Objective lens

Abstract

To provide an objective lens which satisfies specifications of a long working distance and a wide field of view and is well corrected for aberration performance down to the periphery of the field of view.SOLUTION: An objective lens 1 provided herein consists of a positive first lens group G1, a second lens group G2 consisting of a pair of lens components facing each other on concave surfaces thereof, and a positive third lens group G3 arranged in order from the object side. Each of the pair of lens components is a cemented lens. The objective lens 1 satisfies the following conditional expressions: 0.20≤d2 / L≤0.5 ...(1), where d2 represents an optical axial distance from a most image-side surface of an object-side lens component of the pair of lens components to a most object-side surface of an image-side lens component of the pair of lens components, and L represents an optical axial distance from a most object-side surface of the objective lens 1 to a most image-side surface of the objective lens 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The disclosure herein relates to an objective lens. [Background technology]

[0002] Objective lenses used in industrial applications require a high numerical aperture (NA) to achieve high resolution. In addition, to achieve high throughput, they also require a wide field of view and a long working distance (WD) to improve transport speed while avoiding the risk of collision with the objective lens, even in the case of uneven test objects. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 57-52568 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, Patent Document 1 discloses a low-magnification objective lens with a wide field of view, but the working distance of this objective lens is short and insufficient. When attempting to achieve a long working distance with such an objective lens configuration, it becomes difficult to effectively correct chromatic aberration of magnification. As a result, it is difficult to achieve good resolution even at the periphery of a wide field of view.

[0005] In view of the above circumstances, an object of one aspect of the present invention is to provide an objective lens that satisfies the specifications of a long working distance and a wide field of view, and in which aberration performance is well corrected even at the periphery of the field of view. [Means for solving the problem]

[0006] An objective lens according to one aspect of the present invention includes, arranged in order from the object side, a first lens group having positive refractive power, a second lens group consisting of a pair of lens components with their concave surfaces facing each other, and a third lens group having positive refractive power, each of which is a cemented lens. The first lens group consists of one positive lens, the third lens group consists of one positive lens, and the objective lens is an infinity-corrected microscope objective lens used in combination with an imaging lens. The objective lens satisfies the following conditional expression. 0.20≦d2 / L≦0.5 (1) 0.25≦d1 / L≦0.65 (7) where d2 is the distance on the optical axis from the surface closest to the image of the first lens component, which is the lens component closest to the object of the pair of lens components, to the surface closest to the object of the second lens component, which is the lens component closest to the image of the pair of lens components, and L is the distance on the optical axis from the surface closest to the object of the objective lens to the surface closest to the image of the objective lens. d1 is the distance on the optical axis from the surface of the first lens group closest to the image side to the surface of the second lens group closest to the object side. Another aspect of the objective lens of the present invention comprises, arranged in order from the object side, a first lens group having positive refractive power, a second lens group consisting of a pair of lens components with their concave surfaces facing each other, and a third lens group having positive refractive power, each of the pair of lens components being a cemented lens, the first lens group consisting of one positive lens, and the third lens group consisting of one positive lens, and the objective lens is an infinity-corrected microscope objective lens used in combination with an imaging lens, and satisfies the following conditional expression: 0.22≦d2 / L≦0.35 (1-1) 0.22≦R 212 / L≦0.38 ···(2) -12≦L / R 21c ≦-0.4 ···(3) 0≦d1 / L≦0.05 (8) where d2 is the distance on the optical axis from the surface closest to the image of the first lens component, which is the lens component on the object side of the pair of lens components, to the surface closest to the object of the second lens component, which is the lens component on the image side of the pair of lens components. L is the distance on the optical axis from the surface closest to the object of the objective lens to the surface closest to the image of the objective lens. R 212 is the radius of curvature of the surface of the first lens component closest to the image side. 21c is the radius of curvature of the cemented surface of the first lens component, and d1 is the distance on the optical axis from the surface of the first lens group closest to the image to the surface of the second lens group closest to the object. [Effects of the Invention]

[0007] According to the above aspect, it is possible to provide an objective lens that satisfies the specifications of long working distance and wide field of view, and in which aberration performance is well corrected even at the periphery of the field of view. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of an objective lens 1 according to Example 1 of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the imaging lens 10. [Figure 3]1 is an aberration diagram of an optical system consisting of an objective lens 1 and an imaging lens 10. FIG. [Figure 4] FIG. 3 is a cross-sectional view of an objective lens 2 according to Example 2 of the present invention. [Figure 5] 2 is an aberration diagram of an optical system consisting of an objective lens 2 and an imaging lens 10. FIG. [Figure 6] FIG. 10 is a cross-sectional view of an objective lens 3 according to Example 3 of the present invention. [Figure 7] 10 is an aberration diagram of an optical system consisting of an objective lens 3 and an imaging lens 10. FIG. [Figure 8] FIG. 10 is a cross-sectional view of an objective lens 4 according to Example 4 of the present invention. [Figure 9] 10 is an aberration diagram of an optical system consisting of an objective lens 4 and an imaging lens 10. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] An objective lens according to an embodiment of the present invention will be described. The objective lens according to this embodiment (hereinafter simply referred to as the objective lens) is an infinity-corrected microscope objective lens used in combination with an imaging lens.

[0010] The objective lens is composed of, arranged in order from the object side, a first lens group having positive refractive power, a second lens group consisting of a pair of lens components with their concave surfaces facing each other, and a third lens group having positive refractive power. That is, the configuration closer to the object than the pair of lens components is the first lens group, and the configuration closer to the image than the pair of lens components is the third lens group. The second lens group has negative refractive power.

[0011] In this specification, a lens component refers to a single lens block, whether a single lens or a cemented lens, in which only two lens surfaces, the object-side surface and the image-side surface through which light rays from an object point pass, are in contact with air. In other words, one single lens is one lens component, and one cemented lens is also one lens component. On the other hand, multiple single lenses or multiple cemented lenses arranged with air between them are not called one lens component.

[0012] The size of the optical system that constitutes an objective lens is practically limited, and it is necessary to fit it within a certain size. To achieve a wide field of view, i.e., a low-magnification objective lens, using such an optical system of a certain size, it is desirable to adopt a configuration that uses a telephoto type optical system, which allows for a long focal length without increasing the size. However, to achieve the object-side telecentricity required for a microscope objective lens in addition to a long working distance, it is desirable to place a lens group with positive refractive power on the object side. Taking these factors into consideration, it is desirable to adopt the above-mentioned configuration for an objective lens with a wide field of view and a long working distance, in which lens groups with positive refractive power (first lens group, third lens group) are placed on the object side and the image side, respectively, and a lens group with negative refractive power (second lens group) is placed between them.

[0013] Furthermore, in order to provide the second lens group with negative refractive power and to effectively correct aberrations, it is desirable that the second lens group be a pair of lens components with their concave surfaces, each with negative refractive power, facing each other. If the second lens group deviates significantly from such a concentric or nearly concentric arrangement, it becomes difficult to effectively correct coma aberration in particular.

[0014] For these reasons, it is desirable that the objective lens be configured such that a lens group having a positive refractive power is disposed on both sides of a pair of lens components whose concave surfaces face each other.

[0015] In addition, each of the pair of lens components in the objective lens, whose concave surfaces face each other, is a cemented lens. By configuring each of the pair of lens components as a cemented lens in which lenses with different optical properties are cemented together, it becomes possible to sufficiently correct chromatic aberration.

[0016] More specifically, the lens component of the pair of lens components located closer to the object (hereinafter also referred to as the first lens component) is mainly used to effectively correct lateral chromatic aberration, but unless the lens component located closer to the object is configured as a cemented lens, it is difficult to effectively correct lateral chromatic aberration. Furthermore, in order to achieve well-balanced correction of lateral chromatic aberration and longitudinal chromatic aberration with the pair of lens components, the lens component of the pair of lens components located closer to the image (hereinafter also referred to as the second lens component) needs to correct longitudinal chromatic aberration while suppressing the amount of lateral chromatic aberration. Because the marginal ray height is high in the region where the lens component located closer to the image is located, axial chromatic aberration can be effectively corrected by configuring the lens component as a cemented lens. Furthermore, because the lens component located closer to the image is located closer to the object than the third lens group, it is located in a region where the off-axial ray height is small, and as a result, the amount of lateral chromatic aberration can also be suppressed.

[0017] Moreover, the objective lens is configured to satisfy the following conditional expression (1). 0.20≦d2 / L≦0.5 (1) where d2 is the distance on the optical axis from the surface of the lens component (first lens component) closest to the object side of the pair of lens components closest to the image side to the surface of the lens component (second lens component) closest to the image side of the pair of lens components closest to the object side, and L is the distance on the optical axis from the surface of the objective lens closest to the object side to the surface of the objective lens closest to the image side.

[0018] Conditional formula (1) is a conditional formula for effectively correcting mainly lateral chromatic aberration and longitudinal chromatic aberration. As described above, by configuring the first lens component as a cemented lens, the effect of correcting lateral chromatic aberration can be enhanced, and by configuring the second lens component as a cemented lens, longitudinal chromatic aberration can be effectively corrected.

[0019] If d2 / L falls below the lower limit (0.2), the distance between the pair of lens components is limited to a short distance. This makes it difficult to effectively correct lateral chromatic aberration while also effectively correcting axial chromatic aberration. If d2 / L exceeds the upper limit (0.5), the distance between the pair of lens components becomes too long, making it difficult to achieve both low magnification and telecentricity. In addition, the second lens component is positioned farther toward the image than necessary, resulting in excessive lateral chromatic aberration.

[0020] The objective lens configured as described above satisfies the specifications of long working distance and wide field of view, and can correct aberrations well even at the periphery of the field of view.

[0021] The objective lens may be configured to satisfy the following conditional formula (1-1) or (1-2) instead of conditional formula (1). 0.22≦d2 / L≦0.4 (1-1) 0.24≦d2 / L≦0.35 (1-2)

[0022] A desirable configuration of the objective lens will be described below. In order to realize an objective lens with a long WD of a given size, it is desirable for the first lens group to consist of one positive lens. Furthermore, by not using more lenses than necessary in the first lens group, manufacturing costs can be reduced. Furthermore, by reducing the number of lenses, the number of elements that may cause manufacturing errors can be reduced, which ultimately reduces the deterioration of aberrations due to manufacturing errors.

[0023] The third lens group desirably consists of one positive lens to achieve an objective lens with a long focal length within a given size. Furthermore, not using more lenses than necessary in the third lens group reduces manufacturing costs. Furthermore, by reducing the number of lenses, the number of elements that may be subject to manufacturing errors can be reduced, which ultimately reduces the deterioration of aberrations due to manufacturing errors.

[0024] It is also desirable that the objective lens satisfy at least one of the following conditional expressions (2) to (8). 0.22≦R 212 / L≦0.38 (2) -12≦L / R 21c ≦-0.4 (3) -20≦f / f U21 ≦-0.5 (4) -6≦f / f U22 ≦1 (5) 0.7≦L 12 / f G1 ≦2.1 (6) 0.25≦d1 / L≦0.65 (7) 0≦d1 / L≦0.05 (8) However, R 212 is the radius of curvature of the surface of the first lens component closest to the image side. 21c is the radius of curvature of the cemented surface of the first lens component. U21 is the focal length of the first lens component. f U22 is the focal length of the second lens component. L 12 is the distance on the optical axis from the surface of the first lens group closest to the image to the surface of the second lens component closest to the object. G1 is the focal length of the first lens group, and d1 is the distance on the optical axis from the surface of the first lens group closest to the image to the surface of the second lens group closest to the object.

[0025] Condition (2) is a condition mainly for correcting field curvature effectively. As mentioned above, the second lens group is composed of a pair of lens components with their concave surfaces facing each other, and these concave surfaces have the function of correcting Petzval sum. 212 By not exceeding the upper limit (0.38) of R / L, the radius of curvature of the concave surface of the first lens component among the above-mentioned concave surfaces does not become too large, and the first lens component can be provided with a sufficient Petzval sum correction function. This allows for good correction of field curvature in the entire optical system. 212When / L does not fall below the lower limit (0.22), the radius of curvature of the concave surface of the first lens component does not become too small, and it is possible to avoid overcorrection of the Petzval sum, thereby enabling good correction of field curvature throughout the entire optical system.

[0026] In this specification, the radius of curvature of a lens surface is expressed as a positive value when the lens surface has a shape in which the central portion (portion on the optical axis) is located closer to the object than the peripheral portions (portions off the optical axis), and is expressed as a negative value when the lens surface has a shape in which the central portion (portion on the optical axis) is located closer to the image than the peripheral portions (portions off the optical axis). In other words, the radius of curvature is expressed as a positive value when the lens surface has a convex shape on the object side, and as a negative value when the lens surface has a convex shape on the image side.

[0027] Conditional expression (3) is a conditional expression primarily for effectively correcting lateral chromatic aberration. As described above, the first lens component, which is configured as a cemented lens among the pair of lens components, has the effect of correcting lateral chromatic aberration. Furthermore, since the image-side surface of the first lens component is concave, it is desirable to give the image-side lens of the first lens component, which is configured as a cemented lens, negative refractive power, and to construct the lens with negative refractive power from a high-dispersion glass material, thereby providing a chromatic aberration correction effect at the cemented surface. In this case, it is desirable that the cemented surface of the first lens component be a concave surface (with a negative radius of curvature) facing the object side. L / R 21c By ensuring that L / R does not exceed the upper limit (-0.4), the absolute value of the negative radius of curvature of the cemented surface can be made sufficiently small to achieve a large negative refractive power, and the correction effect of lateral chromatic aberration in the first lens component can be made sufficiently large. As a result, lateral chromatic aberration can be corrected well in the entire optical system. 21c is not below the lower limit (-12), the absolute value of the radius of curvature of the cemented surface of the first lens component does not become too small, and it is possible to avoid the difficulty in processing each lens of the cemented lens.

[0028] Conditional expression (4) is a conditional expression that is primarily intended to effectively correct curvature of field. As mentioned above, the second lens group is made up of a pair of lens components with their concave surfaces facing each other, and these concave surfaces have the effect of correcting Petzval sum. f / f U21 When f / f does not exceed the upper limit (-0.5), the negative power of the first lens component does not become too small, and it becomes possible to correct the Petzval sum well. U21 is not below the lower limit (-20), the negative power of the first lens component does not become too large, and therefore it is possible to achieve both telecentricity and a long WD without requiring excessive positive power in the first lens group. As a result, the occurrence of aberrations such as astigmatism in the first group can be kept small.

[0029] Condition (5) is a condition mainly for correcting field curvature well. U22 When f / f does not exceed the upper limit (1), the second lens component does not have an excessively large positive power, and therefore it is possible to correct the Petzval sum well. U22 When the value of (f) is not below the lower limit (-6), the second lens component, which is located in a region of the entire optical system relatively close to the image, does not have excessively large negative power, making it easy to realize a telephoto type lens configuration. This makes it possible to achieve good aberration correction while achieving both a wide field of view and a long working distance.

[0030] Conditional expression (6) is a conditional expression for effectively correcting mainly astigmatism and coma. In order to reduce the amount of astigmatism and coma generated by a pair of lens components with their concave surfaces facing each other while maintaining telecentricity on the object side, it is desirable to configure the lens so that the focal position of the first lens group when parallel light is incident from the object side is located within the second lens group. 12 / f G1 Since L does not exceed the upper limit (2.1), the focal position described above does not get too close to the object side with respect to the second lens component, so that the refraction angle of the off-axis chief ray at the second lens component can be made small. This makes it possible to keep astigmatism and coma small. 12 / f G1 is not below the lower limit (0.7), the focal position described above does not move too far toward the image side with respect to the second lens component, so the refraction angle of the off-axis chief ray at the first lens component can be made small, thereby making it possible to keep astigmatism and coma small.

[0031] Condition (7) is a condition for effectively correcting high-order coma aberrations when realizing an ultra-low magnification objective. An ultra-low magnification objective is one that satisfies f / TL>1. Here, f is the focal length of the objective, and TL is the distance on the optical axis from the object plane to the lens surface closest to the image. To increase the focal length while maintaining a long working distance and telecentricity, the first lens group must refract off-axial rays inward, reducing their height sufficiently to allow them to enter the second lens group. By ensuring that d1 / L does not fall below the lower limit (0.25), a sufficient distance can be secured between the first and second lens groups. This reduces the height of off-axial rays entering the second lens group without requiring excessive refraction in the first lens group. This reduces the amount of coma generated by the first lens group. The height of off-axial rays differs significantly between the first lens group and the subsequent lens groups. For this reason, if low-order coma in the first lens group is corrected by a lens group subsequent to the first lens group, high-order coma tends to remain, but because the amount of coma generated in the first lens group can be reduced as described above, it is possible to effectively correct high-order coma in the entire optical system. Furthermore, because d1 / L does not exceed the upper limit (0.65), it is possible to position the second group close to the object, and for the same reason as described above, it is possible to effectively correct chromatic aberration of magnification.

[0032] Condition (8) is a condition primarily for achieving excellent correction of lateral chromatic aberration when realizing an objective lens with an ultra-long WD. An objective lens with an ultra-long WD is one that satisfies WD / TL > 0.3. Here, WD is the working distance of the objective lens, and TL is the distance on the optical axis from the object plane to the lens surface closest to the image. By ensuring that d1 / L does not exceed the upper limit (0.05), the distance between the first and second lens groups can be made sufficiently small, allowing the second lens group to be positioned closer to the object while maintaining a predetermined WD. This allows the second lens group to have a sufficiently large effect of correcting lateral chromatic aberration, thereby enabling excellent correction of lateral chromatic aberration throughout the entire optical system. It is structurally impossible for d1 / L to fall below the lower limit (0).

[0033] The objective lens may be configured to satisfy the following conditional formula (2-1) or (2-2) instead of conditional formula (2). The objective lens may be configured to satisfy the following conditional formula (3-1) or (3-2) instead of conditional formula (3). The objective lens may be configured to satisfy the following conditional formula (4-1) or (4-2) instead of conditional formula (4). The objective lens may be configured to satisfy the following conditional formula (5-1) or (5-2) instead of conditional formula (5). The objective lens may be configured to satisfy the following conditional formula (6-1) or (6-2) instead of conditional formula (6). The objective lens may be configured to satisfy the following conditional formula (7-1) or (7-2) instead of conditional formula (7). The objective lens may be configured to satisfy the following conditional formula (8-1) or (8-2) instead of conditional formula (8). 0.23≦R 212 / L≦0.35 (2-1) 0.24≦R 212 / L≦0.32 (2-2) -9.6≦L / R 21c ≦-0.6 (3-1) -6.5≦L / R 21c ≦-0.9 (3-2) -16≦f / fU21 ≦-2.8 (4-1) -13≦f / f U21 ≦-5.6 (4-2) -5≦f / f U22 ≦0.5 (5-1) -4≦f / f U22 ≦-0.5 (5-2) 0.75≦L 12 / f G1 ≦1.8 (6-1) 0.8≦L 12 / f G1 ≦1.6 (6-2) 0.30≦d1 / L≦0.55 (7-1) 0.35≦d1 / L≦0.45 (7-2) 0≦d1 / L≦0.04 (8-1) 0≦d1 / L≦0.02 (8-2)

[0034] Examples of the above-mentioned objective lens will now be described in detail. [Example 1] 1 is a cross-sectional view of an objective lens 1 according to this embodiment. The objective lens 1 is a microscope objective lens and is composed of a first lens group G1 having positive refractive power, a second lens group G2 consisting of a pair of lens components, each of which is a cemented lens with its concave surfaces facing each other, and a third lens group G3 having positive refractive power.

[0035] The first lens group G1 is composed of a single lens, and the single lens is lens L1, which is a biconvex lens. The second lens group is composed of cemented lenses CL1 and CL2. The cemented lenses CL1 and CL2 are a pair of lens components arranged with their concave surfaces facing each other. The cemented lens CL1 is a doublet cemented lens and consists, arranged in order from the object side, of lens L2, which is a biconvex lens, and lens L3, which is a biconcave lens. The cemented lens CL2 is a doublet cemented lens and consists, arranged in order from the object side, of lens L4, which is a biconcave lens, and lens L5, which is a biconvex lens. The third lens group G3 is composed of a single lens, and the single lens is lens L6, which is a biconvex lens.

[0036] The various data of the objective lens 1 are as follows. Note that β is the magnification when the objective lens 1 is combined with the imaging lens 10. NA ob is the numerical aperture of the objective lens 1 on the object side. G1 , f G2 , f G3 are the focal length of the objective lens, the focal length of the first lens group G1, the focal length of the second lens group G2, and the focal length of the third lens group G3, respectively. The other parameters are as described above. NA ob =0.08, β=2.5, f=71.962mm, f G1 =22.476mm, f G2 =-6.898mm, f G3 =21.721mm, TL=49.12mm, WD=12.539mm, L=36.581mm, d1=13.657mm, d2=9.869mm, L 12 =26.519mm, f U21 =-7.809mm, f U22 =-78.090mm, R 212 =9.2794mm, R 21c =-6.4679mm

[0037] The lens data of the objective lens 1 is as follows: Note that INF in the lens data represents infinity (∞). Objective lens 1 srd nd νd 1 INF 12.539 2 28.8854 2.578 1.65412 39.68 3 -28.8854 13.657 4 127.4825 2.093 1.43875 94.66 5 -6.4679 0.900 1.75500 52.32 6 9.2794 9.869 7 -16.9117 1.200 1.75500 52.32 8 30.8327 3.000 1.43875 94.66 9 -11.8529 0.250 10 100.5080 3.033 1.49700 81.54 11 -11.9734 110.000

[0038] Here, s represents the surface number, r represents the radius of curvature (mm), d represents the surface spacing (mm), nd represents the refractive index for the d-line, and vd represents the Abbe number. These symbols are the same in the following examples. The surface indicated by surface number s1 is the specimen surface. The surfaces indicated by surface numbers s2 and s11 are the lens surface closest to the object and the lens surface closest to the image of the objective lens 1, respectively. For example, the surface spacing d1 represents the distance on the optical axis from the surface indicated by surface number s1 to the surface indicated by surface number s2. The surface spacing d11 represents the distance (110 mm) on the optical axis from the surface indicated by surface number s11 to the imaging lens.

[0039] The objective lens 1 satisfies the following conditional expressions (1) to (7). (1) d2 / L=0.270 (2)R 212 / L=0.254 (3) L / R 21c =-5.656 (4) f / f U21 =-9.215 (5) f / f U22 =-0.922 (6)L 12 / f G1 =1.180 (7)(8)d1 / L=0.373 (f / TL=1.465, WD / TL=0.255)

[0040] FIG. 2 is a cross-sectional view of an imaging lens 10 used in combination with objective lens 1. The imaging lens 10 is a microscope imaging lens that forms a magnified image of an object in combination with an infinity-corrected objective lens. The imaging lens 10 is a cemented lens CTL1 consisting of a biconvex lens TL1 and a meniscus lens TL2, which is placed on the image side of the biconvex lens and has its concave surface facing the object. The imaging lens 10 is positioned so that the distance on the optical axis from the lens surface (surface number s11) of objective lens 1 closest to the image to the lens surface (surface number s1) of imaging lens 10 closest to the object is 110 mm. The focal length of the imaging lens 10 is 180 mm.

[0041] The lens data of the imaging lens 10 is as follows: Imaging lens 10 srd nd νd 1 193.123 5.5 1.48749 70.23 2 -61.238 4.6 1.72047 34.71 3 -105.391

[0042] FIG. 3 is a diagram of aberrations of an optical system consisting of the objective lens 1 and the imaging lens 10, showing the aberrations at the image plane where the objective lens 1 and the imaging lens 10 form an optical image. FIG. 3(a) is a diagram of spherical aberration. FIG. 3(b) is a diagram showing the amount of violation of the sine condition. FIG. 3(c) is a diagram of astigmatism. FIG. 3(d) is a diagram of coma aberration at an image height ratio of 70% (image height 9.28 mm). In the diagram, "M" indicates the meridional component, and "S" indicates the sagittal component. As shown in FIG. 3, in this embodiment, aberrations are well corrected over a wide field of view.

[0043] [Example 2] 4 is a cross-sectional view of the objective lens 2 according to this embodiment. The objective lens 2 is a microscope objective lens and is composed of a first lens group G1 having a positive refractive power, a second lens group G2 consisting of a pair of lens components each of which is a cemented lens with its concave surfaces facing each other, and a third lens group G3 having a positive refractive power.

[0044] The first lens group G1 is composed of a single lens, and the single lens is lens L1, which is a biconvex lens. The second lens group is composed of cemented lenses CL1 and CL2. The cemented lenses CL1 and CL2 are a pair of lens components arranged with their concave surfaces facing each other. The cemented lens CL1 is a doublet cemented lens and consists, arranged in order from the object side, of lens L2, which is a meniscus lens with its concave surface facing the object side, and lens L3, which is a biconcave lens. The cemented lens CL2 is a doublet cemented lens and consists, arranged in order from the object side, of lens L4, which is a biconcave lens, and lens L5, which is a biconvex lens. The third lens group G3 is composed of a single lens, and the single lens is lens L6, which is a biconvex lens.

[0045] The various data of the objective lens 2 are as follows: NA ob =0.06, β=2.25, f=80mm, f G1 =19.729mm, f G2 =-6.519mm, f G3 =26.469mm, TL=51.02mm, WD=11.609mm, L=39.411mm, d1=10.020mm, d2=17.120mm, L 12 =29.831mm, f U21 =-7.744mm, f U22 =-96.232mm, R 212 =10.1833mm, R 21c =-7.4434mm

[0046] The lens data of the objective lens 2 is as follows: Objective Lens 2 srd nd νd 1 INF 11.609 2 25.1944 3.042 1.65412 39.68 3 -25.1944 10.020 4 -77.8135 1.792 1.43875 94.66 5 -7.4434 0.900 1.77250 49.60 6 10.1833 17.120 7 -22.6363 1.200 1.75500 52.32 8 37.7249 3.000 1.43875 94.66 9 -15.4462 0.250 10 83.5544 2.087 1.49700 81.54 11 -15.4841 110.000

[0047] The objective lens 2 satisfies the following conditional expressions (1) to (7). (1) d2 / L=0.434 (2)R 212 / L=0.258 (3) L / R 21c =-5.295 (4) f / f U21 =-10.331 (5) f / f U22 =-0.831 (6)L 12 / f G1 =1.512 (7)(8)d1 / L=0.254 (f / TL=1.568, WD / TL=0.228)

[0048] FIG. 5 is a diagram of aberrations of an optical system consisting of the objective lens 2 and the imaging lens 10, showing the aberrations at the image plane where the objective lens 2 and the imaging lens 10 form an optical image. FIG. 5(a) is a diagram of spherical aberration. FIG. 5(b) is a diagram showing the amount of violation of the sine condition. FIG. 5(c) is a diagram of astigmatism. FIG. 5(d) is a diagram of coma aberration at an image height ratio of 70% (image height 9.27 mm). As shown in FIG. 5, in this embodiment, aberrations are well corrected over a wide field of view.

[0049] [Example 3] 6 is a cross-sectional view of the objective lens 3 according to this example. The objective lens 3 is a microscope objective lens and is made up of a first lens group G1 having positive refractive power, a second lens group G2 consisting of a pair of lens components each of which is a cemented lens with its concave surfaces facing each other, and a third lens group G3 having positive refractive power.

[0050] The first lens group G1 is composed of a single lens, and the single lens is lens L1, which is a biconvex lens. The second lens group is composed of cemented lenses CL1 and CL2. The cemented lenses CL1 and CL2 are a pair of lens components arranged with their concave surfaces facing each other. The cemented lens CL1 is a doublet cemented lens and consists, arranged in order from the object side, of lens L2, which is a biconvex lens, and lens L3, which is a biconcave lens. The cemented lens CL2 is a doublet cemented lens and consists, arranged in order from the object side, of lens L4, which is a biconcave lens, and lens L5, which is a biconvex lens. The third lens group G3 is composed of a single lens, and the single lens is lens L6, which is a biconvex lens.

[0051] The various data of the objective lens 3 are as follows: NA ob =0.15, β=5, f=36mm, f G1 =20.539mm, f G2 =-10.046mm, f G3 =17.683mm, TL=48.838mm, WD=20.289mm, L=28.549mm, d1=0.200mm, d2=7.807mm, L 12 =18.373mm, f U21 =-34.214mm, f U22 =-12.876mm, R 212 =7.2915mm, R 21c =-15.6126mm

[0052] The lens data of the objective lens 3 is as follows: Objective Lens 3 srd nd νd 1 INF 20.289 2 25.0411 1.847 1.72916 54.68 3 -36.1028 0.200 4 10.4061 5.707 1.43875 94.66 5 -15.6126 4.660 1.61340 44.27 6 7.2915 7.807 7 -5.5361 1.500 1.80400 46.53 8 24.6954 3.133 1.43875 94.66 9 -7.6813 0.535 10 102.0044 3.160 1.51823 58.90 11 -9.9620 110.000

[0053] The objective lens 3 satisfies the following conditional expressions (1) to (6) and (8). (1) d2 / L=0.273 (2)R 212 / L=0.255 (3) L / R 21c =-1.829 (4) f / f U21 =-1.052 (5) f / f U22 =-2.796 (6)L 12 / f G1 =0.895 (7)(8)d1 / L=0.007 (f / TL=0.737, WD / TL=0.415)

[0054] FIG. 7 is a diagram of aberrations of an optical system consisting of the objective lens 3 and the imaging lens 10, showing the aberrations at the image plane where the objective lens 3 and the imaging lens 10 form an optical image. FIG. 7(a) is a diagram of spherical aberration. FIG. 7(b) is a diagram showing the amount of violation of the sine condition. FIG. 7(c) is a diagram of astigmatism. FIG. 7(d) is a diagram of coma aberration at an image height ratio of 70% (image height 9.27 mm). As shown in FIG. 7, in this embodiment, aberrations are well corrected over a wide field of view.

[0055] [Example 4] 8 is a cross-sectional view of the objective lens 4 according to this example. The objective lens 4 is a microscope objective lens and includes a first lens group G1 having a positive refractive power, a second lens group G2 consisting of a pair of lens components each of which is a cemented lens with its concave surfaces facing each other, and a third lens group G3 having a positive refractive power.

[0056] The first lens group G1 is composed of a single lens, and the single lens is lens L1, which is a biconvex lens. The second lens group is composed of cemented lenses CL1 and CL2. The cemented lenses CL1 and CL2 are a pair of lens components arranged with their concave surfaces facing each other. The cemented lens CL1 is a doublet cemented lens and consists, arranged in order from the object side, of lens L2, which is a biconvex lens, and lens L3, which is a biconcave lens. The cemented lens CL2 is a doublet cemented lens and consists, arranged in order from the object side, of lens L4, which is a biconcave lens, and lens L5, which is a biconvex lens. The third lens group G3 is composed of a single lens, and the single lens is lens L6, which is a biconvex lens.

[0057] The various data of the objective lens 4 are as follows: NA ob =0.13, β=4, f=45mm, f G1 =21.547mm, f G2 =-11.001mm, f G3 =21.071mm, TL=50.011mm, WD=16.31mm, L=33.701mm, d1=0.300mm, d2=12.552mm, L 12 =21.342mm, f U21 =-36.799mm, f U22 =-16.932mm, R 212 =8.0645mm, R 21c =-17.3049mm

[0058] The lens data of the objective lens 4 is as follows: Objective Lens 4 srd nd νd 1 INF 16.310 2 26.3865 1.533 1.88300 40.76 3 -66.3467 0.300 4 11.8701 5.159 1.43875 94.66 5 -17.3049 3.331 1.57501 41.50 6 8.0645 12.552 7 -7.3760 3.224 1.80400 46.53 8 29.1238 2.564 1.43875 94.66 9 -9.5667 1.001 10 85.5752 4.037 1.51823 58.90 11 -12.3154 110.000

[0059] The objective lens 4 satisfies the following conditional expressions (1) to (6) and (8). (1) d2 / L=0.372 (2)R 212 / L=0.239 (3) L / R 21c =-1.947 (4) f / f U21 =-1.223 (5) f / f U22 =-2.658 (6)L 12 / f G1 =0.990 (7)(8)d1 / L=0.009 (f / TL=0.900, WD / TL=0.326)

[0060] FIG. 9 is a diagram of aberrations of an optical system consisting of the objective lens 4 and the imaging lens 10, showing the aberrations at the image plane where the objective lens 4 and the imaging lens 10 form an optical image. FIG. 9(a) is a diagram of spherical aberration. FIG. 9(b) is a diagram showing the amount of violation of the sine condition. FIG. 9(c) is a diagram of astigmatism. FIG. 9(d) is a diagram of coma aberration at an image height ratio of 70% (image height 9.27 mm). As shown in FIG. 9, in this embodiment, aberrations are well corrected over a wide field of view. [Explanation of symbols]

[0061] 1, 2, 3, 4...Objective lens 10. Imaging lens G1: First lens group G2: Second lens group L1~L6, TL1, TL2... lenses CL1, CL2, CTL1... cemented lenses

Claims

1. The objective lens is arranged in order from the object side, a first lens group having positive refractive power; a second lens group consisting of a pair of lens components with their concave surfaces facing each other; a third lens group having a positive refractive power, each of the pair of lens components is a cemented lens; the first lens group is composed of one positive lens, the third lens group is composed of one positive lens, the objective lens is an infinity-corrected microscope objective lens used in combination with an imaging lens, An objective lens characterized by satisfying the following conditional expression: 0.20≦d2 / L≦0.5 (1) 0.25≦d1 / L≦0.65 (7) where d2 is the distance on the optical axis from the surface closest to the image of the first lens component, which is the lens component closest to the object of the pair of lens components, to the surface closest to the object of the second lens component, which is the lens component closest to the image of the pair of lens components. L is the distance on the optical axis from the surface closest to the object of the objective lens to the surface closest to the image of the objective lens. d1 is the distance on the optical axis from the surface closest to the image of the first lens group to the surface closest to the object of the second lens group.

2. 2. The objective lens according to claim 1, An objective lens characterized by satisfying the following conditional expression: 0.22≦R ２１２ / L≦0.38 ・・・(2) However, R ２１２ is the radius of curvature of the surface of the first lens component closest to the image side.

3. 3. The objective lens according to claim 1, An objective lens characterized by satisfying the following conditional expression: -12≦L / R ２１ｃ ≦-0.4 ・・・(3) However, R ２１ｃ is the radius of curvature of the cemented surface of the first lens component.

4. The objective lens according to any one of claims 1 to 3, An objective lens characterized by satisfying the following conditional expression: -20≦f / f Ｕ２１ ≦-0.5 ・・・(4) However, f Ｕ２１ is the focal length of the first lens component.

5. The objective lens according to any one of claims 1 to 4, An objective lens characterized by satisfying the following conditional expression: -6≦f / f Ｕ２２ ≦1 ・・・(5) However, f Ｕ２２ is the focal length of the second lens component.

6. The objective lens according to any one of claims 1 to 5, An objective lens characterized by satisfying the following conditional expression: 0.7≦L １２ / f Ｇ１ ≦2.1 ・・・(6) However, L １２ is the distance on the optical axis from the surface of the first lens group closest to the image side to the surface of the second lens component closest to the object side. Ｇ１ is the focal length of the first lens group.

7. An objective lens, arranged in order from the object side, a first lens group having positive refractive power; a second lens group consisting of a pair of lens components with their concave surfaces facing each other; a third lens group having a positive refractive power, each of the pair of lens components is a cemented lens; the first lens group is made up of one positive lens, the third lens group is composed of one positive lens, the objective lens is an infinity-corrected microscope objective lens used in combination with an imaging lens, An objective lens characterized by satisfying the following conditional expression: 0.22≦d2 / L≦0.35 (1-1) 0.22≦R 212 / L≦0.38 (2) -12≦L / R 21c≦-0.4...(3) 0≦d1 / L≦0.05 (8) where d2 is the distance on the optical axis from the surface closest to the image of the first lens component, which is the lens component closest to the object of the pair of lens components, to the surface closest to the object of the second lens component, which is the lens component closest to the image of the pair of lens components. L is the distance on the optical axis from the surface closest to the object of the objective lens to the surface closest to the image of the objective lens. R 212 is the radius of curvature of the surface closest to the image of the first lens component. R 21c is the radius of curvature of the cemented surface of the first lens component. d1 is the distance on the optical axis from the surface closest to the image of the first lens group to the surface closest to the object of the second lens group.

Images