JPH09166753A - Keplerian finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a finder having integrally excellent performance though it has extremely miniaturized and simple structure which is not obtained by conventional technique while utilizing the merits of Keplerian finder capable of clearly dividing a visual field. SOLUTION: The finder is constituted by arranging an objective lens O consisting of a positive lens component O1 turning its convex face having larger curvature toward the pupil side and a positive lens component O2 turning its convex face toward the object side and an eyepiece E including a positive lens component successively from the object side. In order to change angular magnification, an air interval between the components O1, O2 in the lens O is variable, and when it is defined that the focal distances of the components O1, O2 in the lens O are f1 and f2, 0.4<f1/f2<1.2 is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Kepler-type viewfinder having a small and simple structure incorporated in a still camera or the like.

[0002]

2. Description of the Related Art As a conventional finder, an inverse Galilean finder having an objective lens having a negative refractive power and an eyepiece lens having a positive refractive power, and an objective lens having a positive refractive power and a positive refractive power are provided. A Kepler type finder having an eyepiece has is known.

[0003]

Of these, the former reverse Galilean finder has the advantages of being compact and simple in structure, but has the drawback that its field of view cannot be clearly divided. On the other hand, the latter Kepler-type finder, on the contrary, can clearly divide the visual field by installing a visual field frame in the vicinity of the focal point of the objective lens, while it is disclosed in Japanese Utility Model Laid-Open No. 55-149725. However, the configuration is complicated and there is a problem that the cost is increased.

In view of this, the present invention takes advantage of the Kepler-type viewfinder that clearly divides the field of view and, at the same time, has an extremely small and simple structure which has never been seen in the past, but has an overall excellent performance. The purpose is to provide a low-priced viewfinder.

[0005]

In order to achieve the above object, in the present invention, as shown in FIG. 1, in order from the object side, a positive lens component O1 having a convex surface having a stronger curvature toward the pupil side, The objective lens O includes a positive lens component O2 having a convex surface directed toward the object side, and an eyepiece lens E including a positive lens component. The objective lens O and the positive lens component O1 in the objective lens are positive in order to change the angular magnification. It is a Kepler type finder in which the air gap between the lens component O2 and the lens component O2 is variable.

Then, the positive lens component O1 in the objective lens
Of the positive lens component O2 in the objective lens
When the focal length of the lens is f2, 0.4 <f1 / f2 <1.2 (1) is satisfied. Based on this configuration, the angular magnification is continuously or discontinuously changed by continuously or discontinuously changing the air space between the positive lens component O1 and the positive lens component O2 in the objective lens. Is also possible.

A field frame F is provided in the vicinity of the focal position where the inverted image of the objective lens O is formed, and a normal image for erecting the image of the subject is provided between the field frame F and the eyepiece lens E. It is preferable to provide the upright prism P, and it is more desirable that 1.55 <NP (2) is satisfied, where NP is the refractive index of the upright prism P.

Further, in order to reduce the cost, the positive lens component O1 and the positive lens component O2 in the objective lens O may be composed of the same lens component. Further, the positive lens component O2 in the objective lens and the positive lens component in the eyepiece may be composed of the same lens component.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the positive lens component O1 and the positive lens component O2 in the objective lens are arranged with an appropriate air gap, and the convex surfaces of these two positive lens components are opposed to each other. By adopting the configuration, it is possible to achieve a favorable aberration correction while realizing the configuration of the objective lens, which has conventionally required three or more lenses, with two lenses.

That is, the positive lens component O in the objective lens
By arranging 1 and the positive lens component O2 with an appropriate air gap, the positive lens component O2 located on the rearmost side (pupil side) in the objective lens also functions as a so-called field lens. It is possible to properly define the position of the eye point EP and the height of the off-axis light flux passing through the positive lens component O1 located closest to the object side in the objective lens, while eliminating the field lens that was required in the past. And

Based on this structure, by disposing the convex surfaces of the positive lens component O1 and the positive lens component O2 so as to face each other, both distortion and astigmatism can be corrected well. . As described above, in order to achieve good aberration correction while the objective lens O is composed of two positive lens components, it is necessary to appropriately distribute the refractive power of each lens component. Therefore, in the present invention, condition (1) defines an appropriate distribution of the refractive power of the positive lens component O1 and the positive lens component O2 in the objective lens.

When the lower limit of the condition (1) is exceeded, the refractive power of the positive lens component O1 located closest to the object side in the objective lens becomes excessive, and the positive lens component O2 located behind the positive lens component O2 becomes less effective as a field lens. Therefore, the aberration is deteriorated and the effective diameters of the positive lens component O1 and the positive lens component O2 in the objective lens are excessively increased. On the contrary, when the value exceeds the upper limit of the condition (1), the refracting power of the positive lens component O2 becomes excessive, so that it becomes extremely difficult to correct the off-axis aberration.

Further, in the above structure, an inverted image of the subject is formed at the focal position of the objective lens O, and when the image is magnified and observed through the eyepiece E, the inverted image is observed as it is. Arranging an erecting prism between the focal position of the objective lens and the eyepiece lens to erect this inverted image. Generally, there is a close relationship between the effective diameter of the entrance surface and the exit surface of the erecting prism and the optical path length, and it is known that the optical path length will inevitably become longer if the effective diameter is increased. Has been.

That is, this means that the angle of the effective diameter of the entrance surface with respect to the exit surface of the erecting prism does not exceed a certain value. Therefore, in order to obtain a wide apparent field of view in the finder having the above-described structure, it is necessary to set the refractive index of the erecting prism P to be high and to shorten the air-equivalent optical path length in the erecting prism. Therefore, in the present invention, the condition (2) is defined and the appropriate refractive index of the erecting prism P is defined, so that a wide apparent visual field can be secured.

If the range of the condition (2) is exceeded, the optical path length of the erecting prism P in terms of air increases, so that a wide apparent visual field cannot be secured. Further, since the critical angle of total reflection also increases at the reflecting surface in the erecting prism, the light quantity loss at the reflecting surface increases. Further, in order to achieve sufficient aberration correction in the finder of the present invention, it is desirable that the following conditions are further satisfied.

-1.2 <q1 <-0.25 (3) -0.1 <q2 <1.2 (4) where q1 and q2 are the shapes of the positive lens component O1 and the positive lens component O2 in the objective lens, respectively. It is a factor (so-called shape factor). This is defined by the following formula, where the radius of curvature of the object side surface and the radius of curvature of the image side surface of each lens component are RX and RY, respectively.

Q = (RY + RX) / (RY-RX) The condition (3) defines the shape of the positive lens component O1 located closest to the object side in the objective lens. When the upper limit of condition (3) is exceeded, the positive meridional field curvature becomes severe, and on the contrary, when the lower limit of condition (3) is exceeded, the negative meridional field curvature becomes severe, and in all cases, the off-axis viewfinder is off-axis. It deteriorates the performance.

The condition (4) defines the shape of the positive lens component O2 located closest to the pupil in the objective lens. If the upper limit of condition (4) is exceeded, it will be difficult to correct spherical aberration and coma, and if the lower limit of condition (4) is exceeded, negative distortion will increase, which is not preferable. In order to achieve a more well-balanced aberration correction, at least one surface of each of the positive lens component O1 and the positive lens component O2 in the objective lens is surrounded by the positive refractive power of each lens component from the optical axis. It is desirable to construct the aspherical surface so that it becomes gradually weaker as it goes to.

At this time, the aspherical surface can be expressed by the following equation. That is, the aspherical surface shape Sa in the positive lens component O1 is

[0020]

[Equation 1]

The aspherical surface shape Sb of the positive lens component O2 is

[0022]

(Equation 2)

The paraxial radii of curvature ra and rb at Sa and Sb are represented as

[0024]

(Equation 3)

[0025]

(Equation 4)

It is defined as Then, each lens component forming the objective lens O has the following condition (5) and condition (6).
It is desirable to satisfy 0.077 <Sa (0.4ra) / ra <0.082 (5) 0.025 <Sa (0.25rb) / rb <0.0315 (6) However, h is the height from the optical axis, and Sa and Sb are the tangent planes at the surface vertices. Distances measured along the optical axis to the aspherical surface at the height h, ra * and rb * are reference radii of curvature, κa and κb are conic constants, and Ai and Bi are i-th orders (i = 2, 4, 6, 8, 1
0) aspherical coefficient.

The condition (5) is to satisfactorily correct spherical aberration and coma. When the upper limit is exceeded, the effect of the aspherical surface is weak, and when the lower limit is exceeded, the effect of the aspherical surface is strong. Thus, in any case, it becomes difficult to sufficiently correct the aberration. Further, if the upper limit of the condition (6) is exceeded, it will be difficult to satisfactorily correct the negative distortion, and if the lower limit of the condition (6) is exceeded, a significant negative meridional field curvature will occur, which is not preferable.

In the finder according to the present invention, since the positive lens component O1 and the positive lens component O2 forming the objective lens are arranged with an air gap, the air gap formed by this is relatively. By changing it, it is possible to change the focal length of the objective lens. That is, by changing the air gap continuously or discontinuously, it is possible to change the angular magnification continuously or discontinuously to function as a variable power finder. Also in this case, by satisfying the respective conditional expressions of the present invention, it is possible to obtain a high-performance viewfinder in which the fluctuation of aberration during zooming is small.

As described above, when the present invention is constructed as a variable power (zoom) finder, the lower limit of conditional expression (1) is preferably 0.8 in order to obtain a large variable power effect. That is, since the objective lens O of the finder of the present invention has a convex / convex configuration, the greater the distribution of the refractive power with respect to the positive lens component O2 located on the image side in the objective lens, the more advantageous is the large zooming effect. However, as described above, it becomes extremely difficult to correct the off-axis aberration. On the contrary, if the distribution of the refractive power of the positive lens component O2 located closest to the pupil in the objective lens is small, a large zooming effect cannot be expected.

Therefore, if the upper limit of 1.2 to condition (1) is exceeded, it will be difficult to correct off-axis aberrations, and conversely the lower limit of 0.8 will be encountered.
When it exceeds, it becomes impossible to obtain a large zoom effect. Further, as described above, the positive lens component O1 and the positive lens component O2 forming the objective lens O are arranged with an appropriate air gap, but at this time, the positive lens component O
The on-axis thickness from the object side surface of 1 to the image side surface of the positive lens component O2 is D, and the positive lens component O1 forming the objective lens.
And the combined focal length of the positive lens component O2 is fO,
It is desirable to satisfy the following conditions.

0.8 <D / fO <1.5 (7) When the upper limit and the lower limit of this condition (7) are exceeded, the height of the main structure passing through the positive lens component O1 located on the object side in the objective lens is increased. However, it becomes difficult to correct off-axis aberrations such as coma. Further, it becomes difficult to give the function of the field lens to the positive lens component O2 located on the image side in the objective lens.

When the finder of the present invention is used as a variable power finder, it is preferable that the above condition (7) is satisfied in all variable power states, but it is particularly difficult to correct off-axis aberrations at the wide-angle end. In the above, it is more preferable that the upper limit of the above condition (7) is 1.4 or less. That is, when the axial thickness from the object side surface of the positive lens component O1 to the image side surface of the positive lens component O2 at the wide-angle end is Dw, 0.8 <Dw / fO ≤1.4 (8) may be satisfied. desirable.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 3 respectively show a configuration diagram of a Kepler-type finder of first and second embodiments, and this embodiment will be described in detail with reference to these drawings. In each embodiment, in order from the object side, a positive lens O1 having a stronger convex surface toward the pupil (eye point EP) side, and a positive lens O2 having a stronger convex surface toward the object side, an objective lens O composed of two positive lenses. And the field frame F arranged near the focal point
And an erecting prism P having four reflecting surfaces (for simplicity, the reflecting surface is drawn for simplicity), and an eyepiece E which is a positive lens.

The infinity light flux incident on the objective lens O is focused by the refracting power of the positive lens component O1 and the positive lens component O2 forming the objective lens, and is focused on the focal plane of the objective lens. To do. And the inverted image is
It is made erect by the action of the erecting prism P having four reflecting surfaces, and is guided to the position (eye point) EP where the pupil is placed through the eyepiece lens E.

The viewfinders shown in the first and second embodiments are variable-magnification viewfinders in which the angle of view is variable in the order of 37.8 ° to 57.6 ° and 38.6 ° to 56.4 °, respectively. In Tables 1 and 2 below, the values of specifications of the first and second embodiments are listed in order. In the table, the number at the left end represents the order from the object side, r is the radius of curvature of the lens surface (if the surface is an aspherical surface, the reference radius of curvature), d is the lens surface distance, and ν is the Abbe number. Refractive index n is a value for d-line (λ = 587.6 nm), m is angular magnification, z is diopter, 2ω is real visual field, 2ω ′ is apparent visual field, EP is eye point, and aspherical surface is
The surface number is indicated by adding * to the right, and the aspherical surface shape is shown by the aspherical surface equation described above.

In each specification table, the erecting prism P is shown in a developed state.

[0037]

[Table 1] (First Example) m = 0.425X to 0.614X, 2ω = 57.6 ° to 37.8 ° 2ω '= 23.8 °, z = -1.01 (Diopter), EP = 15.0 men rdn ν (1) 24.143 4.26 1.49108 57.6 O1 (2) * -11.558 d1 1.0 (3) * 11.558 4.26 1.49108 57.6 O2 (4) -24.143 d2 1.0 (5) ∞ 33.30 1.58518 31.1 P (6) -25.286 0.30 1.0 (7) 23.635 2.00 1.49108 57.6 E (8) -199.138 2nd surface (aspherical surface) κa = 0, A2 = A4 = A6 = A8 = A10 = 0 ra = ra = -11.558 3rd surface (aspherical surface) κb = 0, B2 = B4 = B6 = B8 = B10 = 0 rb = rb = 11.558 In the present embodiment, by changing the distance between the positive lens O1 and the positive lens O2 forming the objective lens O,
This is a variable-magnification (zoom) finder that changes the magnification.

That is, at the time of zooming from the wide-angle end in the minimum magnification state to the telephoto end in the maximum magnification state, both lenses move in opposite directions so that the lens interval between the positive lens O1 and the positive lens O2 increases. Further, in the objective lens, an aspherical surface whose curvature becomes gentle as it goes from the optical axis to the periphery is provided so that the refractive power of the positive lens gradually becomes weaker as it goes from the optical axis to the periphery. Since a part of the refracting power to be possessed is also shared by the exit surface of the erecting prism P, extremely good aberration correction is achieved overall from the wide-angle end to the telephoto end.

[0039]

(Table 2) (Second Example) m = 0.425X to 0.614X, 2ω = 56.4 ° to 38.6 ° 2ω '= 24.0 °, z = -1.01 (Diopter), EP = 15.0 men rdn ν (1) ∞ 3.50 1.49108 57.6 O1 (2) * -8.135 d1 1.0 (3) * 15.000 3.50 1.49108 57.6 O2 (4) -16.410 d2 1.0 (5) ∞ 33.30 1.58518 31.1 P (6) -25.286 0.30 1.0 (7) 23.635 2.00 1.49108 57.6 E (8) -199.138 2nd surface (aspherical surface) κa = 0.30, A2 = A4 = A6 = A8 = A10 = 0 ra = ra = -8.135 3rd surface (aspherical surface) κb = 0, B2 = B4 = B6 = B8 = B10 = 0 rb = rb = 15.000 Similar to the first embodiment, this embodiment is an example in which a variable power finder is used, and when zooming from the wide-angle end in the lowest magnification state to the telephoto end in the highest magnification state, a positive lens O1 in the objective lens is used. Both lenses are moved in opposite directions so that the air space between the positive lens and O2 is increased.

Then, the commonality of the two positive lenses constituting the objective lens is broken, and aberration correction is prioritized to form a plano-convex positive lens O1 and a biconvex positive lens O2, and an optical axis is provided in the objective lens. From the optical axis to the periphery, an aspherical surface is provided so that the curvature of the lens gradually decreases from the optical axis to the periphery so that the refractive power of the positive lens gradually decreases. Since the part is also shared by the exit surface of the erecting prism P, extremely excellent aberration correction is achieved overall from the wide-angle end to the telephoto end.

FIGS. 2 (a) and 4 (a) are aberration diagrams in the lowest magnification state (wide-angle end) of the first and second examples, respectively, and FIGS. 2 (b) and 4 (b). 6A and 6B are aberration diagrams in the highest magnification state (telephoto end) of the first and second examples, respectively.
It can be understood from the comparison of the aberration diagrams that the aberrations are well-balanced from the wide-angle end to the telephoto end in both Examples.

As described above, in each of the first and second embodiments, each optical member constituting the Kepler type finder, that is, the lens and the prism, can be made of plastic, and therefore can be easily manufactured by injection molding. Not only is it possible, but the cost can be reduced, which is extremely effective. Now, Table 3 below shows a numerical table corresponding to the conditions of each example. When the positive lens O1 and the positive lens O2 forming the objective lens are provided with aspherical surfaces, q1 and q2 corresponding to the shape factors of the positive lens O1 and the positive lens O2 are It is a value obtained from the paraxial radius of curvature.

[0043]

[Table 3] However,

[0044]

(Equation 5)

Is as follows.

[0046]

As can be seen from the above embodiments, according to the present invention, it is possible to obtain a Kepler-type finder which is excellent in aberration correction while having an extremely small size and a simple structure. Moreover, not only can all the optical members that make up the finder be made of plastic, but some of them can be made of a common lens, which is extremely effective because a significant cost reduction can be achieved. is there.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of the present invention.

2A and 2B are aberration diagrams of Example 1, in which FIG. 2A is an aberration diagram in a minimum magnification state (wide angle end), and FIG. 2B is an aberration diagram in a maximum magnification state (telephoto end).

FIG. 3 is a lens configuration diagram of a second embodiment of the present invention.

4A and 4B are aberration diagrams of Example 2, in which FIG. 4A is an aberration diagram at a minimum magnification state (wide-angle end), and FIG. 4B is an aberration diagram at a maximum magnification state (telephoto end).

[Explanation of symbols]

 O: Objective lens O1: Positive lens component O2: Positive lens component F: Field frame P: Erecting prism E: Eyepiece E.P .: Eye point

Claims (6)

[Claims] 1. An objective lens O comprising, in order from the object side, a positive lens component O1 having a convex surface having a stronger curvature toward the pupil side, and a positive lens component O2 having a convex surface facing the object side, and a positive lens component. An eyepiece E, and an air distance between the positive lens component O1 and the positive lens component O2 in the objective lens is variable in order to change an angular magnification, and a focal length of the positive lens component O1 in the objective lens is variable. Where f1 is the focal length of the positive lens component O2 in the objective lens and f2 is the focal length of the objective lens, 0.4 <f1 / f2 <1.2 is satisfied. 2. A field frame F is provided near the focal point of the objective lens O, and an erecting prism P is provided between the field frame F and the eyepiece lens E, and the refractive index of the erecting prism P is NP. The Kepler-type finder according to claim 1, wherein 1.55 <NP is satisfied. 3. The positive lens component O1 in the objective lens
3. The Kepler-type finder according to claim 1, wherein the positive lens component O2 and the positive lens component O2 are composed of the same lens component. 4. The Keplerian finder according to claim 1, wherein the following conditions are satisfied. -1.2 <q1 <-0.25 -0.1 <q2 <1.2 where q1 and q2 are the shape factors of the positive lens component O1 and the positive lens component O2 in the objective lens, respectively. 5. At least one surface of each of the positive lens component O1 and the positive lens component O2 is an aspherical surface, the height from the optical axis is h, and the aspherical surface of the positive lens component O1 is Let Sa be the distance measured from the tangent plane at the surface vertex to the aspheric surface at height h along the optical axis, and let Sa be the distance from the tangent plane at the surface vertex of the aspheric surface of the positive lens component O2 to the aspheric surface at height h. When the distance measured along the optical axis is Sb, the paraxial radius of curvature of the aspherical surface of the positive lens component O1 is ra, and the paraxial radius of curvature of the aspherical surface of the positive lens component O2 is rb, 0.077 <Sa A Kepler-type finder characterized by satisfying (0.4 ra) / ra <0.082 0.025 <Sa (0.25 rb) / rb <0.0315. 6. The Keplerian finder according to claim 1, wherein the following conditions are satisfied. 0.8 <D / fO <1.5 where D is the axial thickness from the object side surface of the positive lens component O1 to the image side surface of the positive lens component O2, and fO is the positive lens component O1 forming the objective lens. It is a combined focal length with the positive lens component O2.