Microscope objective lens, microscope optical system, and microscope apparatus

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 third lens group (G3) having a cemented lens (CL31) including a positive lens and a negative lens. The microscope objective lens satisfies the following conditional expression.　0.1 < tg / LA < 0.4 -35 < νd3P-νd3N < 0 where tg is the total sum of center thicknesses of lenses of the microscope objective lens (OL), LA is the distance on the optical axis from a lens surface closest to the object side to a lens surface closest to the image side of the microscope objective lens (OL), νd3P is the Abbe's number of the positive lens of the cemented lens (CL31), and νd3N is the Abbe's number of the negative lens of the cemented lens (CL31).

Description

Technical Field

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

Background Art

[0002] In recent years, various objective lenses for microscopes with a wide field of view and a low magnification have been proposed (see, for example, Patent Document 1). In such objective lenses, it is required to correct various aberrations such as field curvature well.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The microscope objective lens according to the present invention includes, arranged in order from the object side along the optical axis, 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 first lens group condenses the light beam from the object, the second lens group diverges the light beam from the first lens group, and the third lens group has a cemented lens including a positive lens and a negative lens, and makes the divergent light beam from the second lens group into a parallel light beam, and satisfies the following conditional expressions. First lens and a second lens group having a negative refractive power, Second lens and a third lens group having a positive refractive power, and the first lens group First lens condenses the light beam from the object, and the second lens group Second lens is the first lens group First lens diverges the light beam from the first lens group, and the third lens group has a cemented lens including a positive lens and a negative lens, and the second lens group Second lens makes the divergent light beam into a parallel light beam and satisfies the following conditional expressions. 0.1 < tg / LA < 0.4 -35 < νd3P - νd3N < 0 However, tg: the total center thickness of the lenses in the microscope objective lens LA: the distance on the optical axis from the lens surface on the object side of the microscope objective lens to the lens surface on the image side of the microscope objective lens νd3P: the Abbe number of the positive lens in the cemented lens of the third lens group νd3N: the Abbe number of the negative lens in the cemented lens of the third lens group

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

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

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0008] Hereinafter, preferred embodiments according to the present invention will be described. First, a microscope optical system and a confocal fluorescence microscope (microscope apparatus) including a microscope objective lens according to the present embodiment will be described with reference to FIG. 8. As shown in FIG. 8, the confocal fluorescence microscope 1 includes a stage 10, a light source 20, an illumination optical system 30, a microscope optical system 40, and a detection unit 50. In the following description, a coordinate axis extending in the optical axis direction of the microscope objective lens of the confocal fluorescence microscope 1 is defined as the z-axis. Also, coordinate axes extending in directions perpendicular to each other in a plane perpendicular to the z-axis are defined as the x-axis and the y-axis, respectively.

[0009] On the stage 10, for example, a sample SA held between a slide glass (not shown) and a cover glass (not shown) is placed. Alternatively, a sample SA accommodated 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 or the like that has been fluorescently stained in advance. A stage drive unit 11 is provided near the stage 10. The stage drive unit 11 moves the stage 10 along the z-axis.

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

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

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

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

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

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

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

[0017] When the excitation light is irradiated, the fluorescent substance contained in the sample SA is excited to emit fluorescence. The fluorescence from the sample SA passes through the microscope objective lens OL and becomes parallel light. The fluorescence that has passed through the microscope objective lens OL enters the beam splitter 33 through the scanner 34. The fluorescence that has entered the beam splitter 33 passes through the beam splitter 33 and reaches the fluorescence filter 35. The fluorescence that has reached the fluorescence filter 35 passes through the fluorescence filter 35 and then 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 amount of light (brightness) of the light as a detection signal of the light. The detection unit 50 outputs the generated data to a control unit (not shown). The control unit performs a process of arranging the data input from the detection unit 50 as data for one pixel in synchronization with the two-dimensional scanning by the scanner 34, thereby generating one image data in which data for a plurality of pixels are arranged two-dimensionally (in two directions). In this way, the control unit can acquire an image of the sample SA.

[0019] As an example of the microscope apparatus according to the present embodiment, the confocal fluorescence microscope 1 has been described, but the present invention is not limited thereto. For example, the microscope apparatus according to the present embodiment may be an observation microscope for performing bright-field observation, fluorescence observation, etc., a confocal microscope, a multiphoton excitation microscope, a super-resolution microscope, or the like. Further, the confocal fluorescence microscope 1 may be an upright microscope or an inverted microscope.

[0020] Next, the microscope objective lens according to this embodiment will be described. As an example of the microscope objective lens OL according to this embodiment, the microscope objective lens OL(1) shown in FIG. 1 includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power, which are arranged in order from the object side along the optical axis. The first lens group G1 condenses the light beam from the object. The second lens group G2 diverges the light beam from the first lens group G1. The third lens group G3 has a cemented lens including a positive lens and a negative lens, and makes the divergent light beam from the second lens group G2 into a parallel light beam. In this embodiment, the fact that the first lens group G1 condenses the light beam from the object means that the first lens group G1 has a condensing action. For example, when the divergent light beam from the 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] Under the above configuration, the microscope objective lens OL according to this embodiment satisfies the following conditional expressions (1) and (2). 0.1 < tg / LA < 0.4 ···(1) -35 < νd3P - νd3N < 0 ···(2) However, tg: the total center thickness of the lenses in the microscope objective lens OL LA: the distance on the optical axis from the lens surface closest to the object side of the microscope objective lens OL to the lens surface closest to the image side of the microscope objective lens OL νd3P: the Abbe number of the positive lens in the cemented lens of the third lens group G3 νd3N: the Abbe number of the negative lens in the cemented lens of the third lens group G3

[0022] According to this embodiment, it is possible to obtain a microscope objective lens that is an apochromat with well-corrected field curvature, and a microscope optical system and a microscope apparatus including this microscope objective lens. The microscope objective lens OL according to this embodiment may be the optical system OL(2) shown in FIG. 3 or the optical system OL(3) shown in FIG. 5.

[0023] The conditional expression (1) defines an appropriate relationship between the sum of the central thicknesses of the lenses in the microscope objective lens OL and the distance on the optical axis from the lens surface on the object side of the microscope objective lens OL to the lens surface on the image side of the microscope objective lens OL. Note that the central thickness of a lens is the distance on the optical axis from the lens surface on the object side of the lens to the lens surface on the image side of the lens.

[0024] Incidentally, the thicker the lens, the longer the optical path length of the off-axis ray with respect to the on-axis ray, and the relatively weaker the refractive power of the off-axis ray. Therefore, the off-axis imaging position is likely to shift backward, and the correction of the image plane is likely to be excessive. In addition, the thicker the lens, the greater the difference in curvature between the meridional plane and the sagittal plane at the lens surface on the image side of the lens, and furthermore, a difference in refractive power due to the difference in optical path length between the on-axis ray and the off-axis ray occurs, and the shift of the off-axis imaging position is likely to be amplified. Also, in a low-magnification microscope objective lens, since the overall focal length is longer compared to a high-magnification microscope objective lens, an excessive correction of the Petzval sum due to a relatively negative refractive power occurs, a refractive power deficiency occurs with respect to the image plane, particularly the sagittal image plane, and the off-axis imaging position is likely to shift backward.

[0025] Therefore, by reducing the sum of the central thicknesses of the lenses in the microscope objective lens OL, an effect of making it easier to arrange the off-axis imaging position more forward, an effect of making it easier to match the meridional image plane and the sagittal image plane, and an effect of overall making it easier to relax the curvature of the lens surface to eliminate an excessively strong concave surface, i.e., a diverging surface, and to relax the excessive correction of the Petzval sum can be obtained. As a result, by satisfying the conditional expression (1), the sum of the central thicknesses of the lenses in the microscope objective lens OL can be reduced, so that the excessive correction of the Petzval sum can be relaxed, and the image curvature can be corrected well.

[0026] When the corresponding value of the conditional expression (1) exceeds the upper limit value, the sum of the central thicknesses of the lenses in the microscope objective lens OL increases, so that the correction of the Petzval sum becomes excessive, and it becomes difficult to correct the image curvature well. By setting the upper limit value of the conditional expression (1) to 0.38 and further to 0.35, the effects of the present embodiment can be made more reliable.

[0027] When the corresponding value of conditional expression (1) is less than the lower limit value, the total central thickness of the lenses in the microscope objective lens OL becomes too small, making it difficult to arrange the lenses necessary for correcting chromatic aberration including the secondary spectrum. By setting the lower limit value of conditional expression (1) to 0.2, 0.25, and further to 0.27, the effects of the present embodiment can be made more certain.

[0028] Conditional expression (2) 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. By satisfying conditional expression (2), in addition to the first-order color correction, the secondary spectrum of the axial chromatic aberration can be corrected well in the correction of the axial chromatic aberration.

[0029] When the corresponding value of conditional expression (2) exceeds the upper limit value, it becomes difficult to sufficiently correct the secondary spectrum of the axial chromatic aberration. By setting the upper limit value of conditional expression (2) to -5, -7, and further to -10, the effects of the present embodiment can be made more certain.

[0030] When the corresponding value of conditional expression (2) is less than the lower limit value, the correction of the secondary spectrum of the axial chromatic aberration becomes excessive, making it difficult to correct the axial chromatic aberration well. By setting the lower limit value of conditional expression (2) to -30 and further to -25, the effects of the present embodiment can be made more certain.

[0031] In the microscope objective lens OL according to the present embodiment, it is desirable that the first lens group G1 consists of one lens. As a result, since the first lens group G1 becomes shorter, the total central thickness of the lenses in the microscope objective lens OL can be reduced. Therefore, due to the above-described effects, the field curvature can be corrected well.

[0032] In the microscope objective lens OL according to the present embodiment, it is desirable that the second lens group G2 consists of a single lens. As a result, since the second lens group G2 becomes shorter, the total center thickness of the lenses in the microscope objective lens OL can be reduced. Therefore, due to the above-described effect, field curvature can be corrected favorably.

[0033] Note that the microscope objective lens OL according to the present embodiment may be configured such that the first lens group G1 consists of a single lens and the second lens group G2 consists of a single lens. The microscope objective lens OL according to the present embodiment may be configured such that, among 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, one is the largest lens interval (air interval) in the microscope objective lens OL and the other is the second largest lens interval (air interval) in the microscope objective lens OL.

[0034] In the microscope objective lens OL according to the present embodiment, it is desirable that the second lens group G2 consists of a meniscus lens having a convex surface facing the object side. As a result, since the second lens group G2 becomes shorter, the total center thickness of the lenses in the microscope objective lens OL can be reduced. Therefore, due to the above-described effect, field curvature can be corrected favorably.

[0035] In the microscope objective lens OL according to the present embodiment, it is desirable that the cemented lens of the third lens group G3 consists of a positive lens and a negative lens. In the microscope objective lens OL according to the present embodiment, it is desirable that the cemented lens of the third lens group G3 is disposed on the most object side of the third lens group G3.

[0036] The microscope objective lens OL according to the present embodiment preferably satisfies the following conditional expression (3). 0.1 < t3 / LA < 0.4 ···(3) However, t3: the distance on the optical axis from the lens surface on the most object side of the third lens group G3 to the lens surface on the most image side of the third lens group G3

[0037] Conditional expression (3) defines an appropriate relationship between the distance on the optical axis from the lens surface closest to the object side of the third lens group G3 to the lens surface closest to the image side of the third lens group G3, and the distance on the optical axis from the lens surface closest to the object side of the microscope objective lens OL to the lens surface closest to the image side of the microscope objective lens OL. By satisfying conditional expression (3), the third lens group G3 becomes shorter, so that the total center thickness of the lenses in the microscope objective lens OL can be reduced. Therefore, due to the above-described effect, field curvature can be corrected well.

[0038] When the corresponding value of conditional expression (3) exceeds the upper limit value, the third lens group G3 becomes longer, and the total center thickness of the lenses in the microscope objective lens OL becomes larger. Therefore, the curvature of the diverging surface of the lens is not relaxed and the correction of the Petzval sum tends to be excessive, making it difficult to correct field curvature well. By setting the upper limit value of conditional expression (3) to 0.38, and further to 0.35, the effects of the present embodiment can be made more certain.

[0039] When the corresponding value of conditional expression (3) is below the lower limit value, the third lens group G3 becomes too short, and the total center thickness of the lenses in the microscope objective lens OL becomes too small. Therefore, it becomes difficult to arrange the lenses necessary for correcting chromatic aberration including secondary spectrum. By setting the lower limit value of conditional expression (3) to 0.2, 0.25, and further to 0.27, the effects of the present embodiment can be made more certain.

[0040] The microscope objective lens OL according to the present embodiment preferably satisfies the following conditional expression (4). 0.1 < (Rc2 + Rc1) / (Rc2 - Rc1) < 1 ···(4) However, Rc1: The radius of curvature of the lens surface closest to the object side in the cemented lens of the third lens group G3 Rc2: The radius of curvature of the lens surface closest to the image side in the cemented lens of the third lens group G3

[0041] Conditional expression (4) defines an appropriate range for the shape factor of the cemented lens of the third lens group G3. By satisfying conditional expression (4), it becomes possible to shorten the third lens group G3 and relax the curvature of the diverging surface of the lens in the third lens group G3, and it is possible to reduce the total center thickness of the lenses in the microscope objective lens OL. Therefore, as described above, it becomes possible to relax the excessive correction of the Petzval sum, and it is possible to correct the field curvature well.

[0042] When the corresponding value of conditional expression (4) exceeds the upper limit value, it becomes difficult to shorten the third lens group G3, and the total center thickness of the lenses in the microscope objective lens OL increases. Therefore, the curvature of the diverging surface of the lens in the third lens group G3 cannot be relaxed and the correction of the Petzval sum becomes excessive, making it difficult to correct the field curvature well. By setting the upper limit value of conditional expression (4) to 0.95 and further to 0.9, the effects of this embodiment can be made more certain.

[0043] When the corresponding value of conditional expression (4) is below the lower limit value, it becomes difficult to shorten the third lens group G3, and the total center thickness of the lenses in the microscope objective lens OL increases. Therefore, the curvature of the diverging surface of the lens in the third lens group G3 cannot be relaxed and the correction of the Petzval sum becomes excessive, making it difficult to correct the field curvature well. By setting the lower limit value of conditional expression (4) to 0.15 and further to 0.2, the effects of this embodiment can be made more certain.

[0044] The microscope objective lens OL according to this embodiment preferably satisfies the following conditional expression (5). 0.03 < tc / LA < 0.08 ···(5) However, tc: the distance on the optical axis from the most object-side lens surface of the cemented lens of the third lens group G3 to the most image-side lens surface of the cemented lens of the third lens group G3

[0045] Conditional expression (5) defines an appropriate relationship between the distance on the optical axis from the most object-side lens surface of the cemented lens of the third lens group G3 to the most image-side lens surface of the cemented lens of the third lens group G3, and the distance on the optical axis from the most object-side lens surface of the microscope objective lens OL to the most image-side lens surface of the microscope objective lens OL. By satisfying conditional expression (5), the cemented lens of the third lens group G3 becomes thinner, so that the total center thickness of the lenses in the microscope objective lens OL can be reduced. Therefore, due to the above-described effect, field curvature can be corrected well.

[0046] When the corresponding value of conditional expression (5) exceeds the upper limit value, the cemented lens of the third lens group G3 becomes thicker, and the total center thickness of the lenses in the microscope objective lens OL increases. Therefore, the curvature of the diverging surface of the lens is not relaxed and the correction of the Petzval sum tends to be excessive, making it difficult to correct field curvature well. By setting the upper limit value of conditional expression (5) to 0.07, and further to 0.06, the effects of the present embodiment can be made more reliable.

[0047] When the corresponding value of conditional expression (5) is below the lower limit value, the cemented lens of the third lens group G3 becomes too thin, making it difficult to arrange the lenses necessary for correcting chromatic aberration including secondary spectrum. By setting the lower limit value of conditional expression (5) to 0.035, and further to 0.04, the effects of the present embodiment can be made more reliable.

[0048] The microscope objective lens OL according to the present embodiment preferably satisfies the following conditional expression (6). 0.6 < θgF3P < 0.7 ···(6) However, θgF3P: the partial dispersion ratio of the positive lens in the cemented lens of the third lens group G3. When the refractive index of the positive lens with respect to the g-line is ng3P, the refractive index of the positive lens with respect to the F-line is nF3P, and the refractive index of the positive lens with respect to the C-line is nC3P, it is defined by the following formula θgF3P = (ng3P - nF3P) / (nF3P - nC3P)

[0049] Conditional expression (6) 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 expression (6), in the correction of axial chromatic aberration, in addition to primary color correction, the secondary spectrum can be corrected well.

[0050] When the corresponding value of conditional expression (6) exceeds the upper limit value, the correction of the secondary spectrum of axial chromatic aberration becomes excessive, and it becomes difficult to correct axial chromatic aberration well. By setting the upper limit value of conditional expression (6) to 0.68, and further to 0.65, the effects of this embodiment can be made more certain.

[0051] When the corresponding value of conditional expression (6) is below the lower limit value, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the lower limit value of conditional expression (6) to 0.61, and further to 0.62, the effects of this embodiment can be made more certain.

[0052] The microscope objective lens OL according to this embodiment preferably satisfies the following conditional expressions (7) and (8). 0.02 < θgF3P - (0.645 - 0.0017 × νd3P) < 0.12 ···(7) 20 < νd3P < 35 ···(8) However, θgF3P: is the partial dispersion ratio of the positive lens in the cemented lens of the third lens group G3. When the refractive index of the positive lens with respect to the g-line is ng3P, the refractive index of the positive lens with respect to the F-line is nF3P, and the refractive index of the positive lens with respect to the C-line is nC3P, it is defined by the following formula θgF3P = (ng3P - nF3P) / (nF3P - nC3P)

[0053] 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 the correction of axial chromatic aberration, in addition to primary color correction, secondary spectrum can be corrected well.

[0054] When the corresponding value of conditional expression (7) exceeds the upper limit value, the correction of the secondary spectrum of axial chromatic aberration becomes excessive, and it becomes difficult to correct axial chromatic aberration well. By setting the upper limit value of conditional expression (7) to 0.1, and further to 0.08, the effects of this embodiment can be made more reliable.

[0055] When the corresponding value of conditional expression (7) is below the lower limit value, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the lower limit value of conditional expression (7) to 0.021, and further to 0.022, the effects of this embodiment can be made more reliable.

[0056] When the corresponding value of conditional expression (8) exceeds the upper limit value, it becomes difficult to sufficiently correct the secondary spectrum of axial chromatic aberration. By setting the upper limit value of conditional expression (8) to 33, and further to 30, the effects of this embodiment can be made more reliable.

[0057] When the corresponding value of conditional expression (8) is below the lower limit value, the correction of the secondary spectrum of axial chromatic aberration becomes excessive, and it becomes difficult to correct axial chromatic aberration well. By setting the lower limit value of conditional expression (8) to 21, and further to 22, the effects of this embodiment can be made more reliable.

[0058] It is desirable that the microscope objective lens OL according to this embodiment satisfies the following conditional expression (9). 0.75 < f / LA < 2.2 ···(9) However, f: focal length of the microscope objective lens OL

[0059] The conditional expression (9) defines an appropriate relationship between the focal length of the microscope objective lens OL and the distance on the optical axis from the lens surface closest to the object side of the microscope objective lens OL to the lens surface closest to the image side of the microscope objective lens OL. By satisfying the conditional expression (9), it is preferable because a microscope objective lens with a low magnification can be obtained. By setting the upper limit value of the conditional expression (9) to 2.1, and further to 2, the effects of the present embodiment can be made more certain. By setting the lower limit value of the conditional expression (9) to 0.85, and further to 0.95, the effects of the present embodiment can be made more certain.

Example

[0060] Hereinafter, an example of the microscope objective lens OL according to the present embodiment will be described with reference to the drawings. FIGS. 1, 3, and 5 are optical path diagrams showing the configurations of the microscope objective lenses OL {OL(1) to OL(3)} according to the first to third embodiments. In FIGS. 1, 3, and 5, 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, in order to prevent the types and numbers of symbols and numbers from becoming large and complicated, the lens and the like are represented by independent combinations of symbols and numbers for each embodiment. Therefore, even if the same combination of symbol and number is used between embodiments, it does not mean that they have the same configuration.

[0061] Tables 1 to 3 are shown below. Among these, Table 1 shows the various element data in the first embodiment, Table 2 shows the various element data in the second embodiment, and Table 3 shows the various element data in the third embodiment. In each embodiment, d-line (wavelength λ = 587.6 nm), C-line (wavelength λ = 656.3 nm), F-line (wavelength λ = 486.1 nm), and g-line (wavelength λ = 435.8 nm) are selected as the objects for calculating the aberration characteristics.

[0062] In the table of [[Overall Specifications]], f indicates the focal length of the microscope objective lens. β indicates the magnification of the microscope objective lens. NA indicates the numerical aperture of the microscope objective lens. WD indicates the working distance of the microscope objective lens. LA indicates the distance on the optical axis from the most object-side lens surface of the microscope objective lens to the most image-side lens surface of the microscope objective lens. tg indicates the total sum of the center thicknesses of the lenses in the microscope objective lens. t3 indicates the distance on the optical axis from the most object-side lens surface of the third lens group to the most image-side lens surface of the third lens group. tc indicates the distance on the optical axis from the most object-side lens surface of the cemented lens arranged on the most object side of the third lens group to the most image-side lens surface of the cemented lens arranged on the most object side of the third lens group.

[0063] In the table of [[Lens Data]], the surface number indicates the order of the lens surfaces from the object side. R is the radius of curvature corresponding to each surface number (a positive value for a lens surface convex on the object side). D is the lens thickness or air interval on the optical axis corresponding to each surface number. nd is the refractive index of the optical material corresponding to each surface number with respect to the d-line (wavelength λ = 587.6 nm). νd is the Abbe number of the optical material corresponding to each surface number based on the d-line. θgF indicates the partial dispersion ratio of the material of the optical member corresponding to each surface number. "∞" for the radius of curvature indicates a plane or an aperture. Also, the description of the refractive index of air nd = 1.00000 is omitted.

[0064] Let ng be the refractive index of the material of the optical member with respect to the g-line (wavelength λ = 435.8 nm), nF be the refractive index of the material of the optical member with respect to the F-line (wavelength λ = 486.1 nm), and nC be the refractive index of the material of the optical member with respect to the C-line (wavelength λ = 656.3 nm). At this time, the partial dispersion ratio θgF of the material of the optical member is defined by the following formula (A).

[0065] θgF = (ng - nF) / (nF - nC) …(A)

[0066] In the table of [[Lens Group Data]], the starting surface (the most object-side surface) and the focal length of each lens group are shown.

[0067] Hereinafter, for all the specification values, the focal length f, radius of curvature R, surface interval D, and other lengths, etc. that are published are generally "mm" when not otherwise specified. However, since the optical system can obtain the same optical performance even if it is proportionally enlarged or reduced, it is not limited to this.

[0068] The explanations of the tables up to this point are common to all the embodiments, and the overlapping explanations below are omitted.

[0069] (First Embodiment) The first embodiment will be described with reference to FIGS. 1 to 2 and Table 1. FIG. 1 is an optical path diagram showing the configuration of the microscope objective lens according to the first embodiment. The microscope objective lens OL(1) according to the first embodiment is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power, which are arranged in order from the object side along the optical axis. The space between the tip of the microscope objective lens OL(1) according to the first embodiment and the cover glass CV covering the object is filled with air. Note that the refractive index of the cover glass CV with respect to the d-line (wavelength λ = 587.6 nm) is 1.52216.

[0070] The first lens group G1 condenses the light beam from the object. Also, the first lens group G1 collects the off-axis rays from the object more toward the optical axis. The first lens group G1 is composed of a biconvex positive lens L11.

[0071] The second lens group G2 diverges the light beam from the first lens group G1. The second lens group G2 is composed of a negative meniscus lens 21 with the convex surface facing the object side.

[0072] The third lens group G3 makes the divergent light beam from the second lens group G2 into a parallel light beam. The third lens group G3 is composed of a first cemented lens CL31 formed by cementing a biconcave negative lens L31 and a positive meniscus lens L32 with the convex surface facing the object side, which are arranged in order from the object side along the optical axis, a second cemented lens CL32 formed by cementing a biconcave negative lens L33 and a biconvex positive lens L34, and a biconvex positive lens L35.

[0073] Table 1 below lists the specifications of the microscope objective lens according to the first embodiment.

[0074] (Table 1) [Overall specifications] f = 100 β = 2x NA = 0.1 WD = 9.09 LA = 55.140 tg = 16.063 t3 = 16.670 tc = 2.646 [Lens data] Surface number R D nd νd θg 1 ∞ 0.170 1.52216 58.80 2 ∞ 9.090 3 31.936 2.661 1.67300 38.26 4 -53.740 15.409 5 23.922 1.000 1.65160 58.62 6 8.657 19.399 7 -26.025 1.000 1.78800 47.35 8 22.327 1.646 1.66382 27.35 0.6319 9 76.703 3.971 10 -796.845 1.000 1.83400 37.18 11 55.780 3.730 1.43425 94.77 12 -20.552 0.298 13 187.183 5.026 1.45600 91.37 14 -17.298 ― [Lens group data] Group Starting surface Focal length G1 3 30.14 G2 5 -21.37 G3 7 59.39

[0075] FIG. 2 is a diagram showing various aberrations (spherical aberration and field curvature) of the microscope objective lens according to the first embodiment. Each aberration diagram shows the various aberrations in a state where a second objective lens is combined with the microscope objective lens. In each aberration diagram of FIG. 2, d represents the various aberrations with respect to the d-line (wavelength λ = 587.6 nm), C represents the C-line (wavelength λ = 656.3 nm), F represents the F-line (wavelength λ = 486.1 nm), and g represents the g-line (wavelength λ = 435.8 nm). In the spherical aberration diagram, the vertical axis represents the value normalized with the maximum value of the entrance pupil radius being 1, and the horizontal axis represents the aberration value [mm] for each ray. In the aberration diagram showing field curvature, the solid line represents the meridional image plane for each wavelength, and the dashed line represents the sagittal image plane for each wavelength. Also, in the aberration diagram showing field curvature, the vertical axis represents the image height [mm], and the horizontal axis represents the aberration value [mm]. In the aberration diagrams of each of the following embodiments, the same reference numerals as those in this embodiment are used, and repeated explanations are omitted.

[0076] From each aberration diagram, it can be seen that the microscope objective lens according to the first embodiment has good correction of various aberrations and excellent imaging performance.

[0077] (Second Embodiment) The second embodiment will be described with reference to FIGS. 3 to 4 and Table 2. FIG. 3 is an optical path diagram showing the configuration of the microscope objective lens according to the second embodiment. The microscope objective lens OL(2) according to the second embodiment is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power, which are arranged in order from the object side along the optical axis. The space between the tip of the microscope objective lens OL(2) according to the second embodiment and the cover glass CV covering the object 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 each of the lens groups G1 to G3 in the second embodiment is configured in the same manner as in the first embodiment, the same reference numerals as those in the case of the first embodiment are given, and detailed descriptions of these lenses are omitted.

[0078] The following Table 2 lists the values of the specifications of the microscope objective lens according to the second embodiment.

[0079] (Table 2) [Overall Specifications] f = 100 β = 2 times NA = 0.1 WD = 9.00 LA = 55.140 tg = 16.173 t3 = 15.348 tc = 2.732 [Lens Data] Surface No. R D nd νd θgF 1 ∞ 0.170 1.52216 58.80 2 ∞ 9.000 3 28.627 2.648 1.67300 38.26 4 -68.866 16.273 5 32.926 1.000 1.59319 67.90 6 8.439 19.871 7 -22.962 1.000 1.84000 46.60 8 29.089 1.732 1.66382 27.35 0.6319 9 256.408 1.110 10 -512.897 1.000 1.83400 37.18 11 41.887 3.687 1.43254 94.77 12 -19.058 1.713 13 181.077 5.106 1.49782 82.57 14 -17.032 ― [Lens Group Data] Group Starting Surface Focal Length G1 3 30.38 G2 5 -19.43 G3 7 54.90

[0080] Figure 4 is a diagram showing various aberrations (spherical aberration and field curvature) of the microscope objective lens according to the second embodiment. From each aberration diagram, it can be seen that the microscope objective lens according to the second embodiment has good correction of various aberrations and excellent imaging performance.

[0081] (Third Embodiment) For the third embodiment, it will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 is an optical path diagram showing the configuration of the microscope objective lens according to the third embodiment. The microscope objective lens OL(3) according to the third embodiment is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power, which are arranged in order from the object side along the optical axis. The space between the tip of the microscope objective lens OL(3) according to the third embodiment and the cover glass CV covering the object is filled with air. Note that the refractive index of the cover glass CV with respect to the d-line (wavelength λ = 587.6 nm) is 1.52216. Since each of the lens groups G1 to G3 in the third embodiment is configured in the same manner as in the first embodiment, the same reference numerals as those in the first embodiment are given, and detailed descriptions of these lenses are omitted.

[0082] The following Table 3 lists the specifications of the microscope objective lens according to the third embodiment.

[0083] (Table 3) [Overall specifications] f = 100 β = 2x NA = 0.1 WD = 8.98 LA = 55.050 tg = 16.271 t3 = 15.034 tc = 2.701 [Lens data] Surface number R D nd νd θgF 1 ∞ 0.170 1.52216 58.80 2 ∞ 8.980 3 37.069 2.237 1.67300 38.26 4 -55.854 19.889 5 28.258 1.000 1.59319 67.90 6 8.247 16.889 7 -21.999 1.000 1.83481 42.73 8 31.725 1.701 1.80809 22.74 0.6288 9 345.459 1.000 10 -195.290 1.503 1.83400 37.18 11 39.045 3.877 1.43254 94.77 12 -18.469 1.000 13 158.897 4.953 1.49782 82.57 14 -16.263 ― [Lens group data] Group Starting surface Focal length G1 3 33.43 G2 5 -20.00 G3 7 59.96

[0084] FIG. 6 is a diagram showing various aberrations (spherical aberration and field curvature) of the microscope objective lens according to the third embodiment. From each aberration diagram, it can be seen that the microscope objective lens according to the third embodiment has good correction of various aberrations and excellent imaging performance.

[0085] Since the microscope objective lens according to each embodiment is an infinity-corrected type lens, it is used in combination with a second objective lens that condenses light from the microscope objective lens. Therefore, an example of the second objective lens used in combination with the microscope objective lens will be described with reference to FIGS. 7 and 4. FIG. 7 is a cross-sectional view showing the configuration of the second objective lens used in combination with the microscope objective lens according to each embodiment. The aberration diagrams of the microscope objective lens according to each embodiment are those when used in combination with this second objective lens. The second objective lens IL shown in FIG. 7 is composed of a first cemented lens CL41 formed by cementing a biconvex positive lens L41 and a biconcave negative lens L42 arranged in order from the object side along the optical axis, and a second cemented lens CL42 formed by cementing a biconvex positive lens L43 and a biconcave negative lens L44.

[0086] The following Table 4 lists the values of the specifications of the second objective lens. In the table of [Lens data], the surface number, R, D, nd, and νd are the same as those shown in the descriptions of Tables 1 to 3 above.

[0087] (Table 4) [Lens Data] Surface Number R D nd νd 1 75.043 5.100 1.62280 57.03 2 -75.043 2.000 1.74950 35.19 3 1600.580 7.500 4 50.256 5.100 1.66755 41.96 5 -84.541 1.800 1.61266 44.40 6 36.911 ―

[0088] Next, the table of [Conditional Expression Corresponding Values] is shown below. This table shows the values corresponding to each of the conditional expressions (1) to (9) for all the examples (Examples 1 to 3) summarized together. Conditional Expression (1) 0.1 < tg / LA < 0.4 Conditional Expression (2) -35 < νd3P - νd3N < 0 Conditional Expression (3) 0.1 < t3 / LA < 0.4 Conditional Expression (4) 0.1 < (Rc2 + Rc1) / (Rc2 - Rc1) < 1 Conditional Expression (5) 0.03 < tc / LA < 0.08 Conditional Expression (6) 0.6 < θgF3P < 0.7 Conditional Expression (7) 0.02 < θgF3P - (0.645 - 0.0017×νd3P) < 0.12 Conditional Expression (8) 20 < νd3P < 35 Conditional Expression (9) 0.75 < f / LA < 2.2

[0089] [Conditional Expression Corresponding Values] Conditional Expression Example 1 Example 2 Example 3 (1) 0.29 0.29 0.30 (2) -20.00 -19.25 -19.99 (3) 0.30 0.28 0.27 (4) 0.49 0.84 0.88 (5) 0.048 0.049 0.049 (6) 0.6319 0.6319 0.6288 (7) 0.0334 0.0334 0.0226 (8) 27.35 27.35 22.74 (9) 1.8136 1.8136 1.8165

[0090] According to each of the above embodiments, it is possible to realize a microscope objective lens that is an apochromat with well-corrected field curvature.

[0091] Here, each of the above embodiments shows a specific example of the present embodiment, and the present embodiment is not limited thereto.

Explanation of Reference Numerals

[0092] G1 First lens group G2 Second lens group G3 Third lens group

Claims

1. It consists of a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens group having a positive refractive power, arranged in order from the object side along the optical axis. The first lens condenses the light beam from the object. The second lens diverges the light beam from the first lens. The third lens group has a cemented lens including a positive lens and a negative lens, and collimates the diverging light beam from the second lens. A microscope objective lens that satisfies the following conditional expressions. 0.1 < tg / LA < 0.4 -35 < νd3P - νd3N < 0 However, tg: The total center thickness of the lenses in the microscope objective lens. LA: The distance on the optical axis from the lens surface on the object side of the microscope objective lens to the lens surface on the image side of the microscope objective lens. νd3P: The Abbe number of the positive lens in the cemented lens of the third lens group. νd3N: The Abbe number of the negative lens in the cemented lens of the third lens group.

2. The microscope objective lens according to Claim 1, wherein the second lens consists of a meniscus lens with a convex surface facing the object side.

3. The microscope objective lens according to Claim 1, wherein the cemented lens of the third lens group consists of the positive lens and the negative lens.

4. The microscope objective lens according to Claim 1, wherein the cemented lens of the third lens group is arranged on the most object side of the third lens group.

5. The microscope objective lens according to Claim 4, which satisfies the following conditional expression. 0.1 < t3 / LA < 0.4 However, t3: The distance on the optical axis from the lens surface on the object side of the third lens group to the lens surface on the image side of the third lens group.

6. The microscope objective lens according to Claim 4, which satisfies the following conditional expression. 0.1 < (Rc2 + Rc1) / (Rc2 - Rc1) < 1 However, Rc1: The radius of curvature of the lens surface on the most object side in the cemented lens of the third lens group. Rc2: The radius of curvature of the lens surface on the most image side in the cemented lens of the third lens group.

7. The microscope objective lens according to Claim 4, which satisfies the following conditional expression. 0.03 < tc / LA < 0.08 However, tc: The distance on the optical axis from the lens surface on the object side of the cemented lens of the third lens group to the lens surface on the image side of the cemented lens of the third lens group.

8. The microscope objective lens according to Claim 4, which satisfies the following conditional expression. 0.6 < θgF3P < 0.7 However, θgF3P is the partial dispersion ratio of the positive lens in the cemented lens of the third lens group. When the refractive index of the positive lens with respect to the g-line is ng3P, the refractive index of the positive lens with respect to the F-line is nF3P, and the refractive index of the positive lens with respect to the C-line is nC3P, it is defined by the following formula θgF3P = (ng3P - nF3P) / (nF3P - nC3P)

9. The microscope objective lens according to claim 4, which satisfies the following conditional expression 0.02 < θgF3P - (0.645 - 0.0017 × νd3P) < 0.12 20 < νd3P < 35 However, θgF3P is the partial dispersion ratio of the positive lens in the cemented lens of the third lens group. When the refractive index of the positive lens with respect to the g-line is ng3P, the refractive index of the positive lens with respect to the F-line is nF3P, and the refractive index of the positive lens with respect to the C-line is nC3P, it is defined by the following formula θgF3P = (ng3P - nF3P) / (nF3P - nC3P)

10. The microscope objective lens according to claim 1, which satisfies the following conditional expression 0.75 < f / LA < 2.2 However, f is the focal length of the microscope objective lens

11. A microscope optical system comprising the microscope objective lens according to any one of claims 1 to 10 and a second objective lens that condenses light from the microscope objective lens

12. A microscope apparatus comprising the microscope objective lens according to any one of claims 1 to 10

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