JPH0784195A - Ocular - Google Patents

Abstract

PURPOSE:To provide an ocular having a small lens diameter, short entire length and long eye relief in spite of such an ultrawide angle that the angle of visibility is 80 deg.. CONSTITUTION:A negative lens; a positive meniscus lens whose concave surface turns toward an object side; a bonded negative meniscus lens which is constituted by bonding a negative lens having strong power on the object side and a positive lens having strong power on an observer side and whose concave surface turns toward the object side; a positive lens; a positive lens having strong power on the object side; and a bonded positive meniscus lens which is constituted by bonding a negative meniscus lens whose convex surface turns toward the object side and a positive meniscus lens whose convex surface turns toward the object side, and whose convex surface turns toward the object side are arranged in order from the object side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eyepiece lens used in a telescope, a microscope or the like, and more particularly to an ultra wide-angle eyepiece lens having a viewing angle of about 80 °.

[0002]

2. Description of the Related Art Conventionally, as super wide-angle eyepieces having an apparent field of view of 80 ° or more, those described in US Pat. No. 4,720,183 and US Pat. No. 4,747,675 are known. .

[0003]

However, although the eyepieces disclosed in U.S. Pat. No. 4,720,183 have good aberrations, the focal length of the maximum lens diameter is 3.5 times the total length of the lens. When it is applied to a small telescope or binoculars, which is very large, 7.4 times the focal length,
It had the drawback of being too large and difficult to use.

Further, since the distortion of this eyepiece lens is as large as about 20% around the visual field and the eye relief is as short as about 0.63 times the focal length, it cannot be said that it is easy to see.

The invention is compact, for example with an apparent field of view of 80 °.
The challenge is to achieve an eyepiece that can have a wide angle of view.

[0006]

According to the present invention, in order from the object side (or the main lens side), a negative lens, a positive meniscus lens concave to the object side, a negative lens having a strong power to the object side and an observer side. A cemented negative meniscus lens with a concave surface facing the object side, which is formed by cementing a positive lens with strong power to
Positive lens, positive lens with strong power on the object side, bonded negative meniscus lens with convex surface facing the object side and positive meniscus lens with convex surface facing the object side, bonded positive meniscus with the convex surface facing the object side By constructing the lens, it is possible to realize an eyepiece having a small visual field of 80 ° or more, good aberrations and a long eye relief of 0.9 times the focal length. It should be noted that “strong in the description” is compared with the other side.

Further, it is desirable to satisfy the following conditional expression. 0.3 <r ₄ / r ₅ <1.5 (1) 0.15 <d ₄ /f<0.9 (2) where r _i : radius of curvature of the i-th lens surface from the object side d _i : I-th surface distance from the object side f: focal length of the entire system

On the other hand, it is desirable that the following conditional expression be satisfied. _{0.8 <f 7 / f 3 <} 3 (3) 2 <-f 1 / f <5 (4) 0.5 <r 5 / r 7 <1 (5) 0.5 <| r 5 / r 13 | <2 (6) where f _i : focal length of the i-th lens from the object side

On the other hand, it is desirable that the following conditional expression be satisfied. 20 <ν _P −ν ₃ <40 (7) 20 <ν _P −ν ₇ <40 (8) 0.05 <n _P −n ₁ <0.35 (9) 0.01 <n ₃ −n _P < 0.25 (10) 0.01 <n ₇ −n _P <0.25 (11) where ν _P : average value of Abbe number of convex lens n _P : average value of refractive index of convex lens ν _i : object side Abbe number of the i-th lens n _i : Refractive index of the i-th lens from the object side at d-line Further, it is desirable that an aspherical surface is used for the fourth lens surface from the object side.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An eyepiece lens according to an embodiment of the present invention will be described below with reference to the drawings. 1 to 3 are sectional views of lenses corresponding to numerical embodiments of the present invention described later.

In order to solve the above problems,
The lens structure shown in the lens cross-sectional view is adopted.

First, a negative lens (a negative meniscus lens having a convex surface on the object side in the numerical embodiment) is arranged closest to the object side in order to lengthen the eye relief. The reason why the positive lens is arranged second from the object side is to lengthen the combined focal length of the third and subsequent lenses from the object side to lengthen the eye relief. The cemented negative meniscus lens including the third and fourth lenses from the object side has a small field curvature.

Further, the cemented surface of the cemented negative meniscus lens on the most observer side satisfactorily corrects the chromatic aberration of higher magnification generated on the R4 surface.

Next, the meanings of the upper and lower limits of the conditional expressions (1) and (2) or (3) to (6) or (7) to (11) described above will be described.

Conditional expression (1) limits the ratio of the curvature radii of the fourth and fifth lens surfaces from the object side. In the region where the lower limit of conditional expression (1) is exceeded, the fourth curvature from the object side is obtained. The radius becomes relatively small too much, the astigmatism becomes excessive, and in the region exceeding the upper limit of conditional expression (1), the fifth radius of curvature from the object side becomes too small comparatively,
This is not good because high-order lateral chromatic aberration becomes large.

Conditional expression (2) limits the ratio between the fourth lens surface distance from the object side and the focal length of the entire system.
The correction of distortion is under-corrected in the region where the lower limit of conditional expression (2) is exceeded, and the total lens length becomes large in the region where the upper limit of conditional expression (2) is exceeded.

Conditional expression (3) limits the ratio of the focal length of the third lens to the focal length of the seventh lens from the object side, and in the region where the lower limit of conditional expression (3) is exceeded, from the object side. Since the power of the seventh lens becomes relatively strong, the lens diameter becomes large, and the power of the third lens from the object side becomes relatively strong in a region exceeding the upper limit value of the conditional expression (3). This is not good because the next chromatic aberration of magnification increases.

Conditional expression (4) limits the ratio of the focal length of the first lens from the object side to the focal length of the entire system. Spherical aberration is excessive in the region where the lower limit of conditional expression (4) is exceeded. Therefore, the eye relief becomes short in a region exceeding the upper limit of conditional expression (4), which is not good.

Conditional expression (5) limits the ratio of the radius of curvature of the fifth lens surface and the radius of curvature of the seventh lens surface from the object side, and is not in a region where the lower limit of conditional expression (5) is exceeded. The point aberration becomes excessive, and the coma aberration becomes excessive in a region exceeding the upper limit value of the conditional expression (5), which is not preferable.

Conditional expression (6) limits the ratio of the radius of curvature of the fifth lens surface from the object side to the radius of curvature of the thirteenth lens surface from the object side, and is an area exceeding the lower limit of conditional expression (6). However, the chromatic aberration of higher magnification increases, and in a region exceeding the upper limit value of the conditional expression (6), the correction of the distortion aberration becomes under, which is not good.

Conditional expression (7) limits the difference between the average Abbe's number of the convex lens and the Abbe's number of the third lens from the object side. In the region where the lower limit of conditional expression (7) is exceeded, longitudinal chromatic aberration is exceeded. Since both the lateral chromatic aberrations are under, and the axial chromatic aberration and the lateral chromatic aberration are both over in a region exceeding the upper limit value of the conditional expression (7), it is not good.

Conditional expression (8) limits the difference between the average Abbe number of the convex lens and the Abbe's number of the seventh lens from the object side, and in the region where the lower limit of conditional expression (8) is exceeded, axial chromatic aberration is exceeded. The chromatic aberration of magnification is under, and the axial chromatic aberration and the chromatic aberration of magnification are both over in a region exceeding the upper limit of conditional expression (8), which is not preferable.

Conditional expression (9) limits the difference between the average value of the refractive index of the convex lens and the refractive index of the first lens from the object side, and in the region where the lower limit of conditional expression (9) is exceeded, the field curvature is reduced. Is under, and the field curvature is excessive in a region exceeding the upper limit of conditional expression (9), which is not good.

Conditional expression (10) limits the difference between the refractive index of the third lens from the object side and the average value of the refractive index of the convex lens. If the lower limit of conditional expression (10) is exceeded, coma will increase. However, if the upper limit of conditional expression (10) is exceeded, the field curvature will be under, which is not good.

Conditional expression (11) limits the difference between the refractive index of the seventh lens from the object side and the average value of the refractive index of the convex lens. If the lower limit of conditional expression (11) is exceeded, coma will increase. However, if the upper limit of conditional expression (11) is exceeded, the field curvature will be under, which is not good.

Further, by using an aspherical surface for the fourth lens surface from the object side, distortion can be corrected better.

The aspherical shape is preferably a shape that always passes through the observer side with respect to the paraxial spherical surface inscribed at the apex of the lens in order to correct distortion.

Numerical examples will be shown below.

R _i : radius of curvature of i-th lens surface from object side d _i : i-th surface spacing from object side n _i : refractive index of d-line of i-th lens from object side ν _i : from object side Abbe number of i-th lens The aspherical shape is expressed by the following equation.

[0030]

[Outer 1] Where r: paraxial radius of curvature k: conical constant

[0031]

[Outside 2]

[0032]

[Outside 3]

[0033]

[Outside 4]

[0034]

[Outside 5]

[0035]

As described above, according to the present invention,
Even though the apparent field of view is 80 °, which is an ultra wide angle, an eyepiece lens having a small lens diameter and a long lens length and a long eye relief can be realized. Also, various aberrations are well corrected.

This eyepiece is suitable for use in observing aerial images of astronomical telescopes, binoculars, microscopes, etc., because it provides a clear image with little blurring and distortion to the periphery while having a super wide angle.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view corresponding to Numerical Example 1.

FIG. 2 is a lens cross-sectional view corresponding to Numerical Example 2.

FIG. 3 is a lens cross-sectional view corresponding to Numerical Example 3.

FIG. 4 is a lens cross-sectional view corresponding to Numerical Example 4.

FIG. 5 is a diagram of various types of aberration of Numerical example 1.

FIG. 6 is a diagram of various types of aberration in Numerical example 2.

FIG. 7 is a diagram of various types of aberration in Numerical example 3.

FIG. 8 is a diagram of various types of aberration of Numerical example 4.

[Explanation of symbols]

 C C-line aberration curve d d-line aberration curve F F-line aberration curve M meridional image plane S sagittal image plane

Claims (5)

[Claims] 1. A negative lens, a positive meniscus lens having a concave surface directed toward the object side, a negative lens having a strong power on the object side, and a positive lens having a strong power on the observer side are cemented in order from the object side. A cemented negative meniscus lens with a concave surface facing to, a positive lens, a positive lens with strong power on the object side, a negative meniscus lens with a convex surface facing the object side, and a positive meniscus lens with a convex surface facing the object side. An eyepiece, comprising a cemented positive meniscus lens with a convex surface facing the object side. 2. The eyepiece according to claim 1, wherein the following conditional expression is satisfied. 0.3 <r ₄ / r ₅ <1.5 0.15 <d ₄ /f<0.9 where r _{i is the} radius of curvature of the i-th lens surface from the object side d _{i is the} i-th position from the object side Spacing f: focal length of the entire system 3. The eyepiece according to claim 1, which satisfies the following conditional expression. 0.8 <f ₇ / f ₃ <3 2 <−f ₁ / f <5 0.5 <r ₅ / r ₇ <1 0.5 <| r ₅ / r ₁₃ | <2 where f _i : Focal length of i-th lens from the object side 4. The eyepiece according to claim 1, wherein the following conditional expressions are satisfied. 20 <ν _P −ν ₃ <40 20 <ν _P −ν ₇ <40 0.05 <n _P −n ₁ <0.35 0.01 <n ₃ −n _P <0.25 0.01 <n ₇ where -n _P <0.25, ν _P: average value of Abbe numbers of the convex lens n _P: average value of the refractive index of the convex lens [nu _i: the Abbe number of the i-th lens from the object side n _i: i from the object side Refractive index of d-line of the th lens 5. The eyepiece according to claim 1, wherein an aspherical surface is used for the fourth lens surface counted from the object side.