Image formation lens and microscope device

Abstract

An image formation lens (1L) for a microscope has a negative lens, and a positive lens (L13) that satisfies the following conditional expressions.　-0.002×(νdP-35)+0.602-θgFP < 0 and 23 < νdP < 65 where νdP is the Abbe number of the positive lens, and θgFP is the partial dispersion ratio of the positive lens, and is defined by the following expression: θgFP = (ngP-nFP) / (nFP-nCP) where ngP is the refractive index for the g line of the positive lens, nFP is the refractive index for the F line of the positive lens, and nCP is the refractive index for the C line of the positive lens.

Description

Imaging lens and microscope device

[0001] The present invention relates to an imaging lens and a microscope apparatus.

[0002] In recent years, various imaging lenses for microscopes that can accommodate objective lenses with wide fields of view have been proposed (see, for example, Patent Document 1). Such imaging lenses are required to effectively correct chromatic aberration.

[0003] Patent No. 6397717

[0004] The imaging lens according to the first aspect of the present invention is an imaging lens for a microscope that forms an image from light from an objective lens, and includes a negative lens and a positive lens that satisfies the following conditional expressions: -0.002×(νdP−35)+0.602−θgFP<0 23<νdP<65 where νdP is the Abbe number of the positive lens, and θgFP is the partial dispersion ratio of the positive lens, which is defined by the following expression when the refractive index of the positive lens for the g-line is ngP, the refractive index of the positive lens for the F-line is nFP, and the refractive index of the positive lens for the C-line is nCP: θgFP=(ngP−nFP) / (nFP−nCP).

[0005] The imaging lens according to the second aspect of the present invention is an imaging lens for a microscope that forms an image from light from an objective lens, and includes a positive lens and a negative lens that satisfies the following conditional expressions: -0.0033 × (νdN − 35) + 0.593 − θgFN < 0 20 < νdN < 37 where νdN is the Abbe number of the negative lens, and θgFN is the partial dispersion ratio of the negative lens, which is defined by the following expression when the refractive index of the negative lens for the g-line is ngN, the refractive index of the negative lens for the F-line is nFN, and the refractive index of the negative lens for the C-line is nCN: θgFN = (ngN − nFN) / (nFN − nCN).

[0006] The microscope apparatus according to the present invention includes an objective lens that receives light from an object and converts it into parallel light, and the imaging lens described above.

[0007] FIG. 1 is a cross-sectional view showing the configuration of an imaging lens according to Example 1. FIG. 2 is a diagram showing various aberrations of the imaging lens according to Example 1. FIG. 3 is a diagram showing chromatic aberrations of the imaging lens according to Example 1. FIG. 4 is a diagram showing coma aberrations of the imaging lens according to Example 1. FIG. 5 is a cross-sectional view showing the configuration of an imaging lens according to Example 2. FIG. 6 is a diagram showing various aberrations of the imaging lens according to Example 2. FIG. 7 is a diagram showing chromatic aberrations of the imaging lens according to Example 2. FIG. 8 is a diagram showing coma aberrations of the imaging lens according to Example 2. FIG. 9 is a cross-sectional view showing the configuration of an imaging lens according to Example 3. FIG. 10 is a diagram showing various aberrations of the imaging lens according to Example 3. FIG. 11 is a diagram showing chromatic aberrations of the imaging lens according to Example 3. FIG. 12 is a diagram showing coma aberrations of the imaging lens according to Example 3. FIG. 13 is a cross-sectional view showing the configuration of an imaging lens according to Example 4. FIG. 14 is a diagram showing various aberrations of the imaging lens according to Example 4. FIG. 15 is a diagram showing chromatic aberrations of the imaging lens according to Example 4. FIG. 16 is a cross-sectional view showing the configuration of an imaging lens according to Example 5. FIG. 17 is a diagram showing various aberrations of the imaging lens according to Example 5. FIG. 18 is a diagram showing chromatic aberrations of the imaging lens according to Example 5. Fig. 10 is a diagram illustrating coma aberration of the imaging lens according to Example 5. Fig. 11 is a schematic configuration diagram illustrating a confocal fluorescence microscope, which is an example of a microscope device.

[0008] Preferred embodiments of the present invention will now be described. First, a confocal fluorescence microscope (microscope device) having an imaging lens according to each embodiment will be described with reference to Fig. 21. As shown in Fig. 21, the confocal fluorescence microscope 1 includes an excitation light introducing section 2 that guides illumination laser light from a light source unit 6 onto a sample SA, a scanning device 3 that deflects the laser light focused on the sample SA to scan the sample SA, a photodetector 5 that detects a light intensity signal from the sample SA, and a focusing optical system 4 that guides light from the sample SA to the photodetector 5.

[0009] The light source unit 6 may be provided in the confocal fluorescence microscope 1 or may be provided separately from the confocal fluorescence microscope 1. The light source unit 6 includes a laser light source (not shown), a beam diameter adjustment mechanism (not shown), etc. The light source unit 6 oscillates an illumination laser beam.

[0010] The excitation light introducing section 2 is configured with a collimator lens 21, a dichroic mirror 22, and a microscope optical system 25 having an imaging lens 23 and an objective lens 24. The collimator lens 21 and the dichroic mirror 22 are disposed inside the microscope housing 12 provided on the upper part of the lens barrel 11 of the microscope main body 10. The light source unit 6 and the microscope housing 12 are connected by an optical fiber 69 using connectors C3 and C4. The collimator lens 21 converts the laser light (light beam) emitted from the light source unit 6 into parallel light. The dichroic mirror 22 reflects the laser light from the collimator lens 21 toward the sample SA. The microscope optical system 25 focuses the laser light reflected by the dichroic mirror 22 onto the sample SA using the imaging lens 23 and the objective lens 24. The imaging lens 23 is disposed inside the lens barrel 11 of the microscope main body 10. The imaging lens 23 is also referred to as a second objective lens. The objective lens 24 is attached to the lower part of the lens barrel 11.

[0011] The scanning device 3 includes a scanning mechanism (scanner) 31 and a scanning optical system 32. The scanning device 3 is disposed inside the microscope housing 12 between the dichroic mirror 22 and the imaging lens 23. The scanning mechanism (scanner) 31 includes, for example, a galvanometer mirror (not shown) or a resonant mirror (not shown). The scanning mechanism (scanner) 31 deflects the incident laser light. That is, the scanning mechanism (scanner) 31 deflects the laser light focused on the sample SA to scan the sample SA. The scanning optical system 32 is an optical system provided between the scanning mechanism (scanner) 31 and the imaging lens 23. The scanning optical system 32 is an optical system in which the focal position of the scanning optical system 32 is located on an image plane 13 (also referred to as a primary image plane) conjugate with the sample SA (the scanning plane of the sample SA).

[0012] The focusing optical system 4 includes the objective lens 24 and the imaging lens 23, which constitute the microscope optical system 25, as well as a total reflection mirror 41 and a condenser lens 42. The objective lens 24 receives fluorescence generated by the sample SA and converts it into parallel light. The imaging lens 23 focuses the fluorescence (parallel light) emitted from the objective lens 24 onto the imaging plane 13 (primary image plane) to form an image. As a result, the fluorescence from the sample SA that passes through the objective lens 24 and the imaging lens 23 is focused onto the imaging plane 13, then passes through the scanning device 3 and the dichroic mirror 22 and reaches the total reflection mirror 41. The total reflection mirror 41 and the condenser lens 42 are disposed above the dichroic mirror 22 inside the microscope housing 12. The total reflection mirror 41 reflects the fluorescence from the sample SA that passes through the objective lens 24 and the imaging lens 23. The condenser lens 42 condenses the fluorescence reflected by the total reflection mirror 41 onto a light blocking plate 52 having a pinhole 51 (aperture).

[0013] The light detection device 5 is configured to include a light shielding plate 52 having a pinhole 51, an optical fiber 53, and a detection unit 55. The optical fiber 53 is connected to the microscope housing 12 and the detection unit 55 using connectors C1 and C2. Light (fluorescence) that has passed through the pinhole 51 is incident on the optical fiber 53. The detection unit 55 detects the light (fluorescence) that has passed through the pinhole 51 and the optical fiber 53. A processing unit 57 is electrically connected to the detection unit 55 via a cable 56. The processing unit 57 performs image processing (of the sample SA) based on the detection signal detected by the detection unit 55, and the observed image of the sample SA obtained by the image processing of the processing unit 57 is displayed on a monitor (not shown).

[0014] The laser light from the scanning device 3 is first focused on the image plane 13 (primary image plane) and then focused again on the sample SA by the imaging lens 23 and objective lens 24 of the microscope optical system 25. That is, the scanning surface of the sample SA, the image plane 13, and the pinhole 51 are conjugate with each other. Therefore, by focusing the light on the sample SA by the imaging lens 23 and the objective lens 24, it becomes possible for the fluorescence generated on the scanning surface of the sample SA, out of the light (fluorescence) from the sample SA, to pass through the pinhole 51.

[0015] Although the confocal fluorescence microscope 1 has been described as an example of a microscope apparatus according to this embodiment, the present invention is not limited to this. For example, the microscope apparatus according to this embodiment may be a multiphoton excitation microscope, a super-resolution microscope, or the like. Furthermore, the confocal fluorescence microscope 1 may be an upright microscope or an inverted microscope.

[0016] The imaging lens IL described below can be used as the imaging lens 23 provided in such a confocal fluorescence microscope 1 (microscope device). First, the imaging lens IL according to the first embodiment will be described.

[0017] As an example of the imaging lens IL according to the first embodiment, the imaging lens IL (1) shown in FIG. 1 has a negative lens and a positive lens (L13) that satisfies the following conditional expressions (1) and (2): −0.002×(νdP−35)+0.602−θgFP<0 (1) 23<νdP<65 (2) where νdP is the Abbe number of the positive lens, and θgFP is the partial dispersion ratio of the positive lens, which is defined by the following expression when the refractive index of the positive lens for the g-line is ngP, the refractive index of the positive lens for the F-line is nFP, and the refractive index of the positive lens for the C-line is nCP: θgFP=(ngP−nFP) / (nFP−nCP).

[0018] According to the first embodiment, it is possible to obtain an imaging lens in which chromatic aberration is well corrected over a wide wavelength range, and a microscope apparatus having this imaging lens. The imaging lens IL according to the first embodiment may be the imaging lens IL(2) shown in Fig. 5, the imaging lens IL(3) shown in Fig. 9, the imaging lens IL(4) shown in Fig. 13, or the imaging lens IL(5) shown in Fig. 17.

[0019] Condition (1) appropriately defines the anomalous dispersion of the positive lens element. By satisfying condition (1), the secondary spectrum of axial chromatic aberration can be effectively corrected.

[0020] If the value corresponding to conditional expression (1) falls outside the above range, it becomes difficult to correct the secondary spectrum of axial chromatic aberration. By setting the upper limit of conditional expression (1) to -0.002, or even -0.004, the effect of this embodiment can be further ensured. Furthermore, the lower limit of conditional expression (1) may be set to -0.05, or even -0.025.

[0021] Condition (2) defines an appropriate range for the Abbe number of the positive lens. By satisfying condition (2), first-order axial chromatic aberration can be corrected satisfactorily.

[0022] If the value corresponding to conditional expression (2) falls outside the above range, it becomes difficult to correct first-order axial chromatic aberration. By setting the upper limit of conditional expression (2) to 60, 55, 50, 45, 40, or even 35, the effect of this embodiment can be more reliably achieved. By setting the lower limit of conditional expression (2) to 23.5, 24, or even 24.5, the effect of this embodiment can be more reliably achieved.

[0023] In the imaging lens IL according to the first embodiment, the positive lens may satisfy the following conditional expression (3): 1.55<ndP<1.79 (3) where ndP is the refractive index of the positive lens with respect to the d-line.

[0024] Condition (3) defines an appropriate range for the refractive index of the positive lens with respect to the d-line. By satisfying condition (3), it is possible to effectively correct curvature of field.

[0025] If the value corresponding to conditional expression (3) exceeds the upper limit, the difference in refractive index between the lens adjacent to the positive lens and the positive lens becomes large, making it difficult to correct spherical aberration. By setting the upper limit of conditional expression (3) to 1.78, or even 1.76, the effect of this embodiment can be made more certain.

[0026] If the corresponding value of conditional expression (3) is below the lower limit, the refractive index of the positive lens for the d-line decreases, and the term related to the positive lens in the Petzval sum increases, making it difficult to correct curvature of field. By setting the lower limit of conditional expression (3) to 1.58 or further to 1.60, the effect of this embodiment can be further ensured.

[0027] In the imaging lens IL according to the first embodiment, the positive lens may satisfy the following conditional expression (4): 0.4<fP / f<1.2 (4) where fP is the focal length of the positive lens, and f is the focal length of the imaging lens IL.

[0028] Conditional expression (4) defines an appropriate relationship between the focal length of the positive lens and the focal length of the imaging lens IL. By satisfying conditional expression (4), the secondary spectrum of axial chromatic aberration can be effectively corrected.

[0029] If the value corresponding to conditional expression (4) exceeds the upper limit, the refractive power of the positive lens becomes small, making it difficult to correct the secondary spectrum of axial chromatic aberration. By setting the upper limit of conditional expression (4) to 1.15, or even 1.1, the effect of this embodiment can be made even more certain.

[0030] If the corresponding value of conditional expression (4) is below the lower limit, the refractive power of the positive lens becomes large, causing excessive correction of the secondary spectrum of axial chromatic aberration, making it difficult to effectively correct the secondary spectrum of axial chromatic aberration. By setting the lower limit of conditional expression (4) to 0.41, or even 0.42, the effect of this embodiment can be made even more certain.

[0031] Next, an imaging lens IL according to a second embodiment will be described. The imaging lens IL according to the second embodiment has the same configuration as the imaging lens IL according to the first embodiment, and therefore will be described using the same reference numerals as in the first embodiment.

[0032] As an example of the imaging lens IL according to the second embodiment, the imaging lens IL (1) shown in FIG. 1 has a positive lens and a negative lens (L21) that satisfies the following conditional expressions (5) and (6): −0.0033×(νdN−35)+0.593−θgFN<0 (5) 20<νdN<37 (6) where νdN is the Abbe number of the negative lens, and θgFN is the partial dispersion ratio of the negative lens, which is defined by the following expression when the refractive index of the negative lens for the g-line is ngN, the refractive index of the negative lens for the F-line is nFN, and the refractive index of the negative lens for the C-line is nCN: θgFN=(ngN−nFN) / (nFN−nCN).

[0033] According to the second embodiment, it is possible to obtain an imaging lens in which chromatic aberration is well corrected over a wide wavelength range, and a microscope apparatus having this imaging lens. The imaging lens IL according to the second embodiment may be the imaging lens IL(2) shown in Fig. 5, the imaging lens IL(3) shown in Fig. 9, the imaging lens IL(4) shown in Fig. 13, or the imaging lens IL(5) shown in Fig. 17.

[0034] Condition (5) appropriately defines the anomalous dispersion of the negative lens element. By satisfying condition (5), the secondary spectrum of lateral chromatic aberration can be effectively corrected.

[0035] If the value corresponding to conditional expression (5) falls outside the above range, it becomes difficult to correct the secondary spectrum of lateral chromatic aberration. By setting the upper limit of conditional expression (5) to -0.0005, or even -0.001, the effect of this embodiment can be further ensured. Furthermore, the lower limit of conditional expression (5) may be set to -0.05, or even -0.025.

[0036] Conditional expression (6) defines an appropriate range for the Abbe number of the negative lens. By satisfying conditional expression (6), first-order lateral chromatic aberration can be corrected satisfactorily.

[0037] If the value corresponding to conditional expression (6) falls outside the above range, it becomes difficult to correct first-order lateral chromatic aberration. By setting the upper limit of conditional expression (6) to 36.5, 36, or even 35.5, the effect of this embodiment can be more reliably achieved. By setting the lower limit of conditional expression (6) to 23.5, 24, or even 24.5, the effect of this embodiment can be more reliably achieved.

[0038] In the imaging lens IL according to the second embodiment, the negative lens may satisfy the following conditional expression (7): ndN<1.78 (7) where ndN is the refractive index of the negative lens at the d-line.

[0039] Condition (7) defines an appropriate range for the refractive index of the negative lens with respect to the d-line. By satisfying condition (7), it is possible to effectively correct curvature of field.

[0040] If the corresponding value of conditional expression (7) exceeds the upper limit, the refractive index of the negative lens for the d-line becomes high, and the term related to the positive lens in the Petzval sum cannot be sufficiently canceled out, making it difficult to correct field curvature. By setting the upper limit of conditional expression (7) to 1.77, or even 1.76, the effects of this embodiment can be further ensured. Furthermore, the lower limit of conditional expression (7) may be set to 1.57, or even 1.58.

[0041] In the imaging lens IL according to the second embodiment, the negative lens may satisfy the following conditional expression (8): −1.1<fN / f<−0.2 (8) where fN is the focal length of the negative lens, and f is the focal length of the imaging lens IL.

[0042] Conditional expression (8) defines an appropriate relationship between the focal length of the negative lens and the focal length of the imaging lens IL. By satisfying conditional expression (8), it is possible to satisfactorily correct field curvature.

[0043] If the corresponding value of conditional expression (8) exceeds the upper limit, the focal length of the negative lens becomes short, and the term relating to the positive lens in the Petzval sum is excessively canceled out, making it difficult to correct the curvature of field. By setting the upper limit of conditional expression (8) to −0.22, or even −0.24, the effect of this embodiment can be made even more certain.

[0044] If the corresponding value of conditional expression (8) falls below the lower limit, the focal length of the negative lens becomes long, and the term related to the positive lens in the Petzval sum cannot be sufficiently canceled out, making it difficult to correct the curvature of field. By setting the lower limit of conditional expression (8) to −1.05, the effect of this embodiment can be made more certain.

[0045] In the imaging lens IL according to the first embodiment, the negative lens may satisfy the above-mentioned conditional expression (5). By satisfying conditional expression (5), the secondary spectrum of lateral chromatic aberration can be corrected satisfactorily, as in the case of the second embodiment. Note that by setting the upper limit of conditional expression (5) to -0.0005, or even -0.001, the effect of this embodiment can be made more certain. Furthermore, the lower limit of conditional expression (5) may be set to -0.05, or even -0.025.

[0046] In the imaging lens IL according to the first embodiment, the negative lens may satisfy the above-mentioned conditional expression (6). By satisfying conditional expression (6), first-order chromatic aberration of magnification can be corrected satisfactorily, as in the case of the second embodiment. Note that by setting the upper limit of conditional expression (6) to 36.5, 36, or even 35.5, the effect of this embodiment can be made more certain. By setting the lower limit of conditional expression (6) to 23.5, 24, or even 24.5, the effect of this embodiment can be made more certain.

[0047] In the imaging lens IL according to the first embodiment, the negative lens may satisfy the above-mentioned conditional expression (7). By satisfying conditional expression (7), it is possible to satisfactorily correct field curvature, as in the case of the second embodiment. Note that by setting the upper limit of conditional expression (7) to 1.77, or even 1.76, the effect of this embodiment can be made more certain. Furthermore, the lower limit of conditional expression (7) may be set to 1.57, or even 1.58.

[0048] In the imaging lens IL according to the first embodiment, the negative lens may satisfy the above-mentioned conditional expression (8). By satisfying conditional expression (8), it is possible to satisfactorily correct field curvature, as in the case of the second embodiment. Note that by setting the upper limit of conditional expression (8) to -0.22, or even -0.24, the effect of this embodiment can be made more certain. By setting the lower limit of conditional expression (8) to -1.05, the effect of this embodiment can be made more certain.

[0049] The imaging lens IL according to the first and second embodiments may satisfy the following conditional expression (9): 0.2<Bf / TL<0.6 (9) where Bf is the back focus of the imaging lens IL, and TL is the total length of the imaging lens IL.

[0050] Conditional expression (9) defines an appropriate relationship between the back focus of the imaging lens IL and the overall length of the imaging lens IL. In each embodiment, the overall length of the imaging lens IL indicates the distance on the optical axis from the lens surface of the objective lens closest to the image side to the image plane I. By satisfying conditional expression (9), optical elements such as a prism or a half mirror can be disposed on the object side of the imaging lens IL, making it possible to easily switch between microscopic observation using the microscope apparatus as a confocal fluorescence microscope and microscopic observation using the microscope apparatus as a stereomicroscope, for example.

[0051] If the value corresponding to conditional expression (9) exceeds the upper limit, it becomes necessary to increase the refractive power of the positive lens and the refractive power of the negative lens to increase the telephoto ratio, making it difficult to correct curvature of field and coma. By setting the upper limit of conditional expression (9) to 0.55, or even 0.5, the effects of each embodiment can be made more certain.

[0052] If the corresponding value of conditional expression (9) falls below the lower limit, it becomes difficult to arrange optical elements such as a prism or a half mirror on the object side of the imaging lens IL. By setting the lower limit of conditional expression (9) to 0.21, or even 0.22, the effects of each embodiment can be made more certain.

[0053] The imaging lens IL according to the first and second embodiments 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. It is desirable that the second lens group G2 be composed of one lens component having negative refractive power, and the third lens group G3 be composed of one lens component having positive refractive power. In each embodiment, the lens components refer to single lenses or cemented lenses. This results in a symmetrical lens arrangement, enabling excellent correction of astigmatism.

[0054] The imaging lens IL according to the first and second embodiments may satisfy the following conditional expression (10): 0.45<f1 / f3<2.4 (10) where f1 is the focal length of the first lens group G1 and f3 is the focal length of the third lens group G3.

[0055] Conditional expression (10) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the third lens group G3. By satisfying conditional expression (10), it becomes possible to make the imaging lens IL compact, while widening the field of view and increasing the numerical aperture.

[0056] If the corresponding value of conditional expression (10) exceeds the upper limit, the refractive power of the third lens group G3 becomes too strong, making it difficult to make the imaging lens IL compact, which is undesirable. By setting the upper limit of conditional expression (10) to 2.35, or even 2.3, the effects of each embodiment can be made more certain.

[0057] If the corresponding value of conditional expression (10) is below the lower limit, the refractive power of the first lens group G1 becomes too strong, making it difficult to correct astigmatism, off-axis coma, and distortion. By setting the lower limit of conditional expression (10) to 0.48, or even 0.50, the effects of each embodiment can be made more certain.

[0058] The imaging lens IL according to the first and second embodiments may satisfy the following conditional expression (11): −2.5<f1 / f2<−0.6 (11) where f1 is the focal length of the first lens group G1 and f2 is the focal length of the second lens group G2.

[0059] Conditional expression (11) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the second lens group G2. By satisfying conditional expression (11), it becomes possible to make the imaging lens IL compact, while widening the field of view and increasing the numerical aperture.

[0060] If the corresponding value of conditional expression (11) exceeds the upper limit, the refractive power of the second lens group G2 becomes too weak, making it difficult to make the imaging lens IL compact, which is undesirable. By setting the upper limit of conditional expression (11) to −0.7, or even −0.8, the effects of each embodiment can be made more certain.

[0061] If the corresponding value of conditional expression (11) falls below the lower limit, the refractive power of the second lens group G2 becomes too strong, making it difficult to correct curvature of field and off-axial coma. By setting the lower limit of conditional expression (11) to −2.4, or even −2.3, the effects of each embodiment can be made more certain.

[0062] In a microscope apparatus (confocal fluorescence microscope 1) having the imaging lens IL according to the first or second embodiment, the following conditional expression (12) may be satisfied: 0.3<DA / TL<0.6 (12), where DA is the distance on the optical axis from the lens surface of the objective lens closest to the image to the lens surface of the imaging lens IL closest to the object, and TL is the total length of the imaging lens IL.

[0063] Conditional expression (12) defines an appropriate relationship between the distance on the optical axis from the lens surface of the objective lens closest to the image to the lens surface of the imaging lens IL closest to the object, and the overall length of the imaging lens IL. By satisfying conditional expression (12), optical elements such as a prism or a half mirror can be disposed on the object side of the imaging lens IL, making it possible to easily switch between microscopic observations using the microscope apparatus as a confocal fluorescence microscope and microscopic observations using the microscope apparatus as a stereomicroscope, for example.

[0064] If the corresponding value of conditional expression (12) exceeds the upper limit, the diameter of each lens in the imaging lens IL becomes large, and it becomes difficult to ensure a sufficient back focus. By setting the upper limit of conditional expression (12) to 0.55, 0.5, or even 0.48, the effects of each embodiment can be made more certain.

[0065] If the corresponding value of conditional expression (12) falls below the lower limit, it becomes difficult to arrange optical elements such as a prism or a half mirror on the object side of the imaging lens IL. By setting the lower limit of conditional expression (12) to 0.35, or even 0.38, the effects of each embodiment can be made more certain.

[0066] In a microscope apparatus (confocal fluorescence microscope 1) having the imaging lens IL according to the first or second embodiment, the following conditional expression (13) may be satisfied: 0.1<FDN / f<0.18 (13), where FDN is the field number of the microscope apparatus, and f is the focal length of the imaging lens IL.

[0067] Conditional expression (13) defines an appropriate relationship between the field number of the microscope apparatus and the focal length of the imaging lens IL. By satisfying conditional expression (13), spherical aberration and coma can be corrected well over a wide field of view.

[0068] If the corresponding value of conditional expression (13) exceeds the upper limit, it becomes difficult to correct spherical aberration and coma. By setting the upper limit of conditional expression (13) to 0.17, the effects of each embodiment can be more reliably achieved.

[0069] If the corresponding value of conditional expression (13) falls below the lower limit, sufficient magnification cannot be obtained, and the field of view becomes narrow, which is undesirable. By setting the lower limit of conditional expression (13) to 0.11, the effects of each embodiment can be more reliably achieved.

[0070] Examples of the imaging lens IL according to each embodiment will be described below with reference to the drawings. FIGS. 1, 5, 9, 13, and 17 are cross-sectional views showing the configuration and refractive power distribution of the imaging lenses IL {IL(1) to IL(5)} according to Examples 1 to 5. In FIGS. 1, 5, 9, 13, and 17, each lens group is represented by a combination of the symbol G and a number (or alphabet), and each lens is represented by a combination of the symbol L and a number (or alphabet). In this case, to prevent the number and types of symbols and numbers from becoming too large and cumbersome, lens components, etc. are represented by separate combinations of symbols and numbers for each Example. Therefore, even if the same combinations of symbols and numbers are used between Examples, this does not necessarily mean that the Examples have the same configuration.

[0071] Tables 1 to 5 are shown below, with Table 1 listing the data for the first embodiment, Table 2 for the second embodiment, Table 3 for the third embodiment, Table 4 for the fourth embodiment, and Table 5 for the fifth embodiment. In each embodiment, the d-line (wavelength λ=587.6 nm), C-line (wavelength λ=656.3 nm), F-line (wavelength λ=486.1 nm), g-line (wavelength λ=435.8 nm), and s-line (wavelength λ=851.1 nm) were selected as the targets for calculating aberration characteristics.

[0072] In the table of [Overall Specifications], f indicates the focal length of the imaging lens. FNO indicates the F-number of the imaging lens. NA indicates the numerical aperture of the imaging lens, and Bf indicates the back focus of the imaging lens. TL indicates the total length of the imaging lens (the distance on the optical axis from the lens surface of the objective lens closest to the image plane). DA indicates the distance on the optical axis from the lens surface of the objective lens closest to the image plane to the lens surface of the imaging lens closest to the object plane. FDN indicates the field number of the microscope device.

[0073] In the [Lens Specifications] table, the surface numbers indicate the order of the lens surfaces from the object side. R indicates the radius of curvature of each optical surface (surfaces whose center of curvature is located on the image plane side are given a positive value). D indicates the surface spacing, which is the distance on the optical axis from each optical surface to the next optical surface (or image plane). νd indicates the Abbe number based on the d-line of the material of the optical element. nd indicates the refractive index of the material of the optical element with respect to the d-line. θgF indicates the partial dispersion ratio of the material of the optical element. The "∞" for the radius of curvature indicates a plane or an aperture. The refractive index of air, nd = 1.00000, is omitted.

[0074] Let ng be the refractive index of the material of the optical element with respect to the g-line (wavelength λ=435.8 nm), nF be the refractive index of the material of the optical element with respect to the F-line (wavelength λ=486.1 nm), and nC be the refractive index of the material of the optical element with respect to the C-line (wavelength λ=656.3 nm). In this case, the partial dispersion ratio θgF of the material of the optical element is defined by the following equation (A):

[0075] θgF=(ng-nF) / (nF-nC)...(A)

[0076] The table of [Lens Group Data] shows the first surface (the surface closest to the object) and focal length of each lens group.

[0077] 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.

[0078] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0079] First Example A first example will be described with reference to FIGS. 1 to 4 and Table 1. FIG. 2 is a cross-sectional view showing the configuration of the imaging lens according to the first example. The imaging lens IL(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. The entrance pupil plane P of the imaging lens IL(1) corresponds to the exit pupil plane of the infinity-corrected objective lens 24. The image plane I corresponds to the image plane 13 described above. This also applies to all of the following examples.

[0080] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L11, a cemented lens formed by cementing together a positive meniscus lens L12 with its convex surface facing the object side, a biconvex positive lens L13, and a biconcave negative lens L14. The positive lens L13 of the cemented lens in the first lens group G1 corresponds to a positive lens that satisfies the above-mentioned conditional expression (1) etc.

[0081] The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The negative meniscus lens L21 in the second lens group G2 corresponds to a negative lens that satisfies the above-mentioned conditional expression (5) and the like.

[0082] The third lens group G3 is composed of a positive meniscus lens L31 with its convex surface facing the object side. An image surface I is located on the image side of the third lens group G3.

[0083] The values ​​of the specifications of the imaging lens according to Example 1 are listed in Table 1 below. Note that the first surface is the entrance pupil plane P of the imaging lens.

[0084] (Table 1) [Overall specifications] f = 202.00 FNO = 6.73 NA = 0.07 Bf = 88.65 TL = 350.00 DA = 160.00 FDN = 25.00 [Lens specifications] Surface number R D nd νd θgF 1 ∞ 160.00 2 86.109 6.00 1.45600 91.37 3 -526.020 0.20 4 56.104 4.67 1.49782 82.57 5 100.000 6.00 1.66382 27.35 0.6319 6 -200.000 8.10 1.73800 32.26 7 105.381 9.30 8 217.561 19.37 1.75575 24.71 0.6290 9 40.184 42.71 10 103.799 5.00 1.85025 30.05 11 317.656 Bf [Lens Group Data] Group Initial Surface Focal Length G1 2 95.68 G2 8 -68.43 G3 10 179.41

[0085] FIG. 2 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the imaging lens according to Example 1. FIG. 3 is a diagram showing lateral chromatic aberration of magnification of the imaging lens according to Example 1. FIG. 4 is a diagram showing coma aberrations (meridional coma and sagittal coma) of the imaging lens according to Example 1. In each of the aberration diagrams shown in FIGS. 2 to 4, d indicates aberrations for the d-line (wavelength λ=587.6 nm), C indicates a C-line (wavelength λ=656.3 nm), F indicates a F-line (wavelength λ=486.1 nm), g indicates a g-line (wavelength λ=435.8 nm), and s indicates aberrations for the s-line (wavelength λ=851.1 nm). In the spherical aberration diagrams, the vertical axis indicates values ​​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 diagrams showing field curvature, the solid line indicates the sagittal image plane for each wavelength, and the dashed line indicates the meridional image plane for each wavelength. In the aberration diagrams showing field curvature, the vertical axis indicates image height [mm], and the horizontal axis indicates aberration value [mm]. In the distortion diagrams, the vertical axis indicates image height [mm], and the horizontal axis indicates the aberration ratio as a percentage (% value). In the aberration diagrams showing lateral chromatic aberration, the vertical axis indicates image height [mm], and the horizontal axis indicates aberration value [mm]. Each coma aberration diagram shows the aberration value when the image height ratio RFH (Relative Field Height) is 0.00 and 1.00. Note that the same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below, and redundant explanations will be omitted.

[0086] From each aberration diagram, it can be seen that the imaging lens according to Example 1 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0087] Second Example A second example will be described with reference to Figs. 5 to 8 and Table 2. Fig. 5 is a cross-sectional view showing the configuration of an imaging lens according to the second example. The imaging lens IL(2) according to the second example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power.

[0088] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L11, a positive meniscus lens L12 with its convex surface facing the object side, and a cemented lens formed by cementing together a positive meniscus lens L13 with its convex surface facing the object side and a negative meniscus lens L14 with its convex surface facing the object side. The positive meniscus lens L13 of the cemented lens in the first lens group G1 corresponds to a positive lens that satisfies the above-mentioned conditional expression (1) etc.

[0089] The second lens group G2 is composed of a biconcave negative lens L21. The negative lens L21 in the second lens group G2 corresponds to a negative lens that satisfies the above-mentioned conditional expression (5) and the like.

[0090] The third lens group G3 is composed of a biconvex positive lens L31. An image surface I is disposed on the image side of the third lens group G3.

[0091] The values ​​of the specifications of the imaging lens according to Example 2 are shown in Table 2 below. Note that the first surface is the entrance pupil plane P of the imaging lens.

[0092] (Table 2) [Overall specifications] f = 201.00 FNO = 10.05 NA = 0.05 Bf = 109.11 TL = 350.00 DA = 150.00 FDN = 32.00 [Lens specifications] Surface number R D nd νd θgF 1 ∞ 150.00 2 96.572 12.65 1.45600 91.37 3 -1109.978 26.76 4 45.609 6.61 1.45600 91.37 5 579.024 0.20 6 40.424 4.01 1.61750 30.83 0.6231 7 61.797 3.00 1.73800 32.33 8 30.170 6.82 9 -77.424 9.49 1.59270 35.27 0.5935 10 73.813 17.73 11 2014.458 3.61 1.85025 30.05 12 -114.386 Bf [Lens Group Data] Group Initial Surface Focal Length G1 2 103.23 G2 9 -62.30 G3 11 127.40

[0093] Fig. 6 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the imaging lens according to Example 2. Fig. 7 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the imaging lens according to Example 2. Fig. 8 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the imaging lens according to Example 2. From each aberration diagram, it can be seen that the imaging lens according to Example 2 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0094] Third Example A third example will be described with reference to Figs. 9 to 12 and Table 3. Fig. 9 is a cross-sectional view showing the configuration of an imaging lens according to the third example. The imaging lens IL(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.

[0095] The first lens group G1 is composed of, arranged along the optical axis from the object side, a biconvex positive lens L11, a positive meniscus lens L12 with its convex surface facing the object side, and a cemented lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14. The positive lens L13 of the cemented lens in the first lens group G1 corresponds to a positive lens that satisfies the above-mentioned conditional expression (1) etc.

[0096] The second lens group G2 is composed of a biconcave negative lens L21. The negative lens L21 in the second lens group G2 corresponds to a negative lens that satisfies the above-mentioned conditional expression (5) and the like.

[0097] The third lens group G3 is composed of a biconvex positive lens L31. An image surface I is disposed on the image side of the third lens group G3.

[0098] The values ​​of the specifications of the imaging lens according to Example 3 are shown in Table 3 below. Note that the first surface is the entrance pupil plane P of the imaging lens.

[0099] (Table 3) [Overall specifications] f = 200.25 FNO = 8.01 NA = 0.06 Bf = 100.00 TL = 321.62 DA = 130.00 FDN = 32.00 [Lens specifications] Surface number R D nd νd θgF 1 ∞ 130.00 2 61.153 7.64 1.43425 94.77 3 -5880.256 0.30 4 76.472 5.20 1.56908 71.34 5 198.298 0.30 6 111.442 7.19 1.66382 27.35 0.6319 7 -112.886 3.00 1.73800 32.33 8 115.027 20.21 9 -382.558 5.00 1.75575 24.71 0.6290 10 44.607 37.79 11 141.268 5.00 1.85025 30.05 12 -449.497 Bf [Lens Group Data] Group Initial Surface Focal Length G1 2 87.81 G2 9 -52.60 G3 11 126.91

[0100] Fig. 10 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the imaging lens according to Example 3. Fig. 11 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the imaging lens according to Example 3. Fig. 12 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the imaging lens according to Example 3. From each aberration diagram, it can be seen that the imaging lens according to Example 3 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0101] Fourth Example A fourth example will be described with reference to Figs. 13 to 16 and Table 4. Fig. 13 is a cross-sectional view showing the configuration of an imaging lens according to the fourth example. The imaging lens IL(4) according to the fourth example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power.

[0102] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L11, a positive meniscus lens L12 with its convex surface facing the object side, and a cemented lens formed by cementing a positive meniscus lens L13 with its concave surface facing the object side and a biconcave negative lens L14. The positive meniscus lens L13 of the cemented lens in the first lens group G1 corresponds to a positive lens that satisfies the above-mentioned conditional expression (1) etc.

[0103] The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The negative meniscus lens L21 in the second lens group G2 corresponds to a negative lens that satisfies the above-mentioned conditional expression (5) and the like.

[0104] The third lens group G3 is composed of a positive meniscus lens L31 with its convex surface facing the object side. An image surface I is located on the image side of the third lens group G3.

[0105] The values ​​of the specifications of the imaging lens according to Example 4 are shown in Table 4 below. Note that the first surface is the entrance pupil plane P of the imaging lens.

[0106] (Table 4) [Overall specifications] f = 200.50 FNO = 6.68 NA = 0.07 Bf = 80.00 TL = 348.66 DA = 160.00 FDN = 25.00 [Lens specifications] Surface number R D nd νd θgF 1 ∞ 160.00 2 78.259 10.55 1.45600 91.37 3 -286.156 0.30 4 65.866 6.60 1.45600 91.37 5 286.969 6.00 6 -573.131 4.65 1.66382 27.35 0.6319 7 -114.403 10.82 1.67300 38.26 8 75.339 37.67 9 63.694 4.64 1.61750 30.83 0.6231 10 41.142 22.43 11 76.078 5.00 1.85025 30.05 12 130.046 Bf [Lens Group Data] Group Initial Surface Focal Length G1 2 192.28 G2 9 -204.21 G3 11 206.81

[0107] Fig. 14 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the imaging lens according to Example 4. Fig. 15 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the imaging lens according to Example 4. Fig. 16 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the imaging lens according to Example 4. From each aberration diagram, it can be seen that the imaging lens according to Example 4 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0108] Fifth Example A fifth example will be described with reference to Figs. 17 to 20 and Table 5. Fig. 17 is a cross-sectional view showing the configuration of an imaging lens according to the fifth example. The imaging lens IL (5) according to the fifth example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power.

[0109] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L11, a positive meniscus lens L12 with its convex surface facing the object side, and a cemented lens formed by cementing a positive meniscus lens L13 with its concave surface facing the object side and a biconcave negative lens L14. The positive meniscus lens L13 of the cemented lens in the first lens group G1 corresponds to a positive lens that satisfies the above-mentioned conditional expression (1) etc.

[0110] The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The negative meniscus lens L21 in the second lens group G2 corresponds to a negative lens that satisfies the above-mentioned conditional expression (5) and the like.

[0111] The third lens group G3 is composed of a biconvex positive lens L31. An image surface I is disposed on the image side of the third lens group G3.

[0112] The values ​​of the specifications of the imaging lens according to Example 5 are shown in Table 5 below. Note that the first surface is the entrance pupil plane P of the imaging lens.

[0113] (Table 5) [Overall specifications] f = 200.25 FNO = 8.01 NA = 0.06 Bf = 149.89 TL = 327.69 DA = 140.00 FDN = 25.00 [Lens specifications] Surface number R D nd νd θgF 1 ∞ 140.00 2 50.458 7.00 1.45600 91.37 3 -1015.705 0.30 4 50.531 5.00 1.45600 91.37 5 242.282 3.00 6 -418.199 4.50 1.75575 24.71 0.6290 7 -78.557 3.00 1.67300 38.26 8 48.197 4.00 9 2824.698 4.00 1.61750 30.83 0.6231 10 56.230 3.00 11 117.967 4.00 1.85025 30.05 12 -236.827 Bf [Lens Group Data] Group Initial Surface Focal Length G1 2 204.84 G2 9 -92.96 G3 11 93.10

[0114] Fig. 18 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the imaging lens of Example 5. Fig. 19 is a diagram showing chromatic aberration of magnification (lateral chromatic aberration) of the imaging lens of Example 5. Fig. 20 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the imaging lens of Example 5. It can be seen from each aberration diagram that the imaging lens of Example 5 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0115] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below, which summarizes the values ​​corresponding to each of the conditional expressions (1) to (13) for all the examples (Examples 1 to 5). Conditional expression (1) -0.002×(νdP-35)+0.602-θgFP<0 Conditional expression (2) 23<νdP<65 Conditional expression (3) 1.55<ndP<1.79 Conditional expression (4) 0.4<fP / f<1.2 Conditional expression (5) -0.0033×(νdN-35)+0.593-θgFN<0 Conditional expression (6) 20<νdN<37 Conditional expression (7) ndN<1.78 Conditional expression (8) -1.1<fN / f<-0.2 Conditional expression (9) 0.2<Bf / TL<0.6 Conditional expression (10) 0.45<f1 / f3<2.4 Conditional expression (11) -2.5<f1 / f2<-0.6 Conditional expression (12) 0.3<DA / TL<0.6 Conditional expression (13) 0.1<FDN / f<0.18

[0116] [Values ​​corresponding to conditional expressions] (First to third examples) Conditional Expression First Example Second Example Third Example (1) -0.0146 -0.0128 -0.0146 (2) 27.35 30.83 27.35 (3) 1.6638 1.6175 1.6638 (4) 0.50 0.88 0.43 (5) -0.0020 -0.0014 -0.0020 (6) 24.71 35.27 24.71 (7) 1.7558 1.5927 1.7558 (8) -0.34 -0.31 -0.26 (9) 0.25 0.31 0.31 (10) 0.53 0.81 0.69 (11) -1.40 -1.66 -1.67 (12) 0.46 0.43 0.40 (13) 0.12 0.16 0.16 [Values ​​corresponding to conditional expressions] (Fourth to Fifth Examples) Conditional Expression Fourth Example Fifth Example (1) -0.0146 -0.0064 (2) 27.35 24.71 (3) 1.6638 1.7558 (4) 1.07 0.64 (5) -0.0163 -0.0163 (6) 30.83 30.83 (7) 1.6175 1.6175 (8) -1.02 -0.46 (9) 0.23 0.46 (10) 0.93 2.20 (11) -0.94 -2.20 (12) 0.46 0.43 (13) 0.12 0.12

[0117] According to the above-described embodiments, it is possible to realize an imaging lens in which chromatic aberration is well corrected over a wide wavelength range, and a microscope apparatus having this imaging lens.

[0118] Here, the above examples show specific examples of this embodiment, and this embodiment is not limited to these.

[0119] In each of the above embodiments, the second lens group G2 is composed of one single lens having negative refractive power, but this is not limited to this and may be composed of one cemented lens having negative refractive power. The third lens group G3 is composed of one single lens having positive refractive power, but this is not limited to this and may be composed of one cemented lens having positive refractive power.

[0120] In each of the above examples, one positive lens (L13) in the imaging lens IL corresponds to a positive lens that satisfies the above-mentioned conditional expression (1), etc., but this is not limited to this, and multiple positive lenses in the imaging lens IL may correspond to positive lenses that satisfy the above-mentioned conditional expression (1), etc.

[0121] G1: First lens group G2: Second lens group G3: Third lens group I: Image plane P: Entrance pupil plane

Claims

1. An imaging lens for a microscope that forms an image from light from an objective lens, An imaging lens having a negative lens and a positive lens that satisfies the following conditional expression: -0.002×(νdP-35)+0.602-θgFP<0 23<νdP<65 where νdP is the Abbe number of the positive lens. θgFP: partial dispersion ratio of the positive lens, which is defined by the following formula when the refractive index of the positive lens with respect to the g-line is ngP, the refractive index of the positive lens with respect to the F-line is nFP, and the refractive index of the positive lens with respect to the C-line is nCP. θgFP=(ngP-nFP) / (nFP-nCP)

2. An imaging lens for a microscope that forms an image from light from an objective lens, An imaging lens having a positive lens and a negative lens that satisfies the following conditional expression: -0.0033×(νdN-35)+0.593-θgFN<0 20<νdN<37 where νdN is the Abbe number of the negative lens. θgFN: partial dispersion ratio of the negative lens, which is defined by the following formula when the refractive index of the negative lens for the g-line is ngN, the refractive index of the negative lens for the F-line is nFN, and the refractive index of the negative lens for the C-line is nCN. θgFN=(ngN-nFN) / (nFN-nCN)

3. An imaging lens as described in claim 1, wherein the positive lens satisfying the above conditional expression is arranged as the Npth lens counting from the object side, and satisfies the following conditional expression: Np-N / 2≦0 Here, N is the total number of lenses included in the imaging lens.

4. An imaging lens as described in claim 2, wherein the negative lens satisfying the conditional expression is arranged closest to the object among the negative lenses possessed by the imaging lens.

5. An imaging lens as described in claim 1 or 3, wherein the positive lens satisfies the following conditional expression. 1.55<ndP<1.79 where ndP is the refractive index of the positive lens with respect to the d line.

6. 5. The imaging lens according to claim 2, wherein the negative lens satisfies the following condition: ndN<1.78 where ndN is the refractive index of the negative lens with respect to the d line.

7. 2. The imaging lens according to claim 1, wherein the positive lens satisfies the following condition: 0.4<fP / f<1.2 where fP is the focal length of the positive lens. f: focal length of the imaging lens

8. 3. The imaging lens according to claim 2, wherein the negative lens satisfies the following condition: -1.1<fN / f<-0.2 where fN is the focal length of the negative lens. f: focal length of the imaging lens

9. 3. The imaging lens according to claim 1, which satisfies the following condition: 0.2<Bf / TL<0.6 where Bf is the back focus of the imaging lens. TL: total length of the imaging lens

10. The optical system comprises a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, the second lens group is composed of one lens component having negative refractive power, 3. The imaging lens according to claim 1, wherein the third lens group is composed of one lens component having positive refractive power.

11. 11. The imaging lens according to claim 10, which satisfies the following condition: 0.45<f1 / f3<2.4 where f1 is the focal length of the first lens group. f3: the focal length of the third lens group

12. 11. The imaging lens according to claim 10, which satisfies the following condition: -2.5<f1 / f2<-0.6 where f1 is the focal length of the first lens group. f2: focal length of the second lens group

13. 3. A microscope apparatus comprising: an objective lens for receiving light from an object and converting it into parallel light; and the imaging lens according to claim 1.

14. 14. The microscope apparatus according to claim 13, which satisfies the following conditional expression: 0.3<DA / TL<0.6 where DA is the distance on the optical axis from the lens surface of the objective lens closest to the image side to the lens surface of the imaging lens closest to the object side. TL: total length of the imaging lens

15. 14. The microscope apparatus according to claim 13, which satisfies the following conditional expression: 0.1<FDN / f<0.18 where FDN is the field number of the microscope device. f: focal length of the imaging lens