Microscope objective lens, microscope optical system, and microscope device

Abstract

A microscope objective lens (OL) comprises a first lens group (G1) having positive refractive power, a second lens group (G2) having negative refractive power, and a third lens group (G3) having positive refractive power, the first lens group (G1) having a cemented lens (CL11) including a negative lens. The microscope objective lens satisfies the following conditional expressions.　0.625 < θgF1N < 0.725 22.5 < νd1N < 30 where νd1N is the Abbe's number of the negative lens in the cemented lens (CL11) of the first lens group (G1), and θgF1N is the partial dispersion ratio of the negative lens in the cemented lens (CL11) of the first lens group (G1).

Description

[Technical Field]

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

[0002] In recent years, various objective lenses for microscopes with wide fields of view and low magnification have been proposed (see, for example, Patent Document 1). Such objective lenses are required to effectively correct chromatic aberration of magnification. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-313814 Summary of the Invention

[0004] The microscope objective lens according to the present invention comprises, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, wherein the first lens group has a cemented lens including a negative lens and focuses a light beam from an object, the second lens group diverges the light beam from the first lens group, and the third lens group converts the divergent light beam from the second lens group into a parallel light beam, and satisfies the following conditional expression: 0.625<θgF1N<0.725 23 <νd1N< 29 where νd1N is the Abbe number of the negative lens in the cemented lens of the first lens group. θgF1N: partial dispersion ratio of the negative lens in the cemented lens of the first lens group, which is defined by the following equation, where ng1N is the refractive index of the negative lens for the g-line, nF1N is the refractive index of the negative lens for the F-line, and nC1N is the refractive index of the negative lens for the C-line. θgF1N=(ng1N-nF1N) / (nF1N-nC1N)

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

[0006] A microscope apparatus according to the present invention includes the microscope objective lens described above. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a microscope objective lens according to a first example. [Figure 2] FIG. 2 is a diagram illustrating spherical aberration of the microscope objective lens according to the first example. [Figure 3] FIG. 2 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to the first example. [Figure 4] FIG. 10 is a cross-sectional view showing the configuration of a microscope objective lens according to a second example. [Figure 5] FIG. 10 is a diagram illustrating spherical aberration of the microscope objective lens according to the second example. [Figure 6] FIG. 10 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to the second example. [Figure 7] FIG. 10 is a cross-sectional view showing the configuration of a microscope objective lens according to a third example. [Figure 8] FIG. 10 is a diagram illustrating spherical aberration of the microscope objective lens according to the third example. [Figure 9] FIG. 10 is a diagram showing chromatic aberration of magnification of the microscope objective lens according to the third example. [Figure 10] FIG. 4 is a cross-sectional view showing the configuration of a second objective lens. [Figure 11] FIG. 1 is a schematic diagram illustrating a confocal fluorescence microscope, which is an example of a microscope device. DETAILED DESCRIPTION OF THE INVENTION

[0008] A preferred embodiment of the present invention will now be described. First, a microscope optical system and a confocal fluorescence microscope (microscope device) equipped with a microscope objective lens according to this embodiment will be described with reference to FIG. 11. As shown in FIG. 11, a confocal fluorescence microscope 1 is configured to include 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 direction of the optical axis of the microscope objective lens of the confocal fluorescence microscope 1 will be referred to as the z-axis. Furthermore, coordinate axes extending in directions perpendicular to each other in a plane perpendicular to the z-axis will be referred to as the x-axis and y-axis, respectively.

[0009] A sample SA, for example, held between a slide glass (not shown) and a cover glass (not shown), is placed on the stage 10. Alternatively, a sample SA contained in a sample container (not shown) together with an immersion liquid may be placed on the stage 10. The sample SA contains a fluorescent substance such as a fluorescent dye. The sample SA is, for example, a cell that has been fluorescently stained in advance. A stage driver 11 is provided near the stage 10. The stage driver 11 moves the stage 10 along the z-axis.

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

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

[0012] The beam splitter 33 has the property of reflecting the excitation light from the light source 20 and transmitting the fluorescence from the sample SA. 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 in two directions, the x direction and the y direction, with the excitation light from the light source 20. As the scanner 34, for example, a galvano scanner, a resonant scanner, or the like is used.

[0014] The microscope optical system 40 collects fluorescence generated in the sample SA. The microscope optical system 40 includes, in order from the sample SA side toward the detection unit 50 side, a microscope objective lens OL and a second objective lens IL. The microscope optical system 40 also includes a scanner 34 and a beam splitter 33, which are arranged between the microscope objective lens OL and the second objective lens IL. The microscope objective lens OL is arranged above and facing the stage 10 on which the sample SA is placed. The microscope objective lens OL collects excitation light from the light source 20 and irradiates it onto the sample SA on the stage 10. The microscope objective lens OL also receives fluorescence generated in the sample SA and converts it into parallel light. The second objective lens IL collects the fluorescence (parallel light) from the microscope objective lens OL.

[0015] The detection unit 50 detects fluorescence generated in the sample SA via the microscope optical system 40. For example, a photomultiplier tube is used as the detection unit 50. A pinhole 45 is provided between the microscope optical system 40 and the detection unit 50. The pinhole 45 is positioned conjugate with the focal position of the microscope objective lens OL on the sample SA side. The pinhole 45 passes only light from the focal plane of the microscope objective lens OL (a plane perpendicular to the optical axis of the microscope objective lens OL that passes through the focal position of the microscope objective lens OL) or a plane shifted from the focal plane in the optical axis direction within a predetermined deviation tolerance range, 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 passes through the collimator lens 31 passes through the excitation filter 32 and enters the beam splitter 33. The excitation light that enters the beam splitter 33 is reflected by the beam splitter 33 and enters the scanner 34. The scanner 34 scans the sample SA in two directions, the x direction and the y direction, with the excitation light that entered the scanner 34. The excitation light that enters the scanner 34 passes through the scanner 34 and 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 that overlaps with the focal plane of the microscope objective lens OL) is two-dimensionally scanned in the x direction and the y direction by the scanner 34. In this way, the illumination optical system 30 illuminates the sample SA on the stage 10 with the excitation light emitted from the light source 20.

[0017] Irradiation with excitation light excites fluorescent substances contained in the sample SA, causing them to emit fluorescence. The fluorescence from the sample SA passes through the microscope objective lens OL and becomes parallel light. The fluorescence that passes through the microscope objective lens OL passes through the scanner 34 and enters the beam splitter 33. The fluorescence that enters the beam splitter 33 passes through the beam splitter 33 and reaches the fluorescence filter 35. The fluorescence that reaches the fluorescence filter 35 passes through the fluorescence filter 35 and passes 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 intensity (brightness) of the light as a light detection signal. The detection unit 50 outputs the generated data to a control unit (not shown). The control unit processes the data input from the detection unit 50 as data for one pixel and arranges this in synchronization with two-dimensional scanning by the scanner 34, thereby generating one image data in which data for multiple pixels is arranged two-dimensionally (in two directions). In this way, the control unit can acquire an image of the sample SA.

[0019] 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 an observation microscope for performing bright-field observation, fluorescence observation, etc., a confocal microscope, a multiphoton excitation microscope, a super-resolution microscope, etc. Furthermore, the confocal fluorescence microscope 1 may be an upright microscope or an inverted microscope.

[0020] Next, a microscope objective lens according to this embodiment will be described. As an example of a microscope objective lens OL according to this embodiment, a microscope objective lens OL(1) shown in FIG. 1 includes, in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The first lens group G1 has a cemented lens including a negative lens and focuses a light beam from an object. The second lens group G2 diverges the light beam from the first lens group G1. The third lens group G3 converts the divergent light beam from the second lens group G2 into a parallel light beam. In this embodiment, the first lens group G1 focusing a light beam from an object means that the first lens group G1 has a focusing function. For example, when a divergent light beam from an object passes through the first lens group G1, the light beam from the first lens group G1 may become a divergent light beam whose degree of divergence is weakened by the first lens group G1.

[0021] With the above configuration, the microscope objective lens OL according to this embodiment satisfies the following conditional expressions (1) and (2). 0.625<θgF1N<0.725 (1) 22.5<νd1N<30 (2) where νd1N: Abbe number of the negative lens in the cemented lens of the first lens group G1 θgF1N: partial dispersion ratio of the negative lens in the cemented lens of the first lens group G1, which is defined by the following equation, where ng1N is the refractive index of the negative lens for the g-line, nF1N is the refractive index of the negative lens for the F-line, and nC1N is the refractive index of the negative lens for the C-line. θgF1N=(ng1N-nF1N) / (nF1N-nC1N)

[0022] According to this embodiment, it is possible to obtain a microscope objective lens in which chromatic aberration of magnification is well corrected over a wide wavelength range, 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 Figure 4 or the optical system OL(3) shown in Figure 7.

[0023] Conditional formula (1) defines an appropriate range for the partial dispersion ratio of the negative lens in the cemented lens of the first lens group G1. Conditional formula (2) defines an appropriate range for the Abbe number of the negative lens in the cemented lens of the first lens group G1. By satisfying conditional formulas (1) and (2), lateral chromatic aberration can be effectively corrected over a wide wavelength range.

[0024] If the corresponding value of conditional expression (1) exceeds the upper limit, the secondary spectrum of lateral chromatic aberration will be overcorrected in the wavelength range on the short wavelength side, making it difficult to effectively correct lateral chromatic aberration over a wide wavelength range. By setting the upper limit of conditional expression (1) to 0.72, or even 0.71, the effect of this embodiment can be further ensured.

[0025] If the corresponding value of conditional expression (1) falls below the lower limit, it becomes difficult to sufficiently correct the secondary spectrum of lateral chromatic aberration in the wavelength range on the short wavelength side. By setting the lower limit of conditional expression (1) to 0.629, the effect of this embodiment can be more reliably achieved.

[0026] If the corresponding value of conditional expression (2) exceeds the upper limit, it becomes difficult to sufficiently correct first-order lateral chromatic aberration in the wavelength range on the short wavelength side. By setting the upper limit of conditional expression (2) to 29, or even 28, the effect of this embodiment can be further ensured.

[0027] If the corresponding value of conditional expression (2) is below the lower limit, first-order lateral chromatic aberration will be overcorrected in the wavelength range on the short wavelength side, making it difficult to effectively correct lateral chromatic aberration over a wide wavelength range. By setting the lower limit of conditional expression (2) to 23, or even 25, the effect of this embodiment can be further ensured.

[0028] The microscope objective lens OL according to this embodiment may satisfy the following conditional expression (2-1). 23<νd1N<29 (2-1)

[0029] Conditional expression (2-1) is an expression similar to conditional expression (2), and can provide the same effect as conditional expression (2). By setting the upper limit value of conditional expression (2-1) to 28, the effect of this embodiment can be made more certain. By setting the lower limit value of conditional expression (2-1) to 25, the effect of this embodiment can be made more certain.

[0030] In the microscope objective lens OL according to this embodiment, it is desirable that the second lens group G2 has a cemented lens having negative refractive power and satisfies the following conditional expression (3). -3<(Rc2+Rc1) / (Rc2-Rc1)<-1 ···(3) where Rc1: radius of curvature of the lens surface of the cemented lens in the second lens group G2 closest to the object Rc2: Radius of curvature of the lens surface closest to the image side in the cemented lens in the second lens group G2

[0031] Conditional expression (3) defines an appropriate range for the shape factor of the cemented lens in the second lens group G2. By satisfying conditional expression (3), lateral chromatic aberration can be effectively corrected.

[0032] If the value corresponding to conditional expression (3) is outside the above range, it becomes difficult to correct lateral chromatic aberration. By setting the upper limit of conditional expression (3) to -1.2, or even -1.5, the effect of this embodiment can be made more certain. By setting the lower limit of conditional expression (8) to -2.7, or even -2.5, the effect of this embodiment can be made more certain.

[0033] Note that the microscope objective lens OL according to this embodiment may be configured so that the first lens group G1 is made up of one cemented lens and the second lens group G2 is made up of one cemented lens. The microscope objective lens OL according to this embodiment may be configured so that one of the distance between the first lens group G1 and the second lens group G2 and the distance between the second lens group G2 and the third lens group G3 is the largest lens distance (air distance) in the microscope objective lens OL, and the other is the second largest lens distance (air distance) in the microscope objective lens OL.

[0034] In the microscope objective lens OL according to this embodiment, the third lens group G3 has one or more cemented lenses, and it is desirable that the cemented lenses in the third lens group G3 consist of two lenses, which makes it possible to effectively correct secondary spectrum in addition to primary achromatism in correcting axial chromatic aberration.

[0035] In the microscope objective lens OL according to this embodiment, the third lens group G3 has a cemented lens including a positive lens and a negative lens, and it is desirable that the following conditional expressions (4) and (5) be satisfied. -35<νd3P-νd3N<0 (4) 0.6<θgF3P<0.7 (5) where νd3P is the Abbe number of the positive lens in the cemented lens of the third lens group G3. νd3N: Abbe number of the negative lens in the cemented lens of the third lens group G3 θgF3P: partial dispersion ratio of the positive lens in the cemented lens of the third lens group G3, which is defined by the following equation, where ng3P is the refractive index of the positive lens for the g-line, nF3P is the refractive index of the positive lens for the F-line, and nC3P is the refractive index of the positive lens for the C-line. θgF3P=(ng3P-nF3P) / (nF3P-nC3P)

[0036] Conditional expression (4) defines an appropriate relationship between the Abbe number of the positive lens in the cemented lens of the third lens group G3 and the Abbe number of the negative lens in the cemented lens of the third lens group G3. Conditional expression (5) defines an appropriate range for the partial dispersion ratio of the positive lens in the cemented lens of the third lens group G3. By satisfying conditional expressions (4) and (5), in addition to first-order achromatism, second-order spectrum can be well corrected in the correction of axial chromatic aberration.

[0037] If the corresponding value of conditional expression (4) exceeds the upper limit, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the upper limit of conditional expression (4) to -5, or even -10, the effect of this embodiment can be further ensured.

[0038] If the corresponding value of conditional expression (4) falls below the lower limit, the secondary spectrum of axial chromatic aberration will be overcorrected, making it difficult to effectively correct axial chromatic aberration. By setting the lower limit of conditional expression (4) to -30, or even -25, the effect of this embodiment can be further ensured.

[0039] If the corresponding value of conditional expression (5) exceeds the upper limit, the secondary spectrum of axial chromatic aberration will be overcorrected, making it difficult to effectively correct axial chromatic aberration. By setting the upper limit of conditional expression (5) to 0.68, or even 0.65, the effect of this embodiment can be made even more certain.

[0040] If the corresponding value of conditional expression (5) falls below the lower limit, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the lower limit of conditional expression (5) to 0.61, or even 0.62, the effect of this embodiment can be further ensured.

[0041] It is desirable that the microscope objective lens OL according to this embodiment satisfy the following conditional expression (6). 0.022<θgF1N-(0.645-0.0017×νd1N)<0.125 (6)

[0042] Conditional expression (6) defines an appropriate relationship between the partial dispersion ratio of the negative lens in the cemented lens of the first lens group G1 and the Abbe number of the negative lens in the cemented lens of the first lens group G1. By satisfying conditional expression (6), lateral chromatic aberration can be effectively corrected over a wide wavelength range.

[0043] If the corresponding value of conditional expression (6) exceeds the upper limit, the secondary spectrum of lateral chromatic aberration will be overcorrected in the wavelength range on the short wavelength side, making it difficult to effectively correct lateral chromatic aberration over a wide wavelength range. By setting the upper limit of conditional expression (6) to 0.12, or even 0.1, the effect of this embodiment can be further ensured.

[0044] If the corresponding value of conditional expression (6) falls below the lower limit, it becomes difficult to sufficiently correct the secondary spectrum of lateral chromatic aberration in the wavelength range on the short wavelength side. By setting the lower limit of conditional expression (6) to 0.024, or even 0.026, the effect of this embodiment can be further ensured.

[0045] In the microscope objective lens OL according to this embodiment, it is desirable that the third lens group G3 has a cemented lens including a positive lens, and satisfy the following conditional expressions (7) and (8). 0.02<θgF3P-(0.645-0.0017×νd3P)<0.12 (7) 20<νd3P<35 (8) where νd3P is the Abbe number of the positive lens in the cemented lens of the third lens group G3. θgF3P: partial dispersion ratio of the positive lens in the cemented lens of the third lens group G3, which is defined by the following equation, where ng3P is the refractive index of the positive lens for the g-line, nF3P is the refractive index of the positive lens for the F-line, and nC3P is the refractive index of the positive lens for the C-line. θgF3P=(ng3P-nF3P) / (nF3P-nC3P)

[0046] Conditional expression (7) defines an appropriate relationship between the partial dispersion ratio of the positive lens in the cemented lens of the third lens group G3 and the Abbe number of the positive lens in the cemented lens of the third lens group G3. Conditional expression (8) defines an appropriate range for the Abbe number of the positive lens in the cemented lens of the third lens group G3. By satisfying conditional expressions (7) and (8), in addition to first-order achromatism, second-order spectrum can be well corrected in the correction of axial chromatic aberration.

[0047] If the corresponding value of conditional expression (7) exceeds the upper limit, the secondary spectrum of axial chromatic aberration will be overcorrected, making it difficult to effectively correct axial chromatic aberration. By setting the upper limit of conditional expression (7) to 0.1, or even 0.08, the effect of this embodiment can be further ensured.

[0048] If the corresponding value of conditional expression (7) falls below the lower limit, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the lower limit of conditional expression (7) to 0.021, or even 0.022, the effect of this embodiment can be made even more certain.

[0049] If the corresponding value of conditional expression (8) exceeds the upper limit, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the upper limit of conditional expression (8) to 33, or even 30, the effect of this embodiment can be further ensured.

[0050] If the corresponding value of conditional expression (8) falls below the lower limit, the secondary spectrum of axial chromatic aberration will be overcorrected, making it difficult to effectively correct axial chromatic aberration. By setting the lower limit of conditional expression (8) to 21, or even 22, the effect of this embodiment can be further ensured. [Example]

[0051] Examples of the microscope objective lens OL according to this embodiment will be described below with reference to the drawings. FIGS. 1, 4, and 7 are optical path diagrams showing the configurations of microscope objective lenses OL {OL(1) to OL(3)} according to first to third examples. In FIGS. 1, 4, and 7, 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, to prevent the number and types of symbols and numbers from becoming too large and cumbersome, lenses, etc., are represented by different 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 examples have the same configuration.

[0052] Tables 1 to 3 are shown below, with Table 1 showing data on various specifications for Example 1, Table 2 for Example 2, and Table 3 for Example 3. In each example, the d-line (wavelength λ=587.6 nm), F-line (wavelength λ=486.1 nm), g-line (wavelength λ=435.8 nm), and h-line (wavelength λ=404.7 nm) were selected as the targets for calculating aberration characteristics.

[0053] In the [Overall Specifications] table, f indicates the focal length of the microscope objective. β indicates the magnification of the microscope objective. NA indicates the numerical aperture of the microscope objective. WD indicates the working distance of the microscope objective. θgF1N indicates the partial dispersion ratio of the negative lens in the cemented lens in the first lens group. θgF3P indicates the partial dispersion ratio of the positive lens in the cemented lens closest to the object in the third lens group.

[0054] In the [Lens Data] table, the surface numbers indicate the order of the lens surfaces from the object side, R is the radius of curvature corresponding to each surface number (positive values ​​are used for lens surfaces convex toward the object side), D is the axial lens thickness or air gap corresponding to each surface number, nd is the refractive index of the optical material corresponding to each surface number at the d-line (wavelength λ=587.6 nm), νd is the Abbe number of the optical material corresponding to each surface number, with the d-line as the reference, and θgF is 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.

[0055] Let ng be the refractive index of the optical member material at the g-line (wavelength λ=435.8 nm), nF be the refractive index of the optical member material at the F-line (wavelength λ=486.1 nm), and nC be the refractive index of the optical member material at the C-line (wavelength λ=656.3 nm). In this case, the partial dispersion ratio θgF of the optical member material is defined by the following equation (A).

[0056] θgF=(ng-nF) / (nF-nC) …(A)

[0057] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0058] 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, as the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0059] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0060] (First Example) The first example will be described with reference to FIGS. 1 to 3 and Table 1. FIG. 1 is an optical path diagram showing the configuration of the 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, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. Air is filled between the tip of the microscope objective lens OL(1) according to the first example and the 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 1.52216.

[0061] The first lens group G1 focuses light beams from an object. The first lens group G1 also focuses off-axis light rays from the object closer to the optical axis. The first lens group G1 is composed of, in order from the object side along the optical axis, a cemented lens CL11 having positive refractive power, which is composed of a biconvex positive lens L11 and a negative meniscus lens L12 with its concave surface facing the object side.

[0062] The second lens group G2 diverges the light beam from the first lens group G1. The second lens group G2 is composed of, in order from the object side along the optical axis, a cemented lens CL21 having negative refractive power, which is formed by cementing together a biconvex positive lens L21 and a biconcave negative lens L22.

[0063] The third lens group G3 converts the divergent light beam from the second lens group G2 into a parallel light beam. The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a first cemented lens CL31 formed by cementing together a biconcave negative lens L31 and a biconvex positive lens L32, a second cemented lens CL32 formed by cementing together a biconcave negative lens L33 and a biconvex positive lens L34, and a biconvex positive lens L35.

[0064] Table 1 below lists the values ​​of the specifications of the microscope objective lens according to the first example.

[0065] (Table 1) [Overall specifications] f=100 β=2x NA=0.1 WD=9.00 θgF1N=0.6319 θgF3P=0.6319 [Lens data] Surface number RD nd νd θg 1 ∞ 0.170 1.52216 58.80 2∞9.000 3 18.606 5.002 1.67300 38.26 4 -14.481 1.000 1.66382 27.35 0.6319 5 -221.845 7.083 6 20.393 2.682 1.53172 48.78 7 -12.357 1.000 1.59319 67.90 8 7.645 18.512 9 -23.591 1.000 1.83481 42.73 10 18.490 1.884 1.66382 27.35 0.6319 11 -289.431 3.859 12 -77.261 1.000 1.83400 37.18 13 35.655 3.668 1.43425 94.77 14 -18.472 3.017 15 252.747 5.424 1.49782 82.57 16 -17.110 - [Lens group data] Group starting plane focal length G1 3 25.42 G2 6 -19.35 G3 9 63.66

[0066] FIG. 2 is a diagram showing the spherical aberration of the microscope objective lens according to Example 1. FIG. 3 is a diagram showing the lateral chromatic aberration of the microscope objective lens according to Example 1. Note that each aberration diagram shows various aberrations when the microscope objective lens is combined with a second objective lens. In each aberration diagram of FIGS. 2 and 3, d indicates the aberrations for the d-line (wavelength λ=587.6 nm), F indicates the aberrations for the F-line (wavelength λ=486.1 nm), g indicates the aberrations for the g-line (wavelength λ=435.8 nm), and h indicates the aberrations for the h-line (wavelength λ=404.7 nm). In each spherical aberration diagram, the vertical axis indicates the value normalized with the maximum value of the entrance pupil radius set to 1, and the horizontal axis indicates the aberration value [mm] for each light ray. In the aberration diagram showing the lateral chromatic aberration, the vertical axis indicates the image height [mm], and the horizontal axis indicates the aberration value [mm]. Note that the same symbols as in this Example are used in the aberration diagrams of each Example shown below, and redundant explanations will be omitted.

[0067] From each aberration diagram, it can be seen that the microscope objective lens according to Example 1 has excellent imaging performance with various aberrations corrected well over a wide wavelength range.

[0068] (Second Example) The second example will be described with reference to FIGS. 4 to 6 and Table 2. FIG. 4 is an optical path diagram 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 along the optical axis in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The space between the tip of the microscope objective lens OL(2) according to the second example and the cover glass CV covering the object is filled with air. The refractive index of the cover glass CV with respect to the d-line (wavelength λ=587.6 nm) is 1.52216. Since the lens groups G1 to G3 in the second example are configured in the same way as in the first example, the same reference numerals as in the first example are used, and detailed description of each lens will be omitted.

[0069] Table 2 below lists the values ​​of the specifications of the microscope objective lens according to the second example.

[0070] (Table 2) [Overall specifications] f=100 β=2x NA=0.1 WD=9.00 θgF1N=0.6291 θgF3P=0.6319 [Lens data] Surface number RD nd νd θgF 1 ∞ 0.170 1.52216 58.80 2∞9.000 3 19.231 5.062 1.67300 38.26 4 -14.923 1.000 1.75575 24.71 0.6291 5 -43.104 6.798 6 37.284 2.260 1.53172 48.78 7 -13.393 1.000 1.59319 67.90 8 7.643 18.803 9 -28.414 1.000 1.83481 42.73 10 18.979 2.355 1.66382 27.35 0.6319 11 -397.602 4.025 12 -80.473 1.000 1.83400 37.18 13 36.493 3.514 1.43425 94.77 14 -19.325 3.410 15 229.471 4.903 1.49782 82.57 16 -17.582 - [Lens group data] Group starting plane focal length G1 3 22.02 G2 6 -15.21 G3 9 58.79

[0071] Fig. 5 is a diagram showing the spherical aberration of the microscope objective lens according to Example 2. Fig. 6 is a diagram showing the chromatic aberration of magnification of the microscope objective lens according to Example 2. From these aberration diagrams, it can be seen that the microscope objective lens according to Example 2 has excellent correction of various aberrations over a wide wavelength range and has excellent imaging performance.

[0072] (Third Example) The third example will be described with reference to FIGS. 7 to 9 and Table 3. FIG. 7 is an optical path diagram 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, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The space between the tip of the microscope objective lens OL(3) according to the third 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 1.52216.

[0073] The first lens group G1 focuses light beams from an object. The first lens group G1 also focuses off-axis light rays from the object closer to the optical axis. The first lens group G1 is composed of, in order from the object side along the optical axis, a cemented lens CL11 having positive refractive power, which is composed of a negative meniscus lens L11 with a convex surface facing the object side and a positive meniscus lens L12 with a convex surface facing the object side. The second lens group G2 and the third lens group G3 in the third embodiment are configured in the same manner as in the first embodiment, and therefore the same reference numerals as in the first embodiment are used, and detailed description of these lenses will be omitted.

[0074] Table 3 below lists the values ​​of the specifications of the microscope objective lens according to the third example.

[0075] (Table 3) [Overall specifications] f=100 β=2x NA=0.1 WD=8.95 θgF1N=0.6319 θgF3P=0.6319 [Lens data] Surface number RD nd νd θgF 1 ∞ 0.170 1.52216 58.80 2∞8.950 3 14.268 1.000 1.66382 27.35 0.6319 4 9.446 4.819 1.61266 44.46 5 528.106 7.296 6 23.325 2.911 1.53172 48.78 7 -8.772 1.000 1.59240 68.37 8 7.406 21.332 9 -22.486 1.000 1.88300 40.69 10 32.290 1.717 1.66382 27.35 0.6319 11 -270.274 1.036 12 -207.121 1.000 1.83481 42.73 13 35.026 3.679 1.43384 95.26 14 -17.219 3.406 15 279.391 4.984 1.49782 82.57 16 -17.022 - [Lens group data] Group starting plane focal length G1 3 24.83 G2 6 -16.80 G3 9 57.72

[0076] Fig. 8 is a diagram showing the spherical aberration of the microscope objective lens according to Example 3. Fig. 9 is a diagram showing the chromatic aberration of magnification 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 well corrected over a wide wavelength range.

[0077] Since the microscope objective lens according to each example is an infinity-corrected lens, it is used in combination with a second objective lens that focuses light from the microscope objective lens. An example of a second objective lens used in combination with the microscope objective lens will be described with reference to FIG. 10 and Table 4. FIG. 10 is a cross-sectional view showing the configuration of the second objective lens used in combination with the microscope objective lens according to each example. The aberration diagrams for the microscope objective lens according to each example are those obtained when used in combination with this second objective lens. The second objective lens IL shown in FIG. 10 is composed of, in order from the object side along the optical axis, a first cemented lens CL41 formed by cementing together a biconvex positive lens L41 and a biconcave negative lens L42, and a second cemented lens CL42 formed by cementing together a biconvex positive lens L43 and a biconcave negative lens L44.

[0078] The specifications of the second objective lens are listed in Table 4 below. In the [Lens Data] table, the surface number, R, D, nd, and vd are the same as those shown in the explanations of Tables 1 to 3 above.

[0079] (Table 4) [Lens data] Surface number RD 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 -

[0080] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below. This table shows the values ​​corresponding to each of the conditional expressions (1) to (8) for all the examples (Examples 1 to 3). Conditional expression (1) 0.625<θgF1N<0.725 Conditional expression (2) 22.5<νd1N<30 Conditional expression (2-1) 23<νd1N<29 Conditional expression (3) -3<(Rc2+Rc1) / (Rc2-Rc1)<-1 Conditional expression (4) -35<νd3P-νd3N<0 Conditional expression (5) 0.6<θgF3P<0.7 Conditional expression (6) 0.022<θgF1N-(0.645-0.0017×νd1N)<0.125 Conditional expression (7) 0.02<θgF3P-(0.645-0.0017×νd3P)<0.12 Conditional expression (8) 20<νd3P<35

[0081] [Conditional expression corresponding value] Conditional Expression First Example Second Example Third Example (1) 0.6319 0.6291 0.6319 (2)(2-1) 27.35 24.71 27.35 (3) -2.199 -1.516 -1.93 (4) -15.38 -15.38 -13.34 (5) 0.6319 0.6319 0.6319 (6) 0.0334 0.0261 0.0334 (7) 0.0334 0.0334 0.0334 (8) 27.35 27.35 27.35

[0082] According to each of the above-described embodiments, it is possible to realize a microscope objective lens in which chromatic aberration of magnification is well corrected over a wide wavelength range.

[0083] Here, the above examples show specific examples of this embodiment, and this embodiment is not limited to these. [Explanation of symbols]

[0084] G1 First lens group G2 Second lens group G3 3rd lens group

Claims

1. The lens comprises, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the first lens group has a cemented lens including a negative lens, and condenses a light beam from an object; the second lens group diverges the light beam from the first lens group, the third lens group converts the divergent light beam from the second lens group into a parallel light beam, A microscope objective lens that satisfies the following conditional formula: 0.625<θgF1N<0.725 23<νd1N<29 where νd1N is the Abbe number of the negative lens in the cemented lens of the first lens group. θgF1N: partial dispersion ratio of the negative lens in the cemented lens of the first lens group, which is defined by the following formula when the refractive index of the negative lens for the g-line is ng1N, the refractive index of the negative lens for the F-line is nF1N, and the refractive index of the negative lens for the C-line is nC1N θgF1N=(ng1N-nF1N) / (nF1N-nC1N)

2. The second lens group has a cemented lens having negative refractive power, 2. The microscope objective lens according to claim 1, which satisfies the following condition: -3<(Rc2+Rc1) / (Rc2-Rc1)<-1 where Rc1 is the radius of curvature of the lens surface of the cemented lens in the second lens group that is closest to the object side. Rc2: the radius of curvature of the lens surface of the cemented lens in the second lens group closest to the image

3. the third lens group includes one or more cemented lenses, 2. The microscope objective lens according to claim 1, wherein the cemented lens of the third lens group is made up of two lenses.

4. the third lens group has a cemented lens including a positive lens and a negative lens, 2. The microscope objective lens according to claim 1, which satisfies the following condition: −35<νd3P−νd3N<0 0.6<θgF3P<0.7 where νd3P is the Abbe number of the positive lens in the cemented lens of the third lens group. νd3N: Abbe number of the negative lens in the cemented lens of the third lens group θgF3P: partial dispersion ratio of the positive lens in the cemented lens of the third lens group, which is defined by the following equation, where ng3P is the refractive index of the positive lens with respect to the g-line, nF3P is the refractive index of the positive lens with respect to the F-line, and nC3P is the refractive index of the positive lens with respect to the C-line. θgF3P=(ng3P-nF3P) / (nF3P-nC3P)

5. 2. The microscope objective lens according to claim 1, which satisfies the following condition: 0.022<θgF1N-(0.645-0.0017×νd1N)<0.125

6. the third lens group has a cemented lens including a positive lens, 2. The microscope objective lens according to claim 1, which satisfies the following condition: 0.02<θgF3P-(0.645-0.0017×νd3P)<0.12 20<νd3P<35 where νd3P is the Abbe number of the positive lens in the cemented lens of the third lens group. θgF3P: partial dispersion ratio of the positive lens in the cemented lens of the third lens group, which is defined by the following equation, where ng3P is the refractive index of the positive lens with respect to the g-line, nF3P is the refractive index of the positive lens with respect to the F-line, and nC3P is the refractive index of the positive lens with respect to the C-line. θgF3P=(ng3P-nF3P) / (nF3P-nC3P)

7. 7. A microscope optical system comprising: the microscope objective lens according to claim 1; and a second objective lens that focuses light from the microscope objective lens.

8. A microscope apparatus comprising the microscope objective lens according to any one of claims 1 to 6.

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