JPS60205521A - Microscope objective lens - Google Patents

Abstract

PURPOSE:To compensate the variation in aberrations with the thickness of cover glass by moving the 3nd negative lens group of the microscope objective lens consisting of three lens groups which are positive, negative, and negative in refracting power. CONSTITUTION:The objective lens consists of the 1st lens group G1 with positive refracting power, the 2nd lens group G2 with negative refractive power, and the 3rd lens group G3 with negative refracting power successively from an object side; the 2nd lens group is movable along the optical axis and -50f<f2<-10f, where f2 is the focal length of the 2nd lens group and (f) is the focal length of the whole system. The 2nd lens group G2 is moved according to variation in the thickness of a parallel plane plate P arranged between the object O and the 1st lens group G1 to compensate aberration variation.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention maintains good imaging performance even when the thickness of a microscope objective lens, particularly a parallel plane plate such as a cover glass placed on the object side, changes. The present invention relates to a possible objective lens.

(Background of the Invention) Microscope objective lenses are generally designed on the premise that the thickness of the cover glass is a constant reference value, so if the thickness of the cover glass differs from the reference value, the imaging performance will deteriorate. This tendency is caused by the objective lens N, A, (
The larger the numerical aperture), the more significant this becomes. For this reason, conventional objective lenses with correction rings have been designed to change the lens spacing within the objective lens as the thickness of the cover glass changes, thereby preventing aberrations from worsening and maintaining almost good imaging performance. Are known. However, with conventional general objective lenses with correction rings, the range of aberration correction for changes in cover glass thickness is extremely narrow (0.2 m to 0.3 m in thickness when N, A, and 0.6). The range of the crane was the practical limit.

On the other hand, JP-A-56-1 filed by the same applicant as the present application
Publication No. 42508 describes a microscope objective lens, in order from the object side, a first lens group of a positive cemented meniscus lens with a concave surface facing the object side, a second lens group of a positive lens or a cemented positive lens, and a composite lens group with a positive refractive power. Consisting of a third lens group, only the second lens group is moved along the optical axis according to changes in the thickness of the parallel plane plate disposed between the object plane and the objective lens. A technique is disclosed that maintains good imaging performance even when the thickness of the face plate varies over a wide range. According to this technology, it is true that the thickness change of the parallel plane plate is ±1
．． It is possible to maintain excellent imaging performance over an extremely wide range of zero. However, with the above technology, the practical limit is an objective lens with an N,^, of about 0.6 and a magnification of about 40x, and it is still insufficient for an objective lens with a larger N,^ or a higher magnification. Met.

(Objective of the Invention) The object of the present invention is that, despite having a large numerical aperture and high magnification, the thickness of a parallel plane plate such as a cover glass placed between the object plane and the objective lens is large. To provide a microscope objective lens that can always maintain excellent imaging performance even when it changes.

(Summary of the Invention) As shown in the schematic configuration diagram of FIG. 1, the microscope objective lens according to the present invention includes, in order from the object side, a lens group G1 having a positive refractive power and converting a light beam from the object into a convergent light beam; A second lens movable along the optical axis in the converging beam and having negative refractive power.
a lens group G2 and a third lens group G3 having negative refractive power
When the focal length of the entire system is f and the focal length of the second lens group is r2, the following condition is satisfied: -5Of <f2<-1Of (1).

Then, the second lens group G2 is adjusted relative to the second lens group G1 and the third lens group G3 according to the change in the thickness of the parallel plane plate P disposed between the object 0 and the third lens group Gl. By moving it, variations in aberration due to changes in the thickness of the plane-parallel plate P are corrected. For example, if the thickness of the parallel plane plate P such as a cover glass or culture container is larger than a predetermined design standard value, the second lens group G2 is moved toward the third lens group G3, and conversely, the thickness of the parallel plane plate P is larger than a predetermined design standard value. When the thickness is smaller, by moving the second lens group G2 toward the second lens group Gl, it is possible to always maintain the same aberration correction state as at the design reference value.

In order for the above correction to be made well, it is necessary that the focal length of the second lens group satisfies the condition shown in equation (1) above, and that the aberration structure of each lens group is as follows. be. Incidentally, in order to facilitate understanding of the following explanation, an example of a paraxial ray from an on-axis object point is shown in FIG. The lens group G1 has a strong convergence effect and a fairly large negative spherical aberration. The second lens group G2 has positive spherical aberration, which almost cancels out the negative spherical aberration occurring in the second lens group G1. Therefore, if the lower limit of conditional expression (1) is exceeded, the negative refractive power of the second lens group becomes too weak, the amount of positive spherical aberration generated decreases, and the negative spherical aberration of the second lens group becomes too weak. On the other hand, if the upper limit is exceeded, the refractive power of the second lens group becomes too strong (too much, resulting in over-correction of spherical aberration). Group G3 corrects the Petzval sum of the entire system and maintains the flatness of the image plane.

It is desirable to provide two lens surfaces facing each other with concave surfaces in the third lens group G3 with an air gap in between, and to correct the Petzval sum by the divergence effect of these two concave surfaces. This is not essential to the present invention, whose main purpose is to correct aberrations.

Based on such a basic structure, the spherical aberration can be changed by moving the second lens group G2 relatively on the axis between the lens group Gl and the third lens group G3. That is, since the second lens group G2 with negative refractive power is located in the convergent light beam exiting the lens group Gl, if the second lens group G2 moves from its reference position to the third lens group G3 side, the convergence occurs. The height at which the light beam cuts through the second lens group G2 becomes lower than that at the reference position, and the amount of positive spherical aberration generated in the second lens group G2 becomes smaller. Conversely, if the second lens group G2 moves closer to the first lens group Gl than its reference position, the height at which the convergent light beam cuts through the second lens group G2 becomes higher than that at the reference position, and the second lens The amount of positive spherical aberration in group G2 increases. Therefore, the spherical aberration, which varies greatly depending on the thickness of the parallel plane plate P such as a cover glass placed between the objective lens and the object surface, is corrected by the movement of the second lens group G2. In other words, as the thickness of the parallel plane plate P increases, positive spherical aberration occurs, so in order to correct this, the second lens group G2 must be adjusted to reduce the amount of positive spherical aberration in the second lens group G2. On the other hand, the thickness of the parallel plane plate P is thin (if this happens, negative spherical aberration will occur, so in order to increase the amount of positive spherical aberration in the second lens group G2), It is sufficient to move the second lens group toward the second lens group Gl.

As mentioned above, the basic feature of the present invention is that the light flux from an object is converted into a convergent light flux by the first lens group, and the convergence state of the light flux remains almost constant even after passing through the second lens group with negative refractive power. It is about being maintained. After passing through the third lens group, the light is focused at a predetermined image plane position. For this reason, as shown in Fig. 1, the height at which the paraxial ray from the on-axis object point cuts through each lens group is highest in the 1121st lens group G1, then in the second lens group G2 and third lens group. It is lowest in the order of G3. The highest values of the cutting heights of paraxial rays from the on-axis object point in each of the first and second lens groups are hl and h in order.
2. When the height at which light exits the third lens group is h3, h
It is necessary that l>h2>h3. Therefore, regarding the effective diameter of each lens group, the lth lens group is the largest and the third lens group is the smallest, 6h3>hl>2h
It is desirable to configure the number to about 3. Note that when the present invention is applied to an objective lens with a higher magnification, the value of the ratio of hl to h3 becomes larger, and when the present invention is applied to an objective lens with a lower magnification, the value of the ratio of hl to h3 becomes larger. become smaller. Further, it is desirable that the gradient of the ray passing through the 1121st group G1 has a value that is 5 to 10 times the gradient of the ray passing through the entire system. As mentioned above, this is due to the height of the rays incident on the second lens group G2 when the second lens group G2 moves between the 1121st lens group G1 and the third lens group G3 along the optical axis. This is because the amount of correction of spherical aberration is different, and the higher the magnification of the objective lens, the larger this gradient becomes, and the lower the magnification of the objective lens, the smaller this gradient tends to be. Furthermore, the configuration of the present invention in which the effective diameter of the first lens group is maximized is advantageous for increasing the working distance, and a long working distance is possible as in the embodiments described later.

(Example) Next, a specific lens configuration of each lens group will be described based on an example of the present invention. FIG. 2 shows the first embodiment according to the present invention.
FIGS. 3 and 4 are lens configuration diagrams of an embodiment, respectively. In FIG. It is shown in As per the illustrated embodiment, the 1121st group G1 has a fairly strong positive refractive power for converting the light beam from the object into a convergent light beam, and for this purpose at least three re-lensing components L1.L2.L3 are used. The positive lens L1 closest to the object side must have a meniscus shape with a concave surface facing the object side, and the second positive lens L2 must have a surface with a stronger curvature on the image side. It is desirable that at least one of the three positive lenses be provided with a bonding surface. Therefore, as in the illustrated embodiment, it is formed by laminating a negative meniscus lens L4 convex to the object side, a biconvex positive lens L5, and a negative sinusoid lens 6.The overall shape is a positive lens shape. Since the refractive index of the negative meniscus lens XL4.L6 is higher than that of the biconvex lens L5, the composite has a negative refractive power.This is because the second lens group G2 has the effect of correcting spherical aberration in the positive direction. To have (because it was intended).

The third lens group G3, which is mainly responsible for correcting the Petzval sum, has a negative refractive power as a whole, and has a convex surface facing the object side as in the illustrated embodiment.

It is preferable that the front group G31 is composed of a scarlet-shaped front group G31 and a meniscus-shaped rear group 2G32 having a concave surface of the same number on the object side. Further, it is desirable that the front group G31 has a weak positive refractive power, and the rear group has a weak negative refractive power. Here the front group G3
1, the most image-side concave surface Ra, and the rear group's most object-side concave surface Rh.
and function as mutually opposing concave surfaces as described above in the third lens group.

The front group G31 of the third lens group is a positive lens L7. Negative lens L
8. It is desirable that the lens be constructed by laminating a positive meniscus lens L9 with its convex surface facing the object side, or laminating a positive lens L7 and a negative lens L8. However, since the negative lens L8 and the positive meniscus lens L9 in the front group C31 are bonded together to form a so-called hyperchromatic lens, the direction of the bonded surfaces can also be reversed. Moreover, it is desirable that the rear group G32 of the third lens group is constructed by laminating a biconcave negative lens LIO and a biconvex positive lens Lll.

Examples according to the present invention will be described in detail below.

This embodiment is a so-called dry objective lens designed to be compatible with three types of cover glasses having different refractive indexes and dispersions. All three cases had a magnification of 50x, N, A, = 0
．． 7, working distance 11.0. #1. Of, and has a length equivalent to the focal length f of the entire system. Cover glasses C and G of standard thickness are placed between the object and the objective lens.

FIG. 2 is a diagram showing the structure of the lens with the lens inserted.

The specifications of this example are shown in Tables 1 to 3, respectively. However, the numbers at the left end of the table indicate the order from the object side, do indicates the distance from the vertex of the frontmost lens surface of the objective lens to the surface of the cover glass, and the value of the back focus Bf and the cover glasses C and G. The value of the variable interval when the thickness of , changes, is also shown.

Table 1 (First Example) f=1.000 8f=45.4613The refractive index of the cover glass used in the first example was 1.4910B, and the Abbe number was 57.57. The refractive index of the cover glass used was 1.58518, and the Atsbe number was 30.
24, the refractive index of the cover glass used in the third example is 1.5871G, and the Abbe number is 33.43. Furthermore, in each of the above embodiments, when the focal length of the entire system is f, the focal length of G2 is -26°82f, -2
0.62f, -19.06f.

Figures 5 to 7 are aberration diagrams for each example when the distance from the object surface to the image plane is proportionally enlarged to be 245 mm and used as a practical objective lens, and (A) is A diagram of various aberrations without cover glasses C and G (B) is a diagram of various aberrations with cover glasses C and G in IM (C) is a diagram of various aberrations with cover glasses C and G thickened to 1.5 m. It is a diagram of various aberrations in the state. In each aberration diagram, spherical aberration (Sph),
Astigmatism (Ast), distortion aberration (Dis) r
It shows coma aberration (Coma), and the reference light is d-line (λ-58
7.6 m), and C-line (λ
-656.3 m) and F line (λ-486.1 Tsuru) are also shown. Further, the value of y in the figure represents the image height.

According to each aberration diagram, although the objective lenses of this example all have a high magnification of 50 times, a large numerical aperture of N,^,=0.7, and a long working distance, the thickness of the cover glass It is clear that excellent imaging performance is always maintained over a wide range of 0 to 1.5 m.

(Effects of the Invention) As described above (according to the present invention), despite having a large numerical aperture and high magnification, the parallel plane of the cover glass etc. disposed between the object plane and the objective lens A microscope objective lens that can always maintain excellent imaging performance even when the thickness of the face plate changes greatly is achieved.As shown in the example, the thickness of the cover glass changes from the state where there is no cover glass to the thickness of the cover glass. Since good imaging performance is maintained continuously over a range of up to 1.5 ms+, it is possible to continuously and minutely observe and inspect a transparent object from the surface to the inside of the surface.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the basics of an objective lens according to the present invention, FIG. 2 is a configuration diagram of a lens of a first embodiment according to the present invention,
FIG. 3 is a lens configuration diagram of the second embodiment according to the present invention,
The figures are lens configuration diagrams of the third embodiment of the present invention, and Figs.
FIG. 7 shows various aberration diagrams for each example when the thickness of the cover glass is different. The aberration diagram (C) in the theoretical state is a diagram of various aberrations in a state where the cover glass is thickened to 1.5 mm. [Explanation of symbols of main parts] P... Town cover glass Gl... Second lens group G2... Second lens group G3... Third lens group Applicant Nippon Kogaku Kogyo Co., Ltd. Agent Takao Watanabe Procedural amendment Written (Translated) 1982 Patent Application No. 62934 2 Name of the invention Microscope objective lens 3 Relationship to the case of the person making the correction Patent applicant Nippon Kogaku Kogyo, 3-2-3 Marunouchi, Chiyoda-ku, Tokyo (411) 1 of 1 Witness: Shigetada' Coordinator: Shigetada Fukuoka 4, Agent: 1-6-3-5 Nishi-Oi, Tokyo Parts Ward, 140 ? Date of gong order: June 6, 1980 (Shipping date: June 26, 1982)
6. Subject of correction

Claims (1)

[Claims] In order from the object side, there is a first lens group that has a positive refractive power and converts the light beam from the object into a convergent light beam, and a second lens group that is movable along the optical axis in the convergent light beam and has a negative refractive power. It has two lens groups and a third lens group with negative refractive power, and the focal length of the entire system is f,
When the focal length of the second lens group is f2, the condition of -5Of<f2<-1Of is satisfied, and according to the change in the thickness of the parallel plane plate disposed between the object and the second lens group. A microscope objective lens, wherein fluctuations in aberrations can be corrected by moving the second lens group relative to the first and third lens groups.