Image-formation lens and microscope device

Abstract

An image-formation lens (IL) is for a microscope and forms an image of light from an objective lens. The image-formation lens comprises, in order from the object side, a first lens group (G1) that has a positive refractive power, and a second lens group (G2) that is disposed on the image side of the first lens group and that has a negative refractive power. The second lens group includes a meniscus-shaped lens component that has a concave surface on the object side, and satisfies the following conditional formula.　0.20≤BF / D≤ 0.25, where BF represents the back focus of the image-formation lens (IL), and D represents the distance along the optical axis between the image surface and the lens surface located farthest on the object side in the image-formation lens (IL).

Description

Imaging lens and microscope device

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

[0002] Conventionally, an inverted microscope in which a photographing optical system and a transmitted illumination optical system are arranged on either side of a sample is known as an apparatus for observing a subject such as a cell without labeling (see, for example, Patent Document 1). However, in the case of a sample observation apparatus or the like installed in an incubator, the size of the apparatus needs to be small in order to enable sample exchange in a limited working space, and therefore the transmitted illumination optical system, photographing optical system, etc. need to be designed to be compact overall.

[0003] US Publication No. 2021 / 0033839

[0004] The imaging lens according to the present invention is an imaging lens for a microscope that forms an image from light from an objective lens, and includes, in order from the object side, a first lens group having positive refractive power and a second lens group having negative refractive power that is arranged closer to the image side than the first lens group, the second lens group including a meniscus lens component with a concave surface facing the object side, and satisfies the following condition: 0.20≦BF / D≦0.25, where BF is the back focal length of the imaging lens, and D is the distance on the optical axis from the lens surface of the imaging lens closest to the object side to the image plane.

[0005] A microscope apparatus according to the present invention includes an objective lens that receives light from an object and converts it into parallel light, the above-described imaging lens, and an image sensor that captures the image of the object formed by the imaging lens.

[0006] FIG. 1 is a cross-sectional view showing the configuration of an imaging lens according to a first example. FIG. 2 is a diagram showing various aberrations of the imaging lens according to the first example. FIG. 3 is a cross-sectional view showing the configuration of an imaging lens according to a second example. FIG. 4 is a diagram showing various aberrations of the imaging lens according to the second example. FIG. 5 is a cross-sectional view showing the configuration of an imaging lens according to a third example. FIG. 6 is a diagram showing various aberrations of the imaging lens according to the third example. FIG. 7 is a cross-sectional view showing the configuration of an imaging lens according to a fourth example. FIG. 8 is a diagram showing various aberrations of the imaging lens according to the fourth example. FIG. 9 is a cross-sectional view showing the configuration of an imaging lens according to a fifth example. FIG. 10 is a diagram showing various aberrations of the imaging lens according to the fifth example. FIG. 11 is a schematic diagram showing an example of a microscope device. FIG. 12 is a schematic diagram showing a time-lapse observation device in which a microscope device is installed.

[0007] A preferred embodiment of the present invention will now be described. FIG. 11 shows a microscope MS equipped with an imaging lens according to this embodiment. The imaging lens of the microscope is a lens that focuses an infinitely focused beam of light from an objective lens. When used in combination with an infinity-corrected objective lens, it can magnify and display light from a sample on an image plane. This allows the microscope to observe a magnified sample. The microscope MS according to this embodiment is a microscope that uses epi-illumination to observe a sample as a reflected bright-field image. The microscope MS includes a light source 10 via an objective lens OBL, a light source unit 11 that irradiates a sample SA mounted on a sample stage 12 above the optical system with light from the light source 10, a reflective member 14 such as a mirror mounted above the sample SA and facing the objective lens OBL, the objective lens OBL, an imaging lens IL according to the present invention, an image sensor 15 positioned at the image plane I formed by the imaging lens IL, and a movable stage 16. The sample SA is placed in an observation container 13 on the sample stage 12, which is transparent to the light from the light source 10. Light from the light source 10 is emitted upward in FIG. 11 by a half mirror in the light source unit 11, and then passes through the objective lens OBL and the sample stage 12 to perpendicularly irradiate the sample SA. The light irradiated onto the sample SA and the transmitted light that passes through the sample and is reflected by the reflecting member 14 or the culture medium in the observation container 13 or the container itself and returns to the microscope device MS are imaged on the image plane I by the objective optical system located below the sample SA, thereby obtaining a reflected bright-field image. The observation container 13 can be, for example, a well plate.

[0008] The objective optical system is composed of an objective lens OBL and an imaging lens IL. An image sensor 15 is disposed at the image plane I of the imaging lens IL. The objective lens OBL focuses and magnifies light transmitted through the sample SA, and the transmitted light is then focused on the image plane I of the image sensor 15 by the imaging lens IL. The image sensor 15 is a solid-state image sensor having multiple pixels. The image on the image sensor 15 can be observed on a monitor (not shown) by photoelectrically converting the image focused on the image plane I by the imaging lens IL. The microscope MS can be remotely controlled by the control device 103. The objective optical system can change the field of view of the resulting image by moving the movable stage 16 in the X direction, which is the left-right direction in FIG. 11 , and in the Y direction, which is perpendicular to the X direction. The objective optical system can also be moved in the Z direction, which is perpendicular to both the X and Y directions, which is the up-down direction in FIG. 11 , to adjust the focal position. The objective optical system, the image sensor 15, the light source 10, the light source unit 11, the movable stage 16, etc. are arranged in a sealed container 17.

[0009] Next, a time-lapse observation device including the imaging lens and microscope apparatus according to this embodiment will be described with reference to FIG. 12 . FIG. 12 is a perspective view showing the schematic configuration of a microscope apparatus including the imaging lens according to this embodiment and a time-lapse observation device including the microscope apparatus. FIG. 12 shows the main components described below, but does not show all of the components of the time-lapse observation device. The microscope apparatus MS is installed inside a time-lapse observation device 100, such as an incubator shown in FIG. 12 , allowing for sample observation while maintaining a constant internal environment. The time-lapse observation device 100 includes a time-lapse observation chamber 101, which includes a door 102 that opens and closes to allow samples to be inserted and removed. The sample observation device 100 may also include an artificial climate generator (not shown) that maintains a constant internal environment. The microscope apparatus MS according to this embodiment is placed inside the time-lapse observation chamber 101, and the above-mentioned control device 103 is installed outside the time-lapse observation chamber 101, allowing for remote control of the microscope apparatus MS for observation. Furthermore, the control device 103 may be configured to be able to perform image processing on the obtained images using hardware and software, in addition to remote control.

[0010] The control device 103 is composed of a processing unit 1, an operation unit 2, a display unit 3, and a memory unit 4. The processing unit 1 executes various processes using computer programs and data stored in a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory). The operation unit 2 is a user interface including a keyboard, mouse, touch panel, and various buttons, and is capable of inputting various instructions and information into the processing unit 1. The operation unit 2 can also remotely control the microscope device MS. The display unit 3 is a display device such as an LCD screen or touch panel screen, and can display the results of processing performed by the processing unit 1, images of the sample obtained from the microscope device MS, or images that have undergone image processing. The memory unit 4 is a large-capacity storage device such as a hard disk drive. The storage unit 4 stores various data such as programs for executing processing in the processing unit 1, image data acquired from the microscope device MS, temporary image data during the image processing, device settings of the microscope device MS, values ​​set by the user, etc. The control device 103 may include an image processing unit that executes image processing on images acquired by the microscope device MS.

[0011] Although the above-described device has been described as an example of a microscope device according to this embodiment, the present invention is not limited to this. Although the microscope device using reflected bright-field observation has been described, a fluorescent microscope device using fluorescent observation may also be used.

[0012] As the imaging lens provided in such a microscope apparatus, the imaging lens IL described below can be used. First, the imaging lens IL according to the first embodiment will be described.

[0013] 1, an example of the imaging lens IL according to the first embodiment, is an imaging lens IL(1) that has, from the object side, a first lens group having positive refractive power, and a second lens group having negative refractive power that is arranged closer to the image plane than the first lens group, and the second lens group includes a meniscus-shaped lens component with its concave surface facing the object side, and satisfies the following conditional expression (1): 0.2≦BF / D≦0.25 (1), where BF is the back focal length of the imaging lens, and D is the distance on the optical axis from the lens surface of the imaging lens closest to the object to the image plane.

[0014] According to the first embodiment, it is possible to obtain a compact imaging lens in which aberrations are well corrected over a wide field of view, and a microscope apparatus having this imaging lens. Note that the term "lens component" is sometimes used in this specification, and in this case, the term "lens component" is used to mean both a single lens and a cemented lens. The imaging lens IL according to the first embodiment may be the imaging lens IL(2) shown in FIG. 3, the imaging lens IL(3) shown in FIG. 5, the imaging lens IL(4) shown in FIG. 7, or the imaging lens IL(5) shown in FIG. 9.

[0015] Conditional expression (1) defines an appropriate relationship between the back focus of the imaging lens IL and the distance on the optical axis from the lens surface of the imaging lens closest to the object to the image plane (total optical length of the imaging lens). By satisfying conditional expression (1), optical elements such as prisms and half mirrors can be disposed within the optical system of the imaging lens, preventing the optical path from becoming long in one direction and enabling the miniaturization of a microscope apparatus using the imaging lens. Note that the back focus is the distance on the optical axis from the lens surface of the imaging lens closest to the image plane to the image plane.

[0016] If the value corresponding to condition (1) exceeds the upper limit, it becomes difficult to correct curvature of field and coma, and if the value corresponding to condition (1) falls below the lower limit, it becomes difficult to arrange optical elements such as prisms and half mirrors in the imaging lens optical system.

[0017] The imaging lens IL according to the first embodiment may satisfy the following conditional expression (2): 0≦RMS(Fiy)≦0.1[λF] (2), where RMS(Fiy): the amount of wavefront aberration of the F-line relative to the optimal defocus position for the d-line, which depends on the image height ratio Fiy to the maximum image height Y (where 0≦Fiy≦1.0), and λF: the wavelength of the F-line.

[0018] Conditional expression (2) defines the amount of RMS wavefront aberration for the F-line relative to the optimal defocus position for the d-line within an appropriate range. By satisfying conditional expression (2), chromatic aberration of the imaging lens can be effectively corrected.

[0019] If the corresponding value of conditional expression (2) exceeds the upper limit, it becomes difficult to correct chromatic aberration. By setting the upper limit of conditional expression (2) to 0.095, or even 0.090, the effect of this embodiment can be made more certain.

[0020] If the corresponding value of conditional expression (2) falls below the lower limit, it becomes difficult to correct chromatic aberration. By setting the lower limit of conditional expression (2) to 0.01, 0.03, or even 0.05, the effect of this embodiment can be made more certain.

[0021] A microscope apparatus having the imaging lens IL according to the first embodiment includes an objective lens that receives light from an object and converts it into parallel light, an objective optical system that includes the imaging lens IL according to the first embodiment, and an image sensor that captures the image of the object formed by the imaging lens, and may satisfy the following conditional expression: 0<Pz / {(3×λ) / {2×{φ / (2×f2ndobj)}2×Y2}}<1 (3) where Pz is the Petzval sum of the imaging lens, λ is the detection wavelength detected by the image sensor, φ is the maximum objective pupil diameter of the objective optical system, f2ndobj is the focal length of the imaging lens, and Y is the maximum image height.

[0022] Conditional expression (3) defines an appropriate relationship between the amount of field curvature and the Petzval sum. By satisfying conditional expression (3), field curvature can be corrected well. The detected wavelength is the wavelength detected by the image sensor, and may be 587.00 nm to 656.00 nm, or may be in the visible light wavelength range (approximately 400 nm to 700 nm).

[0023] If the corresponding value of conditional expression (3) exceeds the upper limit, it becomes difficult to correct the curvature of field. By setting the upper limit of conditional expression (3) to 0.90, or even 0.80, the effect of this embodiment can be made more certain.

[0024] If the corresponding value of conditional expression (3) falls below the lower limit, it becomes difficult to correct chromatic aberration. Setting the lower limit of conditional expression (3) to 0.01 further ensures the effects of this embodiment. Note that a negative Petzval sum Pz tends to tilt the image plane toward the rear of the image sensor, degrading off-axis imaging performance, so a positive value is desirable. Note that the microscope apparatus may include an illumination optical system that uses epi-illumination and a reflecting member installed above the object, and may capture images of at least light irradiated onto the object by the illumination optical system and light that passes through the object, is reflected by the reflecting member, and returns to the microscope apparatus.

[0025] A microscope apparatus having the imaging lens IL according to the first embodiment may have an image sensor that captures an image of an object formed by the imaging lens IL, and may satisfy the following conditional expression: 0.335<NA / (0.61×λ / P)×fbasis / (β×f2ndobj)<1 (4) where NA is the numerical aperture of the objective lens having the largest objective pupil diameter, λ is the detection wavelength detected by the image sensor, P is the pixel size of the image sensor, fbasis is the focal length of the imaging lens used as a basis when designing the magnification of the objective lens, β is the objective magnification of the objective optical system, and f2ndobj is the focal length of the imaging lens.

[0026] Conditional expression (4) defines an appropriate relationship between the pixel size of the image sensor and the focal length of the imaging lens. The detection wavelength is the wavelength detected by the image sensor, and may be a wavelength of 587.00 nm to 656.00 nm, or may be in the visible light wavelength range (approximately 400 nm to approximately 700 nm). By satisfying conditional expression (4), it is possible to design an imaging lens having a focal length appropriate for the pixel size of the image sensor.

[0027] If the value corresponding to conditional expression (4) exceeds the upper limit, the sampling frequency of photoelectric conversion in the image sensor will be lowered, which is undesirable as it will cause aliasing and result in a deterioration in image quality. Furthermore, if the value corresponding to conditional expression (4) exceeds the upper limit, it will be undesirable as it will not resolve the object structure of high-frequency components up to the cutoff frequency of the numerical aperture of the objective lens having the largest objective pupil diameter. Setting the upper limit of conditional expression (4) to 0.98 further ensures the effects of this embodiment.

[0028] If the corresponding value of conditional expression (4) falls below the lower limit, the sampling frequency of photoelectric conversion in the image sensor becomes excessively high, and the focal length of the imaging lens becomes long, which makes it difficult to make the device compact, which is undesirable. By setting the lower limit of conditional expression (4) to 0.40, 0.50, or even 0.60, the effect of this embodiment can be made more certain.

[0029] Examples of the imaging lens IL according to each embodiment will be described below with reference to the drawings. FIGS. 1, 3, 5, 7, and 9 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, 3, 5, 7, and 9, 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.

[0030] Tables 1 to 5 are shown below, with Table 1 showing data on the various specifications for Example 1, Table 2 for Example 2, Table 3 for Example 3, Table 4 for Example 4, and Table 5 for Example 5. In each example, the d-line (wavelength λ=587.00 nm), C-line (wavelength λ=656.00 nm), F-line (wavelength λ=486.00 nm), and g-line (wavelength λ=435.00 nm) were selected as the targets for calculating aberration characteristics.

[0031] In the [Overall Specifications] table, β indicates the magnification of the objective lens. f2ndobj indicates the focal length of the imaging lens, fbasis indicates the focal length of the imaging lens used as the basis for designing the magnification of the objective lens, f1 indicates the focal length of the first lens group of the imaging lens, and f2 indicates the focal length of the second lens group of the imaging lens. FNO indicates the F-number of the imaging lens, NA indicates the numerical aperture of the objective lens with the largest objective pupil diameter, and NA' indicates the numerical aperture of the imaging lens on the image plane side. BF indicates the back focus of the imaging lens, and D indicates the total length of the imaging lens (the distance on the optical axis from the lens surface of the imaging lens closest to the object to the image plane). Pz indicates the Petzval sum of the imaging lens. P indicates the pixel size [μm] of the image sensor. φ indicates the maximum objective pupil diameter [μm]. λ indicates the detection wavelength [μm] detected by the image sensor.

[0032] 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 have 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. The "∞" in the radius of curvature indicates a plane or an aperture.

[0033] The table of [Lens Group Data] shows the first surface (the surface closest to the object) and focal length of each lens group.

[0034] In the following, for all specifications, the focal length, radius of curvature r, surface spacing d, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this because the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0035] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0036] (First Example) The first example will be described with reference to FIGS. 1, 2, and Table 1. FIG. 1 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 pentaprism OE, and a second lens group G2 having negative 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 OBL. The image plane I corresponds to the image plane of the imaging lens IL(1). This also applies to all the following examples.

[0037] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented lens of a biconvex positive lens L11 and a meniscus negative lens L12 with its concave surface facing the object side.

[0038] The second lens group G2 is composed of a negative meniscus lens L21 with its convex surface facing the object side.

[0039] The optical element, the pentaprism OE, is a pentagonal prism with two internal reflecting surfaces. The pentaprism OE is positioned between the optical paths of the first lens group G1 and the second lens group G2 so that light passing through the first lens group is reflected twice at 45 degrees and enters the second lens group G2.

[0040] Table 1 below lists the specifications of the imaging lens according to Example 1. Surface 1 is the entrance pupil plane P of the imaging lens. Surface 2 is the lens surface of the imaging lens closest to the object, and surface 8 is the lens surface of the imaging lens closest to the image plane. Surfaces 5 and 6 are the object-side entrance surface and image-side exit surface of the pentaprism OE on the optical path.

[0041] (Table 1) [Overall specifications] β=2 FNO=7.0213 NA'=0.0714 NA=0.1 f2ndobj=140.0 fbasis=200.0 BF=35.1 D=160.0 Pz=0.00138 P=4.8 φ=20 Y=8.75 [Lens specifications] Surface number r d nd νd 1 ∞ 1.00000 2 64.5000 5.500 1.59319 67.902 3 -64.5000 2.000 1.66755 41.874 4 -650.0000 5.000 1.00000 5 ∞ 102.426 1.56883 55.998 6 ∞ 7.000 1.00000 7 -31.0000 3.000 1.56732 42.579 8 -51.0000 BF 1.00000 [Lens group data] Group Initial surface Focal length G1 2 110.3 G2 7 -147.3

[0042] FIG. 2 shows the spherical aberration, field curvature (meridional coma and sagittal coma), distortion, lateral chromatic aberration (lateral chromatic aberration), and coma of the imaging lens according to Example 1. In each aberration diagram in FIG. 2, d indicates aberrations for the d-line (wavelength λ=587.00 nm), C indicates aberrations for the C-line (wavelength λ=656.00 nm), F indicates aberrations for the F-line (wavelength λ=486.00 nm), and g indicates aberrations for the g-line (wavelength λ=435.00 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 addition, in the aberration diagrams showing field curvature, the vertical axis represents image height [mm], and the horizontal axis represents aberration value [mm]. In the distortion diagrams, the vertical axis represents image height [mm], and the horizontal axis represents the aberration ratio as a percentage (% value). In the aberration diagrams showing lateral chromatic aberration, the vertical axis represents image height [mm], and the horizontal axis represents aberration value [mm]. Each coma aberration diagram shows the aberration value at each image height from the maximum image height to the on-axis image, from top to bottom. 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.

[0043] 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.

[0044] Second Example A second example will be described with reference to Figs. 3, 4, and Table 2. Fig. 3 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 mirror OE arranged at an angle of 45 degrees with respect to the optical path, and a second lens group G2 having negative refractive power.

[0045] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented lens of a biconvex positive lens L11 and a meniscus negative lens L12 with its concave surface facing the object side.

[0046] The second lens group G2 is composed of a cemented lens of a biconcave negative lens L21 and a biconvex positive lens L22.

[0047] The mirror OE, an optical element, is positioned between the optical paths of the first lens group G1 and the second lens group G2, and is positioned so that light passing through the first lens group is reflected once at 90 degrees by the mirror OE and enters the second lens group G2.

[0048] Table 2 below lists the specifications of the imaging lens according to the second example. Note that the first surface is the entrance pupil plane P of the imaging lens. The second surface is the lens surface of the imaging lens closest to the object, and the eighth surface is the lens surface of the imaging lens closest to the image plane. Furthermore, the fifth surface is the reflective surface of the mirror OE.

[0049] (Table 2) [Overall specifications] β=2 FNO=8.0051 NA'=0.0625 NA=0.1 f2ndobj=160.0 fbasis=200.0 BF=30.4 D=149.4 Pz=0.00084 P=4.8 φ=20 Y=10.00 [Lens specifications] Surface number r d nd νd 1 ∞ 1.00000 2 70.0000 5.000 1.56907 71.312 3 -70.0000 2.000 1.65412 39.682 4 80.0000 50.000 1.00000 5 ∞ 53.0000 1.00000 6 -27.8000 2.500 1.58313 59.424 7 27.8000 6.500 1.69680 55.517 8 -54.0000 BF 1.00000 [Lens group data] Group Initial surface Focal length G1 2 160.0 G2 6 -385.7

[0050] 4 is a diagram showing the spherical aberration, curvature of field (meridional coma and sagittal coma), distortion, chromatic aberration of magnification (lateral chromatic aberration), and coma of the imaging lens of Example 2. From each aberration diagram, it can be seen that the imaging lens of Example 2 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0051] Third Example A third example will be described with reference to Figs. 5, 6 and Table 3. Fig. 5 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 pentaprism OE, and a second lens group G2 having negative refractive power.

[0052] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented lens of a biconvex positive lens L11 and a meniscus negative lens L12 with its concave surface facing the object side.

[0053] The second lens group G2 is composed of a negative meniscus lens L21 with its concave surface facing the object side.

[0054] The optical element, the pentaprism OE, is a pentagonal prism with five internal reflecting surfaces. The pentaprism OE is positioned between the optical paths of the first lens group G1 and the second lens group G2 so that light passing through the first lens group is reflected twice at 45 degrees before entering the second lens group G2.

[0055] Table 3 below lists the specifications of the imaging lens according to the third example. Note that surface 1 is the entrance pupil plane P of the imaging lens. Surface 2 is the lens surface of the imaging lens closest to the object, and surface 8 is the lens surface of the imaging lens closest to the image plane. Surfaces 5 and 6 are the object-side and image-plane-side surfaces of the pentaprism OE on the optical path.

[0056] (Table 3) [Overall specifications] β=2 FNO=10.0018 NA'=0.0500 NA=0.1 f2ndobj=200.0 fbasis=200.0 BF=52.4 D=210.0 Pz=0.00006 P=4.8[μm] φ=20[mm] Y=12.50 [Lens specifications] Surface number r d nd νd 1 ∞ 1.00000 2 83.4000 7.800 1.59319 67.902 3 -83.4000 2.680 1.66755 41.874 4 -829.0000 7.200 1.00000 5 ∞ 119.497 1.56883 55.998 6 ∞ 13.000 1.00000 7 -41.3000 7.500 1.51742 52.201 8 -93.0000 52.4 1.00000 [Lens group data] Group Initial surface Focal length G1 2 142.4 G2 7 -152.4

[0057] 6 is a diagram showing the spherical aberration, curvature of field (meridional coma and sagittal coma), distortion, chromatic aberration of magnification (lateral chromatic aberration), and coma of the imaging lens of Example 3. From each aberration diagram, it can be seen that the imaging lens of Example 3 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0058] Fourth Example A fourth example will be described with reference to Figs. 7, 8 and Table 4. Fig. 7 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 prism OE, and a second lens group G2 having negative refractive power.

[0059] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented lens of a biconvex positive lens L11 and a meniscus negative lens L12 with its concave surface facing the object side.

[0060] The second lens group G2 is composed of a cemented lens of a biconcave negative lens L21 and a biconvex positive lens L22.

[0061] The prism OE, an optical element, is a triangular prism with three internal reflecting surfaces. The prism OE is positioned between the optical paths of the first lens group G1 and the second lens group G2 so that light passing through the first lens group is reflected once at 90 degrees by the prism OE and enters the second lens group G2.

[0062] Table 4 below lists the specifications of the imaging lens according to Example 4. Surface 1 is the entrance pupil plane P of the imaging lens. Surface 2 is the lens surface of the imaging lens closest to the object, and Surface 9 is the lens surface of the imaging lens closest to the image plane. Surfaces 5 and 6 are the object-side and image-plane-side surfaces of the prism OE on the optical path.

[0063] (Table 4) [Overall specifications] β=2 FNO=8.0081 NA'=0.0625 NA=0.1 f2ndobj=160.0 fbasis=200.0 BF=35.3 D=159.8 Pz=0.00160 P=4.8 φ=20 Y=10.00 [Lens specifications] Surface number r d nd νd 1 ∞ 1.00000 2 71.5000 5.500 1.56907 71.312 3 -71.5000 2.000 1.65412 39.682 4 -850.0000 37.000 1.00000 5 32.000 1.56883 55.998 6 39.000 1.00000 7 -29.0000 2.500 1.60311 60.693 8 29.0000 6.500 1.65160 58.571 9 -44.5000 BF 1.00000 [Lens group data] Group Initial surface Focal length G1 2 132.5 G2 7 -350.4

[0064] 8 is a diagram showing the spherical aberration, curvature of field (meridional coma and sagittal coma), distortion, chromatic aberration of magnification (lateral chromatic aberration), and coma of the imaging lens of Example 4. From each aberration diagram, it can be seen that the imaging lens of Example 4 has excellent optical performance, with various aberrations including chromatic aberration being well corrected over a wide wavelength range.

[0065] Fifth Example A fifth example will be described with reference to Figs. 9, 10 and Table 5. Fig. 9 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 mirror OE1, a mirror OE2, and a second lens group G2 having negative refractive power.

[0066] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented lens of a biconvex positive lens L11 and a meniscus negative lens L12 with its concave surface facing the object side.

[0067] The second lens group G2 is composed of a cemented lens of a biconcave negative lens L21 and a biconvex positive lens L22.

[0068] The optical elements, mirrors OE1 and OE2, are arranged between the optical paths of the first and second lens groups, and are arranged so that light passing through the first lens group is first reflected at 45 degrees by mirror OE1, then reflected at 45 degrees by mirror OE2, and enters the second lens group G2.

[0069] Table 5 below lists the specifications of the imaging lens according to Example 5. Surface 1 is the entrance pupil plane P of the imaging lens. Surface 2 is the lens surface of the imaging lens closest to the object, and Surface 9 is the lens surface of the imaging lens closest to the image plane. Surfaces 5 and 6 are reflective surfaces of mirror OE on the optical path.

[0070] (Table 5) [Overall specifications] β=2 FNO=8.0051 NA'=0.0625 NA=0.1 f2ndobj=160.0 fbasis=200.0 BF=30.4 D=149.4 Pz=0.00084 P=4.8 φ=20[mm] Y=10.00 [Lens specifications] Surface number r d nd νd 1 ∞ 1.00000 2 70.0000 5.000 1.56907 71.312 3 -70.0000 2.000 1.65412 39.682 4 -1580.0000 38.000 1.00000 5 28.000 1.00000 6 37.000 1.00000 7 -27.8000 2.500 1.58313 59.424 8 27.8000 6.500 1.69680 55.517 9 -54.0000 BF 1.00000 [Lens group data] Group Initial surface Focal length G1 2 136.1 G2 7 -385.7

[0071] 10 is a diagram showing the spherical aberration, curvature of field (meridional coma and sagittal coma), distortion, chromatic aberration of magnification (lateral chromatic aberration), and coma of the imaging lens of Example 5. From each aberration diagram, it can be seen 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.

[0072] Next, a table of [Values ​​Corresponding to Conditional Expressions] is shown below. This table summarizes the values ​​corresponding to each of conditional expressions (1) to (4) for all examples (Examples 1 to 5). For conditional expression (2), Fiy (the image height ratio to the maximum image height Y) is set to 1.0. For conditional expressions (3) and (4), λ (the wavelength detected by the image sensor) is set to the wavelength of the d-line (wavelength λ=0.587 μm) as a representative wavelength. Conditional expression (1) 0.2≦BF / D≦0.25 Conditional expression (2) 0≦RMS(Fiy)≦0.1[λF] Conditional expression (3) 0<Pz / {(3×λ) / {2×{φ / (2×f2ndоbj)}2×Y2}}<1 Conditional expression (4) 0.335<NA / (0.61×λ / P)×fbasis / (β×f2ndоbj)<1

[0073] [Conditional expression corresponding values] (First to fifth examples) Conditional expression First example Second example Third example (1) 0.22 0.20 0.25 (2) 0.061 0.068 0.087 (3) 0.612 0.373 0.027 (4) 0.958 0.838 0.670 [Conditional expression corresponding values] (Fourth and fifth examples) Conditional expression Fourth example Fifth example (1) 0.22 0.20 (2) 0.087 0.0683 (3) 0.710 0.373 (4) 0.838 0.838

[0074] 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.

[0075] Here, the above examples show specific examples of this embodiment, and this embodiment is not limited to these.

[0076] G1: First lens group G2: Second lens group OE, OE1, OE2: Optical elements I: Image plane P: Entrance pupil plane

Claims

1. An objective optical system comprising an objective lens that receives light from an object and converts it into parallel light, and an imaging lens for a microscope that forms an image from the light from the objective lens, and an image sensor that captures an image of the object formed by the imaging lens, The following conditional expression is satisfied: 0<Pz / {(3×λ) / {2×{φ / (2×f2ndоbj)} 2×Y 2}}<1 where Pz is the Petzval sum of the imaging lens. λ: detection wavelength detected by the imaging element φ: maximum objective pupil diameter of the objective optical system f2ndobj: focal length of the imaging lens Y: Maximum image height the imaging lens includes, in order from the object side, a first lens group having positive refractive power and a second lens group having negative refractive power and disposed closer to the image side than the first lens group; the second lens group includes a meniscus lens component with a concave surface facing the object side, A microscope apparatus that satisfies the following conditional expressions: 0.20≦BF / D≦0.25 where BF is the back focus of the imaging lens. D: the distance on the optical axis from the lens surface closest to the object in the imaging lens to the image plane

2. 2. The microscope apparatus according to claim 1, wherein the following condition is satisfied: 0≦RMS(Fiy)≦0.1[λF] where RMS(Fiy): the amount of wavefront aberration of the F-line relative to the optimal defocus position for the d-line, which depends on the image height ratio Fiy relative to the maximum image height Y (where 0≦Fiy≦1.0). λF: wavelength of F line

3. A microscope device as described in claim 1, which satisfies the following conditional expression. 0.335<NA / (0.61×λ / P)×fbasis / (β×f2ndоbj)<1 where NA is the numerical aperture of the objective lens having the largest objective pupil diameter. λ: detection wavelength detected by the imaging element P: pixel size of the imaging element fbasis: the focal length of the imaging lens used as a basis when designing the magnification of the objective lens β: objective magnification of the objective optical system f2ndobj: focal length of the imaging lens