JP2000249926A - Microscope objective lens and microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-magnification microscope objective lens which is constituted so that flare is reduced and the aberration of an exit pupil is excellently corrected even when the pupil is made to near to an object side, whose NA is large and whose operating distance is long. SOLUTION: This objective lens is provided with a 1st lens group G1 having positive refractive power, a 2nd lens group G2 having negative refractive power, an object-side lens G21 and an imageside lens G22 and being the joined meniscus lens whose convex surface faces an object side, a 3rd lens group G3 having negative refractive power, an objet side lens G31 and an image-side lens G32 and being the joined meniscus lens whose concave surface faces an image side and a 4th lens group G4 having positive refractive power in turn from the object side. When the Abbe number of the group G1 is defined as (ν1), the radius of the curvature of the object-side surface thereof is defined as (r1), that of the image-side surface is defined as (r2), the refractive index of the lens G21 of the group G2 is defined as (n2), the radius of the curvature of the most object side thereof is defined as (r3) and the focal distance of a whole lens system at a (d) line is defined as (f), the conditions of 60<=ν1<=70, -0.06<=(r2+r1)/(r2-r1)<=0.06 and 5.9<=n2.f/r3<=6.4 are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a microscope objective and a microscope, and more particularly to a low-magnification microscope objective and a microscope equipped with such an objective.

[0002]

2. Description of the Related Art An objective lens of a microscope is required to have various conditions in addition to good correction of various aberrations.
For example, if the working distance is short, operability is deteriorated, and there is a practical problem even if aberrations are well corrected. In an industrial microscope represented by a metal microscope, a sample is illuminated by so-called epi-illumination. At the time of bright field observation, since the objective lens also serves as a condenser lens of the illumination system, the objective lens must be configured to have a small flare. If the flare is a phenomenon in which a part of light is reflected and scattered in the optical system, the contrast is lowered, and even if the aberration is corrected well, there is a practical problem. In particular, with a low-magnification objective lens, it is difficult to remove flare from a surface close to the object. In order to remove flare, it is necessary to have a certain refractive power. However, if the refractive power is increased on a surface close to the object, it becomes difficult to correct aberrations. Further, if the number of constituent lenses is increased for aberration correction, the air surface increases and flare increases. Therefore, in a conventional low-magnification objective lens, the number of lens elements is as small as possible, and
It was necessary to have a certain level of refractive power.

[0003]

According to the conventional microscope objective lens described above, the number of constituent lens elements is as small as possible, and all the lens elements are made to have a certain level of refractive power. However, the degree of freedom in the position of the exit pupil is reduced, and the position is often shifted from the exit pupil of the high-magnification objective lens. Although it was possible to bring the position of the exit pupil closer to the object side, the chromatic aberration of the pupil and the spherical aberration of the pupil increased, which was a practical problem.

Accordingly, the present invention provides an objective lens of a low-magnification microscope and a microscope equipped with such an objective lens, in which the flare is small and the aberration of the pupil is well corrected even when the exit pupil is close to the object side. It is intended to provide.

[0005]

In order to achieve the above object, a microscope objective according to the first aspect of the present invention has a first objective lens having a positive refractive power in order from the object side as shown in FIG. A second lens group G, which is a cemented meniscus lens having a negative refractive power and having an object-side lens G21 and an image-side lens G22 and having a convex surface facing the object side;
A third lens group G3 which is a cemented meniscus lens having a negative refractive power and having an object side lens G31 and an image side lens G32 and having a convex surface facing the image side; and a fourth lens group having a positive refractive power. A lens group G4; the Abbe number of the first lens group G1 is ν1, the radius of curvature of the object-side surface of the first lens group G1 is r1, and the radius of curvature of the image-side surface of the first lens group G1 is r.
2. The refractive index of the object side lens G21 of the second lens group G2 is n2, and the radius of curvature of the second lens group G2 on the most object side is r.
3. When the focal length at d-line of all lens systems including the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 is f, 60 ≦ ν1 ≦ 70 (1) −0.06 ≦ (r2 + r1) / (r2-r1) ≦ 0.06 (2) 5.9 ≦ n2 · f / r3 ≦ 6.4 (3) It is characterized by doing. Where n2 · f /
The reason why r is multiplied by f is to make dimensionless (normalization). The reason for multiplying or dividing by f in other conditional expressions is the same.

[0006] With this configuration, for example, crown glass is used for the first lens group to make the Abbe number larger than 60, so that dispersion is suppressed. Further, since the Abbe number is made smaller than 70, glass having a high refractive index is used. As a result, the radius of curvature of the lens is not made too small to have the same refractive power, and spherical aberration can be suppressed. Further, the upper limit of (r2 + r1) / (r2-r1) is set to 0.06 and the lower limit is set to -0.06, so that the flare is not made too large. Further, since n2 · f / r3 is maintained at a value larger than 5.9, flare can be suppressed, and since it does not exceed 6.4, the position of the exit pupil can be placed on the object side.

In the above microscope objective lens, the focal length of the first lens group G1 is set to f1.
In this case, it is preferable to satisfy the following condition: 0.4 ≦ f1 / f ≦ 0.5 (4)

In this case, since the lower limit of the refractive power of the first lens unit is set to 0.4, it is easy to correct the pupil aberration, and the upper limit is set to 0.5, so that flare can be suppressed.

Further, as described in claim 3, claim 1
Alternatively, in the microscope objective lens according to claim 2, the refractive index of the image-side lens G22 of the second lens group G2 is n3, and the radius of curvature of the junction surface between the object-side lens G21 and the image-side lens G22 of the second lens group G2. When r is set to r4, it is preferable to satisfy the following condition: 0.43 ≦ | (n3-n2) · f / r4 | ≦ 0.87 (5) In this case, since the upper limit of the refractive power of the cemented surface of the second lens group is set to 0.87, the correction of coma is easy, and the lower limit is set to 0.43.
Therefore, it is easy to correct spherical aberration, chromatic aberration, pupil chromatic aberration, and pupil spherical aberration generated in the first lens group.

[0010] Further, as described in claim 4, claim 1 is provided.
In the microscope objective lens according to any one of claims 3 to 3, the refractive index of the image-side lens G22 of the second lens group G2 is set to n.
When it is set to 3, it is preferable to satisfy the following condition: 1.78 ≦ n3 (6). In this case, the lower limit of the refractive index of the image side lens of the second lens group is set to 1.7.
Since it is 8, the Petzval sum does not become too negative.

[0011] Further, as described in claim 5, claim 1 is
In the microscope objective lens according to any one of claims 4 to 4, when the distance between the second lens group G2 and the third lens group G3 is d23, 0.14 ≦ d23 / f ≦ 0.16 ... ( It is preferable to satisfy condition 7). In this case, since the lower and upper limits of the distance between the second lens group and the third lens group are suppressed, the correction of the image plane does not become too difficult.

In order to achieve the above object, a microscope according to a sixth aspect of the present invention includes a microscope objective lens L1 according to any one of the first to fifth aspects, for example, as shown in FIG. An imaging lens L2 for imaging light from the object OB through the microscope objective lens L1.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding members are denoted by the same or similar reference numerals, and duplicate description is omitted.

FIG. 1 is a side sectional view of a microscope objective lens according to an embodiment of the present invention. The microscope objective lens includes, in order from the object OB side in the figure, a convex lens G1 as a first lens group, a cemented meniscus lens G2 as a second lens group, a cemented meniscus lens G3 as a third lens group, and a fourth lens The convex lenses G4 as a group are arranged.

The convex lens G1 may be a combination of a plurality of lenses, but typically comprises one convex lens as shown in the figure. Joint meniscus lens G2
Is a lens group having a negative refractive power as a whole and having a convex surface facing the object OB side, in which the object side lens G21 and the image side lens G22 are joined. Joint meniscus lens G
Reference numeral 3 denotes a lens group in which the object-side lens G31 and the image-side lens G32 are cemented and have a negative refractive power as a whole and have a convex surface facing the image IG side. The convex lens G4 may be a combination of a plurality of lenses, but typically includes one convex lens as shown in the figure.

Here, the meaning of the expressions (1) to (7) will be described. Condition 1 defines the Abbe number of the lens G1 closest to the object. One of the objects of the present invention is to reduce flare, but for that purpose, the lens G1 needs to have a large refractive power. Further, it is preferable to make the exit pupil closer to the object side. But large power (refractive power) with convex lens
Therefore, the chromatic aberration generated in the lens G1 increases. The longer the working distance, the greater the chromatic aberration. Therefore, it is preferable to use, for example, crown glass having a small dispersion as the lens G1. However, if a glass material having a small dispersion is selected, when the same power is given, the radius of curvature of the lens becomes small and a large spherical aberration is generated, so that it is difficult to correct it. In particular, it becomes difficult to correct spherical aberration of the pupil. Lens G1
Is set to an Abbe number that satisfies the conditional expression (1), appropriate dispersion is achieved, and flare can be reduced.

Here, the flare will be described. Flare is a phenomenon in which a part of light is reflected and scattered in an optical system. For example, in a metallographic microscope, epi-illumination is used to observe a sample that does not transmit light, such as a silicon wafer to be inspected. In epi-illumination, the objective lens also serves as a condenser lens. In such a case, since the illumination light passes through the objective lens, the flare on the surface of the lens constituting the objective lens is combined with the observation light, which causes a decrease in contrast. In particular, when a light beam enters the lens surface perpendicularly, the reflected light passes through the same path as the observation light, so that flare increases. For this reason, it is necessary that each surface of the lens element has a certain level of refracting power, and measures for reducing flare and correcting aberrations are generally incompatible.

Conditional expression (2) defines the shape of the lens G1. If the radius of curvature exceeds the upper or lower limit of this equation, the flare becomes too large.

Conditional expression (3) defines the power of the surface of the second lens group G2 closest to the object. If this power exceeds the lower limit of conditional expression (3), the flare becomes too large, and if it exceeds the upper limit, the exit pupil will be on the image side.

Conditional expression (4) defines the power of the lens G1. If the power of the lens G1 exceeds the lower limit of the conditional expression (4), it becomes difficult to correct pupil aberration, and if it exceeds the upper limit, flare increases.

Conditional expression (5) defines the power of the cemented surface of the second lens group G2. This surface is the lens G1
This has the effect of correcting the spherical aberration, chromatic aberration and pupil chromatic aberration generated in the above, and also corrects the image plane. If the power of the second lens group G2 exceeds the upper limit of the conditional expression (5), it is advantageous for correcting the aberration, but it is difficult to correct the coma. Conversely, if the lower limit is exceeded, aberration correction will be insufficient.

Conditional expression (6) defines the refractive index of the image side lens G22 of the second lens group. The objective lens according to the embodiment of the present invention belongs to a so-called Gauss type. The Gauss type is characterized by a small Petzval sum, and is often used in a plan objective lens whose image plane is corrected. If a glass material having a low refractive index such that the refractive index of the image-side lens G22 exceeds the lower limit of conditional expression (6),
The Petzval sum becomes too large in the minus direction, making it difficult to correct image plane distortion.

Conditional expression (7) defines the distance between the lens groups G2 and G3. If this interval exceeds the upper limit or the lower limit of conditional expression (7), the Petzval sum becomes plus or minus, and it becomes difficult to correct the image plane.

Table 1 (A) in FIG. 4 shows specific lens data as Example 1 in the above embodiment. Here, the surface numbers indicate the surfaces of the lens elements constituting the lens group. For example, surface 1 is the object-side surface of convex lens G1, surface 2
Denotes the image-side surface. r is the radius of curvature of the surface indicated by each surface number of the lens, and takes a positive value when it is convex on the object side and a negative value when it is concave on the object side. d is the distance between the surfaces. For example, the thickness of the lens G1 is 2.8 mm because it is the distance between the surfaces 1 and 2. n is the refractive index of the lens material between the surfaces. Here, the refractive index is a value at the d-line (λ = 587.56 nm) unless otherwise specified. In the table (A), for example, the refractive index of the lens G1 is between the surface 1 and the surface 2, so that it is 1.603.
νd indicates the Abbe number of a lens which is a component of the microscope objective lens.

The table in FIG. 5 shows the values corresponding to the conditions of the microscope objective lens of the embodiment. The condition number is defined by the above formulas (1) to
This corresponds to (7). In Example 1, as shown in Table (A), regarding Condition 1, the Abbe number ν1 is 65.4,
Equation (1) falls within the range of 60 to 70.

Regarding condition 2, the value that defines the shape of the lens group G1 is 0.05, which satisfies the conditional expression (2).

Regarding condition 3, the power of the surface of the second lens group closest to the object is 6.22, which satisfies the conditional expression (3).

Regarding condition 4, the power of the lens G1 is
0.475, which satisfies the conditional expression (4).

Regarding condition 5, the power of the cemented surface of the second lens unit is 0.446, which satisfies the conditional expression (5).

Regarding condition 6, the refractive index of the image side lens G22 is 1.797, which satisfies the conditional expression (6).

Regarding condition 7, the lenses G2 and G3
Is a dimensionless interval of 0.141, which satisfies the conditional expression (7).

Since the lens of the above embodiment does not form an image by itself, it is used in combination with an imaging lens whose side cross section and lens data are shown in FIG. 6, for example. FIG.
The aberration diagrams shown in FIG. 9 to FIG. 9 are obtained when the objective lens of the example is combined with the imaging lens of FIG.

FIG. 7 is an aberration diagram for the first embodiment.
Here, spherical aberration, astigmatism, meridional coma, and distortion are shown. In each of the figures, the solid line is the d-line (reference wavelength 587.56 nm), the broken line is the C line (wavelength 656.27 nm), and the dashed line is the F line (wavelength 486.1).
3 nm), and the two-dot chain line shows the aberration due to the g-line (wavelength 435.84 nm). As shown in this figure, the microscope objective lens of Example 1 has a relatively large NA of 0.15,
In addition, although the working distance is long, it can be seen that the aberration is corrected in a well-balanced manner.

FIG. 2 is a side sectional view of the microscope objective lens of Example 2, FIG. 4B shows lens data, and FIG. 5B shows a table.
8 shows the values corresponding to the conditions, and FIG. 8 shows the values of the resulting aberrations.
It can be seen that the aberration is corrected in a well-balanced manner as in the first embodiment.

FIG. 3 is a side sectional view of the microscope objective lens of Example 3, FIG. 4 is a table (C) showing lens data, and FIG. 5 is a table (C).
9 shows the values corresponding to the conditions, and FIG. 9 shows the values of the resulting aberrations.
It can be seen that the aberrations are well-balanced as in the first and second embodiments.

The microscope objective lens according to the above-described embodiment is suitable for use in a low-magnification microscope having a large NA of, for example, 0.15 and a long working distance of about 5 times.

FIG. 10 is a schematic side view of a microscope according to an embodiment of the present invention. In the drawing, as the objective lens L1, for example, any of the lens groups shown in FIGS. 1, 2, and 3 is used. As the imaging lens L2, for example, a lens group illustrated in FIG. 6 is used. The inspection object OB is illuminated by light falling through the objective lens L1 by an illumination optical system (not shown). The illuminated light from the inspection object OB passes through the objective lens L1.
Is guided to the image forming lens L2 via the lens and is imaged. In this microscope, since the objective lens shown in FIGS. 1 to 3 is used, an observation image with less flare, excellent contrast, and a well-corrected aberration can be obtained.

[0038]

As described above, according to the present invention, in a microscope objective lens, the Abbe number of the first lens unit, the shape of the first lens unit, the power of the surface closest to the object of the second lens unit, Since the power of the first lens group, the power of the cemented surface of the second lens group, the refractive index of the image side lens of the second lens group, and the distance between the second lens group and the third lens group are defined, the flare is small. In addition, it is possible to provide a microscope objective lens in which various aberrations of the pupil are well corrected.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a microscope objective lens of Example 1.

FIG. 2 is a side sectional view of a microscope objective lens of Example 2.

FIG. 3 is a side cross-sectional view of a microscope objective lens of Example 3.

FIG. 4 is a diagram showing a table of lens data of Examples 1, 2, and 3;

FIG. 5 is a diagram showing a table of condition corresponding values of Examples 1, 2, and 3.

FIG. 6 is a diagram showing a side cross-sectional view and a table of lens data of an imaging lens used in combination with the microscope objective lenses of Examples 1, 2, and 3.

FIG. 7 is an aberration diagram of the first embodiment.

FIG. 8 is an aberration diagram of the second embodiment.

FIG. 9 is an aberration diagram of the third embodiment.

FIG. 10 is a schematic side view of a microscope according to an embodiment of the present invention.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G21 Object-side lens of second lens group G22 Image-side lens of second lens group G31 Object-side lens of third lens group G32 Third Image side lens of lens group OB Object IM image L1 Objective lens L2 Imaging lens

Claims (6)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
A second lens group, which is a cemented meniscus lens having a negative refractive power and having an object-side lens and an image-side lens, and having a convex surface facing the object side; and an object-side lens having a negative refractive power A third lens group, which is a cemented meniscus lens having a convex surface facing the image side, and a fourth lens group having a positive refractive power; the Abbe number of the first lens group being ν1 The radius of curvature of the object-side surface of the first lens group is r1, and the radius of curvature of the image-side surface of the first lens group is r.
2. The refractive index of the object-side lens of the second lens group is n2,
The radius of curvature of the second lens unit closest to the object side is r3, and d of the entire lens system including the first lens unit, the second lens unit, the third lens unit, and the fourth lens unit.
When the focal length of the line is f, 60 ≦ ν1 ≦ 70−0.06 ≦ (r2 + r1) / (r2−r1) ≦ 0.0
6 A microscope objective lens characterized by satisfying the following condition: 5.9 ≦ n2 · f / r3 ≦ 6.4. 2. The microscope objective lens according to claim 1, wherein when a focal length of the first lens group is f1, a condition of 0.4 ≦ f1 / f ≦ 0.5 is satisfied. . 3. When the refractive index of the image-side lens of the second lens group is n3, and the radius of curvature of the junction surface between the object-side lens and the image-side lens of the second lens group is r4, 0.43 ≦ The microscope objective lens according to claim 1 or 2, wherein a condition of | (n3-n2) · f / r4 | ≦ 0.87 is satisfied. 4. The image forming apparatus according to claim 1, wherein a condition of 1.78 ≦ n3 is satisfied, where n3 is the refractive index of the image-side lens of the second lens group. The microscope objective described. 5. The condition of 0.14 ≦ d23 / f ≦ 0.16, wherein d23 is the distance between the second lens group and the third lens group. A microscope objective lens according to claim 1. 6. A microscope objective lens according to claim 1, further comprising: an imaging lens configured to image light from an object to be inspected through the microscope objective lens; microscope.