JP2001147377A - Microscope objective lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microscope objective lens system where a nitrate material having durability and sufficient transmission factor with respect to the light of two wavelengths of an ultraviolet region and a near-infrared region is used and an axial chromatic difference and various aberrations are corrected satisfactorily, especially the microscope objective lens system of an achromat class. SOLUTION: A meniscus lens L1, whose concave is turned to an object-side and at least one of joint lenses L3 and L4 are installed in the order from the object-side. A first lens group G1 having positive refraction force as a whole and at least one of joint lenses L5 and L6 are installed. A second lens group G2 having positive refraction force as a whole and a third lens group G3 having negative refraction force are installed. Then, prescribed conditions 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 system for a microscope, and more particularly to a two-color achromatic microscope having a magnification of about 100 times and correcting chromatic aberration in two wavelength regions of ultraviolet light and near-infrared light. It relates to an objective lens system.

[0002]

2. Description of the Related Art Conventionally, as an objective lens for an ultraviolet region, a lens system disclosed in Japanese Patent Application Laid-Open No. 11-167067 for laser processing, a high-magnification objective lens system for general ultraviolet fluorescence, and the like are known. .

[0003]

The objective lens system of the prior art is a fourth harmonic (.lambda. = 266n) of a YAG laser used as a light source for laser processing in recent years.
m) or the third harmonic (λ = 352 nm), or the like, and can be used for ultraviolet light. However, when the same objective lens system is used for near-infrared light, the following disadvantages occur. For example, in a microscope equipped with an automatic focus detection device that performs autofocus on a test surface, near-infrared light is projected onto the test surface to be observed, and a focus position is detected based on reflected light from the test surface. In this case, in the conventional microscope objective lens system, the focal position of near-infrared light and the focal position of ultraviolet light do not match. For this reason, when observation is performed using ultraviolet light in a state in which focus is achieved by near-infrared light, an out-of-focus image is observed, and it is difficult to accurately focus on the surface to be inspected.

Further, when the objective lens system is used in the ultraviolet region, depending on the glass material constituting the lens system, a sharp decrease in transmittance or solarization occurs. For this reason, there are restrictions on the materials constituting the lens system used in the ultraviolet region. Furthermore, since the adhesive material used for the cemented surface of the cemented lens is deteriorated by the light in the ultraviolet region, the adhesive material used is limited.

Therefore, using a limited glass material, the image plane of the wavelength used for observing the surface to be inspected and the wavelength used for automatic focus detection of the surface to be inspected are made substantially coincident with each other while the image plane is kept high. It is extremely difficult to realize a microscope objective lens system which has a high numerical aperture, high magnification, and satisfactorily corrects axial chromatic aberration of two wavelengths.

The present invention has been made in view of the above problems, and uses a glass material having durability and a sufficient transmittance for light of two wavelengths, an ultraviolet region and a near-infrared region. It is an object of the present invention to provide a microscope objective lens system in which chromatic aberration and various aberrations are well corrected, particularly an achromat-class microscope objective lens system.

[0007]

In order to solve the above problems, the present invention comprises, in order from the object side, a meniscus lens having a concave surface facing the object side and at least one cemented lens. A first lens group having a refractive power, a second lens group having at least one cemented lens and having a positive refractive power as a whole, and a third lens group having a negative refractive power as a whole; And a microscope objective lens system characterized by satisfying the following. (1) 4 <| f1 / f | <4.8 (2) 3 <| f3 / f | <6 (3) 0.6 <| f3 / φ3 | <1.1 where f1 is the first value. The focal length of the lens group, f3 represents the focal length of the third lens group, f represents the focal length of the microscope objective lens system, and φ3 represents the effective diameter of the lens component closest to the object side of the third lens group.

Conditional expression (1) defines conditions for ensuring a sufficient working distance and not deteriorating the residual secondary spectrum of axial chromatic aberration. If the value exceeds the upper limit of conditional expression (1), the working distance becomes longer, but the residual secondary spectrum of axial chromatic aberration deteriorates, which is not preferable. Conversely, if the value is below the lower limit of conditional expression (1), a sufficient working distance cannot be obtained, and workability when exchanging a sample is deteriorated.

The conditional expression (2) defines an appropriate range of the focal length of the third lens unit having a negative refractive power.
When the value exceeds the upper limit of conditional expression (2), the negative refractive power of the third lens group becomes too weak, and the Petzval sum is insufficiently corrected, so that the field curvature becomes worse. If the refractive power of each lens surface is changed in order to improve this, spherical aberration and coma on the short wavelength side will deteriorate, and sufficient aberration correction cannot be performed. On the other hand, if the lower limit of conditional expression (2) is not reached, the negative refractive power of the third lens group becomes too strong, so that the Petzval sum and the spherical aberration and coma on the short wavelength side cannot be sufficiently corrected.

Condition (3) defines an appropriate range of the ratio of the effective diameter of the lens closest to the object side among the lenses constituting the third lens group to the focal length of the third lens group having negative refractive power. Has been stipulated. If the upper limit of conditional expression (3) is exceeded, the effective diameter of the lens that is closest to the object side among the lenses that form the third lens group will be too large, and the spherical aberration will worsen. If the refractive power of each lens surface is changed in order to improve this, the curvature of field deteriorates, and it becomes impossible to perform sufficient aberration correction. Conversely, if the lower limit of conditional expression (3) is not reached, the effective diameter of the lens constituting the third lens group closest to the object side is too small, and the negative refractive power of the third lens group is reduced. It will be too weak. For this reason, axial chromatic aberration, spherical aberration, and coma cannot be sufficiently corrected.

In the present invention, the second lens group includes:
It is desirable to have at least three groups of cemented lenses including at least one cemented surface.

In the present invention, the third lens group includes:
Desirably, the lens unit includes at least one cemented lens having at least one cemented surface and at least one cemented lens having at least two cemented surfaces.

In the present invention, the first lens group includes:
At least one or more convex meniscus lens, one or more cemented lenses having at least one cemented surface,
Desirably, it is composed of at least one single lens.

In the present invention, it is preferable to use a large number of cemented lenses as described above. At this time, in order to achieve a state in which there is almost no axial chromatic aberration or lateral chromatic aberration by the objective lens system alone, the cemented lens in the first lens group and the second lens group is achromatized and the third lens group is achromatic. It is preferable that the cemented lens be colored. Therefore, the Abbe number of the positive lens of the cemented lens in the first lens group and the second lens group is configured to be larger than the Abbe number of the negative lens, and the cemented lens of the third lens group is It is preferable that the Abbe number of the positive lens be smaller than the Abbe number of the negative lens.

In the present invention, it is preferable that each of the lenses is made of at least one of fluorite and quartz. Conventionally, it is well known that a cemented lens is made of at least two or more types of glass materials in order to correct chromatic aberration. In particular, in the objective lens system that transmits ultraviolet light and near-infrared light as in the present invention, fluorite, quartz,
240 nm wavelength of barium fluoride, lithium fluoride, etc.
From the vicinity to around 800 nm, it is preferable to use only a material having a sufficient transmittance. Here, ultraviolet light is
Light having a wavelength of about 200 nm to about 400 nm, particularly 2
It refers to light of 66 nm.

[0016]

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 lens system according to a first embodiment of the present invention. Meniscus lens L1 having a concave surface facing the object side in order from the object side
A first lens having a positive refractive power as a whole having a lens L2 and a cemented lens composed of lenses L3 and L4.
A lens group G1, a cemented doublet composed of lenses L5 and L6, a cemented triplet composed of lenses L7, L8 and L9, and a cemented triplet composed of lenses L10, L11 and L12.
It has a cemented lens, a cemented lens composed of lenses L13 and L14, a second lens group G2 having a positive refractive power as a whole, a single lens L15, and lenses L16, L17 and L18. Three cemented lens and lens L
A third lens group G3 having a cemented doublet composed of lenses L19 and L20 and having a negative refractive power.

Table 2 below shows values of specifications of the microscope objective lens system according to the present embodiment. In the table, f is the focal length of the microscope objective lens system, NA is the numerical aperture, β is the magnification, and W.F.
D. Indicates a working distance. The numbers at the left end represent the order of the lens surfaces counted from the object surface, R represents the radius of curvature of the lens surfaces, and d represents the distance between the lens surfaces.
The unit such as length and radius of curvature is mm. Also,
Table 1 shows the refractive index of the glass material. Here, n226, n78
0 indicates the refractive index for wavelengths λ = 266 nm and 780 nm, respectively. Further, ν represents the Abbe number calculated based on the following equation (A), based on the wavelength λ = 266 nm of each lens. (A) ν = (n266-1) / (n266-n780)

[0018]

[Table 1] Material n266 n780 ν Quartz 1.499715 1.453715 10.863 Fluorite 1.462076 1.430753 14.752

[0019]

[Table 2] (Values Corresponding to Conditional Expressions) (1) f1 / f = 4.069 (2) f3 / f = 5.841 (3) f3 / φ3 = 1.031 FIG. 2 shows a microscope objective lens system according to the present embodiment. It is a figure showing various aberrations. In the spherical aberration diagram, the solid line is 266n.
m and the broken line show the aberration at 780 nm. In the astigmatism diagram, a broken line indicates a meridional image plane, and a solid line indicates a sagittal image plane. The same reference numerals as in the present embodiment are used in the various aberration diagrams in all the embodiments below. As is apparent from FIG.
It turns out that it has good optical performance with respect to light of two wavelengths, 66 nm and 780 nm.

(Second Embodiment) FIG. 3 is a view showing a lens configuration of a microscope objective lens system according to a second embodiment of the present invention. A first lens group having, in order from the object side, a meniscus lens L1 having a concave surface facing the object side, a single lens L2, and a doublet cemented lens composed of lenses L3 and L4, and having a positive refractive power as a whole G1, a cemented lens composed of lenses L5 and L6, a cemented lens composed of lenses L7, L8 and L9, and lenses L10, L11 and L1
2 and three lenses L13 and L14
And a second lens group G2 having a positive refractive power as a whole, and lenses L15 and L1.
6 and lenses L17 and L18
And a third lens group G3 having a negative refractive power.

Table 3 below shows data values of the microscope objective lens system according to the present embodiment.

[0022]

[Table 3] (Values Corresponding to Conditional Expressions) (1) f1 / f = 4.745 (2) f3 / f = 3.411 (3) f3 / φ3 = 0.699 FIG. 4 shows a microscope objective lens system according to the present embodiment. It is a figure showing various aberrations. As is clear from the figure, it is understood that the present example has good optical performance with respect to light having two wavelengths of 266 nm and 780 nm.

Further, since the microscope objective lens according to each of the above embodiments is of the infinity type correction type, it is used, for example, together with an imaging lens whose specification values are listed in Table 4 below. FIG. 5 shows a lens configuration of the imaging lens.

[0024]

[Table 4] Surface number Rd Material 1 -30.630 2.00 Quartz 2 2406.000 5.00 Fluorite 3 -39.100 1.00 4 417.400 5.00 Quartz 5 -51.920

[0025]

As described above, according to the present invention,
Various aberrations are corrected satisfactorily, especially excellent in axial chromatic aberration characteristics,
An achromat-class microscope objective lens that can be used in the ultraviolet wavelength region and the near-infrared wavelength region can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens 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 lens 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.

FIG. 5 is a diagram illustrating a lens configuration of an imaging lens.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group L1 to L20 Each lens component

Claims (5)

[Claims] 1. A first lens group having a meniscus lens having a concave surface facing the object side and at least one cemented lens in order from the object side, and having a positive refractive power as a whole, and at least one cemented lens. A microscope objective lens system comprising: a second lens group having a positive refractive power as a whole; and a third lens group having a negative refractive power, and satisfying the following conditions. 4 <| f1 / f | <4.8 3 <| f3 / f | <6 0.6 <| f3 / φ3 | <1.1 where f1 is the focal length of the first lens group, and f3 is the The focal length of the third lens group, f represents the focal length of the microscope objective lens system, and φ3 represents the effective diameter of the lens component closest to the object in the third lens group. 2. The microscope objective lens system according to claim 1, wherein the second lens group includes three or more cemented lenses including at least one cemented surface. 3. The third lens group includes at least one cemented lens including at least one cemented surface, and at least one cemented lens including at least two cemented surfaces. 3. A microscope objective lens system according to claim 1, wherein 4. The first lens group includes at least one or more convex meniscus lenses, at least one or more cemented lenses having at least one or more cemented surfaces, and one or more single lenses. The microscope objective lens system according to any one of claims 1 to 3, wherein: 5. The microscope objective lens system according to claim 1, wherein each lens is formed of at least one of fluorite and quartz.