JP2000338424A - Finder optical system and photographing device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent visibility by constituting an ocular of two lenses being a single lens and making the two lenses have appropriate shape satisfying a specified conditional expression. SOLUTION: The ocular is constituted of a roof mirror 5 having reflection surfaces orthogonal to each other and reflecting emitted light from the emitting surface 4d of a prism 4 on the respective reflection surfaces so as to reverse the right and the left of an image and guiding the reflected light downward or lower obliquely backward, a 1st lens 6 having positive refractive power, a plane reflection mirror 7 reflecting a light beam reflected by the mirror 5 and guided through the lens part 6 backward (observation side), and a 2nd lens part 8 having negative refractive power. When the radii of curvature of the lens surfaces of the lens part 6 on a focusing screen side and on an observation side are respectively defined as R1a and R1b, and the radii of curvature of the lens surfaces of the lens part 8 on the focusing screen side and on the observation side are respectively defined as R2a and R2b, the condition shown by the expression is satisfied.

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 and an image pickup apparatus using the same, and more particularly, to a still camera,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system used in an image pickup apparatus such as a video camera and a digital camera, in which an observation position of the finder can be arranged sufficiently behind the image pickup apparatus body.

[0002]

2. Description of the Related Art In general, in a viewfinder optical system of a single-lens reflex camera, a focusing screen is disposed at a position equivalent to a predetermined focal plane of a photographing lens, and is used for framing a photographed image and checking a focus adjustment state. Such a viewfinder optical system has a configuration in which the observation magnification of the subject image is large and the visibility is good, and the entire field of view can be observed even if the observer's eyes are placed at a certain distance from the eyepiece. Is desired.

In recent years, a condensing lens has been arranged near a predetermined focal plane of a photographing lens, and subject light (subject image) is contracted by an image forming optical system converged behind the condensing lens, and an image pickup device such as a CCD is formed. There has been proposed a single-lens reflex type electronic camera configured to re-image the image. When configuring such a single-lens reflex type electronic camera, it is necessary to arrange the observation position of the finder optical system to a certain extent behind the apparatus main body in consideration of the size of the entire apparatus. For this purpose, various types of single-lens reflex cameras with improved finder optical systems have been proposed.

In a first conventional example disclosed in Japanese Patent Laid-Open Publication No. Hei 6-300964, a subject image projected above a reticle (above a camera body) is positioned above a reticle of a single-lens reflex camera. A plane reflecting mirror for reflecting light to the observation side), a re-imaging optical system for re-imaging a subject image behind the flat reflecting mirror, and an exit pupil of the re-imaging optical system is substantially imaged on a pupil of an observer. A condensing lens that focuses light for focusing and an eyepiece that magnifies and observes the subject image re-imaged by the re-imaging optical system are arranged to re-focus the subject image formed on the focusing screen. A configuration for observing the image as an erect aerial image is proposed.

A second conventional example disclosed in Japanese Patent Application Laid-Open No. 6-235870 discloses a most common single-lens reflex camera which forms an erect image by disposing a pentaprism above a focusing screen. By constructing the eyepiece placed behind this from a plurality of appropriately shaped lenses, we proposed a configuration that made it possible to place the observation position sufficiently rearward while maintaining a large observation magnification. ing.

On the other hand, a third conventional example disclosed in Japanese Utility Model Publication No. 52-13975 proposes a finder optical system having a configuration combining prisms, and reflects a subject image formed on a focusing screen. The observation position is arranged rearward without remarkably increasing the optical path length by gradually leading backward while repeating the above.

A fourth conventional example disclosed in Japanese Patent Application Laid-Open No. 2-166430 is an improvement of the above-mentioned third conventional example, in which the number of prisms is reduced to reduce the weight of the entire apparatus. It is. In the fourth conventional example, a prism is arranged above a focusing screen to reflect a subject image obliquely backward and downward and then obliquely backward, and a roof mirror is arranged behind an exit surface of the prism to form a subject image. The mirror is inverted right and left to reflect downward, and further reflected backward by a plane reflecting mirror to be observed with an eyepiece having a positive refractive power. There has been proposed a configuration in which an optical element (convex lens) is arranged to maintain a large observation magnification of a finder.

[0008]

In a viewfinder optical system of a single-lens reflex camera, there is a demand for an apparatus which maintains good visibility while increasing the observation magnification of a subject image and arranges an observation position to a certain extent rearward. However, the above-described conventional examples have the following problems.

In the first conventional example, the number of lenses constituting the finder optical system is increased and the observation position is too rearward, and the optical characteristics of the finder optical system composed of a large number of these lenses are increased. There is a problem that these holding structures for achieving sufficiently high performance are difficult.

In the second conventional example, it is necessary to set a large pentaprism in advance when arranging the observation position behind while maintaining a large observation magnification. It is not suitable where rearward placement is required.

In the third conventional example, it is possible to arrange the observation position behind while maintaining the observation magnification of the finder relatively large, but there is a problem that the whole apparatus becomes heavy and expensive. Was.

In view of the above, a configuration as in the fourth conventional example has been proposed by improving the third conventional example. However, such a configuration makes it possible to substantially correct various aberrations generated in the finder optical system. The problem that it becomes difficult is generated. With the configuration as in the fourth conventional example, the curvature of field or distortion generated by the convergent optical element (convex lens) disposed in the finder optical system, or the chromatic aberration of magnification is increased, and the positive lens disposed rearward. It is difficult to cancel and correct them with an eyepiece having a refractive power of. In order to satisfactorily correct the various aberrations that occur in these viewfinder optical systems with a small number of lenses, the lens components that make up the viewfinder optical system are divided into lens components with positive refractive power and lens components with negative refractive power. It is desirable to configure
It is not preferable to form the configuration as disclosed in the fourth conventional example with two positive lens components. The fourth
The reason why the refractive powers of the two lens components are both positive in the conventional example is that the principal point position of the entire finder optical system for obtaining a desired observation magnification is set between the two lens components. Is required, and the position for disposing the first positive lens component is inappropriate.

According to the present invention, there is provided a finder optical system in which an observation position is arranged to some extent behind a main body of a device, various aberrations can be satisfactorily corrected while maintaining a large observation magnification, and a good finder image can be observed. It is an object of the present invention to provide an imaging device using the same.

[0014]

According to a first aspect of the present invention, there is provided a finder optical system for observing an object image formed on a reticle, wherein the finder optical system includes an entrance surface facing the reticle. A first prism having a reflecting surface for reflecting the incident light from the incident surface, and an exit surface for emitting the reflected light reflected by the reflecting surface totally reflected on the same surface as the incident surface, and A roof-type reflecting member for reflecting the light emitted from the exit surface of the first prism on a reflecting surface orthogonal to each other to invert the image left and right and emitting the light, and a reflecting member for reflecting the light beam reflected by the roof-type reflecting member And an eyepiece including a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. The lens surface of the first lens unit on the reticle side and the observation side The curvature radii of the lens surfaces of R1a, R1b, The radius of curvature of the viewing-side lens surface and the focal point plate side lens surface of the second lens unit each R2a, R2
b

[0015]

(Equation 3)

It is characterized by satisfying the following conditions.

According to a second aspect of the present invention, in the first aspect of the invention, the focal lengths of the first lens portion and the second lens portion are f ₁ and f ₂ , respectively, and the focal lengths of the first lens portion and the second lens portion are determined from the observation side lens surface of the first lens portion. Assuming that the distance between the second lens and the lens surface on the reticle side is d, the following condition is satisfied: 0.10 <(d / f ₂ ) · (d / f ₁ −1) <0.30 (3) It is characterized by doing.

According to a third aspect of the present invention, in the first aspect of the present invention, the combined focal length of the first lens unit and the second lens unit is f _e , and the distance between the second lens unit and the observation surface of the first lens unit. When the distance to the lens surface on the reticle side is d, the condition 0.10 <d / _fe <0.40 (4) is satisfied.

According to a fourth aspect of the present invention, in the first, second or third aspect, the roof-type reflecting member and the reflecting member for reflecting the light beam reflected by the roof-type reflecting member are three plane reflecting mirrors. Are characterized by the combination of

According to a fifth aspect of the present invention, in the fourth aspect, a reflecting member for reflecting the light beam reflected by the roof-type reflecting member is disposed between the first lens portion and the second lens portion, It is characterized by being integrally held by a holding member.

According to a sixth aspect of the present invention, in the first, second or third aspect of the present invention, the roof-type reflecting member is configured to be orthogonal to an incident surface on which the light emitted from the first prism is incident. A second prism having a roof-type reflecting surface for reflecting incident light from the incident surface, and an exit surface for emitting light rays reflected by the roof-type reflecting surface after being totally reflected on the same surface as the incident surface; It is characterized by doing.

According to a seventh aspect of the present invention, in the sixth aspect, the exit surface of the first prism and the incident surface of the second prism are joined.

According to an eighth aspect of the present invention, in the first, second or third aspect of the present invention, the first lens portion and the second lens portion are closer to the viewing side than the reflecting member for reflecting the light beam reflected by the roof type reflecting member. And held integrally with the reflection member by a holding member.

According to a ninth aspect of the present invention, in any one of the first to eighth aspects, at least one of the lens surfaces of the first lens portion and the second lens portion is aspheric. Features.

A tenth aspect of the present invention is characterized in that, in the ninth aspect of the present invention, both the first lens portion and the second lens portion include aspherical lenses made of acrylic resin.

According to an eleventh aspect of the present invention, an object image formed on a reticle by a rotating mirror disposed on the image side of a photographing lens as an erect image via various optical members and an eyepiece. In an imaging device for observation, in a finder optical path from a reticle to a pupil of an observer, an incident surface facing the reticle, a reflecting surface for reflecting incident light from the incident surface obliquely downward and the reflecting surface. A first prism having an exit surface for totally reflecting the reflected light at the same angle as the incident angle, guiding the light obliquely rearward and exiting, and reflecting surfaces orthogonal to each other, the exit surface of the prism A roof-type reflecting member that reflects reflected light from each of the reflecting surfaces to invert the image from side to side and guides the reflected light downward or obliquely backward, and reflects the light reflected by the roof-type reflecting member backward. A reflecting member; And a second lens unit having a negative refractive power. The eyepiece comprises a first lens unit having a negative refractive power and a second lens unit having a negative refractive power. The radii of curvature are R1a and R
1b, when the radii of curvature of the lens surface on the reticle side and the lens surface on the observation side of the second lens unit are R2a and R2b, respectively:

[0027]

(Equation 4)

It is characterized by satisfying the following conditions.

According to a twelfth aspect of the present invention, there is provided an image pickup apparatus for observing an object image formed on a reticle by a photographing lens using the finder optical system according to any one of the first to tenth aspects. And

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a main part of a first embodiment when a finder optical system according to the present invention is applied to a single-lens reflex camera. FIG. 2 is a perspective view of a main part of the imaging optical system of a part of FIG. 1, and FIG. 3 is a developed view of an optical path of a part of FIG. 1 to 3, reference numeral 1 denotes a photographing lens, and 2 denotes a rotating mirror, which rotates based on a photographing operation. Reference numeral 3 denotes a reticle on which an object image formed by the photographing lens 1 is formed. 4 is a prism (first prism), 5 is a roof mirror (roof-type reflecting member), 6 is a first lens (first lens portion) having a positive refractive power, 7 is a plane reflecting mirror (reflecting member), 8
Denotes a second lens (second lens unit) having a negative refractive power, 9
Represents the position of the pupil of the observer. Reference numeral 10 denotes a planned imaging plane of the photographing lens 1, and reference numeral 11 denotes a mirror 14, 15 which collects subject light emitted from an exit pupil of the photographing lens 1.
Condensing lens for guiding to the re-imaging optical system 12 through
Reference numerals 4 and 15 denote reflecting mirrors that bend the optical path from the condenser lens 11 to the re-imaging optical system 12, 13 denotes an image sensor, and 20 denotes an outline of the camera body.

Next, the schematic configuration of the imaging optical system shown in FIG. 2 will be described. In the present invention, as shown in FIG. 2, when the rotating mirror 2 disposed on the image side of the photographing lens 1 is in the retracted state, the subject image is collected near the predetermined focal plane 10 of the photographing lens 1. The light is condensed by the optical lens 11, guided to the re-imaging optical system 12 via the mirrors 14 and 15, reduced by the re-imaging optical system 12, and re-imaged on the image sensor 13. In an imaging optical system 101 composed of a condenser lens 11, a re-imaging optical system 12, and an imaging device 13, reflecting mirrors 14 and 15 are arranged, and a camera body 2 is provided.
The imaging optical system is encapsulated without significantly increasing the size of the lens. Depending on the arrangement of the imaging optical system 101, the camera body 2
The magnitude of 0 is determined, and the pupil position 9 of the finder optical system shown in FIG. 1 is also substantially determined by this.

The schematic configuration of the single-lens reflex camera of this embodiment is determined as described above, and a finder optical system suitable for the single-lens reflex camera having such a configuration is realized. The finder optical system according to the present embodiment includes a reticle 3
And a reflecting surface 4b for reflecting the incident light from the incident surface 4a downward and obliquely rearward (downward oblique to the camera body on the observing side) and the reflected light reflected by the reflecting surface 4b. A prism 4 having an exit surface 4d that is totally reflected by a total reflection surface 4c, which is the same as the surface, and is guided obliquely rearward to exit.
And the prism 4 having reflecting surfaces orthogonal to each other.
A roof mirror 5 that reflects the light emitted from the light exit surface 4d on each reflection surface to invert the image horizontally and guides the reflected light downward or obliquely backward, and a first lens 6 having a positive refractive power. A plane reflecting mirror 7 for reflecting light rays reflected by the roof mirror 5 and guided through the first lens unit 6 backward (to the observation side), and a second lens unit 8 having a negative refractive power. ing.

In the present embodiment, by adopting such a structure, the position 9 of the pupil of the observer can be arranged sufficiently behind the camera body 20 so that the subject image can be easily observed when the camera is held. ing. Since the prism 4, the roof mirror 5, and the plane reflecting mirror 7 are arranged to pass through optical members to form an erect image of the finder image, the geometric optical path length becomes longer.

Therefore, in the present embodiment, the eyepiece lens 10
2 is a single lens for the first lens unit 6 having a positive refractive power, and the second lens unit 8 for a negative refractive power is formed of two lenses of a single lens, and these two lenses are disclosed above. By forming an appropriate shape that satisfies the conditional expressions (1) and (2), a finder optical system of a single-lens reflex camera having good visibility is realized.

Each of the first lens unit 6 and the second lens unit 8 is composed of a single lens or a plurality of lenses. The first embodiment shows a case where the first and second lens units 6 and 8 are formed of a single lens.

Conditional expressions (1) and (2) are for the eyepiece 1
02 is a formula that defines the shape factor of each of the first lens 6 and the second lens 8 that make up the lens 02, and satisfactorily corrects various aberrations that occur when the configuration is such that the observation magnification of the finder is maintained sufficiently large. 3 is a formula that discloses a shape suitable for a finder optical system that can be used.

Conditional expression (1) defines the shape factor of the first lens having a positive refractive power on the reticle side of the two lenses constituting the eyepiece lens. It is desirable to use a positive lens with a relatively strong convex surface facing the reticle within a range satisfying the expression (1). With such a configuration, the positive lens satisfactorily corrects various aberrations such as spherical aberration and coma generated by the positive lens while arranging the principal point position of the entire eyepiece on the reticle side.

Conditional expression (2) defines the shape factor of the second lens on the observer side having a negative refractive power, which constitutes the eyepiece, and this second lens satisfies this conditional expression (2). It is desirable to use a negative lens having a relatively strong concave surface facing the reticle within a satisfactory range. Considering only aberration correction, it is conceivable to adopt a configuration with a strong concave surface facing the observer side, but the outer peripheral portion of the lens has a shape protruding backward, making it unsuitable for the external configuration of the camera. There is a problem that the assembling workability is deteriorated, which is not preferable. In the present invention, the two lenses have such a configuration so that aberrations occurring in the entire eyepiece are corrected in a well-balanced manner while maintaining a sufficiently large observation magnification of the finder.

In order to obtain better optical performance in the finder optical system of the present invention, it is preferable to satisfy at least one of the following conditions.

(A-1) The focal lengths of the first lens unit and the second lens unit are f ₁ and f ₂ , respectively, and the distance from the observation side lens surface of the first lens unit to the focusing plate side of the second lens unit is Assuming that the distance to the lens surface is d, the conditional expression 0.10 <(d / f ₂ ) · (d / f ₁ −1) <0.30 (3) is satisfied.

Conditional expression (3) is to appropriately set the focal length of the first and second lens units and the distance between the vertices of the lenses to appropriately set the front principal point position of the entire eyepiece.
This is a conditional expression for sufficiently increasing the observation magnification of the finder in a range where various aberrations can be favorably corrected. Conditional expression (3) indicates that when the eyepiece can be regarded as two thin single lenses, the distance from the front principal point of the entire eyepiece to the first lens, which is located closer to the reticle than the first lens, and the eyepiece This corresponds to an equation that defines the ratio of the entire focal length. In a finder optical system in which the geometric optical path length of an optical member for erect image formation is relatively long, an eyepiece is configured to maintain a sufficiently large observation magnification of the finder while favorably correcting various aberrations. It is preferable that each lens is configured so as to satisfy the conditional expression (3).

(A-2) The combined focal length of the first lens unit and the second lens unit is f _e , and the distance from the observation-side lens surface of the first lens unit to the focusing plate-side lens surface of the second lens unit is f _e . Distance d
In this case, the conditional expression 0.10 <d / _fe <0.40 (4) is satisfied.

Conditional expression (4) defines the ratio between the air gap between the first and second lens units and the combined focal length of the eyepiece. The lens interval required for arranging the front principal point at an appropriate position is expressed by the ratio of two simple numerical values. If the lower limit of conditional expression (4) is exceeded and the distance between the first and second lens units becomes smaller, it becomes difficult to increase the observation magnification of the finder. Also,
Conversely, if the size exceeds the upper limit, the size of the camera tends to increase, which is not preferable.

(A-3) The roof type reflection member and the reflection member for reflecting the light beam reflected by the roof type reflection member are constituted by a combination of three plane reflecting mirrors.

With such a configuration, there is a characteristic that the apparatus can be reduced in weight especially because of the hollow structure.

(A-4) A reflecting member for reflecting the light beam reflected by the roof-type reflecting member is disposed between the first lens portion and the second lens portion, and is integrally held by a holding member. That is.

This is a configuration which can be realized only when these reflecting members are constituted by hollow reflecting mirrors, and can be said to be an example in which space is effectively used. With such a configuration, it is possible to increase the distance between the vertices of the lenses of the first and second lens units without increasing the size of the entire apparatus, and to maintain a sufficiently large observation magnification of the finder. At this time, the influence of the relative decentering of the eyepiece on the image performance of the viewfinder optical system tends to be relatively large, so that these optical members must be held together in order to prevent manufacturing problems. It is desirable to hold the member integrally.

(A-5) The roof-type reflecting member is configured to be orthogonal to an incident surface on which the light emitted from the first prism is incident, and to be a roof-type reflecting member for reflecting the incident light from the incident surface. A second prism having a surface and an exit surface from which light rays reflected by the roof-type reflection surface are totally reflected on the same surface as the incident surface and then exit.

When the roof-type reflecting member is formed as a prism in this way, the weight of the apparatus is slightly increased, but the optical path length of the roof-type reflecting member is shortened in inverse proportion to the refractive index, so that the observation magnification of the finder is automatically increased. Become. Therefore, in such a case, the finder magnification can be increased without difficulty even if the eyepiece is arranged behind the prism.

(A-6) The exit surface of the first prism and the entrance surface of the second prism are joined.

With such a structure, not only the assembling work is simplified, but also the number of prism surfaces which cause a loss of light quantity is reduced.

(A-7) The first lens portion and the second lens portion are arranged closer to the observation side than the reflecting member that reflects the light beam reflected by the roof-type reflecting member, and are integrated with the reflecting member by a holding member. That is, it was held in a proper manner.

Even in this case, if the first and second lens portions are configured to be integrally held, a preferred embodiment of the present invention is provided as in the case described above.

(A-8) The first lens portion and the second lens portion are disposed closer to the observation side than the reflecting member that reflects the light beam reflected by the roof type reflecting member, and are integrally held by a holding member. That is.

If at least one of the lens surfaces of the first lens portion and the second lens portion is aspheric, various aberrations of the observation optical system can be satisfactorily corrected. Can be realized.

In particular, in the present invention, among the lenses constituting the eyepiece, the positive lens surface on the reticle side of the first lens portion having a positive refractive power and the reticle of the second lens portion having a negative refractive power are provided. A better embodiment can be realized if the negative lens surface on the side is made aspherical and spherical aberration, coma and the like generated by the eyepiece are corrected well. At this time, the aspherical surface of the positive lens on the reticle side of the first lens unit is an aspherical surface whose positive refraction becomes stronger as the distance from the optical axis increases, and
The aspheric surface of the negative lens on the reticle side of the lens unit has an aspheric surface in which the negative refraction becomes stronger as the distance from the optical axis increases, and various aberrations can be particularly favorably set by appropriately setting the amount of aspheric surface of these two lens surfaces. It becomes possible to correct.

(A-9) The first lens portion and the second lens portion both include an aspheric lens made of acrylic resin.

If the material of each lens of the first lens portion and the second lens portion is an aspheric lens made of acrylic resin, it is more desirable to realize a relatively low-cost and simple structure.

Next, features other than the above-described configuration of the first embodiment of FIG. 1 will be described.

In the first embodiment, the roof member (refraction-type reflection member) 5 is used as a part of an optical member for forming an erect image to reduce the weight, and to prevent a decrease in the observation magnification of the finder at this time. the first lens 6, and the focal length f _l of the second lens 8, the value of f ₂ and the vertex distance d is configured so as to satisfy the condition described above (3).

In particular, in the present embodiment, the first reflecting mirror 7, which is a part of the reflecting optical member for forming an erect image, is disposed between the first lens 6 and the second lens 8 by tilting.
The space between the lens 6 and the second lens 8 is ensured to be sufficiently wide, and the space is effectively used to reduce the size of the entire apparatus. With such an arrangement of the optical members, the observation magnification of the finder is maintained sufficiently large. And
When the finder optical system having such a configuration is used, the first lens 6 and the plane reflecting mirror are used to reduce the influence of the optical eccentricity of the first lens 6 and the second lens 8 on the image performance of the finder optical system. The mechanism structure is such that the lens 7 and the second lens 8 are integrally held by one holding member 16.
By configuring such that the relative eccentricity of these optical members 6, 7, 8 is reduced, even if the combined system is decentered to some extent with respect to the reflective optical member or the like, the influence on the image performance of the finder optical system is reduced. Is to be reduced.

In addition, in the present embodiment, the first lens 6 and the second lens 8 are both made of acrylic resin, and the lens surface of the first lens 6 on the side of the reticle 3 and the reticle 3 of the second lens 8 are formed. Various aberrations are particularly well corrected by making the lens surface on the side aspherical. Detailed lens shapes and the like are disclosed in numerical examples described later.

The optical path of the finder optical system from the focus plate 3 to the lens 8 can be developed as shown in FIG. 3, and the aberration diagram at this time is shown in FIG. As a finder optical system, the distance from the reticle 3 to the prism 4 is 4.
6 mm, the distance (eye relief) from the exit surface of the second lens 8 of the eyepiece 102 to the pupil position 9 of the observer is 20.
mm, the maximum object height on the reticle 3 is 16 mm, which is about 13.5 ° in terms of an apparent viewing angle. In various numerical examples disclosed below, these specifications are common except for the apparent viewing angle.

(Other Examples) FIG. 5 is a sectional view of a finder optical system and a main part according to a second embodiment of the present invention. FIG. 6 is a developed view of a part of the optical path in FIG. 5 and 6
In the second embodiment shown in FIG. 1, the same components as those in the first embodiment shown in FIG.

In the second embodiment, the roof mirror 5 and the plane reflecting mirror 7 shown in FIG. 1 are integrally formed as a roof prism 41, and the object image formed on the focusing plate 3 by the prism 4 and the roof prism 41 is used as an erect image. I have. Further, in the present embodiment, the prism 4 and the roof prism 41 are joined, and the first refracting power having the positive refractive power constituting the eyepiece lens is formed.
The lens 6 and the second lens 8 having a negative refractive power include the roof prism 4
It is arranged behind one emission surface 41c.

In the finder optical system of the present embodiment, a glass material is used for the optical members 4 and 41 for erect image formation. Therefore, compared with the finder optical system of Embodiment 1, the optical members for erect image formation are used. There is a feature that the optical path length of the portion can be shortened. Therefore, in the present embodiment, the two lenses 6 and 8 are arranged behind the optical member for erect image formation, and the first lens 6 and the second lens
The desired observation magnification is realized by widening the distance between the lenses 8 to some extent. Also in the configuration of the present embodiment, a configuration is adopted in which the first lens 6 and the second lens 8 are integrally held by one holding member 42 so that the relative eccentricity of these optical members is reduced. In addition, the problem of manufacturing the image performance of the finder optical system is reduced.

In this embodiment, the first lens 6 and the second lens 8 are both made of acrylic resin, and the lens surface of the first lens 6 on the side of the focusing plate 3 and the focusing plate of the second lens 8 are also formed. Various aberrations are corrected particularly well by making the lens surface on the third side an aspheric surface. Detailed lens shapes and the like are disclosed in numerical examples described later.

The finder optical system extending from the focus plate 3 to the lens 8 can be developed as shown in FIG. 6, and the aberration diagram at this time is shown in FIG.

FIG. 8 is a developed view of the optical path of the finder optical system according to the third embodiment of the present invention. The third embodiment is different from the first embodiment only in that the first lens unit 6 is satisfactorily corrected for chromatic aberration as a cemented lens of two lenses, a positive lens and a negative lens, and other configurations are the same. is there.

FIG. 9 shows an aberration diagram of the finder optical system of the single-lens reflex camera of the third embodiment.

FIG. 10 is a sectional view of a finder optical system of a single-lens reflex camera according to Embodiment 4 of the present invention.

FIG. 11 is an optical path development view of a part of FIG. The fourth embodiment is different from the roof prism 4 of the second embodiment in FIG.
In place of the first embodiment, two lenses 6, 8 for the eyepiece 102 are provided behind the optical systems 4, 5, 7 for forming the erect image, after being constituted by a combination of the reflecting mirrors 5, 7 as in the first embodiment. Are different only in the arrangement thereof, and the other configurations are the same. The present embodiment realizes a small finder optical system with a simple configuration although the observation magnification is slightly smaller than that of the first embodiment.

FIG. 12 shows an aberration diagram of the finder optical system of the single-lens reflex camera of the fourth embodiment.

FIG. 13 is a developed view of an optical path of a finder optical system of a single-lens reflex camera according to a fifth embodiment of the present invention.
4 is an aberration diagram. In this embodiment, all the lenses of the eyepiece 102 are constituted by spherical lenses.

In this embodiment, various numerical modifications are conceivable as described above. However, as described above, the lens shape of the eyepiece including the two lenses satisfies the essential components. With such a configuration, it is possible to realize a finder optical system having a relatively large observation magnification and good visibility.

Hereinafter, numerical examples of the finder optical system according to the first to fifth embodiments of the present invention will be described.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th surface in order from the object side, Di is the thickness or air gap of the i-th optical member from the object side, and Ni and νi are the i-th optical members in order from the object side. And the Abbe number. In the aspherical shape, the radius of curvature at the center of the lens surface is R, the optical axis direction (the traveling direction of light) is the X axis, the direction perpendicular to the optical axis is the Y axis, and B, C, D,
When E is an aspheric coefficient,

[0078]

(Equation 5)

This is expressed by the following equation. “ ^DX ” means “× 10 ^−X ”.

In the numerical examples, r1 and r2 indicate glass blocks such as a first prism and a second prism. Numerical example 1 r 1 = ∞ d 1 = 43.08 n 1 = 1.51633 ν1 = 64.2 r 2 = ∞ d 2 = 50.64 * r 3 = 28.339 d 3 = 5.50 n 2 = 1.49171 ν2 = 57.4 r 4 = -125.000 d 4 = 23.00 * r 5 = -37.595 d 5 = 2.50 n 3 = 1.49171 ν3 = 57.4 r 6 = ∞ Aspherical surface third surface k BCD -8.40901D-01 1.78653D-06 1.89626D-09 -1.37935D-12 5 side k BCD -4.29917D-01 -9.72511D-06 -4.54385D-08 2.50935D-10 f _e = 66.15 f ₁ = 47.54 f ₂ = -76.46 d = 23.00 SF ₁ = -0.63 SF ₂ = -1.00 ( d / f _z ) ・ (d / f ₁ -1) = 0.16 d / f _e = 0.35 Numerical example 2 r 1 = ∞ d 1 = 112.00 n 1 = 1.51633 ν1 = 64.2 r 2 = ∞ d 2 = 0.60 * r 3 = 27.412 d 3 = 5.00 n 2 = 1.49171 ν2 = 57.4 r 4 = -61.384 d 4 = 10.50 * r 5 = -29.605 d 5 = 2.50 n 3 = 1.49171 ν3 = 57.4 r 6 = ∞ Aspheric coefficient No. 3 Surface k BCD -8.39769D-01 3.05915D-06 2.31439D-08 -4.42040D-11 Surface 5 k BCD -4.31131D-01 -7.87253D-06 -7.80423D-08 4.33427D-10 f _e = 69.94 f ₁ = 39.27 f ₂ = -60.21 d = 10.50 SF ₁ = -0.38 SF ₂ = -1.00 (d / f _z ) ・ (d / f ₁ -1) = 0.13 d / f _e = 0.15 Numerical Example 3 r 1 = ∞ d 1 = 43.08 n 1 = 1.51633 ν1 = 64.2 r 2 = ∞ d 2 = 50.64 r 3 = 36.130 d 3 = 5.50 n 2 = 1.77250 ν2 = 49.6 r 4 = -84.609 d 4 = 1.50 n 3 = 1.84666 ν3 = 23.8 r 5 = 7251.037 d 5 = 23.00 * r 6 = -40.892 d 6 = 2.50 n 4 = 1.49171 ν4 = 57.4 r 7 = ∞ Aspheric coefficient 6th surface k BCD 0.00000D + 00 -1.28755D-05 -5.43759D-09 6.76246D-11 f _e = 66.28 f ₁ = 48.89 f ₂ = -83.16 d = 23.00 SF ₁ = -1.01 SF ₂ = -1.00 (d / f _z ) ・ (d / f ₁ -1) = 0.15 d / f _e = 0.35 Numerical example 4 r 1 = ∞ d 1 = 39.00 n 1 = 1.51633 ν1 = 64.2 r 2 = ∞ d 2 = 64.00 * r 3 = 26.324 d 3 = 5.50 n 2 = 1.49171 ν2 = 57.4 r 4 = -48.432 d 4 = 10.50 * r 5 = -23.936 d 5 = 2.50 n 3 = 1.49171 ν3 = 57.4 r 6 = 144.100 non Spherical coefficient 3rd surface k BCD 5.83307D-01 -1.06152D-05 2.25786D-08 -1.40329D-10 5th surface k BCD 3.04422D-02 4.50683D-06 -1.00823D-07 9.69418D-10 f _e = 76.98 f ₁ = 35.55 f ₂ = -41.54 d = 10.50 SF ₁ = -0.30 SF ₂ = -0.72 (d / f _z ) ・ (d / f ₁ -1) = 0.18 d / f _e = 0.14 Numerical Example 5 r 1 = ∞ d 1 = 43.08 n 1 = 1.51633 ν1 = 64.2 r 2 = ∞ d 2 = 50.64 r 3 = 47.954 d 3 = 5.50 n 2 = 1.77250 ν2 = 49.6 r 4 = -64.936 d 4 = 1.50 n 3 = 1.84666 ν3 = 23.8 r 5 = -183.858 d 5 = 24.00 r 6 = -31.758 d 6 = 1.50 n 4 = 1.51633 ν4 = 64 .2 r 7 = -89.387 f _e = 69.87 f ₁ = 51.70 f ₂ = -96.25 d = 24.00 SF ₁ = -0.59 SF ₂ = -2.10 (d / f _z ) ・ (d / f ₁ -1) = 0.13 d / f _e = 0.34

[0081]

According to the present invention, by adopting the structure described above, the observation position of the finder can be set at an appropriate rear position depending on the size of the entire apparatus, while having a relatively simple structure. It is possible to achieve a finder optical system suitable for a single-lens reflex camera with good visibility, in which the observation magnification is maintained sufficiently high and the various aberrations are well corrected, and an imaging apparatus using the same.

[Brief description of the drawings]

FIG. 1 is a sectional view of a finder optical system and a main part according to a first embodiment.

FIG. 2 is an explanatory diagram of an imaging optical system of the present invention.

FIG. 3 is a development view of a finder optical system according to the first embodiment.

FIG. 4 is an aberration diagram of the finder optical system according to the first embodiment.

FIG. 5 is a sectional view of a finder optical system according to a second embodiment.

FIG. 6 is a development view of a finder optical system according to the second embodiment.

FIG. 7 is an aberration diagram of a finder optical system according to a second embodiment.

FIG. 8 is a development view of a finder optical system according to a third embodiment.

FIG. 9 is an aberration diagram of a finder optical system according to a third embodiment.

FIG. 10 is a sectional view of a finder optical system according to a fourth embodiment.

FIG. 11 is a development view of a finder optical system according to a fourth embodiment.

FIG. 12 is an aberration diagram of a finder optical system according to a fourth embodiment.

FIG. 13 is a development view of a finder optical system according to the fifth embodiment.

FIG. 14 is an aberration diagram of a finder optical system according to the fifth embodiment.

[Description of Signs] 1 is a photographing lens 2 is a rotating mirror 3 is a focusing plate 4 is a prism 5 is a roof mirror 6 is a first lens 7 is a plane reflecting mirror 8 is a second lens 9 is an observer's pupil position 10 is a photographing Expected focal plane of lens 11 Condenser lens 12 Re-imaging optical system 13 Image sensor 14, 15 Reflector mirror 16, 42 Eyepiece holding member 20 Camera body 41 Dach prism

Claims (12)

[Claims] 1. A finder optical system for observing an object image formed on a reticle, wherein the finder optical system comprises:
An incident surface facing the reticle, a reflecting surface for reflecting the incident light from the incident surface, and an emitting surface from which reflected light reflected on the reflecting surface is totally reflected on the same surface as the incident surface and exits. A first prism having the same, a roof-type reflecting member that reflects light emitted from the light-emitting surface of the first prism on reflecting surfaces orthogonal to each other to perform left-right reversal of the image and emits the light, and a reflection by the roof-type reflecting member. A reflecting member for reflecting the reflected light beam, and an eyepiece including a first lens portion having a positive refractive power and a second lens portion having a negative refractive power, wherein the focal point of the first lens portion is provided. The radii of curvature of the plate-side lens surface and the observation-side lens surface are each R
1a and R1b, when the radii of curvature of the lens surface on the focusing screen side and the lens surface on the observation side of the second lens unit are R2a and R2b, respectively: A finder optical system that satisfies certain conditions. 2. The focal lengths of the first lens unit and the second lens unit are f ₁ and f ₂ , respectively, from the observation-side lens surface of the first lens unit to the reticle-side lens surface of the second lens. _2. The finder optical system according to claim 1, wherein a condition of 0.10 <(d / f ₂ ) · (d / f ₁ −1) <0.30 is satisfied, where d is a distance. 3. The composite focal length of the first lens unit and the second lens unit is f _e , and the distance from the observation-side lens surface of the first lens unit to the reticle-side lens surface of the second lens is d. 2. The finder optical system according to claim 1, wherein the following condition is satisfied: 0.10 <d / _fe <0.40. 4. The apparatus according to claim 1, wherein the roof-type reflection member and the reflection member for reflecting the light beam reflected by the roof-type reflection member are constituted by a combination of three plane reflecting mirrors. , 2 or 3 viewfinder optical systems. 5. A reflecting member for reflecting a light beam reflected by the roof-type reflecting member is disposed between the first lens portion and the second lens portion, and is integrally held by a holding member. 5. The finder optical system according to claim 4, wherein: 6. The roof-type reflecting member is configured to be orthogonal to each other and an incident surface on which the light emitted from the first prism is incident, and a roof-type reflective surface for reflecting the incident light from the incident surface. 2. The device according to claim 1, further comprising: a second prism having an exit surface from which light rays reflected by the roof-type reflection surface are totally reflected on the same surface as the incident surface, and then exit.
2 or 3 viewfinder optical systems. 7. The finder optical system according to claim 6, wherein an exit surface of said first prism and an entrance surface of said second prism are joined. 8. The first lens portion and the second lens portion are disposed closer to the observation side than a reflection member that reflects light rays reflected by the roof-type reflection member, and are held integrally with the reflection member by a holding member. The finder optical system according to claim 1, 2 or 3, wherein 9. The finder optical system according to claim 1, wherein at least one of the lens surfaces of the first lens unit and the second lens unit is an aspheric surface. 10. The finder optical system according to claim 9, wherein said first lens portion and said second lens portion both include an aspheric lens made of acrylic resin. 11. An image pickup apparatus for observing a subject image formed on a reticle by a rotating mirror disposed on the image side of a photographic lens as an erect image through various optical members and an eyepiece. In the finder optical path from the light source to the observer's pupil, the incident surface facing the reticle, the reflecting surface that reflects the incident light from the incident surface downward and obliquely backward, and the reflected light reflected by the reflecting surface are incident on the finder optical path. A first prism having an exit surface that is totally reflected at the same plane as the corner and guides the light obliquely rearward and exits, and a reflection surface that is orthogonal to each other, and that reflects the exit light from the exit surface of the prism A roof-type reflecting member that reflects the light on the surface to invert the image from side to side and guides the reflected light downward or obliquely backward, a reflecting member that reflects the light reflected by the roof-type reflecting member backward, and a positive refractive power First lens having An eyepiece comprising a lens unit and a second lens unit having a negative refractive power;
The radii of curvature of the lens surface on the reticle side and the lens surface on the observation side of the lens unit are R1a and R1b, respectively, and the radii of curvature of the lens surface on the reticle side and the lens surface on the observation side of the second lens unit are R2a. , R2b, An imaging apparatus characterized by satisfying the following conditions. 12. An imaging apparatus using the finder optical system according to claim 1 to observe an object image formed on a reticle by a photographic lens.