JPH1138330A - Eyepiece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eyepiece capable of satisfactorily suppressing chromatic difference of magnification and capable of securing eye-relief for a long enough period, even though the eyepiece is simply constituted of a small number of lenses. SOLUTION: The macroscopic shape of the eyepiece is a modified Ramsden type, the eyepiece is constituted of a 1st nearly flat convex lens 10 and a 2nd flat convex lens 11, which are arranged in order from an object side so that both convex faces may face each other. Provided that the 1st to 4th faces of two positive refractive lenses 10 and 11 are expressed by 10a, 10b, 11a and 11b, a diffraction face is formed on at least one face, for example, the 1st face 10a.

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 an optical system having a relatively wide angle of view, such as an astronomical telescope or binoculars.

[0002]

2. Description of the Related Art An eyepiece is disposed between an eye and a real image formed by an objective optical system or between a display device such as a liquid crystal display device or a CRT and an eye to enlarge a real image or a displayed image. Has an action. Since the eyepiece needs to form the exit pupil at a position protruding toward the eye from the lens in order to secure a predetermined eye relief, coma aberration, field curvature, chromatic aberration of magnification, and the like are likely to occur.

As an inexpensive eyepiece having a simple structure,
Conventionally, a Ramsden-type eyepiece has been known. The Ramsden type eyepiece is configured by arranging two plano-convex lenses having the same focal length with their convex surfaces facing each other at an interval equal to the entire focal length, and can theoretically suppress the occurrence of lateral chromatic aberration.

However, the Ramsden-type eyepiece has the disadvantage that the eye relief is relatively short and dust and scratches on the lens appear conspicuous in the field of view because the eye is in focus on the lens surface of the plano-convex lens on the object side. is there. Therefore, the conventional two-piece eyepiece is configured to improve the above-mentioned disadvantages to some extent by removing the above-mentioned disadvantages from the balance between the focal lengths of the two plano-convex lenses and the lens interval from the above-mentioned conditions. ing.

FIG. 1 is a lens diagram showing an example of the above-mentioned conventional modified Ramsden type eyepiece. Two plano-convex lenses 1 and 2 having the same focal length are arranged face-to-face in order from the object side on the left side in the drawing. Table 1 shows the numerical configuration of the lens shown in FIG.
R is the diameter of the eye ring, B is the angle formed by the emitted light beam with respect to the optical axis, f is the focal length of the entire system, r is the radius of curvature of each lens surface, d is the lens thickness or lens interval, and n is the distance of each lens. d-
The index of refraction at the line (588 nm) and ν indicate the Abbe number of each lens. The surface number S indicates the stop position. The distance d2 between the two lenses is set shorter than the focal length f of the entire system.

[0006]

[Table 1]

FIGS. 2A and 2B show various aberrations of the conventional eyepiece. FIG. 2A shows spherical aberration at d-line, g-line and C-line, FIG. 2B shows chromatic aberration of magnification at g-line and C-line, and FIG. Astigmatism (S: sagittal, M: meridional), (D) shows distortion. The unit of the horizontal axis indicating the amount of distortion is percent (%),
The unit of the horizontal axis showing other aberration amounts is mm.

[0008]

However, when the condition of the Ramsden type is removed so that the eye relief is lengthened as in the above-described conventional example, the amount of chromatic aberration of magnification increases as shown in FIG. 2 (B). . That is, the conventional eyepiece of this type has a problem that the eye relief cannot be sufficiently long while the chromatic aberration of magnification is sufficiently small.

The present invention has been made in view of the above-mentioned problems of the prior art, and has a simple configuration with a small number of lenses, while suppressing lateral chromatic aberration sufficiently small.
It is an object of the present invention to provide an eyepiece that can ensure a sufficiently long eye relief.

[0010]

In order to achieve the above object, an eyepiece according to the present invention has a magnification by combining a plurality of refractive lenses having a positive power and a diffraction surface having a positive power. It is characterized in that occurrence of chromatic aberration is suppressed. That is, in the eyepiece of the present invention, at least two refractive lenses having positive power and at least one phase-type diffractive surface having positive power are arranged closer to the eye than the image formation position. It is characterized by.

The two refracting lenses can both be composed of plano-convex lenses, in which case the convex surfaces can be arranged facing each other. The diffractive surface may be formed on the lens surface of the refractive lens, or may be formed on a diffractive element independent of the refractive lens. Further, the diffractive surface may be formed on the lens surface of a single refractive lens, or may be formed on the lens surfaces of a plurality of refractive lenses. Among the lens surfaces of the lens on which the diffraction surface is formed, the surface on which the diffraction surface is not formed can be made aspheric.

When the diffractive surface is provided as an element independent of the refraction lens, and when two refraction lenses are disposed, they can be disposed between them. When the diffraction surface is formed by concentrically forming a plurality of orbicular zones formed of a plane perpendicular to the optical axis around the optical axis, the macroscopic shape is a concave surface.

When the eyepiece of the present invention is used for guiding an image formed by the objective lens to the eye, a first lens group having a weak power can be provided on the objective lens side of the field stop. It is desirable that the diffractive surface is composed of a plurality of annular zones concentric with the optical axis, and is set so that the gap in the optical axis direction between adjacent annular zones increases as the distance from the optical axis increases.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an eyepiece according to the present invention will be described below. The eyepiece according to the embodiment includes at least two refractive lenses and at least one phase-type diffractive surface having a positive power, and is disposed between the image forming position and the eye to enlarge the image. It has the effect of doing.
In this specification, “image forming position” is used as a concept including a real image formed by an objective optical system and an image forming position of a display element such as a liquid crystal display element or a CRT.

Since a diffractive lens has a dispersion characteristic of an opposite sign to that of a refractive lens and is equivalent to a refractive lens having a negative Abbe number, a diffractive lens having a positive power and a diffractive lens having a positive power are used. Chromatic aberration can be corrected by combining them. As a result, of the positive power of the whole eyepiece system, the power to be borne by the refraction lens can be suppressed to about 2/3 as compared with a lens having no diffraction lens, and a glass material having a low refractive index can be used. In addition, since the cost of the glass material is low and the curvature may be small, the amount of off-axis aberrations can be suppressed to a small value. In addition, since it is not necessary to use a refractive lens having negative power for correcting chromatic aberration, the weight can be reduced without increasing the number of lenses.

The diffractive surface may be formed on one surface of the refractive lens, or may be formed as a diffractive element independent of the refractive lens. 3 to 5 are explanatory views showing variations when a diffraction surface is formed on one surface of a refractive lens. In each case, FIG. 3 (A), FIG. 4 (A), FIG. 5 (A)
As shown in (1), the diffraction surface is constituted by a plurality of concentric annular zones centered on the optical axis. As shown in FIG. 3 (B), in the case where a diffractive surface in which each orbicular zone is a plane perpendicular to the optical axis is formed on a surface S11 of a substantially plano-convex lens L10 having no power as a refractive lens, As shown in FIG. 3C, the macroscopic shape of the surface S11 is concave.

When each annular zone is formed of a flat surface as shown in FIG. 3, a lens having a diffractive surface can be formed by a mold. In this case, the processing accuracy of the mold at the time of molding determines the accuracy of the diffraction surface formed on the lens. The mold is cut with a lathe using a cutting tool having a planar edge. Since the plane of the diamond bite is a plane due to the crystal structure, the precision is extremely high, and since the contact area is large, the wear is relatively small, so that a shape as designed can be accurately processed.

As shown in FIG. 4B, a Fresnel lens type diffraction element in which each annular zone is not perpendicular to the optical axis is formed on a plane S21 of the plano-convex lens L20 having no power as a refractive lens. When a surface is formed, the macroscopic shape of the surface S11 is a plane as shown in FIG. In the case of forming a Fresnel lens-shaped diffraction surface in a macroscopic planar shape as shown in FIG. 4, the diffraction surface can be formed by a lithography technique.

As shown in FIG. 5B, a case where a diffractive surface in which each ring zone is not perpendicular to the optical axis is formed on a convex surface S31 having power as a refractive lens of a plano-convex lens L30. As shown in FIG. 5 (C), the macroscopic shape of the convex surface S31 is the same curved surface as when no diffraction surface is formed.

In an eyepiece, on a lens surface close to a field stop, an area where a light beam emitted from one object spreads is small, and a range of an incident angle of a light beam passing through one point on the lens surface is narrow. On the other hand, in the lens close to the eye side, since the luminous flux emitted from one object point greatly spreads on the lens surface and overlaps each other, the range of the incident angle of the light beam passing through one point on the lens surface is wide. When a phase-type diffractive lens is formed of a material having a finite refractive index, the amount of phase shift increases as the angle of incidence increases, so the amount of phase shift depends on the angle of incidence for a lens closer to the eye. As a result, the diffraction efficiency is greatly reduced. Therefore, when focusing on diffraction efficiency, it is desirable that the diffraction surface is arranged at a position close to the field stop.

On the other hand, in view of the visibility of the annular zone in the visual field, it is desirable that the diffractive surface is as far away from the image forming position as possible. If the diopter between the diffraction plane and the position where the image is formed differs by about 10 diopters, the annular pattern seen in the field of view does not hinder the view. Therefore, the eyepiece lens has a combined focal length of the lens closer to the eye than the image forming position (position of the field stop), f, the distance between the image forming position and the apparent diffraction plane position viewed from the image forming position. Where L is
It is desirable to satisfy (1). ^{f 2/100 <L ... (} 1)

The condition (1) is an expression that specifies that the diopter difference between the diffraction surface and the image forming position is greater than 10 diopters. It doesn't hinder your view. When the condition (1) is not satisfied, the annular structure hinders observation in the visual field.

Further focusing on the effect of correcting the chromatic aberration of magnification, the chromatic aberration of magnification can be corrected better as the product of the height of the paraxial ray and the height of the marginal ray increases. When the diffraction surface is provided at a position close to the eye or at a position close to the eye side where the height of the paraxial ray is low, the power of the diffraction lens must be set relatively large. However, in order to increase the power, the width of the orbicular zone must be narrowed and the processing becomes difficult. Therefore, it is desirable that the position of the diffraction surface satisfies the following condition (2). 0.30 <L / f (2)

When the condition (2) is satisfied, the height of the marginal ray at the position of the diffractive surface becomes sufficiently high. Therefore, even if the power of the diffractive lens is not so increased, that is, the annular zone becomes difficult to process. , A sufficient effect of correcting lateral chromatic aberration can be obtained.

Since it is difficult to wipe off dirt and hard coat the diffractive surface, it is desirable to arrange the diffractive surface at a position inside the lens system where dirt and scratches are less likely to occur. When a thick coating layer such as a hard coat is provided on the phase type diffraction surface, the coating layer fills the steps of the diffraction surface,
Unnecessary diffracted light is generated because the diffracting surface cannot perform the function as designed, and the contrast of the image may be reduced. Therefore, it is desirable that the phase type diffraction surface is formed on a lens surface other than the surface closest to the eye.

In the case of an eyepiece, if dirt or dirt adheres to the lens surface near the position where the eye is in focus, these flaws or dirt can be seen in the observation visual field. It is desirable to be arranged in a difficult closed space. By placing a lens with low power in front of the field stop and sealing the space where the lens near the focus position is located across the field stop, even if there is dust or dirt, they will not be noticeable Can be.
Such a configuration is particularly effective when applied to a device in which the eyepiece can be replaced.

Although one diffractive surface may be provided for two refracting lenses, the width of the orbicular zone becomes smaller as the distance from the optical axis becomes smaller. It may be too narrow, making processing difficult. In such a case, by providing two or more diffractive surfaces and sharing the function of correcting the chromatic aberration of magnification, a large effect of correcting the chromatic aberration of magnification can be exerted even when the annular width of each diffraction surface is increased.

Furthermore, of the lens surfaces of the refractive lens, the surface on which no diffractive surface is formed is an aspheric surface whose curvature becomes weaker toward the periphery, so that not only lateral chromatic aberration but also coma aberration, distortion and the like can be reduced. Various aberrations can be corrected at the same time.

[0029]

EXAMPLES Next, eight specific examples satisfying the conditions of the above-described embodiment will be presented. Examples 1 to 5 are modified Ramsden eyepieces, which are closer to the eye than the field stop.
The two positive lenses are arranged such that surfaces having relatively large positive power are opposed to each other. First from object side
When the surface, the second surface, the third surface, and the fourth surface are defined, Example 1 diffracts into the first surface, Example 2 diffracts into the second surface, Example 3 diffracts into the third surface, and Example 4 diffracts into the fourth surface. Embodiment 5 The surface is integrally formed.
In this example, an element having a diffraction surface is arranged as an independent element between two lenses. In Examples 1, 4, and 5, the diffractive surface is formed on a surface having no power as a refractive lens, and the orbicular zone is formed as a plane perpendicular to the optical axis as shown in FIG. In another embodiment, a diffractive surface is formed on a surface having power as a refractive lens, and is formed as a surface having a curved macroscopic shape as shown in FIG. When a diffractive surface is formed on a convex surface as shown in FIG.
For phase matching, it is necessary to increase the gap in the optical axis direction between the annular zones as the distance from the optical axis increases.

In the following embodiments, the diffractive surface is represented by a macroscopic radius of curvature and an optical path difference function indicating the additional amount of the optical path length that the diffractive lens should have as a function of the height h from the optical axis. Is done. The optical path difference added by the diffraction lens, △ φ (h) = represented by ^{(P2h 2 + P4h 4 + P6h} 6 ...) × λ. P2, P4, ... are second, fourth, sixth, respectively ...
Is the coefficient of In this representation format means having a paraxial manner positive power when the coefficient P2 sections of h ² is negative. h ⁴
When the coefficient P4 of the term is positive, the negative power increases toward the periphery.

The actual microscopic shape of the lens is determined so as to have a Fresnel lens-shaped additional optical path length △ φ ′ in which a component of an integral multiple of the wavelength of the optical path length is eliminated. △ φ '(h) = ( MOD (P2h 2 + P4h 4 + P6h 6 ... + Const, l) -
Const) × λ The constant term Const is a constant for setting the phase at the boundary position of the annular zone, and takes an arbitrary number from 0 to 1. MOD (X, Y) is a function that gives the remainder of X divided by Y. ^{MOD (P2h 2 + P4h 4 +} ...
The point of h where the value of + Const, 1) becomes 0 is the boundary of the ring zone. A gradient and a step are set on the base shape so as to have an optical path difference of △ φ ′ (h). In the embodiments described below,
Const = 0.5.

[0032]

Embodiment 1 FIG. 6 shows a lens configuration of an eyepiece according to Embodiment 1. The macroscopic shape of the eyepiece of Example 1 is a modified Ramsden type similar to that of the conventional example, and the first lens 10 which is almost plano-convex in order from the object side on the left side in the drawing.
And a plano-convex second lens 11 are arranged with their convex surfaces facing each other. The first surface to the fourth surface are 10a,
Assuming that the diffraction surfaces are 10b, 11a, and 11b, in the first embodiment, a diffraction surface is formed on the first surface 10a.

Table 2 shows a specific numerical configuration of the eyepiece of the first embodiment. In the table, ER is the diameter of the eye ring, B is the angle formed by the emitted light beam with respect to the optical axis, f is the focal length of the entire system, fa is the focal length of the lens closer to the eye than the field stop, and L is the image formation position. The distance between (field stop position) and the apparent diffraction plane position viewed from the image formation position, P2, P4, P6
Are the coefficients of the second, fourth and sixth order terms of the optical path difference function,
fd is the focal length of only the diffractive component of the diffractive surface at d-line (588 nm), φ (h) is the value of the optical path difference function of the diffractive surface at the height h from the optical axis, and r is the A radius of curvature, d is a lens thickness or a lens interval, n is a refractive index of each lens in d-line, and ν is an Abbe number of each lens. The surface number S indicates the position of the field stop. In the table, the surface on which the diffraction surface is formed is indicated by “*”.

[0034]

[Table 2]

FIG. 7 shows various aberrations of the eyepiece of Example 1, (A) is spherical aberration at d-line, g-line and C-line, (B) is chromatic aberration of magnification at g-line and C-line, and (C) Denotes astigmatism (S: sagittal, M: meridional), and (D) denotes distortion. The unit of the horizontal axis indicating the amount of distortion is percent (%),
The unit of the horizontal axis showing other aberration amounts is mm.

The first embodiment shown in Table 2 is different from the conventional example shown in Table 1 only in the presence or absence of the diffraction surface.
Comparing FIG. 2 with FIG. 7, it can be understood that the introduction of the diffractive surface satisfactorily corrects both lateral chromatic aberration and axial chromatic aberration without deteriorating other aberrations.

[0037]

[Embodiment 2] FIG. 8 is a lens diagram showing a configuration of an eyepiece according to Embodiment 2. FIG. The macroscopic shape of the eyepiece of Example 2 is a modified Ramsden type similar to the conventional example, and the plano-convex first lens 12 and the plano-convex second lens 13 are arranged in order from the object side on the left side in the drawing. Are arranged with the convex surfaces facing each other. The first to fourth surfaces are 12a, 12b,
13a and 13b, a diffraction surface is formed on the second surface 12b in the second embodiment. Table 3 shows a specific numerical configuration of the second embodiment. Each graph of FIG. 9 shows various aberrations due to the configuration of the second embodiment.

[0038]

[Table 3]

[0039]

Third Embodiment FIG. 10 is a lens diagram showing a configuration of an eyepiece according to a third embodiment. The macroscopic shape of the eyepiece of Example 3 is a modified Ramsden type similar to the conventional example, and the plano-convex first lens 14 and the plano-convex second lens 15 are arranged in order from the object side on the left side in the figure. Are arranged with the convex surfaces facing each other. The first to fourth surfaces are 14a, 14
b, 15a, and 15b, the third surface 15 in the third embodiment.
A diffraction surface is formed on a. Table 4 shows a specific numerical configuration of the third embodiment. Each graph in FIG. 11 shows various aberrations due to the configuration of the third embodiment.

[0040]

[Table 4]

[0041]

Fourth Embodiment FIG. 12 is a lens diagram showing a configuration of an eyepiece according to a fourth embodiment. The macroscopic shape of the eyepiece of Example 4 is a modified Ramsden type similar to the conventional example, and the plano-convex first lens 16 and the plano-convex second lens 17 are arranged in order from the object side on the left side in the figure. Are arranged with the convex surfaces facing each other. The first to fourth surfaces are 16a, 16
b, 17a, and 17b, the fourth surface 17 in the fourth embodiment.
b has a diffraction surface. Table 5 shows a specific numerical configuration of the fourth embodiment. Each graph of FIG. 13 shows various aberrations due to the configuration of the fourth embodiment.

[0042]

[Table 5]

[0043]

Fifth Embodiment FIG. 14 is a lens diagram showing a configuration of an eyepiece according to a fifth embodiment. The eyepiece of the fifth embodiment is similar to the conventional example, and is a modified Ramsden type two plano-convex lenses 18 and 1.
9, a diffraction element 20 having a diffraction surface formed on one surface is arranged as an element independent of a plano-convex lens. The first to sixth surfaces are 18a, 18b, 20a, 20
b, 19a, and 19b, the third surface 20 in the fifth embodiment.
A diffraction surface is formed on a. Table 5 shows a specific numerical configuration of the fifth embodiment. Each graph of FIG. 15 shows various aberrations due to the configuration of the fifth embodiment.

[0044]

[Table 6]

In the structure of the fifth embodiment, the diffractive surface is formed on an element having a center thickness of 0 disposed between the first and second lenses. It is formed on a device having a finite center thickness. In that case, the distance between the lenses may be changed according to the thickness of the element and the refractive index.

The first to fourth embodiments described above are designed with priority given to the correction of the chromatic aberration of magnification, so that axial chromatic aberration occurs within the allowable range. As is clear from the aberration diagrams of the respective embodiments, when the lateral chromatic aberration is corrected to the same level, the axial chromatic aberration is insufficiently corrected in the first and second embodiments.
In No. 4, axial chromatic aberration is overcorrected. When the diffractive surface is provided as an element independent of the refractive lens as in the fifth embodiment, axial chromatic aberration can be corrected well.

Embodiments 6 to 8 to be described below are examples of eyepieces for observing a real image formed by an objective lens. A lens having a weak power is arranged closer to the objective lens than the position where the image is formed. I have. That is, the image forming position is inside the eyepiece lens system. When observing an image formed by an objective lens, if a negative lens is arranged closer to the objective lens side than the image plane of the objective lens, field curvature and distortion can be corrected well.

[0048]

Sixth Embodiment FIG. 16 is a lens diagram showing a configuration of an eyepiece according to a sixth embodiment. The eyepiece according to the sixth embodiment has a negative meniscus lens 21 as a first lens group on the objective lens side on the left side in FIG.
Are arranged, and a biconvex lens 22 as a second lens group and a biconvex lens 23 as a third lens group are arranged closer to the eye than the stop S. Assuming that the first to sixth surfaces are 21a, 21b, 22a, 22b, 23a, and 23b, the third surface 22 included in the second lens group in the sixth embodiment.
A diffraction surface is formed on a. Table 7 shows a specific numerical configuration of the sixth embodiment. Each graph of FIG. 17 shows various aberrations due to the configuration of the sixth embodiment.

In the sixth embodiment, the fourth surface 22b is formed of a rotationally symmetric aspheric surface. For the aspherical surface, the distance (sag amount) from the tangent plane on the optical axis of the aspherical surface to the coordinate point on the aspherical surface whose height from the optical axis is h is X, and the curvature of the aspherical surface on the optical axis. Assuming that (1 / r) is C, the conic coefficient is K, the fourth and sixth order aspherical coefficients are A4 and A6, and are represented by the following equations. The radius of curvature of the aspheric surface in Table 7 is the radius of curvature on the optical axis, and the conical coefficient and the aspheric surface coefficient are shown in Table 8. ^{X = Ch 2 / (1 +} √ (1- (1 + K) C2h 2)) + A4h 4 + A6h 6

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

Seventh Embodiment FIG. 18 is a lens diagram showing a configuration of an eyepiece according to a seventh embodiment. In the eyepiece according to the seventh embodiment, the negative meniscus lens 24 as the first lens group and the two biconvex lenses 25 and 26 as the second and third lens groups sandwich the stop S, as in the sixth embodiment. It is arranged and configured. The first to sixth surfaces are 24a, 24b, 25a, 25b, 26
a, 26b, the diffraction surface is formed on the fourth surface 25b included in the second lens group in the seventh embodiment.
5a is formed as a rotationally symmetric aspherical surface. Table 9 shows the specific numerical configuration of the seventh embodiment, and Table 10 shows the number of cones and the aspheric coefficient. Each graph of FIG. 19 shows various aberrations due to the configuration of the seventh embodiment.

[0053]

[Table 9]

[0054]

[Table 10]

[0055]

Eighth Embodiment FIG. 20 is a lens diagram showing a configuration of an eyepiece according to an eighth embodiment. The eyepiece according to the eighth embodiment has a negative meniscus lens 27 as a first lens group on the objective lens side on the left side in the drawing with respect to the stop S arranged at the image forming position.
Are arranged, and two biconvex lenses 28 and 29 constituting the second lens group and a biconvex lens 30 constituting the third lens group are arranged on the eye side of the stop S. The first to eighth surfaces 27a, 27b, 28a, 28
Assuming that b, 29a, 29b, 30a, and 30b, in the eighth embodiment, the fourth surface 28b and the sixth surface 29b have the same diffraction surface formed on the two surfaces, and the third surface 28a and the fifth surface 29
a is formed as a rotationally symmetric aspherical surface. Example 8
Is shown in Table 11, and the conical number and aspheric coefficient are shown in Table 12. Symbol L1 in Table 11 is the distance from the image forming surface to the first diffraction surface (fourth surface), L2 is the distance from the image forming surface to the second diffraction surface (sixth surface), and φ (15.67 ) Is the value of the optical path difference function on the fourth surface, φ (1
6.33) is the value of the optical path difference function on the sixth surface. FIG.
Each graph of the graph shows various aberrations due to the configuration of the eighth embodiment.

[0056]

[Table 11]

[0057]

[Table 12]

Table 13 below shows the conditions (1) and (2) described above.
The values of the respective examples are shown below. In each embodiment, each condition is satisfied, and the annular pattern seen in the field of view does not obstruct the view, and the height of the marginal ray at the position of the diffraction surface is sufficiently high. A sufficient magnification chromatic aberration correction effect can be obtained without increasing the power of the diffraction lens so much.

[0059]

[Table 13]

[0060]

As described above, according to the present invention, by forming a diffractive surface on at least one surface of at least two positive refraction lenses, it is possible to improve the chromatic aberration of magnification while ensuring a predetermined eye relief. A corrected eyepiece can be provided.

[Brief description of the drawings]

FIG. 1 is a lens diagram showing a configuration of a conventional Ramsden type eyepiece.

FIG. 2 is a graph showing various aberrations of the eyepiece of FIG.

FIG. 3 is an explanatory diagram showing a first variation when a diffractive surface is formed on a lens surface of a refractive lens.

FIG. 4 is an explanatory diagram showing a second variation when a diffraction surface is formed on the lens surface of a refractive lens.

FIG. 5 is an explanatory diagram showing a third variation in the case where a diffraction surface is formed on the lens surface of a refractive lens.

FIG. 6 is a lens diagram illustrating a configuration of an eyepiece according to a first embodiment.

FIG. 7 is a graph showing various aberrations of the eyepiece of Example 1.

FIG. 8 is a lens diagram illustrating a configuration of an eyepiece according to a second embodiment.

FIG. 9 is a graph showing various aberrations of the eyepiece of Example 2.

FIG. 10 is a lens diagram illustrating a configuration of an eyepiece according to a third embodiment.

FIG. 11 is a graph showing various aberrations of the eyepiece of Example 3;

FIG. 12 is a lens diagram illustrating a configuration of an eyepiece according to a fourth embodiment.

FIG. 13 is a graph showing various aberrations of the eyepiece of Example 4.

FIG. 14 is a lens diagram showing a configuration of an eyepiece according to a fifth embodiment.

FIG. 15 is a graph showing various aberrations of the eyepiece of Example 5.

FIG. 16 is a lens diagram showing a configuration of an eyepiece according to a sixth embodiment.

FIG. 17 is a graph showing various aberrations of the eyepiece of Example 6;

FIG. 18 is a lens diagram illustrating a configuration of an eyepiece according to a seventh embodiment.

FIG. 19 is a graph showing various aberrations of the eyepiece of Example 7.

FIG. 20 is a lens diagram illustrating a configuration of an eyepiece according to an eighth embodiment.

FIG. 21 is a graph showing various aberrations of the eyepiece of Example 8.

[Explanation of symbols]

 10 First lens 11 Second lens

Claims (13)

[Claims] 1. An eyepiece for observing an image, comprising: at least two positive power refracting lenses closer to the eye than a position where the image is formed; and a phase having at least one surface having positive power. An eyepiece comprising: a diffractive surface of a mold. 2. The eyepiece according to claim 1, wherein the two refracting lenses are both plano-convex lenses, and are arranged with their convex surfaces facing each other. 3. The eyepiece according to claim 1, wherein the diffraction surface is formed on a lens surface of the refractive lens. 4. The apparatus according to claim 1, wherein the diffraction surface is formed on lens surfaces of the plurality of refractive lenses.
An eyepiece according to item 1. 5. The lens on which the diffraction surface is formed,
The eyepiece according to claim 3, wherein the surface on which the diffraction surface is not formed is an aspheric surface. 6. The eyepiece according to claim 1, wherein the diffraction surface is formed on a diffraction element independent of the refractive lens. 7. The eyepiece according to claim 6, wherein the diffractive element is disposed between the two refractive lenses. 8. The diffractive surface is characterized in that a plurality of orbicular zones composed of planes perpendicular to the optical axis are formed concentrically about the optical axis, and the macroscopic shape is a concave surface. The eyepiece according to claim 1, wherein 9. A composite focal length of a lens closer to the eye than the image forming position is defined as f, and an interval between the image forming position and an apparent diffraction plane position viewed from the image forming position is defined as L. 2. The eyepiece according to claim 1, wherein the following condition (1) is satisfied. ^{f 2/100 <L ... (} 1) 10. A synthetic focal length of a lens closer to the eye than the image forming position is defined as f, and an interval between the image forming position and an apparent diffraction surface position viewed from the image forming position is defined as L. The eyepiece according to claim 1, wherein the condition (2) is satisfied. 0.30 <L / f (2) 11. An eyepiece for guiding an image formed by an objective lens to an eye, wherein, in order from the objective lens side,
A first lens group having a weak power, a field stop, a second lens group having a positive power, and a third lens group having a positive power are arranged, and the second lens group has at least one lens.
One of the lens surfaces has a diffractive surface having a positive power, and the diffractive surface is composed of a plurality of concentric zones with respect to an optical axis, and a gap in the optical axis direction between the adjacent annular zones is formed by light. An eyepiece characterized in that it becomes larger as the distance from the axis increases. 12. The eyepiece according to claim 11, wherein the second lens group includes a single lens, and the diffraction surface is formed on one of the lens surfaces. 13. The eyepiece according to claim 11, wherein the second lens group includes two lenses, and the diffractive surface is formed on one lens surface of each lens. .