Objective lens

Abstract

To provide an objective lens that has a high NA and a long WD, and allows aberration to be corrected satisfactorily in a fully wide visual field.SOLUTION: An objective lens 1 comprises a first positive lens group that has a first meniscus component that has a concave surface in an object side and has a positive refractive power in a side closest to the object and has a positive refractive power, a second lens group comprising first three positive, negative, and positive cemented lenses, a third lens group comprising second three negative, positive, and negative cemented lenses, a fourth negative lens group having a second meniscus lens component having a concave surface in an image side and a negative refractive power in a side closest to the image, and a fifth lens group having a third meniscus lens component that has a concave surface in an object side and a negative refractive power in a side closest to the object that are disposed in order from the object side. The objective lens 1 satisfies the following conditional expression, where f shows a focal length of the objective lens and f2 shows a focal length of the second lens group. 0.21<|f / f2|<0.3...(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 such as wafer inspection are required to have both a high numerical aperture (NA) and a wide field of view in order to achieve high resolution and high throughput. In order to achieve even higher throughput, it is necessary to increase the transfer speed while avoiding the risk of collision between the specimen and the objective lens, so a long working distance (WD) is also required.

[0003] A technique related to such technical issues is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3093835 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes a 20X objective lens that achieves a high NA, but the WD is about 1 mm, and an objective lens with a longer WD is desired.

[0006] In view of the above circumstances, an object of one aspect of the present invention is to provide an objective lens that has a high NA and a long WD, and in which aberrations are well corrected within a sufficiently wide field of view. [Means for solving the problem]

[0007] The objective lens according to one aspect of the present invention includes a first lens group having positive refractive power, the first lens group being closest to the object side to a first meniscus lens component having a concave surface on the object side and having positive refractive power; a second lens group being a first triplet cemented lens made of a positive lens, a negative lens, and a positive lens; a third lens group being a second triplet cemented lens made of a negative lens, a positive lens, and a negative lens; a fourth lens group having negative refractive power, the fourth lens group being closest to the image side to a second meniscus lens component having a concave surface on the image side and having negative refractive power; and a fifth lens group being closest to the object side to a third meniscus lens component having a concave surface on the object side and having negative refractive power. The objective lens satisfies the following conditional formula. Here, f is the focal length of the objective lens. f2 is the focal length of the second lens group. 0.21 < |f / f2| < 0.3 (1)

[0008] According to another aspect of the present invention, an objective lens for a white light interferometer includes, in order from the object side, a beam splitter, a reference mirror, a first lens group having positive refractive power, the first lens group including a first meniscus lens component having a concave surface on the object side and the first meniscus lens component having positive refractive power closest to the object side, a second lens group including a first triplet cemented lens including a positive lens, a negative lens, and a positive lens, a third lens group including a second triplet cemented lens including a negative lens, a positive lens, and a negative lens, a fourth lens group having negative refractive power, the fourth lens group including a second meniscus lens component having a concave surface on the image side and the second meniscus lens component having negative refractive power closest to the image side, and a fifth lens group including a third meniscus lens component having a concave surface on the object side and the third meniscus lens component having negative refractive power closest to the object side. where f is the focal length of the objective lens, and f2 is the focal length of the second lens group. 0.21 < |f / f2| < 0.3 (1) Effect of the Invention

[0009] According to the above aspect, it is possible to provide an objective lens that has a high NA and a long WD, and in which aberrations are well corrected within a sufficiently wide field of view. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an objective lens 1 according to Example 1 of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the imaging lens 10. [Diagram 3] 2 is an aberration diagram of an optical system consisting of an objective lens 1 and an imaging lens 10. FIG. [Figure 4] FIG. 4 is a cross-sectional view of an objective lens 2 according to Example 2 of the present invention. [Diagram 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. 11 is a cross-sectional view of an objective lens 3 according to Example 3 of the present invention. [Figure 7] 2 is an aberration diagram of an optical system consisting of an objective lens 3 and an imaging lens 10. FIG. [Figure 8] FIG. 11 is a cross-sectional view of an objective lens 4 according to Example 4 of the present invention. [Figure 9] 2 is an aberration diagram of an optical system consisting of an objective lens 4 and an imaging lens 10. FIG. [Figure 10] FIG. 11 is a cross-sectional view of an objective lens 5 according to Example 5 of the present invention. [Figure 11] 2 is an aberration diagram of an optical system consisting of an objective lens 5 and an imaging lens 10. FIG. [Figure 12] FIG. 11 is a cross-sectional view of an objective lens 6 according to Example 6 of the present invention. [Figure 13] 2 is an aberration diagram of an optical system consisting of an objective lens 6 and an imaging lens 10. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An objective lens according to an embodiment of the present application will be described. The objective lens according to the embodiment (hereinafter simply referred to as the objective lens) is an infinity-corrected microscope objective lens used in combination with an imaging lens.

[0012] The objective lens consists of, arranged in order from the object side, a first lens group having positive refractive power, a second lens group and a third lens group each consisting of a cemented triplet lens, and a fourth lens group and a fifth lens group with their concave surfaces facing each other.

[0013] The first lens group has a positive refractive power to bring the divergent light from the specimen surface closer to a convergent state. The first lens group has a meniscus lens component having a concave surface on the object side closest to the object. This meniscus lens component is the first meniscus lens component of the objective lens and has a positive refractive power. By including a positive meniscus lens component with its concave surface facing the object side in the first lens group arranged closest to the object side, the first lens group can bring the divergent light from the specimen surface closer to a convergent state while suppressing the occurrence of spherical aberration.

[0014] In this specification, a lens component refers to a 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.

[0015] The second lens group has a relatively large positive refractive power in order to converge the incident light or to bring it closer to a convergent state. The second lens group is made of a triplet cemented lens consisting of a positive lens, a negative lens, and a positive lens. This triplet cemented lens is the first triplet cemented lens of the objective lens. By configuring the second lens group with a relatively strong positive refractive power using a positive-negative-positive triplet cemented lens that includes more positive lenses than negative lenses, it is possible to effectively correct spherical aberration and coma aberration while suppressing the occurrence of chromatic aberration.

[0016] The third lens group has a positive refractive power to further converge the incident light. The third lens group is composed of a triplet cemented lens consisting of a negative lens, a positive lens, and a negative lens. This triplet cemented lens is the second triplet cemented lens of the objective lens. Since the light emitted from the second lens group is convergent light or in a nearly convergent state, the third lens group does not need to have an excessively large refractive power, and it is desirable for the third lens group to have a relatively weak positive refractive power. By configuring the third lens group with a relatively weak positive refractive power using a negative-positive-negative triplet cemented lens that contains more negative lenses than positive lenses, it is possible to effectively correct spherical aberration and coma aberration while suppressing the occurrence of chromatic aberration.

[0017] The fourth and fifth lens groups are of the so-called Gauss type (double Gauss type) configuration, with a convex and concave surface facing each other, and convert the convergent light emitted from the third lens group into parallel light. For this reason, at least the fourth lens group has negative refractive power. It is also desirable for the fifth lens group to have negative refractive power as well.

[0018] To configure a Gaussian type, the fourth lens group has a meniscus lens component with a concave surface on the image side closest to the image. This meniscus lens component is the second meniscus lens component of the objective lens and has negative refractive power.

[0019] Similarly, to configure a Gaussian type, the fifth lens group has a meniscus lens component with a concave surface facing the object side closest to the object. This meniscus lens component is the third meniscus lens component of the objective lens and has negative refractive power.

[0020] By configuring the fourth lens group and the fifth lens group as a Gaussian type, it is possible to convert the convergent light emerging from the third lens group into a parallel light while satisfactorily correcting spherical aberration, coma aberration, and astigmatism.

[0021] The objective lens constructed as above is configured to satisfy the following conditional expression (1): where f is the focal length of the objective lens, and f2 is the focal length of the second lens group. 0.21 < |f / f2| < 0.3 (1)

[0022] Conditional formula (1) specifies the power of the second lens group. By satisfying this conditional formula, spherical aberration and coma can be effectively corrected. If |f / f2| is equal to or greater than the upper limit (0.3), the power of the second lens group becomes too strong relative to the focal length of the entire system, resulting in overcorrection and worsening of spherical aberration and coma. If |f / f2| is equal to or less than the lower limit (0.21), the power of the second lens group becomes too weak, resulting in undercorrection.

[0023] The objective lens configured as above has a high NA and a long WD, and can satisfactorily correct aberrations within a sufficiently wide field of view.

[0024] The objective lens may be configured so as to satisfy the following conditional formula (1-1) instead of or in addition to conditional formula (1). 0.24 < |f / f2| < 0.26 ···(1-1)

[0025] A desirable configuration of the objective lens will now be described. It is desirable for the objective lens to satisfy the following conditional expression (2): where f3 is the focal length of the third lens group. 0.05 < |f / f3| < 0.2 (2)

[0026] Conditional formula (2) specifies the power of the third lens group. By satisfying this conditional formula, spherical aberration and coma can be effectively corrected. If |f / f3| is equal to or greater than the upper limit (0.2), the power of the third lens group becomes too strong relative to the focal length of the entire system, resulting in overcorrection and worsening of spherical aberration and coma. If |f / f3| is equal to or less than the lower limit (0.05), the power of the third lens group becomes too weak, resulting in undercorrection.

[0027] The objective lens may be configured so as to satisfy the following conditional formula (2-1) instead of or in addition to conditional formula (2). 0.06 < |f / f3| < 0.17 ···(2-1)

[0028] It is preferable that the first meniscus lens component is a cemented lens formed by cementing together two meniscus lenses with their concave surfaces facing the object side. In this case, it is preferable that the objective lens satisfies the following conditional expression (3). 17 < |ν1-ν2| < 40 (3)

[0029] Here, ν1 is the Abbe number for the d-line of the meniscus lens arranged on the object side of the two meniscus lenses constituting the first meniscus lens component (i.e., the meniscus lens arranged closest to the object side), and ν2 is the Abbe number for the d-line of the meniscus lens arranged on the image side of the first meniscus lens component (i.e., the second meniscus lens counting from the object side).

[0030] Conditional formula (3) specifies the Abbe number difference between the two meniscus lenses that make up the first meniscus lens component. When the first meniscus lens component is composed of a cemented lens and this conditional formula is satisfied, the Abbe number difference between the two lenses is appropriately set, so that axial chromatic aberration and lateral chromatic aberration can be corrected well. If |ν1-ν2| is equal to or greater than the upper limit (40), axial chromatic aberration and lateral chromatic aberration are overcorrected, and if |ν1-ν2| is equal to or less than the lower limit (17), they are undercorrected.

[0031] The objective lens may be configured so as to satisfy the following conditional formula (3-1) instead of or in addition to conditional formula (3). 17.9 < |ν1-ν2| < 39.8 ···(3-1)

[0032] Furthermore, in the case where the first meniscus lens component is a cemented lens in which two meniscus lenses are cemented together with their concave surfaces facing the object side, it is desirable that the objective lens satisfy the following conditional expression (4). 3.4 < n1 + n2 < 4.0 (4)

[0033] Here, n1 is the refractive index for the e-line of the meniscus lens arranged on the object side of the two meniscus lenses constituting the first meniscus lens component (i.e., the meniscus lens arranged closest to the object side), and n2 is the refractive index for the e-line of the meniscus lens arranged on the image side of the first meniscus lens component (i.e., the second meniscus lens counting from the object side).

[0034] Conditional formula (4) is a conditional formula that specifies the sum of the refractive indices of the two meniscus lenses that make up the first meniscus lens component. By satisfying this conditional formula, it is possible to achieve a high NA while effectively correcting the curvature of field. When n1+n2 is equal to or greater than the upper limit (4.0), the difference in refractive power between the colors in the first lens group becomes too large, and as a result, it becomes difficult to effectively correct the axial chromatic aberration. When n1+n2 is equal to or less than the lower limit (3.4), the radius of curvature is reduced to obtain the power required for the first lens group. In this case, the Petzval sum is significantly biased toward the positive side in the first lens group, and therefore the Petzval sum cannot be fully corrected in the entire optical system including the fourth lens group (and the fifth lens group) that has a negative refractive power.

[0035] The objective lens may be configured so as to satisfy the following conditional formula (4-1) instead of or in addition to conditional formula (4). 3.5 < n1 + n2 < 3.8 (4-1)

[0036] The first lens group may be composed of a single positive meniscus lens with its concave surface facing the object side. In particular, when the second lens group and the third lens group satisfy conditional expressions (1) and (2), chromatic aberration, spherical aberration, and coma can be well corrected in the entire objective lens, so that the first lens group may be composed of a single lens to reduce the number of lenses constituting the objective lens.

[0037] The second meniscus lens component may be a cemented lens formed by cementing together two meniscus lenses with their concave surfaces facing the image side. The second meniscus lens component may also be made up of one negative meniscus lens with its concave surface facing the image side, and the fourth lens group may be made up of one negative meniscus lens. In particular, when the second lens group and the third lens group satisfy conditional expressions (1) and (2), chromatic aberration, spherical aberration, and coma aberration can be well corrected in the entire objective lens, so that the fourth lens group may be made up of a single lens to reduce the number of lenses constituting the objective lens.

[0038] It is desirable for the objective lens to satisfy the following conditional formula (5). Here, WD is the air-equivalent length of the distance on the optical axis from the specimen surface to the surface of the first lens group closest to the object. More specifically, WD is the air-equivalent length of the distance on the optical axis from the specimen surface to the surface of the first lens group closest to the object when the specimen surface is focused. L is the optical axial distance from the surface of the first lens group closest to the object to the surface of the fifth lens group closest to the image. WD / L > 0.065 (5)

[0039] Conditional formula (5) specifies the WD. By satisfying this conditional formula, a compact objective lens can achieve high throughput when used in industrial applications. If WD / L is below the lower limit (0.065), the distance between the specimen and the objective lens becomes short, increasing the risk of collision. As a result, in order to avoid collisions, the high-speed movement of the objective lens or stage, for example when changing the observation position, is restricted, and sufficient throughput cannot be obtained.

[0040] The objective lens may be configured so as to satisfy the following conditional formula (5-1) instead of or in addition to conditional formula (5). 0.08 < WD / L < 0.12 (5-1)

[0041] 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 the present embodiment. The objective lens 1 is a microscope objective lens, and is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power. The fourth lens group G4 and the fifth lens group G5 are Gaussian type lens groups composed of meniscus lens components with their concave surfaces facing each other.

[0042] The first lens group G1 is composed of a cemented lens CL1, which is a meniscus lens component with a concave surface facing the object side. The cemented lens CL1 is a meniscus lens component with positive refractive power, and is a cemented two-piece lens composed of a lens L1, which is a meniscus lens with a concave surface facing the object side, and a lens L2, which is a meniscus lens with a concave surface facing the object side, arranged in order from the object side. Both the lens L1 and the lens L2 are positive lenses.

[0043] The second lens group G2 is composed of a cemented lens CL2 having positive refractive power, which is a positive-negative-positive triplet lens composed of, in order from the object side, a biconvex lens L3, a biconcave lens L4, and a biconvex lens L5.

[0044] The third lens group G3 is composed of a cemented lens CL3 having positive refractive power. The cemented lens CL3 is a negative-positive-negative triplet cemented lens composed of, in order from the object side, lens L6 which is a meniscus lens with its concave surface facing the image side, lens L7 which is a biconvex lens, and lens L8 which is a meniscus lens with its concave surface facing the object side.

[0045] The fourth lens group G4 is composed of a cemented lens CL4 having negative refractive power. The cemented lens CL4 is a meniscus lens component having a concave surface on the image side, and is a cemented two-element lens composed of lens L9, which is a meniscus lens with its concave surface facing the image side, and lens L10, which is a meniscus lens with its concave surface facing the image side, arranged in order from the object side.

[0046] The fifth lens group G5 is a lens L11 consisting of one negative meniscus lens with its concave surface facing the object side.

[0047] The various data of the objective lens 1 are as follows. Note that f, f1, f2, f3, f4, and f5 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, the focal length of the third lens group G3, the focal length of the fourth lens group G4, and the focal length of the fifth lens group G5, respectively. The other parameters are as described above. f=9mm, f1=19.24mm, f2=36.18mm, f3=72.06mm, f4=-78.84mm, f5=-109.68mm NA=0.6,ν1=46.62,ν2=22.76,n1=1.82017,n2=1.81643,WD=4.689mm,L=44.93mm

[0048] The lens data of the objective lens 1 is as follows. Note that INF in the lens data indicates infinity (∞). Objective lens 1 srd ne νd s1 INF 4.69 s2 -14.693 3.47 1.82017 46.62 s3 -8.005 4.55 1.81643 22.76 s4 -9.474 0.15 s5 21.039 5.27 1.43986 94.66 s6 -13.258 1.30 1.61669 44.27 s7 18.450 5.04 1.43986 94.66 s8 -14.496 0.15 s9 17.894 1.30 1.86290 24.80 s10 11.692 5.29 1.43494 94.99 s11 -15.260 1.30 1.65803 39.68 s12 -41.846 0.15 s13 10.771 5.75 1.76760 48.49 s14 8.765 2.86 1.65376 56.24 s15 5.854 3.78 s16 -5.876 4.58 1.90314 20.36 s17 -8.558 56.38

[0049] Here, s is the surface number, r is the radius of curvature (mm), d is the surface spacing (mm), ne is the refractive index for the e-line, and νd is the Abbe number for the d-line. 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 s17 are the lens surface closest to the object side and the lens surface closest to the image side of the objective lens 1, respectively. For example, the surface spacing d1 indicates 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 d17 indicates the distance on the optical axis (56.38 mm) from the surface indicated by surface number s17 to the surface closest to the object side of the imaging lens.

[0050] The objective lens 1 satisfies the following conditional expressions (1) to (5). (1) |f / f2|=0.249 (2) |f / f3|=0.125 (3) |ν1-ν2|=23.86 (4) n1 + n2 = 3.637 (5) WD / L=0.104

[0051] FIG. 2 is a cross-sectional view of the imaging lens 10 used in combination with the objective lens 1. The imaging lens 10 is a microscope imaging lens that forms an image of an object in combination with an infinity-corrected objective lens. The imaging lens 10 is composed of a cemented lens CTL1 and a cemented lens CTL2. The cemented lens CTL1 is composed of a lens TL1 that is a biconvex lens and a lens TL2 that is a meniscus lens with a concave surface facing the object side. The cemented lens CTL2 is composed of a lens TL3 that is a biconvex lens and a lens TL4 that is a biconcave lens. The imaging lens 10 is arranged so that the distance on the optical axis from the lens surface (surface number s17) of the objective lens 1 closest to the image to the lens surface (surface number s1) of the imaging lens 10 closest to the object is 56.38 mm. The focal length of the imaging lens 10 is 180 mm.

[0052] The lens data of the imaging lens 10 is as follows. Imaging Lens 10 srd ne νd s1 69.950 8.00 1.48915 70.23 s2 -38.132 3.30 1.83945 42.71 s3 -95.720 0.67 s4 85.872 6.05 1.83932 37.16 s5 -50.111 3.30 1.65803 39.68 s6 41.656

[0053] FIG. 3 is an aberration diagram of an optical system consisting of an objective lens 1 and an imaging lens 10, showing the aberration on the image plane obtained by tracing rays from the object side to the image side. FIG. 3(a) is a spherical aberration diagram. FIG. 3(b) is a diagram showing the amount of violation of the sine condition. FIG. 3(c) is an astigmatism diagram. FIG. 3(d) is a coma aberration diagram at an image height ratio of 0.8 (image height 8.80 mm). In the diagram, "M" indicates the meridional component, and "S" indicates the sagittal component. As shown in FIG. 3, in this embodiment, the aberration is well corrected over a wide field of view.

[0054] 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 for a white light interferometer, and includes, in order from the object side, a beam splitter BS, a reference mirror RM, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group G5 having a negative refractive power. The fourth lens group G4 and the fifth lens group G5 are Gaussian type lens groups consisting of meniscus lens components with their concave surfaces facing each other.

[0055] The first lens group G1 is composed of a cemented lens CL1, which is a meniscus lens component with a concave surface facing the object side. The cemented lens CL1 is a meniscus lens component with positive refractive power, and is a cemented two-piece lens composed of a lens L1, which is a meniscus lens with a concave surface facing the object side, and a lens L2, which is a meniscus lens with a concave surface facing the object side, arranged in order from the object side. Both the lens L1 and the lens L2 are positive lenses.

[0056] The second lens group G2 is composed of a cemented lens CL2 having positive refractive power, which is a positive-negative-positive triplet lens composed of, in order from the object side, a biconvex lens L3, a biconcave lens L4, and a biconvex lens L5.

[0057] The third lens group G3 is composed of a cemented lens CL3 having positive refractive power. The cemented lens CL3 is a negative-positive-negative triplet cemented lens composed of, in order from the object side, lens L6 which is a meniscus lens with its concave surface facing the image side, lens L7 which is a biconvex lens, and lens L8 which is a meniscus lens with its concave surface facing the object side.

[0058] The fourth lens group G4 is composed of a cemented lens CL4 having negative refractive power. The cemented lens CL4 is a meniscus lens component having a concave surface on the image side, and is a cemented two-element lens composed of lens L9, which is a meniscus lens with its concave surface facing the image side, and lens L10, which is a meniscus lens with its concave surface facing the image side, arranged in order from the object side.

[0059] The fifth lens group G5 is a lens L11 consisting of one negative meniscus lens with its concave surface facing the object side.

[0060] Various data of the objective lens 2 are as follows: f=9mm, f1=19.14mm, f2=34.73mm, f3=79.32mm, f4=-86.13mm, f5=-111.38mm NA=0.6,ν1=46.62,ν2=22.76,n1=1.82017,n2=1.81643,WD=4.689mm,L=44.25mm

[0061] The lens data of the objective lens 2 is as follows: Objective lens 2 srd ne νd s1 INF 1.10 s2 INF 1.00 1.51825 64.14 s3 INF 1.10 s4 INF 1.00 1.51825 64.14 s5 INF 1.17 s6 -14.693 3.34 1.82017 46.62 s7 -7.790 4.40 1.81643 22.76 s8 -9.385 0.15 s9 21.965 4.94 1.43986 94.66 s10 -14.872 1.30 1.61669 44.27 s11 17.418 5.49 1.43986 94.66 s12 -13.935 0.15 s13 16.566 1.30 1.86290 24.80 s14 11.136 5.25 1.43494 94.99 s15 -18.315 1.30 1.65803 39.68 s16 -69.134 0.15 s17 10.626 5.69 1.76760 48.49 s18 8.490 2.82 1.65376 56.24 s19 5.882 3.27 s20 -5.899 4.71 1.90314 20.36 s21 -8.639 56.38

[0062] The objective lens 2 satisfies the following conditional expressions (1) to (5). (1) |f / f2|=0.259 (2) |f / f3|=0.114 (3) |ν1-ν2|=23.86 (4) n1 + n2 = 3.637 (5) WD / L=0.106

[0063] FIG. 5 is an aberration diagram of an optical system consisting of the objective lens 2 and the imaging lens 10, showing the aberration on the image plane obtained by tracing rays from the object side to the image side. FIG. 5(a) is a spherical aberration diagram. FIG. 5(b) is a diagram showing the amount of violation of the sine condition. FIG. 5(c) is an astigmatism diagram. FIG. 5(d) is a coma aberration diagram at an image height ratio of 0.8 (image height 8.80 mm). As shown in FIG. 5, in this embodiment, aberration is well corrected over a wide field of view.

[0064] Example 3 6 is a cross-sectional view of the objective lens 3 according to this embodiment. The objective lens 3 is a microscope objective lens, and is composed of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group G5 having a negative refractive power. The fourth lens group G4 and the fifth lens group G5 are Gaussian type lens groups composed of meniscus lens components with their concave surfaces facing each other.

[0065] The first lens group G1 is made up of a single positive meniscus lens L1 with its concave surface facing the object side.

[0066] The second lens group G2 is composed of a cemented lens CL1 having positive refractive power, which is a positive-negative-positive triplet lens composed of, in order from the object side, a biconvex lens L2, a biconcave lens L3, and a biconvex lens L4.

[0067] The third lens group G3 is composed of a cemented lens CL2 having positive refractive power. The cemented lens CL2 is a negative-positive-negative triplet lens composed of, in order from the object side, lens L5 which is a meniscus lens with its concave surface facing the image side, lens L6 which is a biconvex lens, and lens L7 which is a meniscus lens with its concave surface facing the object side.

[0068] The fourth lens group G4 is composed of a lens L8 which is a negative meniscus lens with its concave surface facing the image side.

[0069] The fifth lens group G5 is composed of a lens L9 which is a negative meniscus lens with its concave surface facing the object side.

[0070] Various data of the objective lens 3 are as follows: f=9mm, f1=17.64mm, f2=35.57mm, f3=53.96mm, f4=-44.48mm, f5=-115.81mm NA=0.6,WD=4.681mm,L=44.30mm

[0071] The lens data of the objective lens 3 is as follows: Objective Lens 3 srd ne νd s1 INF 4.68 s2 -15.686 7.68 1.91137 35.04 s3 -9.792 0.15 s4 21.990 4.78 1.43986 94.66 s5 -12.026 1.30 1.61669 44.27 s6 20.493 5.71 1.43986 94.66 s7 -13.784 0.15 s8 16.763 1.30 1.86290 24.80 s9 11.798 5.55 1.43494 94.99 s10 -13.376 1.30 1.65803 39.68 s11 -34.714 0.15 s12 11.948 8.05 1.76760 48.49 s13 6.262 3.50 s14 -5.735 4.70 1.90314 20.36 s15 -8.426 57.02

[0072] The objective lens 3 satisfies the conditions (1), (2), and (5) as shown below. (1) |f / f2|=0.253 (2) |f / f3|=0.167 (5) WD / L=0.106

[0073] FIG. 7 is an aberration diagram of an optical system consisting of the objective lens 3 and the imaging lens 10, showing the aberration on the image plane obtained by tracing rays from the object side to the image side. FIG. 7(a) is a spherical aberration diagram. FIG. 7(b) is a diagram showing the amount of violation of the sine condition. FIG. 7(c) is an astigmatism diagram. FIG. 7(d) is a coma aberration diagram at an image height ratio of 0.8 (image height 8.80 mm). As shown in FIG. 7, in this embodiment, aberration is well corrected over a wide field of view.

[0074] Example 4 8 is a cross-sectional view of the objective lens 4 according to this embodiment. The objective lens 4 is a microscope objective lens for a white light interferometer, and includes, in order from the object side, a beam splitter BS, a reference mirror RM, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group G5 having a negative refractive power. The fourth lens group G4 and the fifth lens group G5 are Gaussian type lens groups consisting of meniscus lens components with their concave surfaces facing each other.

[0075] The first lens group G1 is made up of a single positive meniscus lens L1 with its concave surface facing the object side.

[0076] The second lens group G2 is composed of a cemented lens CL1 having positive refractive power, which is a positive-negative-positive triplet lens composed of, in order from the object side, a biconvex lens L2, a biconcave lens L3, and a biconvex lens L4.

[0077] The third lens group G3 is composed of a cemented lens CL2 having positive refractive power. The cemented lens CL2 is a negative-positive-negative triplet lens composed of, in order from the object side, lens L5 which is a meniscus lens with its concave surface facing the image side, lens L6 which is a biconvex lens, and lens L7 which is a meniscus lens with its concave surface facing the object side.

[0078] The fourth lens group G4 is composed of a lens L8 which is a negative meniscus lens with its concave surface facing the image side.

[0079] The fifth lens group G5 is composed of a lens L9 which is a negative meniscus lens with its concave surface facing the object side.

[0080] Various data of the objective lens 4 are as follows: f=9mm, f1=16.82mm, f2=37.43mm, f3=53.26mm, f4=-43.42mm, f5=-123.91mm NA=0.6,WD=4.682mm,L=44.27mm

[0081] The lens data of the objective lens 4 is as follows: Objective lens 4 srd ne νd s1 INF 1.10 s2 INF 1.00 1.51825 64.14 s3 INF 1.10 s4 INF 1.00 1.51825 64.14 s5 INF 1.16 s6 -17.916 7.68 1.91137 35.04 s7 -9.950 0.15 s8 25.393 4.42 1.43986 94.66 s9 -11.866 1.30 1.61669 44.27 s10 19.588 6.29 1.43986 94.66 s11 -13.287 0.15 s12 14.871 1.30 1.86290 24.80 s13 10.846 5.50 1.43494 94.99 s14 -17.371 1.30 1.65803 39.68 s15 -57.954 0.15 s16 12.224 8.00 1.76760 48.49 s17 6.401 3.50 s18 -5.670 4.53 1.90314 20.36 s19 -8.236 56.37

[0082] The objective lens 3 satisfies the conditions (1), (2), and (5) as shown below. (1) |f / f2|=0.240 (2) |f / f3|=0.169 (5) WD / L=0.106

[0083] FIG. 9 is an aberration diagram of an optical system consisting of the objective lens 4 and the imaging lens 10, showing the aberration on the image plane obtained by tracing rays from the object side to the image side. FIG. 9(a) is a spherical aberration diagram. FIG. 9(b) is a diagram showing the amount of violation of the sine condition. FIG. 9(c) is an astigmatism diagram. FIG. 9(d) is a coma aberration diagram at an image height ratio of 0.8 (image height 8.80 mm). As shown in FIG. 9, in this embodiment, aberration is well corrected over a wide field of view.

[0084] Example 5 10 is a cross-sectional view of the objective lens 5 according to this embodiment. The objective lens 5 is a microscope objective lens, and is composed of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group G5 having a negative refractive power. The fourth lens group G4 and the fifth lens group G5 are Gaussian type lens groups composed of meniscus lens components with their concave surfaces facing each other.

[0085] The first lens group G1 is composed of a cemented lens CL1, which is a meniscus lens component with a concave surface facing the object side. The cemented lens CL1 is a meniscus lens component with positive refractive power, and is a cemented two-piece lens composed of a lens L1, which is a meniscus lens with a concave surface facing the object side, and a lens L2, which is a meniscus lens with a concave surface facing the object side, arranged in order from the object side. Both the lens L1 and the lens L2 are positive lenses.

[0086] The second lens group G2 is composed of a cemented lens CL2 having positive refractive power, which is a positive-negative-positive triplet lens composed of, in order from the object side, a biconvex lens L3, a biconcave lens L4, and a biconvex lens L5.

[0087] The third lens group G3 is composed of a cemented lens CL3 having positive refractive power. The cemented lens CL3 is a negative-positive-negative triplet cemented lens composed of, in order from the object side, lens L6 which is a meniscus lens with its concave surface facing the image side, lens L7 which is a biconvex lens, and lens L8 which is a meniscus lens with its concave surface facing the object side.

[0088] The fourth lens group G4 is made of a cemented lens CL4 having negative refractive power. The cemented lens CL4 is a meniscus lens component having a concave surface on the image side, and is a cemented two-piece lens made of, in order from the object side, a biconvex lens L9 and a biconcave lens L10.

[0089] The fifth lens group G5 is a lens L11 consisting of one negative meniscus lens with its concave surface facing the object side.

[0090] Various data of the objective lens 5 are as follows: f=9mm, f1=20.11mm, f2=33.14mm, f3=149.64mm, f4=-3101.38mm, f5=-105.79mm NA=0.6,ν1=60.08,ν2=20.36,n1=1.64254,n2=1.90314,WD=4.691mm,L=44.93mm

[0091] The lens data of the objective lens 5 is as follows: Objective lens 5 srd ne νd s1 INF 4.69 s2 -16.602 3.40 1.64254 60.08 s3 -7.840 4.14 1.90314 20.36 s4 -9.026 0.15 s5 19.506 5.90 1.43986 94.66 s6 -11.363 1.30 1.61669 44.27 s7 37.864 4.16 1.43986 94.66 s8 -15.059 0.15 s9 17.983 1.30 1.86290 24.80 s10 9.962 5.51 1.43494 94.99 s11 -18.066 1.30 1.65803 39.68 s12 -52.530 0.15 s13 11.286 6.55 1.76760 48.49 s14 -123.032 2.85 1.65376 56.24 s15 5.963 3.70 s16 -5.925 4.37 1.90314 20.36 s17 -8.528 56.38

[0092] The objective lens 5 satisfies the following conditional expressions (1) to (5). (1) |f / f2|=0.272 (2) |f / f3|=0.060 (3) |ν1-ν2|=39.72 (4) n1 + n2 = 3.546 (5) WD / L=0.104

[0093] FIG. 11 is an aberration diagram of an optical system consisting of an objective lens 5 and an imaging lens 10, showing the aberration on the image plane obtained by tracing rays from the object side to the image side. FIG. 11(a) is a spherical aberration diagram. FIG. 11(b) is a diagram showing the amount of violation of the sine condition. FIG. 11(c) is an astigmatism diagram. FIG. 11(d) is a coma aberration diagram at an image height ratio of 0.8 (image height 8.80 mm). As shown in FIG. 11, in this embodiment, aberration is well corrected over a wide field of view.

[0094] Example 6 12 is a cross-sectional view of the objective lens 6 according to this embodiment. The objective lens 6 is a microscope objective lens, and is composed of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a negative refractive power, and a fifth lens group G5 having a negative refractive power. The fourth lens group G4 and the fifth lens group G5 are Gaussian type lens groups composed of meniscus lens components with their concave surfaces facing each other.

[0095] The first lens group G1 is composed of a cemented lens CL1, which is a meniscus lens component with a concave surface facing the object side. The cemented lens CL1 is a meniscus lens component with positive refractive power, and is a cemented two-piece lens composed of a lens L1, which is a meniscus lens with a concave surface facing the object side, and a lens L2, which is a meniscus lens with a concave surface facing the object side, arranged in order from the object side. Both the lens L1 and the lens L2 are positive lenses.

[0096] The second lens group G2 is composed of a cemented lens CL2 having positive refractive power, which is a positive-negative-positive triplet lens composed of, in order from the object side, a biconvex lens L3, a biconcave lens L4, and a biconvex lens L5.

[0097] The third lens group G3 is composed of a cemented lens CL3 having positive refractive power. The cemented lens CL3 is a negative-positive-negative triplet cemented lens composed of, in order from the object side, lens L6 which is a meniscus lens with its concave surface facing the image side, lens L7 which is a biconvex lens, and lens L8 which is a meniscus lens with its concave surface facing the object side.

[0098] The fourth lens group G4 is composed of a cemented lens CL4 having negative refractive power. The cemented lens CL4 is a meniscus lens component having a concave surface on the image side, and is a cemented two-element lens composed of lens L9, which is a meniscus lens with its concave surface facing the image side, and lens L10, which is a meniscus lens with its concave surface facing the image side, arranged in order from the object side.

[0099] The fifth lens group G5 is a lens L11 consisting of one negative meniscus lens with its concave surface facing the object side.

[0100] Various data of the objective lens 6 are as follows: f=9mm, f1=19.21mm, f2=34.66mm, f3=81.47mm, f4=-66.84mm, f5=-120.34mm NA=0.6,ν1=42.74,ν2=24.80,n1=1.83945,n2=1.86290,WD=4.687mm,L=44.93mm

[0101] The lens data of the objective lens 6 is as follows: Objective Lens 6 srd ne νd s1 INF 4.69 s2 -14.693 3.57 1.83945 42.74 s3 -8.398 4.70 1.86290 24.80 s4 -9.705 0.15 s5 21.253 4.92 1.43986 94.66 s6 -12.598 1.30 1.61669 44.27 s7 19.925 4.92 1.43986 94.66 s8 -13.843 0.15 s9 18.935 1.30 1.86290 24.80 s10 12.740 5.34 1.43494 94.99 s11 -12.457 1.30 1.65803 39.68 s12 -38.672 0.15 s13 10.715 5.75 1.76760 48.49 s14 6.981 2.85 1.65376 56.24 s15 5.871 3.70 s16 -5.960 4.84 1.90314 20.36 s17 -8.734 56.38

[0102] The objective lens 6 satisfies the following conditional expressions (1) to (5). (1) |f / f2|=0.260 (2) |f / f3|=0.111 (3) |ν1-ν2|=17.94 (4) n1 + n2 = 3.702 (5) WD / L=0.104

[0103] FIG. 13 is an aberration diagram of an optical system consisting of an objective lens 6 and an imaging lens 10, showing the aberration on the image plane obtained by tracing rays from the object side to the image side. FIG. 13(a) is a spherical aberration diagram. FIG. 13(b) is a diagram showing the amount of violation of the sine condition. FIG. 13(c) is an astigmatism diagram. FIG. 13(d) is a coma aberration diagram at an image height ratio of 0.8 (image height 8.80 mm). As shown in FIG. 13, in this embodiment, aberration is well corrected over a wide field of view. [Explanation of symbols]

[0104] 1, 2, 3, 4, 5, 6...Objective lens 10 Imaging lens G1: First lens group G2: Second lens group G3: Third lens group G4: Fourth lens group G5: Fifth lens group L1~L11, TL1~TL4... Lenses CL1~CL4, CTL1, CTL2...Cemented lenses

Claims

1. The objective lens is arranged in order from the object side, a first lens group having a positive refractive power, the first lens group including a first meniscus lens component having a concave surface on the object side, the first meniscus lens component having a positive refractive power being closest to the object; a second lens group including a first triplet cemented lens including a positive lens, a negative lens, and a positive lens; a third lens group including a second triplet cemented lens including a negative lens, a positive lens, and a negative lens; a fourth lens group having negative refractive power, the fourth lens group including a second meniscus lens component having a concave surface on an image side, the second meniscus lens component having negative refractive power being closest to the image side; a fifth lens group including a third meniscus lens component having a concave surface on the object side and negative refractive power, the fifth lens group being closest to the object side; The following conditional expression 0.21 < | f / f2 | < 0.3 ... (1) Fulfill An objective lens characterized by: where f is the focal length of the objective lens, and f2 is the focal length of the second lens group.

2. An objective lens for a white light interferometer, arranged in order from the object side, A beam splitter; A reference mirror; a first lens group having a positive refractive power, the first lens group including a first meniscus lens component having a concave surface on the object side, the first meniscus lens component having a positive refractive power being closest to the object; a second lens group including a first triplet cemented lens including a positive lens, a negative lens, and a positive lens; a third lens group including a second triplet cemented lens including a negative lens, a positive lens, and a negative lens; a fourth lens group having negative refractive power, the fourth lens group including a second meniscus lens component having a concave surface on an image side, the second meniscus lens component having negative refractive power being closest to the image side; a fifth lens group including a third meniscus lens component having a concave surface on the object side and negative refractive power, the fifth lens group being closest to the object side; The following conditional expression 0.21 < | f / f2 | < 0.3 ... (1) Fulfill An objective lens characterized by: where f is the focal length of the objective lens, and f2 is the focal length of the second lens group.

3. 3. The objective lens according to claim 1, The following conditional expression 0.05 < | f / f3 | < 0.2 ... (2) An objective lens characterized by satisfying the above. Here, f3 is the focal length of the third lens group.

4. 3. The objective lens according to claim 1, the first meniscus lens component is a cemented lens in which two meniscus lenses are cemented together, The following conditional expression 17 < | ν1 - ν2 | < 40 ... (3) An objective lens characterized by satisfying the above. Here, v1 is the Abbe number for the d-line of the meniscus lens arranged on the object side of the two meniscus lenses, and v2 is the Abbe number for the d-line of the meniscus lens arranged on the image side of the two meniscus lenses.

5. 3. The objective lens according to claim 1, the first meniscus lens component is a cemented lens in which two meniscus lenses are cemented together, The following conditional expression 3.4 < n1 + n2 < 4.0 (4) An objective lens characterized by satisfying the above. Here, n1 is the refractive index for the e-line of the meniscus lens arranged on the object side of the two meniscus lenses, and n2 is the refractive index for the e-line of the meniscus lens arranged on the image side of the two meniscus lenses.

6. 3. The objective lens according to claim 1, The following conditional expression WD / L > 0.065...(5) An objective lens characterized by satisfying the above. Here, WD is the air-equivalent length of the distance on the optical axis from the sample surface to the surface of the first lens group closest to the object, and L is the distance on the optical axis from the surface of the first lens group closest to the object to the surface of the fifth lens group closest to the image.

7. 3. The objective lens according to claim 1, The first lens group is composed of one positive meniscus lens having a concave surface facing the object side. An objective lens characterized by:

8. 3. The objective lens according to claim 1, The fourth lens group is composed of one negative meniscus lens having a concave surface facing the image side. An objective lens characterized by:

9. 4. The objective lens according to claim 3, the first meniscus lens component is a cemented lens in which two meniscus lenses are cemented together, The following conditional expression 17 < | ν1 - ν2 | < 40 ... (3) An objective lens characterized by satisfying the above. Here, v1 is the Abbe number for the d-line of the meniscus lens arranged on the object side of the two meniscus lenses, and v2 is the Abbe number for the d-line of the meniscus lens arranged on the image side of the two meniscus lenses.

10. 4. The objective lens according to claim 3, the first meniscus lens component is a cemented lens in which two meniscus lenses are cemented together, The following conditional expression 3.4 < n1 + n2 < 4.0 (4) An objective lens characterized by satisfying the above. Here, n1 is the refractive index for the e-line of the meniscus lens arranged on the object side of the two meniscus lenses, and n2 is the refractive index for the e-line of the meniscus lens arranged on the image side of the two meniscus lenses.

11. 4. The objective lens according to claim 3, The following conditional expression WD / L > 0.065...(5) An objective lens characterized by satisfying the above. Here, WD is the air-equivalent length of the distance on the optical axis from the sample surface to the surface of the first lens group closest to the object, and L is the distance on the optical axis from the surface of the first lens group closest to the object to the surface of the fifth lens group closest to the image.

12. 4. The objective lens according to claim 3, The first lens group is composed of one positive meniscus lens having a concave surface facing the object side. An objective lens characterized by:

13. 4. The objective lens according to claim 3, The fourth lens group is composed of one negative meniscus lens having a concave surface facing the image side. An objective lens characterized by:

14. 10. The objective lens according to claim 9, The following conditional expression 3.4 < n1 + n2 < 4.0 (4) An objective lens characterized by satisfying the above. Here, n1 is the refractive index for the e-line of the meniscus lens arranged on the object side of the two meniscus lenses, and n2 is the refractive index for the e-line of the meniscus lens arranged on the image side of the two meniscus lenses.

15. 10. The objective lens according to claim 9, The following conditional expression WD / L > 0.065...(5) An objective lens characterized by satisfying the above. Here, WD is the air-equivalent length of the distance on the optical axis from the sample surface to the surface of the first lens group closest to the object, and L is the distance on the optical axis from the surface of the first lens group closest to the object to the surface of the fifth lens group closest to the image.

16. 10. The objective lens according to claim 9, The fourth lens group is composed of one negative meniscus lens having a concave surface facing the image side. An objective lens characterized by:

17. The objective lens according to claim 12, The fourth lens group is composed of one negative meniscus lens having a concave surface facing the image side. An objective lens characterized by:

18. 15. The objective lens according to claim 14, The following conditional expression WD / L > 0.065...(5) An objective lens characterized by satisfying the above. Here, WD is the air-equivalent length of the distance on the optical axis from the sample surface to the surface of the first lens group closest to the object, and L is the distance on the optical axis from the surface of the first lens group closest to the object to the surface of the fifth lens group closest to the image.

19. 15. The objective lens according to claim 14, The fourth lens group is composed of one negative meniscus lens having a concave surface facing the image side. An objective lens characterized by:

20. 20. The objective lens according to claim 18, The fourth lens group is composed of one negative meniscus lens having a concave surface facing the image side. An objective lens characterized by:

Images