JP3510401B2 - Microscope objective lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope objective lens, and more particularly to an apochromat microscope having a magnification of about 100 times, a numerical aperture of about 0.95, and a flat image surface. It relates to an objective lens. 2. Description of the Related Art As a conventional example of a microscope objective lens similar to the objective lens of the present invention, a lens system described in Japanese Patent Publication No. 3-58495 is known. This objective lens has, in order from the object side, a positive meniscus lens component having a concave surface facing the object side, a positive meniscus lens component, and a cemented lens component, and has a positive refraction that converts a light beam from the object into a convergent light beam. A first lens unit having a power, a second lens unit having a cemented lens having a small refractive power disposed in the convergent light beam, a meniscus lens component having a convex surface facing the object side, and a negative lens component following the meniscus lens component The third of negative refractive power having
And a lens group. [0003] In the conventional microscope objective lens, spherical aberration and axial chromatic aberration are not corrected to the apochromatic level. The reason for this is to increase the target working distance in this conventional example, and if the working distance is increased, it becomes inevitably difficult to correct aberrations. An object of the present invention is to provide a magnification of about 100 times,
An object of the present invention is to provide an apochromat class microscope objective lens having a numerical aperture of about 0.95. [0005] The above-described dry high NA, high magnification apochromatic objective lens is particularly useful for high resolution observation and measurement of a semiconductor, a magnetic head, and the like. A microscope objective according to the present invention has at least a positive meniscus lens having a concave surface facing the object side and a plurality of cemented positive lens components in order from the object side. A first lens group having a positive refractive power that converts a light beam from an object into a convergent light beam; a negative lens and a positive lens having a convex surface closest to the object side and a concave surface closest to the image side having a concave shape on the image side ; A second lens group including a cemented lens component cemented with a negative lens, and a third lens group including a meniscus lens component having a convex surface closest to the object side and a meniscus lens component having a concave surface facing the object side. Condition (1),
(2) and (3) are satisfied. (1) 0.7 <R ₂ / R ₃ <1.3 (2) N ₁ > N ₂ , N ₃ > N ₂ (3) f / f ₂ <−0.1 where R ₂ , R ₃ is the radius of curvature of the surface closest to the image in the second lens group and the radius of curvature of the surface closest to the object in the third lens group, and N ₁ , N ₂ , and N ₃ are three cemented elements of the second lens group, respectively. negative lens on the object side of the lens, a positive lens, the refractive index of the negative lens on the image side, f is the focal length of the entire system, f ₂ is the focal length of the second lens group. In general, in a dry plan objective having a flat image surface, a positive meniscus lens having a concave surface facing the most object side is arranged so as not to adversely affect aberration. The reason why a plurality of cemented lens components are arranged is to satisfactorily correct chromatic aberration. The first lens group having a positive refractive power and having these lens components has a function of converting a light beam from an object into a convergent light beam. Also, the second lens group,
The third lens group is provided with a lens having a negative refractive power in order to correct an aberration that is insufficiently corrected in the first lens group. That is, the second lens group is composed of a negative lens, a positive lens, and a negative lens.
A cemented lens was arranged. This three-element cemented lens corrects chromatic aberration and sets the refractive index of these three lenses as shown in the condition (2) so that the two cemented surfaces have a negative refractive power. It also corrects the curvature of spherical aberration and axial chromatic aberration. The overall shape of the three-element cemented lens is such that the most object side surface is a convex surface on the object side, and the most image side surface is a strongly concave surface on the image side, thereby minimizing the occurrence of aberration in a convergent light beam. . Further, in combination with making the most object side surface of the third lens group a strong convex surface, the negative refracting power of the most image side surface of the second lens group is effectively used. The condition (1) defines the relationship between the radius of curvature of the surface closest to the image in the second lens unit and the surface closest to the object in the third lens unit. The closer the radii of curvature of the two surfaces are to each other, the more effective the negative refractive power due to the action of the air lens formed by the two surfaces is for correcting aberrations. In other words, the occurrence of aberration in the convergent light beam can be reduced as much as possible, and the negative refractive power can be effectively used. If the upper limit of 1.3 of the condition (1) is exceeded, the positive refractive power of the surface closest to the object side of the third lens unit becomes too strong. In this case, the negative refracting power of the most image-side surface becomes too strong, and in any case, the occurrence of aberration in the convergent light beam increases. If the condition (2) is not satisfied, both cemented surfaces of the three cemented lens will have a positive refractive power, and a negative refractive power will be insufficient, making it difficult to correct spherical aberration and axial chromatic aberration. The condition (3) defines the focal length of the second lens group, and favorably corrects the aberration by the negative refractive power of this lens group. If the condition (3) is not satisfied, the negative refractive power of the second lens group is insufficient, and the spherical aberration and the axial chromatic aberration are insufficiently corrected. The third lens group has a role of correcting off-axis aberrations centering on coma with a meniscus lens component having a concave surface facing the object side to improve image plane flatness. Next, embodiments of a microscope objective lens according to the present invention will be described with reference to examples. The microscope objective lens of the present invention has a first lens group G1 as shown in FIG.
Consists of a meniscus lens having a concave surface facing the object side, three cemented lens components, and a biconvex lens.
Reference numeral 2 denotes a cemented meniscus lens component having a negative lens, a positive lens and a negative lens, and a third lens group G3 includes a cemented meniscus lens component having a convex surface facing the object side and a cemented meniscus lens component having a concave surface facing the object side. . Hereinafter, data of Examples 1 and 2 of the microscope objective according to the present invention will be shown. Example 1 f = 1.8, magnification = 100 ×, NA = 0.95, working distance = 0.77 r ₁ = −2.2936 d ₁ = 1.7700 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = −2.1326 d ₂ = 0.1416 r ₃ = − _{10.6925 d 3 = 1.1000 n 2 =} 1.61340 ν 2 = 43.84 r 4 = 7.1166 d 4 = 5.5000 n 3 = 1.61800 ν 3 = 63.39 r 5 = -7.6238 d 5 = 0.2000 r 6 = -64.2877 d 6 = 1.0000 n 4 = 1.52944 ν ₄ = 51.72 r ₇ = 10.2264 d ₇ = 6.2000 n ₅ = 1.43875 ν ₅ = 94.97 r ₈ = -9.6473 d ₈ = 0.2000 r ₉ = 57.3942 d ₉ = 1.2000 n ₆ = 1.61340 ν ₆ = 43.84 r ₁₀ = 9.2329 d ₁₀ = 5.2000 n ₇ = 1.43875 v ₇ = 94.97 r ₁₁ = -18.4308 d ₁₁ = 0.3000 r ₁₂ = 15.2753 d ₁₂ = 2.5000 n ₈ = 1.56907 v ₈ = 71.30 r ₁₃ = -147.8112 d ₁₃ = 0.2000 r ₁₄ = 13.4472 _{d 14 = 1.3000 n 9 = 1.52944} ν 9 = 51.72 r 15 = 5.5507 d 15 = 5.5000 n 10 = 1.43875 ν 10 = 94.97 r 16 = -9.4406 d 16 = 1.0001 n 11 = 1.51633 ν 11 = 64.15 r 17 = 4.6960 d ₁₇ = 1.00 _{00 r 18 = 4.5949 d 18 =} 3.2000 n 12 = 1.49700 ν 12 = 81.61 r 19 = -9.4136 d 19 = 1.8812 n 13 = 1.78650 ν 13 = 50.00 r 20 = 5.2173 d 20 = 4.5626 r 21 = -5.3868 d 21 = _{1.5744 n 14 = 1.77250 ν 14 =} 49.60 r 22 = 9.3410 d 22 = 1.7000 n 15 = 1.80518 ν 15 = 25.43 r 23 = -10.1181 R 2 = 4.696, R 3 = 4.5949, R 2 / R 3 = 1.022 n 1 = _{1.52944, N 2 = 1.43875, N} 3 = 1.51633 f 2 = -12.69, f / f 2 = -0.14 [0017] example 2 f = 1.8, magnification = 100 ×, NA = 0.95, working distance = 0.77 r ₁ = -2.4614 d ₁ = 1.7700 n ₁ = 1.88300 v ₁ = 40.78 r ₂ = -2.1687 d ₂ = 0.1416 r ₃ = -7.7870 d ₃ = 1.1000 n ₂ = 1.61340 v ₂ = 43.84 r ₄ = 7.4898 d ₄ = 5.5000 n _{3 = 1.61800 ν 3 = 63.39 r 5} = -7.4334 d 5 = 0.2000 r 6 = -101.0399 d 6 = 1.0000 n 4 = 1.52944 ν 4 = 51.72 r 7 = 10.6481 d 7 = 6.2000 n 5 = 1.43875 ν 5 = 94.97 r 8 = -10.1545 d ₈ = 0.2000 r ₉ = 82.7234 d ₉ = 1.2000 n ₆ = 1.61340 ν ₆ = 43.84 r ₁₀ = 10.8219 d ₁₀ = 5.2000 n ₇ = 1.43875 ν ₇ = 94.97 r ₁₁ = -22.0339 d ₁₁ = 0.3000 r ₁₂ = 16.1904 d ₁₂ = 2.5000 n _{8 = 1.56907 ν 8 = 71.30 r} 13 = -61.7442 d 13 = 0.2000 r 14 = 14.3636 d 14 = 1.3000 n 9 = 1.52944 ν 9 = 51.72 r 15 = 5.0644 d 15 = 5.5000 n 10 = 1.43875 ν 10 = 94.97 r 16 _{= -9.3845 d 16 = 1.0001 n 11} = 1.51633 ν 11 = 64.15 r 17 = 5.3935 d 17 = 1.0000 r 18 = 5.2205 d 18 = 3.2000 n 12 = 1.49700 ν 12 = 81.61 r 19 = 36.9783 d 19 = 2.0552 n 13 = _{1.78650 ν 13 = 50.00 r 20 =} 6.4087 d 20 = 4.8806 r 21 = -4.0037 d 21 = 1.0824 n 14 = 1.77250 ν 14 = 49.60 r 22 = 7.2400 d 22 = 1.7000 n 15 = 1.80518 ν 15 = 25.43 r 23 = - 9.6973 R ₂ = 5.3935, R ₃ = 5.2205, R ₂ / R ₃ = 1.033 N ₁ = 1.52944, N ₂ = 1.43875, N ₃ = 1.51633 f ₂ = -13.75, f / f ₂ = -0.13, r ₁ , r _2, · · · is the radius of curvature of each lens surface shown in order from the object side, d _1, d _2, ··· the spacing between the lens surfaces in order from the object side, n _1, n _2, ··· Is the refractive index of each lens shown in order from the object side, and ν ₁ , ν ₂ ,... Are the Abbe numbers of each lens shown in order from the object side. Embodiments 1 and 2 each have the lens configuration shown in FIG. 1 and are all designed at infinity, and do not form an image by themselves. For this reason, for example, an imaging lens having the following data is arranged and used on the image side of the objective lens in a configuration as shown in FIG. _{r 1 '= 68.7541 d 1'} = 7.7321 n 1 '= 1.48749 ν 1' = 70.20 r 2 '= -37.5679 d 2' = 3.4742 n 2 '= 1.80610 ν 2' = 40.95 r 3 '= -102.8477 d 3' _{= 0.6973 r 4 '= 84.3099 d} 4' = 6.0238 n 3 '= 1.83400 ν 3' = 37.16 r 5 '= -50.7100 d 5' = 3.0298 n 4 '= 1.64450 ν 4' = 40.82 r 6 '= 40.6619 said binding In the data of the image lens, r ₁ ′, r ₂ ′,.
Is the radius of curvature of each lens surface shown in order from the object side, d ₁ ′,
d ₂ ′,... are the distances between the lens surfaces in order from the object side,
n ₁ ′, n ₂ ′,... are the refractive indices of each lens with respect to the d-line in order from the object side, and ν ₁ ′, ν ₂ ′,. Note that the unit of the data length of Examples 1 and 2 and the imaging lens is mm. The distance between the first and second embodiments and the imaging lens may be any value between 50 mm and 170 mm. The aberration states of the first and second embodiments are as shown in FIGS. 3 and 4, respectively. These aberration diagrams are obtained when the imaging lens having the above data and shown in FIG. 2 is arranged. The air gap between the objective lens and the imaging lens in each embodiment is 116 mm.
It is. However, if the interval is a value between 50 mm and 170 mm, even if the value is other than 116 mm, almost the same aberration situation is obtained. The present invention has the above-described configuration,
As a result, an apochromat-class microscope objective lens having a magnification of about 100 times and an NA of about 0.95 was realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration of a microscope objective lens of the present invention. FIG. 2 is a diagram showing an example of an imaging lens used together with the microscope objective lens of the present invention. FIG. 4 is an aberration curve diagram according to the first embodiment. FIG. 4 is an aberration curve diagram according to the second embodiment of the present invention.

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Claims (1)

(57) [Claims 1] In order from the object side, at least a positive meniscus lens having a concave surface facing the object side and a plurality of cemented positive lens components are used to converge a light beam from the object. A first lens group having a positive refractive power to make a light beam, and a negative lens, a positive lens, and a negative lens having a convex surface closest to the object side and a concave surface closest to the image side having a concave shape on the image side . A second lens group including a triplet lens component, and a third lens group including a meniscus lens component having a convex surface closest to the object side and a meniscus lens component having a concave surface facing the object side, are provided with the following conditions (1) and ( A microscope objective lens that satisfies 2) and (3). _{(1) 0.7 <R 2 /} R 3 <1.3 (2) N 1> N 2, N 3> N 2 (3) f / f 2 <-0.1 proviso, R _2, R ₃ is object of each curvature of the most object-side surface of radius of curvature and the third lens group on the most image side surface of the second lens _{group, N 1, N 2, N} 3 is cemented triplet lens in the second lens group, respectively a negative lens, a positive lens, the refractive index of the negative lens on the image side of the side, f is the focal length of the entire system, f ₂ is the focal length of the second lens group.