JP3530032B2 - Wide-field eyepiece - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a wide-field eyepiece used for a telescope or binoculars. 2. Description of the Related Art Wide-field eyepieces used for telescopes and binoculars include, for example,
Although a lens disclosed in Japanese Patent Application Laid-Open No. 2-222914 is known, this lens system requires six or more lenses. It should be noted that, in the claims of the publication, a wide range of conditions is set, and it is difficult to reliably obtain good performance only under such conditions. Further, in the wide-field eyepiece disclosed in Japanese Patent Application Laid-Open No. 6-175046, the number of lens elements is as small as five, but the distortion is insufficiently corrected, which results in about 9% distortion. [0003] The present invention has been made in view of the above circumstances,
Wide viewing angle of 65 ° or more, 5 to 6 lenses
It is an object of the present invention to provide a wide-field eyepiece in which the number of aberrations is good and the distortion is particularly excellently corrected to 6% or less. A wide-field eyepiece according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a positive lens unit as a whole. The third lens group includes a cemented lens having a refractive power, the fourth lens group having a positive refractive power, the first lens group includes a single lens having a concave surface on both sides, and the second lens group includes one or two lenses. The third lens group is composed of a cemented lens in which a convex lens and a concave lens are arranged in order from the object side, and the fourth lens group has a surface with a larger curvature directed to the object side. It is constituted by a convex lens, and further satisfies the following conditional expressions (1) to (7). (1) 1.3 <−f ₁ /f<2.2 (2) 2.0 <R _1b /f<4.0 (3) 1.3 <f ₂ /f<2.2 (4) 2 0.0 <f ₃ /f<4.5 (5) 1.8 <f ₄ /f<3.2 (6) 0.05 <N ₃₂ −N ₃₁ (7) 0.015 <1 / ν ₃₂ − 1 / ν ₃₁ where f _i : focal length of the i-th lens group f: focal length of the entire system R _1b : radius of curvature v _{31 of} the first lens group on the eye side, N ₃₁ : convex lens of the third lens group Abbe number and refractive index ν ₃₂ , N ₃₂ : Abbe number and refractive index of the concave lens of the third lens group. Generally, in a telescope system combining an objective lens and an eyepiece, the angle of view of the objective lens is Since the principal ray is small and passes near the center of the objective lens, almost no distortion occurs in the objective lens. On the other hand, the eyepiece has positive power as a whole, and its exit pupil is located behind the eyepiece, so that the principal ray from the objective is sharply bent in the optical axis direction by the eyepiece,
As a result, most of the distortion is caused by the eyepiece. By the way, the distortion becomes conspicuous when it exceeds 6%. Therefore, the first lens group located closest to the object side of the eyepiece is made a negative single lens to rapidly diverge the principal ray, thereby generating negative distortion and reducing positive distortion. The first lens unit has concave surfaces on both surfaces to suppress other aberrations, particularly coma. Here, when the value exceeds the upper limit of the conditional expression (1), the divergence of the principal ray is reduced, and the distortion is increased. When the value is below the lower limit, the distortion decreases, but other aberrations increase. When the value exceeds the upper limit of the conditional expression (2), the radius of curvature of the second surface of the first lens unit becomes excessively large, and the coma in the entire system becomes insufficiently corrected. On the other hand, when the value is below the lower limit, the principal ray is rapidly diverged on this surface, and the distortion is reduced, but other aberrations are increased. Further, if the chief ray diverged by the first lens group is suddenly brought closer to the optical axis by the positive power of a part of the subsequent lens group, the positive distortion increases. Therefore, it is necessary to divide the power in each lens unit of the fourth lens unit and gradually change the direction of the principal ray. From such a viewpoint, when the value goes below the lower limit of conditional expressions (3) to (5), distortion increases. If the value exceeds the upper limit, it becomes difficult to obtain a desired focal length. The objective lens usually has a positive Petzval sum, and the meridional image plane and the sagittal image plane are curved toward the objective lens. If the average image plane of the meridional image plane and the sagittal image plane of the eyepiece is made flat, the average image plane will not be flat in combination with the objective lens. Therefore, by making the surface of the fourth lens group having a larger curvature the surface on the object side, various aberrations are improved, and the average image plane of the eyepiece can be matched with the average image plane of the objective lens. The conditional expression (6) is to give a predetermined diverging effect to the joint surface. By satisfying conditional expression (6), it is possible to suppress an increase in curvature of field and distortion. Further, the conditional expression (7) indicates a difference in chromatic dispersion by a reciprocal difference of the Abbe number of the cemented lens. By satisfying conditional expression (7), lateral chromatic aberration and axial chromatic aberration can be favorably corrected. A wide-field eyepiece according to an embodiment of the present invention will be described below with reference to the drawings. <Embodiment 1> Here, FIG. 1 shows the basic configuration of a lens according to Embodiment 1. As shown in FIG. 1, the wide-field eyepiece according to the present embodiment is disposed in the eyepiece of the monocular, and includes five lenses L _{1 to} L ₅ . First bi-concave lens L ₁ facing the surface of larger curvature
A first lens group G ₁ , a second lens group G ₂ composed of a biconvex second lens L ₂ having a surface with a larger curvature directed to the eye side, and a biconvex lens arranged in order from the object side a third lens L ₃ made of, a third lens group G ₃ formed by joining the fourth lens L ₄ consisting of a negative meniscus lens having a concave surface facing the object side, the object side, the face of the larger curvature and a fourth lens group G ₄ consisting of the fifth lens L ₅ of biconvex lens made by arranging from the object side in this order. Further, it is configured as in the following conditional expression. (1) 1.3 <−f ₁ /f<2.2 (2) 2.0 <R _1b /f<4.0 (3) 1.3 <f ₂ /f<2.2 (4) 2 0.0 <f ₃ /f<4.5 (5) 1.8 <f ₄ /f<3.2 (6) 0.05 <N ₃₂ −N ₃₁ (7) 0.015 <1 / ν ₃₂ − 1 / ν ₃₁ where f _i : focal length of the i-th lens group f: focal length of the entire system R _1b : radius of curvature v _{31 of} the first lens group on the eye side, N ₃₁ : convex lens of the third lens group Abbe number and refractive index ν ₃₂ , N ₃₂ : Abbe number and refractive index of the concave lens of the third lens group. According to the wide-field eyepiece thus constructed, the object image (not shown) by the objective lens (not shown) The object image position 1 is shown) for each of the lens groups G _{1 to} G ₄
Thereby, the image is guided to the eye point position EP and an image is formed again on the retina. Next, in Example 1, the radius of curvature R (mm) of each lens surface, the center thickness of each lens, the air gap d (mm) between each lens, and the d line of each lens (λ = 587.6 nm) Are shown in Table 1 below. However, in Table 1 and Tables 2 and 3 described later, the numbers corresponding to each of R, d, N, and ν are sequentially increased from the object side. [Table 1] Further, in the first embodiment, -f ₁ /
f, R _1b / f, f ₂ / f, f ₃ / f, f ₄ / f, N
The respective values of _32- N ₃₁ , 1 / ν ₃₂ −1 / ν ₃₁ , the distortion, and the viewing angle are set as shown in Table 4 below. Accordingly, all of the conditional expressions (1) to (7) are satisfied, and a distortion of 6% or less and a viewing angle of 65 degrees or more are achieved. <Embodiment 2> Next, FIG. 2 shows a lens configuration of Embodiment 2. The first lens L ₁ is the object side, toward the face of greater curvature, except that the second lens L ₂ is a positive meniscus lens having a concave surface on the object side, the lens arrangement and conditions Equations (1) to (7) are substantially the same as in the first embodiment. The radius of curvature R (mm) of each lens surface, the center thickness of each lens, the air gap d (mm) between each lens, the refractive index N and d-line Abbe number ν of each lens in Example 2 are as follows. It is shown in Table 2. [Table 2] Further, -f ₁ /
f, R _1b / f, f ₂ / f, f ₃ / f, f ₄ / f, N
The respective values of _32- N ₃₁ , 1 / ν ₃₂ −1 / ν ₃₁ , the distortion, and the viewing angle are set as shown in Table 4 below. Therefore, all of the conditional expressions (1) to (7) are satisfied, and a distortion of 6% or less and a viewing angle of 65 degrees or more are achieved. <Embodiment 3> Next, FIG. 3 shows a lens configuration of Embodiment 3. The second lens group G ₂ is constituted by two biconvex lens L _2, L _3, except that there is a six element, the lens arrangement and conditional expressions (1) to (7) above embodiment It is almost the same as 1. However, the fifth lens L ₅ is a biconcave lens, the sixth lens L ₆ is a meniscus lens. Table 3 below shows the radius of curvature R (mm) of each lens surface, the center thickness of each lens, the air gap d (mm) between each lens, the refractive index N and d-line Abbe number ν of each lens in the third embodiment. 3 is shown. [Table 3] Further, in the third embodiment, -f ₁ /
f, R _1b / f, f ₂ / f, f ₃ / f, f ₄ / f, N
The respective values of _32- N ₃₁ , 1 / ν ₃₂ −1 / ν ₃₁ , the distortion, and the viewing angle are set as shown in Table 4 below. Therefore, all of the conditional expressions (1) to (7) are satisfied, and a distortion of 6% or less and a viewing angle of 65 degrees or more are achieved. [Table 4] Incidentally, Embodiments 1, 2, and 3
4, (a), (b), (a), (b), and (b) of FIG. As is apparent from FIGS. 4 to 6, according to the above-described embodiments, various aberrations can be improved, and performance that can be favorably used as a wide-field eyepiece can be obtained. It should be noted that the wide-field eyepiece of the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the curvature radius R of each lens can be changed.
The distance (or the lens thickness) d can be changed as appropriate. As described above, according to the wide-field ocular lens of the present invention, the four-group lens arrangement as described above is used, and by satisfying a predetermined conditional expression, the viewing angle is 65 ° or more. And a wide angle, the number of lenses can be reduced to 5 or 6, and various aberrations can be improved. In particular, distortion can be reduced to 6% or less.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a basic lens configuration according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing a basic lens configuration according to a second embodiment of the present invention. FIG. 4 is a schematic diagram illustrating a basic configuration of a lens according to a third embodiment of the invention. FIG. 4 is a diagram illustrating each aberration of the lens according to the first embodiment. FIG. 5 is a diagram illustrating each aberration of the lens according to the second embodiment. each aberration diagram G ₁ first lens group G ₂ the second lens group G ₃ third lens group G ₄ fourth lens group L ₁ ~L ₆ lenses X optical axis EP eyepoint first object eXPLANATION oF REFERENCE nUMERALS lens according Image position

Continuation of front page (56) References JP-A-10-39225 (JP, A) JP-A-9-90246 (JP, A) JP-A-9-5646 (JP, A) JP-A-9-5645 (JP) JP-A-7-333526 (JP, A) JP-A-6-148534 (JP, A) JP-A-6-109983 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G02B 25/00

Claims (1)

(57) [Claims 1] A first lens unit having a negative refractive power, a second lens group having a positive refractive power, and a cemented lens having a positive refractive power as a whole, in order from the object side. A third lens group, a fourth lens group having a positive refractive power; the first lens group is formed by a single lens having a concave surface on both sides; the second lens group is formed by one or two convex lenses; The third lens group is composed of a cemented lens of a convex lens and a concave lens in order from the object side,
The fourth lens group is composed of a convex lens having a surface with a larger curvature directed to the object side.
A wide-field eyepiece that satisfies (7). (1) 1.3 <−f ₁ /f<2.2 (2) 2.0 <R _1b /f<4.0 (3) 1.3 <f ₂ /f<2.2 (4) 2 0.0 <f ₃ /f<4.5 (5) 1.8 <f ₄ /f<3.2 (6) 0.05 <N ₃₂ −N ₃₁ (7) 0.015 <1 / ν ₃₂ − 1 / ν ₃₁ where f _i : focal length of the i-th lens group f: focal length of the entire system R _1b : radius of curvature v _{31 of} the first lens group on the eye side, N ₃₁ : convex lens of the third lens group Abbe number and refractive index ν ₃₂ , N ₃₂ : Abbe number and refractive index of the concave lens of the third lens group