JP2021139919A - Objective lens, optical system, and microscope - Google Patents

Abstract

To provide a microscope objective lens which has an image plane that is flat over an entire field of view, and is well corrected for axial chromatic aberration and for magnification chromatic aberration over the entire field of view.SOLUTION: A microscope objective lens OL provided herein comprises a first lens group G1 having positive refractive power and a second lens group G2 having negative refractive power, the first lens group G1 having a diffraction optical element DOE, and the second lens group G2 consisting of a first cemented lens CL21 obtained by cementing a positive lens L21 and a negative lens L22 with a concave surface on the image side together, and a second cemented lens CL22 obtained by cementing a negative lens L23 with a concave surface on the object side and a positive lens L24 together. The microscope objective lens OL satisfies the following conditional expressions: 65.0<νd1, 0.0045<θgd1+(0.002076×νd1)-1.36467, where νd1 represents an Abbe number based on a d-line of the negative lens L23 and θgd1 represents a partial dispersion ratio of the negative lens L23.SELECTED DRAWING: Figure 1

Description

The present invention relates to objective lenses, optical systems and microscopes.

The objective lens of the microscope is required to have a flat image plane and to be well corrected for axial chromatic aberration. In order to solve this problem, various objective lenses using diffractive optical elements have been proposed (see, for example, Patent Document 1). However, with such an objective lens, the correction of chromatic aberration of magnification over the entire field of view has not been sufficient.

Japanese Unexamined Patent Publication No. 6-331898

The objective lens according to the first aspect includes a first lens group having a positive refractive force and a second lens group having a negative refractive force arranged in order from the object side, and the first lens group includes the first lens group. It has a diffractive optical element including a first diffractive element element and a second diffractive element element, and the diffractive optical element is formed on a junction surface between the first diffractive element element and the second diffractive element element. The second lens group includes a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image side, which are arranged in order from the object side. It is composed of a first junction lens formed by joining, a negative lens having a concave surface facing the object side, and a second junction lens formed by joining a positive lens having a convex surface facing the image side, and satisfies the following conditional expression.
65.0 <νd1
0.0045 <θgd1 + (0.002076 × νd1) -1.36467
However, νd1: the abbe number θgd1: the partial dispersion ratio of the negative lens constituting the second junction lens based on the d line of the negative lens constituting the second junction lens, and the g line of the negative lens. When the refractive index of the negative lens with respect to the d line is nd1, the refractive index of the negative lens with respect to the F line is nF1, and the refractive index of the negative lens with respect to the C line is nC1, the following equation is obtained. Θgd1 = (ng1-nd1) / (nF1-nC1) defined by

The optical system according to the second aspect includes an objective lens according to the first aspect and an imaging lens.

The microscope according to the third aspect includes an objective lens according to the first aspect.

It is sectional drawing which shows the structure of the microscope objective lens which concerns on 1st Example. It is a figure of various aberrations of the microscope objective lens which concerns on 1st Example. It is sectional drawing which shows the structure of the microscope objective lens which concerns on 2nd Example. It is a figure of various aberrations of the microscope objective lens which concerns on 2nd Example. It is sectional drawing which shows the structure of the imaging lens. It is a schematic diagram of the main part of a microscope provided with a microscope objective lens.

Hereinafter, the objective lens, the microscope, and the optical system used in the microscope of the present embodiment will be described with reference to the drawings. In the present embodiment, a microscope objective lens having a flat image plane over the entire field of view, in which axial chromatic aberration is satisfactorily corrected and chromatic aberration of magnification in the entire field of view is satisfactorily corrected will be described.

As an example of the microscope objective lens OL according to the present embodiment, the microscope objective lens OL (1) shown in FIG. 1 has a first lens group G1 having a positive refractive power arranged in order from the object side and a negative refractive power. It is configured to include a second lens group G2 having the above. The microscope objective lens OL according to the present embodiment may be the microscope objective lens OL (2) shown in FIG. Each lens of the microscope objective lens OL (2) shown in FIG. 3 is configured in the same manner as the microscope objective lens OL (1) shown in FIG.

The first lens group G1 is a lens group that condenses the divergent light flux emitted from the object Ob into a convergent light flux. The first lens group G1 includes a diffraction optical element DOE formed by joining two diffraction element elements made of different types of optical materials. A diffraction optical surface Dm forming a diffraction grating groove is formed on the junction surface of the two diffraction element elements. As described above, in the first lens group G1, in order to correct the chromatic aberration, a diffractive optical surface Dm is formed on any surface of the optical elements constituting the first lens group G1. In addition, in FIG. 1 and FIG. 3, the object Ob indicates an object point on the optical axis.

The diffractive optical element DOE is a so-called close contact multi-layer diffractive optical element, and can increase the diffraction efficiency in a wide wavelength range including g-line to C-line. Therefore, the microscope objective lens OL according to the present embodiment can be used in a wide wavelength range. When the primary diffracted light is used in the transmission type diffractive optical element DOE, the diffraction efficiency is the ratio η (that is, η =) of the intensity I0 of the incident light to the diffractive optical element DOE and the intensity I1 of the primary diffracted light. I1 / I0 × 100 [%]) is shown. A resin material may be used as the optical material of the diffraction element element constituting the diffraction optical element DOE. For example, by resin molding using an ultraviolet curable resin (photocurable resin material), the diffraction optical surface Dm can be formed more easily than when optical glass is used as the optical material of the diffraction element element.

On the diffractive optical surface Dm, several to several hundred fine groove-like or slit-like lattice structures per 1 mm are concentrically formed. The diffractive optical surface Dm has a property that the incident light incident on the diffractive optical surface Dm is diffracted in a direction determined by the lattice pitch (interval between the diffraction grating grooves) and the wavelength of the incident light. The refractive power of a normal refracting lens has a characteristic that it changes greatly with a change in wavelength as the wavelength becomes shorter. On the other hand, the refractive power of the diffractive optical element DOE including the diffractive optical surface Dm as described above has a characteristic of linearly changing with a change in wavelength. Therefore, by combining a plurality of refracting lenses that are combined so that the change in refractive power with respect to a change in wavelength becomes linear, and the diffractive optical element DOE, a large achromatic effect can be obtained, so that chromatic aberration is satisfactorily corrected. It becomes possible to do.

The second lens group G2 is a lens group that converts the converged light converged by the first lens group G1 into parallel light. The second lens group G2 includes a first junction lens CL21 formed by joining a positive lens L21 having a convex surface facing the object side and a negative lens L22 having a concave surface facing the image side, which are arranged in order from the object side, and the object side. It is composed of a negative lens L23 with a concave surface and a second junction lens CL22 formed by bonding a positive lens L24 with a convex surface toward the image side. The concave surface of the negative lens L22 constituting the first junction lens CL21 and the concave surface of the negative lens L23 constituting the second junction lens CL22 are arranged so as to face each other. The first junction lens CL21 and the second junction lens CL22 have a so-called Gauss type configuration in order to correct the Petzval sum. With such a configuration, it is possible to correct axial chromatic aberration and lateral chromatic aberration in a well-balanced manner while reducing the Petzval sum.

Under the above configuration, the microscope objective lens OL according to the present embodiment has the following conditional expressions (1) to (2).
To be satisfied.

65.0 <νd1 ・ ・ ・ (1)
0.0045 <θgd1 + (0.002076 × νd1) -1.36467
... (2)
However, νd1: Abbe number based on the d line (wavelength λ = 587.6 nm) of the negative lens L23 constituting the second junction lens CL22 θgd1: Partial dispersion ratio of the negative lens L23 constituting the second junction lens CL22. The refractive index of the negative lens L23 with respect to the g line (wavelength λ = 435.8 nm) is ng1, the refractive index of the negative lens L23 with respect to the d line is nd1, and the F line of the negative lens L23 (wavelength λ = 486.1 nm).
When the refractive index for the negative lens L23 is nF1 and the refractive index for the C line (wavelength λ = 656.3 nm) of the negative lens L23 is nC1, θgd1 = (ng1-nd1) / (nF1-nC1) defined by the following equation.

The conditional expression (1) is a conditional expression that defines an appropriate Abbe number of the glass material of the negative lens L23 with the concave surface facing the object side in the second lens group G2. When the corresponding value of the conditional expression (1) is less than the lower limit value, the variance becomes large, and it becomes difficult to satisfactorily correct the axial chromatic aberration and the chromatic aberration of magnification at the same time. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (1) may be preferably 70.0, more preferably 80.0. Further, the upper limit value of the conditional expression (1) may be preferably less than 96.0 so as not to make it difficult to generate the glass material of the negative lens L23.

The conditional expression (2) is a conditional expression that defines the abnormal dispersibility of the glass material of the negative lens L23 with the concave surface facing the object side in the second lens group G2. On the right side of the conditional equation (2), the vertical axis is the partial dispersion ratio θgd (θgd = (ng-nd) / (nF-nC)), and the horizontal axis is the Abbe number νd (based on the d line). In the vertical direction, the coordinate points (θgd1, νd1) corresponding to the glass material of the negative lens L23 and the straight line passing through the two coordinate points corresponding to the glasses “NSL7” and “PBM2” (both are glass type names manufactured by O'Hara Co., Ltd.). The difference in the axial direction is shown. When the partial dispersion ratio of the glass “NSL7” is θgd2 and the Abbe number of the glass “NSL7” is νd2, θgd2 = 1.2391 and νd2 = 60.49. When the partial dispersion ratio of the glass “PBM2” is θgd3 and the Abbe number of the glass “PBM2” is νd3, then θgd3 = 1.2894 and νd3 = 36.26.

When the corresponding value of the conditional expression (2) is less than the lower limit value, the anomalous dispersibility is weakened, so that the chromatic aberration of magnification of the g-line increases. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (2) may be preferably 0.0062, more preferably 0.0202. Further, the upper limit of the conditional expression (2) may be preferably less than 0.0700 so as not to make it difficult to generate the glass material of the negative lens L23.

The microscope objective lens OL of the present embodiment may satisfy the following conditional expression (3).

100 <fDOE / f <500 ... (3)
However, fDOE: focal length of the diffractive optical element DOE f: focal length of the microscope objective lens OL

The conditional expression (3) is a conditional expression that defines the ratio of the focal length of the diffractive optical element DOE to the focal length of the microscope objective lens OL. In the present embodiment, the focal length of the diffractive optical element DOE indicates the focal length of the diffractive optical surface Dm in the diffractive optical element DOE. If the corresponding value of the conditional expression (3) is less than the lower limit value, the lattice pitch (interval of the diffraction grating grooves) of the diffraction optical element DOE becomes small, and diffracted light other than the design order is generated to cause flare, which is not preferable. .. In order to ensure the effect of this embodiment, the lower limit of the conditional expression (3) may be preferably 200.

When the corresponding value of the conditional expression (3) exceeds the upper limit value, the effect of correcting the axial chromatic aberration by the diffractive optical element DOE becomes small, and the correction of the axial chromatic aberration becomes insufficient. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (3) may be preferably 400.

The microscope objective lens OL of the present embodiment may satisfy the following conditional expression (4).
0 ° <θmax <40 ° ・ ・ ・ (4)
However, θmax: the maximum value of the incident angle when the light ray having the maximum numerical aperture among the light rays from the center of the object is incident on the diffractive optical surface Dm.

The conditional expression (4) is a conditional expression that defines the maximum incident angle (based on the optical axis Ax) of the light beam incident on the diffractive optical surface Dm. If the corresponding value of the conditional expression (4) exceeds the upper limit value, the maximum incident angle of the light beam incident on the diffractive optical surface Dm is too large, so that the diffraction efficiency of the diffractive optical element DOE is lowered and the diffracted light other than the design order is generated. It is not preferable because it occurs and causes flare. In order to ensure the effect of this embodiment, the upper limit of the conditional expression (4) may be preferably 30 °.

When the diffractive optical element DOE includes a parallel flat plate, if the maximum incident angle of the light beam incident on the diffractive optical surface Dm is close to 0 °, the parallel flat plate and the light transmitting parallel flat plate Cv such as the cover glass have two surfaces. Flare occurs due to reflection. Therefore, in order to suppress flare due to two-sided reflection, the lower limit value of the conditional expression (4) may be preferably set to 3 °.

In the microscope objective lens OL of the present embodiment, the diameter of the light beam is determined by the light beam having the maximum numerical aperture in the case of the light beam emitted from the on-axis object point, and in the case of the light beam emitted from the off-axis object point. Is determined by the outermost ray. Here, among the light rays emitted from the off-axis object point, the light rays emitted to the side farthest from the optical axis Ax are the light rays having the maximum numerical aperture from the on-axis object point and an appropriate light ray in the first lens group G1. It is limited by the intersection with the lens surface (for example, the lens surface on the image side of the negative lens L2 in FIG. 1). Of the light rays emitted from the off-axis object point, the light ray emitted on the side opposite to the side farthest from the optical axis Ax (based on the optical axis Ax) is the light ray having the maximum numerical aperture from the on-axis object point. It is limited by the intersection of and an appropriate lens surface in the second lens group G2 (for example, the lens surface on the object side of the negative lens L23 in FIG. 1). In the luminous flux in which the outermost ray is determined (emitted from the off-axis object point) in this way, the ray passing through the center of the luminous flux emitted from the off-axis object point at the maximum object height is defined as the main ray Pr.

When the main ray Pr is defined as described above, the diffractive optical element DOE may be arranged on the object side of the position where the main ray Pr intersects the optical axis Ax. As a result, axial chromatic aberration can be effectively corrected. Further, the diffractive optical element DOE may be arranged on the object side of the portion having the largest diameter in the light flux passing through the first lens group G1. Thereby, the axial chromatic aberration can be corrected more effectively.

When the chromatic aberration is corrected only by the diffractive optical element DOE in the first lens group G1, if the minimum lattice pitch (distance of the diffraction grating groove) of the diffractive optical element DOE becomes too small, the diffractive optical element DOE is manufactured. It becomes difficult. Therefore, in order to share the correction of chromatic aberration, the first lens group G1 may be configured to have a plurality of bonded lenses. In this case, at least one of the plurality of junction lenses constituting the first lens group G1 is arranged on the image side of the diffractive optical element DOE. Further, in this case, among the plurality of bonded lenses constituting the first lens group G1, the bonded lens arranged on the image side has a negative refractive power, and the other bonded lens has a positive refractive power. May be good. One of the plurality of junction lenses constituting the first lens group G1 may be configured to include a diffractive optical element DOE so as to have a positive refractive power.

For example, the first lens group G1 shown in FIG. 1 includes a first junction lens CL11 having a positive refractive power arranged in order from the object side, a meniscus-shaped positive lens L3 with a concave surface facing the object side, and positive lenses. A second junction lens CL12 having a refractive power, a third junction lens CL13 having a positive refractive power, a fourth junction lens CL14 having a positive refractive power, and a fifth junction lens CL15 having a negative refractive power. The third junction lens CL13 includes a diffraction optical element DOE. Further, for example, the first lens group G1 shown in FIG. 3 includes a first junction lens CL11 having a positive refractive power arranged in order from the object side, and a meniscus-shaped positive lens L3 having a concave surface facing the object side. The second junction lens CL12 having a positive refractive power, the third junction lens CL13 having a positive refractive power, the fourth junction lens CL14 having a positive refractive power, and the fifth junction lens CL15 having a negative refractive power. The fourth junction lens CL14 includes a diffraction optical element DOE.

The microscope of the present embodiment is configured to include the microscope objective lens OL having the above-described configuration. As a specific example thereof, a microscope (immersion microscope) provided with the microscope objective lens OL according to the present embodiment will be described with reference to FIG. The microscope 100 includes a stand 101, a stage 111 attached to the base 102 of the stand 101, a lens barrel 121 attached to the arm 103 of the stand 101, and an imaging unit 131 connected to the lens barrel 121. Consists of having. An observation object (biological sample, etc.) (not shown) held between the slide glass B and a light-transmitting parallel flat plate Cv (numbering is omitted in FIG. 6) such as a cover glass is placed on the stage 111. Will be done. A condenser lens 117 constituting the transmission illumination device 116 is attached to the lower side of the stage 111. In addition to the stage 111, the above-mentioned transmission illumination device 116, a transmission illumination light source 118, and the like are attached to the base portion 102 of the stand 101.

The objective lens 122 is attached to the revolver 126 provided below the lens barrel 121. Immersion is filled between the tip of the objective lens 122 and the light-transmitting parallel flat plate Cv. As the objective lens 122 attached below the lens barrel 121, the microscope objective lens OL according to the present embodiment is used. The lens barrel 121 is provided with an imaging lens 123 and a prism 124. As the imaging lens 123 provided on the lens barrel 121, the imaging lens IL described later is used. The epi-fluorescence device 127, the epi-fluorescence light source 128, the eyepiece 129, and the like are attached to the lens barrel 121. The image pickup unit 131 is provided with an image pickup element 132.

In such a microscope 100, the light from the observation object passes through the light transmitting parallel plane plate Cv and the immersion liquid, the objective lens 122, the imaging lens 123, and the prism 124, and reaches the imaging element 132. The image pickup lens 123 forms an image of the observation object on the image pickup surface of the image pickup element 132, and the image pickup element 132 takes an image of the observation object. The image of the observation object captured and acquired by the image pickup device 132 is displayed on the monitor MT via an external computer PC. The external computer PC can perform various image processing on the image data of the observation object imaged and acquired by the image sensor 132. According to such a configuration, by mounting the microscope objective lens OL according to the above embodiment, a flat image plane is provided over the entire field of view, axial chromatic aberration is satisfactorily corrected, and a magnification over the entire field of view is obtained. It becomes possible to obtain a microscope in which chromatic aberration is well corrected. The microscope 100 may be an upright microscope or an inverted microscope.

The objective lens 122 is an infinity correction type lens. In the microscope 100, the objective lens 122 is used in the form of a finite distance correction optical system combined with an imaging lens 123 that forms an image of an observation object. As described above, by using the microscope objective lens OL according to the present embodiment as the objective lens 122, the image plane has a flat image over the entire field of view, axial chromatic aberration is satisfactorily corrected, and the entire field of view is corrected. It is possible to obtain an optical system in which the chromatic aberration of magnification is well corrected.

Hereinafter, the microscope objective lens OL according to the embodiment of the present embodiment will be described with reference to the drawings. In the microscope objective lens OL according to each embodiment, an object (observation object) Ob is arranged under a light transmitting parallel flat plate Cv such as a cover glass, and a liquid is immersed between the tip portion and the light transmitting parallel flat plate Cv. For example, it is an objective lens for a immersion microscope that observes this object (observation object) Ob in a state of being filled with silicone oil or the like. In each embodiment, when the refractive index of the immersion liquid (oil) to be used with respect to the d-line (wavelength λ = 587.56 nm) is nd4 and the Abbe number based on the d-line is νd4, nd4 = 1.515, νd4. = 41.4.

1 and 3 are cross-sectional views showing the configuration of the microscope objective lenses OL {OL (1) to OL (2)} according to the first to second embodiments. In FIGS. 1 and 3, each lens group is represented by a combination of reference numerals G and a number (or alphabet), and each lens is represented by a combination of reference numerals L and a number (or alphabet). In this case, in order to prevent the types and numbers of the symbols and numbers from becoming large and complicated, the lenses and the like are represented by independently using combinations of the symbols and numbers for each embodiment. Therefore, even if the same combination of reference numerals and numbers is used between the examples, it does not mean that they have the same configuration.

Tables 1 and 2 are shown below. Among them, Table 1 is a table showing each specification data in the first embodiment, and Table 2 is a table showing each specification data in the second embodiment. In each embodiment, the d-line (wavelength λ = 587.6 nm), g-line (wavelength λ = 435.8 nm), C-line (wavelength λ = 656.3 nm), and F-line (wavelength λ = 486.1 nm) are calculated as the aberration characteristics. Is selected.

In the [Overall Specifications] table, f indicates the focal length of the microscope objective lens OL at the d line (wavelength λ = 587.6 nm), NA indicates the numerical aperture, and β indicates the magnification. D0 is the working distance, and is the lens surface closest to the object in the microscope objective lens OL from the object Ob, excluding the thickness of the light-transmitting parallel flat plate Cv such as the cover glass (first described later). Indicates the distance on the optical axis to the surface).

In the [Lens Data] table, the surface numbers indicate the order of the lens surfaces from the object side, and R is the radius of curvature corresponding to each surface number (the case of a lens surface convex to the object side is a positive value). D is the lens thickness or air spacing 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), and νd corresponds to each surface number. Optical material d
The Abbe number with respect to the line is shown respectively. The radius of curvature "∞" indicates a plane or an opening. Further, the description of the refractive index nd of air = 1.00000 is omitted. When the optical surface is a diffractive optical surface, the surface number is marked with *, and the near-axis radius of curvature is indicated in the column of radius of curvature R.

The phase shape Φ (h) of the diffractive optical surface Dm shown in [Diffractive optical surface data] is represented by the following equation (A).

Φ (h) = (2π / λ) × (C2 × h ² + C4 × h ⁴ + C6 × h ⁶ + C8 × h ⁸ )… (A)
However, h: height in the direction perpendicular to the optical axis λ: wavelength Ci: phase coefficient (i = 2, 4, 6, 8)

In the table of [Diffractive optical surface data], regarding the diffractive optical surface shown in [Lens data], the second-order phase coefficient C2 in the formula (A), the fourth-order phase coefficient C4, and the sixth-order phase coefficient C6, 8 The following phase coefficient C8 is shown. In [diffraction optical surface data], "E-n" indicates " ^{x10 -n} ". For example, 1.234E-05 = 1.234 × 10 ^-5 .

The diffraction optical surface Dm is formed on the junction surface of two diffraction element elements made of different types of optical materials. In the table of [Resin Refractive Index Data], the refraction of a resin material having a relatively high refractive index (low dispersion) and a resin material having a relatively low refractive index (high dispersion) as optical materials used for these two diffraction element elements. Shows the rate. In the [Resin Refractive Index Data] table, nC indicates the refractive index for the C line (wavelength λ = 656.3 nm), nd indicates the refractive index for the d line (wavelength λ = 587.6 nm), and nF indicates the F line (wavelength λ = 587.6 nm). λ = 486.1 nm), and ng indicates the refractive index for the g-line (wavelength λ = 435.8 nm). Further, each resin material is an ultraviolet curable resin, and the table of [Resin Refractive Index Data] shows the refractive index after ultraviolet curing.

The table of [Conditional expression corresponding values] shows the values corresponding to the above conditional expressions (1) to (4). The [Reference Value] table shows the value of the partial dispersion ratio θgd1 of the negative lens L23 constituting the second junction lens CL22 in the second lens group G2.

Examples of a method for manufacturing a close-contact multi-layer diffractive optical element using a resin material having a high refractive index (low dispersion) and a resin material having a low refractive index (high dispersion) are described in European Patent Publication No. 1830204 and Europe. It is described in Japanese Patent Publication No. 1830205. Further, it is desirable that each resin material has an internal transmittance of 0.5 or more in a light beam having a wavelength near 350 nm.

Hereinafter, in all the specification values, "mm" is generally used for the focal length f, the radius of curvature R, the plane spacing D, other lengths, etc., unless otherwise specified, but the optical system is expanded proportionally. Alternatively, it is not limited to this because the same optical performance can be obtained even if the proportional reduction is performed.

The description of the table so far is common to all the examples, and the duplicate description below is omitted.

(First Example)
The first embodiment will be described with reference to FIGS. 1 to 2 and Table 1. FIG. 1 is a cross-sectional view showing a configuration of a microscope objective lens according to a first embodiment of the present 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 and a second lens group G2 having a negative refractive power arranged in order from the object side. NS.

The first lens group G1 is formed by joining a plano-convex positive lens L1 having a plane facing the object side and a meniscus-shaped negative lens L2 having a concave surface having a strong curvature facing the object side, which are arranged in order from the object side. The first junction lens CL11, the meniscus-shaped positive lens L3 with the concave surface facing the object side, the second junction lens CL12 formed by joining the biconcave negative lens L4 and the biconvex positive lens L5, and the second Bi-convex to the diffraction optical element DOE in which the parallel flat plate L6 and the plano-concave negative lens L7 with the concave surface facing the image side are joined via the first and second resin layers (diffraction element elements) Da and Db. A third junction lens CL13 formed by joining a positive lens L8 having a shape, a fourth junction lens CL14 formed by joining a meniscus-shaped negative lens L9 having a convex surface facing the object side, and a biconvex positive lens L10. It is composed of a fifth junction lens CL15 formed by bonding a biconvex positive lens L11 and a biconcave negative lens L12. The first to fourth junction lenses CL11 to CL14 each have a positive refractive power as a whole. The fifth junction lens CL15 has a negative refractive power as a whole.

The first resin layer Da is formed using a resin material having a relatively high refractive index (low dispersion), and the second resin layer Db uses a resin material having a relatively low refractive index (high dispersion). Is formed. A diffraction optical surface Dm forming a diffraction grating groove is formed on the bonding surface between the first resin layer Da and the second resin layer Db, and the first resin layer Da and the second resin layer Db are bonded to each other. NS. A light transmitting parallel plane plate Cv such as a cover glass is arranged on the object side of the first lens group G1, and the positive lens L1 and the light transmitting parallel plane plate Cv arranged on the most object side of the first lens group G1 The space is filled with immersion liquid.

The second lens group G2 is a first junction lens CL21 formed by joining a biconvex positive lens L21 arranged in order from the object side and a biconcave negative lens L22 with a concave surface having a strong curvature facing the image side. It is composed of a meniscus-shaped negative lens L23 having a concave surface with a strong curvature facing the object side and a second junction lens CL22 formed by joining a meniscus-shaped positive lens L24 having a convex surface facing the image side. The first junction lens CL21 has a negative refractive power as a whole. The second junction lens CL22 has a positive refractive power as a whole.

Table 1 below lists the values of the specifications of the microscope objective lens according to the first embodiment.

(Table 1)
[Overall specifications]
f = 5.02
NA = 1.3
D0 = 0.28
β = 40x [lens data]
Surface number RD nd νd
1 ∞ 0.6 1.518229 58.90
2 -1.101 3.3 1.882997 40.77
3 -3.673 0.1
4-9.662 3.8 1.729157 54.68
5 -6.883 0.1
6 -380.000 1.0 1.613397 44.27
7 16.703 6.0 1.651597 58.55
8 -20.056 0.1
9 ∞ 1.4 1.516330 64.14
10 ∞ 0.1 1.557100 49.74
11 * ∞ 0.1 1.527800 33.41
12 ∞ 1.0 1.772500 49.61
13 18.495 7.6 1.438750 94.95
14 -15.616 0.1
15 120.000 1.0 1.804000 46.57
16 23.463 6.2 1.438750 94.95
17 -18.850 0.1
18 12.130 6.1 1.438750 94.95
19 -27.101 1.0 1.816000 46.62
20 18.174 0.1
21 9.479 5.6 1.592399 68.37
22 -50.368 4.4 1.672999 38.15
23 5.121 4.6
24 -5.200 6.1 1.497820 82.57
25 -537.425 3.6 1.834807 42.71
26 -13.193 150.0
[Diffraction optical surface data]
11th surface C2 = -3.80E-04
C4 = 2.27E-06
C6 = -2.41E-08
C8 = 8.68E-11
[Resin refractive index data]
nC nd nF ng
Low refractive index 1.523300 1.527800 1.539100 1.549100
High refractive index 1.553800 1.557100 1.565000 1.571300
[Conditional expression correspondence value]
Conditional expression (1) νd1 = 82.57
Conditional expression (2) θgd1 + (0.002076 × νd1) -1.36467
= 0.0401
Conditional expression (3) fDOE / f = 262
Conditional expression (4) θmax = 3.4 °
[Reference value]
θdg1 = 1.2334

FIG. 2 is a diagram showing various aberrations (spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma) of the microscope objective lens according to the first embodiment. In this figure, various aberrations in a state where the above-mentioned imaging lens 123 (imaging lens IL) and prism 124 are combined with the microscope objective lens are shown. In each aberration diagram of FIG. 2, NA indicates numerical aperture, Y indicates image height, d is d line (wavelength λ = 587.6 nm), g is g line (wavelength λ = 435.8 nm), and C is C line (wavelength). λ = 656.3 nm) and F indicate various aberrations with respect to the F line (wavelength λ = 486.1 nm), respectively. In the spherical aberration diagram, the vertical axis shows the standardized value with the maximum value of the entrance pupil radius as 1, and the horizontal axis shows the aberration value [mm] in each light ray. In the astigmatism diagram, the solid line shows the meridional image plane for each wavelength, and the broken line shows the sagittal image plane for each wavelength. Further, in the astigmatism diagram, the vertical axis represents the image height [mm] and the horizontal axis represents the aberration value [mm]. In the distortion diagram (distortion), the vertical axis shows the image height [mm], and the horizontal axis shows the ratio of the aberration as a percentage (% value). In the chromatic aberration of magnification diagram, the vertical axis represents the image height [mm], and the horizontal axis represents the aberration value [mm]. The coma aberration diagram shows the aberration value [mm] when the image height Y is 12.5 mm, 10.6 mm, 9.0 mm, 6.2 mm, and 0 mm. In the aberration diagrams of each of the following examples, the same reference numerals as those of the present embodiment will be used, and duplicate description will be omitted.

From each aberration diagram, it can be seen that the microscope objective lens according to the first embodiment has various aberrations satisfactorily corrected in the region of C line to g line and has excellent imaging performance.

(Second Example)
The second embodiment will be described with reference to FIGS. 3 to 4 and Table 2. FIG. 3 is a cross-sectional view showing the configuration of the microscope objective lens according to the second embodiment of the present 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 and a second lens group G2 having a negative refractive power arranged in order from the object side. NS.

The first lens group G1 is formed by joining a plano-convex positive lens L1 having a plane facing the object side and a meniscus-shaped negative lens L2 having a concave surface having a strong curvature facing the object side, which are arranged in order from the object side. The first junction lens CL11, the meniscus-shaped positive lens L3 with the concave surface facing the object side, the second junction lens CL12 formed by joining the biconcave negative lens L4 and the biconvex positive lens L5, and the object. Through a third junction lens CL13 formed by bonding a meniscus-shaped negative lens L6 with a convex surface facing side and a biconvex positive lens L7, and first and second resin layers (diffraction element elements) Da and Db. The fourth junction lens CL14, which is formed by joining a meniscus-shaped negative lens L8 with a convex surface facing the object side and a biconvex positive lens L9 to form a diffractive optical element DOE, a biconvex positive lens L10, and both. It is composed of a fifth junction lens CL15 formed by bonding a concave negative lens L11. The first to fourth junction lenses CL11 to CL14 each have a positive refractive power as a whole. The fifth junction lens CL15 has a negative refractive power as a whole.

The first resin layer Da is formed using a resin material having a relatively low refractive index (high dispersion), and the second resin layer Db uses a resin material having a relatively high refractive index (low dispersion). Is formed. A diffraction optical surface Dm forming a diffraction grating groove is formed on the bonding surface between the first resin layer Da and the second resin layer Db, and the first resin layer Da and the second resin layer Db are bonded to each other. NS. A light transmitting parallel plane plate Cv such as a cover glass is arranged on the object side of the first lens group G1, and the positive lens L1 and the light transmitting parallel plane plate Cv arranged on the most object side of the first lens group G1 The space is filled with immersion liquid.

The second lens group G2 is a first junction lens CL21 formed by joining a biconvex positive lens L21 arranged in order from the object side and a biconcave negative lens L22 with a concave surface having a strong curvature facing the image side. It is composed of a meniscus-shaped negative lens L23 having a concave surface with a strong curvature facing the object side and a second junction lens CL22 formed by joining a meniscus-shaped positive lens L24 having a convex surface facing the image side. The first junction lens CL21 has a negative refractive power as a whole. The second junction lens CL22 has a positive refractive power as a whole.

Table 2 below lists the values of the specifications of the microscope objective lens according to the second embodiment.

(Table 2)
[Overall specifications]
f = 5.02
NA = 1.3
D0 = 0.28
β = 40x [lens data]
Surface number RD nd νd
1 ∞ 0.6 1.518230 58.90
2 -1.101 3.6 1.882997 40.77
3 -3.908 0.1
4 -9.887 4.0 1.729157 54.68
5 -7.086 0.1
6 -380.000 1.0 1.613397 44.27
7 16.219 6.1 1.651597 58.55
8 -23.570 0.1
9 108.856 1.0 1.772500 49.61
10 18.112 7.7 1.438750 94.95
11 -16.406 0.1
12 120.000 1.0 1.804000 46.57
13 23.744 0.2 1.527800 33.41
14 * 23.744 0.2 1.557100 49.74
15 23.744 6.1 1.438750 94.95
16 -19.785 0.1
17 12.327 6.1 1.438750 94.95
18 -24.942 1.0 1.816000 46.62
19 16.896 0.1
20 9.904 4.7 1.592399 68.37
21 -52.389 6.2 1.672999 38.15
22 5.402 5.5
23 -5.200 4.7 1.497820 82.57
24-45.132 3.6 1.834807 42.71
25 -11.231 150.0
[Diffraction optical surface data]
Surface 14 C2 = -2.61E-04
C4 = 7.03E-07
C6 = -7.81E-09
C8 = 0.00E + 00
[Resin refractive index data]
nC nd nF ng
Low refractive index 1.523300 1.527800 1.539100 1.549100
High refractive index 1.553800 1.557100 1.565000 1.571300
[Conditional expression correspondence value]
Conditional expression (1) νd1 = 82.57
Conditional expression (2) θgd1 + (0.002076 × νd1) -1.36467
= 0.0401
Conditional expression (3) fDOE / f = 381
Conditional expression (4) θmax = 26.4 °
[Reference value]
θdg1 = 1.2334

FIG. 4 is an aberration diagram of the microscope objective lens according to the second embodiment. From each aberration diagram, it can be seen that the microscope objective lens according to the second embodiment has various aberrations satisfactorily corrected in the C-line to g-line region and has excellent imaging performance.

Since the microscope objective lens according to each embodiment is an infinity correction type lens, it is used in combination with an imaging lens that forms an image of an object. Therefore, an example of an imaging lens used in combination with a microscope objective lens will be described with reference to FIGS. 5 and 3. FIG. 5 is a cross-sectional view showing the configuration of an imaging lens used in combination with the microscope objective lens according to each embodiment. The various aberration diagrams of the microscope objective lens according to each embodiment are those when used in combination with this imaging lens. The imaging lens IL shown in FIG. 5 includes a first junction lens CL31 formed by joining a biconvex positive lens L31 and a biconcave negative lens L32 arranged in order from the object side, and a biconvex positive lens. It is composed of a second junction lens CL32 formed by bonding L33 and a biconcave negative lens L34. The imaging lens IL is arranged on the image side of the microscope objective lens according to each embodiment.

Table 3 below lists the specifications of the imaging lens. In the [Overall specifications] table, fi indicates the focal length of the entire system of the imaging lens. In the table of [lens data], the surface numbers, R, D, nd, and νd are the same as those shown in the above description of Tables 1 and 2.

(Table 3)
[Overall specifications]
fi = 200
[Lens data]
Surface number RD nd νd
1 75.043 5.10 1.622801 57.03
2 -75.043 2.00 1.749501 35.19
3 1600.580 7.50
4 50.256 5.10 1.667551 41.96
5 -84.541 1.80 1.612658 44.41
6 36.911

According to each of the above embodiments, it is possible to realize a microscope objective lens having a flat image plane over the entire field of view, satisfactorily correcting axial chromatic aberration, and satisfactorily correcting chromatic aberration of magnification over the entire field of view. can.

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

G1 1st lens group G2 2nd lens group DOE diffractive optical element

Claims (15)

A first lens group having a positive refractive power and a second lens group having a negative refractive power arranged in order from the object side are provided.
The first lens group includes a diffraction optical element including a first diffraction element element and a second diffraction element element.
The diffractive optical element has a diffractive optical surface forming a diffraction grating groove formed on a junction surface between the first diffractive element and the second diffractive element.
The second lens group consists of a first junction lens in which a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image side are joined in order from the object side, and a concave surface facing the object side. It consists of a negative lens and a second lens made by joining a positive lens with a convex surface facing the image side.
An objective lens that satisfies the following conditional expression.
65.0 <νd1
0.0045 <θgd1 + (0.002076 × νd1) -1.36467
However, νd1: the abbe number θgd1: the partial dispersion ratio of the negative lens constituting the second junction lens based on the d line of the negative lens constituting the second junction lens, and the g line of the negative lens. When the refractive index of the negative lens with respect to the d line is nd1, the refractive index of the negative lens with respect to the F line is nF1, and the refractive index of the negative lens with respect to the C line is nC1, the following equation is obtained. Θgd1 = (ng1-nd1) / (nF1-nC1) defined by The objective lens according to claim 1, which satisfies the following conditional expression.
100 <fDOE / f <500
However, fDOE: focal length of the diffractive optical element f: focal length of the objective lens The objective lens according to claim 1 or 2, which satisfies the following conditional expression.
0 ° <θmax <40 °
However, θmax: the maximum value of the incident angle when the light ray having the maximum numerical aperture among the light rays from the center of the object is incident on the diffractive optical surface. The objective lens according to any one of claims 1 to 3, wherein the diffractive optical element is arranged closer to an object than a position where a main ray intersects an optical axis. The first lens group has a plurality of junction lenses and has a plurality of junction lenses.
The objective lens according to any one of claims 1 to 4, wherein at least one of the plurality of bonded lenses constituting the first lens group is arranged on the image side of the diffractive optical element. The fifth aspect of claim 5, wherein the bonded lens arranged on the image side of the plurality of bonded lenses constituting the first lens group has a negative refractive power, and the other bonded lens has a positive refractive power. Objective lens. The objective lens according to claim 5 or 6, wherein one of the plurality of junction lenses constituting the first lens group includes the diffractive optical element and has a positive refractive power. The first lens group includes a first junction lens having a positive refractive power arranged in order from the object side, a meniscus-shaped positive lens having a concave surface facing the object side, and a second junction lens having a positive refractive power. A third junction lens having a positive refractive power, a fourth junction lens having a positive refractive power, and a fifth junction lens having a negative refractive power.
The objective lens according to any one of claims 1 to 7, wherein the third junction lens includes the diffractive optical element. The first lens group includes a first junction lens having a positive refractive power arranged in order from the object side, a meniscus-shaped positive lens having a concave surface facing the object side, and a second junction lens having a positive refractive power. A third junction lens having a positive refractive power, a fourth junction lens having a positive refractive power, and a fifth junction lens having a negative refractive power.
The objective lens according to any one of claims 1 to 7, wherein the fourth junction lens includes the diffractive optical element. The objective lens according to any one of claims 1 to 9, wherein the first diffraction element element is made of a resin material. The objective lens according to any one of claims 1 to 10, wherein the first diffraction element element is made of a photocurable resin material. The objective lens according to any one of claims 1 to 11, wherein the second diffraction element element is made of a resin material. The objective lens according to any one of claims 1 to 12, wherein the second diffraction element element is made of a photocurable resin material. An optical system including the objective lens according to any one of claims 1 to 13 and an imaging lens. A microscope comprising the objective lens according to any one of claims 1 to 13.

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