JPS6132646B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a microscope photography lens for re-imaging an object image formed by an objective lens of a microscope on a film surface to take a photograph. For example, when a photograph is taken using this type of photographic lens in a gold-phase microscope, the image becomes distorted due to distortion aberration. It is difficult to correct this defect with microscope objectives. Most objective lenses have positive distortion, and most sleep lenses also have positive distortion. For this reason, pictures taken with a microscope have pincushion distortion. In order to eliminate this drawback, it is necessary to use approximately 0.0
It is necessary to use a distortion aberration close to (even if it is positive, it is extremely small) or negative. A conventional microscopic photography lens of this type is described in Japanese Patent Application Laid-Open No. 11754/1983.
In this conventional example, the distortion aberration is approximately +3% at the outermost periphery. Furthermore, since the lens system was composed of four groups, there was a lot of surface reflection, which caused some problems in terms of contrast. Furthermore, spherical aberration has become somewhat large. The present invention eliminates the drawbacks of the conventional ones as described above, and provides a microscope that uses a lens system that has a distortion aberration close to zero or has a negative value, thereby making it possible to take images with good images with little distortion. It provides photographic lenses. The lens system of the present invention includes a first lens group consisting of a positive meniscus lens with a convex surface facing the objective lens, a second lens group consisting of a cemented negative meniscus lens with a convex surface facing the objective lens, and a second lens group consisting of a double-convex cemented lens. The lens system is composed of three lens groups, and is further characterized in that it satisfies the following conditions. (1) 2.4≦f ₁ /f ₂₃ ≦2.9 (2) 0.345≦r ₁ /f≦0.39 (3) 0.11≦d ₃ +d ₄ /f≦0.16 (4) 0.01≦n ₃ −n ₂ ≦0.05 where f is the focal length of the entire system, f ₁ is the focal length of the first group lens (front group), f ₂₃ is the combined focal length of the second group lens and third group lens (rear group), r ₁ is the first group lens The radius of curvature of the surface on the objective lens side, d ₃ and d ₄ are the second
The thicknesses of both lenses of the group lens, n ₂ and n ₃ are the refractive indices of both lenses of the second group lens. The above conditions will be explained below. In a lens system like the present invention, distortion is almost determined by the power distribution of each group in the entire system. Condition (1) is a condition established in order to make distortion aberration a value close to zero or to a slightly negative value, which is the purpose of the present application, and to correct various aberrations in a well-balanced manner.
If the lower limit of condition (1) is exceeded, the distortion becomes a positive value and cannot be made close to zero. Moreover, if the condition (1) is exceeded, the distortion becomes too large although it is a negative value, which is not preferable. Condition (2) is a condition provided in order to further correct distortion aberration satisfactorily within the framework of the basic configuration defined in condition (1) and to maintain balance with other aberrations. If this condition is not satisfied, when the distortion aberration is set to a desired value, other aberrations will worsen and it will become impossible to correct them completely. In other words, if the lower limit of condition (2) is exceeded, the lower rays of the frame will be insufficiently corrected and astigmatism at the periphery of the screen will not be fully corrected. Furthermore, if the upper limit of condition (2) is exceeded, the lower rays of the frame will be overcorrected and it will be difficult to correct astigmatism around the screen. Condition (3) is necessary for correcting the Petzval sum to maintain flatness of the image and for balancing coma aberration. If the lower limit of this condition is exceeded, the field curvature will be under-corrected and the lower ray of the frame will be over-corrected. If the upper limit is exceeded, the field curvature will be over-corrected, and the upper ray of the frame will be over-corrected. Condition (4) defines the refractive index of both lenses of the second group lens, and also relates to the cemented surface r ₄ of the second group lens to correct the astigmatism difference, and also the thickness of both lenses of the second group lens. Relatedly, coma aberration is corrected. When the lower limit of this condition is exceeded, the curvature of surface _r4 becomes strong, the lower ray of the coma becomes over-corrected, Δm becomes over-corrected, and the astigmatism difference becomes large. Moreover, when the upper limit is exceeded, _r4 becomes loose, the upper ray of the coma becomes over-corrected, and Δm becomes under-corrected. Next, embodiments of the microscope photography lens of the present invention described above will be shown. Example 1

【table】 Example 2

【table】 Example 3

【table】 Example 4

【table】

[Table] However, r ₁ , r ₂ , ..., r ₈ is the radius of curvature of each lens surface, d ₁ , d ₂ , ..., d ₇ is the wall thickness and air gap of each lens, n ₁ , n ₂ , ..., n ₅ is the refractive index of each lens,
ν ₁ , ν ₂ , . . . , ν ₅ are Abbe numbers of each lens. Among the above embodiments, Examples 1, 2, and 4 all have positive distortion values. However, it can be said that the value is within 0.5%, which is extremely close to zero compared to the generally 3% for conventional lenses of this type. With this degree of distortion, good photographs can be obtained even when used with a general microscope objective lens.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the photographing lens of the present invention, and FIGS. 2 to 5 are aberration curve diagrams of Examples 1 to 4 of the present invention, respectively.

Claims (1)

[Claims] 1. A first group lens of a positive meniscus lens with a convex surface facing the objective lens side, a second group lens of a cemented negative meniscus lens with a convex surface facing the objective lens side, and a double convex cemented lens. A microscopic photography lens consisting of a third lens group of lenses and satisfying each of the following conditions. (1) 2.4≦f ₁ /f ₂₃ ≦2.9 (2) 0.345≦r ₁ /f≦0.39 (3) 0.11≦d ₃ +d ₄ /f≦0.16 (4) 0.01≦n ₃ −n ₂ ≦0.05 where f is the focal length of the entire system, f ₁ is the focal length of the first group lens (front group), f ₂₃ is the combined focal length of the second group lens and third group lens (rear group), r ₁ is the first group lens The radius of curvature of the surface on the objective lens side, d ₃ and d ₄ are the second
The thickness of each lens of the group lens, n ₂ and n ₃ is the refractive index of each lens of the second group lens.