip of the microscope objective lens OL(4) according to the fourth example and the cover glass CV that covers the object is filled with air. The refractive index of the cover glass CV for the d-line (wavelength λ=587.6 nm) is 1.5244.

[0096] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L101 with a concave surface facing the object side, a positive meniscus lens L102 with a concave surface facing the object side, a first cemented lens CL11 formed by cementing a biconcave negative lens L103 and a biconvex positive lens L104, a positive meniscus lens L105 with a concave surface facing the object side, a second cemented lens CL12 formed by cementing a negative meniscus lens L106 with a convex surface facing the object side and a biconvex positive lens L107, and a third cemented lens CL13 formed by cementing a biconvex positive lens L108 and a biconcave negative lens L109. The positive meniscus lens L101, which is arranged closest to the object side of the first lens group G1, corresponds to the aforementioned predetermined positive lens. The positive meniscus lens L105 in the first lens group G1 corresponds to the image-side lens that satisfies the above-mentioned conditional expressions (8) and (9).

[0097] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a first cemented meniscus lens CL21 formed by cementing a biconvex positive lens L201 and a biconcave negative lens L202 together, and a second cemented meniscus lens CL22 formed by cementing a negative meniscus lens L203 with its concave surface facing the object side and a positive meniscus lens L204 with its concave surface facing the object side. The first cemented meniscus lens CL21 is a cemented meniscus lens with its concave surface facing the image side. The second cemented meniscus lens CL22 is a cemented meniscus lens (meniscus lens component) with its concave surface facing the object side.

[0098] The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 are configured to be movable along the optical axis in accordance with the thickness of the cover glass CV. The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 constitute the sub-group G1a.

[0099] The values ​​of the specifications of the microscope objective lens according to Example 4 are listed in Table 4 below. Note that the first surface is the object surface.

[0100] (Table 4) [Overall specifications] β = 40.0 times f = 5.000 φ = 9.500 NA = 0.950 TL = 63.499 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.000 2 ∞ 0.170(CG) 1.5244 54.30 3 ∞ 0.540(D0) 4 -4.105 3.159 1.6285 59.17 0.5557 5 -2.998 3.000 6 -13.623 3.651 1.6285 59.17 0.5557 7 -7.981 0.250 8 -14.505 0.700 1.6127 44.46 9 11.828 8.225 1.5932 67.90 10 -13.634 0.250 11 -519.714 2.092 1.6638 27.35 0.6319 12 -50.651 (D12) 13 70.731 0.700 1.7340 51.51 14 13.211 7.483 1.4978 82.57 15 -17.971 0.287 16 25.896 4.301 1.4978 82.57 17 -21.034 2.967 1.6838 37.64 18 48.861 (D18) 19 9.527 4.392 1.4343 94.77 20 -47.855 9.504 1.7321 46.18 21 5.499 3.300 22 -5.020 0.825 1.8010 34.92 23 -9.888 5.379 1.7888 28.43 24 -8.038 140.000 [Variable interval data] CG 0.170 0.110 0.230 D0 0.540 0.545 0.534 D12 1.500 0.353 2.685 D18 1.536 2.724 0.392 [Lens Group Data] Group Initial Surface Focal Length G1 4 9.930 G2 19 -28.940

[0101] Fig. 14 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to Example 4. Fig. 15 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to Example 4. Fig. 16 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to Example 4. From each aberration diagram, it can be seen that the microscope objective lens according to Example 4 has excellent imaging performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0102] Fifth Example The fifth example will be described using FIGS. 17 to 20 and Table 5. FIG. 17 is a cross-sectional view showing the configuration of a microscope objective lens according to the fifth example. The microscope objective lens OL(5) according to the fifth example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power. The space between the tip of the microscope objective lens OL(5) according to the fifth example and the cover glass CV that covers the object is filled with air. The refractive index of the cover glass CV for the d-line (wavelength λ=587.6 nm) is 1.5244.

[0103] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L101 with a concave surface facing the object side, a positive meniscus lens L102 with a concave surface facing the object side, a first cemented lens CL11 formed by cementing a biconcave negative lens L103 and a biconvex positive lens L104, a positive meniscus lens L105 with a concave surface facing the object side, a second cemented lens CL12 formed by cementing a negative meniscus lens L106 with a convex surface facing the object side and a biconvex positive lens L107, and a third cemented lens CL13 formed by cementing a biconvex positive lens L108 and a biconcave negative lens L109. The positive meniscus lens L101, which is arranged closest to the object side of the first lens group G1, corresponds to the aforementioned predetermined positive lens. The positive meniscus lens L105 in the first lens group G1 corresponds to the image-side lens that satisfies the above-mentioned conditional expressions (8) and (9).

[0104] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a first cemented meniscus lens CL21 formed by cementing a biconvex positive lens L201 and a biconcave negative lens L202 together, and a second cemented meniscus lens CL22 formed by cementing a negative meniscus lens L203 with its concave surface facing the object side and a positive meniscus lens L204 with its concave surface facing the object side. The first cemented meniscus lens CL21 is a cemented meniscus lens with its concave surface facing the image side. The second cemented meniscus lens CL22 is a cemented meniscus lens (meniscus lens component) with its concave surface facing the object side.

[0105] The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 are configured to be movable along the optical axis in accordance with the thickness of the cover glass CV. The second cemented lens CL12 and the third cemented lens CL13 of the first lens group G1 constitute the sub-group G1a.

[0106] Table 5 below lists the values ​​of the specifications of the microscope objective lens according to Example 5. Note that the first surface is the object surface.

[0107] (Table 5) [Overall specifications] β = 40.0 times f = 5.000 φ = 9.500 NA = 0.950 TL = 63.531 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.000 2 ∞ 0.170(CG) 1.5244 54.30 3 ∞ 0.540(D0) 4 -3.695 3.035 1.6287 59.20 0.5545 5 -3.037 2.805 6 -12.594 3.733 1.4978 82.57 7 -6.972 0.250 8 -21.421 0.700 1.6127 44.46 9 11.280 7.838 1.5932 67.90 10 -17.009 0.250 11 -74.011 2.629 1.6460 30.86 0.6151 12 -24.445 (D12) 13 90.678 0.700 1.7340 51.51 14 13.544 7.509 1.4978 82.57 15 -17.652 0.250 16 29.670 4.252 1.4978 82.57 17 -20.065 3.336 1.6838 37.64 18 65.602 (D18) 19 9.637 4.399 1.4339 95.25 20 -46.286 9.488 1.7321 46.18 21 5.624 3.454 22 -5.114 0.720 1.8010 34.92 23 -9.918 5.184 1.7888 28.43 24 -7.992 135.000 [Variable interval data] CG 0.170 0.110 0.230 D0 0.540 0.545 0.534 D12 1.500 0.339 2.615 D18 1.500 2.669 0.394 [Lens group data] Group Initial surface Focal length G1 4 9.847 G2 19 -28.671.

[0108] Fig. 18 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to Example 5. Fig. 19 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to Example 5. Fig. 20 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to Example 5. From each aberration diagram, it can be seen that the microscope objective lens according to Example 5 has excellent imaging performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0109] Sixth Example The sixth example will be described with reference to FIGS. 21 to 24 and Table 6. FIG. 21 is a cross-sectional view showing the configuration of the microscope objective lens according to the sixth example. The microscope objective lens OL(6) according to the sixth example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power. The space between the tip of the microscope objective lens OL(6) according to the sixth example and the cover glass CV covering the object is filled with an immersion liquid (water). The refractive index of the immersion liquid for the d-line (wavelength λ=587.6 nm) is 1.3326. The refractive index of the cover glass CV for the d-line is 1.5244.

[0110] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a first cemented lens CL11 formed by cementing together a plano-convex positive lens L101 with a flat surface facing the object side and a negative meniscus lens L102 with a concave surface facing the object side; a positive meniscus lens L103 with a concave surface facing the object side; a second cemented lens CL12 formed by cementing together a positive meniscus lens L104 with a concave surface facing the object side and a negative meniscus lens L105 with a concave surface facing the object side; a biconvex positive lens L106; a third cemented lens CL13 formed by cementing together a biconvex positive lens L108, a biconcave negative lens L108, and a biconvex positive lens L109; and a fourth cemented lens CL14 formed by cementing together a negative meniscus lens L110 with a convex surface facing the object side and a biconvex positive lens L111. The positive meniscus lens L103 arranged next to the first cemented lens CL11 on the image side in the first lens group G1 corresponds to the above-mentioned predetermined positive lens, and the positive meniscus lens L104 in the first lens group G1 corresponds to the image-side lens that satisfies the above-mentioned conditional expressions (10) to (13).

[0111] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a first cemented meniscus lens CL21 formed by cementing a positive meniscus lens L201 having a convex surface facing the object side with a negative meniscus lens L202 having a convex surface facing the object side, and a second cemented meniscus lens CL22 formed by cementing a negative meniscus lens L203 having a concave surface facing the object side with a positive meniscus lens L204 having a concave surface facing the object side. The first cemented meniscus lens CL21 is a cemented meniscus lens with a concave surface facing the image side. The second cemented meniscus lens CL22 is a cemented meniscus lens (meniscus lens component) with a concave surface facing the object side.

[0112] The fourth cemented lens CL14 of the first lens group G1 and the second lens group G2 are configured to be movable along the optical axis in accordance with the thickness of the cover glass CV. The fourth cemented lens CL14 of the first lens group G1 constitutes the subgroup G1a described above.

[0113] Table 6 below lists the values ​​of the specifications of the microscope objective lens according to Example 6. Note that the first surface is the object surface.

[0114] (Table 6) [Overall specifications] β = 20.0 times f = 10.000 φ = 19.000 NA = 0.950 TL = 62.975 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.000 1.3326 55.89 2 ∞ 0.170(CG) 1.5244 54.28 3 ∞ 1.055(D0) 1.3326 55.89 4 ∞ 0.990 1.4585 67.85 5 -1.976 6.211 2.0509 26.94 6 -8.274 0.200 7 -19.747 2.923 1.6693 49.05 0.5681 8 -10.945 0.200 9 -109.950 5.369 1.6285 59.17 0.5557 10 -11.683 1.000 1.6127 44.46 11 -27.810 0.200 12 53.865 4.109 1.4560 91.37 13 -36.420 0.200 14 18.273 6.254 1.4343 94.77 15 -49.852 0.700 1.7340 51.47 16 17.007 6.434 1.4339 95.25 17 -32.905 (D17) 18 51.956 0.700 1.8340 37.16 19 12.028 5.596 1.4343 94.77 20 -53.519 0.200 21 12.434 3.621 1.5691 71.34 22 33.553 2.771 1.7321 46.18 23 10.691 6.753 24 -9.194 3.088 1.6393 44.87 25 -30.497 3.657 1.9037 31.34 26 -14.194 136.000 [Variable distance data] CG 0.170 0.110 0.230 D0 1.055 1.109 1.001 D17 1.800 1.720 1.884 [Lens group data] Group Initial surface Focal length G1 4 9.366 G2 21 -426.746.

[0115] Fig. 22 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to Example 6. Fig. 23 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to Example 6. Fig. 24 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to Example 6. From each aberration diagram, it can be seen that the microscope objective lens according to Example 6 satisfactorily corrects various aberrations, including chromatic aberration, over a wide wavelength range, and has excellent imaging performance.

[0116] Because the microscope objective lens according to each example is an infinity-corrected lens, it is used in combination with an imaging lens that forms an image from the light from the microscope objective lens. An example of an imaging lens used in combination with a microscope objective lens will be described using FIG. 25 and Table 7. FIG. 25 is a cross-sectional view showing the configuration of an imaging lens used in combination with a microscope objective lens according to each example. The aberration diagrams for the microscope objective lens according to each example are for when the objective lens is used in combination with this imaging lens. The imaging lens IL shown in FIG. 25 is composed of, arranged in order from the object side, a cemented lens formed by cementing a biconvex positive lens L51 and a biconcave negative lens L52, and a cemented lens formed by cementing a biconvex positive lens L53 and a biconcave negative lens L54. The imaging lens IL is disposed on the image side of the microscope objective lens according to each example. FIG. 25 also shows the entrance pupil plane Pu of the imaging lens IL.

[0117] The specifications of the imaging lens are listed in Table 7 below. In the [Overall Specifications] table, f' indicates the focal length of the imaging lens. In the [Lens Data] table, the surface numbers R, D, nd, and vd are the same as those shown in the explanations of Tables 1 to 6 above.

[0118] (Table 7) [Overall specifications] f' = 200 [Lens data] Surface number R D nd νd 1 75.043 5.100 1.6228 57.03 2 -75.043 2.000 1.7495 35.19 3 1600.580 7.500 4 50.256 5.100 1.6676 41.96 5 -84.541 1.800 1.6127 44.40 6 36.911 168.438

[0119] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below, which summarizes the values ​​corresponding to each of the conditional expressions (1) to (13) for all the examples (Examples 1 to 6). Conditional expression (1) 0<θgFA+0.0015×νdA−0.6395 Conditional expression (2) 1.60<ndA<1.85 Conditional expression (3) 39.50<νdA<75.00 Conditional expression (4) 0<θgFA+0.0016×νdA−0.6460 Conditional expression (5) -10<GAR1 / DGA1<1 Conditional expression (6) -10<GAR2 / DGA2<0 Conditional expression (7) -0.3<(GAR2-GAR1+GAL) / TL<0.3 Conditional expression (8) 0<θgFB1+0.0015×νdB1-0.6395 Conditional expression (9) νdB1<40.00 Conditional expression (10) 0<θgFB2+0.0015×νdB2−0.6395 Conditional expression (11) 1.60<ndB2<1.85 Conditional expression (12) 39.50<νdB2<75.00 Conditional expression (13) 0<θgFB2+0.0016×νdB2−0.6460

[0120] [Values ​​corresponding to conditional expressions] (Examples 1 to 3) Conditional Expression Example 1 Example 2 Example 3 (1) 0.0050 0.0050 0.0050 (2) 1.6285 1.6285 1.6285 (3) 59.17 59.17 59.17 (4) 0.0044 0.0044 0.0044 (5) -5.0111 -4.7611 -2.4557 (6) -0.8259 -0.7852 -0.9740 (7) 0.0549 0.0585 0.2075 (8) 0.0266 0.0266 - (9) 24.71 24.71 - (10) - - 0.0050 (11) - - 1.6285 (12) - - 59.17 (13) - - 0.0044 [Conditional expression corresponding values] (Examples 4 to 6) Conditional expression Example 4 Example 5 Example 6 (1) 0.0050 0.0038 0.0022 (2) 1.6285 1.6287 1.6693 (3) 59.17 59.20 49.05 (4) 0.0044 0.0032 0.0006 (5) -5.7812 -5.2049 -2.2891 (6) -0.7749 -0.8110 -0.9477 (7) 0.0672 0.0581 0.1862 (8) 0.0334 0.0219 - (9) 27.35 30.86 - (10) - - 0.0050 (11) - - 1.6285 (12) - - 59.17 (13) - - 0.0044.

[0121] According to each of the above-described embodiments, it is possible to realize a microscope objective lens in which various aberrations including chromatic aberration are well corrected.

[0122] Here, the above examples show specific examples of this embodiment, and this embodiment is not limited to these.

[0123] G1: First lens group G2: Second lens group

Claims

1. the first lens group and the second lens group having negative refractive power, the second lens group includes, arranged in order from the object side along the optical axis, a cemented meniscus lens having a concave surface facing the image side, and a meniscus lens component having a concave surface facing the object side, The first lens group is a microscope objective lens having a predetermined positive meniscus lens that satisfies the following conditional expression: 0<θgFA+0.0015×νdA-0.6395 1.60<ndA<1.85 39.50<νdA<75.00 where ndA is the refractive index of the predetermined positive lens with respect to the d line. νdA: Abbe number of the given positive lens θgFA: partial dispersion ratio of the specified positive lens, which is defined by the following formula when the refractive index of the specified positive lens with respect to the g-line is ngA, the refractive index of the specified positive lens with respect to the F-line is nFA, and the refractive index of the specified positive lens with respect to the C-line is nCA. θgFA=(ngA-nFA) / (nFA-nCA)

2. the first lens group and the second lens group having negative refractive power, the second lens group includes, arranged in order from the object side along the optical axis, a cemented meniscus lens having a concave surface facing the image side, and a meniscus lens component having a concave surface facing the object side, The first lens group is a microscope objective lens having a predetermined positive meniscus lens that satisfies the following conditional expression: 0<θgFA+0.0016×νdA-0.6460 1.60<ndA<1.85 39.50<νdA<75.00 where ndA is the refractive index of the predetermined positive lens with respect to the d line. νdA: Abbe number of the given positive lens θgFA: partial dispersion ratio of the specified positive lens, which is defined by the following formula when the refractive index of the specified positive lens with respect to the g-line is ngA, the refractive index of the specified positive lens with respect to the F-line is nFA, and the refractive index of the specified positive lens with respect to the C-line is nCA. θgFA=(ngA-nFA) / (nFA-nCA)

3. 3. The microscope objective lens according to claim 1, wherein the predetermined positive meniscus lens is a positive meniscus lens that satisfies the following conditional expression: -10<GAR1 / DGA1<1 where GAR1 is the radius of curvature of the lens surface on the object side of the positive meniscus lens. DGA1: the distance on the optical axis from the object-side lens surface of the positive meniscus lens to the object

4. 3. The microscope objective lens according to claim 1, wherein the predetermined positive meniscus lens is a positive meniscus lens that satisfies the following conditional expression: -10<GAR2 / DGA2<0 where GAR2 is the radius of curvature of the image-side lens surface of the positive meniscus lens. DGA2: the distance on the optical axis from the image-side lens surface of the positive meniscus lens to the object

5. 3. The microscope objective lens according to claim 1, wherein the predetermined positive meniscus lens is a positive meniscus lens that satisfies the following conditional expression: -0.3<(GAR2-GAR1+GAL) / TL<0.3 where GAR1 is the radius of curvature of the lens surface on the object side of the positive meniscus lens. GAR2: Radius of curvature of the image-side lens surface of the positive meniscus lens GAL: The length of the positive meniscus lens on the optical axis TL: the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the microscope objective lens

6. 3. The microscope objective lens according to claim 1, wherein the positive meniscus lens is disposed closest to the object side in the first lens group.

7. The microscope objective lens according to claim 6 , wherein the first lens group has a subgroup movable along the optical axis.

8. the first lens group includes an image-side lens having a positive refractive power, the image-side lens being disposed closer to the image side than the positive meniscus lens; 7. The microscope objective lens according to claim 6, wherein the image-side lens satisfies the following condition: 0<θgFB1+0.0015×νdB1-0.6395 νdB1<40.00 where νdB1 is the Abbe number of the image-side lens. θgFB1: partial dispersion ratio of the image-side lens, which is defined by the following formula when the refractive index of the image-side lens with respect to the g-line is ngB1, the refractive index of the image-side lens with respect to the F-line is nFB1, and the refractive index of the image-side lens with respect to the C-line is nCB1. θgFB1=(ngB1-nFB1) / (nFB1-nCB1)

9. the first lens group has a lens component that is disposed closest to the object side in the first lens group and has a flat surface facing the object side, 3. The microscope objective lens according to claim 1, wherein the positive meniscus lens is arranged next to the image side of the lens component.

10. the second lens group is movable along an optical axis; The microscope objective lens according to claim 9 , wherein the first lens group has a subgroup that is movable along the optical axis together with the second lens group.

11. the first lens group includes an image-side lens having a positive refractive power, the image-side lens being disposed closer to the image side than the positive meniscus lens; 10. The microscope objective lens according to claim 9, wherein the image-side lens satisfies the following condition: 0<θgFB2+0.0015×νdB2-0.6395 1.60<ndB2<1.85 39.50<νdB2<75.00 where ndB2 is the refractive index of the image-side lens with respect to the d-line νdB2: Abbe number of the image-side lens θgFB2: partial dispersion ratio of the image side lens, which is defined by the following formula when the refractive index of the image side lens with respect to the g line is ngB2, the refractive index of the image side lens with respect to the F line is nFB2, and the refractive index of the image side lens with respect to the C line is nCB2. θgFB2=(ngB2-nFB2) / (nFB2-nCB2)

12. the first lens group includes an image-side lens having a positive refractive power, the image-side lens being disposed closer to the image side than the positive meniscus lens; 10. The microscope objective lens according to claim 9, wherein the image-side lens satisfies the following condition: 0<θgFB2+0.0016×νdB2-0.6460 1.60<ndB2<1.85 39.50<νdB2<75.00 where ndB2 is the refractive index of the image-side lens with respect to the d-line νdB2: Abbe number of the image-side lens θgFB2: partial dispersion ratio of the image side lens, which is defined by the following formula when the refractive index of the image side lens with respect to the g line is ngB2, the refractive index of the image side lens with respect to the F line is nFB2, and the refractive index of the image side lens with respect to the C line is nCB2. θgFB2=(ngB2-nFB2) / (nFB2-nCB2)

13. 3. A microscope optical system comprising: the microscope objective lens according to claim 1; and an imaging lens that forms an image from light from the microscope objective lens.

14. A microscope apparatus comprising the microscope objective lens according to claim 1 or 2.