Microscope objective lens, microscope optical system, and microscope device

Abstract

To provide a microscope objective lens which is well corrected for aberrations, a microscope optical system, and a microscope device.SOLUTION: A microscope objective lens OL provided herein consists of a first lens group G1, a second lens group G2 having positive refractive power, a third lens group G3 having a concave surface on the image side, and a fourth lens group G4 having a concave surface on the object side, arranged in order from the object side along an optical axis, the first lens group G1 consisting of a positive plano-convex lens having a flat surface on the object side and a negative lens arranged in order from the object side along the optical axis. The microscope objective lens satisfies the following conditional expressions: 1.8<H1 / H2<3.5, 1.3<DLe / H2<3.5.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[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). In such objective lenses, it is required to correct various aberrations including chromatic aberration of magnification well.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The microscope objective lens according to the present invention comprises a first lens group, a second lens group having a positive refractive power, a third lens group having a concave surface facing the image side, and a fourth lens group having a concave surface facing the object side, which are arranged in order from the object side along the optical axis. The first lens group consists of a plano - convex positive lens with a plane facing the object side and a negative lens, which are arranged in order from the object side along the optical axis, and satisfies the following conditional expressions. 1.8 < H1 / H2 < 3.5 1.3 < DLe / H2 < 3.5 However, H1: the distance between the optical axis and the ray farthest from the optical axis among the rays emitted from an object on the optical axis in the second lens group H2: the distance between the optical axis and the ray farthest from the optical axis among the rays on the image - side lens surface of the final lens arranged most on the image side in the microscope objective lens among the rays emitted from an object on the optical axis DLe: the length of the final lens on the optical axis

[0005] The microscope optical system according to the present invention includes the above-described microscope objective lens and a second objective lens that condenses light from the microscope objective lens.

[0006] The microscope apparatus according to the present invention includes the above-described microscope objective lens.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] Hereinafter, preferred embodiments according to the present invention will be described. First, a microscope optical system and a confocal fluorescence microscope (microscope apparatus) equipped with the microscope objective lens according to the present embodiment will be described with reference to FIG. 18. As shown in FIG. 18, the confocal fluorescence microscope 1 includes a stage 10, a light source 20, an illumination optical system 30, a microscope optical system 40, and a detection unit 50. In the following description, the coordinate axis extending in the optical axis direction of the microscope objective lens of the confocal fluorescence microscope 1 is defined as the z-axis. Also, the coordinate axes extending in directions orthogonal to each other in the plane perpendicular to the z-axis are defined as the x-axis and the y-axis, respectively.

[0009] On the stage 10, for example, a sample SA held between a slide glass (not shown) and a cover glass (not shown) is placed. Also, on the stage 10, a sample SA accommodated in a sample container (not shown) together with an immersion liquid may be placed. The sample SA contains a fluorescent substance such as a fluorescent dye. The sample SA is, for example, cells or the like that have been fluorescently stained in advance. Near the stage 10, a stage drive unit 11 is provided. The stage drive unit 11 moves the stage 10 along the z-axis.

[0010] The light source 20 generates excitation light in a predetermined wavelength band. As the light source 20, for example, a laser light source or the like capable of emitting laser light (excitation light) in a predetermined wavelength band is used. The predetermined wavelength band is set to a wavelength band capable of exciting the sample SA containing the fluorescent substance. The excitation light emitted from the light source 20 enters the illumination optical system 30.

[0011] The illumination optical system 30 illuminates the sample SA on the stage 10 with the excitation light emitted from the light source 20. The illumination optical system 30 includes a collimator lens 31, a beam splitter 33, and a scanner 34 in order from the light source 20 side toward the sample SA side. Further, the illumination optical system 30 includes the microscope objective lens OL of the microscope optical system 40. The collimator lens 31 makes the excitation light emitted from the light source 20 into parallel light.

[0012] The beam splitter 33 has the property that the excitation light from the light source 20 is reflected and the fluorescence from the sample SA is transmitted. The beam splitter 33 reflects the excitation light from the light source 20 toward the sample SA on the stage 10. The beam splitter 33 transmits the fluorescence generated in the sample SA toward the detection unit 50. An excitation filter 32 that transmits the excitation light from the light source 20 is disposed between the beam splitter 33 and the collimator lens 31. A fluorescence filter 35 that transmits the fluorescence from the sample SA is disposed between the beam splitter 33 and the second objective lens IL of the microscope optical system 40.

[0013] The scanner 34 scans the sample SA with the excitation light from the light source 20 in two directions, the x direction and the y direction. As the scanner 34, for example, a galvanometer scanner, a resonant scanner, or the like is used.

[0014] The microscope optical system 40 condenses the fluorescence generated in the sample SA. The microscope optical system 40 includes a microscope objective lens OL and a second objective lens IL in order from the sample SA side toward the detection unit 50 side. Further, the microscope optical system 40 includes the scanner 34 and the beam splitter 33 disposed between the microscope objective lens OL and the second objective lens IL. The microscope objective lens OL is disposed to face upward above the stage 10 on which the sample SA is placed. The microscope objective lens OL condenses the excitation light from the light source 20 and irradiates the sample SA on the stage 10. Further, the microscope objective lens OL receives the fluorescence generated in the sample SA and makes it into parallel light. The second objective lens IL condenses the fluorescence (parallel light) from the microscope objective lens OL.

[0015] The detection unit 50 detects the fluorescence generated in the sample SA via the microscope optical system 40. As the detection unit 50, for example, a photomultiplier tube is used. A pinhole 45 is provided between the microscope optical system 40 and the detection unit 50. The pinhole 45 is disposed at a position conjugate to the focal position on the sample SA side of the microscope objective lens OL. The pinhole 45 allows only the light from the focal plane of the microscope objective lens OL (a plane perpendicular to the optical axis of the microscope objective lens OL passing through the focal position of the microscope objective lens OL) or a plane shifted in the optical axis direction within a predetermined deviation tolerance range from the focal plane to pass through, and blocks other light.

[0016] In the confocal fluorescence microscope 1 configured as described above, the excitation light emitted from the light source 20 passes through the collimator lens 31 and becomes parallel light. The excitation light that has passed through the collimator lens 31 enters the beam splitter 33 through the excitation filter 32. The excitation light that has entered the beam splitter 33 is reflected by the beam splitter 33 and enters the scanner 34. The scanner 34 scans the sample SA with the excitation light that has entered the scanner 34 in two directions, the x direction and the y direction. The excitation light that has entered the scanner 34 passes through the scanner 34, passes through the microscope objective lens OL, and is focused on the focal plane of the microscope objective lens OL. The portion of the sample SA where the excitation light is focused (i.e., the portion overlapping the focal plane of the microscope objective lens OL) is two-dimensionally scanned in two directions, the x direction and the y direction, by the scanner 34. Thereby, the illumination optical system 30 illuminates the sample SA on the stage 10 with the excitation light emitted from the light source 20.

[0017] When the excitation light is irradiated, the fluorescent substance contained in the sample SA is excited to emit fluorescence. The fluorescence from the sample SA passes through the microscope objective lens OL and becomes parallel light. The fluorescence that has passed through the microscope objective lens OL enters the beam splitter 33 through the scanner 34. The fluorescence incident on the beam splitter 33 passes through the beam splitter 33 and reaches the fluorescence filter 35. The fluorescence that has reached the fluorescence filter 35 passes through the fluorescence filter 35 and then through the second objective lens IL, and is focused at a position conjugate to the focal position of the microscope objective lens OL. The fluorescence focused at a position conjugate to the focal position of the microscope objective lens OL passes through the pinhole 45 and enters the detection unit 50.

[0018] The detection unit 50 performs photoelectric conversion of the light (fluorescence) incident on the detection unit 50, and generates data corresponding to the light amount (brightness) of the light as a detection signal of the light. The detection unit 50 outputs the generated data to a control unit (not shown). The control unit performs a process of arranging the data input from the detection unit 50 as data for one pixel in synchronization with the two-dimensional scanning by the scanner 34, thereby generating one image data in which data for a plurality of pixels are arranged two-dimensionally (in two directions). In this way, the control unit can acquire an image of the sample SA.

[0019] As an example of the microscope apparatus according to the present embodiment, the confocal fluorescence microscope 1 has been described, but the present invention is not limited thereto. For example, the microscope apparatus according to the present embodiment may be a confocal microscope, a multi-photon excitation microscope, or the like. Further, the confocal fluorescence microscope 1 may be an upright microscope or an inverted microscope.

[0020] Next, the microscope objective lens according to this embodiment will be described. As an example of the microscope objective lens OL according to this embodiment, the microscope objective lens OL(1) shown in FIG. 1 includes a first lens group G1, a second lens group G2 having a positive refractive power, a third lens group G3 with a concave surface facing the image plane side, and a fourth lens group G4 with a concave surface facing the object side, arranged in order from the object side along the optical axis. The first lens group G1 is composed of a positive lens (L101) with a plano-convex shape having a plane facing the object side and a negative lens (L102), arranged in order from the object side along the optical axis. Note that it is desirable that the positive lens (L101) and the negative lens (L102) of the first lens group G1 be joined. Also, in FIG. 1 and the like, the object OB indicates the object plane.

[0021] Under the above configuration, the microscope objective lens OL according to this embodiment satisfies the following conditional expressions (1) and (2). 1.8 < H1 / H2 < 3.5 ···(1) 1.3 < DLe / H2 < 3.5 ···(2) However, H1: The distance between the optical axis and the ray that is farthest from the optical axis in the second lens group G2 among the rays emitted from the object OB on the optical axis. H2: The distance between the optical axis and the ray that is farthest from the optical axis on the image-side lens surface of the final lens Le that is arranged most on the image side in the microscope objective lens OL among the rays emitted from the object OB on the optical axis. DLe: The length of the final lens Le on the optical axis.

[0022] According to this embodiment, it is possible to obtain a microscope objective lens in which various aberrations including chromatic aberration of magnification are well corrected, as well as a microscope optical system and a microscope apparatus equipped with this microscope objective lens. The microscope objective lens OL according to this embodiment may be the optical system OL(2) shown in FIG. 5, may be the optical system OL(3) shown in FIG. 9, or may be the optical system OL(4) shown in FIG. 13.

[0023] Conditional expression (1) defines an appropriate relationship between the distance between the optical axis and the ray that is farthest from the optical axis among the rays emitted from the object OB on the optical axis in the second lens group G2, and the distance between the optical axis and the ray that is farthest from the optical axis on the image-side lens surface of the final lens Le among the rays emitted from the object OB on the optical axis. By satisfying conditional expression (1), in a microscope objective lens with a high magnification and a large numerical aperture, spherical aberration can be corrected well.

[0024] When the corresponding value of conditional expression (1) exceeds the upper limit value, it becomes difficult to correct spherical aberration while increasing the magnification and the numerical aperture. By setting the upper limit value of conditional expression (1) to 3.45, 3.4, 3.25, 3.0, 2.75, 2.5, and further 2.3, the effects of this embodiment can be made more certain.

[0025] Even when the corresponding value of conditional expression (1) is below the lower limit value, it becomes difficult to correct spherical aberration while increasing the magnification and the numerical aperture. By setting the lower limit value of conditional expression (1) to 1.85 and further 1.9, the effects of this embodiment can be made more certain.

[0026] Conditional expression (2) defines an appropriate relationship between the length of the final lens Le on the optical axis and the distance between the optical axis and the ray that is farthest from the optical axis on the image-side lens surface of the final lens Le among the rays emitted from the object OB on the optical axis. By satisfying conditional expression (2), chromatic aberration of magnification can be corrected well.

[0027] When the corresponding value of conditional expression (2) exceeds the upper limit value, the length of the final lens Le on the optical axis is too large, making it difficult to correct coma aberration. By setting the upper limit value of conditional expression (2) to 3.4, 3.2, and further 3.17, the effects of this embodiment can be made more certain.

[0028] When the corresponding value of conditional expression (2) is less than the lower limit value, since the length on the optical axis of the final lens Le is small, it becomes difficult to correct the chromatic aberration of magnification. By setting the lower limit value of conditional expression (2) to 1.33, 1.35, and further 1.37, the effects of the present embodiment can be made more certain.

[0029] In the microscope objective lens OL according to the present embodiment, the fourth lens group G4 is composed of a negative lens L401 with a concave surface facing the object side and a positive lens L402 arranged in order from the object side along the optical axis, and it is desirable that the final lens Le is the positive lens L402 of the fourth lens group G4. Note that it is desirable that the negative lens L401 and the positive lens L402 of the fourth lens group G4 are joined. The third lens group G3 is desirably composed of a positive lens L301 and a negative lens L302 with a concave surface facing the image side arranged in order from the object side along the optical axis. It is desirable that the positive lens L301 and the negative lens L302 of the third lens group G3 are joined.

[0030] The microscope objective lens OL according to the present embodiment preferably satisfies the following conditional expressions (3) and (4). 20 < νdLe < 30 ···(3) 0 < -0.0035×(νdLe - 20) + 0.63 - θgFLe ···(4) However, νdLe: Abbe number of the final lens Le θgFLe: partial dispersion ratio of the final lens Le. When the refractive index of the final lens Le with respect to the g-line is ngLe, the refractive index of the final lens Le with respect to the F-line is nFLe, and the refractive index of the final lens Le with respect to the C-line is nCLe, it is defined by the following formula θgFLe = (ngLe - nFLe) / (nFLe - nCLe)

[0031] Conditional expression (3) defines an appropriate range for the Abbe number of the final lens Le. By satisfying conditional expression (3), the chromatic aberration of magnification can be corrected well.

[0032] When the corresponding value of conditional expression (3) exceeds the upper limit value, it becomes difficult to correct the magnification chromatic aberration. By setting the upper limit value of conditional expression (3) to 28.5, 26.5, and further to 25.5, the effects of this embodiment can be made more certain.

[0033] Even when the corresponding value of conditional expression (3) is below the lower limit value, it becomes difficult to correct the magnification chromatic aberration. By setting the lower limit value of conditional expression (3) to 21.5, 23, and further to 24, the effects of this embodiment can be made more certain.

[0034] Conditional expression (4) defines an appropriate relationship between the Abbe number of the final lens Le and the partial dispersion ratio of the final lens Le. By satisfying conditional expression (4), the magnification chromatic aberration can be corrected well. When the corresponding value of conditional expression (4) is below the lower limit value, it becomes difficult to correct the magnification chromatic aberration.

[0035] The microscope objective lens OL according to this embodiment may satisfy the following conditional expression (3-1). 20 < νdLe < 26 ···(3-1)

[0036] Conditional expression (3-1) is the same formula as conditional expression (3), and the same effects as conditional expression (3) can be obtained. By setting the upper limit value of conditional expression (3-1) to 25.75 and further to 25.5, the effects of this embodiment can be made more certain. By setting the lower limit value of conditional expression (3-1) to 21.5, 23, and further to 24, the effects of this embodiment can be made more certain.

[0037] In the microscope objective lens OL according to this embodiment, the second lens group G2 has a plurality of positive lenses, and among the plurality of positive lenses of the second lens group G2, it is desirable that at least one positive lens satisfies the following conditional expressions (5) and (6). 20 < νdLp < 40 ···(5) 0.55 < θgFLp ···(6) However, νdLp: Abbe number of the positive lens θgFLp: The partial dispersion ratio of the positive lens. When the refractive index of the positive lens with respect to the g-line is ngLp, the refractive index with respect to the F-line is nFLp, and the refractive index with respect to the C-line is nCLp, it is defined by the following formula θgFLp=(ngLp - nFLp) / (nFLp - nCLp)

[0038] Conditional expression (5) defines an appropriate range for the Abbe number of the positive lens of the second lens group G2. By satisfying conditional expression (5), the secondary spectrum of axial chromatic aberration can be corrected well.

[0039] When the corresponding value of conditional expression (5) exceeds the upper limit value, it becomes difficult to correct the secondary spectrum of axial chromatic aberration. By setting the upper limit value of conditional expression (5) to 38.5, 37.5, 35, 32, and further to 30, the effects of the present embodiment can be made more reliable.

[0040] Even when the corresponding value of conditional expression (5) is below the lower limit value, it becomes difficult to correct the secondary spectrum of axial chromatic aberration. By setting the lower limit value of conditional expression (5) to 20.5 and further to 21, the effects of the present embodiment can be made more reliable.

[0041] Conditional expression (6) defines an appropriate range for the partial dispersion ratio of the positive lens of the second lens group G2. By satisfying conditional expression (6), the secondary spectrum of axial chromatic aberration can be corrected well.

[0042] When the corresponding value of conditional expression (6) is below the lower limit value, it becomes difficult to correct the secondary spectrum of axial chromatic aberration. By setting the lower limit value of conditional expression (6) to 0.57 and further to 0.60, the effects of the present embodiment can be made more reliable.

[0043] In the microscope objective lens OL according to the present embodiment, it is desirable that at least one of the plurality of positive lenses of the second lens group G2 satisfies the following conditional expression (7). 0 < fLp / f < 45 ···(7) However, fLp: focal length of the positive lens f: focal length of the microscope objective lens OL

[0044] The conditional expression (7) defines an appropriate relationship between the focal length of the positive lens of the second lens group G2 and the focal length of the microscope objective lens OL. By satisfying the conditional expression (7), the secondary spectrum of the axial chromatic aberration can be corrected well.

[0045] When the corresponding value of the conditional expression (7) exceeds the upper limit value, it becomes difficult to correct the secondary spectrum of the axial chromatic aberration. By setting the upper limit value of the conditional expression (7) to 42.5, 40, 35, 30, and further to 25, the effects of the present embodiment can be made more certain.

[0046] Even when the corresponding value of the conditional expression (7) is below the lower limit value, it becomes difficult to correct the secondary spectrum of the axial chromatic aberration. By setting the lower limit value of the conditional expression (7) to 5, 7.5, 10, and further to 12, the effects of the present embodiment can be made more certain.

[0047] In the microscope objective lens OL according to the present embodiment, at least one positive lens among the plurality of positive lenses of the second lens group G2 may satisfy the following conditional expression (7-1). 12.5 < fLp / f < 45 ···(7-1)

[0048] The conditional expression (7-1) is the same conditional expression as the conditional expression (7), and the same effects as the conditional expression (7) can be obtained. By setting the upper limit value of the conditional expression (7-1) to 42.5, 40, 35, 30, and further to 25, the effects of the present embodiment can be made more certain. By setting the lower limit value of the conditional expression (7-1) to 13, 13.5, 14, 14.5, and further to 15, the effects of the present embodiment can be made more certain.

[0049] In the microscope objective lens OL according to the present embodiment, it is desirable that the positive lens of the second lens group G2 is disposed on the image side with respect to the lens surface through which the light ray farthest from the optical axis in the second lens group G2 passes. In the microscope objective lens OL according to the present embodiment, the positive lens of the second lens group G2 may be disposed on the most object side of the second lens group G2.

[0050] It is desirable that the microscope objective lens OL according to the present embodiment satisfies the following conditional expression (8). 1.75 < f1 / f < 2.5 ···(8) However, f1: focal length of the first lens group G1 f: focal length of the microscope objective lens OL

[0051] The conditional expression (8) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the microscope objective lens OL. By satisfying the conditional expression (8), the field curvature can be corrected favorably.

[0052] When the corresponding value of the conditional expression (8) exceeds the upper limit value, it becomes difficult to correct the field curvature. By setting the upper limit value of the conditional expression (8) to 2.45, 2.35, 2.25, and further 2.2, the effect of the present embodiment can be made more certain.

[0053] Even when the corresponding value of the conditional expression (8) is below the lower limit value, it becomes difficult to correct the field curvature. By setting the lower limit value of the conditional expression (8) to 1.76 and further 1.78, the effect of the present embodiment can be made more certain.

[0054] It is desirable that the microscope objective lens OL according to the present embodiment satisfies the following conditional expression (9). 3 < f2 / f < 7 ···(9) However, f2: focal length of the second lens group G2 f: focal length of the microscope objective lens OL

[0055] The conditional expression (9) defines an appropriate relationship between the focal length of the second lens group G2 and the focal length of the microscope objective lens OL. By satisfying the conditional expression (9), it is possible to satisfactorily correct spherical aberration, coma aberration, and axial chromatic aberration in a microscope objective lens with a large numerical aperture.

[0056] When the corresponding value of the conditional expression (9) exceeds the upper limit value, it becomes difficult to correct spherical aberration, coma aberration, and axial chromatic aberration while increasing the numerical aperture. By setting the upper limit value of the conditional expression (9) to 6.8, 6.5, 6.3, 6, and further 5.85, the effects of the present embodiment can be made more certain.

[0057] Even when the corresponding value of the conditional expression (9) is below the lower limit value, it becomes difficult to correct spherical aberration, coma aberration, and axial chromatic aberration while increasing the numerical aperture. By setting the lower limit value of the conditional expression (9) to 3.15, 3.3, 3.4, and further 3.5, the effects of the present embodiment can be made more certain.

[0058] The microscope objective lens OL according to the present embodiment preferably satisfies the following conditional expression (10). f3 / f < 0 ···(10) However, f3: the focal length of the third lens group G3 f: the focal length of the microscope objective lens OL

[0059] The conditional expression (10) defines an appropriate relationship between the focal length of the third lens group G3 and the focal length of the microscope objective lens OL. By satisfying the conditional expression (10), it is possible to satisfactorily correct field curvature, coma aberration, and astigmatism in a microscope objective lens with a large numerical aperture.

[0060] When the corresponding value of the conditional expression (10) exceeds the upper limit value, it becomes difficult to correct field curvature, coma aberration, and astigmatism while increasing the numerical aperture. By setting the upper limit value of the conditional expression (10) to -1, -5, -7.5, and further -10, the effects of the present embodiment can be made more certain.

[0061] The microscope objective lens OL according to this embodiment desirably satisfies the following conditional expression (11). f4 / f < 0 ···(11) However, f4: focal length of the fourth lens group G4 f: focal length of the microscope objective lens OL

[0062] The conditional expression (11) defines an appropriate relationship between the focal length of the fourth lens group G4 and the focal length of the microscope objective lens OL. By satisfying the conditional expression (11), in a microscope objective lens with a large numerical aperture, field curvature, coma aberration, and astigmatism can be corrected well.

[0063] When the corresponding value of the conditional expression (11) exceeds the upper limit value, it becomes difficult to correct field curvature, coma aberration, and astigmatism while increasing the numerical aperture. By setting the upper limit value of the conditional expression (11) to -1, -2.5, -5, -7.5, and further -10, the effects of this embodiment can be made more certain.

[0064] In the microscope objective lens OL according to this embodiment, it is desirable that the interval between the second lens group G2 and the third lens group G3 can be changed. By changing the interval between the second lens group G2 and the third lens group G3 according to the thickness of the cover glass CV, the aberration that changes according to the thickness of the cover glass CV can be corrected.

Example

[0065] Hereinafter, an example of the microscope objective lens OL according to the present embodiment will be described with reference to the drawings. FIGS. 1, 5, 9, and 13 are optical path diagrams showing the configurations of the microscope objective lenses OL {OL(1) to OL(4)} according to the first to fourth embodiments. In FIGS. 1, 5, 9, and 13, each lens group is represented by a combination of a symbol G and a number (or alphabet), and each lens is represented by a combination of a symbol L and a number (or alphabet). In this case, in order to prevent the types and numbers of symbols and numbers from becoming large and complicated, the lens and the like are represented using a combination of symbols and numbers independently for each embodiment. Therefore, even if the same combination of symbols and numbers is used between embodiments, it does not mean that they have the same configuration.

[0066] Tables 1 to 4 are shown below. Among these, Table 1 shows the specification data in the first embodiment, Table 2 shows the specification data in the second embodiment, Table 3 shows the specification data in the third embodiment, and Table 4 shows the specification data in the fourth embodiment. In each embodiment, the d-line (wavelength λ = 587.6 nm), C-line (wavelength λ = 656.3 nm), and F-line (wavelength λ = 486.1 nm) are selected as the objects for calculating the aberration characteristics.

[0067] 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. NA indicates the numerical aperture on the object side of the microscope objective lens. WD is the working distance, and it indicates the distance on the optical axis from the object (excluding the thickness of the cover glass) to the most object-side lens surface (the first surface described later) of the microscope objective lens. H1 indicates the distance between the optical axis and the ray that is farthest from the optical axis among the rays emitted from the object on the optical axis in the second lens group. H2 indicates the distance between the optical axis and the ray that is farthest from the optical axis at the image-side lens surface of the final lens among the rays emitted from the object on the optical axis. νdLe indicates the Abbe number of the final lens. θgFLe indicates the partial dispersion ratio of the final lens. DLe indicates the length of the final lens on the optical axis. νdLp indicates the Abbe number of at least one positive lens among the plurality of positive lenses in the second lens group. θgFLp indicates the partial dispersion ratio of at least one positive lens among the plurality of positive lenses in the second lens group. fLp indicates the focal length of at least one positive lens among the plurality of positive lenses in the second lens group.

[0068] In the table of [[Lens Data]], the surface number indicates the order of the lens surfaces from the object side. R is the radius of curvature corresponding to each surface number (a positive value for a lens surface convex on the object side). D is the lens thickness or air gap on the optical axis corresponding to each surface number. nd is the refractive index with respect to the d-line (wavelength λ = 587.6 nm) of the optical material corresponding to each surface number. νd is the Abbe number based on the d-line of the optical material corresponding to each surface number. H is the distance between the optical axis and the ray that is farthest from the optical axis at the lens surface corresponding to each surface number. θgF indicates the partial dispersion ratio of the material of the optical member corresponding to each surface number. "∞" for the radius of curvature indicates a plane or an aperture. Also, the description of the refractive index of air nd = 1.00000 is omitted.

[0069] Let ng be the refractive index of the material of the optical member with respect to the g-line (wavelength λ = 435.8 nm), nF be the refractive index of the material of the optical member with respect to the F-line (wavelength λ = 486.1 nm), and nC be the refractive index of the material of the optical member with respect to the C-line (wavelength λ = 656.3 nm). At this time, the partial dispersion ratio θgF of the material of the optical member is defined by the following formula (A).

[0070] θgF = (ng - nF) / (nF - nC) …(A)

[0071] The table of [lens group data] shows the start surface (the surface closest to the object side) and the focal length of each lens group respectively.

[0072] Hereinafter, for all specification values, the published focal length f, radius of curvature R, surface interval D, other lengths, etc. generally use "mm" when not otherwise specified. However, since the same optical performance can be obtained even if the optical system is proportionally enlarged or reduced, it is not limited to this.

[0073] The explanations of the table so far are common to all examples, and the overlapping explanations below are omitted.

[0074] (First Embodiment) The first embodiment will be described with reference to FIGS. 1 to 4 and Table 1. FIG. 1 is an optical path diagram showing the configuration of the microscope objective lens according to the first embodiment. The microscope objective lens OL(1) according to the first embodiment is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a negative refractive power, which are arranged in order from the object side along the optical axis. Between the tip of the microscope objective lens OL(1) according to the first embodiment and the cover glass CV covering the object OB, it is filled with an immersion liquid (oil). Between the cover glass CV and the object OB is also filled with an immersion liquid (oil). Note that the refractive index of the immersion liquid with respect to the d-line (wavelength λ = 587.6 nm) is 1.5148. The refractive index of the cover glass CV with respect to the d-line is 1.5244.

[0075] The first lens group G1 is composed of a cemented lens in which a plano-convex positive lens L101 with a plane facing the object side and a negative meniscus lens L102 with a concave surface facing the object side are cemented in order from the object side along the optical axis.

[0076] The second lens group G2 is composed of a cemented lens in which a positive meniscus lens L201 with a concave surface facing the object side, a negative meniscus lens L202 with a convex surface facing the object side, and a positive lens L203 with a biconvex shape are cemented together in order from the object side along the optical axis, a cemented lens in which a negative lens L204 with a biconcave shape and a positive lens L205 with a biconvex shape are cemented together, a cemented lens in which a negative meniscus lens L206 with a convex surface facing the object side and a positive lens L207 with a biconvex shape are cemented together, a positive meniscus lens L208 with a concave surface facing the object side, and a cemented lens in which a negative meniscus lens L209 with a convex surface facing the object side, a positive lens L210 with a biconvex shape, and a negative lens L211 with a biconcave shape are cemented together. The image-side lens surface of the positive lens L205 in the second lens group G2 corresponds to the lens surface through which the ray that is farthest from the optical axis among the rays emitted from the object OB on the optical axis passes in the second lens group G2. The positive meniscus lens L208 of the second lens group G2 corresponds to a positive lens that satisfies the aforementioned conditional expressions (5) to (7) and the like.

[0077] The third lens group G3 is composed of a cemented lens in which a positive lens L301 with a biconvex shape and a negative lens L302 with a biconcave shape are cemented together in order from the object side along the optical axis.

[0078] The fourth lens group G4 is composed of a cemented lens in which a negative lens L401 with a biconcave shape and a positive lens L402 with a biconvex shape are cemented together in order from the object side along the optical axis. The positive lens L402 of the fourth lens group G4 corresponds to the final lens Le that is disposed closest to the image side in the microscope objective lens OL.

[0079] Also, by integrally moving the third lens group G3 and the fourth lens group G4 along the optical axis, the distance between the second lens group G2 and the third lens group G3 can be changed according to the thickness of the cover glass CV. The third lens group G3 and the fourth lens group G4 function as a so-called correction ring when moved along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0080] In addition, by moving integrally along the optical axis each lens on the image side of the positive meniscus lens L208 that satisfies the aforementioned conditional expressions (5) to (7) and the like in the second lens group G2 (that is, the cemented lens in which the negative meniscus lens L209, the positive lens L210, and the negative lens L211 are cemented), the distance between the positive meniscus lens L208 and the negative meniscus lens L209 in the second lens group G2 can be changed according to the thickness of the cover glass CV. In this case, each lens on the image side of the positive meniscus lens L208 in the second lens group G2, the third lens group G3, and the fourth lens group G4 function as a so-called correction ring by being moved along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0081] The following Table 1 lists the specifications of the microscope objective lens according to the first embodiment. Note that the first surface is the object surface (OB).

[0082] (Table 1) [Overall specifications] β = 60x f = 3.34 NA = 1.40 WD = 0.15 H1 = 9.00 H2 = 4.67 νdLe = 24.80 θgFLe = 0.6122 DLe = 8.08 νdLp = 37.00 θgFLp = 0.5862 fLp = 70.17 [Lens data] Surface number R D nd νd H θgF 1 ∞ 0.10 1.5148 40.31 2 ∞ 0.17 1.5244 54.28 3 ∞ 0.05 1.5148 40.31 4 ∞ 0.48 1.5182 58.90 5 -1.801 3.99 1.9538 32.33 6 -3.490 0.20 7 -238.272 2.85 1.5932 67.90 5.68 8 -15.393 0.20 6.32 9 78.562 1.00 1.6127 44.46 7.04 10 15.775 6.96 1.4388 94.94 7.53 11 -10.917 0.20 7.99 12 -33.640 1.75 1.6541 39.68 8.00 13 14.722 8.26 1.4339 95.25 8.54 14 -12.905 0.20 9.00 15 22.204 1.00 1.7880 47.37 8.78 16 9.945 5.51 1.5691 71.34 8.08 17 -89.209 0.20 8.02 18 -165.025 1.73 1.6129 37.00 7.96 0.5862 19 -34.254 0.20 7.88 20 15.433 1.00 1.6127 44.46 7.06 21 7.252 5.15 1.4388 94.94 6.09 22 -20.439 1.00 1.8160 46.62 5.82 23 18.433 0.20 5.44 24 7.922 5.85 1.8503 32.35 25 -10.069 3.31 1.8548 24.80 26 3.696 2.07 27 -4.379 2.35 1.9165 31.60 28 163.784 8.08 1.8548 24.80 2.99 0.6122 29 -9.674 ― 4.67 [Lens group data] Group Starting surface Focal length G1 4 6.01 G2 7 12.07 G3 24 -631.75 G4 27 -55.56

[0083] FIG. 2 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to the first embodiment. FIG. 3 is a diagram showing the chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to the first embodiment. FIG. 4 is a diagram showing the coma aberration (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to the first embodiment. Each aberration diagram shows various aberrations in a state where a second objective lens is combined with the microscope objective lens. In each aberration diagram of FIGS. 2 to 4, d represents various aberrations with respect to the d-line (wavelength λ = 587.6 nm), C represents the C-line (wavelength λ = 656.3 nm), and F represents the F-line (wavelength λ = 486.1 nm). In the spherical aberration diagram, the vertical axis represents a value normalized with the maximum value of the entrance pupil radius as 1, and the horizontal axis represents the value of aberration [mm] for each ray. In the aberration diagram showing field curvature, the solid line represents the meridional image plane for each wavelength, and the dashed line represents the sagittal image plane for each wavelength. Also, in the aberration diagram showing field curvature, the vertical axis represents the image height [mm], and the horizontal axis represents the value of aberration [mm]. In the distortion aberration diagram (distortion), the vertical axis represents the image height [mm], and the horizontal axis represents the ratio of aberration as a percentage (% value). In the aberration diagram showing chromatic aberration of magnification, the vertical axis represents the image height [mm], and the horizontal axis represents the value of aberration [mm]. Each coma aberration diagram shows the value of aberration when the relative field height (RFH) of the image height ratio is 0.00 to 1.00. Note that, in the aberration diagrams of each of the following embodiments, the same reference numerals as those in the present embodiment are used, and overlapping descriptions are omitted.

[0084] From each aberration diagram, it can be seen that the microscope objective lens according to the first embodiment has good correction of various aberrations including chromatic aberration of magnification and has excellent imaging performance.

[0085] (Second Embodiment) The second embodiment will be described with reference to FIGS. 5 to 8 and Table 2. FIG. 5 is an optical path diagram showing the configuration of the microscope objective lens according to the second embodiment. The microscope objective lens OL(2) according to the second embodiment includes a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a negative refractive power, which are arranged in order from the object side along the optical axis. The space between the tip of the microscope objective lens OL(2) according to the second embodiment and the cover glass CV covering the object OB is filled with an immersion liquid (oil). The space between the cover glass CV and the object OB is also filled with an immersion liquid (oil). The refractive index of the immersion liquid with respect to the d-line (wavelength λ = 587.6 nm) is 1.5148. The refractive index of the cover glass CV with respect to the d-line is 1.5244.

[0086] In the second embodiment, since the first lens group G1, the second lens group G2, and the third lens group G3 are configured in the same manner as in the first embodiment, the same reference numerals as those in the first embodiment are used, and detailed descriptions of these lenses are omitted. In this embodiment, the image-side lens surface of the positive lens L205 in the second lens group G2 corresponds to the lens surface through which the ray that is farthest from the optical axis in the second lens group G2 among the rays emitted from the object OB on the optical axis passes. The positive meniscus lens L208 of the second lens group G2 corresponds to a positive lens that satisfies the above-described conditional expressions (5) to (7) and the like.

[0087] The fourth lens group G4 is composed of a cemented lens in which a negative meniscus lens L401 with a concave surface facing the object side and a positive meniscus lens L402 with a concave surface facing the object side are cemented in order from the object side along the optical axis. The positive meniscus lens L402 of the fourth lens group G4 corresponds to the final lens Le that is disposed closest to the image side in the microscope objective lens OL.

[0088] Further, by moving the third lens group G3 and the fourth lens group G4 integrally along the optical axis, the distance between the second lens group G2 and the third lens group G3 can be changed according to the thickness of the cover glass CV. The third lens group G3 and the fourth lens group G4 function as a so-called correction ring by moving along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0089] In addition, by moving integrally along the optical axis each lens on the image side of the positive meniscus lens L208 that satisfies the above-described conditional expressions (5) to (7) and the like in the second lens group G2 (that is, the cemented lens in which the negative meniscus lens L209, the positive lens L210, and the negative lens L211 are cemented), the third lens group G3, and the fourth lens group G4, the distance between the positive meniscus lens L208 and the negative meniscus lens L209 in the second lens group G2 can be changed according to the thickness of the cover glass CV. In this case, each lens on the image side of the positive meniscus lens L208 in the second lens group G2, the third lens group G3, and the fourth lens group G4 function as a so-called correction ring by moving along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0090] The following Table 2 shows the specifications of the microscope objective lens according to the second embodiment. Note that the first surface is the object surface (OB).

[0091] (Table 2) [Overall specifications] β = 60x f = 3.33 NA = 1.42 WD = 0.15 H1 = 9.06 H2 = 4.68 νdLe = 25.15 θgFLe = 0.6102 DLe = 6.50 νdLp = 27.35 θgFLp = 0.6319 fLp = 128.46 [Lens data] Surface number R D nd νd H θgF 1 ∞ 0.10 1.5148 40.31 2 ∞ 0.17 1.5244 54.28 3 ∞ 0.05 1.5148 40.31 4 ∞ 0.48 1.5182 58.90 5 -1.801 3.98 1.9538 32.33 6 -3.490 0.20 7 -53.550 2.73 1.5932 67.90 5.54 8 -13.100 0.20 6.20 9 80.000 0.93 1.6127 44.46 7.04 10 17.298 6.84 1.4388 94.94 7.50 11 -11.149 0.20 8.02 12 -39.599 0.90 1.6541 39.68 8.09 13 15.062 8.64 1.4339 95.25 8.52 14 -12.884 0.20 9.06 15 21.270 0.90 1.7880 47.37 8.71 16 9.501 5.80 1.5691 71.34 7.95 17 -49.451 0.20 7.89 18 -63.109 1.30 1.6638 27.35 7.81 0.6319 19 -36.566 0.20 7.74 20 17.265 0.91 1.6127 44.46 7.00 21 7.928 4.77 1.4388 94.94 6.17 22 -18.436 0.92 1.8160 46.62 5.95 23 22.698 0.20 5.62 24 7.950 5.77 1.8503 32.35 25 -11.102 3.15 1.8548 24.80 26 3.629 3.11 27 -4.692 4.84 1.9165 31.60 28 -44.290 6.50 1.8545 25.15 3.45 0.6102 29 -10.482 ― 4.68 [Lens group data] Group Starting surface Focal length G1 4 6.03 G2 7 12.12 G3 24 -131.43 G4 27 -61.23

[0092] FIG. 6 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to the second embodiment. FIG. 7 is a diagram showing the longitudinal chromatic aberration (lateral chromatic aberration) of the microscope objective lens according to the second embodiment. FIG. 8 is a diagram showing the coma aberration (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to the second embodiment. From each aberration diagram, it can be seen that the microscope objective lens according to the second embodiment has various aberrations including longitudinal chromatic aberration well corrected and has excellent imaging performance.

[0093] (Third Embodiment) The third embodiment will be described with reference to FIGS. 9 to 12 and Table 3. FIG. 9 is an optical path diagram showing the configuration of the microscope objective lens according to the third embodiment. The microscope objective lens OL(3) according to the third embodiment is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a negative refractive power, arranged in order from the object side along the optical axis. The space between the tip of the microscope objective lens OL(3) according to the third embodiment and the cover glass CV covering the object OB is filled with an immersion liquid (oil). The space between the cover glass CV and the object OB is also filled with an immersion liquid (oil). Note that the refractive index of the immersion liquid with respect to the d-line (wavelength λ = 587.6 nm) is 1.5148. The refractive index of the cover glass CV with respect to the d-line is 1.5244.

[0094] In the third embodiment, since the first lens group G1 and the third lens group G3 are configured in the same manner as in the first embodiment, the same reference numerals as those in the first embodiment are given, and detailed descriptions of these lenses are omitted. The second lens group G2 is composed of, in order from the object side along the optical axis, a positive meniscus lens L201 with a concave surface facing the object side, a negative lens L202 with both concave surfaces, a cemented lens formed by cementing a positive lens L203 with both convex surfaces, a cemented lens formed by cementing a negative meniscus lens L204 with a convex surface facing the object side and a positive lens L205 with both convex surfaces, a cemented lens formed by cementing a negative meniscus lens L206 with a convex surface facing the object side and a positive lens L207 with both convex surfaces, a positive lens L208 with both convex surfaces, and a cemented lens formed by cementing a negative meniscus lens L209 with a convex surface facing the object side, a positive lens L210 with both convex surfaces, and a negative lens L211 with both concave surfaces. The image-side lens surface of the positive lens L205 in the second lens group G2 corresponds to the lens surface through which the light ray that is farthest from the optical axis in the second lens group G2 among the light rays emitted from the object OB on the optical axis passes. The positive lens L208 in the second lens group G2 corresponds to a positive lens that satisfies the above-mentioned conditional expressions (5) to (7) and the like.

[0095] The fourth lens group G4 is composed of, in order from the object side along the optical axis, a cemented lens formed by cementing a negative meniscus lens L401 with a concave surface facing the object side and a positive meniscus lens L402 with a concave surface facing the object side. The positive meniscus lens L402 in the fourth lens group G4 corresponds to the final lens Le that is disposed closest to the image side in the microscope objective lens OL.

[0096] Further, by integrally moving the third lens group G3 and the fourth lens group G4 along the optical axis, the distance between the second lens group G2 and the third lens group G3 can be changed according to the thickness of the cover glass CV. The third lens group G3 and the fourth lens group G4 function as a so-called correction ring when moved along the optical axis, and can correct the aberration that changes according to the thickness of the cover glass CV.

[0097] In addition, by moving integrally along the optical axis each lens on the image side of the positive lens L208 that satisfies the above-described conditional expressions (5) to (7) and the like in the second lens group G2 (that is, the cemented lens in which the negative meniscus lens L209, the positive lens L210, and the negative lens L211 are cemented), the third lens group G3, and the fourth lens group G4, it may be configured such that the distance between the positive lens L208 and the negative meniscus lens L209 in the second lens group G2 can be changed according to the thickness of the cover glass CV. In this case, each lens on the image side of the positive lens L208 in the second lens group G2, the third lens group G3, and the fourth lens group G4 function as a so-called correction ring by being moved along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0098] The following Table 3 shows the specifications of the microscope objective lens according to the third embodiment. Note that the first surface is the object surface (OB).

[0099] (Table 3) [Overall specifications] β = 100x f = 2.00 NA = 1.45 WD = 0.14 H1 = 9.16 H2 = 2.85 νdLe = 24.80 θgFLe = 0.6122 DLe = 9.01 νdLp = 27.79 θgFLp = 0.6095 fLp = 32.35 [Lens data] Surface number R D nd νd H θgF 1 ∞ 0.10 1.5148 40.31 2 ∞ 0.17 1.5244 54.28 3 ∞ 0.04 1.5148 40.31 4 ∞ 0.60 1.5400 59.46 5 -2.353 2.79 1.9538 32.33 6 -2.884 0.20 7 -40.868 2.54 1.5924 68.37 4.94 8 -9.178 0.30 5.48 9 -37.924 0.96 1.6127 44.46 6.13 10 17.353 6.38 1.4343 94.77 7.05 11 -10.916 0.20 7.77 12 145.940 0.95 1.7205 34.71 8.66 13 21.720 6.73 1.4339 95.25 8.95 14 -12.641 0.20 9.16 15 59.190 0.95 1.7410 52.64 8.74 16 11.812 6.32 1.4339 95.25 8.32 17 -17.813 0.20 8.38 18 36.385 2.13 1.7408 27.79 7.95 0.6095 19 -68.478 0.20 7.81 20 22.711 0.96 1.7432 49.34 7.07 21 8.793 4.83 1.4388 94.94 6.17 22 -12.569 0.95 1.6910 54.82 5.95 23 31.942 0.20 5.56 24 7.299 5.07 1.6230 58.16 25 -22.161 8.01 1.8548 24.80 26 2.713 2.18 27 -2.969 1.33 1.9037 31.34 28 -24.035 9.01 1.8548 24.80 1.49 0.6122 29 -8.581 ― 2.85 [Lens group data] Group Starting surface Focal length G1 4 4.20 G2 7 11.27 G3 24 -20.92 G4 27 - 28.48

[0100] FIG. 10 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to the third embodiment. FIG. 11 is a diagram showing the chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to the third embodiment. FIG. 12 is a diagram showing the coma aberration (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to the third embodiment. From each aberration diagram, it can be seen that the microscope objective lens according to the third embodiment has good correction of various aberrations including chromatic aberration of magnification and has excellent imaging performance.

[0101] (Fourth Embodiment) The fourth embodiment will be described with reference to FIGS. 13 to 16 and Table 4. FIG. 13 is an optical path diagram showing the configuration of the microscope objective lens according to the fourth embodiment. The microscope objective lens OL(4) according to the fourth embodiment is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a negative refractive power, which are arranged in order from the object side along the optical axis. The space between the tip of the microscope objective lens OL(4) according to the fourth embodiment and the cover glass CV covering the object OB is filled with an immersion liquid (oil). The space between the cover glass CV and the object OB is also filled with an immersion liquid (oil). The refractive index of the immersion liquid with respect to the d-line (wavelength λ = 587.6 nm) is 1.5148. The refractive index of the cover glass CV with respect to the d-line is 1.5244.

[0102] In the fourth embodiment, since the first lens group G1 and the third lens group G3 are configured in the same manner as in the first embodiment, they are given the same reference numerals as in the first embodiment, and detailed descriptions of these lenses are omitted. The second lens group G2 includes, arranged in order from the object side along the optical axis, a positive meniscus lens L201 with a concave surface facing the object side, a negative lens L202 with a biconcave shape, a positive lens L203 with a biconvex shape, a cemented lens in which they are cemented together, a negative lens L204 with a biconcave shape, a positive lens L205 with a biconvex shape, a cemented lens in which they are cemented together, a positive meniscus lens L206 with a concave surface facing the object side, a negative meniscus lens L207 with a convex surface facing the object side, a cemented lens in which a positive lens L208 with a biconvex shape is cemented together, a negative meniscus lens L209 with a convex surface facing the object side, a positive meniscus lens L210 with a convex surface facing the object side, and a cemented lens in which a negative meniscus lens L211 with a convex surface facing the object side is cemented together. The image-side lens surface of the positive lens L205 in the second lens group G2 corresponds to the lens surface through which the ray that is farthest from the optical axis among the rays emitted from the object OB on the optical axis passes in the second lens group G2. The positive meniscus lens L206 of the second lens group G2 corresponds to a positive lens that satisfies the above-described conditional expressions (5) to (7) and the like.

[0103] The fourth lens group G4 includes, arranged in order from the object side along the optical axis, a cemented lens in which a negative meniscus lens L401 with a concave surface facing the object side and a positive meniscus lens L402 with a concave surface facing the object side are cemented together. The positive meniscus lens L402 of the fourth lens group G4 corresponds to the final lens Le that is arranged closest to the image side in the microscope objective lens OL.

[0104] Also, by integrally moving the third lens group G3 and the fourth lens group G4 along the optical axis, the distance between the second lens group G2 and the third lens group G3 can be changed according to the thickness of the cover glass CV. The third lens group G3 and the fourth lens group G4 function as a so-called correction ring when moved along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0105] In addition, by moving integrally along the optical axis each lens on the image side of the positive meniscus lens L206 that satisfies the aforementioned conditional expressions (5) to (7) and the like in the second lens group G2 (that is, the cemented lens in which the negative meniscus lens L207 and the positive lens L208 are cemented, and the cemented lens in which the negative meniscus lens L209, the positive meniscus lens L210, and the negative meniscus lens L211 are cemented), the third lens group G3, and the fourth lens group G4, the interval between the positive meniscus lens L206 and the negative meniscus lens L207 in the second lens group G2 can be changed according to the thickness of the cover glass CV. In this case, each lens on the image side of the positive meniscus lens L206 in the second lens group G2, the third lens group G3, and the fourth lens group G4 function as a so-called correction ring by being moved along the optical axis, and can correct aberrations that change according to the thickness of the cover glass CV.

[0106] The following Table 4 shows the specification values of the microscope objective lens according to the fourth embodiment. Note that the first surface is the object surface (OB).

[0107] (Table 4) [Overall specifications] β = 60x f = 3.32 NA = 1.40 WD = 0.14 H1 = 9.65 H2 = 4.64 νdLe = 24.80 θgFLe = 0.6122 DLe = 5.67 νdLp = 24.71 θgFLp = 0.6291 fLp = 55.54 [Lens data] Surface number R D nd νd H θgF 1 ∞ 0.10 1.5148 40.31 2 ∞ 0.17 1.5244 54.28 3 ∞ 0.05 1.5148 40.31 4 ∞ 0.50 1.5182 58.90 5 -1.609 3.94 1.9538 32.33 6 -3.613 0.20 7 -48.280 3.31 1.5932 67.90 5.99 8 -10.543 0.20 6.68 9 -106.359 1.00 1.6127 44.46 7.56 10 20.636 7.00 1.4388 94.94 8.34 11 -11.034 0.20 8.70 12 -50.111 0.85 1.6541 39.68 8.86 13 15.708 8.21 1.4339 95.25 9.32 14 -14.005 0.20 9.65 15 -150.000 2.00 1.7558 24.71 9.56 0.6291 16 -32.984 0.20 9.57 17 86.174 0.85 1.7880 47.37 9.12 18 10.681 5.75 1.5691 71.34 8.38 19 -88.353 0.20 8.34 20 13.721 0.85 1.6127 44.46 8.01 21 8.768 5.17 1.4388 94.94 7.31 22 407.881 1.44 1.8160 46.62 7.04 23 21.613 0.20 6.63 24 8.628 5.41 1.7880 47.35 25 -97.965 4.95 1.8548 24.80 26 3.733 3.72 27 -4.355 1.70 1.9165 31.60 28 -140.078 5.67 1.8548 24.80 3.32 0.6122 29 -7.944 ― 4.64 [Lens group data] Group Starting surface Focal length G1 4 7.27 G2 7 13.15 G3 24 -51.56 G4 27 -76.08

[0108] FIG. 14 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the microscope objective lens according to the fourth embodiment. FIG. 15 is a diagram showing the chromatic aberration of magnification (lateral chromatic aberration) of the microscope objective lens according to the fourth embodiment. FIG. 16 is a diagram showing the coma aberration (meridional coma aberration and sagittal coma aberration) of the microscope objective lens according to the fourth embodiment. From each aberration diagram, it can be seen that the microscope objective lens according to the fourth embodiment has good correction of various aberrations including chromatic aberration of magnification and has excellent imaging performance.

[0109] Since the microscope objective lens according to each embodiment is an infinity-corrected lens, it is used in combination with a second objective lens that condenses the light from the microscope objective lens. Therefore, an example of the second objective lens used in combination with the microscope objective lens will be described with reference to FIGS. 17 and 5. FIG. 17 is an optical path diagram showing the configuration of the second objective lens used in combination with the microscope objective lens according to each embodiment. The diagrams of various aberrations of the microscope objective lens according to each embodiment are those when used in combination with this second objective lens. The second objective lens IL shown in FIG. 17 is composed of a cemented lens in which a positive lens L51 with a biconvex shape and a negative lens L52 with a biconcave shape are cemented together, arranged in order from the object side, and a cemented lens in which a positive lens L53 with a biconvex shape and a negative lens L54 with a biconcave shape are cemented together. The second objective lens IL is arranged on the image side of the microscope objective lens according to each embodiment. Also, in FIG. 17, the entrance pupil plane Pu of the second objective lens IL is shown.

[0110] The following Table 5 lists the values of the specifications of the second objective lens. In the table of [Overall Specifications], f' indicates the focal length of the second objective lens. In the table of [Lens Data], the surface number, R, D, nd, and νd are the same as those shown in the descriptions of Tables 1 to 4 above.

[0111] (Table 5) Overall Specifications f´ = 200 Lens Data Surface Number R D nd νd 1 75.043 5.100 1.62280 57.03 2 -75.043 2.000 1.74950 35.19 3 1600.580 7.500 4 50.256 5.100 1.66755 41.96 5 -84.541 1.800 1.61266 44.40 6 36.911 168.438

[0112] Next, the table of [Condition Formula Corresponding Values] is shown below. This table shows the values corresponding to each of the condition formulas (1) to (11) grouped together for all the examples (Example 1 to Example 4). Condition Formula (1): 1.8 < H1 / H2 < 3.5 Condition Formula (2): 1.3 < DLe / H2 < 3.5 Condition Formula (3): 20 < νdLe < 30 Condition Formula (3 - 1): 20 < νdLe < 26 Condition Formula (4): 0 < -0.0035×(νdLe - 20) + 0.63 - θgFLe Condition Formula (5): 20 < νdLp < 40 Condition Formula (6): 0.55 < θgFLp Condition Formula (7): 0 < fLp / f < 45 Condition Formula (7 - 1): 12.5 < fLp / f < 45 Condition Formula (8): 1.75 < f1 / f < 2.5 Condition Formula (9): 3 < f2 / f < 7 Condition Formula (10): f3 / f < 0 Condition Formula (11): f4 / f < 0

[0113] [Condition Formula Corresponding Values] Condition Formula Example 1 Example 2 Example 3 Example 4 (1) 1.93 1.93 3.21 2.08 (2) 1.73 1.39 3.16 1.22 (3)(3 - 1) 24.80 25.15 24.80 24.80 (4) 0.001 0.002 0.001 0.001 (5) 37.00 27.35 27.79 24.71 (6) 0.5862 0.6319 0.6095 0.6291 (7)(7 - 1) 21.02 38.56 16.18 16.74 (8) 1.80 1.81 2.10 2.19 (9) 3.62 3.64 5.64 3.96 (10) -189.26 -39.45 -10.46 -15.55 (11) -16.64 -18.38 -14.24 -22.94

[0114] According to each of the above embodiments, a microscope objective lens in which various aberrations including magnification chromatic aberration are well corrected can be realized.

[0115] Here, each of the above embodiments shows a specific example of the present embodiment, and the present embodiment is not limited thereto.

Explanation of Reference Numerals

[0116] G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group

Claims

1. It consists of a first lens group arranged in order from the object side along the optical axis, a second lens group having a positive refractive power, a third lens group with a concave surface facing the image side, and a fourth lens group with a concave surface facing the object side, wherein the first lens group consists of a plano-convex positive lens with a plane surface facing the object side and a negative lens, arranged in order from the object side along the optical axis, A microscope objective lens that satisfies the following conditional expressions. 1.8 < H1 / H2 < 3.5 1.3 < DLe / H2 < 3.5 However, H1: the distance between the optical axis and the ray that is farthest from the optical axis in the second lens group among the rays emitted from an object on the optical axis H2: the distance between the optical axis and the ray that is farthest from the optical axis on the image-side lens surface of the final lens that is arranged most on the image side in the microscope objective lens among the rays emitted from an object on the optical axis DLe: the length of the final lens on the optical axis

2. The fourth lens group consists of a negative lens with a concave surface facing the object side and a positive lens, arranged in order from the object side along the optical axis, The microscope objective lens according to Claim 1, wherein the final lens is the positive lens of the fourth lens group.

3. The microscope objective lens according to Claim 1 or 2 that satisfies the following conditional expressions. 20 < νdLe < 30 0 < -0.0035×(νdLe - 20) + 0.63 - θgFLe However, νdLe: the Abbe number of the final lens θgFLe: the partial dispersion ratio of the final lens. When the refractive index of the final lens with respect to the g-line is ngLe, the refractive index of the final lens with respect to the F-line is nFLe, and the refractive index of the final lens with respect to the C-line is nCle, it is defined by the following formula θgFLe = (ngLe - nFLe) / (nFLe - nCle)

4. The microscope objective lens according to Claim 3 that satisfies the following conditional expressions. 20 < νdLe < 26

5. The second lens group has a plurality of positive lenses, Among the plurality of positive lenses of the second lens group, at least one positive lens satisfies the microscope objective lens according to any one of Claims 1 to 4. 20 < νdLp < 40 0.55 < θgFLp However, νdLp: the Abbe number of the positive lens θgFLp: the partial dispersion ratio of the positive lens. When the refractive index of the positive lens with respect to the g-line is ngLp, the refractive index of the positive lens with respect to the F-line is nFLp, and the refractive index of the positive lens with respect to the C-line is nCLp, it is defined by the following formula θgFLp = (ngLp - nFLp) / (nFLp - nCLp)

6. The microscope objective lens according to claim 5, wherein the at least one positive lens satisfies the following conditional expression: 0 < fLp / f < 45 where fLp: the focal length of the positive lens f: the focal length of the microscope objective lens

7. The microscope objective lens according to claim 6, wherein the at least one positive lens satisfies the following conditional expression: 12.5 < fLp / f < 45

8. The microscope objective lens according to any one of claims 5 to 7, wherein the positive lens is disposed on the image side with respect to a lens surface through which a ray of light farthest from the optical axis in the second lens group passes.

9. The microscope objective lens according to any one of claims 1 to 8, which satisfies the following conditional expression: 1.75 < f1 / f < 2.5 where f1: the focal length of the first lens group f: the focal length of the microscope objective lens

10. The microscope objective lens according to any one of claims 1 to 9, which satisfies the following conditional expression: 3 < f2 / f < 7 where f2: the focal length of the second lens group f: the focal length of the microscope objective lens

11. The microscope objective lens according to any one of claims 1 to 10, which satisfies the following conditional expression: f3 / f < 0 where f3: the focal length of the third lens group f: the focal length of the microscope objective lens

12. The microscope objective lens according to any one of claims 1 to 11, which satisfies the following conditional expression: f4 / f < 0 where f4: the focal length of the fourth lens group f: the focal length of the microscope objective lens

13. The microscope objective lens according to any one of claims 1 to 12, wherein the distance between the second lens group and the third lens group can be changed.

14. A microscope optical system comprising the microscope objective lens according to any one of claims 1 to 13 and a second objective lens that condenses light from the microscope objective lens.

15. A microscope apparatus comprising the microscope objective lens according to any one of claims 1 to 13.

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