JP3306134B2 - Eyepiece - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eyepiece used in combination with an objective lens of a telescope, and more particularly to an eyepiece having an apparent field of view of 6.
The present invention relates to a wide-field eyepiece of 0 ° or more.

[0002]

2. Description of the Related Art Some conventional examples of wide-field eyepieces have been known, such as Japanese Patent Application Laid-Open No. 60-159719. However, the conventional wide-field eyepiece focuses on correcting coma, chromatic aberration of magnification, astigmatism, etc., and does not correct distortion. For this reason, there is a disadvantage that the peripheral image in the visual field looks distorted.

In the example disclosed in Japanese Patent Application Laid-Open No. 60-159719, since a negative lens is disposed on the first lens on the objective side, the light beam incident on the negative lens is once diffused. For this reason, the lens diameters of the second lens and thereafter become large, and the whole system becomes large and heavy. Japanese Patent Application Laid-Open (JP-A) No. 60-48014 and Japanese Patent Application Laid-Open (JP-A) No. 4-28285 disclose examples in which a negative lens is arranged at the center of a lens system to thereby satisfactorily correct field curvature and distortion. The apparent field of view of these conventional examples is about 40 °.

[0004]

SUMMARY OF THE INVENTION Based on the above problem awareness, various aberrations such as coma, chromatic aberration of magnification, field curvature, distortion and the like can be satisfactorily corrected in a wide field of view of 60 ° or more based on the above problem awareness. Another object of the present invention is to obtain a low-cost, compact, and lightweight wide-field eyepiece having a small lens diameter and a small number of components.

[0005]

SUMMARY OF THE INVENTION An eyepiece according to the present invention comprises, in order from the object side, a positive first lens having a strong convex surface facing the eye side, and a positive second lens.
Lens, biconcave third lens, positive fourth lens, positive fifth
It is composed of a lens and satisfies the following conditional expression. _{-1.0 ≦ f 3 / f ≦ -0.7} 0.45 ≦ L / f A ≦ 0.8 0.3 ≦ f 5 / f 4 ≦ 0.8 , however, f _n: a focal length of the n lens f: focal length f _A of the system as a whole: the Focal length from the first lens to the second lens L: distance from the first surface of the first lens to the first surface of the third lens.

Generally, an eyepiece of a telescope converges a luminous flux generated by an objective lens or a telecentric luminous flux. In order to make observation easier, an exit pupil is formed as far away from the lens system as possible. Is preferred. For this reason, coma aberration, curvature of field, distortion, and the like are excessively generated as the apparent visual field becomes wider. That is,
As the apparent field of view increases, it becomes more difficult to correct various aberrations.

[0007] The present invention provides a wide apparent field of view, aberrations,
In particular, in order to satisfactorily correct distortion, a biconcave lens with appropriate power is placed at the center of the lens system, and good performance is obtained by canceling out various aberrations that occur in the entire lens system due to its diverging effect. By arranging a positive lens having appropriate power before and after that, a low-cost, compact, and lightweight wide-field eyepiece having a small number of components and a small lens diameter is obtained.

The conditional expression is for appropriately correcting distortion, curvature of field, coma and the like by appropriately applying the power of the third lens. As described above, in general, an eyepiece has a strong convergence effect in the entire system, so that positive distortion and coma tend to be excessively generated. In addition, Petzuba
Since the sum is positive and large, the field curvature is likely to be large. By giving an appropriate diverging effect to the third lens by the conditional expression, the distortion and coma can be corrected by one negative lens, and the Petzval sum can be kept small. Good performance can be obtained with the number of components. If the lower limit of the conditional expression is exceeded, the diverging effect of the third lens will be too small to correct the various aberrations. On the other hand, if the upper limit is exceeded, the diverging effect becomes too large, negative coma is excessively generated, and the lens system after the third lens becomes large.

The conditional expression is such that by appropriately giving the convergence of the first and second lenses, the lens diameter is reduced and an appropriate eye relief is ensured. This is intended to make it easy to correct distortion and coma by the third lens by appropriately setting the incident height of the light beam incident on the lens. If the lower limit of the conditional expression is exceeded, the difference between the convergence of the first and second lenses will be too weak and the lens diameter will be too large, and the incident height of the light beam incident on the third lens will be too high, and the light beam by the third lens will be too high. Divergence becomes excessively strong, and negative coma aberration occurs excessively. If the upper limit is exceeded, the convergence action of the first and second lenses becomes too strong, and the divergence action of the appropriate third lens cannot be obtained. Therefore, correction of distortion, coma and the like is not sufficient. And the eye relief becomes too short.

The conditional expression is to maintain the balance between the positive power of the fourth lens and the fifth lens at an appropriate level, thereby preventing the luminous flux diverged by the third lens from increasing the coma aberration and increasing the lens diameter. This is to prevent convergence while preventing and to secure an appropriate eye relief. If the lower limit of the conditional expression is exceeded, the convergence of the fourth lens will be too weak, and the lens diameter of the fifth lens will be too large.
The convergence effect of the fifth lens is too strong, and positive coma is excessively generated. If the upper limit is exceeded, the convergence of the fourth lens will be too strong, and the eye relief will be too short.

[0011]

Next, examples of the present invention will be described. FIG. 1 is a lens configuration diagram of a wide-field objective lens according to the present invention. Positive first lens 1 with a strong convex surface facing the eye side in order from the objective side
1, a positive second lens 12, a biconcave third lens 13, a positive fourth lens 14, and a positive fifth lens 15.

The numerical values of the following embodiments 1 to 4 are specific lens data. In the data, f is the focal length (mm), r
Is the radius of curvature (mm) of each lens surface, d is the lens thickness or lens interval (mm), n is the d-line refractive index of each lens, and ν is the Abbe number of each lens.

[Example 1] f = 40.0 Surface No. rdn n1 292.600 9.800 1.65844 50.86 2 -63.324 4.600 3 63.324 9.800 1.65840 50.86 4 -292.600 3.680 5 -46.800 3.000 1.72825 28.46 6 46.800 3.680 7 292.600 6.700 1.59240 68.30 8 -63.324 0.200 9 46.800 9.800 1.69680 55.53 10 -71.700 20.000 (eye relief) FIGS. 2 and 3 are aberration diagrams of the wide-field eyepiece based on the above lens data.

"Example 2" f = 40.0 Surface No. rdn ν1 257.812 9.800 1.48749 70.20 2 -49.313 4.687 3 59.860 8.000 1.69680 55.504 4 -409.497 4.139 5 -46.033 3.000 1.71736 29.50 6 48.134 3.724 7 404.275 7.000 1.62041 60.30 8 -66.732 0.276 9 48.077 9.000 1.69680 55.50 10 -71.813 20.000 (eye relief) FIGS. 4 and 5 are diagrams of various aberrations of the wide-field eyepiece based on the above lens data.

"Example 3" f = 40.0 Surface No. rdnv 1 860.727 9.800 1.58913 61.20 2 -58.940 0.200 3 74.864 8.000 1.65844 50.90 4 -159.722 7.680 5 -44.395 3.000 1.72825 28.50 6 46.651 2.812 7 118.443 7.000 1.65844 50.90 8 -79.802 1.188 9 49.903 9.000 1.69680 55.50 10 -68.820 20.000 (eye relief) FIGS. 6 and 7 are graphs showing various aberrations of the wide-field eyepiece based on the above lens data.

Example 4 f = 40.0 Surface No. rdn n1 569.022 9.800 1.51633 64.10 2 -51.915 0.200 3 59.739 8.000 1.62041 60.30 4 -260.381 6.848 5 -49.644 3.000 1.76182 26.60 6 46.652 4.744 7 265.709 7.000 1.65844 50.90 8 -62.809 0.200 9 43.134 9.000 1.65844 50.90 10 -79.100 20.000 (eye relief) FIGS. 8 and 9 show various aberrations of the wide-field eyepiece based on the above lens data.

Next, the following table is a table in which the numerical values of the conditional expressions are calculated for Examples 1 to 4 described above. All satisfy the conditional expressions of the present invention.

First Embodiment Second Embodiment Third Embodiment Fourth Embodiment f 39.996 40.000 40.000 40.000 f _A 41.723 41.806 43.313 43.801 L 27.880 26.626 25.680 24.848 f ₃ -31.704 -32.370 -30.808 -31.151 f ₄ 88.496 92.850 73.441 _{77.811 f 5 42.067 42.643 42.848 43.669 f} 3 / f -0.793 -0.809 -0.770 -0.779 L / f A 0.668 0.637 0.593 0.577 f 5 / f 4 0.475 0.459 0.583 0.561

[0019]

According to the present invention, various aberrations such as distortion, coma, field curvature and the like are well corrected while having a wide visual field of 60 ° or more in apparent field of view, and the lens diameter is small. It is possible to obtain a small-sized, lightweight, and low-cost wide-field eyepiece having a small size.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a wide-field eyepiece according to the present invention.

FIG. 2

FIG. 3 is a diagram illustrating various aberrations of the wide-field ocular lens according to the first embodiment of the present invention.

FIG. 4

FIG. 5 is a diagram illustrating various aberrations of the wide-field eyepiece according to the second embodiment of the present invention.

FIG. 6

FIG. 7 is a diagram illustrating various aberrations of the wide-field eyepiece according to the third embodiment of the present invention.

FIG. 8

FIG. 9 is a diagram illustrating various aberrations of the wide-field ocular lens according to the fourth embodiment of the present invention.

Claims (1)

(57) [Claims] 1. A positive first lens having a strong convex surface facing the eye, a positive second lens, a biconcave third lens, a positive fourth lens, and a positive fifth lens in order from the objective side. And an eyepiece that satisfies the following conditional expression: _{-1.0 ≦ f 3 / f ≦ -0.7} 0.45 ≦ L / f A ≦ 0.8 0.3 ≦ f 5 / f 4 ≦ 0.8 , however, f _n: a focal length of the n lens f: focal length f _A of the system as a whole: the Focal length from the first lens to the second lens L: distance from the first surface of the first lens to the first surface of the third lens