JPH07261243A - Finder optical system - Google Patents

Abstract

PURPOSE:To remove vignetting caused by the outside case part of a camera and to realize pleasant photographing by arranging a specified powerless plane parallel plate to a subject side in the optical path of a finder optical system and moving the entrance pupil position of the finder optical system to the subject side. CONSTITUTION:This system is constituted by inserting the plane parallel plate 20 between the entrance pupil position 5 and an objective lens system 1 in the optical path and moving the position 5 to the subject side. Therefore, an unnecessary thing other than the subject is prevented from being taken within a finder visual field and the clear finder visual field 10 is obtained. The refractive index of glass material forming the plate 20 is set to >=1.51. The higher this value becomes, the clearer finder visual field 10 is obtained. The thickness of the plate 20 is >=2.5mm and the position 5 is set nearly in the vicinity of the incident surface of the plate 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system suitable for use in a small camera such as a photographic camera or a video camera.

[0002]

2. Description of the Related Art In recent years, the popularity of small cameras has increased remarkably.
The development competition is intensifying. Due to the miniaturization of the camera, it is unavoidable due to the layout of the camera that the lens barrel of the taking lens or the like will enter the field of view of the finder. FIG. 6A is a sectional view taken along the optical axis of a finder optical system mounted on a conventional small camera. In the figure, 1 is an objective lens system, 2 is a first reflecting member, 3 is a second reflecting member, 4 is an eyepiece lens system, 5
Is an entrance pupil position of the finder optical system, 6 is an eye point, 7 and 8 are cover glasses, 9 is a taking lens barrel of a camera, α is a viewfinder angle of view, and L _C is an optical axis. In this way, if a part of the taking lens barrel 9 enters the viewfinder field, when the user of the camera looks into the viewfinder, the taking lens mirror will appear within the viewfinder field 10 as shown in FIG. 6B. A part of the cylinder 9 (hatched portion in the figure) is visible (so-called vignetting), which is very troublesome and difficult to use. This causes the user to be very uncomfortable, and is a problem that should be avoided.

[0003]

As a measure for avoiding the above-mentioned vignetting, the camera may be constructed with a distance between the finder optical system and the exterior part of the camera that is in the viewfinder field. However, it is difficult to change the layout of the camera body, and if the distance is set to a certain distance or more, the size of the camera may be increased. In the worst case, if you want to configure the camera in a small size, vignetting may be tolerated. Conventionally, a finder optical system for moving the light emitted from the eyepiece lens relative to the light incident on the objective lens by decentering the objective lens and the eyepiece lens, even if the purpose is different, , Already well known. For example, this is the finder optical system described in Japanese Examined Patent Publication No. 2-19930. Vignetting can also be dealt with by the optical system described in this publication, but such an optical system complicates the frame structure and makes lens processing difficult, which inevitably leads to an increase in cost in the manufacturing process.

Therefore, the present invention has been made in view of the above-mentioned problems of the prior art, and a very simple method is used to determine the position of the entrance pupil as a subject without degrading the performance of the conventional finder optical system. It is an object of the present invention to provide a convenient finder optical system that can be moved to the side to remove vignetting due to the camera exterior such as the taking lens barrel in the finder field.

[0005]

In order to achieve the above object, the finder optical system according to the present invention has a thickness of 2.5 mm or more in a finder optical system constructed separately from the photographing optical system. By disposing a substantially powerless parallel plate having a refractive index of 1.51 or more on the subject side in the optical path of the finder optical system, the entrance pupil position of the finder optical system is moved to the subject side. Is characterized by. Further, the finder optical system of the present invention is configured so that the entrance pupil position is located within a range of ± 2 mm near the entrance surface of the parallel plate by disposing the substantially powerless parallel plate. The powerless parallel plate is also characterized in that it is configured as a cemented parallel plate of a plano-convex lens and a plano-concave lens.

By taking the above means, in the optical system of the present invention, the relationship between the finder optical system shown in FIG. 6 and the taking lens barrel is improved as shown in FIG.
That is, as shown in FIG. 4A, in the finder optical system according to the present invention, the parallel flat plate 20 is inserted between the entrance pupil position 5 and the objective lens system 1 in the optical path, and the entrance pupil position 5 is changed to the conventional one. It is configured to be moved to the subject side of the above (other configurations are the same as the conventional one). Therefore,
It is possible to obtain a clear viewfinder field 10 as shown in FIG. 4 (b) without capturing an extra object other than the subject in the viewfinder field.
At this time, the higher the refractive index of the glass material forming the parallel flat plate 20, the clearer the viewfinder field can be obtained, and the thickness of the parallel flat plate 20 is substantially equal to that of the parallel flat plate 20 at the entrance pupil position 5. It is preferable to set it so that it can be located near the incident surface. The vicinity here is preferably within a range of ± 2 mm with reference to the incident surface of the parallel plate 20. Further, with this configuration, the flare stop can be formed with the entrance pupil diameter, so that it is possible to control the on-axis light flux and the off-axis light flux at the same time, and it is possible to suppress the occurrence of ghost flare. . By such means, aberration is not affected and only the position of the entrance pupil is moved to the front (subject side) of the optical system, so that it can be applied to any finder optical system. The thickness of the parallel plate 20 is
It is also limited by the thickness of the camera body.

The parallel plate 20 may be constructed as a cemented parallel plate of a plano-convex lens and a plano-concave lens. If the convex lens and the concave lens constituting this cemented parallel plate have substantially the same refractive index n _d at the reference wavelength, and the Abbe number of the convex lens is large and the Abbe number of the concave lens is small, the aberration at the reference wavelength becomes large. The effect of vignetting is not affected, and the effect of achromatism is also obtained.
Further, the Abbe number ν _T of the convex lens and the Abbe number ν _{O of the} concave lens constituting the cemented parallel plate are ν _T > 45 and ν _O <4, respectively.
When it is set to 0, the above effect becomes more remarkable.
In addition, in order to obtain further effects in the measures against vignetting,
By decentering the parallel plate, the light emitted from the central portion of the eyepiece lens system 4 can be moved in parallel relative to the incident light of the central portion of the objective lens system 1, and vignetting can be removed. The parallel movement amount Y of the incident light is Y = (D / cos θ ′) × sin (θ−θ, where n _{d is} the refractive index of the glass material of the parallel plate, D is the wall thickness, and θ is the decentering angle. ') ^{(where, θ' = sin -1 (sinθ} / n d)) can be calculated as ... (1). Therefore, the optimum eccentric angle θ of the parallel plate may be obtained from the relationship between Y and θ, and the parallel plate may be eccentric.

Although the above-mentioned means can be applied to any finder optical system, it exhibits an excellent effect particularly in a real image finder. FIG. 5A is a conceptual diagram of a light beam incident on the real image type finder optical system. In the real image finder optical system, since the entrance window of the optical system is formed small, the size of the incident light beam diameter also becomes small. Therefore, it is convenient that the parallel plate used in this optical system can be made small. On the other hand, FIG. 5B is a conceptual diagram of a light beam incident on the virtual image finder optical system. As described above, even in the virtual image finder optical system, the size of the light flux incident on the optical system on the object side becomes large, but it is possible to move the entrance pupil position to the object side by using the parallel plate. is there.

It is an object of the present invention to move the entrance pupil position of the finder optical system to the subject side by using a substantially powerless parallel plate, but a minute power is used instead of the parallel plate. Even if the lens having the same is used, as long as the lens has a thickness of 2.5 mm or more and a refractive index of 1.51 or more, the same effect as that of the parallel plate can be obtained, and The purpose can be achieved. Further, if the object-side surface of the parallel plate is formed as a flat surface, this parallel plate can also be used as a cover glass.

[0010]

The present invention will be described in detail below with reference to the illustrated embodiments. First Embodiment FIG. 1A is a sectional view taken along the optical axis of a finder optical system according to the present invention. As shown in the figure, the optical system of the present invention is
The objective lens system 1 is a real image type finder having an incident half angle of view ω = 28.6 ° and a finder magnification of 0.5 times, and has a positive refracting power as a whole, and a first reflecting member (prism) for erecting an image. 2), a second reflecting member (prism) 3 for erecting an image, and an eyepiece 4 having a positive refractive power. Further, 5 is the entrance pupil position, 6 is the eye point, 11 is the intermediate image plane, and L _C is the optical axis. Thus, in the real image type finder in which the exit surface of the first reflecting member 2 following the objective lens system 1 is the intermediate image forming surface 11, the first reflecting member 2 has the short side twice and the second reflecting member 3 In an optical system having a configuration in which the long side is reflected twice, the optical path length of the second reflecting member 3 is long and the ray height is also high, so that as shown in FIG. , The second reflecting member 3
Since it is configured to project toward the subject side from the position where the objective lens system 1 is arranged, a space is created between the camera exterior part (cover glass or the like) and the objective lens system 1. Incidentally, FIG.
In the optical system shown in (a), the entrance pupil position 5 is 4.8 from the first negative lens first surface of the objective lens system 1 to the subject side.
It is at a position of 2 mm.

FIG. 1B is a sectional view taken along the optical axis of the finder optical system according to this embodiment. As described above, the optical system of the present embodiment is configured by inserting the parallel flat plate 20 into the space formed in the optical system shown in FIG. Since the parallel plate 20 is inserted, the optical system of the present embodiment can obtain the effect of preventing vignetting as in the previous operation. Further, since the parallel plate 20 is inserted in the space generated due to the structure of the optical system, the above effect can be obtained without changing the original size of the camera body. In the optical system of the present embodiment shown in FIG. 1B, the entrance pupil position 5 is 6.80 m from the first negative lens first surface of the objective lens system 1 to the subject side.
The parallel plate 20 located at the position m (position 0 mm from the incident surface of the parallel plate 20) and having the refractive index n _d
= 1.65844, Abbe number ν _d = 50.9, wall thickness D =
It is 5 mm.

Next, the refractive index n _d of the parallel plate 20 when the parallel plate 20 is inserted in the optical path of the finder optical system according to the present embodiment, its thickness D, and the first surface of the objective lens system 1. Table 1 shows the relationship with the distance from the top of the plane to the entrance pupil position 5. Further, the air gap between the parallel plate 20 and the objective lens system 1 is 1.8 mm, and the wall thickness D of the parallel plate 20 is set so that the entrance pupil position 5 and the entrance surface position of the parallel plate 20 substantially coincide with each other. It is set.

The lens numerical data of the finder optical system according to the present invention will be shown below. _{r 1 = -3.7570 d 1 = 2.000} n 1 = 1.68893 ν 1 = 31.08 r 2 = -5.6540 d 2 = 0.200 r 3 = 19.3240 d 3 = 6.400 n 3 = 1.69350 ν 3 = 53.23 r 4 = -8.8145 ( aspherical _{) d 4 = 0.380 r 5 =} ∞ d 5 = 19.200 n 5 = 1.72000 ν 5 = 50.25 r 6 = ∞ d 6 = 0.000

R ₇ = ∞ d ₇ = 1.000 r ₈ = ∞ d ₈ = 31.000 n ₈ = 1.88300 ν ₈ = 40.78 r ₉ = -45.2500 d ₉ = 2.000 r ₁₀ = 37.3030 (aspherical surface) d ₁₀ = 3.000 n ₁₀ = 1.69350 ν ₁₀ ＝ 53.23 r ₁₁ ＝ -44.6400 d ₁₁ ＝ 16.152 r ₁₂ (eyepoint)

Aspheric coefficient 4th surface P = -0.4485 E = 0.58242 × 10 ^-4 , F = 0.16251 × 10 ^-5 G = -0.20633 × 10 ^-7 , H = 0.11541 × 10 ^-9 10th surface P = 1.0000 E = -0.28894 x 10 ^-5 , F = -0.104 64 x 10 ^-6 G = 0.18183 x 10 ^-8 , H = -0.12462 x 10 ^-10

However, in the numerical data of the above lens,
r ₁ , r ₂ , ... Are the radii of curvature of the respective lens surfaces, d ₁ ,
d ₂ , ..., Thickness or spacing of each lens, n ₁ ,
n ₂ , ..., Refractive index of each lens, ν ₁ , ν ₂ ,
.. is the Abbe number of each lens, and P, E, F, G, and H are aspherical coefficients, respectively. Also, the aspherical shape is expressed by the following equation using the above-mentioned aspherical surface coefficients, where X is the coordinate in the optical axis direction and Y is the coordinate in the direction perpendicular to the optical axis. However, C is the curvature (= 1 / r) at the aspherical vertex.

Second Embodiment FIG. 2 is a sectional view taken along the optical axis of the finder optical system according to this embodiment. As shown in the figure, the parallel plate 20 inserted in the optical path of the optical system of the present embodiment has a convex lens 20a.
And a concave lens 20b. This convex lens 20a has a refractive index n _d = 1.7410.
0, Abbe number ν _d = 52.7, wall thickness D = 3.4 mm, and the concave lens 20b has a refractive index n _d = 1.7.
4077, Abbe number ν _d = 27.8, wall thickness D = 1 mm. The cemented surface R of the convex lens 20a and the concave lens 20b is R = -5. The entrance pupil position 5 is closer to the object side than the top of the first negative lens first surface of the objective lens system 1.
It is at a position of 70 mm (a position of 0.5 mm from the incident surface of the parallel plate 20 to the subject side). The other optical system configurations are the same as those shown in the first embodiment.

In this embodiment, since the parallel plate 20 is constructed as a cemented parallel plate, it has an excellent effect of improving the chromatic aberration of magnification of the finder optical system. For example, the chromatic aberration of magnification of the optical system shown in the first embodiment has a diagonal of 6.18.
6 ', long side 4.818', short side 2.460 ', but in the optical system of this embodiment, the diagonal is 0.078', long side is 0.60 ', short side is 0.78'. Can be improved to However,
The chromatic aberration of magnification referred to here is represented by a value obtained by converting the difference (C-line and F-line) of the exit angle of the finder optical system depending on the wavelength into minutes.

Third Embodiment FIG. 3A is a sectional view taken along the optical axis of the finder optical system according to this embodiment. As shown in the figure, in the optical system of the present embodiment, the parallel flat plate 20 is inserted into the optical path with an inclination of 10 ° with respect to the optical axis L _C. This parallel plate 20
Has a refractive index n _d = 1.65844 and an Abbe number ν _d = 5
0.9, thickness D = 4 mm. The configuration of the optical system other than the parallel plate 20 is the same as that shown in the first embodiment. In this way, by decentering the parallel plate 20 with respect to the optical axis L _C , the light emitted from the center of the eyepiece lens system 4 is moved in parallel with the light incident on the center of the objective lens system 1. (Upward or downward in the figure), it becomes possible to suppress the occurrence of vignetting. This parallel plate 20
The state of the angle θ for eccentricity and the parallel movement amount Y of the incident light beam is as shown in FIG. 3B, and the individual specific numerical values are determined by the above equation (1). When the parallel plate is decentered with respect to the optical axis as in the present embodiment, in order to enhance this effect, the entrance pupil position 5 is parallel to the optical axis L _C as shown in FIG. 3C. It is preferable to set the range within ± 2 mm before and after the intersection point a with the incident surface of the flat plate 20 as a reference.

The finder optical system shown in each of the above-mentioned embodiments exhibits more excellent effects when used as a real image finder.

[0021]

As described above, the finder optical system according to the present invention is a finder optical system which is formed separately from the taking optical system. In view of the layout of the camera body, the taking lens barrel and the like are within the viewfinder field. When vignetting or the like occurs due to the camera exterior part, the vignetting can be prevented by taking a simple measure, and comfortable photography can be performed. Further, the optical system of the present invention can be applied to all kinds of finder optical systems, and has an advantage in practical use that vignetting can be prevented without impairing the original optical performance.

[Brief description of drawings]

1A is a sectional view taken along the optical axis of a finder optical system according to the present invention, and FIG. 1B is a sectional view taken along the optical axis of a finder optical system according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the optical axis of the finder optical system according to the second embodiment of the present invention.

3A is a sectional view taken along the optical axis of a finder optical system according to a third embodiment of the present invention, FIG. 3B is an explanatory view for determining an angle for decentering a parallel plate, and FIG. It is a figure for demonstrating the relationship between the position of a parallel plate, and an entrance pupil position.

4A is a sectional view taken along the optical axis of the finder optical system showing a state in which the finder optical system of the present invention is incorporated in a camera body, and FIG. 4B is a view in the finder field of view of the camera shown in FIG. It is a figure which shows a mode.

5A is a conceptual diagram showing a state of incident light to a real image type finder optical system, and FIG. 5B is a conceptual diagram showing a state of incident light to a virtual image type finder optical system.

6A is a cross-sectional view taken along the optical axis of a finder optical system mounted on a conventional camera, and FIG. 6B is a diagram showing a state within a viewfinder field of the camera shown in FIG.

[Explanation of symbols]

1 Objective Lens System 2 First Reflecting Member 3 Second Reflecting Member 4 Eyepiece System 5 Entrance Pupil Position 6 Eyepoints 7, 8 Cover Glass 9 Camera Lens Lens 10 Finder Field of View 11 Intermediate Image Forming Surface 20 Parallel Plate α Image Angle L _C Optical axis

Claims (3)

[Claims] 1. A finder optical system, which is formed separately from the taking optical system, has a thickness of 2.5 mm or more and 1.
By disposing a substantially powerless parallel plate having a refractive index of 51 or more on the object side in the optical path of the finder optical system, the entrance pupil position of the finder optical system is moved to the object side. Viewfinder optical system. 2. By arranging the substantially powerless parallel plate, the entrance pupil position is ± 2 near the plane of incidence of the parallel plate.
The finder optical system according to claim 1, wherein the finder optical system is located in a range of mm. 3. The finder optical system according to claim 1, wherein the substantially powerless parallel plate is configured as a cemented parallel plate of a plano-convex lens and a plano-concave lens.