JP2000241710A - Microscope objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microscope objective lens whose NA(numerical aperture) is about 0.9, whose actuation distance is long and whose magnification is about 100. SOLUTION: This lens is equipped with a 1st lens group G1 consisting of a positive meniscus lens component L11 whose concave surface faces to an object side, a 2nd lens group G2 consisting of a positive meniscus lens component L21 whose concave surface faces to the object side, a 3rd lens group G3 consisting of a combined lens obtained by sticking three lenses being a positive lens component L31, a negative lens component L32 and a positive lens component L33, a 4th positive lens group G4, a 5th lens group G5 consisting of a combined lens obtained by sticking three lenses being a negative lens component L51, a positive lens component L52 and a negative lens component L53, and a 6th negative lens group G6 in order from the object side. The refractive index n1 of the meniscus lens L11 to a d-line satisfies a condition n1>1.7.

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 a magnification of about 100 times and a numerical aperture (hereinafter, referred to as "NA") of about 0.9, and particularly to an achromat-class microscope objective.

[0002]

2. Description of the Related Art An achromat class microscope objective lens having a magnification of about 100 times is disclosed in Japanese Patent Application Laid-Open No. 59-292.
A lens and the like disclosed in Japanese Patent Application Laid-Open No. 16-216 are known.

[0003]

SUMMARY OF THE INVENTION In microscopic observation,
When observing the bottom of the concave portion of the test sample, a working distance longer than the depth of the concave portion is required. In addition, when any environmental change is applied to the sample from the outside, for example, when an electric field or a magnetic field is applied, or when cooling or heating is performed, a long working distance is required to attach various devices for these. . The lens disclosed in JP-A-59-29216 has a large NA of 0.95, but does not have good operability during observation because the working distance is relatively short. In particular, N
A high-magnification objective lens in which A is larger than 0.9 and has a magnification of about 100 times is problematic because the working distance is extremely short.

The present invention has been made in view of the above problems, and has a large NA of about 0.9, a long working distance, and a microscope objective lens having a magnification of about 100, particularly an achromat class microscope objective lens. The purpose is to provide.

[0005]

In order to solve the above problems, the present invention provides, in order from the object side, a first lens group composed of a positive meniscus lens component having a concave surface facing the object side, and a concave surface facing the object side. Second lens composed of positive meniscus lens component
A lens group, a third lens group including three cemented lenses of a positive lens component, a negative lens component, and a positive lens component, a fourth lens group having a positive refractive power, a negative lens component, and a positive lens component. The fifth lens group includes a negative lens component and three cemented lenses, and the sixth lens group has negative refractive power.

It has a magnification greater than about 40 times and has a high NA
In the microscope objective lens described above, the radius of curvature of the lens component closest to the object side on the image side satisfies the aplanatic condition, so that spherical aberration is aberration-free and a positive refractive power is obtained. Is common. Since the positive refractive power of the lens having such a configuration is very large, it is a basic lens configuration that is indispensable for efficiently obtaining high magnification without aberration.

Further, by making the radius of curvature of the object-side lens surface of the lens component closest to the object side negative, that is, by turning the concave surface toward the object side, light rays are gently refracted by the lens surface. For this reason, it is a configuration indispensable for preventing a large aberration generated due to a sharp bending of a light beam and efficiently obtaining a negative Petzval value.

At this time, if the absolute value of the radius of curvature of the concave surface is equal to the on-axis distance d0 from the object to the concave surface, a light ray emitted from the on-axis object enters the concave surface perpendicularly. Therefore, light rays emitted from the on-axis object pass through the concave surface without generating aberration. On the other hand, when performing oblique illumination with a metal microscope or the like, light rays incident perpendicularly or almost perpendicularly to the lens surface cause flare. For this reason, if the use of falling illumination is assumed,
The above-mentioned normal incidence condition is not used.

In the present invention, it is desirable to satisfy the following conditional expressions (1) and (1): n1> 1.7. Here, n1 is the first
The d-line of the positive meniscus lens L11 of the lens group G1 (λ =
587.56 nm).

The conditional expression (1) defines an appropriate range of the refractive index of the positive meniscus lens L11 of the first lens group G1. By increasing the refractive index of the positive meniscus lens L11, it is possible to reduce the curvature of the lens on the image side, thereby preventing the occurrence of various aberrations. Further, the divergent refracting power of the concave lens surface on the image side is strengthened, the negative Petzval sum is increased, and a flat image surface can be maintained. When the value goes below the lower limit of conditional expression (1), various aberrations occur largely, and the flatness of the image plane cannot be maintained.

It is preferable that the present invention satisfies the following conditional expressions (2) and (2): 1.25 × d0 <| r1 | <2.25 × d0. Here, d0 is a positive meniscus lens component L11 of the first lens group G1 from the object.
And r1 represent the radius of curvature of the object side lens surface of the positive meniscus lens component L11 of the first lens group G1.

Conditional expression (2) defines an appropriate range of the radius of curvature of the object-side lens surface of the positive meniscus lens component L11 of the first lens group G1. When the value exceeds the upper limit of conditional expression (2), the Petzval sum becomes larger than an appropriate value, and it becomes difficult to secure the flatness of the image surface. Conversely, when the value goes below the lower limit of conditional expression (2), the radius of curvature r1 and the distance d0 from the object to the first surface of the lens become close, and a large flare occurs. It becomes inappropriate.

Further, the present invention provides the following conditional expression (3),
(4), (3) f3> 0 (4) It is desirable that each of f5> 0 is satisfied. Here, f3 represents the focal length of the third lens group G3, and f5 represents the focal length of the fifth lens group G5.

Conditional expression (3) defines an appropriate range of the focal length of the third lens group G3, and conditional expression (4) defines an appropriate range of the focal length of the fifth lens group G5.

In the first lens group G1 and the second lens group G2, chromatic aberration correction is not performed, and spherical aberration and coma are suppressed to a minimum. However, since the spherical aberration and the like are not corrected in the first and second lens groups, the subsequent third lens group G3 is formed as a three-piece cemented lens including a positive biconvex lens component, a negative biconcave lens component, and a positive biconvex lens component. , Spherical aberration and the like are corrected.

Similarly, in the fifth lens group G5, three cemented lenses including a negative biconcave lens, a positive biconvex lens, and a negative concave lens are arranged to correct spherical aberration and the like. Such aberration correction can be performed by using a two-element laminated lens having a negative refractive power on the surface of the laminated lens, but more preferably, by using a three-element laminated lens, the chromatic aberration, particularly the secondary spectrum, is reduced. Can be effectively corrected.

The smaller the absolute value of the radius of curvature of the bonding surface becomes, the larger the correction amount of the various aberrations becomes. If the absolute value of the radius of curvature of the bonding surface becomes smaller than a certain value, the focal length of the lens group becomes negative. Become. However, the first lens group G
Since it is preferable to converge light rays from the first to fifth lens groups G5 without sharply bending them, the third lens group G5
Third, it is desirable that the focal length of the fifth lens group G5 is also positive. Also, when the absolute value of the radius of curvature of the bonding surface is small, manufacturing becomes difficult, which leads to an increase in manufacturing cost.

Further, the present invention provides the following conditional expression (5),
(6), (5) ν _3p > 65 (6) It is desirable to satisfy each condition of ν _5p > 65. Here, ν _3p represents the Abbe number of the positive lens component in the third lens group G3, and ν _5p represents the Abbe number of the positive lens component in the fifth lens group G5.

Conditional expressions (5) and (6) define a range of an appropriate Abbe number for correcting chromatic aberration. If the lower limit of conditional expressions (5) and (6) is not reached, chromatic aberration cannot be satisfactorily corrected.

In the present invention, it is preferable that the sixth lens group G6 includes a negative lens component and a positive lens component, and satisfy the following conditional expressions (7) and (7): ν _6n −ν _6p > 20. . Here, ν _6n represents the Abbe number of the negative lens component of the sixth lens group, and ν _6p represents the Abbe number of the positive lens component of the sixth lens group.

Conditional expression (7) defines an appropriate Abbe number range for correcting chromatic aberration. If the lower limit of conditional expression (7) is not reached, chromatic aberration, especially chromatic aberration of magnification, cannot be corrected well.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, numerical embodiments of the present invention will be described with reference to the accompanying drawings. (First Embodiment) FIG. 1 is a diagram showing a lens configuration of a microscope objective according to a first embodiment of the present invention. A first lens group G1 including, in order from the object side, one meniscus lens L11 having a positive refractive power with the concave surface facing the object side;
A second lens group G2 including one meniscus lens L21 having a positive refractive power with the concave surface facing the object side; a positive biconvex lens L31; a negative biconcave lens L32; and a positive biconvex lens L3
A third lens group G3 composed of three cemented lenses obtained by combining the third lens G3, a fourth lens group G4 composed of a lens L41 having a positive refractive power, a negative lens L51, a positive biconvex lens L52, and a negative lens L53. A fifth lens group G5 including three combined laminated lenses and a sixth lens group G6 having a negative refractive power are provided.

Table 1 below shows data values of the present embodiment.
In the table, f represents the focal length of the microscope objective lens, NA represents the numerical aperture, β represents the magnification, d0 represents the distance from the object to the first surface of the lens, and WD represents the working distance. The surface number is the order of the lens surfaces counted from the object side, r is the radius of curvature of the lens, d is the air gap between the lens surfaces, and nd and νd are d
The refractive index and Abbe number for the line (λ = 587.56 nm) are shown, respectively. Note that the same reference numerals as in the first embodiment are used in the specification values of all the embodiments below.

[0024]

Table 1 f = 2mm NA = 0.9 β = -100 d0 = 2.18 WD = 1.0mm Surface number rd nd νd 1 -3.250 2.85 1.8830 40.80 2 -3.817 0.10 1.0000 3 -29.726 3.35 1.4978 85.52 4 -7.818 0.15 1.0000 5 53.707 3.65 1.4978 85.52 6 -12.262 1.00 1.6716 38.80 7 18.902 6.35 1.4343 95.00 8 -11.557 0.15 1.0000 9 61.690 2.80 1.6030 65.42 10 -35.099 0.20 1.0000 11 33.500 1.30 1.6127 44.41 12 8.303 6.65 1.4339 95.25 13 -15.41 1.20 1.6127 44. -38.479 25.50 1.0000 15 -37.675 1.40 1.8467 23.78 16 -6.698 0.90 1.6516 58.50 17 6.562 (Conditional value) (1) n1 = 1.8830 (2) | r1 | = 3.250 (3) f3 = 43.96 (4) f4 = 720.26 ( 5) ν _3p = 82.52, 95.00 (6) ν _5p = 95.25 (7) ν _6n −ν _6p = 34.72

FIG. 2 is a diagram showing various aberrations of the present embodiment.
In each aberration diagram, d is d-line (wavelength 587.6 nm), C
Is C line (wavelength 656.3 nm), F is F line (wavelength 48
6.1 g) and g indicate the g-line (wavelength 435.8 nm). In the figures showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Note that the same reference numerals as in the first embodiment are used in the aberration diagrams of all the embodiments below. As can be seen from the drawing, various aberrations are satisfactorily corrected in the present embodiment.

In this embodiment, a working distance of 1 mm or more is secured, and the fourth lens group G4 is connected to one biconvex lens L41.
, And various aberrations are sufficiently corrected.

(Second Embodiment) FIG. 3 is a diagram showing a lens configuration of a microscope objective according to a second embodiment of the present invention. In order from the object side, a first lens group G1 including one meniscus lens L11 having a positive refractive power with a concave surface facing the object side, and one meniscus lens having a positive refractive power with a concave surface facing the object side Second lens group G composed of L21
2, a third lens group G3 including three cemented lenses in which a positive biconvex lens L31, a negative biconcave lens L32, and a positive biconvex lens L33 are combined, and a fourth lens group G4 including a lens L41 having a positive refractive power. A fifth lens group G5 composed of three cemented lenses in which a negative lens L51, a positive biconvex lens L52, and a negative lens L53 are combined, and a sixth lens group G6 having negative refractive power.

Table 2 below shows data values of the present embodiment.

[0029]

[Table 2] f = 2 mm NA = 0.9 β = −100 d0 = 2.18 WD = 1.0 mm Surface number rd nd νd 1 -3.250 2.85 1.8830 40.80 2 -3.841 0.10 1.0000 3 -29.726 3.35 1.4978 85.52 4 -7.690 0.15 1.0000 5 53.646 3.55 1.4978 85.52 6 -12.702 1.00 1.6716 38.80 7 18.104 6.50 1.4343 95.00 8 -11.631 0.15 1.0000 9 53.000 2.80 1.5691 71.31 10 -36.411 0.20 1.0000 11 30.675 1.30 1.6127 44.41 12 8.360 7.00 1.4339 95.25 13 -16.41 1.20 1.6127 -44.393 24.90 1.0000 15 -48.938 1.40 1.9229 18.90 16 -9.182 0.90 1.7130 53.96 17 7.344 (Conditional value) (1) n1 = 1.8830 (2) | r1 | = 3.250 (3) f3 = 44.41 (4) f4 = 544.98 ( 5) ν _3p = 82.52, 95.00 (6) ν _5p = 95.25 (7) ν _6n −ν _6p = 35.06

FIG. 4 is a diagram showing various aberrations of this embodiment.
As can be seen from the drawing, various aberrations are satisfactorily corrected in the present embodiment.

In this embodiment, a working distance of 1 mm or more is secured, and the fourth lens group G4 is connected to one biconvex lens L41.
, And various aberrations are sufficiently corrected.

Since the microscope objective lens according to the above embodiment is of the infinity type correction type, for example, the following Table 3 is used.
Is used together with the imaging lens which has the following specification values.

[0033]

[Table 3] Surface number r d nd νd 1 75.04300 5.10 1.62280 57.03 2 -75.04300 2.00 1.74950 35.19 3 1600.58000 7.50 4 50.25600 5.10 1.66755 41.96 5 -84.54100 1.80 1.61266 44.40 6 36.911

[0034]

As described above, according to the present invention, a microscope objective lens having a relatively long working distance, a NA of about 0.9, and a high magnification (about 100 times), particularly an achromat class microscope objective lens, is provided. Can be obtained.

[Brief description of the 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 diagram illustrating various aberrations of the microscope objective lens according to the first example.

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

FIG. 4 is a diagram illustrating various aberrations of the microscope objective lens according to the second example.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G5 Fifth lens group G6 Sixth lens group

Claims (4)

[Claims] 1. A first lens group consisting of a positive meniscus lens component having a concave surface facing the object side, and a second lens group consisting of a positive meniscus lens component having a concave surface facing the object side, in order from the object side. A third lens group including three cemented lenses of a positive lens component, a negative lens component, and a positive lens component, a fourth lens group having a positive refractive power, a negative lens component, a positive lens component, and a negative lens component. And a sixth lens group having a negative refractive power. The positive meniscus lens component of the first lens group is d-line (λ = 587.56 nm). A microscope objective lens, which satisfies a condition of n1> 1.7, where n1 is a refractive index. 2. An axial distance from the object to the object side lens surface of the positive meniscus lens component of the first lens group is d0, and a curvature of an object side lens surface of the positive meniscus lens component of the first lens group. 2. The microscope objective lens according to claim 1, wherein when the radius is defined as r1, a condition of 1.25 × d0 <| r1 | <2.25 × d0 is satisfied. 3. The microscope objective lens according to claim 1, wherein when the Abbe number of the positive lens component in the third lens group is ν _3p , the condition of ν _3p > 65 is satisfied. . 4. The optical system according to claim 1, wherein when the Abbe number of the positive lens component in the fifth lens group is ν _5p , a condition of ν _5p > 65 is satisfied. The microscope objective described.