JPS6155656B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an objective lens for a microscope, and in particular,
This invention relates to a so-called infinite correction type long-action plan apochromatic objective lens for a microscope that forms an image using an imaging lens. In general, to improve the operability of a microscope,
It is necessary to increase the working distance of the objective lens, but the working distance of a conventional microscope objective lens with a magnification of about 5x is about 0.2 to 0.5 times the focal length.
It was not sufficient and the operability was poor. Also, numerical aperture NA
However, most of them have a diameter of about 0.1 to 0.13, and there are few cases where the image plane is flat over a sufficiently wide field of view. That is, when attempting to obtain a long working distance in an objective lens, the amount of secondary spectrum increases and chromatic aberration and spherical aberration become large, so conventionally, the working distance had to be shortened at the cost. On the other hand, in order to design an apollochromatic objective lens with a large numerical aperture NA, appropriate and effective use of glass materials and appropriate power distribution of each lens are required. It was one of the difficult things. The present invention was made to solve the above-mentioned conventional problems, and has a large numerical aperture NA of about 0.14.
In addition, it has a long working distance of about 0.8 times the focal length, a flat image plane over a wide field of view, and the objective lens itself has excellent correction for lateral chromatic aberration and other aberrations. The purpose is to provide objective lenses. The present invention provides an objective lens for a microscope including a first group consisting of a positive single lens disposed on the image side, and an object disposed on the object side of the first group with a convex surface facing the image side. A second group consisting of a cemented meniscus lens with a radius of curvature of r ₅ on the side surface, and a lens center wall with a radius of curvature of r ₆ on the image side surface disposed on the object side of the second group with the concave surface facing the image side. A third group consisting of a meniscus lens with a thickness of d ₆ , and a cemented positive lens disposed on the object side of the third group and including a positive lens and a negative lens with Abbe numbers of ν ₈ and ν ₉ , respectively. It consists of 4 groups, and when the focal length of the entire system is f, each optical constant has the following relationship: ν ₈ - _{ν 9} > 10 …………(1) f/8<d ₆ …… …(2) 0.15f＜r ₅ ＜0.3f …………(3) 0.15f＜−r ₆ ＜0.3f …………(4) is satisfied to achieve the above purpose. . Here, the above equation (1) defines the difference between the Atsube number ν ₆ of the positive lens included in the fourth group and the Atsube number ν ₉ of the negative lens, and it corrects the longitudinal chromatic aberration and also adjusts the magnification. This is to satisfactorily correct chromatic aberration using the objective lens itself. In addition, the above equation (2) defines the center thickness _d6 of the meniscus lens in the third group, and if this condition is waived, it will be difficult to correct comatic aberration and field curvature at the same time. Become. Also, mentioned above
Equations (3) and (4) define the radius of curvature r ₅ of the object side surface of the cemented meniscus lens in the second group and the radius of curvature r ₆ of the image side surface of the meniscus lens in the third group. This is to correct field curvature. Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG _. 1, this embodiment consists of a first group G1 consisting of a positive single lens _L1 disposed on the image side, and an object in the first group _G1 with its convex surface facing the image side. A second group G ₂ is disposed on the side and includes a positive lens L ₂ and a negative lens L ₃ , and is composed of a cemented meniscus lens with a radius of curvature r ₅ on the object side. group
The radius of curvature of the image side located on the object side of G ₂ is
r ₆ and _a meniscus lens _{L 4} with _a lens center thickness _{of d 6 ;} It is composed of a fourth group _G4 consisting of a cemented positive lens including a lens _L5 and a negative lens _L6 . With the above configuration, the magnification when forming an image with an imaging lens with a focal length of 200 mm is 5x, and the numerical aperture on the object side is
The optical constants of each lens are set as shown in Table 1 below, satisfying the relationships of formulas (1) to (4) above so that the NA is 0.14 and the focal length f of the entire system is 40.01mm. As a result, the distance (working distance) WD from the apex of the final lens to the object surface is 32.3 mm, that is, the focal length f.
It was 0.81 times larger, and a longer working distance could be obtained. Here, r ₁ ...... r ₁₀ is the radius of curvature of each lens surface, d ₁ ...... d ₉ is the center thickness of each lens or the lens spacing, n ₁ ...... n ₉ is, The refractive index of each lens, ν ₁ ..... ν ₉ , is the Abbe number of each lens. FIG. 2 shows the measurement results of spherical aberration, astigmatism, distortion, and lateral chromatic aberration in this example.
This figure 2 was obtained by tracing rays from the image side toward the object plane, and Y' is
This represents the image height when combined using an imaging lens with a focal length of 200 mm. As is clear from the figure, various aberrations are well corrected despite the extremely long working distance WD and large numerical aperture NA.

[Table] As explained above, according to the present invention, it is possible to obtain high performance and a very long working distance of about 0.8 times the focal length without sacrificing chromatic aberration and other chromatic aberrations. Therefore, the operability of the microscope can be greatly improved, and it has the excellent effect of being extremely useful as an objective lens for a microscope.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the lens configuration of an example of the objective lens for a microscope according to the present invention, and FIG. 2 is a diagram showing various aberrations of the example. G ₁ ... 1st group, G ₂ ... 2nd group, G ₃ ... 3rd group
Group, G ₄ ... Fourth group, L ₁ to L ₆ ... Lens.

Claims (1)

[Claims] 1. A first group consisting of a positive single lens disposed on the image side, and a curvature of the object side surface disposed on the object side of the first group with a convex surface facing the image side. A second group consisting of a cemented meniscus lens with a radius r ₅ and a concave surface facing the image side, which is disposed on the object side of the second group, the radius of curvature of the image side surface is r ₆ , and the lens center thickness is d. ₆ , and a fourth group consisting of a cemented positive lens, which is disposed on the object side of the third group and includes a positive lens and a negative lens with Abbe numbers of ν ₈ and ν _9, respectively.
When the focal length of the entire system is f, each optical constant has the following relationship: ν ₈ - _{ν 9} > 10 f/8 < d ₆ 0.15f < r ₅ < 0.3f 0.15f < An objective lens for a microscope, characterized in that it satisfies −r ₆ <0.3f.