JPH09258107A - Microscopic objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To well correct the fluctuation in various aberrations occurring due to change in the thickness of cover glass. SOLUTION: A first lens group G1 includes a combined positive lens L11 which has a joint surface s2 with its convex face of a curvature directed toward an image side and of which the face on an object side is nearly a plane shape. A second lens group G2 includes a joint surface having negative refracting power and converts the luminous flux via the first lens group G1 to a convergent luminous flux. A third lens group G3 has a lens face s20 of which the lens face on the extreme object side directs its convex face toward the object side and its concave face of a large curvature to the image side in contact with air. The fluctuation in the aberrations is corrected by moving the third lens group G3 along the optical axis relatively with the first lens group G1 and the second 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 a liquid immersion apochromat microscope objective lens capable of correcting variations in various aberrations caused by changes in the cover glass thickness.

[0002]

2. Description of the Related Art Generally, in observation with a microscope, the numerical aperture may be increased to improve the resolution. It is well known that in order to increase the numerical aperture, the optical path between the sample to be observed and the objective lens should be filled with a liquid (hereinafter referred to as "immersion liquid"). Usually, as immersion liquid, oil (refractive index for d line is about 1.52), glycerin (refractive index for d line is about 1.47), water (refractive index for d line is about 1.33), etc. Is used.

Focusing only on the resolving power, a so-called oil-immersion type microscope objective lens using oil having a large refractive index as the immersion liquid is advantageous. Moreover, since there is almost no difference between the refractive index of the cover glass made of a transparent plane-parallel plate arranged on the object side (the refractive index for the d line is about 1.5) and the refractive index of the oil, the thickness of the cover glass is There is an advantage that the variation of aberration is small even if is slightly changed. However, there are drawbacks that the oil is not easy to handle and the cells of the specimen may die due to the action of the oil.

Therefore, recently, a so-called water-immersion microscope objective lens, which uses water as an immersion liquid, which is easy to handle and allows cells of a specimen to be observed alive, has been attracting attention. However, in the water immersion microscope objective lens, since the difference between the refractive index of water and the refractive index of the cover glass is large, various aberrations (particularly spherical aberration) greatly change when the thickness of the cover glass changes. Therefore, the water-immersion microscope objective requires a so-called objective lens with a correction ring, which is provided with a correction lens group for correcting aberration fluctuations.

Generally, in an objective lens with a correction ring, a cemented surface having a strong negative refractive power (hereinafter referred to as “F surface”)
By adjusting the height of the incident ray with respect to, the variation of the spherical aberration due to the change of the thickness of the cover glass is corrected. As a method of adjusting the height of this incident light beam, the correction lens group itself has an F surface, and the correction lens group
There is a method of adjusting the height of the incident light ray with respect to the F surface by moving the surface along the optical axis.

In this adjusting method, since the spherical aberration is proportional to the height of the light beam, the larger the effective diameter of the F surface, the smaller the amount of movement of the correction lens group, which is advantageous. However, since the fluctuation of the spherical aberration is too sensitive to the movement of the F surface, there is a disadvantage that the aberration is apt to be deteriorated due to the decentering of the F surface. If chromatic aberration exists in the correction lens group itself that moves along the optical axis, the movement of the correction lens group causes a new spherical aberration of color (a change in spherical aberration for each wavelength of light). Therefore, the chromatic aberration must be corrected individually in each of the correction lens group and the other lens groups.

As a dry objective lens with a correction ring,
For example, JP-A-61-275812 and JP-A-3-
A microscope objective lens disclosed in Japanese Patent No. 50517 is known. As a liquid immersion type objective lens with a correction ring, for example, a microscope objective lens disclosed in JP-A-6-281864 is known.

[0008]

[Problems to be Solved by the Invention] First, JP-A-61-2
The conventional microscope objective lens disclosed in Japanese Patent No. 75812 is a second lens having a first lens group having a positive refracting power, a divergent (negative refracting power) cemented surface, and a convergent (positive refractive power) cemented surface. And a third lens unit having a negative refractive power. Then, the second lens group and the third lens group constitute a correction lens group that moves along the optical axis. This microscope objective lens has a numerical aperture NA of 0.95, which is almost the maximum brightness for a dry system, while supporting a wide range of changes in the cover glass thickness from 0.11 to 0.23. It is possible. However, the correction of the spherical aberration of color due to the movement of the correction lens group is not sufficient.

Further, the conventional microscope objective lens disclosed in Japanese Patent Laid-Open No. 3-50517 has a positive, positive, and negative three-group structure in order from the object side, and the second lens group is along the optical axis. And a correction lens group that moves by moving. However, the second lens group includes four lens components (three cemented lenses and one single lens), and the number of lenses is too large for the correction lens group. Further, since the lens diameter is large, the aberration is likely to be deteriorated due to decentering (particularly shift with respect to the optical axis). Furthermore, chromatic spherical aberration also remains.

On the other hand, the conventional immersion microscope objective lens disclosed in Japanese Unexamined Patent Publication No. 6-281864 has three groups of positive, positive, and negative in order from the object side. The second lens unit having a positive refractive power constitutes a correction lens unit, and the numerical aperture NA
Is as large as 1.15. However, JP-A-3-505
Similar to the microscope objective lens disclosed in Japanese Patent No. 17, the lens diameter is large and the aberration is easily deteriorated due to decentering.

The present invention has been made in view of the above-mentioned problems, and has a large numerical aperture, which causes variations in various aberrations due to changes in the thickness of the cover glass and changes in the refractive index of cells to be observed. An object of the present invention is to provide an immersion-type apochromat microscope objective lens that can be satisfactorily corrected.

[0012]

In order to solve the above problems, according to the present invention, a first lens group G1 having a positive refractive power and a second lens group having a positive refractive power are arranged in order from the object side. G1 and a third lens group G3 having negative refracting power, the first lens group G1 has a cemented surface s2 having a convex surface with a strong curvature facing the image side, and the surface on the object side is substantially flat. The second lens group G2 includes a cemented positive lens L11 formed in a circular shape, and the second lens group G2 includes a cemented surface having a negative refracting power. The third lens group G3 has a lens surface s18 in which the most object side lens surface faces the object side, the convex surface faces the image side, and the concave surface having a strong curvature faces the air, and the third lens group G3 contacts the air. The third lens group G3 is moved relative to the lens group G2 along the optical axis. Provided is an immersion microscope objective lens characterized by being moved to correct aberration variation.

According to a preferred embodiment of the present invention, the radius of curvature of the cemented surface s2 of the cemented positive lens L11 is r2, the radius of curvature of the lens surface s18 of the third lens group G3 is r18, and the focal length of the entire system is Where f is and the magnification is β, the condition of −0.01 <r2 / (f · β) <− 0.004 0.015 <r18 / (f · β) <0.035 is satisfied.

When the radius of curvature of the most object side surface of the third lens group G3 is r16 and the radius of curvature of the most image side surface of the third lens group G3 is r21, -2 <r16 /
It is preferable to satisfy the condition of r21 <-0.5. Further, it is preferable that the Abbe number ν3d of at least one positive lens among the lenses constituting the third lens group G3 satisfies the condition of ν3d <40.

According to another aspect of the present invention, the first lens group G1 having a positive refractive power, the second lens group G2 having a positive refractive power, and the third lens group are arranged in this order from the object side. G
And the third lens group G3 is moved relative to the first lens group G1 and the second lens group G2 along the optical axis to correct aberration fluctuations. A microscope objective lens is provided.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, a microscope objective lens according to the present invention comprises, in order from the object side, a first lens having a positive refractive power.
The lens group G1 and the second lens group G2 having a positive refractive power
And a third lens group G3 having a negative refractive power
The group structure is the basic structure. Then, the third lens group G
Reference numeral 3 constitutes a correction lens group that moves relative to the first lens group G1 and the second lens group G2 along the optical axis.

In the third lens group G3, which is a correction lens group, the lens surface closest to the object is convex on the object side. This most object-side lens surface has a function of making spherical aberration negative as the incident light ray is further away from the optical axis.
Therefore, when a light beam having a spherical aberration generated due to a change in the thickness of the cover glass is incident on the microscope objective lens, the third lens group G3 and thus the lens surface on the most object side is moved along the optical axis. By doing so, the spherical aberration of the incident ray can be canceled by the spherical aberration generated on the lens surface closest to the object.

In a liquid immersion type microscope objective lens, since the immersion liquid enters the lens surface closest to the object side, the immersion liquid must be wiped off from the lens surface after use. Further, the air must not be mixed in the immersion liquid to deteriorate the performance. Therefore, it is necessary to form the most object-side lens surface that comes into contact with the immersion liquid into a substantially flat shape. As a result, it becomes more difficult to correct the field curvature in the immersion microscope objective lens than in a normal microscope objective lens.

Therefore, in the immersion microscope objective lens,
In general, a cemented lens, which is generally called an embedded lens, is arranged closest to the object side to correct the Petzval sum.
Also in the present invention, in the first lens group G1, the cemented positive lens L11 having the cemented surface s2 with the convex surface having a strong curvature facing the image side and having the object side surface formed in a substantially flat surface is used as the embedded lens. I have it.

The second lens group G2 has a cemented surface (F surface) having a negative refracting power in order to convert the divergent light flux passing through the first lens group G1 into a convergent light flux while correcting chromatic aberration and spherical aberration. (Corresponding to) and has a positive refracting power as a whole. Further, as described above, the third lens group G3 is a correction lens group, and corrects variations in various aberrations caused by changes in the thickness of the cover glass, particularly variations in spherical aberration.
Therefore, the third lens group G3 has a lens surface s18 in which the lens surface closest to the object is in contact with air with the convex surface facing the object side and the concave surface having a strong curvature facing the image side.

Hereinafter, each conditional expression of the present invention will be described. In the present invention, it is desirable to satisfy the following conditional expressions (1) and (2). -0.01 <r2 / (f · β) <− 0.004 (1) 0.015 <r18 / (f · β) <0.035 (2)

Where f is the focal length of the entire system, β is the magnification, r2 is the radius of curvature of the cemented surface s2 of the cemented positive lens L11, r18 is the radius of curvature of the lens surface s18 of the third lens group G3.

Conditional expression (1) defines an appropriate range for the radius of curvature of the cemented surface s2 of the cemented positive lens L11 which is an embedded lens. If the upper limit of conditional expression (1) is exceeded, the Petzval sum will be overcorrected (the value will increase toward the negative side), and field curvature and coma will deteriorate. On the other hand, if the lower limit of conditional expression (1) is exceeded, the Petzval sum will be undercorrected (the value will increase toward the positive side),
The field curvature becomes worse. If the upper limit value and the lower limit value of conditional expression (1) are set to -0.006 and -0.008, respectively, a better result can be obtained.

Conditional expression (2) is the same as conditional expression (1).
It is a conditional expression for correcting Petzval sum, and defines an appropriate range for the radius of curvature of the lens surface s18 of the third lens group G3. When the value exceeds the upper limit of conditional expression (2),
The Petzval sum is undercorrected and the field curvature deteriorates. On the other hand, when the value goes below the lower limit of conditional expression (2), the Petzval sum is overcorrected, and the field curvature is deteriorated. If the upper limit and the lower limit of conditional expression (2) are set to 0.03 and 0.018, respectively, a better result can be obtained.

Further, in the present invention, when the radius of curvature of the most object side surface s16 of the third lens group G3 is r16 and the radius of curvature of the most image side surface s21 of the third lens group G3 is r21,
It is desirable to satisfy the following conditional expression (3). -2 <r16 / r21 <-0.5 (3)

Conditional expression (3) is a conditional expression that defines the shape of the third lens group G3, and is set so that the value of r16 / r21 is about -1. If conditional expression (3) is satisfied,
The shape of the third lens group G3 is spherical or nearly spherical. If for some reason the third lens group G
Even if 3 is rotated (tilted) with respect to the optical axis, by making the entire shape spherical, it is possible to suppress variation in aberration due to tilt to be small. If the upper limit value of conditional expression (3) is set to -0.75 and the lower limit value is set to -1.5, a better result can be obtained.

Further, in the present invention, in order to obtain a better imaging performance, the Abbe number ν3d of at least one positive lens of the lenses constituting the third lens group G3 satisfies the following conditional expression (4). It is desirable to do. ν3d <40 (4) If the upper limit of conditional expression (4) is exceeded, chromatic aberration of magnification will be undercorrected (g-line will move away from the optical axis), and good imaging performance will not be obtained. .

[0028]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each example, the microscope objective lens of the present invention is a water immersion system using water as an immersion liquid, and has a first lens group G1 having a positive refractive power and a positive refractive power in order from the object side. It includes a second lens group G2 and a third lens group G3 having a negative refractive power. In each example, the refractive index of water is 1.33306 and the Abbe number is 53.98.

The first lens group G1 includes a cemented positive lens L11 having a cemented surface s2 with a convex surface having a strong curvature facing the image side, and a surface on the object side formed substantially flat. Also,
The second lens group G2 includes a cemented surface s13 having a negative refractive power, and converts the light flux that has passed through the first lens group G1 into a convergent light flux. Further, the third lens group G3 has a lens surface s18 that is in contact with air, with the lens surface closest to the object facing the object side and the concave surface having a strong curvature facing the image side.

In each embodiment, an image forming lens (second objective lens) is arranged on the image side of the microscope objective lens with an axial air distance of 150 mm. And
By combining the microscope objective lens and the imaging lens,
A finite optical system is formed. The various aberration diagrams shown in each of the following examples are various aberration diagrams when the axial air gap between the microscope objective lens and the imaging lens is 150 mm. However, the present inventors have verified that even if the on-axis air gap changes to some extent, there is almost no change in aberration.

The imaging lens in each embodiment is a cemented positive lens G4 composed of a biconvex lens and a biconcave lens in order from the object side.
And a cemented positive lens G5 composed of a biconvex lens and a biconcave lens. The following table (1) lists values of specifications of the imaging lens in each example. In Table (1), the number at the left end indicates the order of each lens surface from the object side, r indicates the radius of curvature of each lens surface, d indicates the distance between the lens surfaces, and n and ν indicate d lines (λ = 587). .6 nm).

[0032]

[Table 1] r d n ν 1 75.0450 5.1 1.6228 57.0 G4 2 -75.045 2.0 1.7500 35.2 3 1600.5800 7.5 4 50.2560 5.1 1.6676 42.0 G5 5 -84.5410 1.8 1.6127 44.4 6 36.9110

[Embodiment 1] FIG. 1 is a view showing the arrangement of a water immersion microscope objective according to the first embodiment of the present invention. In the illustrated water immersion microscope objective lens, the first lens group G1 includes, in order from the object side, a cemented plano-convex lens L11 including a plano-convex lens having a flat surface facing the object side and a negative meniscus lens having a concave surface facing the object side. It is composed of a positive meniscus lens having a concave surface directed to the side, and a cemented positive lens composed of a biconcave lens and a biconvex lens.

The second lens group G2 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens, and a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens. And a biconcave lens, which is a cemented positive lens. Further, the third lens group G3
Is composed of, in order from the object side, a cemented negative lens of a biconvex lens and a biconcave lens, and a cemented negative lens of a biconcave lens and a biconvex lens.

The following table (2) lists the values of specifications of the first embodiment of the present invention. In Table (2), f is the focal length of only the objective lens, NA is the numerical aperture, β is the magnification when the imaging lens is used, and WD is the working distance.
Furthermore, the number at the left end is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and n and ν are d lines (λ = 587.63 m).
Shows the refractive index and the Abbe number with respect to.

[0036]

[Table 2] f = 3.3 NA = 1.2 β = 60 × WD = 0.22 rd n ν 1 ∞ 0.95 1.45847 67.72 G1 2 -1.4005 3.55 1.90265 35.72 3 -3.6312 0.10 4 -19.0102 3.25 1.49782 82.52 5 -8.3011 0.10 6 -32.4210 1.00 1.67163 38.80 7 21.6003 8.00 1.49782 82.52 8 -11.3644 0.50 9 60.0610 1.20 1.61266 44.41 G2 10 24.3609 7.20 1.43388 95.57 11 -17.8502 0.15 12 16.0000 2.00 1.74400 45.00 13 8.6199 8.20 1.43388 95.57 14. 47.762 (d15 = variable) 16 8.5714 5.15 1.49782 82.52 G3 17 -52.4010 6.35 1.61266 44.41 18 4.6607 2.90 19 -5.3822 2.45 1.69680 55.60 20 33.2070 2.85 1.61750 30.83 21 -7.5344 (variable distance in correcting aberration variation) Cover glass thickness variable Interval d15 0.15 1.35 0.17 0.88 0.19 0.45 (value corresponding to the condition) (1) r2 / (f · β) = − 0.0071 (2) r18 / (f · β) = 0.0235 (3) r16 / r21 = -1.137 6 (4) ν3d = 30.83

FIG. 2 is a spherical aberration diagram of the first embodiment. And, in (a), the cover glass has a thickness of 0.15.
, (B) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the spherical aberration when the cover glass has a thickness of 0.19. Shows. In each spherical aberration diagram, NA is the numerical aperture,
d is the d line (λ = 587.6 nm) and C is the C line (λ = 6 nm).
56.3 nm) and f is the F line (λ = 486.1 nm)
, G indicates the g-line (λ = 435.6 nm). As is clear from each spherical aberration diagram, in this example, it is understood that the variation of the spherical aberration due to the change of the thickness of the cover glass is well corrected.

[Embodiment 2] FIG. 3 is a view showing the arrangement of a water immersion microscope objective according to the second embodiment of the present invention. In the illustrated water immersion microscope objective lens, the first lens group G1 includes, in order from the object side, a cemented plano-convex lens L11 including a plano-convex lens having a flat surface facing the object side and a negative meniscus lens having a concave surface facing the object side. It is composed of a positive meniscus lens having a concave surface directed to the side, and a cemented positive lens composed of a biconcave lens and a biconvex lens.

The second lens group G2 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens, and a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens. And a biconcave lens, which is a cemented positive lens. Further, the third lens group G3
Is composed of, in order from the object side, a cemented negative lens of a biconvex lens and a biconcave lens, and a cemented negative lens of a biconcave lens and a biconvex lens.

The following table (3) lists the values of specifications of the second embodiment of the present invention. In Table (3), f is the focal length of only the objective lens, NA is the numerical aperture, β is the magnification when the imaging lens is used, and WD is the working distance.
Furthermore, the number at the left end is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and n and ν are d lines (λ = 587.63 m).
Shows the refractive index and the Abbe number with respect to.

[0041]

[Table 3] f = 3.3 NA = 1.15 β = 60 x WD = 0.21 rd n ν 1 ∞ 0.95 1.45847 67.72 G1 2 -1.2900 3.55 1.90265 35.72 3 -3.5870 0.08 4 -19.1910 3.25 1.49782 82.52 5 -8.4373 0.09 6 -41.9343 1.00 1.67163 38.80 7 20.2530 7.99 1.49782 82.52 8 -12.1025 0.50 9 42.3801 1.20 1.61266 44.41 G2 10 24.5534 7.20 1.43388 95.57 11 -18.4120 0.15 12 16.0000 2.00 1.74400 45.00 13 8.6199 8.20 1.43388 95.57 14. 40.7521 (d15 = variable) 16 8.6200 5.18 1.49782 82.52 G3 17 -51.6832 6.28 1.61266 44.41 18 5.10261 2.90 19 -5.2704 2.40 1.71300 53.93 20 32.8101 3.00 1.61750 30.83 21 -7.4653 (variable distance for correcting aberration variation) Cover glass thickness Variable Interval d15 0.15 1.33 0.17 0.8 0.19 0.25 (Value corresponding to condition) (1) r2 / (f · β) = − 0.0065 (2) r18 / (f · β) = 0.0258 (3) r16 / r21 = -1.15 47 (4) ν3d = 30.83

FIG. 4 is a spherical aberration diagram in the second embodiment. And, in (a), the cover glass has a thickness of 0.15.
, (B) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the spherical aberration when the cover glass has a thickness of 0.19. Shows. In each spherical aberration diagram, NA is the numerical aperture,
d is the d line (λ = 587.6 nm) and C is the C line (λ = 6 nm).
56.3 nm) and f is the F line (λ = 486.1 nm)
, G indicates the g-line (λ = 435.6 nm). As is clear from each spherical aberration diagram, in this example, it is understood that the variation of the spherical aberration due to the change of the thickness of the cover glass is well corrected.

[Embodiment 3] FIG. 5 is a view showing the arrangement of a water immersion microscope objective lens according to the third embodiment of the present invention. In the illustrated water immersion microscope objective lens, the first lens group G1 includes, in order from the object side, a cemented plano-convex lens L11 including a plano-convex lens having a flat surface facing the object side and a negative meniscus lens having a concave surface facing the object side. It is composed of a positive meniscus lens having a concave surface directed to the side, and a cemented positive lens composed of a biconcave lens and a biconvex lens.

The second lens group G2 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens, and a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens. And a biconcave lens, which is a cemented positive lens. Further, the third lens group G3
Is composed of, in order from the object side, a cemented negative lens of a biconvex lens and a biconcave lens, and a cemented negative lens of a biconcave lens and a biconvex lens.

Table (4) below shows the values of specifications of the third embodiment of the present invention. In Table (4), f is the focal length of only the objective lens, NA is the numerical aperture, β is the magnification when the imaging lens is used, and WD is the working distance.
Furthermore, the number at the left end is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and n and ν are d lines (λ = 587.63 m).
Shows the refractive index and the Abbe number with respect to.

[0046]

[Table 4] f = 3.3 NA = 1.15 β = 60 x WD = 0.21 rd n ν 1 ∞ 0.95 1.45847 67.72 G1 2 -1.5438 3.55 1.90265 35.72 3 -3.5734 0.07 4 -16.6074 3.25 1.49782 82.52 5 -9.0287 0.08 6 -36.8686 1.00 1.67163 38.80 7 18.7765 7.98 1.49782 82.52 8 -11.8720 0.50 9 48.7655 1.20 1.61266 44.41 G2 10 27.7934 7.20 1.43388 95.57 11 -16.9358 0.15 12 16.0000 2.01 1.74400 45.00 13 8.6199 8.19 1.43883 95.57 14 -26.2 45.0608 (d15 = variable) 16 8.6200 5.14 1.49782 82.52 G3 17 -50.1533 6.25 1.61266 44.41 18 5.0642 2.90 19 -5.1861 2.40 1.71300 53.93 20 32.0438 3.00 1.61750 30.83 21 -7.4704 (variable distance in correcting aberration variation) Cover glass thickness variable Interval d15 0.15 1.33 0.17 0.8 0.19 0.25 (value corresponding to the condition) (1) r2 / (f · β) = − 0.0078 (2) r18 / (f · β) = 0.0256 (3) r16 / r21 = -1.15 9 (4) ν3d = 30.83

FIG. 6 is a spherical aberration diagram in the third embodiment. And, in (a), the cover glass has a thickness of 0.15.
, (B) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the spherical aberration when the cover glass has a thickness of 0.19. Shows. In each spherical aberration diagram, NA is the numerical aperture,
d is the d line (λ = 587.6 nm) and C is the C line (λ = 6 nm).
56.3 nm) and f is the F line (λ = 486.1 nm)
, G indicates the g-line (λ = 435.6 nm). As is clear from each spherical aberration diagram, in this example, it is understood that the variation of the spherical aberration due to the change of the thickness of the cover glass is well corrected.

[Embodiment 4] FIG. 7 is a diagram showing the structure of a water immersion microscope objective lens according to a fourth embodiment of the present invention. In the illustrated water immersion microscope objective lens, the first lens group G1 includes, in order from the object side, a cemented plano-convex lens L11 including a plano-convex lens having a flat surface facing the object side and a negative meniscus lens having a concave surface facing the object side. It is composed of a positive meniscus lens having a concave surface directed to the side, and a cemented positive lens composed of a biconcave lens and a biconvex lens.

The second lens group G2 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens, and a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens. And a biconcave lens, which is a cemented positive lens. Further, the third lens group G3
Is composed of, in order from the object side, a cemented negative lens of a biconvex lens and a biconcave lens, and a cemented negative lens of a biconcave lens and a biconvex lens.

Table (5) below shows the values of specifications of the fourth embodiment of the present invention. In Table (5), f is the focal length of only the objective lens, NA is the numerical aperture, β is the magnification when the imaging lens is used, and WD is the working distance.
Furthermore, the number at the left end is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and n and ν are d lines (λ = 587.63 m).
Shows the refractive index and the Abbe number with respect to.

[0051]

[Table 5] f = 3.3 NA = 1.15 β = 60 x WD = 0.21 r d n ν 1 ∞ 0.95 1.45847 67.72 G1 2 -1.4011 3.55 1.90265 35.72 3 -3.5540 0.11 4 -19.1695 3.25 1.49782 82.52 5 -8.0045 0.10 6 -31.3114 1.00 1.67163 38.80 7 19.6019 8.00 1.49782 82.52 8 -11.2428 0.50 9 59.1366 1.20 1.61266 44.41 G2 10 22.2513 7.20 1.43388 95.57 11 -17.7453 0.15 12 16.0000 2.00 1.74400 45.00 13 8.6199 8.20 1.43883 95.57 14 -95.57 14. 49.1098 (d15 = variable) 16 8.5714 5.22 1.49782 82.52 G3 17 -49.9726 6.32 1.61266 44.41 18 3.9054 2.90 19 -5.5117 2.40 1.71700 48.04 20 34.0448 3.00 1.61750 30.83 21 -6.8632 (variable distance in correcting aberration variation) Cover glass thickness variable Interval d15 0.15 1.33 0.17 0.8 0.19 0.25 (value corresponding to the condition) (1) r2 / (f · β) = − 0.0071 (2) r18 / (f · β) = 0.0197 (3) r16 / r21 = -1.248 9 (4) ν3d = 30.83

FIG. 8 is a spherical aberration diagram of the fourth embodiment. And, in (a), the cover glass has a thickness of 0.15.
, (B) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the spherical aberration when the cover glass has a thickness of 0.19. Shows. In each spherical aberration diagram, NA is the numerical aperture,
d is the d line (λ = 587.6 nm) and C is the C line (λ = 6 nm).
56.3 nm) and f is the F line (λ = 486.1 nm)
, G indicates the g-line (λ = 435.6 nm). As is clear from each spherical aberration diagram, in this example, it is understood that the variation of the spherical aberration due to the change of the thickness of the cover glass is well corrected.

[0053]

As described above, according to the present invention, the magnification is about 60 times, the numerical aperture NA is large at about 1.15 to 1.2, the thickness of the cover glass changes and the cells to be observed are It is possible to realize an immersion apochromat microscope objective lens capable of excellently correcting variations in various aberrations (particularly spherical aberration) due to changes in the refractive index.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a water immersion microscope objective lens according to a first example of the present invention.

FIG. 2 is a spherical aberration diagram of the first embodiment,
(A) shows the spherical aberration when the cover glass has a thickness of 0.15, (b) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the thickness of the cover glass. Spherical aberrations are shown when the value is 0.19.

FIG. 3 is a diagram showing a configuration of a water immersion microscope objective lens according to a second example of the present invention.

FIG. 4 is a spherical aberration diagram of the second embodiment,
(A) shows the spherical aberration when the cover glass has a thickness of 0.15, (b) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the thickness of the cover glass. Spherical aberrations are shown when the value is 0.19.

FIG. 5 is a diagram showing a configuration of a water immersion microscope objective lens according to a third example of the present invention.

FIG. 6 is a spherical aberration diagram of the third example,
(A) shows the spherical aberration when the cover glass has a thickness of 0.15, (b) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the thickness of the cover glass. Spherical aberrations are shown when the value is 0.19.

FIG. 7 is a diagram showing a configuration of a water immersion microscope objective lens according to a fourth example of the present invention.

FIG. 8 is a spherical aberration diagram in the fourth example,
(A) shows the spherical aberration when the cover glass has a thickness of 0.15, (b) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the thickness of the cover glass. Spherical aberrations are shown when the value is 0.19.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group L11 Embedded lens

Claims (5)

[Claims] 1. A first lens group G1 having a positive refractive power and a second lens group G having a positive refractive power in order from the object side.
2 and a third lens group G3 having a negative refractive power, the first lens group G1 has a cemented surface s2 having a convex surface with a strong curvature facing the image side, and the object side surface is substantially flat. The second lens group G2 includes a cemented surface having a negative refracting power, converts the light flux that has passed through the first lens group G1 into a convergent light flux, and The third lens group G3 has a lens surface s18 in which the lens surface closest to the object is in contact with air by directing a convex surface toward the object side and a concave surface having a strong curvature toward the image side, and the first lens group G1 and the second lens group G1. An immersion microscope objective lens, characterized in that the third lens group G3 is moved relative to the lens group G2 along the optical axis to correct aberration variation. 2. The radius of curvature of the cemented surface s2 of the cemented positive lens L11 is r2, and the lens surface s of the third lens group G3 is
When the radius of curvature of 18 is r18, the focal length of the entire system is f, and the magnification is β, -0.01 <r2 / (f · β) <− 0.004 0.015 <r18 / (f · The immersion microscope objective lens according to claim 1, wherein the condition β) <0.035 is satisfied. 3. When the radius of curvature of the most object side surface of the third lens group G3 is r16 and the radius of curvature of the most image side surface of the third lens group G3 is r21, −2 <r16 / The immersion microscope objective lens according to claim 1 or 2, which satisfies the condition of r21 <-0.5. 4. The Abbe number ν3d of at least one positive lens among the lenses constituting the third lens group G3, satisfies the condition of ν3d <40. An immersion microscope objective lens according to item. 5. A first lens group G1 having a positive refractive power and a second lens group G having a positive refractive power in order from the object side.
2 and a third lens group G3, and the first lens group G
1. An immersion microscope objective lens, characterized in that the third lens group G3 is moved relative to the first and second lens groups G2 along the optical axis to correct aberration variation.