JPH08313814A - Objective lens for microscope - Google Patents

Abstract

PURPOSE: To provide an objective lens for an achromat-class microscope of low magnification compensating various aberrations, correcting off-axial chromatic aberration solely by the objective lens and having an extremly flat image plane over a wide visual field in spite of a comparatively short focal distance and the simple lens constitution. CONSTITUTION: This lens is composed of a first lens group G1 having a positive lens, a second lens group G2 composed of a single negative lens and a third lens group G3 having a joined lens of a positive refractive power and, by representing the focal distance of a whole system by (f), the focal distance of the first lens group by f1 , the focal distance of the second lens group by f2 , the Abbe number of the positive lens of the first lens group by ν1 and the Abbe number of the negative lens of the second lens group by ν2 , the respective conditions: (ν2 -ν1 )>10, 0.05<=|f2 /f|<=0.12, 0.28<=|f2 /f1 |<=0.40 are satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens for a microscope, and more particularly to an objective lens for a low-magnification microscope of an achromat class having an extremely flat image plane over a wide field of view.

[0002]

2. Description of the Related Art As a technique close to the objective lens for a microscope of the present invention described later, there is an objective lens disclosed in JP-A-58-201212. This has a magnification of 2.5 and a numerical aperture (NA)
Is 0.07, and as the lens configuration, a positive meniscus lens having a convex surface or a first lens group of biconvex lenses, a second lens group of negative lenses, and a positive lens and a negative lens are attached in order from the object side. It is composed of a third lens group and a fourth lens group of cemented cemented lenses, and a fifth lens group of a positive cemented lens in which a negative lens and a positive lens are cemented together.

Further, there is an objective lens of Japanese Patent Publication No. 54-10456. This has a magnification of 5 times and an NA of 0.1, and the lens configuration is a positive first lens group, a second negative lens group, and a positive cemented lens including a positive lens and a negative lens. The third lens group and the fourth lens group of the positive lens are composed of five lens groups in four groups.

There is also a Japanese Patent Publication No. 53-7814. This has a magnification of 2 times and an NA of 0.085. As for the lens configuration, the first lens group consisting of a single lens or a cemented lens and a considerable distance from the first lens group are arranged from the object side. It is composed of a second lens group of the negative lens arranged and a third lens group which is arranged at a considerable distance from the second lens group and which is composed of a relatively thick positive meniscus lens and a cemented lens.

Further, there is an objective lens of Japanese Patent Publication No. 1-50885. This is because the magnification is 2 times and the NA is 0.055, and from the object side, the first lens group of the biconvex lens, the second lens group of the biconcave lens, the third lens group of the positive meniscus lens, and the second lens group of the biconvex lens. It consists of 4 lens groups.

Further, there is an objective lens of Japanese Examined Patent Publication No. 57-52568. This has a magnification of 1 to 2 and an NA of 0.03.
.About.0.08, and as a lens configuration, a first lens group having at least one positive lens in order from the object side,
It comprises a second lens group including a negative meniscus lens having a convex surface directed toward the object side, and a third lens group including a positive meniscus lens having a convex surface directed toward the image side and a positive lens.

Finally, there is the objective lens of US Pat. No. 3,176,583. This has a magnification of 2 times, and the lens configuration is, in order from the object side, a first lens group of a biconvex lens, a second lens group formed by cementing a positive meniscus lens and a biconcave lens, a negative meniscus lens and a positive lens. It is composed of a third lens group formed by cementing.

[0008]

Generally, in an objective lens for a microscope, the distance from the specimen to the revolver (with the body) to which the objective lens is attached is adjusted as shown in FIG. The focal length) is fixed. Since the focal length of the low-magnification objective lens is longer than the focal length of the objective lens, a telephoto type lens structure in which a convex lens and a concave lens are arranged on the object side of the objective lens is generally used. In this case, as shown in FIG. 2, the convex lens of the first lens group G1 must have a relatively strong power. When the power of the convex lens of the first lens group G1 is weak, the rear focal position of the objective lens is largely displaced to the image side of the objective lens. On the other hand, the rear focal position of the objective lens having a high magnification and a short focal length is arranged in the objective lens.
In this way, when the rear focal position of the low-magnification objective lens and the high-magnification objective lens largely deviates, the off-axis rays incident on the lens system following the objective lens may have low and high magnifications. The difference greatly changes, and it becomes difficult to correct the aberration of the lens system that follows the objective lens. Therefore, in a low-magnification objective lens, as shown in FIG. 2, the power of the convex lens of the first lens group G1 is made relatively strong and the rear focal position (pupil position) of the objective lens is arranged in the objective lens. There is a need to.

Unlike a camera lens, an objective lens for a microscope uses Koehler illumination that uniformly illuminates an object. Therefore, the principal rays incident on the objective lens must be parallel. Further, the lower the magnification of the objective lens, the wider the range of the object to be observed, so that the chief ray height on the most off-axis becomes high. In addition, as described above, since the convex lens of the first lens group has a relatively strong convex power, the off-axis chief ray must be largely bent in the front group, and chromatic aberration of pupil and chromatic aberration of magnification must be corrected. It is difficult. When pupil chromatic aberration occurs, the ray height for each wavelength after exiting the objective lens is different, which makes it difficult to correct off-axis chromatic aberration of the lens that follows, and vignetting of rays differs depending on the wavelength. Is colored. Therefore, in a low-magnification objective lens, how to correct pupil chromatic aberration and lateral chromatic aberration becomes important.

The above-mentioned objective lenses of JP-A-58-192012, JP-B-54-10456 and JP-B-53-7814 have no problem in axial performance. However, the positive lens of the first lens group and the negative lens of the second lens group have not corrected the chromatic aberration of magnification and the coma aberration due to each wavelength. This is because, in particular, the off-axis chromatic aberration is large due to the large dispersion of the glass material despite the strong power of the negative lens of the second lens group. Therefore, the off-axis performance of the objective lens alone is not very good.

The objective lens of Japanese Examined Patent Publication No. 1-50885 has no problem in on-axis performance and off-axis performance, but the total length of the objective lens, that is, the focal length is the same as the objective lens of the present invention described later and other objective lenses. On the other hand, it is twice as large.

The objective lens of Japanese Examined Patent Publication No. 57-52568 has no problem in terms of performance, but in order to suppress the coma aberration generated in the negative lens of the second lens group, a cemented lens or two concave surfaces is provided in the second lens group. It uses a lens type that faces each other. Therefore, the lens configuration is complicated.

The objective lens of US Pat. No. 3,176,583 has particularly poor off-axis performance. Since the power of the first lens group is strong and the off-axis chief ray is largely bent in the first lens group, the chromatic aberration of magnification, the coma aberration, the coma aberration due to each wavelength, and the chromatic aberration of the pupil generated in the first lens group are corrected. It has not been.

The conventional objective lens has a large second lens group G2 in order to correct the off-axis chromatic aberration generated by the convex lens in the first lens group G1 and the field curvature generated in the entire system. Although a negative lens having a refractive power is arranged, the number of lenses is increased to complicate the configuration in order to prevent excessive aberration from being generated by this negative lens. In the case of an objective lens having a simple structure, the chromatic aberration of magnification generated by the objective lens is canceled by generating chromatic aberration of the opposite magnification by the eyepiece lens.

The present invention has been made in view of the above-mentioned conventional technique, and an object thereof is to correct various aberrations despite a relatively short parfocal distance and a simple lens configuration. Corrects off-axis chromatic aberration with the objective lens alone,
An object of the present invention is to provide an objective lens for an achromatic class low magnification microscope, which has an extremely flat image plane over a wide field of view.

[0016]

An objective lens for a microscope according to the present invention which achieves the above object comprises, in order from the object side, a first lens group having a positive lens, a second lens group consisting of a single negative lens, and a positive lens group. It is characterized in that it is composed of a third lens group having a cemented lens having a refractive power and satisfies the following respective conditions. (1) (ν ₂ −ν ₁ )> 10 (2) 0.05 ≦ | f ₂ /f|≦0.12 (3) 0.28 ≦ | f ₂ / f ₁ | ≦ 0.40 where f Is the focal length of the entire system, f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, ν ₁ is the Abbe number of the positive lens of the first lens group, and ν ₂ is the second lens group Is the Abbe number of the negative lens of.

In this case, the focal length of the third lens group is f ₃
Then, (4) it is desirable to satisfy the condition of 0.56 ≦ | f ₁ / f ₃ | ≦ 0.90.

Separately from this, the third lens group includes a cemented lens composed of a positive lens and a negative lens, the Abbe number ν ₃ of the negative lens of this cemented lens, and the Abbe ν of the positive lens.
_{When it is 4} , it is desirable that the condition of (5) 20 <| ν ₃ −ν ₄ | <50 is satisfied.

[0019]

The reason why the above structure is adopted and the function of the present invention will be described below. Generally, a telephoto type objective lens for a low magnification microscope has a power arrangement as shown in FIG.
A convex-concave type first lens group G1 and a second lens group G2 that have a function of bringing the pupil position closer to the objective lens side and a function of increasing the focal length, and an image is formed at a predetermined position to set the magnification to a desired value. And a third lens group G3 that

This is similar to the triplet and tesser type lens configuration of the camera lens, but in the case of the camera lens, as shown in FIG. 3, since the lens diaphragm position is located in the lens, the axis passing through the central concave lens is used. The outside chief ray has a low ray height, and the off-axis chief ray passing through the image-side and the object-side convex lens sandwiching the concave lens passes through the heights opposite to the optical axis. Therefore, in order to correct the chromatic aberration of magnification, if the dispersion of the convex lenses on the object side and the image side is about the same,
Even if the concave lenses were dispersed, there was no problem. On the other hand, the chromatic aberration on the axis is corrected by using a glass material having a large dispersion and a strong dispersion of the power of the concave lens.

However, in the low magnification microscope objective lens, if the pupil position (corresponding to the diaphragm position of the camera) is designed to be located in the center of the objective lens, as described in the conventional example, the off-axis main light incident on the objective lens is used. Since the Koehler illumination in which the light rays are parallel is used, the off-axis chief ray must be largely bent in the first lens group, and the power of the convex lens of the first lens group becomes strong. Therefore, it becomes difficult to satisfactorily correct aberrations with a configuration such as a camera lens.

In order to solve the above problem, the objective lens for the low magnification microscope can correct various aberrations by setting the pupil position near the third lens group G3 as shown in FIG. According to this configuration, since the off-axis chief ray that passes through the first lens group G1 and the second lens group G2 is far from the optical axis, the chromatic aberration of magnification and the chromatic aberration of pupil are the first and second lens groups G1 and G1. Although it occurs in G2, off-axis chromatic aberration hardly occurs in the third lens group G3 because the off-axis chief ray is close to the optical axis.

In the conventional objective lens, the first lens group G1
Since a glass material having a large Abbe number, that is, a small dispersion is used for the second lens group G2, and a glass material having a small Abbe number, that is, a large dispersion is used for the second lens group G2, the second lens group G2 is cemented to correct the above aberrations. A method of correcting the aberration by increasing the number of lenses has been used.

In the present invention, since the second lens group G2 is composed of a single concave lens having a strong negative power, the dispersion of the convex lenses in the first lens group G1 is increased (the Abbe number is decreased), and the second lens group G2 is increased. Off-axis aberrations are corrected by a method reverse to the conventional method, which reduces the dispersion of the concave lens that is the lens group G2 (increases the Abbe number).

Since the second lens group G2 has a considerably large power as compared with other lens groups, it is possible to use a glass material having a small dispersion of off-axis aberrations and on-axis aberrations generated in the second lens group G2. Can be suppressed. Further, it is no longer necessary to correct the axial and off-axis chromatic aberrations that have conventionally occurred in the second lens group G2 by the lens groups after the second lens group G2, and the configuration can be simplified as in the present invention. .

Further, in the present invention, the chromatic aberration is corrected substantially by the first lens group G1 and the second lens group G2 both on-axis and off-axis, so that the third lens group G3 independently produces on-axis chromatic aberration. It needs to be corrected and uses cemented lenses.

Next, each of the above conditional expressions will be described. Conditional expression (1) is a condition for correcting chromatic aberration of magnification and chromatic aberration of pupil, and if the lower limit of 10 is exceeded, large off-axis chromatic aberration occurs, Aberration correction cannot be performed with a simple lens configuration as in the present invention.

Conditional expression (2) is a condition that defines the power range of the second lens group G2 at the focal length of the entire system, and when the lower limit of 0.05 is exceeded, the refraction of the second lens group G2 is The force becomes too strong, and it becomes impossible to correct off-axis aberrations generated in the second lens group G2, particularly chromatic aberration of magnification and coma. When the upper limit of 0.12 is exceeded, the refracting power of the second lens group G2 becomes weak, and chromatic aberration of magnification and pupil aberration that occur in the first lens group G1 and axial aberration and total aberration that occur in the third lens group G3. The field curvature of the system cannot be corrected by the simple lens structure as in the present invention.

Conditional expression (3) is a condition of the power ratio of the first lens group G1 and the second lens group G2 for satisfactorily correcting the off-axis aberration. If the lower limit of 0.28 is exceeded, the second expression is satisfied. The chromatic aberration of magnification and the coma aberration at each wavelength generated in the lens group G2 cannot be corrected by one negative lens. If the upper limit of 0.40 is exceeded, the chromatic aberration of magnification and the chromatic aberration of the pupil generated in the first lens group G1 having a positive refractive power cannot be corrected by the configuration of the present invention.

Conditional expressions (4) and (5) are conditions for further satisfactorily correcting various aberrations. Conditional expression (4) defines the ratio between the focal length of the first lens group G1 and the focal length of the third lens group G3. When the upper limit value 0.90 is exceeded, the power of the third lens group G3 is increased. When the lower limit of 0.56 is exceeded, the first
The power of the lens group G1 becomes large, it becomes impossible to correct pupil aberration and chromatic aberration of magnification, and the number of lenses must be increased.

Conditional expression (5) is a conditional expression capable of correcting axial chromatic aberration generated in the third lens group G3. Lower limit 2
When it is smaller than 0, the axial chromatic aberration is insufficiently corrected, and when it is larger than the upper limit value 50, the correction is excessive.

[0032]

EXAMPLES Examples 1 to 3 of the microscope objective lens of the present invention will be described below. The lens data will be described later,
Sections showing the lens configurations of Examples 1 to 3 are shown in FIGS. 4 to 6, respectively.

In the first embodiment, as shown in FIG. 4, the first lens group G1 is composed of one biconvex positive lens, the second lens group G2 is composed of one biconcave negative lens, and The third lens group G3 is composed of a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens.

In the second embodiment, as shown in FIG. 5, the first lens group G1 consists of one biconvex positive lens, and the second lens group G2 consists of one biconcave negative lens. The third lens group G3 includes a positive meniscus lens having a convex surface directed toward the image side, a negative meniscus lens having a convex surface directed toward the object side, and a cemented lens having a biconvex positive lens.

In the third embodiment, as shown in FIG. 6, the first lens group G1 is composed of one biconvex positive lens, the second lens group G2 is composed of one biconcave negative lens, and The third lens group G3 includes a cemented lens of a biconcave negative lens and a biconvex positive lens, and a biconvex positive lens.

The lens data of each embodiment will be shown below. In addition to the above, the symbols are β, the magnification, NA is the numerical aperture, f is the combined focal length of the entire system, and D is the first lens surface of the entire system. To the final lens surface, WD is the working distance. Also, r
₁ , r ₂ ... are the radii of curvature of the respective lens surfaces shown in order from the object side, d ₁ , d ₂ ... are the intervals between the lens surfaces shown in order from the object side, and n _d1 , n _d2 ... are shown in order from the object side. The d-line refractive index of each lens shown, ν _d1 , ν _d2 ... Is the Abbe number of each lens shown in order from the object side.

Example 1 β = −2 ×, NA = 0.05, f = 90, D = 43.79, WD = 5.1 r ₁ = 17.2961 d ₁ = 2.4207 n _d1 = 1.71736 ν _d1 = 29.51 r ₂ = -143.3176 d ₂ = 12.7148 r ₃ = -23.8077 d ₃ = 1.2402 n _d2 = 1.62230 ν _d2 = 53.20 r ₄ = 6.3955 d ₄ = 23.5856 r ₅ = 75.9065 d ₅ = 0.8000 n _d3 = 1.74400 ν _d3 = 44.79 r ₆ = 18.4550 d ₆ = 3.0287 n _d4 = 1.49700 ν _d4 = 81.61 r ₇ = -14.3907 (1) (ν ₂ −ν ₁ ) = 23.69 (2) ｜ f ₂ / f ｜ ＝ 0.0886 (3) ｜ f ₂ / f ₁ ｜ = 0.3683 ( _{4) | f 1 / f 3} | = 0.6735 (5) | ν 3 -ν 4 | = 36.82
.

Example 2 β = −2 ×, NA = 0.055, f = 90, D = 41.97, WD = 6.0 r ₁ = 18.0432 d ₁ = 3.0000 n _d1 = 1.59551 ν _d1 = 39.21 r ₂ = −48.9969 d ₂ = 14.4614 r ₃ = -20.8625 d ₃ = 1.0000 n _d2 = 1.67790 ν _d2 = 55.33 r ₄ = 5.8434 d ₄ = 17.8086 r ₅ = -24.4349 d ₅ = 2.0000 n _d3 = 1.51633 ν _d3 = 64.15 r ₆ = -11.5342 d _{6 = 0.2000 r 7 = 126.7406 d} 7 = 1.0000 n d4 = 1.71736 ν d4 = 29.51 r 8 = 23.9531 d 8 = 2.5000 n d5 = 1.48749 ν d5 = 70.20 r 9 = -27.4770 (1) (ν 2 -ν 1) _{= 16.12 (2) | f 2} / f | = 0.0737 (3) | f 2 / f 1 | = 0.2945 (4) | f 1 / f 3 | = 0.861 (5) | ν 3 -ν 4 | = 40.69
.

Example 3 β = -2 ×, NA = 0.05, f = 90, D = 43.7789, WD = 5.1 r ₁ = 24.6208 d ₁ = 2.4207 n _d1 = 1.71736 ν _d1 = 29.51 r ₂ = -74.8577 d ₂ = 16.5490 r ₃ = -509.3208 d ₃ = 2.9292 n _d2 = 1.62230 ν _d2 = 53.20 r ₄ = 5.7290 d ₄ = 15.4739 r ₅ = -13.9802 d ₅ = 0.8000 n _d3 = 1.74400 ν _d3 = 44.79 r ₆ = 464.7170 d ₆ = 3.4061 n _d4 = 1.49700 ν _d4 = 81.61 r ₇ = -9.4914 d ₇ = 0.2000 r ₈ = 139.1062 d ₈ = 2.0000 n _d5 = 1.49700 ν _d5 = 81.61 r ₉ = -23.5891 (1) (ν ₂ −ν ₁ ) _{= 23.69 (2) | f 2} / f | = 0.1012 (3) | f 2 / f 1 | = 0.3489 (4) | f 1 / f 3 | = 0.8928 (5) | ν 3 -ν 4 | = 36.82
.

All of the first to third embodiments are objective lenses of infinity correction type in which the light emitted from the objective lens is a parallel light beam, and it does not form an image by itself. Therefore, for example, it is used in combination with an imaging lens having the following lens data and having the lens cross section shown in FIG. However, in the lens data, r ₁ ′, r ₂ ′ ... Are the radii of curvature of the respective lens surfaces shown in order from the object side, d ₁ ′, d ₂ ′ ... are the intervals between the lens surfaces shown in order from the object side, n _d1 ', n _d2 ' ... are d-line refractive indices of the lenses shown in order from the object side, and v _d1 ', v _d2 ' ... are Abbe numbers of the lenses shown in order from the object side.

R ₁ '= 68.7541 d ₁ ' = 7.7321 n _d1 '= 1.48749 ν _d1 ' = 70.20 r ₂ '= -37.5679 d ₂ ' = 3.4742 n _d2 '= 1.80610 ν _d2 ' = 40.95 r ₃ '= -102.8477 d ₃ '= 0.6973 r ₄ ' = 84.3099 d ₄ '= 6.0238 n _d3 ' = 1.83400 ν _d3 '= 37.16 r ₅ ' = -50.7100 d ₅ '= 3.0298 n _d4 ' = 1.64450 ν _d4 '= 40.82 r ₆ ' = 40.6619.

In this case, the distance between the objective lens of Examples 1 to 3 and the imaging lens of FIG. 7 may be any position between 50 mm and 170 mm, but Example 1 when this distance is 107 mm 8 to 10 show aberration diagrams of FIGS. However, in these aberration diagrams, (a) shows spherical aberration, (b) shows distortion, (c) shows astigmatism, (d) shows lateral chromatic aberration, and (e) shows coma. In these aberration diagrams,
y indicates the image height. The distance is 50 mm to 170 m
Almost the same aberration situation is exhibited at positions other than 107 mm between m.

[0043]

As is apparent from the above description, according to the present invention, although the parfocal distance is relatively short and the lens configuration is simple, various aberrations are corrected and the objective lens is corrected. It is possible to provide an objective lens for a low-magnification microscope of an achromat class in which an image plane is extremely flat over a wide field of view by correcting off-axis chromatic aberration by itself.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a parfocal distance of a microscope objective lens.

FIG. 2 is a diagram showing a power arrangement and a light beam passage position of a microscope objective lens according to the present invention.

FIG. 3 is a diagram showing a power arrangement and a ray passing position in the case of a camera lens.

FIG. 4 is a lens sectional view of Example 1 of the microscope objective lens of the present invention.

FIG. 5 is a lens cross-sectional view of Example 2.

FIG. 6 is a lens cross-sectional view of Example 3.

FIG. 7 is a lens cross-sectional view of an example of an imaging lens used together with the microscope objective lens of each example.

FIG. 8 is an aberration diagram showing spherical aberration, distortion, astigmatism, lateral chromatic aberration, and coma of Example 1.

FIG. 9 is an aberration diagram similar to FIG. 8 of Example 2.

FIG. 10 is an aberration diagram similar to FIG. 8 of Example 3.

[Explanation of symbols]

 G1 ... 1st lens group G2 ... 2nd lens group G3 ... 3rd lens group

Claims (3)

[Claims] 1. A first lens having a positive lens in order from the object side.
An objective lens for a microscope, comprising a lens group, a second lens group consisting of a single negative lens, and a third lens group having a cemented lens of positive refractive power, and satisfying the following conditions. (1) (ν ₂ −ν ₁ )> 10 (2) 0.05 ≦ | f ₂ /f|≦0.12 (3) 0.28 ≦ | f ₂ / f ₁ | ≦ 0.40 where f Is the focal length of the entire system, f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, ν ₁ is the Abbe number of the positive lens of the first lens group, and ν ₂ is the second lens group Is the Abbe number of the negative lens of. 2. The objective lens for a microscope according to claim 1, wherein, when the focal length of the third lens group is f ₃ , (4) the condition of 0.56 ≦ | f ₁ / f ₃ | ≦ 0.90 is satisfied. An objective lens for a microscope characterized by satisfying. 3. The objective lens for a microscope according to claim 1, wherein the third lens group includes a cemented lens including a positive lens and a negative lens, and the Abbe number ν of the negative lens of the cemented lens is ν.
_{3. When} the positive lens Abbe ν ₄ is satisfied, (5) 20 <| ν ₃ −ν ₄ | <50 is satisfied.