JP2000206414A - Long working distance objective lens for microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens for a microscope, whose magnification is high, NA(numerical aperture) is high, which is provided with a long working distance and whose various aberration is satisfactorily corrected over a wide visual field. SOLUTION: This objective lens is provided with a 1st positive lens group G1, consisting of a first, second and 3rd positive lens components L1, L2 and L3 whose surface having larger refractive power faces an image side, a 2nd positive lens group G2 which includes a doublet component L5 consisting of a positive lens component L23, a negative lens component L24 and a positive lens component L25 and 3rd negative lens group G3 in turn from an object side. Then, when the refractive index for the d-line (λ=587.56 nm) of the component L1 is defined as (n11), the condition of n11>1.78 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope objective having high magnification and a long working distance.

[0002]

2. Description of the Related Art When observing an integrated circuit or the like with a microscope, it is necessary to have a high magnification and a high resolution in accordance with the high integration of the integrated circuit and a sufficiently long working distance to ensure good operability. is necessary. A microscope objective lens having a long working distance requires a larger focal length of the front group as compared with a normal microscope objective lens, so that the amount of spherical aberration and chromatic aberration generated in the front group increases. In particular, the numerical aperture (hereinafter, referred to as
The larger the “NA”, the longer the working distance, the greater the amount of aberration, so that it becomes more difficult to correct aberration.

As a microscope objective lens having a high magnification and a long working distance, Japanese Patent Publication No. 3-58493 and Japanese Patent Publication No. 4-26
A lens disclosed in Japanese Patent No. 447 or Japanese Patent Application Laid-Open No. 4-40409 has been proposed.

[0004]

[Problems to be solved by the invention]
No. 8493 discloses an objective lens having an NA of 0.1.
Although it is as large as 9, the working distance is only about 1 mm, which is insufficient. The objective lens disclosed in Japanese Patent Publication No. 4-26447 also has a large NA of 0.8, but the working distance of about 2 mm is not sufficient. Further, Japanese Unexamined Patent Application Publication No.
The objective lens disclosed in Japanese Patent No. 0409 is large in both NA and working distance, but is problematic because the number of lenses constituting the objective lens is too large.

The present invention has been made in view of such circumstances, and has a high magnification and a high NA (specifically, an NA of 0.7
It is an object of the present invention to provide a microscope objective lens having a long working distance and having various aberrations well corrected over a wide field of view.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its contents will be described below with reference to the drawings shown in the embodiments.

[0007] The long working distance microscope objective of the present invention comprises:
In order from the object side, a first lens component L1 having a positive refractive power whose surface has a larger refractive power toward the image side, a second lens component L2 having a positive refractive power having a surface having a larger refractive power facing the image side, and an image. A first lens unit G1 having a positive refractive power, comprising a third lens component L3 having a positive refractive power with a surface having a higher refractive power directed to the side;
A second lens group G2 having a positive refractive power including a cemented lens component L5 including a positive lens component L23, a negative lens component L24, and a positive lens component L25, and a third lens group G3 having a negative refractive power.

With this configuration, a long working distance is secured by weakening the refractive power of the first lens group G1. The second lens group G2 converts divergent light from the first lens group G1 into convergent light, and corrects spherical aberration and axial chromatic aberration by bonding a positive lens component and a negative lens component. . Further, since the third lens group G3 has a strong negative refractive power, the Petzval sum is reduced and a high magnification is achieved. The light beam emitted from the object is gently bent by the first, second, and third lens components L1 to L3, which are meniscus single lenses having a positive refractive power. In this case, the image side is provided with a surface having a larger refracting power so that the angle of deviation of the marginal ray is made as small as possible.

It is preferable that the present invention satisfies the following conditional expressions (1) and (1): n11> 1.78. Here, n11 represents the refractive index of the first lens component L1 at the d-line (λ = 587.56 nm).

Conditional expression (1) defines an appropriate range of the refractive index of the first lens component L1. In general, in a lens having a positive and equal refractive power, a larger refractive index can reduce the Petzval sum and increase the radius of curvature. Therefore, generation of spherical aberration can be suppressed, which is advantageous in correcting aberration. When the value goes below the lower limit of conditional expression (1), not only the flatness of the image becomes poor, but also it becomes difficult to correct spherical aberration. More preferably, the refractive index n11 of the first lens component L1 is desirably greater than 1.8 in order to favorably correct the curvature of field up to a field number of 25.

In the present invention, it is desirable that the following conditional expressions (2) and (2) (ν12 + ν13) / 2> 70 are satisfied. Here, ν12 or ν13
Represents the Abbe number of the second lens component L2 or the third lens component L3 in the first lens group G1 at the d-line (λ = 587.6 nm).

Conditional expression (2) defines an appropriate range of the average Abbe number between the second lens component L2 and the third lens component L3, each of which is composed of a single lens having a positive refractive power and the surface having a higher refractive power on the image side. Stipulates. When the value goes below the lower limit of conditional expression (2), the chromatic aberration generated in the first lens group G1 becomes too large, so that it becomes difficult to correct the aberration. More preferably,
In order to satisfactorily correct chromatic aberration, it is desirable that the average Abbe number of the second lens component L2 and the third lens component L3 is larger than 80.

In the present invention, the second lens group G2 is
A cemented lens component L having a cemented surface with the convex surface facing the object side
4 and a cemented lens component L6 having a cemented surface with a concave surface facing the object side. More preferably,
It is desirable that the cemented lens component L6 of the second lens group G2 having a cemented surface with the concave surface facing the object side has a weak negative refractive power.

The fourth, fifth, and sixth lens components L4, L5,
L6 corrects spherical aberration and axial chromatic aberration by converting divergent light from the third lens component L3 into convergent light and bonding a positive lens and a negative lens having a difference in refractive index and dispersion to each other. In particular, the fourth lens component L4 has a cemented surface with the convex surface facing the object side, and the fifth lens component L5 is a triple cemented lens component of a positive lens component L23, a negative lens component L24, and a positive lens component L25. And the sixth lens component L
No. 6 can more efficiently correct spherical aberration and axial chromatic aberration by providing a cemented surface with a concave surface facing the object side.

In the present invention, the third lens group G3 is
It is desirable that the cemented lens L7 be composed of a negative lens component L31, a positive lens component L32, and a negative lens component L33. The Petzval sum is reduced by giving the seventh lens component L7 a strong negative refractive power, and the negative lens component L31,
By using a cemented lens composed of a positive lens component L32 and a negative lens component L33, axial chromatic aberration and lateral chromatic aberration can be corrected in a well-balanced manner.

In the present invention, it is desirable that the following conditions (3) and (3) ν32 <38 are satisfied. Here, ν32 is the d-line (λ = 58) of the positive lens component L32 of the third lens group G3.
7.56 nm).

Conditional expression (3) defines an appropriate range of the Abbe number of the positive lens component L32 of the seventh lens component L3. When the value exceeds the upper limit of conditional expression (3), the radius of curvature of the cemented surface becomes too small to correct lateral chromatic aberration, and coma aberration on the short wavelength side deteriorates. More preferably, in order to correct the axial chromatic aberration and the chromatic aberration of magnification in a well-balanced manner, it is preferable to use the seventh method.
The Abbe number of the positive lens component L32 of the lens component L7 is 31
Desirably smaller.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A long working distance microscope objective according to a numerical embodiment of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a view showing a lens configuration of a long working distance microscope lens according to a first embodiment.
In order from the object, the first, second, and third lens components L1, L2, and L3, each of which is a meniscus-shaped single lens having a positive refractive power with a surface having a higher refractive power directed toward the image side, and a negative lens component L21 and a positive lens. A fourth lens component L4 having a cemented surface with a convex surface facing the object side, the fourth lens component L4 being laminated with the lens component L22.
And a fifth lens component L5 in which three lenses of a positive lens component L23, a negative lens component L24, and a positive lens component L25 are stuck.
And a sixth lens having a cemented surface formed by bonding the positive lens component L26 and the negative lens component L27 and having a concave surface facing the object side.
It is composed of a lens component L6, and a seventh lens component L7 of a cemented lens in which three negative lens components L31, a positive lens component L32, and a negative lens component L33 are attached.

Table 1 below shows data values of the long working distance microscope objective according to the first embodiment. In Table 1,
β is the magnification, NA is the numerical aperture, F is the total focal length of the entire system (unit: mm), the surface number is the order of the lens surfaces counted from the object side, r is the radius of curvature of each lens surface (unit: mm), d is the distance between the lens surfaces (unit: mm), and nd is the d line (λ = 587.
The refractive index at 6 nm) and νd represent Abbe numbers at the d-line, respectively. D0 is the distance from the object plane to the first lens surface of the first lens group G1. Note that the same reference numerals as those of the present embodiment are used in the specification values of all the embodiments below.

(First Embodiment)

[Table 1] β = -100.0 NA = 0.8 d0 = 5.246 F = 2.000 Face number rd nd νd 1 -8.644 3.0 1.80400 46.60 2 -6.735 0.1 1.00000 3 -19.166 3.0 1.49782 82.52 4 -10.625 0.15 1.00000 5 -78.756 3.2 1.49782 82.52 6 -18.337 0.2 1.00000 7 363.421 1.5 1.61266 44.41 8 18.300 6.7 1.43385 95.25 9 -20.978 0.2 1.00000 10 24.276 6.7 1.49782 82.52 11 -18.300 1.5 1.61266 44.41 12 18.000 6.2 1.43385 95.25 13 -18.666 0.2 1.00000 17.295 4.7 1.43385 95.52 15 -16.622 1.0 1.74950 41.42 16 50.824 15.841 1.00000 17 -12.914 1.0 1.73350 51.09 18 4.261 2.0 1.73046 25.43 19 -4.153 1.0 1.67163 38.80 20 6.776 (Values for conditional expressions) (1) n11 = 1.80400 (2) (Ν12 + ν13) /2=82.52 (3) ν32 = 25.43

FIG. 2 is a diagram showing various aberrations in the first embodiment. In each aberration diagram, d is a d-line (λ = 587.
56 nm), C is a C line (λ = 656.28 nm), F is an F line (λ = 486.13 nm) line, g is a g line (λ = 43 nm).
(5.84 nm). In the figures showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. In the following embodiments, the same reference numerals are used as in the present embodiment. As is clear from the aberration diagrams, it is understood that various aberrations are sufficiently corrected.

(Second Embodiment) FIG. 3 is a diagram showing a lens configuration of a long working distance microscope lens according to a second embodiment. In order from the object, the first, second, and third lens components L1, L2, and L3, each of which is a meniscus-shaped single lens having a positive refractive power with a surface having a higher refractive power directed toward the image side, and a negative lens component L21 and a positive lens. Fourth lens component L4 having a cemented surface with the convex surface facing the object side, which is made by laminating lens component L22, and three lenses of positive lens component L23, negative lens component L24, and positive lens component L25 are laminated. A fifth lens component L5 of the lens, a sixth lens component L6 formed by bonding a positive lens component L26 and a negative lens component L27 and having a cemented surface with a concave surface facing the object side, and a negative lens component L3
The seventh lens component L7 of the cemented lens obtained by laminating three lenses 1, a positive lens component L32, and a negative lens component L33.

Table 2 below shows the specification values of the long working distance microscope objective according to the present embodiment.

[0025]

[Table 2] β = -100.0 NA = 0.8 d0 = 5.208 F = 2.000 Face number rd nd νd 1 -8.831 3.0 1.80400 46.60 2 -6.711 0.1 1.00000 3 -18.541 3.0 1.49782 82.52 4 -10.602 0.15 1.00000 5 -58.182 3.2 1.49782 82.52 6 -18.558 0.2 1.00000 7 162.212 1.5 1.61266 44.41 8 18.300 6.7 1.43385 95.25 9 -20.959 0.2 1.00000 10 23.138 6.7 1.49782 82.52 11 -18.300 1.5 1.61266 44.41 12 18.000 6.2 1.43385 95.25 13 -18.768 0.2 1.00000 14 17.414 4.7 1.43385 95.25 15 -16.417 1.0 1.74950 41.42 16 41.355 16.441 1.00000 17 -8.101 1.0 1.56384 60.69 18 5.030 2.0 1.61750 30.83 19 -3.521 1.0 1.56384 60.69 20 6.257 (Values for conditional expressions) (1) n11 = 1.80400 ( 2) (ν12 + ν13) /2=82.52 (3) ν32 = 30.83

FIG. 4 is a diagram showing various aberrations of this embodiment. As is apparent from the figure, various aberrations are satisfactorily corrected.

The microscope objective lens in each of the above embodiments is a lens of an infinity correction type, and is used in combination with, for example, an imaging lens whose specification values are listed in Table 3. FIG.
FIG. 3 is a diagram illustrating a lens configuration of the imaging lens.

[0028]

[Table 3] Surface number r d nd νd 1 75.040 5.1 1.62280 57.03 2 -75.040 2.0 1.74950 35.19 3 1600.580 7.5 1.00000 4 50.260 5.1 1.66755 41.96 5 -84.540 1.8 1.61266 44.41

The distance between the microscope objective lens and the imaging lens according to each of the above embodiments may be any position between 50 mm and 180 mm. The various aberrations shown in FIG. 2 or FIG. 4 are obtained when the interval is set to 150 mm. The interval is 5
If the value is between 0 mm and 180 mm, a value other than 150 mm shows almost the same aberration situation as in FIG. 2 or FIG.

[0030]

As described above, according to the present invention,
It is possible to provide a long working distance microscope objective lens having a magnification of about 100 times, a large NA of about 0.8, and excellent imaging performance over a wide field of view.

[Brief description of the drawings]

FIG. 1 is a diagram showing a lens configuration of a long working distance microscope objective according to a first embodiment of the present invention.

FIG. 2 is a diagram showing various aberrations of the first embodiment.

FIG. 3 is a diagram illustrating a lens configuration of a long working distance microscope objective according to the first example of the present invention.

FIG. 4 is a diagram illustrating various aberrations of the second example.

FIG. 5 is a diagram showing a configuration of an imaging lens used with a long working distance microscope objective according to each embodiment.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group

Claims (4)

[Claims] 1. A first lens component having a positive refractive power having a surface having a larger refractive power directed toward the image side and a second lens component having a positive refractive power having a surface having a larger refractive power directed toward the image side. And a first lens unit having a positive refractive power composed of a third lens component having a positive refractive power with the surface having a larger refractive power directed to the image side; and a junction composed of a positive lens component, a negative lens component, and a positive lens component. A second lens group having a positive refractive power including a lens component; and a third lens group G3 having a negative refractive power. The refractive index of the first lens component at d-line (λ = 587.56 nm) is represented by n11. (1) A long working distance microscope objective lens characterized by satisfying the following condition: n11> 1.78. 2. The long working distance microscope objective lens according to claim 1, wherein the third lens group includes a cemented lens including a negative lens component, a positive lens component, and a negative lens component. 3. The d-line (λ = 587.56n) of the second lens component or the third lens component in the first lens group G1.
The long working distance microscope objective lens according to claim 1 or 2, wherein, when the Abbe number in m) is defined as ν12 or ν13, respectively, the following condition is satisfied: (ν12 + ν13) / 2> 70. 4. The second lens group includes a cemented lens component having a cemented surface with a convex surface facing the object side, and a cemented lens component having a cemented surface with a concave surface facing the object side. A long working distance microscope objective according to any one of claims 1 to 3.