JP2966043B2 - Viewfinder optical thread and eyepiece - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a finder optical system and an eyepiece used for an imaging device such as a silver halide camera and an electronic photographing camera.

[Prior Art] Conventional examples of a finder optical system and an eyepiece used in the above-mentioned photographing apparatus are described in JP-A-63-121008 and JP-A-1-129225.

The former conventional example is an eyepiece comprising two lenses, a positive lens and a negative lens. The purpose of this prior art constituted by two lenses is to realize achromatism and improve the performance. Certain conditions are set so that ghosts generated at that time are not noticeable.

The latter eyepiece is a three-piece eyepiece consisting of a positive lens, a positive lens, and a negative lens, and has a variable magnification with a variable air space between the second positive lens and the negative lens. is there.

[Problems to be Solved by the Invention] Among the above conventional examples, the eyepiece disclosed in Japanese Patent Application Laid-Open No. 63-121008 has an observation image arranged at an appropriate diopter because its front principal point is close to the eyepiece. If this is attempted, the air-equivalent length from the intermediate image forming surface to the eyepiece cannot be made too large, and this greatly restricts the configuration of the finder optical system.

In Japanese Patent Application Laid-Open No. 1-129225, the configuration length of the eyepiece lens is large, so that the miniaturization of the photographing equipment which anticipates this is prevented.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an eyepiece that can have a small and simple configuration even when the air conversion length from the intermediate image forming surface to the eyepiece is large.

It is another object of the present invention to provide a finder optical system which is low in height and in which an eyepiece can be arranged behind.

[Means for Solving the Problems] In order to achieve the above object, an eyepiece of the present invention comprises:
In an eyepiece for observing an image formed by an objective lens or an imaging lens through a reflecting system including a plurality of reflecting surfaces having an inverting action, a front group having a positive refractive power in order from the image forming surface side, Consisting of a rear group having refractive power,
The front group includes two positive lenses, and the rear group includes one negative lens, and satisfies the following conditions (1), (2), and (3).

(1) f _p /f<0.42 (2) | f _n / f _p | <1.5 (3) n _N <1.7 where f is the focal length of the eyepiece, f _p and f _n are the front group and the rear group, respectively. And n _N is the refractive index of the negative lens.

Further, the first finder optical system of the present invention is a finder optical system in which an optical axis on an image plane formed by an objective lens or an imaging lens does not intersect with an optical axis of an eyepiece. Guide to the eyepiece with multiple reflective surfaces that bend closer to the lens,
A reflective system arranged so that the optical path does not form a loop;
The front group includes a front group having a positive refractive power and a rear group having a negative refractive power in order from the image forming surface side.
The rear unit includes an eyepiece including one negative lens, and satisfies the following conditions (1), (2), and (3).

(1) f _p /f<0.42 (2) | f _n / f _p | <1.5 (3) n _N <1.7 where f is the focal length of the eyepiece, f _p and f _n are the front group and the rear group, respectively. And n _N is the refractive index of the negative lens.

Furthermore, a second finder optical system according to the present invention is characterized in that, in the first finder optical system, in the reflection system, an optical path in a section from the incident path to the last reflection surface is substantially M-shaped. .

In order to observe an image with an appropriate diopter in the eyepiece, it is necessary to arrange the eyepiece so that an intermediate image formed by the objective lens or the imaging lens comes near the front focal point of the eyepiece.

When the air-equivalent length between the intermediate image and the eyepiece increases, the above arrangement condition can be satisfied by increasing the focal length of the eyepiece. However, when the focal length of the eyepiece is increased, the viewfinder magnification is reduced, making observation difficult.

When the focal length of the eyepiece and f with respect to the focal length f ₀ of the objective lens to be commonly used finder magnification β holds the following relation.

βf ₀ / f In other words, in order to keep the magnification of the viewfinder system unchanged, it is necessary to keep the focal length of the eyepiece unchanged.
In order to match the diopter under this condition, it is necessary to make the front focal point larger than the eyepiece.

If the eyepiece has a positive refractive power in the front group and a negative refractive power in the rear group as shown in FIG. 3, the front focal point generally tends to come forward from the eyepiece. The relationship between the paraxial amounts at this time is as shown in the following equations (i) and (ii).

_{| f F / f | = f} p / f + | f p / f n | (i) | D / f | = (1+ | f n / f |) (f p / f) - | f n / f | ( ii) However f is the focal length of the eyepiece, f _p is the focal length of the front group, the focal length of f _n is the rear group, f _F the distance to the front focal point, D is the distance between the front and rear groups It is.

In order to increase | f _F / f | and decrease | D / f | in the above relationship, it is necessary to satisfy the conditions (1) and (2).

When the value exceeds the upper limit of the condition (1), the component length increases from the formula (ii). When the value exceeds the upper limit of the condition (2), the distance from the expression (i) to the front focal point is reduced.

If the above conditions (1) and (2) are satisfied, the power of the front group and the rear group becomes strong, so that the radius of curvature of the lens becomes too small and the occurrence of aberration becomes large. To prevent this, it is necessary to use a material having a high refractive index or use an aspherical surface.

If the refractive power of the negative lens is too high, the curvature of field increases, so that it is necessary to satisfy the condition (3) shown above in order to correct this.

(3) n _N <1.7 where n _N is the refractive index of the negative lens. Deviating from this condition undesirably increases field curvature.

Further, if a part or all of the lens of the eyepiece of the present invention is formed of plastic, the processing is simplified and the cost is advantageous.

Embodiment FIG. 1 is a diagram showing an optical system having an eyepiece according to Embodiment 1 of the present invention, wherein 1 is a focusing plate on which an image is formed by an imaging lens, 2 is a condenser lens, 3 is a prism, Is a roof mirror, 5 is a plane mirror, and 6 is an eyepiece.

In Example 1 shown in this figure, the front group includes one positive lens, and the rear group includes one negative lens.

 The data of Example 1 is as follows.

Example 1 R ₁ = 199.733 D ₁ = 4.7 N ₁ = 1.4923 V ₁ = 57.7 R ₂ = −80.004 D ₂ = 0.8 R ₃ = ∽ D ₃ = 33.75 N ₂ = 1.51633 V ₂ = 64.2 R ₄ = ∽ D ₄ = 50.3 r ₁ = 26.962 d ₁ = 5.4 n ₁ = 1.4923 ν ₁ = 57.7 r ₂ = −26.082 (aspheric surface) d ₂ = 3.08 r ₃ = −24.174 (aspheric surface) d ₃ = 1.0 n ₂ = 1.4923 ν ₂ = 57.7 r ₄ = 67.592 Aspheric coefficient (second surface r ₂ ) P = 1, E = 0.18146 × 10 ^-4 F = 0.12775 × 10 ^-7 , G = 0.34631 × 10 ^-9 (third surface r ₃ ) P = 1, E = 0.38669 × 10 ^-4 F = 0.75018 × 10 ^-7 , G = −0.1887 × 10 ^-8 f _p /f=0.368,|f _n / f _p | = 1.293 where R ₁ , R ₂ , ... , r ₁ ,… are the radii of curvature of each surface of the lens, D ₁ , D
_2, ..., d _1, ... are each a surface _{distance, N 1, N 2, ...} , n 1, n 2 is the refractive index of each _{lens, V 1, V 2, ...} , 1, 2 is Abbe of each lens Is a number.

In _{R 1, R 2, ... R} 4 is the objective lens in the above data, r _1, ..., r ₄
Is the eyepiece of the first embodiment.

The data of Examples 2, 3, 4, and 5 (only the eyepiece) are shown below.

Example 2 r ₁ = 26.962 d ₁ = 5.4 n ₁ = 1.4923 ν ₁ = 57.7 r ₂ = −26.082 (aspheric surface) d ₂ = 2.91 r ₃ = −30.912 (aspheric surface) d ₃ = 1.17 n ₂ = 1.58423 ν ₂ = 30.5 r ₄ = 67.592 Aspherical surface coefficient (second surface r ₂ ) P = 1, E = 0.35235 × 10 ⁻⁴ F = −0.34085 × 10 ⁻⁷ , G = −0.1789 × 10 ⁻⁹ (third surface r ₃ ) P = 1, E = −0.18146 × 10 ⁻⁴ F = −0.12775 × 10 ⁻⁷ , G = −0.34631 × 10 ⁻⁹ f _p /f=0.368, | f _n / f _p | = 1.297 Example 3 r ₁ = 21.141 d ₁ = 4.1 n ₁ = 1.72916 ν ₁ = 54.7 r ₂ = −63.537 d ₂ = 4.14 r ₃ = −23.706 d ₃ = 1.0 n ₂ = 1.4926 ν ₂ = 58.0 r ₄ = 25.241 f _p / f = 0.354, | f _n / f _p | = 1.110 Example 4 r ₁ = 16.713 d ₁ = 4.1 n ₁ = 1.72916 ν ₁ = 54.7 r ₂ = −116.225 d ₂ = 4.94 r ₃ = −20.793 d ₃ = 1.0 n _{2 = 1.4926 ν 2 = 58.0 r} 4 = 15.305 f p /f=0.274,|f n / f p | = 0.873 example _{5 r 1 = 31.791 d 1 =} 2.6 n 1 = 1.49309 ν 1 = 57.5 r 2 = - 216.150 d ₂ = 0.2 r ₃ = 31.791 d ₃ = 2.6 n ₂ = 1.49309 ν ₂ = 57.5 r _{4 = -216.150 d 4 = 2.84 r} 5 = -83.362 d 5 = 1 n 3 = 1.58423 ν 3 = 30.5 r 6 = 29.718 f p /f=0.388,|f n / f p | = 1.303 in the above embodiment, Embodiments 2 to 4 have a configuration similar to that of Embodiment 1 and include a front group of a positive lens and a rear group of a negative lens.

In the second embodiment, the chromatic aberration is further improved by forming the negative lens with a high dispersion material.

In the fifth embodiment, the front unit includes two positive lenses, and the rear unit includes one negative lens. The positive lens in the front group is composed of lenses of exactly the same shape, and has the advantage of reducing costs and simplifying management by sharing parts.

The aspherical surface used in the first and second embodiments is represented by the following equation.

Where Y is the distance from the optical axis, ΔX is the amount of deviation from the reference sphere, r is the radius of curvature of the reference sphere, P is the conic constant, E, F, G
Is an aspheric coefficient.

The distance between the reticle and the condenser is 3.5. The eyepieces of Examples 2, 3, 4, and 5 are disposed at the rear of the condenser and the prism at 50.3, 44.32, 69.57, and 50.3, respectively. The diopters of Examples 1 to 5 are -0.75, -0.75, -1.0,-
1.0, -0.75 (diopter).

Further, the reflection system for inverting the image of the present invention has a configuration in which a plurality of reflection surfaces are formed therein and a plurality of reflection members are provided therein as shown in FIG. 1, for example, and all of these members are separated. included. Further, as shown in this figure, each reflecting surface (including the reflecting surface of the reflecting member) is arranged so that the optical path does not form a loop.

[Effects of the Invention] The eyepiece of the present invention can observe an image with an appropriate diopter even when the air-converted length from the intermediate image plane to the eyepiece is large, and can be a small and simple lens system.

ADVANTAGE OF THE INVENTION The finder optical system of this invention can provide a finder optical system which is low and which can arrange | position an eyepiece to the back.

[Brief description of the drawings]

FIG. 1 is a sectional view of the first to fourth embodiments of the present invention, and FIG.
The figure is a cross-sectional view of Example 5, and FIG. 3 is a conceptual diagram of an eyepiece including a positive front group and a negative rear group.

Claims (3)

(57) [Claims] In a finder optical system in which an optical axis on an image plane formed by an objective lens or an imaging lens does not intersect with an optical axis of an eyepiece, a plurality of images are bent so that an optical path approaches the eyepiece. A reflection system, which is arranged so that the optical path does not form a loop, and a front group having a positive refractive power and a rear group having a negative refractive power in order from the imaging surface side, leading to the eyepiece by the reflecting surface. And the front group includes an eyepiece including one positive lens, and the rear group includes an eyepiece including one negative lens, and satisfies the following conditions (1), (2), and (3). Viewfinder optical system. (1) f _p /f<0.42 (2) | f _n / f _p | <1.5 (3) n _N <1.7 where f is the focal length of the eyepiece, f _p and f _n are the front group and the rear group, respectively. And n _N is the refractive index of the negative lens. 2. An eyepiece lens for observing an image formed by an objective lens or an imaging lens through a reflecting system having a plurality of reflecting surfaces having an inverting action. A front group consisting of two positive lenses, a rear group consisting of one negative lens, and the following condition (1):
An eyepiece that satisfies (2) and (3). (1) f _p /f<0.42 (2) | f _n / f _p | <1.5 (3) n _N <1.7 where f is the focal length of the eyepiece, f _p and f _n are the front group and the rear group, respectively. And n _N is the refractive index of the negative lens. 3. The finder optical system according to claim 1, wherein in the reflection system, an optical path in a section from the incident path to the last reflection surface is substantially M-shaped.