JPH0567005B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) The present invention relates to an eyepiece, particularly a high-magnification eyepiece used for a microscope or the like. (Background of the invention) The fields in which microscopes are used can be broadly divided into biological fields and industrial fields. In the biological field, the specimens to be observed are often irregular in shape and thick, so even if some curvature of field and distortion of the objective and eyepiece lenses remain, they do not cause much of a problem. It seems not to happen. On the other hand, especially in the field of IC, which has recently seen remarkable development, the patterns of the target specimens are mostly fine, regular, continuous patterns, and are often flat, such as wafers and masks. Therefore, unlike in the biological field, when observing these specimens, an optical system with high magnification and low field curvature and distortion is required, and objective lenses and eyepieces must also be designed to minimize these aberrations. More corrections will be needed. In the case of a normal eyepiece, its flatness depends mostly on the Petzvaar sum, and the Petzvaar sum generally becomes smaller as the focal length becomes smaller.
On the contrary, it tends to become larger, so if you think about it simply, the smaller the focal length and the higher the magnification, the larger the
It can be seen that the Petzval sum tends to become large, making it difficult to correct the curvature of field. Most conventional eyepiece lenses are often composed of only a positive single lens or a cemented lens, and as a result, the Petzval sum is large and curvature of field often remains. On the other hand, when considering the eyepoint position, the distance to the eyepoint tends to become shorter as the magnification increases and the focal length decreases. for example,
Even if the eyepoint position is 20mm with a 10x eyepiece (f = 25), it will be 10mm if you change it to a 20x eyepiece (f = 12.5),
6 when using a 33x eyepiece (f = 7.6)
mm, and in reality it will be almost useless. It is generally said that the eye point position needs to be 19 to 20 mm when wearing glasses, and at least 11 to 12 mm even when glasses are removed. Therefore, for a 33x eyepiece, indeed,
An eyepoint length that is at least 1.5 times the focal length is required, and if this is simply converted to a 10x eyepiece, it is equivalent to an eyepoint length of 38mm, and will continue to be achieved with a high magnification of 33x. You can imagine how difficult it is to ensure the eyepoint length in an eyepiece. As an eyepiece lens having a relatively long eye point distance, for example, one disclosed in Japanese Patent Application Laid-open No. 181012/1983 is known. This eyepiece has an eyepoint distance of 20mm, which is almost sufficient for an eyepiece with 10x magnification.
Since it was only 0.8x, the eyepoint length was still insufficient for a high-magnification eyepiece of 20x or 33x. (Object of the Invention) An object of the present invention is to provide a high-magnification eyepiece that has an eyepoint length that is at least 1.5 times the focal length, has an excellent flatness of the image plane, and has little distortion. . (Summary of the Invention) The high magnification eyepiece according to the present invention comprises, in order from the object side, a first lens group _G1 having a bonded negative lens component, a bonded lens component having a concave surface facing the object side, and a positive lens. a second lens group having a positive lens component with a surface having a stronger curvature facing toward the object side;
_G2 , and an object image is formed by an objective lens (not shown) between the first lens group _G1 and the second lens group _G2 . Then, the composite focal length of the entire eyepiece system is F,
When the composite focal length of the first lens group G ₁ is f ₁ , the composite focal length of the second lens group G ₂ is f ₂ , and the air distance between the first lens group G ₁ and the second lens group G ₂ is D , (1) −0.5<F/f ₁ <0 (2) F<f ₂ <1.42F (3) 0.7<D/F<2.5. Each of the above conditions according to the present invention will be explained below. Condition (1) relates to the ratio of the focal lengths of the entire system and the first lens group _G1 . The first lens group _G1 forms an image formed by the objective lens near the second lens group _G2 by its divergent action, and also changes the pupil position relative to the second lens group _G2 .
Its role is to bring the lens closer and lengthen the eye point. As a result, the position where the pupil is imaged by the second lens group _G2 , that is, the position of the eye point, is
It can be placed further away from the final surface of lens group _G2 , allowing the eye point to be extended. If the upper limit of equation (1) is exceeded and the first lens group G ₁ has a positive power, the pupil of the objective lens will change to the second lens group G ₂ due to the convergence effect of the first lens group G ₁ .
However, the image is formed far away. At this time, for example, if we assume that the principal ray is parallel to the optical axis, the eyepoint position will be the rear focal position of the lens of the second lens group _G2 , so the eyepoint will be It will be seen that it is impossible to make it longer. That is, when the first lens group _G1 has positive power, it is basically difficult to increase the eyepoint distance, and therefore the first lens group _G1 needs to have a diverging effect. be.
By having a negative refractive power, the Petzvaar sum becomes smaller, which greatly helps in improving image flatness and correcting distortion aberration. On the other hand, if the lower limit of condition (1) is exceeded, the first lens group
Since the negative refractive power as G ₁ is too strong, the light beam passes through the outermost edge of the second lens group due to the divergence effect, resulting in an excessively positive distortion. In particular, since the value suddenly becomes positive at a large angle of view, a U-turn phenomenon of distortion aberration, that is, bending occurs. Condition (2) relates to the ratio of the focal lengths of the second lens group _G2 and the entire system. The chief ray from the objective lens, which has undergone the diverging action by the first lens group, then passes through the second lens group _G2 .
If the focal length of the G ₂ is small, the back focus will also be small, so the eyepoint position will not be extended. Therefore, the focal length of the second lens group _G2 is
It must be at least larger than the composite focal length of the entire system, otherwise the eyepoint distance cannot be 1.5 times the composite focal length f of the entire system, and therefore exceeds the lower limit of equation (2). This makes it difficult to secure eye points. Conversely, exceeding the upper limit of equation (2), the second
As the focal length of the lens group _G2 increases, the focal length of the first lens group _G1 must also be increased, and the negative power of the first lens group _G1 becomes weaker. The sum becomes larger and the flatness of the image plane deteriorates. The condition of equation (3) defines the optimum range of the air distance D between the first lens group _G1 and the second lens group _G2 . Simply reducing the distance between both lens groups will increase the focal length of the entire system, and conversely, increasing the distance will decrease the focal length of the entire system, so in order to maintain the focal length of the entire system, it is necessary to need to be proportionally reduced or expanded. That is, if the distance between both lens groups is made smaller, the focal length of the entire system will actually increase, so the distance will be further reduced proportionally, so the actual distance will become even smaller. Here, if the distance between both lens groups exceeds the lower limit of equation (3), the focal lengths of the first lens group and the second lens group will become smaller, so first the Petzval sum will increase and the flatness will deteriorate. In addition, since the focal length of the second lens group becomes smaller, the back focus of the second lens group on the object side also becomes smaller, and when used as an eyepiece, the intermediate image of the object formed between both lens groups becomes smaller. As it approaches the second lens group _G2 , scratches on the lens surface become more visible. On the other hand, if the distance between both lens groups increases beyond the upper limit, the eye point will become too long, the lens outer diameter will become too large, and various aberrations will occur significantly.
Processability deteriorates, such as not being able to remove the edge thickness of the lens. In addition, the chromatic aberration of magnification when considering only the second lens group becomes undersized, and the viewing ring, scale, etc. placed between the first and second lens groups are observed as colored, making it difficult to perform clear observation. Furthermore, negative distortion also increases. In the configuration of the present invention as described above, the first lens group _G1 is composed of a bonded negative lens component L1 consisting of a positive meniscus lens _L11 with a concave surface facing the object side and _a biconcave negative lens _L12 . Furthermore, it is desirable that the meniscus component _L2 in the second lens group _G2 , which has a concave surface facing the object side, is composed of a cemented double-concave negative lens _L21 and a double-convex positive lens _L22 . When the focal length of the bonded component L ₂ with the concave surface facing the object side in the second lens group G ₂ is f ₂₁ , it is desirable to satisfy the following condition (4) |f ₂₁ |>3F. This condition defines an appropriate range of power for the bonded meniscus component _L2 in the second lens group _G2 , and enables the second lens group _G2 to effectively correct lateral chromatic aberration and distortion aberration. These are the conditions for making the lens function properly and for greatly correcting the spherical aberration of the pupil at the cemented surface of the bonded meniscus component. When the focal length of the bonded meniscus component in the second lens group _G2 becomes negative and small, the negative power becomes too strong, making it difficult to correct lateral chromatic aberration. On the other hand, if it is positive and small, the lateral chromatic aberration will be over-corrected. In addition, the cemented surface corrects the distortion aberration caused by a single lens and the spherical aberration of the pupil, and maintains the overall balance. It becomes difficult to correct spherical aberration. When the Atsube numbers of the biconcave negative lens L ₂₁ and the biconvex positive lens L ₂₂ forming the bonded meniscus component L ₂ in the second lens group G ₂ are ν ₃ and ν ₄ , respectively, (5) It is also desirable to satisfy the condition of 15<ν ₄ −ν ₃ . This condition is the difference in the Atsube number between the positive lens and the negative lens that constitute the bonded meniscus component in the second lens group _G2 , and is related to the above conditional expression (4) to ensure good chromatic aberration of magnification. This is for realizing correction. Generally speaking, in the case of internal focus type eyepieces, lateral chromatic aberration is corrected not only for the entire system, but also for the second lens group.
It is also necessary to correct _G2 as a whole.
This is because, as mentioned above, in the case of the internal focus type, the field ring, reticle, scale, etc. are placed at the focal position of the second group, so if they become colored, it is a problem when observing. This is to become. For this reason, it is desirable to correct the second lens group _G2 as a whole. The condition of equation (5) is a condition for correcting the lateral chromatic aberration not only for the entire eyepiece lens but also for the second lens group _G2 .
The lateral chromatic aberration of both the lens group and the lens group as a whole was too low, and the positive lens in the second lens group _G2
Good correction is difficult even if the Atsube numbers of L ₃ and L ₄ are increased. It is also possible to achromatize the positive lenses L ₃ and L ₄ by using cemented lenses, but this is not preferable because the number of lenses increases and the cost increases. (Example) Examples of the high magnification eyepiece according to the present invention will be described below. FIG. 1 shows the configuration of a first embodiment according to the present invention, and in the figure, the axial light flux is shown by a solid line, and the light flux at the maximum angle of view is shown by a broken line. In addition, I ₀ in the figure is the position of the object image formed by an objective lens (not shown), and I indicates the intermediate image position where the object image is actually formed when an internal focusing type eyepiece according to the present invention is provided. . Each example has a focal length of 7.6 mm,
It was designed as a 33x eyepiece. The lens configuration is basically the same as that of the first embodiment shown in FIG. 1, but the fourth embodiment has a slightly different lens shape.
A lens configuration diagram of the example is shown in FIG. 5. Tables 1 to 4 below show specifications of examples according to the present invention. In each table, the leftmost number indicates the order from the object side, EP indicates the distance to the eye point, and ΣP indicates the Petzval sum. Further, the refractive index and Abbe number are values for the d-line (λ=587.6 nm).

【table】

【table】

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[Table] Various aberration diagrams for the above-mentioned first to fourth embodiments are shown below.
Figure 2, Figure 3, Figure 4 and Figure 6, respectively.
As shown in the figure. In each aberration diagram, the spherical aberration of the pupil,
Astigmatism and distortion for imaging are shown. According to each aberration diagram, it is clear that each example has a sufficiently long eyepoint distance and excellent optical performance despite the high magnification of 33 times. The above embodiments are all designed with a magnification of 33x and a focal length of 7.6mm, but this is not the only specification; eyepieces with other magnifications, such as 20x magnification, may be designed in proportion to the focal length. Needless to say, it can be expanded and used. (Effects of the Invention) As described above, according to the present invention, the focal length is 1.5
A high-magnification eyepiece lens having an eyepoint length more than twice as long as that of the first embodiment, excellent flatness of the image plane, and little distortion can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a lens configuration diagram of the first embodiment according to the present invention, Fig. 2 is a diagram of various aberrations of the first embodiment, Fig. 3 is a diagram of various aberrations of the second embodiment, and Fig. 4 is a diagram of the third embodiment. FIG. 5 is a diagram of the lens configuration of the fourth embodiment, and FIG. 6 is a diagram of various aberrations of the fourth embodiment. Explanation of symbols of main parts, G ₁ ... first lens group,
G ₂ ... Second lens group, L ₁ ... Bonded negative lens component, L ₂ ... Bonded meniscus lens component, L ₃ ...
...Positive lens component, L ₄ ...Positive lens component.

Claims (1)

[Claims] 1. In order from the object side, the first lens group _G1 has a negative lens component bonded together, a bonded lens component with a concave surface facing the object side, a positive lens component, and a lens group G1 having a negative curvature on the object side. and a second lens group _G2 having a positive lens component with a strong surface facing, the composite focal length of the entire eyepiece lens system is F, and the first lens group _G1
f ₁ is the composite focal length of the second lens group G ₂ , f ₂ is the composite focal length of the first lens group G ₁ and the second lens group
When the air distance with G ₂ is D, the following conditions are satisfied: (1) −0.5<F/f ₁ <0 (2) F<f ₂ <1.42F (3) 0.7<D/F<2.5 A high-magnification eyepiece lens characterized by: