JPH09236753A - Microscope objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily compensate the fluctuation in various aberrations caused by the changes in the thickness of a cover glass by specifying the relationships among the refractive indexes of negative and positive lenses with respect to a 'd' line, the on-axis space interval between first and second lens groups and the focal distance of the entire system. SOLUTION: A second lens group G2 is a combined lens made of a negative lens L2n and a positive lens L2p and has a joined lens L21 having a negative refractive power joined surface and a joint lens L22 having a positive refractive power joined surface. Various aberrations (especially spherical surface aberration) caused by the changes in the thickness of a cover glass are compensated for by the movement of the compensation lens group and adjusting the height of the incident light means with respect to the joined surface which constitutes an F surface. Also conditional equations 0.33<N2n-N2p and 0.02<D12/f<1.3 (where, N2n and N2p are the refractive indexes of the lenses L2n and L2p with respect to the d line, D12 is the on-axis space interval between the lens groups G1 and G2 and f is the focal distance of the entire system) are 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 lens, and more particularly to an 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, a microscope objective lens is designed with respect to a cover glass (a transparent plane-parallel plate disposed between a specimen and an objective lens) having a predetermined thickness.
However, there are some variations in the thickness of the cover glass that is actually used, and this change in the thickness of the cover glass affects the imaging performance. The influence of the change in the thickness of the cover glass on the imaging performance is small when the numerical aperture NA is 0.5 or less, for example, but the numerical aperture NA is 0.7.
When it exceeds 5, it becomes apparent.

Further, in an objective lens having a high numerical aperture, for example, a numerical aperture NA exceeding 0.85, the image forming performance is significantly deteriorated due to a change in the thickness of the cover glass, and the objective lens is used as it is. Becomes impossible. Therefore, in a bright microscope objective lens having a high numerical aperture with a numerical aperture NA exceeding 0.85, a so-called correction lens group that includes a correction lens group for correcting the aberration variation caused by the change in the thickness of the cover glass is used. An objective lens with a ring is needed.

As the objective lens with a correction ring, for example, JP-A-61-275812 and JP-A-3-5051 are known.
The microscope objective lens disclosed in Japanese Patent Laid-Open No. 7 and Japanese Patent Laid-Open No. 5-119263 is known.

[0005]

[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.

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.

In the conventional microscope objective lens disclosed in Japanese Patent Laid-Open No. 5-119263, only one doublet lens constitutes the correction lens group, and the numerical aperture N
A is as large as 0.93. However, the number of lenses constituting the entire lens system is 13 or more, which is too many.

The present invention has been made in view of the above-mentioned problems, and is capable of satisfactorily correcting fluctuations in various aberrations caused by changes in the thickness of the cover glass. It is an object of the present invention to provide a numerical aperture apochromatic grade microscope objective lens.

[0009]

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. G2 and a third lens group G3 having a negative refractive power, the first lens group G1 includes a positive meniscus lens having a concave surface facing the object side, and the second lens group G2.
Includes a cemented lens L21 having a cemented surface with a negative refractive power and a cemented lens L22 having a cemented surface with a positive refractive power, which is formed by bonding a negative lens L2n and a positive lens L2p.
The lens group G3 has at least one cemented lens,
The second lens group G2 and the third lens group G3 are relatively moved with respect to the first lens group G1 along the optical axis to correct aberration variation caused by a change in the thickness of the cover glass, The refractive index of the negative lens L2n for the d line is N2n, the refractive index of the positive lens L2p for the d line is N2p, and the axial air gap between the first lens group G1 and the second lens group G2 is D12. And a focal length of the entire system is f, the microscope objective lens is characterized by satisfying the following condition: 0.33 <N2n-N2p 0.02 <D12 / f <1.3.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is generally known that the Petzval sum may be set to almost zero in order to improve the flatness of the image plane. Further, a telephoto type lens system is known as a lens system capable of favorably correcting Petzval sum with a relatively simple configuration. It should be noted that the telephoto type lens system includes a front group having a positive refractive power and a rear group having a negative refractive power, and cannot secure a very large angle of view. Therefore, in a high-magnification objective lens having a relatively small angle of view, a telephoto type lens system is often used. Also in the present invention, this telephoto type lens system is adopted for a relatively high-power dry objective lens.

The second lens group G2 has a negative lens L2n.
And a positive lens L2p, and a cemented lens L21 having a cemented surface of negative refractive power and a cemented lens L22 having a cemented surface of positive refractive power. That is, in the present invention,
In the second lens group G2 and the third lens group G3, which are the correction lens groups, the cemented surface of the cemented lens L21 having the negative refracting power constitutes a so-called F surface.

Here, the F surface refers to a cemented surface having a strong negative refractive power, and generally, the thickness of the cover glass is changed by adjusting the height of the incident light ray with respect to the F surface. The variation of spherical aberration due to is corrected. In the present invention, the correction lens group itself is provided with the F surface, and the height of the incident light ray with respect to the F surface is adjusted by moving the correction lens group and thus the F surface along the optical axis.

Then, by moving the correction lens group, the height of the incident light ray with respect to the cemented surface forming the F surface is adjusted to correct various aberrations (particularly spherical aberration) due to the change in the thickness of the cover glass. doing. Since the spherical aberration is proportional to the height of the light ray, the method of the present invention has an advantage that the larger the effective diameter of the F surface, the smaller the amount of movement of the correction lens group can be.

Hereinafter, the conditional expressions of the present invention will be described. In the present invention, the following conditional expressions (1) and (2) are satisfied. 0.33 <N2n-N2p (1) 0.02 <D12 / f <1.3 (2)

Here, N2n: Refractive index of the negative lens L2n with respect to the d line N2p: Refractive index of the positive lens L2p with respect to the d line D12: On-axis air gap f between the first lens group G1 and the second lens group G2 : Focal length of entire system The axial air distance between the first lens group G1 and the second lens group G2 is the most image-side surface of the first lens group G1 and the most object of the second lens group G2. The distance along the optical axis between the side surface.

Conditional expression (1) defines an appropriate range for the difference in refractive index between the negative lens L2n and the positive lens L2p forming the cemented surface (F surface) of negative refractive power in the second lens group G2. There is. If the lower limit of conditional expression (1) is not reached, the refractive index difference between the negative lens L2n and the positive lens L2p becomes too small,
In order to satisfactorily correct the fluctuation of spherical aberration, it is necessary to increase the curvature of the cemented surface forming the F surface, and as a result, new spherical aberration of higher color is generated.

Conditional expression (2) is a conditional expression concerning the moving range of the correction lens group, and defines an appropriate range for the axial air gap between the first lens group G1 and the second lens group G2. If the upper limit of conditional expression (2) is exceeded, the distance between the first lens group G1 and the second lens group G2 becomes too large, and the chromatic aberration of magnification is unbalanced. Fluctuates. Further, if the first lens group G1 and the second lens group G2 are too close to each other, it is inconvenient in manufacturing. In the present invention, the first lens group G
It is preferable that the chromatic aberration of magnification is satisfactorily corrected independently in each of the first and second lens groups G2.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each of the examples, the microscope objective lens of the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and
A third lens group G3 having a negative refractive power.

The first lens group G1 includes a positive meniscus lens having a concave surface facing the object side. The second lens group G2 includes a cemented lens L21 having a cemented surface having a negative refractive power, which is formed by bonding a negative lens L2n and a positive lens L2p.
And a cemented lens L22 having a cemented surface of positive refractive power.
Further, the third lens group G3 has at least one cemented lens.

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 image forming 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).

[0022]

[Table 1]

Example 1 FIG. 1 is a diagram showing the structure of a microscope objective lens according to Example 1 of the present invention. In the illustrated microscope objective lens, the first lens group G1 includes, in order from the object side, a negative meniscus lens having a concave surface facing the object side, a positive meniscus lens having a concave surface facing the object side, and a positive meniscus lens having a concave surface facing the object side. It is composed of a lens and a cemented positive lens composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens.

The second lens group G2 includes, in order from the object side, a cemented positive lens L21 composed of a negative meniscus lens L2n having a convex surface facing the object side and a biconvex lens L2p, and a cemented negative lens composed of a biconvex lens and a biconcave lens. It is composed of L22. The cemented surface of the cemented positive lens L21 has a negative refractive power,
The cemented surface of the cemented negative lens L22 has a positive refractive power. Further, the third lens group G3 is composed of, in order from the object side, a cemented negative lens composed 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 microscope objective lens, NA is the numerical aperture, β is the magnification of the system including the imaging lens, and WD is the working distance. Further, the leftmost number 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 each lens surface, and n and ν are d lines (λ = 587.63).
m) shows the refractive index and Abbe number.

[0026]

[Table 2] f = 5.0 NA = 0.95 β = 40 × WD = 0.14 (Variable Interval in Correcting Aberration Variation) Cover Glass Thickness Variable Interval d9 0.11 0.65 0.17 1.785 0.23 3.19 (Value Corresponding to Condition) (1) N2n-N2p = 0.37 (2) D12 / f = 0.13 to 0.638

FIG. 2 is a spherical aberration diagram of the first embodiment. And, in (a), the thickness of the cover glass is 0.11.
, (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 0.23. 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 indicates the F line (λ = 486.1 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 diagram showing the structure of a microscope objective lens according to a second embodiment of the present invention. In the illustrated microscope objective lens, the first lens group G1 includes, in order from the object side, a negative meniscus lens having a concave surface facing the object side, a positive meniscus lens having a concave surface facing the object side, and a positive meniscus lens having a concave surface facing the object side. It is composed of a lens and a cemented positive lens composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens.

The second lens group G2 includes, in order from the object side, a positive lens L21 cemented with a negative meniscus lens L2n having a convex surface facing the object side and a biconvex lens L2p, and a positive meniscus lens having a concave surface facing the object side. And a biconcave lens cemented with a negative lens L22. The cemented positive lens L
The cemented surface of 21 has a negative refractive power, and the cemented surface of the cemented negative lens L22 has a positive refractive power. Furthermore, the third lens group G3
It is composed of a cemented negative lens composed of a biconvex lens and a biconcave lens in order from the object side.

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 microscope objective lens, NA is the numerical aperture, β is the magnification of the system including the imaging lens, and WD is the working distance. Further, the leftmost number 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 each lens surface, and n and ν are d lines (λ = 587.63).
m) shows the refractive index and Abbe number.

[0031]

[Table 3] f = 5.0 NA = 0.9 β = 40 x WD = 0.14 (Variable Interval in Correction of Aberration Variation) Cover Glass Thickness Variable Interval d9 0.08 0.39 0.17 1.89 0.3 4.8 (Condition-Compliant Value) (1) N2n-N2p = 0.37 (2) D12 / f = 0.078-0.96

FIG. 4 is a spherical aberration diagram of the second embodiment. And in (a), the cover glass has a thickness of 0.08.
, (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 0.3. 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 = 65 nm).
6.3 nm) and F indicates the F line (λ = 486.1 nm). As is clear from each spherical aberration diagram,
In this example, it can be seen that the variation in spherical aberration due to the change in the thickness of the cover glass is well corrected.

[0033]

As described above, according to the present invention, the magnification is about 40 times, the numerical aperture NA is large, and the fluctuations of various aberrations (particularly spherical aberration) due to the change of the thickness of the cover glass can be improved. It is possible to realize an apochromat-class microscope objective lens that can be corrected and has a small number of constituent lenses.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a 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 0.11, (b) shows the spherical aberration when the cover glass has a thickness of 0.17, and (c) shows the thickness of the cover glass. The spherical aberrations are shown when the value is 0.23.

FIG. 3 is a diagram showing a configuration of a 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 thickness of the cover glass is 0.08, (b) shows the spherical aberration when the thickness of the cover glass is 0.17, and (c) shows the thickness of the cover glass. The spherical aberrations are shown in the case where is 0.3.

[Explanation of symbols]

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

Claims (1)

[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 negative refractive power, the first lens group G1 includes a positive meniscus lens having a concave surface facing the object side, and the second lens group G2 includes a negative lens L2n. And positive lens L2p
And a cemented lens L21 having a cemented surface of negative refractive power and a cemented lens L having a cemented surface of positive refractive power.
22 and the third lens group G3 has at least one cemented lens, and the second lens group G2 and the third lens group G3 are arranged along the optical axis with respect to the first lens group G1. To correct the aberration variation caused by the change in the thickness of the cover glass, the refractive index of the negative lens L2n for the d line is N2n, and the refractive index of the positive lens L2p for the d line is N2p, When the axial air distance between the first lens group G1 and the second lens group G2 is D12 and the focal length of the entire system is f, 0.33 <N2n-N2p 0.02 <D12 / f A microscope objective lens characterized by satisfying the condition of <1.3.