JPH10312004A - Finder optical system for single lens reflex camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a finder optical system for a single lens reflex camera capable of observing a subject, in a state where finder magnification is high, while shortening the dimension in the direction of optical axis of the finder. SOLUTION: A photographing luminous flux from a photographic lens 2 is reflected by a first reflection surface 3 for refracting the photographing luminous flux into a second optical axial direction nearly perpendicular to a first optical axis, to form the image of an object 1 on a primary image forming surface on a second optical axis or a focusing plate 4 provided in the vicinity of the primary image forming surface. The luminous flux of the subject is reflected by a second reflection surface 5, into a second plane inclined toward a first plane including the first and second optical axes. Further, the subject is reimaged on a secondary image forming surface by a secondary image forming lens 6 located on a third optical axis refracted by the second reflection surface 5, with a third reflection surface 7 for refracting the third optical axis, to obtain a fourth optical axis in a direction nearly parallel with the second optical axis. Then, the luminous flux of the subject is reflected by a fourth reflection surface 9 for refracting the fourth optical axis into a fifth optical axial direction parallel with the first optical axis, to observe the subject by an eyepiece 2.

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 of a single-lens reflex camera, and more particularly to a plurality of reflecting surfaces, a secondary imaging lens, and an eyepiece in which a subject image (finder image) formed by a photographing lens is appropriately set. This is related to the viewfinder optical system of a single-lens reflex camera, which can increase the viewfinder magnification by using a lens and reduce the size of the camera in the optical axis direction (thin the thickness) while reducing the weight. It is.

[0002]

2. Description of the Related Art Conventionally, a single-lens reflex camera using a penta roof prism for 35 mm film has been greatly developed as an optimum one for developing a system.

However, if the above-mentioned penta roof prism is used in a finder optical system of a so-called single-lens reflex electronic camera using a solid-state imaging device such as a CCD, a field rate and a field magnification similar to those of a conventional single-lens reflex camera can be obtained. Becomes difficult.

Further, since the penta roof prism is made of a glass block, and since many optical surfaces must be polished with high precision, there is a problem that manufacturing is difficult, expensive and heavy.

On the other hand, there have been proposed various finder optical systems for a single-lens reflex camera using a so-called "hollow penta" in which a roof surface is formed by a molded product. This is lighter in weight than a single-lens reflex camera using the above penta roof prism, and has been used in some single-lens reflex cameras as an inexpensive finder. However, the viewfinder optical system of a single-lens reflex camera using this “hollow penta” has an optical path length longer than that of a penta roof prism because the viewfinder optical path is air instead of a medium having a refractive index. As a result, the viewfinder magnification is 20%. 30% lower than that of the finder image, and the finder image becomes smaller.

In recent years, various finder optical systems for a single-lens reflex camera of the type comprising a secondary imaging lens and a plurality of reflecting surfaces have been proposed. This single-lens reflex camera has features that the finder magnification can be increased, and that the weight and cost can be reduced.

FIG. 4 is a schematic view of a principal part of a finder optical system of this kind of single-lens reflex camera.

In FIG. 1, a photographing light beam from a subject 41 passing through a photographing lens 42 is reflected upward by a first mirror 43 and forms a primary image (subject image) on a focus plate 44. The light beam based on the subject image formed on the focus plate 44 is reflected by the second mirror 45 to the rear of the lens and bent, and then reflected by the third mirror 46 to the side of the lens.
The image is relayed by the secondary imaging lens 47 and re-imaged on the secondary imaging surface 48. And the re-formed secondary image (subject image)
Is observed at the eye point 51 by the eyepiece 50 via the fourth mirror 49.

In the same manner as described above, the finder optical system
A finder optical system of a single-lens reflex camera composed of a secondary imaging system and a plurality of reflecting surfaces is disclosed in, for example,
No. pp. 139 to 163. The same publication discloses that the viewfinder of a single-lens reflex camera is a secondary imaging system and that the optical path is appropriately bent by multiple reflections to make the high-magnification viewfinder compact. It has the feature of being able to.

[0010]

In the viewfinder system of the conventional single-lens reflex camera shown in FIG.
A light beam based on the primary image formed on the
The optical member protrudes rearward by an amount corresponding to the third mirror 46 because the third mirror 46 bends the lens sideward after the lens is bent rearward at 5.
There is a problem that the size of the camera in the optical axis direction becomes long (thick).

The above-mentioned Japanese Patent Application Laid-Open No. 1-118119 is also disclosed.
In the publication, the optical axis of the secondary imaging lens is on the optical path oriented in the same direction as the optical axis of the photographing lens, and the optical path is bent many times. Dimensions tended to be long.

According to the present invention, the finder magnification is increased and the weight is reduced by using a plurality of reflection surfaces, a secondary imaging lens, an eyepiece, and the like in which a subject image formed by a photographing lens is appropriately set. It is an object of the present invention to provide a viewfinder optical system of a single-lens reflex camera that allows observation while reducing the size of the camera in the optical axis direction.

[0013]

A finder optical system of a single-lens reflex camera of the present invention, in order to solve the problems] (1) a first optical axis L ₁ of the photographing lens imaging light beam from the subject passing through the photographing lens, contrast Te is reflected by the first reflecting surface which is to be bent to a second optical axis L ₂ direction substantially orthogonal, an object image on the primary image plane or focal plate provided in the vicinity of the second optical axis L ₂ The first optical axis L ₁ and the second optical axis L ₁
The third optical axis L reflected by the second reflecting surface into a second plane inclined with respect to the first plane including the optical axis L ₂ and bent by the second reflecting surface of the second optical axis L _{2 The} object image formed on the focus plate by the secondary imaging lens located on the third optical axis L ₃ is shifted to the fourth optical axis L in a direction substantially parallel to the second optical axis L _2.
The light flux based on the subject image re-imaged on the secondary image forming surface via the third reflecting surface which is bent to ₄ and the fourth optical axis L _{4 is changed} to the first light. a fourth is reflected by the reflecting surface for bending the fifth optical axis L ₅ axis L ₁ and parallel guided to the eyepiece, the eyepiece, observing the object image formed on the secondary imaging plane It is characterized by doing.

In particular, (1-1) the secondary imaging lens comprises a reduction optical system, and (1-2) when the imaging magnification of the _secondary imaging lens is β ₂ , -0.7 <Β ₂ <−0.2 or (1-3) When an angle between the second optical axis L ₂ and the third optical axis L ₃ is θ ₁₂ , 50 ° < including and satisfying the θ ₁₂ <85 ° becomes conditions, the first optical axis L ₁ perpendicular to the (1-4) said first optical axis L ₁ and the third optical axis L ₃ of the first plane It is characterized by satisfying a condition of 50 ° <θ ₀₂ <85 ° when an angle formed when projected onto a plane is θ ₀₂ .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a subject, and 2 denotes a photographing lens. 3 is a first reflecting surface (reflecting mirror), substantially perpendicular to the spatial direction (second optical axis imaging light beam to the first optical axis L ₁ of the photographing lens 2 from the object 1 which has passed through the photographic lens 2 L _{(In two} directions, Y direction), and retracted outside the imaging optical path during exposure. Reference numeral 4 denotes a focus plate provided on or near the primary image forming surface, on which a subject image (finder image) formed by the photographing lens 2 is optically substantially equal to an image pickup surface of an image pickup device unit (not shown). It is arranged in a position. Reference numeral 5 denotes a second reflection surface (reflection mirror), and a second optical axis (finder optical axis) obtained by bending a light beam based on the subject image formed on the focus plate 4 by the first reflection surface 3.
L ₂ and is bent into a second plane inclined with respect to the first plane (XY plane) including a first optical axis L ₁ of the taking lens 2. Reference numeral 6 denotes a secondary imaging lens formed of a reduction optical system, which is located on the third optical axis L ₃ bent by the second reflecting surface 5, and which converts an object image formed on the focusing plate 4 by the photographing lens 2 into a second image. Secondary imaging surface 8 via three reflection surfaces (reflection mirrors) 7
The image is re-imaged as an erect upright image. The third reflecting surface 7 moves the third optical axis L ₃ bent by the second reflecting surface 5 to the first position.
Second optical axis L ₂ substantially the same direction as the bent by the reflecting surface 3 (the fourth optical axis L ₄ direction, Y-direction) is bent to. 9
Is a fourth reflecting surface (reflecting mirror), and the fourth optical axis L ₄ bent by the third reflecting surface 7 is connected to the optical axis L of the photographing lens 2.
₁ substantially the same direction as (fifth optical axis L ₅ direction, X direction) is bent to. 10 is an eyepiece lens, are positioned on the fifth optical axis L ₅ which is bent in the fourth reflecting surface 9. Reference numeral 11 denotes an eye point, where the subject image formed on the secondary imaging plane 8 is observed through the eyepiece lens 10.

[0017] In this embodiment the first and so folded into a second optical axis L ₂ direction substantially perpendicular to photographing light beam from an object passed through the photographic lens 2 with respect to the first optical axis L ₁ of the photographing lens 2 is reflected by first reflecting surface 3, the focusing screen 4 provided on the primary image forming surface or the vicinity thereof on said second optical axis L ₂ forms a primary image (object image). Light beam and the second reflection to a second plane inclined with respect to the first plane including the first optical axis L ₁ and the second optical axis L ₂ (XY plane) based on the primary image formed on the focusing screen 4 1 formed on the focus plate 4 by the secondary imaging lens 6 located on the third optical axis L ₃ reflected by the surface 5 and bent by the second reflection surface 5 of the second optical axis L ₂ 2 of erecting the secondary imaging plane 8 through the third reflecting surface 7 for bending the next image a third optical axis L ₃ to the second optical axis L ₂ and the fourth optical axis L ₄ substantially parallel direction The next image (subject image) is re-imaged. The light flux based on the secondary image re-imaged on the secondary image forming plane 8 has a fourth optical axis L
₄ is reflected by the fourth reflecting surface 9 for bending the fifth optical axis L ₅ direction of the first optical axis L ₁ and the parallel light is guided to the eyepiece 10, the eyepiece 10, the secondary imaging plane The subject image formed at 8 is observed at the eye point 11.

In this embodiment, a third optical axis (finder optical axis) L ₃ near the second reflecting surface 5 having a wide effective light flux width.
Into a second plane inclined with respect to a plane (XY plane) including the second optical axis L ₂ bent by the first reflection surface 3 and the first optical axis (photographing optical axis) L ₁ of the photographing lens 2. With the configuration in which the optical member is bent at the second reflection surface 5, the protrusion to the rear side of the optical member can be reduced, whereby the size of the camera in the optical axis direction can be shortened (thickness is reduced) and the entire device is reduced. The size is reduced.

In this embodiment, the size of the secondary image formed on the secondary image forming surface 8 is formed on the primary image forming surface 4 by forming the secondary image forming lens 6 from a reduction optical system. Smaller than the size of the primary image.
The size of the reflection surface 7 and the fourth reflection surface 9 is reduced to reduce the dimension in the optical axis direction.

Further, in the present embodiment, when the imaging magnification of the _secondary imaging lens 6 is β ₂ , the condition of −0.7 <β ₂ <−0.2 ＜ (1) is satisfied. I have.

The conditional expression (1) relates to the imaging magnification β ₂ of the _secondary imaging lens 6. If the conditional expression (1) is not satisfied, it becomes difficult to shorten the dimension in the optical axis direction. Absent. In the present embodiment, the imaging magnification β of the secondary imaging lens 6
₂ is set to β ₂ = −0.3, which satisfies the conditional expression (1).

FIG. 2 is a schematic view showing a main part of a part of the second embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

The present embodiment is different from the first embodiment in that the second optical axis L bent by the first reflecting surface 3
₂ is that defined by the to meet the angle θ condition to be described later ₁₂ (2) and the third optical axis L ₃ that is bent by the second reflecting surface 5. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in this embodiment, the second optical axis L ₂ and the third optical axis L ₂
And to satisfy the _{50 ° <θ 12 <85 °} ‥‥‥‥ (2) becomes a condition when the angle between the optical axis L ₃ and the theta _12.

Conditional expression (2) represents the second optical axis L ₂ and the third optical axis L
It is intended to define an angle theta ₁₂ conditions the _3, not good since it becomes impossible to Deviation conditional expression (2) to reduce the height dimension of the camera. In the present embodiment, the angle θ ₁₂ is set to 80 °, which satisfies the conditional expression (2).

As described above, in the present embodiment, the position of the third reflecting surface 7 and the fourth reflecting surface 9 is lowered by appropriately setting the angle θ ₁₂ so as to satisfy the conditional expression (2). As a result, the height of the camera can be reduced, and the overall size of the apparatus can be reduced.

FIG. 3 is a schematic view showing a main part of a part of the third embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

This embodiment is different from the first embodiment in that the first optical axis L ₁ of the taking lens 2 and the third optical axis L ₃ bent by the second reflecting surface 5 are defined by a first plane (XY plane).
Is the angle theta ₀₂ when projected onto the plane (XZ plane) including the first optical axis L ₁ perpendicular to defined so as to satisfy the condition described below (3) and. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in this embodiment, the first optical axis L ₁ and the third optical axis L ₁
First optical axis L ₁ perpendicular to the optical axis L ₃ and the first plane (XY plane)
Angle of theta ₀₂ when projected onto the plane (XZ plane) including the
In this case, the condition 50 ° <θ ₀₂ <85 ° ‥‥‥‥ (3) is satisfied.

Conditional expression (3) represents the first optical axis L ₁ and the third optical axis L
₃ stipulates a condition of an angle θ ₀₂ formed when projecting 3 onto a plane (XZ plane) including the first optical axis L ₁ orthogonal to the first plane (XY plane), and deviates from conditional expression (3). It is not good because it becomes difficult to shorten the size of the camera in the optical axis direction. In the present embodiment, the angle θ ₀₂ is set to 78 °, which satisfies the conditional expression (3).

As described above, in the present embodiment, by setting the angle θ ₀₂ so as to satisfy the conditional expression (3), the positions of the third reflecting surface 7 and the fourth reflecting surface 9 are set slightly forward (subject). Side). As a result, the protrusion of the eyepiece lens 10 on the rear side (eye point side) is reduced, and the size of the camera in the optical axis direction is shortened, so that the overall size of the apparatus is reduced.

It goes without saying that the above-described conditional expressions (2) and (3) may be applied to the first embodiment.

[0033]

According to the present invention, a single-lens reflex camera having the following effects can be obtained by using a plurality of reflecting surfaces, secondary imaging lenses, eyepieces and the like appropriately set as described above. A finder optical system can be achieved.

The magnification of the finder can be increased, and the subject image (secondary image) can be favorably observed with a finder having a short dimension (thin thickness) in the optical axis direction of the finder.

A thin single-lens reflex camera can be realized.

The height of the finder can be reduced.

Even when the size of the eyepiece becomes large, it is possible to reduce the protrusion to the rear of the camera.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part of a part of Embodiment 2 of the present invention.

FIG. 3 is a schematic view of a main part of a part of a third embodiment of the present invention.

FIG. 4 is a schematic diagram of a main part of a viewfinder optical system of a conventional single-lens reflex camera.

[Description of Signs] 1 subject 2 photographing lens 3 first reflecting surface 4 focus plate 5 second reflecting surface 6 secondary imaging lens 7 third reflecting surface 8 secondary imaging surface 9 fourth reflecting surface 10 eyepiece 11 eye point

Claims (5)

[Claims] 1. A first optical axis L ₁ of the photographing lens imaging light beam from the subject passing through the photographing lens, the was so bent to the second optical axis L ₂ direction substantially perpendicular thereto 1
Is reflected by the reflecting surface, said luminous flux which an object image is formed on the primary image plane or focal plate provided in the vicinity of the second optical axis L _2, based on the object image formed on the focusing plate One optical axis L
Is reflected by ₁ and the second optical axis L ₂ and the second reflecting surface to the second plane inclined with respect to the first plane containing a folded by the second second reflecting surfaces of the optical axis L ₂ The subject image formed on the focus plate by the secondary imaging lens positioned on the third optical axis L ₃ is shifted from the third optical axis L ₃ to the fourth optical axis in a direction substantially parallel to the second optical axis L _2. The image is re-imaged on the secondary image forming surface via the third reflecting surface bent to L ₄ , and the light flux based on the object image re-imaged on the secondary image forming surface is connected to the fourth optical axis L ₄ by the first optical axis L ₄ . is reflected by the fourth reflecting surface for bending the fifth optical axis L ₅ direction of the optical axis L ₁ and parallel guided to the eyepiece, the eyepiece, the 2
A viewfinder optical system for a single-lens reflex camera, wherein an image of a subject formed on a next imaging plane is observed. 2. A finder optical system for a single-lens reflex camera according to claim 1, wherein said secondary imaging lens comprises a reduction optical system. 3. The single-lens reflex camera according to claim 1, wherein, when an imaging magnification of said secondary imaging lens is β ₂ , a condition of −0.7 <β ₂ <−0.2 is satisfied. Camera viewfinder optical system. 4. When the angle between the second optical axis L ₂ and the third optical axis L ₃ is θ ₁₂ , the condition 50 ° <θ ₁₂ <85 ° is satisfied. Item 1. A finder optical system of the single-lens reflex camera. 5. An angle formed when the first optical axis L ₁ and the third optical axis L ₃ are projected onto a plane including the first optical axis L ₁ orthogonal to the first plane and defined as θ ₀₂ . 2. The viewfinder optical system for a single-lens reflex camera according to claim 1, wherein the following condition is satisfied: 50 ° <θ ₀₂ <85 °.