Microscope objective

Abstract

The present invention provides a microscope objective which realizes a high numerical aperture and a long working distance at an appropriate magnification. The microscope objective (1) comprises: a positive first lens group (G1) comprising a plurality of meniscus lenses with a concave surface toward an object side; a second lens group (G2) comprising, on the most object side, a first cemented lens composed of a positive lens and a negative lens; a third lens group (G3) composed of a positive single lens; a fourth lens group (G4) comprising a first cemented meniscus lens with a concave surface toward the object side; a fifth lens group (G5) comprising a second cemented meniscus lens with a concave surface toward an image side composed of a positive lens and a negative lens; and a sixth lens group (G6) comprising a third cemented meniscus lens with a concave surface toward the object side composed of a positive lens and a negative lens, and satisfies the following conditional expression 0 < |f / f5| < 0.15... (1) where f is a focal length of the microscope objective (1) and f5 is a focal length of the fifth lens group (G5).

Description

TECHNICAL FIELD

[0001] The disclosure of the present specification relates to a microscope objective lens. BACKGROUND

[0002] For an objective lens used in an industrial use such as inspection of a wafer, a high numerical aperture (hereinafter referred to as NA) is required in order to achieve high resolution. In addition, a wide field of view is required in order to achieve high productivity, and a long working distance (hereinafter referred to as WD) is also required in order to increase the conveyance speed while avoiding the risk of collision between the object to be detected and the objective lens.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent No. 3093835 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] For example, an objective lens of 20x, NA 0.7 is disclosed in Patent Document 1, but the WD of this objective lens is as short as 1 mm, which is insufficient.

[0008] In view of the above actual situation, an object of one aspect of the present application is to provide an objective lens that achieves a high numerical aperture and a long working distance at an appropriate magnification.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] An objective lens of one embodiment of the present application includes, in order from the object side, a first lens group including a plurality of meniscus lenses with concave surfaces facing the object side, having positive refractive power; a second lens group including a first joint lens closest to the object side, the first joint lens being composed of a positive lens and a negative lens; a third lens group composed of a single positive lens; a fourth lens group including a first joint meniscus lens with a concave surface facing the object side; a fifth lens group composed of a second joint meniscus lens with a concave surface facing the image side, the second joint meniscus lens being composed of a positive lens and a negative lens; and a sixth lens group including a third joint meniscus lens with a concave surface facing the object side, the third joint meniscus lens being composed of a positive lens and a negative lens. The objective lens satisfies the following conditional expression.

[0011] 0 < |f / f5| < 0.15... (1)

[0012] where f is the focal length of the objective lens. f5 is the focal length of the fifth lens group.

[0013] EFFECT OF THE INVENTION

[0014] According to the above-described configuration, it is possible to provide an objective lens that realizes a high numerical aperture and a long working distance at an appropriate magnification. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a sectional view of a microscope objective 1 of Embodiment 1 of the present application.

[0016] Figure 2 is a sectional view of an imaging lens 10.

[0017] Figure 3 is an aberration diagram of an optical system composed of the microscope objective 1 and the imaging lens 10.

[0018] Figure 4 is a sectional view of a microscope objective 2 of Embodiment 2 of the present application.

[0019] Figure 5 is an aberration diagram of an optical system composed of the microscope objective 2 and the imaging lens 10.

[0020] Figure 6 is a sectional view of a microscope objective 3 of Embodiment 3 of the present application.

[0021] Figure 7 is an aberration diagram of an optical system composed of the microscope objective 3 and the imaging lens 10.

[0022] REFERENCE NUMERALS

[0023] 1, 2, 3 microscope objective

[0024] 10 imaging lens

[0025] G1 first lens group

[0026] G2 second lens group

[0027] G3 third lens group

[0028] G4 fourth lens group

[0029] G5 fifth lens group

[0030] G6 sixth lens group

[0031] L1 to L11, TL1 to TL4 lens

[0032] CL1 to CL4, CTL1, CTL2 cemented lens DETAILED DESCRIPTION

[0033] A microscope objective of one embodiment of the present application will be described. The microscope objective of the present application (hereinafter referred to simply as microscope objective) is an infinity-corrected microscope objective used in combination with an imaging lens.

[0034] The microscope objective lens includes a first lens group to a sixth lens group arranged in order from the object side. The first lens group includes a plurality of meniscus lenses having positive refractive power and concave toward the object side. The second lens group includes a cemented lens (hereinafter referred to as a first cemented lens) composed of a positive lens and a negative lens at the most object side. The third lens group is composed of a positive single lens. The fourth lens group includes a cemented meniscus lens (hereinafter referred to as a first cemented meniscus lens) having a meniscus shape as a whole with a concave surface toward the object side. The fifth lens group is composed of a cemented meniscus lens (hereinafter referred to as a second cemented meniscus lens) having a meniscus shape as a whole with a concave surface toward the image side. The sixth lens group includes a cemented meniscus lens (hereinafter referred to as a third cemented meniscus lens) having a meniscus shape as a whole with a concave surface toward the object side. In addition, the second cemented meniscus lens and the third cemented meniscus lens are each composed of a positive lens and a negative lens.

[0035] Light from an object point is incident on the first lens group to the third lens group as divergent light, and the third lens group converts the divergent light into convergent light to be incident on the fourth lens group. The fourth lens group to the sixth lens group convert the convergent light from the third lens group into parallel light. By temporarily converting the divergent light from the object point into convergent light by the first lens group to the third lens group to be incident on the fourth lens group, the marginal ray height after the fourth lens group can be made lower than the marginal ray height inside the first lens group. Thus, coma can be effectively corrected by the fifth lens group and the sixth lens group which constitute a Gauss group, and as a result, the image surface curvature can be well corrected over a wide field of view.

[0036] Further, by arranging the cemented lenses (the first cemented lens, the first cemented meniscus lens) in the peripheral regions of the third lens group (the second lens group, the fourth lens group) where the ray height is the highest, chromatic aberration can be corrected. In particular, by configuring these cemented lenses as achromatic lenses composed of a positive lens with low dispersion and a negative lens with high dispersion, good chromatic aberration can be achieved.

[0037] In addition, the microscope objective lens is configured to satisfy the following conditional expression (1).

[0038] 0 < |f / f5| < 0.15... (1)

[0039] where f is the focal length of the microscope objective lens. f5 is the focal length of the fifth lens group.

[0040] The conditional expression (1) specifies the power of the fifth lens group, and is a conditional expression mainly for well correcting coma. If |f / f5| exceeds the upper limit value (0.15), the power of the fifth lens group becomes too large with respect to the focal length. As a result, large coma occurs, and the symmetry of the coma deteriorates.

[0041] According to the microscope objective configured as above, a high numerical aperture and a long working distance can be achieved with an appropriate magnification power.

[0042] Further, the objective lens can be configured to satisfy the following conditional expression (1-1) instead of the conditional expression (1).

[0043] -0.15 < f / f5 < 0... (1-1)

[0044] The conditional expression (1-1) further specifies the power of the fifth lens group in the conditional expression (1), which is a conditional expression for also well correcting weak coma generated in the imaging lens 10.

[0045] Hereinafter, a preferred structure of the microscope objective will be described.

[0046] It is preferable that the first lens group be configured of a first meniscus lens having a concave surface toward the object side and a second meniscus lens having a concave surface toward the object side. By configuring the first lens group of only two meniscus lenses having a concave surface toward the object side, generation of spherical aberration can be reduced, and light rays can be gradually converged.

[0047] It is preferable that the second lens group be configured of a first cemented lens. By configuring the second lens group of only the first cemented lens, chromatic aberration generated by the first lens group can be corrected, and light rays can be gradually converged.

[0048] It is preferable that the fourth lens group be configured of a first cemented meniscus lens. By configuring the fourth lens group of only the first cemented meniscus lens, chromatic aberration can be reduced, and generation of high-order spherical aberration can be reduced.

[0049] It is preferable that the sixth lens group be configured of a third cemented meniscus lens. By configuring the sixth lens group of only the third cemented meniscus lens, Petzval sum can be effectively corrected, and magnification chromatic aberration can be well corrected.

[0050] Further, it is preferable that the microscope objective satisfy at least one of the following conditional expressions (2) to (4).

[0051] 0.5 < f / f1 < 1.0... (2)

[0052] 3.4 < n1 + n2 < 4.0... (3)

[0053] 60 < v3 < 90... (4)

[0054] where f1 is the focal length of the first lens group. n1 is the refractive index for e-line of the meniscus lens disposed on the most object side among the plurality of meniscus lenses included in the first lens group. n2 is the refractive index for e-line of the meniscus lens disposed on the second most object side among the plurality of meniscus lenses included in the first lens group. v3 is the Abbe number of the single lens configuring the third lens group.

[0055] The conditional expression (2) specifies the power of the first lens group, and is a conditional expression mainly for effectively correcting spherical aberration. If f / f1 is lower than the lower limit value (0.5), the power of the first lens group is too weak, and thus it is difficult to achieve a balance with Petzval sum. As a result, the performance of the entire optical system deteriorates. When f / f1 exceeds the upper limit value (1.0), the power of the first lens group is too large, and thus a large negative spherical aberration is generated in the first lens group. As a result, the spherical aberration cannot be completely corrected with the other lens groups, and it is difficult to perform good aberration correction.

[0056] The conditional expression (3) specifies the sum of the refractive indexes of the two meniscus lenses from the object side in the meniscus lens included in the first lens group, and is a conditional expression mainly for realizing a high-NA microscope objective and reducing the Petzval sum. If n1+n2 is lower than the lower limit value (3.4), in order to obtain the power of the first lens group, it is necessary to reduce the radii of curvature of the meniscus lenses, and as a result, the Petzval sum cannot be completely corrected in the entire optical system. When n1+n2 exceeds the upper limit value (4.0), the difference in refractive power between colors becomes too large, and it is difficult to correct the on-axis chromatic aberration well.

[0057] The conditional expression (4) specifies the Abbe number of the third lens group, and is a conditional expression mainly for correcting chromatic aberration well. If v3 is lower than the lower limit value (60), the on-axis chromatic aberration increases, and it is difficult to correct the on-axis chromatic aberration well. If v3 exceeds the upper limit value (90), the correction of the magnification chromatic aberration becomes difficult.

[0058] In addition, the microscope objective of the above-described structure is a microscope objective of about 20 times, high NA, and long WD. More specifically, the microscope objective has a focal length of 8 mm or more and 10 mm or less, and also has a WD of 3 mm or more and 6 mm or less.

[0059] Hereinafter, an embodiment of the above-described microscope objective will be specifically described.

[0060] [Embodiment 1]

[0061] Figure 1 is a sectional view of the microscope objective 1 of the present embodiment. The microscope objective (1) includes the following lens groups arranged in order from the object side: a first lens group (G1) having positive refractive power including a plurality of meniscus lenses with concave surfaces facing the object side; a second lens group (G2) including a first cemented lens on the most object side; a third lens group (G3) composed of a positive single lens; a fourth lens group (G4) including a first cemented meniscus lens with a concave surface facing the object side; a fifth lens group (G5) composed of a second cemented meniscus lens with a concave surface facing the image side; and a sixth lens group (G6) including a third cemented meniscus lens with a concave surface facing the object side.

[0062] The first lens group G1 is composed of a lens L1 which is a meniscus lens having a concave surface toward the object side and a lens L2 which is a meniscus lens having a concave surface toward the object side, arranged in this order from the object side.

[0063] The second lens group G2 is composed of a cemented lens CL1 which is a first cemented lens. The cemented lens CL1 is a 2-piece cemented lens composed of a lens L3 which is a double convex lens and a lens L4 which is a meniscus lens having a concave surface toward the object side, arranged in this order from the object side. The lens L4 is a negative lens.

[0064] The third lens group G3 is composed of a positive single lens, more specifically, a lens L5 which is a double convex lens.

[0065] The fourth lens group G4 is composed of a cemented lens CL2 which is a first cemented meniscus lens. The cemented lens CL2 is composed of a lens L6 which is a double concave lens and a lens L7 which is a double convex lens, arranged in this order from the object side.

[0066] The fifth lens group G5 is composed of a cemented lens CL3 which is a second cemented meniscus lens. The cemented lens CL3 is composed of a lens L8 which is a double convex lens and a lens L9 which is a double concave lens, arranged in this order from the object side.

[0067] The sixth lens group G6 is composed of a cemented lens CL4 which is a third cemented meniscus lens. The cemented lens CL4 is composed of a lens L10 which is a meniscus lens having a concave surface toward the object side and a lens L11 which is a meniscus lens having a concave surface toward the object side, arranged in this order from the object side. The lens L10 is a negative lens and the lens L11 is a positive lens.

[0068] Various data of the microscope objective 1 are as follows. In addition, NA ob is the numerical aperture on the object side of the microscope objective 1. WD is the working distance of the microscope objective 1. f2, f3, f4, f6 are 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, the focal length of the sixth lens group G6, respectively. Other parameters are as described above.

[0069] NA ob = 0.6, WD = 3.6004 mm, f = 8.9968 mm, f1 = 13.5880 mm, f2 = 1789.8 mm,

[0070] f3 = 26.2961 mm, f4 = -104.3538 mm, f5 = -63.4877 mm, f6 = -98.2662 mm, n1 = 1.88815, n2 = 1.75844, v3 = 71.3

[0071] The lens data of the microscope objective 1 is as follows. In addition, INF in the lens data indicates infinity (∞).

[0072] Microscope Objective 1

[0073]

[0074]

[0075] Here, s indicates a surface number, r indicates a curvature radius (mm), d indicates a surface interval (mm), ne indicates a refractive index for e line, and vd indicates an Abbe number. These symbols are also the same in the following examples. In addition, the surface indicated by the surface number s1 is a specimen surface. The surfaces indicated by the surface numbers s2, s19 are a lens surface closest to the object side and a lens surface closest to the image side of the microscope objective 1, respectively. In addition, for example, the surface interval d1 indicates a distance on the optical axis from the surface indicated by the surface number s1 to the surface indicated by the surface number s2. In addition, the surface interval d19 indicates a distance on the optical axis from the surface indicated by the surface number s19 to the imaging lens (120 mm).

[0076] The microscope objective 1 satisfies the conditional expressions (1) to (4) as follows.

[0077] (1) |f / f5| = |-0.142| = 0.142

[0078] (2) f / f1 = 0.66

[0079] (3) n1 + n2 = 3.65

[0080] (4) v3 = 71.3

[0081] Figure 2 is a sectional view of an imaging lens 10 used in combination with the microscope objective 1. The imaging lens 10 is a microscope imaging lens that forms a magnified image of an object in combination with an objective of an infinite correction type. The imaging lens 10 is composed of a cemented lens TCL1 and a cemented lens TCL2 disposed in this order from the object side. The cemented lens TCL1 is composed of a lens TL1 that is a double convex lens and a lens TL2 that is a meniscus lens with a concave surface facing the object side, disposed in this order from the object side. The cemented lens TCL2 is composed of a lens TL3 that is a double convex lens and a lens TL4 that is a double concave lens, disposed in this order from the object side. The imaging lens 10 is disposed in a manner that a distance on the optical axis from a lens surface (surface number s19) closest to the image side of the microscope objective 1 to a lens surface (surface number s1) closest to the object side of the imaging lens 10 is 120 mm. In addition, the focal length of the imaging lens 10 is 180 mm.

[0082] The lens data of the imaging lens 10 is as follows.

[0083] Imaging lens 10

[0084]

[0085] Figure 3 is an aberration map of the optical system composed of the microscope objective 1 and the imaging lens 10, showing aberrations on the image plane where the microscope objective 1 and the imaging lens 10 form an optical image. Figure 3 (a) of FIG. 1 is a spherical aberration map. Figure 3 (b) of FIG. 1 is a map showing a sine condition violation amount. Figure 3 (c) of FIG. 1 is a coma map. Figure 3 (d) of FIG. 1 is a coma map at an image height ratio of 8 (image height of 10.60 mm). In addition, "M" in the figure indicates a meridional component, and "S" indicates a sagittal component. As shown in Figure 3 in the present embodiment, aberrations are corrected well in a wide field of view.

[0086] [Embodiment 2]

[0087] Figure 4 is a sectional view of the microscope objective 2 of the present embodiment. The microscope objective (2) includes, disposed in order from the object side, the following lens groups: a first lens group G1 having positive refractive power including a plurality of meniscus lenses with concave surfaces toward the object side; a second lens group G2 including a first cemented lens at the most object side; a third lens group G3 composed of a positive single lens; a fourth lens group G4 including a first cemented meniscus lens with a concave surface toward the object side; a fifth lens group G5 composed of a second cemented meniscus lens with a concave surface toward the image side; and a sixth lens group G6 including a third cemented meniscus lens with a concave surface toward the object side.

[0088] The first lens group G1 is composed of a lens L1 which is a meniscus lens with a concave surface toward the object side, and a lens L2 which is a meniscus lens with a concave surface toward the object side, disposed in order from the object side.

[0089] The second lens group G2 is composed of a cemented lens CL1 which is a first cemented lens. The cemented lens CL1 is a 2-piece cemented lens composed of a lens L3 which is a biconvex lens, and a lens L4 which is a meniscus lens with a concave surface toward the object side, disposed in order from the object side. The lens L4 is a negative lens.

[0090] The third lens group G3 is composed of a positive single lens, more specifically, a lens L5 which is a biconvex lens.

[0091] The fourth lens group G4 is composed of a cemented lens CL2 which is a first cemented meniscus lens. The cemented lens CL2 is composed of a lens L6 which is a biconcave lens, and a lens L7 which is a biconvex lens, disposed in order from the object side.

[0092] The fifth lens group G5 is constituted by a cemented lens CL3 which is a second cemented meniscus lens. The cemented lens CL3 is constituted by a lens L8 which is a biconvex lens and a lens L9 which is a biconcave lens disposed in this order from the object side.

[0093] The sixth lens group G6 is constituted by a cemented lens CL4 which is a third cemented meniscus lens. The cemented lens CL4 is constituted by a lens L10 which is a plano-concave lens with the concave surface facing the object side and a lens L11 which is a plano-convex lens with the convex surface facing the image side disposed in this order from the object side.

[0094] Various data of the microscope objective 2 are as follows.

[0095] NA ob = 0.55, WD = 3.4666 mm, f = 8.9970 mm, fl = 13.8127 mm, f2 = 106.4855 mm,

[0096] f3 = 29.9445 mm, f4 = -60.8870 mm, f5 = -65.0208 mm, f6 = -122.8208 mm, nl = 1.88815, n2 = 1.75844, v3 = 81.54

[0097] Lens data of the microscope objective 2 are as follows.

[0098] Microscope objective 2

[0099]

[0100] The microscope objective 2 satisfies the conditional expressions (1) to (4) as shown below.

[0101] (1) |f / f5| = |-0.138| = 0.138

[0102] (2) f / fl = 0.65

[0103] (3) nl + n2 = 3.65

[0104] (4) v3 = 81.5

[0105] Figure 5 The aberration map of the optical system constituted by the microscope objective 2 and the imaging lens 10 shows the aberration on the image plane on which the microscope objective 2 and the imaging lens 10 form an optical image. Figure 5 (a) of FIG. 10 is a spherical aberration map. Figure 5 (b) of FIG. 10 is a map showing the amount of violation of the sine condition. Figure 5 (c) of FIG. 10 is a coma map. Figure 5 (d) of FIG. 10 is a coma map at an image height ratio of 8 (image height 10.60 mm). As Figure 5In the present embodiment, aberration is corrected well over a wide field of view.

[0106] [Embodiment 3]

[0107] Figure 6 is a sectional view of the microscope objective 3 of the present embodiment. The microscope objective 3 includes, disposed in order from the object side, the following lens groups: a first lens group Gl having positive refractive power including a plurality of meniscus lenses with the concave surface toward the object side; a second lens group G2 including a first cemented lens on the most object side; a third lens group G3 composed of a positive single lens; a fourth lens group G4 including a first cemented meniscus lens with the concave surface toward the object side; a fifth lens group G5 composed of a second cemented meniscus lens with the concave surface toward the image side; and a sixth lens group G6 including a third cemented meniscus lens with the concave surface toward the object side.

[0108] The first lens group Gl is composed of, disposed in order from the object side, a lens LI that is a meniscus lens with the concave surface toward the object side, and a lens L2 that is a meniscus lens with the concave surface toward the object side.

[0109] The second lens group G2 is composed of a cemented lens CL1 that is a first cemented lens. The cemented lens CL1 is a 2-element cemented lens composed of, disposed in order from the object side, a lens L3 that is a biconvex lens, and a lens L4 that is a meniscus lens with the concave surface toward the object side. The lens L4 is a negative lens.

[0110] The third lens group G3 is composed of a positive single lens, more specifically, a lens L5 that is a biconvex lens.

[0111] The fourth lens group G4 is composed of a cemented lens CL2 that is a first cemented meniscus lens. The cemented lens CL2 is composed of, disposed in order from the object side, a lens L6 that is a biconcave lens, and a lens L7 that is a biconvex lens.

[0112] The fifth lens group G5 is composed of a cemented lens CL3 that is a second cemented meniscus lens. The cemented lens CL3 is composed of, disposed in order from the object side, a lens L8 that is a biconvex lens, and a lens L9 that is a biconcave lens.

[0113] The sixth lens group G6 is composed of a cemented lens CL4 that is a third cemented meniscus lens. The cemented lens CL4 is composed of, disposed in order from the object side, a lens LI 0 that is a meniscus lens with the concave surface toward the object side, and a lens LI 1 that is a meniscus lens with the concave surface toward the object side. The lens LI 0 is a negative lens, and the lens LI 1 is a positive lens.

[0114] Various data of the microscope objective 3 are as follows.

[0115] NA ob= 0.65, WD = 3.4661 mm, f = 8.9970 mm, fl = 15.6389 mm, f2 = 109.3313 mm,

[0116] f3 = 29.0448 mm, f4 = -101.9587 mm, f5 = -67.4160 mm, f6 = -128.6295 mm, nl = 1.8976, n2 = 1.82017, v3 = 71.3

[0117] The lens data of the microscope objective 3 is as follows.

[0118] Microscope objective 3

[0119]

[0120] As shown below, the microscope objective 3 satisfies the conditional expressions (1) to (4).

[0121] (1) |f / f5| = |-0.133| = 0.133

[0122] (2) f / fl = 0.58

[0123] (3) nl + n2 = 3.72

[0124] (4) v3 = 71.3

[0125] Figure 7 is an aberration map of the optical system composed of the microscope objective 3 and the imaging lens 10, and shows the aberration on the image plane on which the microscope objective 3 and the imaging lens 10 form an optical image. Figure 7 (a) of is a spherical aberration map. Figure 7 (b) of is a graph showing a sine condition violation amount. Figure 7 (c) of is a coma map. Figure 7 (d) of is a coma map at an image height ratio of 8 (image height 10.60 mm). As Figure 7 shown, in the present embodiment, the aberration is well corrected over a wide field of view.

Claims

1. A microscope objective, characterized in that A microscope objective comprising, in order from an object side, the following lens groups: a first lens group composed of two meniscus lenses having a concave surface toward the object side, having positive refractive power; a second lens group composed of a first combined lens composed of a lenticular lens and a negative lens; a third lens group composed of a lenticular lens; a fourth lens group composed of a first combined meniscus lens having a concave surface toward the object side; a fifth lens group composed of a second combined meniscus lens having a concave surface toward an image side, the second combined meniscus lens being composed of a lenticular lens and a biconcave lens; and a sixth lens group composed of a third combined meniscus lens having a concave surface toward the object side, the third combined meniscus lens being composed of a positive lens and a negative lens, the microscope objective satisfying the following conditional expression 0 < |f / f5| < 0.15... (1) where f is a focal length of the microscope objective, and f5 is a focal length of the fifth lens group.

2. The microscope objective according to claim 1, wherein the microscope objective satisfies the following conditional expression 0.5 < f / f1 < 1.0... (2) where f1 is a focal length of the first lens group.

3. The microscope objective according to claim 1 or 2, wherein the microscope objective satisfies the following conditional expression 3.4 < n1 + n2 < 4.0... (3) where n1 is a refractive index for e-line of a meniscus lens disposed closest to the object side among the two meniscus lenses included in the first lens group, and n2 is a refractive index for e-line of a meniscus lens disposed second closest to the object side among the two meniscus lenses included in the first lens group.

4. The microscope objective according to claim 1 or 2, wherein the microscope objective satisfies the following conditional expression 60 < v3 < 90... (4) where v3 is an Abbe number of the lenticular lens constituting the third lens group.

5. The microscope objective according to claim 3, wherein the microscope objective satisfies the following conditional expression 60 < v3 < 90... (4) where v3 is an Abbe number of the lenticular lens constituting the third lens group.

Images