JPH09101462A - Microscope objective - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a microscope objective of an apochromatic lens class which has about ×100 power and about 0.95 numerical aperture by composing the objective of three lens groups which meet specific requirements. SOLUTION: A 1st lens group G1 consists of a meniscus lens 3 which is concave to an object, a cemented lens element, and a biconvex lens. A 2nd lens group G 2 consists of a three-element cemented meniscus lens element of a negative lens, a positive lens, and a negative lens. The three lens groups meet requirements of 0.7<R2 /R3 <1.3, N1 >N2 , and f<f2 <-0.1. Here, R2 and R3 are the radii of curvature of the most image-side surface of the 2nd lens group G2 and the most object side surfaces of the 3rd lens group G3, N1 , N2 , and N3 the focal lengths of the refractive indexes of the object-side negative lens and positive lens, and image-side negative lens of the 2nd lens group G2, (f) the focal length of the whole system, and f2 the focal length of the 2nd lens group G2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 objective lens having a magnification of about 100 times, a numerical aperture of about 0.95 and a flat image plane.

[0002]

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 a positive refraction that converts a light beam from an object into a convergent light beam. A first lens group having a power, a second lens group having a cemented lens having a small refractive power, which is arranged in the convergent light beam, a meniscus lens component having a convex surface directed toward the object side, and a negative lens component following the meniscus lens component. Negative refractive power third with and
It consists of a lens group.

[0003]

In the conventional microscope objective lens, spherical aberration and axial chromatic aberration are not corrected to the apochromat level. This is to increase the target working distance of this conventional example, and it is inevitably difficult to correct the aberration when the working distance is increased.

An object of the present invention is that the magnification is about 100 times,
It is to provide an apochromat-class microscope objective lens having a numerical aperture of about 0.95.

The dry high NA, high magnification apochromat objective lens as described above is particularly useful for high resolution observation and measurement for semiconductors and magnetic heads.

[0006]

A microscope objective lens 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 refracting power for converting a light beam into a convergent light beam, and a negative lens, a positive lens, and a negative lens having a convex surface closest to the object side and a surface closest to the image side having a strong concave shape toward the image side. And a third lens group having a three-lens cemented lens component cemented with and a convex meniscus lens component having the strongest object side and a meniscus lens component having a concave surface facing the object side. It is characterized by satisfying (1), (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 where R ₂ , R ₃ is the radius of curvature of the most image-side surface of the second lens group, and the radius of curvature of the most object-side surface of the third lens group, and N ₁ , N ₂ , and N ₃ are the three lenses of the second lens group cemented together. Refractive indexes of the negative lens on the object side of the lens, the positive lens, and the negative lens on the image side, f is the focal length of the entire system, and f ₂ is the focal length of the second lens group.

In general, a dry plan objective lens having a flat image surface is provided with a positive meniscus lens having a concave surface closest to the object side so as not to adversely affect aberrations. Further, the plurality of cemented lens components are arranged in order to satisfactorily correct chromatic aberration. The first lens group having these lens components and having a positive refractive power has a function of converting a light flux from an object into a convergent light flux. Also, the second lens group,
The third lens group is provided with a lens having a negative refracting power in order to correct the 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-lens cemented lens corrects chromatic aberration and sets the refractive indices of these three lenses as shown in the condition (2) so that two cemented surfaces have a negative refractive power. It also corrects the curvature of spherical aberration and axial chromatic aberration. In addition, the shape of the entire three-lens cemented lens is such that the surface closest to the object side is a convex surface toward the object side and the surface closest to the image side is a strong concave surface toward the image side to minimize the occurrence of aberrations in the convergent light beam. . Further, the most object-side surface of the third lens group is made to have a strong convex surface, and the negative refracting power of the most image-side surface of the second lens group is effectively exerted.

The condition (1) defines the relationship between the radii of curvature of the most image-side surface of the second lens group and the most object-side surface of the third lens group.

The closer the radii of curvature of the two surfaces are to each other, the more effective the negative refracting power due to the action of the air lens formed by these two surfaces becomes for aberration correction. In other words, it is possible to reduce the occurrence of aberrations in the convergent light flux as much as possible, and to effectively use the negative refracting power.

If the upper limit of 1.3 of this condition (1) is exceeded, the positive refracting power of the surface of the third lens group closest to the object side will become too strong, and if the lower limit of 0.7 is exceeded, the second lens group will become too strong. The negative refracting power of the surface closest to the image side becomes too strong, and the occurrence of aberrations in the convergent light beam increases in both cases.

If the condition (2) is not satisfied, both cemented surfaces of the triplet cemented lens will have a positive refractive power, and the 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 is for correcting aberrations favorably by the negative refracting power of this lens group. If this condition (3) is not satisfied, the negative refracting power of the second lens group will be insufficient, and the curvature of spherical aberration and axial chromatic aberration will be undercorrected.

The third lens group has a role of correcting off-axis aberrations centering on coma aberration by a meniscus lens component having a concave surface facing the object side to improve image plane flatness.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the microscope objective lens of the present invention will be described based on Examples. The microscope objective lens of the present invention is as shown in FIG.
Is a meniscus lens having a concave surface facing the object side, three cemented lens components, and a biconvex lens.
The second 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. .

The data of Examples 1 and 2 of the microscope objective lens of the present invention are shown below. 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 v 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 v ₄ = 51.72 r ₇ = 10.2264 d ₇ = 6.2000 n ₅ = 1.43875 v ₅ = 94.97 r ₈ = -9.6473 d ₈ = 0.2000 r ₉ = 57.3942 d ₉ = 1.2000 n ₆ = 1.61340 v ₆ = 43.84 r ₁₀ = 9.2329 _{d 10 = 5.2000 n 7 = 1.43875} ν 7 = 94.97 r 11 = -18.4308 d 11 = 0.3000 r 12 = 15.2753 d 12 = 2.5000 n 8 = 1.56907 ν 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

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 ν ₁ = 40.78 r ₂ = -2.1687 d ₂ = 0.1416 r _{3 = -7.7870 d 3 = 1.1000 n} 2 = 1.61340 ν 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 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 where r ₁ , r ₂ , ... Are the radius of curvature of each lens surface shown in order from the object side. , D ₁ , d ₂ , ... Are the intervals between the lens surfaces in order from the object side, n ₁ , n ₂ , ... Are the refractive indices of the lenses shown in order from the object side, ν ₁ , ν ₂ , ... is the Abbe number of each lens shown in order from the object side.

Each of the first and second embodiments has the lens configuration shown in FIG. 1 and has an infinity design, and does not form an image by itself. Therefore, for example, in the configuration as shown in FIG. 2, an imaging lens having the following data is arranged on the image side of the objective lens and used. 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 image lens data, r ₁ ′, r ₂ ′, ...
Is the radius of curvature of each lens surface shown in order from the object side, d ₁ ',
d ₂ ', ... is the distance between the lens surfaces in order from the object side,
n ₁ ′, n ₂ ′, ... Are the refractive indices of the lenses for the d-line in order from the object side, and ν ₁ ′, ν ₂ ′, ... Are the Abbe numbers of the lenses in order from the object side. The unit of the length of the data 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 aberrations of Examples 1 and 2 are as shown in FIGS. 3 and 4, respectively. These aberration charts are obtained when the image forming lens shown in FIG. 2 having the above data is arranged, and the air gap between the objective lens and the image forming lens of each example is 116 mm.
It is. However, if the distance is a value between 50 mm and 170 mm, the aberration situation is almost the same even if it is a value other than 116 mm.

[0020]

The present invention has the above-mentioned constitution,
As a result, it was possible to realize an apochromat-class microscope objective lens with a magnification of about 100 and an NA of about 0.95.

[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. 3 is an aberration curve diagram of Example 1 of the present invention.

FIG. 4 is an aberration curve diagram of Example 2 of the present invention.

Claims (1)

[Claims] 1. A first refracting power having 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 and having a positive refracting power for converting a light beam from an object into a convergent light beam. A first lens group, and a three-lens cemented lens component having a negative lens, a positive lens, and a negative lens cemented to each other, having a convex surface closest to the object side and a surface closest to the image side having a strong concave shape toward the image side. The following conditions (1), (2), and (3) are provided, including two lens groups and a third lens group having a convex meniscus lens component with the strongest object side and a meniscus lens component with a concave surface facing the object side. A satisfying microscope objective lens. _{(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 The radius of curvature of the most image-side surface of the second lens group and the radius of curvature of the most object-side surface of the third lens group, N ₁ , N ₂ , and N ₃ are respectively objects of the three-lens cemented lens of the second lens group. Of the negative lens, the positive lens, and the negative lens on the image side, f is the focal length of the entire system, and f ₂ is the focal length of the second lens group.