JP2003005075A - Finder optical system and optical apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a finder optical system is liable to be increased in size when the finder optical system is made into higher variable power. SOLUTION: An eyepiece optical element 21 of the finder optical system is formed to have a first reflecting surface 212 which reflects the luminous flux from an object, a second reflecting surface 213 which reflects the luminous flux reflected by the first reflecting surface and a third reflecting surface 214 reflects the luminous flux reflected by the second reflecting surface. When the reference axes of the routes of the rays passing the center of the pupil S from the center of the object surface are defined as reference axes ST, the reference axes are so formed as to have two intersection positions; the intersection positive of the optical paths from the second reflecting surface to the third reflecting surface to the paths from the object to the first reflecting surface and the intersection position of the optical paths from the third reflecting surface to the pupil. In addition, the optical element is so constituted that the luminous fluxes undergo intermediate image formation within the region enclosed by the respective reflecting surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type finder optical system used in optical equipment such as a photographing device such as a still camera or a video camera.

[0002]

2. Description of the Related Art Conventionally, a real image finder optical system for observing, through an eyepiece, a finder image of a real image formed on a primary image forming surface by an objective lens in an optical finder of a photographic camera, a video camera or the like. Have been proposed.

This real image type finder optical system has been widely used in cameras with zoom lenses recently because it is easy to downsize the entire optical system as compared with the virtual image type finder optical system.

In a real image type finder optical system using an image inverting means such as a Porro prism for an erect image, the optical action of the objective lens for forming an object image on the primary image plane and the image inverting means is clear. Are distinguished.

For example, the image inverting means is constructed so as not to have a refracting power when the object image is formed on the primary image plane.

In this case, in a finder optical system in which a part of the image inverting means (for example, a prism member) is provided between the objective lens and the primary image forming surface, the objective lens is retrofitted to increase the back focus of the objective lens. It is necessary to configure the focus type and increase the degree of retrofocus at this time according to the length of the back focus. Therefore, the objective lens tends to be large.

Further, a part of the image inverting means exists between the objective lens and the primary image forming surface, and a finder optical system having a reflecting surface for bending the optical path on the object side of the primary image forming surface. Then, in order to efficiently reflect the entire light flux on the reflecting surface, it is necessary to configure the objective lens in the exit side telecentric system. As a result, the objective lens tends to increase in size.

Further, the finder image formed on the primary image plane by the objective lens is relay lens system (relay system).
A secondary imaging type finder optical system that uses a relay system to form a secondary imaging surface on the secondary imaging surface and observes this finder image with an eyepiece requires a plurality of lenses for re-imaging. The total lens length becomes long, and more lenses are needed to correct chromatic aberration.

Further, in a camera in which the taking optical system and the finder optical system are separately configured, when the taking optical system is a variable power system, the viewfinder optical system is also configured as a variable power system, and the variable power of the taking optical system is changed. It is configured so that the viewfinder field magnification changes in accordance with.

Generally, since the variable magnification finder optical system is incorporated in a camera, it is required to have a small size and a structure capable of easily obtaining a predetermined variable magnification ratio.

The applicant of the present invention has disclosed in Japanese Patent Laid-Open No. 61-156018, Japanese Patent Laid-Open No. 1-116616, etc. that the objective lens is composed of a multi-lens group, and the air gap between the lens groups is varied during zooming. The object image with various magnifications changed by the objective lens is made an erect image through an image inverting member such as a Porro prism, and this erect image is observed with an eyepiece lens. Proposing a variable magnification finder.

[0012]

Recent cameras are required to have a high zoom ratio of a photographing optical system and a compact camera body. Along with this, even in the finder optical system to be mounted, further high zooming and downsizing have become problems.

FIG. 7 shows a sectional view of a conventional finder optical system. These viewfinder optical systems are real image type viewfinders that observe an object image formed in the vicinity of the diaphragm (field frame) S1 by the objective optical system 10 through the eyepiece optical system Le.

Both of them have roof reflecting surfaces 82a and 83a for image reversal in their optical paths. The accuracy of the roof reflective surface has a great influence on the appearance of the viewfinder image.

However, particularly when the prism is molded by a mold, there is a problem that the edge portion of the roof angle is difficult to obtain accuracy.

Further, in the finder optical system having the configuration shown in FIG. 7, the thickness of the camera is determined to some extent by the total length of the objective optical system. Therefore, it is considered that the refracting power of each group should be strengthened in order to suppress the enlargement of the objective optical system when the zoom ratio becomes high, but if the refracting power of each group is simply strengthened, Aberration variation during zooming increases, and it becomes particularly difficult to correct aberrations of off-axis light flux. Therefore,
It becomes difficult to observe a good viewfinder image in the entire zoom range. Further, there is a problem that the movement accuracy of each group at the time of zooming is required to be very high.

On the other hand, in order to solve such a problem,
A finder optical system that utilizes a lateral space of a camera and is thin in the thickness direction has been proposed. For example, JP-A-3
In the viewfinder optical system proposed in Japanese Patent Publication No. 287216, the optical path is bent twice at a right angle.

However, this Japanese Patent Laid-Open No. 3-28721
In the viewfinder optical system proposed in Japanese Patent Publication No. 6, the mechanism is complicated because the two groups move in directions orthogonal to each other. For this reason, the finder optical system is becoming larger.
Further, since the number of lenses constituting the finder optical system is large, the cost including the member for group movement becomes high.

Further, in the viewfinder optical system proposed in Japanese Patent Laid-Open No. 7-5360, the objective optical system is composed of negative, positive, and positive, and has a mechanism in which the lens group moves in one direction during zooming. . Then, the first group is provided with a reflecting surface, and is configured as a real image type finder which is developed in the lateral direction of the camera.

However, in the viewfinder optical system proposed in Japanese Patent Application Laid-Open No. 7-5360, the prism portion for erecting the image is arranged in the vertical direction, so that the viewfinder unit becomes large. Further, since only the eyepiece lens is projected, there is a problem that it cannot be made sufficiently thin when incorporated in a camera.

Therefore, it is an object of the present invention to provide a finder optical system that is small in size and capable of inverting an object image with a minimum number of reflecting surfaces.

[0022]

In order to achieve the above object, the present invention provides a viewfinder optical system for guiding a light beam from an object to an observer's eye through the eyepiece optical element. Having a first reflecting surface that reflects the light flux from the second reflecting surface, a second reflecting surface that reflects the light flux reflected by the first reflecting surface, and a third reflecting surface that reflects the light flux reflected by the second reflecting surface When a path of a light ray reflected from each of the reflecting surfaces from the center of the object surface and passing through the center of the pupil is used as a reference axis, this reference axis is defined as a first axis with respect to an optical path from the object surface to the first reflecting surface. It is assumed that there are two intersecting points at a position where the optical paths from the two reflecting surfaces to the third reflecting surface intersect, and a position where the optical paths from the third reflecting surface to the pupil intersect, and by each reflecting surface. Intermediate image of the light flux within the enclosed area It is configured to.

In this way, the optical path is bent by three reflections by the eyepiece optical element, and at the same time from the second reflection surface to the third reflection surface.
2 between the reflective surface and the third reflective surface to the pupil
By intersecting the reference axes once, the image path can be inverted with a small size and a minimum number of reflecting surfaces, even though the optical path length becomes long for intermediate image formation in the area surrounded by the reflecting surfaces. It is possible to realize a finder optical system that is compact as a whole and that includes an eyepiece optical system.

In the region surrounded by the reflecting surfaces, the light flux reflected by the second reflecting surface is formed into an intermediate image between the second reflecting surface and the third reflecting surface,
It is possible to reduce the size of each of the above reflecting surfaces by collecting light fluxes into a small size, and to further reduce the size of the eyepiece optical system and thus the finder optical system. Particularly, it is preferable to form an intermediate image at a position near the second reflecting surface between the second reflecting surface and the third reflecting surface.

Further, by making at least one of the first to third reflecting surfaces a rotationally asymmetric surface, it becomes possible to satisfactorily correct various aberrations.

The angle α formed by the reference axis from the object surface to the first reflecting surface and the reference axis from the third reflecting surface to the pupil is 50 ° <α <110 °, preferably 60 °. If the condition of <α <90 ° is satisfied, the eyepiece optical element (that is, the finder optical system) can be made thin in the object side-observer side direction (for example, the thickness direction of the camera) even if the zoom ratio is increased. It becomes possible to configure.

In the eyepiece optical element, the first refracting surface on which the light beam from the object is incident, the inner reflecting surface as the first to third reflecting surfaces, and the light beam reflected by the third reflecting surface are emitted. It may be configured as a prism shape in which the birefringent surface is integrally formed with a transparent body.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The optical system according to the embodiment of the present invention includes
There is no axis of symmetry such as the optical axis in ordinary optical systems. Therefore, a "reference axis" is set in the optical system, and the configuration of various elements in the optical system is described based on this reference axis.

First, the reference axis will be described. In the embodiment of the present invention, a ray that exits from the center of the object plane and passes through the center of the pupil is the reference axis ray, and the path of this ray is the reference axis.

As shown in FIGS. 3, 4 and 5, the reference axis ST passes through the center point TO of the effective ray diameter of the first surface R1 and reaches the center TO 'of the pupil S (reference axis ray). ) Sets the path refracted / reflected by each refraction surface and reflection surface as the reference axis. The order of each surface is set in the order in which the reference axis ray is refracted and reflected. Therefore, the reference axis finally reaches the center of the pupil S while changing its direction according to the law of refraction or reflection along the set order of each surface.

Next, the coordinate system in the embodiment of the present invention will be described. FIG. 6 is an explanatory diagram of a coordinate system that defines the constituent data of the optical system according to the embodiment of the present invention. In the embodiment of the present invention, the i-th surface is defined as the i-th surface along one light ray (shown by the one-dot chain line in FIG. 6 and referred to as a reference axis light ray) traveling from the object side to the image surface.

In FIG. 6, the first surface R1 is a diaphragm (field frame), the second surface R2 is a refracting surface coaxial with the first surface, and the third surface R3.
Is the reflecting surface tilted with respect to the second surface R2, and the fourth surface R
4, the fifth surface R5 is a reflecting surface which is shifted and tilted with respect to each front surface, the sixth surface R6 is shifted with respect to the fifth surface R5,
It is a tilted refractive surface. Second surface R2 to sixth surface R6
Each surface up to is formed on one optical element (eyepiece optical element) made of a medium such as glass or plastic, and is referred to as an optical element B1 in FIG.

Therefore, in the configuration of FIG. 6, the medium from the object surface (not shown) to the second surface R2 is air, and the medium from the second surface R2 to the sixth surface R2.
The medium up to the surface R6 is a common medium such as glass or plastic, and the medium from the sixth surface R6 to the seventh surface R7 (not shown) is air.

In the optical system according to the embodiment of the present invention, each surface forming the optical system does not have a common optical axis. Therefore, in the embodiment of the present invention, first, an absolute coordinate system is set with the origin being the center of the effective ray diameter of the first surface which is the diaphragm. Then, in the embodiment of the present invention, each axis of the absolute coordinate system is defined as follows.

Z-axis: Reference axis passing through the origin toward the second surface R2 Y-axis: Straight X-axis passing through the origin and forming 90 ° counterclockwise with respect to the Z-axis in the tilt plane (in the plane of the paper of FIG. 6) : A straight line passing through the origin and perpendicular to each of the Z and Y axes (a straight line perpendicular to the paper surface of FIG. 6).

Further, in order to express the surface shape of the i-th surface forming the optical system, rather than expressing the shape of the surface in the absolute coordinate system, the local point whose origin is the point where the reference axis and the i-th surface intersect It is easier to understand the shape by recognizing the shape by setting the coordinate system and expressing the surface shape of the surface in the local coordinate system. Therefore, in the numerical example for displaying the configuration data of the embodiment of the present invention,
The surface shape of the surface is represented by the local coordinate system.

The tilt angle of the i-th surface in the YZ plane is represented by an angle θi (unit: °) with the counterclockwise direction being positive with respect to the Z axis of the absolute coordinate system. Therefore, in the embodiment of the present invention, the origin of the local coordinates of each surface is on the YZ plane in FIG. Further, there is no tilt or shift of the surface in the XZ and XY planes.

Furthermore, the local coordinates (x, y,
The y and z axes of z) are Y with respect to the absolute coordinate system (X, Y, Z).
The angle θi is tilted in the Z plane, and is specifically set as follows.

Z-axis: a straight line passing through the origin of local coordinates and forming an angle θi in the counterclockwise direction in the YZ plane with respect to the Z direction of the absolute coordinate system. Y-axis: passing through the origin of local coordinates and YZ with respect to the z direction. Straight line forming 90 ° counterclockwise in the plane x-axis: A straight line passing through the origin of local coordinates and perpendicular to the YZ plane.

Di is a scalar quantity representing the distance between the origins of the local coordinates of the i-th surface and the (i + 1) -th surface, Ndi,
νdi is the refractive index and Abbe number of the medium between the i-th surface and the (i + 1) -th surface, respectively. The diaphragm and the final image plane are also displayed as one plane.

Embodiments of the present invention have a spherical surface and a rotationally asymmetric aspherical surface. The spherical portion of these has a radius of curvature Ri as a spherical shape. Radius of curvature Ri
The sign of is negative when the center of curvature is on the first surface side along the reference axis (dotted line in FIG. 6) that advances from the first surface to the image surface, and is positive when it is on the image forming surface side.

Here, the spherical surface has a shape represented by the following equation.

Z = {(x ² + y ² ) / Ri} / [1+ {1- (x ² + y ² ) / Ri ² } 1/2] Further, the rotationally symmetric aspherical surface is expressed by the following equation. The shape is represented.

Z = {(x²+ y²) / Ri} / (1+ {1- (1 + k) ・ (x²+ y²)
/ Ri²} 1/2] + ka (x²+ y²)²+ kb (x²+ y ²)³+ kc (x²+ y²)⁶+
… Further, the optical system of the embodiment of the present invention is at least non-rotatable.
It has one or more symmetric aspherical surfaces and its shape is
Express

A = (a + b) ・ (y ²・ cos ² t + x ² ) B = 2a ・ b ・ cos t [1 + {(ba) ・ y ・ sin t / (2a ・ b)} + 〔1 + {(ba)
・ Y ・ sin t / (a ・ b)}-{y ² / (a ・ b)}-{4a ・ b ・ cos ² t + (a + b) ² sin
² t} x ² / (4a ² b ² cos ² t)] 1/2], z = A / B + C0 ² y ² + C11xy + C20x ² + C03y ³ + C12xy ² + C2
1x ² y + C30x ³ + C04y ⁴ + C13xy ³ + C22x ² y ² + C31x ³ y + C40
x ⁴ ... The shape of each rotationally asymmetric surface in the numerical example of the present invention is a plane-based aspherical surface where a = b = ∞, t = 0 in the above curved surface equation, and By using only the even-order terms and setting the odd-order terms to 0, yz
It has a plane-symmetrical shape with the plane as a plane of symmetry. Further, when the following conditions are satisfied, the shape is symmetrical with respect to the xz plane.

Further, when C03 = C21 = 0, and C02 = C20 C04 = C40 = C22 / 2, the rotationally symmetrical shape is represented. If the above conditions are not satisfied, the shape is non-rotationally symmetric.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
It is a principal part sectional view which shows the structure of the eyepiece optical system in the finder optical system which is embodiment. The eyepiece optical system Le is composed of an eyepiece prism 21 having a refractive index larger than 1, and transmits a light flux from an object image formed in the vicinity of MI1 by an unillustrated objective optical system to the entrance surface of the eyepiece prism 21 (first refraction). Light is guided from the surface 211 to the inside of the eyepiece prism 21.

The light beam entering the eyepiece prism 21 from the entrance surface 211 is reflected by the first reflecting surface 212 and guided to the second reflecting surface 213. The light flux reflected by the second reflecting surface 213 is guided to the third reflecting surface 214, and is further converted into the third reflecting surface 214.
The light flux reflected by the reflecting surface 214 is the exit surface (second refracting surface) 2
It is guided to 15 and is emitted out of the prism 21. The light flux emitted to the outside of the prism 21 passes through the pupil S and reaches the eye of the observer who is observing the finder image.

In the eyepiece prism 21, the second
The light flux traveling from the reflecting surface 213 to the third reflecting surface 214 is intermediately imaged between the second reflecting surface 213 and the third reflecting surface 214 and in the vicinity of the region MI2 near the second reflecting surface 213 to form an object image. To be observed as an erect image.

Numerical examples of the embodiment shown in FIG. 1 will be shown below. Since the eyepiece prism 21 shown in FIG. 1 is an eyepiece optical system, in the present numerical example, the center of the pupil S is the origin of the absolute coordinate system, and the diaphragm provided at the position of the pupil S is R1.
Surface, the second refracting surface 215 which is the exit surface is the R2 surface, the third reflecting surface 214 is the R3 surface, the second reflecting surface 213 is the R4 surface,
The first reflecting surface 212 surface is described as an R5 surface, the first refracting surface 211 surface that is an incident surface is a R6 surface, and the primary imaging surface position R7 surface is an image surface.

Numerical Example 1 i Yi Zi θi Di Ndi νdi 1 0.00 0.00 0.00 15.00 1 Aperture 2 0.00 15.00 0.00 14.00 1.49171 57.40 Refractive surface 3 0.00 29.00 -16.00 15.00 1.49171 57.40 Reflective surface 4 7.95 16.28 3.00 8.00 1.49171 57.40 Reflection Surface 5 12.88 22.62 64.00 20.00 1.49171 57.40 Reflecting surface 6 -7.12 22.62 90.00 0.00 1 Refracting surface 7 -7.12 22.62 90.00 0.00 1 Image surface spherical shape R1 surface R1 = ∞ R6 surface R6 = 15.000 Rotationally symmetric aspherical surface R2 surface R2 = 12.251 k = 0 ka = -0.67731E-03 kb = 0.16394E-04 kc = -0.32619E-06 Rotating asymmetric aspherical shape R3 surface C02 = -0.16147E-01 C20 = -0.40750E-03 C04 = -0.12742E- 04 C22 = -0.96860E-04 C40 = -0.33490E-04 R4 surface C02 = 0.14590E-01 C20 = -0.20640E-02 C04 = 0.30955E-03 C22 = -0.45726E-02 C40 = 0.33869E-01 R5 Surface C02 = -0.23063E-01 C20 = -0.61302E-01 C04 = -0.24134E-03 C22 = -0.91348E-02 C40 = -0.10363E + 00 In the present embodiment, image deterioration occurs during image inversion. The Dach reflection surface, which is a factor, becomes unnecessary. Further, the three reflecting surfaces are set as rotationally asymmetric aspherical surfaces and are eccentrically arranged, so that various aberrations are satisfactorily corrected. With this configuration, the finder optical system has good visibility.

In the eyepiece prism 21, the reference axis between the incident surface 211 and the first reflecting surface 212 and the reference axis between the second reflecting surface 213 and the third reflecting surface 214 intersect each other. The reference axis between the entrance surface 211 and the first reflection surface 212 and the reference axis between the third reflection surface 214 and the exit surface 215 intersect with each other.

As a result, the optical path length, which becomes long due to the formation of the intermediate image, is efficiently folded in the same plane with a minimum number of reflection surfaces.

Furthermore, the intermediate image formation position of each surface is located so as to be located in the region MI2 between the second reflection surface 213 and the third reflection surface 214 near the observation side (particularly near the second reflection surface 213). By setting the curvature, the powers are appropriately shared by the respective surfaces, the eccentric aberration is suppressed, the luminous fluxes are made small, and the effective diameter on the reflecting surface does not become large. With this configuration, the viewfinder optical system is downsized and the visibility is good.

When the optical path is turned back in this embodiment, the angle difference between the exit surface 215 and the second reflecting surface 213 is small, and the exit surface 215, the second reflecting surface 213, and the two surfaces are arranged so as to face each other. The angle of the third reflecting surface 214 with respect to the Y axis in the figure is small.

For this reason, it is possible to arrange such that the protrusion of the surface in the Z-axis direction is reduced. A thin finder optical system can be realized by applying this arrangement in the thickness direction of the camera. Further, the angle difference between the first reflecting surface 212 and the fourth reflecting surface 214 that are adjacent on the same side, the exit surface 215 and the second reflecting surface 21.
Since the angle difference with 3 is small, the shape is advantageous in terms of performance and surface accuracy at the time of molding.

Further, the eyepiece prism 21 of this embodiment is
An image erecting system and an eyepiece for observing an image are integrally molded as one optical element. By using this eyepiece prism 21, an independent eyepiece lens is not required, so that cost reduction can be realized.

The overall structure of the finder optical system of this embodiment will be described below with reference to FIG.

The objective optical system 10 is composed of a fixed first group I, a negative second group II, and a positive third group III in order from the object side. The second group and the third group are used for zooming. And move.

The type of the objective optical system 10 is not limited to that shown in FIG. In addition, the objective optical system 1
0 may be a single focus.

In FIG. 2, (W), (M), and (T) indicate the wide-angle end, the intermediate position, and the telephoto end, respectively. Objective optical system 10
The light flux from is reflected to the object side by a reflection prism (reflection optical element) P1 having a reflection surface, and forms an intermediate image near the diaphragm (field frame) S1. The optical path in the eyepiece optical system after this primary imaging plane is the same as that shown in FIG.

However, in this structure, in order to make the finder optical system thin in the direction from the object side to the observer side (the left-right direction in the drawing), the finder optical system is reflected by the reflecting surface of the reflecting prism P1, and the diaphragm S1 and the eyepiece prism 21 are reflected. The angle α formed by the reference axis that passes through the entrance surface 211 and reaches the first reflection surface 212 and the reference axis that extends from the third reflection surface 214 through the exit surface 215 to the center of the pupil S satisfy the following condition. preferable.

50 ° <α <110 ° When the lower limit is exceeded, the reflecting surface of the reflecting prism P1 projects toward the observing side, which makes it difficult to hold the field frame (arrangement of holding members) and is small. Becomes difficult. If the upper limit is exceeded, the distance from the entrance surface of the reflecting prism P1 to the most eye-side surface of the eyepiece optical system becomes long, so that the total length in the thickness direction of the camera equipped with this finder optical system increases.

More preferably, the angle α satisfies the following condition.

60 ° <α <90 ° As described above, by arranging the objective optical system and the eyepiece optical system at appropriate angles, even if the total length of the objective optical system is long and the magnification is high, the finder optical system Can be made thinner. Further, there are two optical members other than the objective optical system (the reflecting prism P
1 and the eyepiece prism 21), the cost can be reduced.

(Second Embodiment) Next, as compared with the first embodiment, at the time of higher zooming, and while the objective optical system is developed in the lateral direction (direction substantially orthogonal to the object-observation direction). A viewfinder optical system according to a second embodiment of the present invention, which can achieve miniaturization, will be described.

FIG. 3 shows a plane cross section (cross section viewed from above the camera) of the finder optical system of this embodiment. FIG. 4 shows a still camera equipped with the finder optical system of this embodiment.

In FIG. 3, the objective optical system 10 is composed of a negative first group I in the traveling direction of light from an object and lens groups II and III which move as indicated by arrows during zooming. , An intermediate image is formed in the vicinity of the diaphragm S1. Further, this finder optical system has the same eyepiece prism 2 as that of the first embodiment.
1 as the eyepiece optical system Le.

In FIG. 3, (W) and (T) indicate the wide-angle end and the telephoto end, respectively. The optical path in the eyepiece optical system after the primary imaging plane near the diaphragm S1 is the same as that shown in FIG.

In FIGS. 4A to 4C, 91 is a camera body, and 92 is a finder optical system of this embodiment. Reference numeral 92a in FIG. 4A is a viewfinder front window arranged in front of the objective optical system 10. Reference numeral 93 is a photographing optical system. Reference numeral 92b in FIG. 4C is an eyepiece window facing the exit surface of the eyepiece prism 21.

In this embodiment, a reflecting surface is provided in the first group I of the objective optical system 10 in order to make the finder optical system thin, and a space in the lateral direction is used.

In this case, the total length of the objective optical system can be secured without difficulty even if the zoom ratio becomes high, and a good viewfinder field can be obtained while maintaining the performance.

Further, by guiding the object image by the objective optical system 10 which is developed in the lateral direction by folding back the optical path like the eyepiece optical system Le of the present embodiment, the eyepiece optical system Le.
The most eye-side surface of the does not protrude from the back surface of the camera body 92,
It is possible to reduce the thickness of the camera.

Further, since the optical path is folded back within the same horizontal plane, there is a space in the vertical direction of the camera.

As described above, in this embodiment, the finder optical system is downsized with a simple structure, and the camera equipped with the finder optical system is downsized.

The finder optical system described in the first embodiment may be mounted on the camera body 92 in place of the finder optical system of this embodiment.

The finder optical system of the first and second embodiments can be mounted not only on the so-called compact still camera shown in FIG. 4 but also on a single-lens reflex camera or a video camera.

(Third Embodiment) FIG. 5 shows a third embodiment of the present invention.
1 illustrates a cross section of a finder optical system that is an embodiment.

In the finder optical system of this embodiment, the light flux from the object guided from the objective optical system (not shown) is passed through the eyepiece prism 61 similar to that described in the first embodiment to the observer. Leading to the eyes.

However, in the present embodiment, the eyepiece prism 61
An eyepiece lens 62 is arranged on the eye side from the exit surface of the.

As a result, in addition to the aberration correction function of the eyepiece prism 61, a further aberration correction function of the eyepiece lens 62 and a diopter correction function for the observer can be obtained.

In each of the above embodiments, the case where the eyepiece prism in which two refracting surfaces and three inner reflecting surfaces are integrally formed in a transparent body is used has been described, but a surface reflecting surface (a mirror instead of the inner reflecting surface is used. ) May be combined to form the eyepiece optical system.

[0083]

As described above, according to the present invention,
The optical path is bent by three reflections by the eyepiece optical element, and the reference axis is crossed twice between the second reflection surface and the third reflection surface and twice between the third reflection surface and the pupil. To realize a small finder optical system as a whole, which is compact and has an eyepiece optical system capable of reversing the image with the minimum number of reflection surfaces, despite the fact that the optical path length is long to form an intermediate image in the system. You can

In the area surrounded by the reflecting surfaces of the eyepiece optical element, the light flux reflected by the second reflecting surface is intermediately imaged between the second reflecting surface and the third reflecting surface. With such a configuration, it is possible to reduce the size of each of the above reflecting surfaces by collecting light fluxes, and to further reduce the size of the eyepiece optical system and thus the finder optical system.

Further, by making at least one of the first to third reflecting surfaces a rotationally asymmetric surface, various aberrations can be corrected well.

The angle α formed by the reference axis from the object surface to the first reflecting surface and the reference axis from the third reflecting surface to the pupil is 50 ° <α <110 ° or 60 ° <α. If the condition of <90 ° is satisfied, the viewfinder optical system can be made thin in the direction from the object side to the observer side (for example, the thickness direction of the camera) even if the zoom ratio is increased.

[Brief description of drawings]

FIG. 1 is a sectional view of an eyepiece prism used in a finder optical system according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the overall configuration of the finder optical system.

FIG. 3 is a sectional view showing the overall configuration of a finder optical system that is a second embodiment of the present invention.

FIG. 4 is a front view, a side sectional view, and a rear view of a camera equipped with the finder optical system according to the second embodiment.

FIG. 5 is a sectional view of an eyepiece prism used in the finder optical system according to the third embodiment of the present invention.

FIG. 6 is an explanatory diagram of an eyepiece optical element according to each embodiment of the present invention.

FIG. 7 is a sectional view of a conventional finder optical system.

[Explanation of symbols]

10 Objective optical system 21,61 Eyepiece prism W wide-angle end M intermediate angle of view T telephoto end Le eyepiece optical system S1 aperture (field frame) S pupil P1 reflective prism ST reference axis

[Procedure amendment]

[Submission date] June 20, 2002 (2002.6.2)
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

As shown in FIGS. 2 and 3 , the reference axis ST
Passes through the center point TO of the effective ray diameter of the first surface R1 and the pupil S
A path through which a light ray (reference axis light ray) reaching the center TO ′ of is refracted / reflected by each refraction surface and reflection surface is set as a reference axis. The order of each surface is set in the order in which the reference axis ray is refracted and reflected. Therefore, the reference axis finally reaches the center of the pupil S while changing its direction according to the law of refraction or reflection along the set order of each surface.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction content]

Z-axis: a straight line passing through the origin of local coordinates and forming an angle θi in the counterclockwise direction in the YZ plane with respect to the Z direction of the absolute coordinate system. Y-axis: passing through the origin of local coordinates and YZ with respect to the z- axis. Straight line forming 90 ° counterclockwise in the plane x-axis: A straight line passing through the origin of local coordinates and perpendicular to the YZ plane.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

Z = [(x ² + y ² ) / Ri] / [1+ [1- (x ² + y ² ) / Ri ² ] ^1/2 ] Further, the rotationally symmetric aspherical surface is expressed by the following formula. The shape is represented.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

Z = [(x²+ y²) / Ri] / [1+ [1- (1 + k) ・ (x²+ y²)
/ Ri²] ^1/2 ] + Ka (x²+ y²)²+ kb (x²+ y²) ³+ kc (x²+ y²)⁶+
… Further, the optical system of the embodiment of the present invention is at least non-rotatable.
It has one or more symmetric aspherical surfaces and its shape is
Express

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

A = (a + b) ・ (y ²・ cos ² t + x ² ) B = 2a ・ b ・ cos t [1 + [(ba) ・ y ・ sin t / (2a ・ b)] + 〔1 + [(ba)
・ Y ・ sin t / (a ・ b)]-[y ² / (a ・ b)]-[4a ・ b ・ cos ² t + (a + b) ² sin ²
t] x ² / (4a ² b ² cos ² t)] ^1/2 ], z = A / B + C0 ² y ² + C11xy + C20x ² + C03y ³ + C12xy ² + C2
1x ² y + C30x ³ + C04y ⁴ + C13xy ³ + C22x ² y ² + C31x ³ y + C40
x ⁴ ... The shape of each rotationally asymmetric surface in the numerical example of the present invention is a plane-based aspherical surface where a = b = ∞, t = 0 in the above curved surface equation, and By using only the even-order terms and setting the odd-order terms to 0, yz
It has a plane-symmetrical shape with the plane as a plane of symmetry. Further, when the following conditions are satisfied, the shape is symmetrical with respect to the xz plane.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction content]

Numerical examples of the embodiment shown in FIG. 1 will be shown below. Since the eyepiece prism 21 shown in FIG. 1 is an eyepiece optical system, in the present numerical example, the center of the pupil S is the origin of the absolute coordinate system, and the diaphragm provided at the position of the pupil S is R1.
Surface, the second refracting surface 215 which is the exit surface is the R2 surface, the third reflecting surface 214 is the R3 surface, the second reflecting surface 213 is the R4 surface,
The first reflection surface 212 surface is represented as R5 surface, the first refraction surface 211 surface which is the incident surface is represented as R6 surface, and the position of the primary image formation surface (MI1) is represented as R7 surface .

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction content]

Numerical Example 1 i Yi Zi θi Di Ndi νdi 1 0.00 0.00 0.00 15.00 1 Aperture 2 0.00 15.00 0.00 14.00 1.49171 57.40 Refractive surface 3 0.00 29.00 -16.00 15.00 1.49171 57.40 Reflective surface 4 7.95 16.28 3.00 8.00 1.49171 57.40 Reflection Surface 5 12.88 22.62 64.00 20.00 1.49171 57.40 Reflecting surface 6 -7.12 22.62 90.00 0.00 1 Refracting surface 7 -7.12 22.62 90.00 0.00 1 Primary image plane Spherical shape R1 surface R1 = ∞ R6 Surface R6 = 15.000 Rotationally symmetric aspherical surface R2 surface R2 = 12.251 k = 0 ka = -0.67731E-03 kb = 0.16394E-04 kc = -0.32619E-06 Rotating asymmetric aspherical surface R3 surface C02 = -0.16147E-01 C20 = -0.40750E-03 C04 = -0.12742 E-04 C22 = -0.96860E-04 C40 = -0.33490E-04 R4 surface C02 = 0.14590E-01 C20 = -0.20640E-02 C04 = 0.30955E-03 C22 = -0.45726E-02 C40 = 0.33869E- 01 R5 surface C02 = -0.23063E-01 C20 = -0.61302E-01 C04 = -0.24134E-03 C22 = -0.91348E-02 C40 = -0.10363E + 00 In the present embodiment, an image is formed at the time of image inversion. It eliminates the need for a roof reflective surface that contributes to deterioration. Further, the three reflecting surfaces are set as rotationally asymmetric aspherical surfaces and are eccentrically arranged, so that various aberrations are satisfactorily corrected. With this configuration, the finder optical system has good visibility.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0056

[Correction method] Change

[Correction content]

For this reason, it is possible to arrange such that the protrusion of the surface in the Z-axis direction is reduced. A thin finder optical system can be realized by applying this arrangement in the thickness direction of the camera. Further, the angle difference between the first reflecting surface 212 and the third reflecting surface 214 which are adjacent on the same side, the exit surface 215 and the second reflecting surface 21.
Since the angle difference with 3 is small, the shape is advantageous in terms of performance and surface accuracy at the time of molding.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0073

[Correction method] Change

[Correction content]

Further, by guiding the object image by the objective optical system 10 which is developed in the lateral direction by folding back the optical path like the eyepiece optical system Le of the present embodiment, the eyepiece optical system Le.
The most eye-side surface of the does not protrude from the back surface of the camera body 91 ,
It is possible to reduce the thickness of the camera.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0076

[Correction method] Change

[Correction content]

The finder optical system described in the first embodiment may be mounted on the camera body 91 instead of the finder optical system of this embodiment.

Claims (11)

[Claims] 1. A finder optical system for guiding a light beam from an object to an observer's eye through an eyepiece optical element, wherein the eyepiece optical element includes a first reflecting surface for reflecting the light beam from the object, 1 has a second reflecting surface that reflects the light flux reflected by the reflecting surface and a third reflecting surface that reflects the light flux reflected by the second reflecting surface, and reflects by the respective reflecting surfaces from the center of the object surface. When the path of a light ray passing through the center of the pupil is used as a reference axis, the reference axis extends from the second reflecting surface to the third reflecting surface with respect to the optical path from the object surface to the first reflecting surface. In the area surrounded by the first to third reflecting surfaces, and at the position where the optical paths from the third reflecting surface to the pupil intersect. , Finder light characterized by intermediately forming a light flux System. 2. A light flux reflected by the second reflecting surface forms an intermediate image between the second reflecting surface and the third reflecting surface in a region surrounded by the respective reflecting surfaces. The finder optical system according to claim 1. 3. A position of a light beam reflected by the second reflecting surface in a region surrounded by the reflecting surfaces, the position being near the second reflecting surface between the second reflecting surface and the third reflecting surface. The finder optical system according to claim 2, wherein an intermediate image is formed by. 4. The finder optical system according to claim 1, wherein at least one of the first to third reflecting surfaces is a rotationally asymmetric surface. 5. An angle α formed by a reference axis from the first refracting surface to the first reflecting surface and a reference axis from the third reflecting surface to the pupil is 50 ° <α <110. The finder optical system according to any one of claims 1 to 4, which satisfies the condition of °. 6. The viewfinder optical system according to claim 5, wherein the angle α satisfies a condition of 60 ° <α <90 °. 7. The eyepiece optical element emits a light beam reflected by a first refracting surface on which a light beam from an object is incident, an inner reflection surface as the first to third reflection surfaces, and a third reflection surface. The finder optical system according to any one of claims 1 to 6, wherein the second refracting surface to be formed is integrally formed with a transparent body. 8. The finder optical system according to claim 1, further comprising a reflective optical element that reflects a light beam from the object and guides it to the eyepiece optical system. 9. The viewfinder optical system according to claim 1, further comprising an objective optical system having a positive refractive power. 10. An optical apparatus comprising the finder optical system according to claim 1. Description: 11. The optical apparatus according to claim 10, further comprising a photographing optical system in addition to the finder optical system.