JP2000019402A - Image-formation optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-performance image-formation optical system which is miniaturized and thinned by folding an optical path by the use of a reflection surface on which the number of reflecting times is small. SOLUTION: This optical system is provided with a 1st prism 10 on the object side and a 2nd prism 20 on the image side and does not form an intermediate image. The 1st surface 11 of the 1st prism 10 makes luminous flux from the object incident on the prism, the 2nd surface 12 thereof reflects the luminous flux made incident from the 1st surface inside the prism and also emits the luminous flux reflected by the 3rd surface thereof to the outside of the prism, and the 3rd surface 13 reflects the luminous flux reflected by the 2nd surface. Either of the 2nd surface 12 and the 3rd surface 13 has a rotationally asymmetric surface shape to give power to the luminous flux. Furthermore, the 2nd prism 20 is provided with at least one reflection surface 22 reflecting the luminous flux inside the prism and the reflection surface 22 has a rotationally asymmetric surface shape to give the power to the luminous flux and correct the aberration caused by an eccentricity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming optical system, and more particularly, to a reflecting surface for an optical device using a small image pickup device such as a video camera, a digital still camera, a film scanner, and an endoscope. The present invention relates to a decentered optical system having power.

[0002]

2. Description of the Related Art In recent years, in image forming optical systems for video cameras, digital still cameras, film scanners, endoscopes, etc., the optical systems themselves have become smaller and lighter with the downsizing of image pickup devices.
Cost reduction is required.

However, in a general rotationally symmetric coaxial optical system,
Since the thickness of the optical system is such that the optical elements are arranged in the direction of the optical axis, there is a limit in miniaturization. At the same time, in order to correct chromatic aberration caused by using a rotationally symmetric refractive lens, an increase in the number of lenses is inevitable, and cost reduction is difficult. Therefore, recently, there has been proposed an optical system in which the size of the optical system is reduced by giving power to a reflecting surface in which chromatic aberration does not occur and folding the optical path in the optical axis direction.

Japanese Unexamined Patent Publication No. Hei 7-333505 proposes that the optical path be folded by applying power to the eccentric reflecting surface to reduce the thickness of the optical system.
The number of constituent optical members is as many as five, and the actual optical performance is unknown. Also, no mention is made of the shape of the reflection surface.

In Japanese Patent Application Laid-Open Nos. 8-292371, 9-5650 and 9-90229,
An optical system is shown in which one or a plurality of mirrors are formed as a single member to form a block, thereby folding an optical path and relaying an image inside the optical system to form a final image. However, in these examples, the number of reflections is increased to relay the image, and the surface accuracy error and the eccentricity accuracy error are integrated and transferred. . At the same time, the volume of the entire optical system for relaying an image is undesirably increased.

Japanese Patent Application Laid-Open No. 9-222563 discloses an example in which a plurality of prisms are used. However, this is not preferable because relaying an image leads to an increase in cost and an increase in the size of an optical system. Also, Japanese Patent Application Laid-Open No. 9-21133
No. 1 discloses an example in which the optical path is folded by using one prism to reduce the size of the optical system, but the aberration is not sufficiently corrected.

[0007] Further, in JP-A-8-292368, JP-A-8-292372, JP-A-9-222561, JP-A-9-258105, and JP-A-9-258106, all are examples of zoom lenses. is there. However, also in these examples, since the image is relayed inside the prism, the number of reflections is large, and the surface accuracy error and the eccentricity error of the reflecting surface are accumulated and transferred, which is not preferable. At the same time, an increase in the size of the optical system is inevitable, which is not preferable.

Japanese Unexamined Patent Application Publication No. 10-20196 discloses a prism having a negative power on the object side with a diaphragm interposed between a positive front group of a positive / negative two-group zoom lens and a positive power prism on the image side. This is an example of the configuration. Also, the positive front group composed of the negative prism and the positive prism is divided into two,
There is also disclosed an example in which a negative, positive, and negative three-group zoom lens is configured. However, in the prism used in these examples, the two transmission surfaces and the two reflection surfaces are independent surfaces, so that it is necessary to secure the space, and at the same time, the imaging surface is large, which is a Leica size film format. In addition, the size of the prism itself is inevitable. In addition, since the image side is not telecentric, it is difficult to cope with an image pickup device such as a CCD. In addition, in any of the examples of the zoom lens, since the magnification is changed by moving the prism, the eccentricity of the reflection surface becomes stricter to maintain the performance in all the magnification regions, and the cost increases. Have a problem.

[0009]

When a desired refractive power is to be obtained by a general refractive optical system, chromatic aberration occurs at the boundary surface due to the chromatic dispersion characteristics of the optical element. In order to correct this and to correct other ray aberrations, the refractive optical system has a problem that many components are required and the cost is high. At the same time, since the optical path is straight along the optical axis, the entire optical system becomes longer in the optical axis direction, resulting in a problem that the imaging device becomes larger.

Further, in the decentered optical system as described in the prior art, an image is formed if the aberration of the formed image is properly corrected, and especially if the rotationally asymmetric distortion is not properly corrected. There is a problem that a figure or the like is distorted and cannot be reproduced in a correct shape.

Further, when a reflecting surface is used in the decentering optical system, the sensitivity of the decentering error is doubled as compared with that of the refracting surface. As the number of reflections is increased, the decentering error is integrated and transferred as the number of reflections increases. There is also a problem that the manufacturing accuracy such as the surface accuracy and the eccentricity of the reflection surface and the assembly accuracy are severe.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a high-performance, low-cost imaging optical system with a small number of optical elements. .

It is another object of the present invention to provide a high-performance imaging optical system which is reduced in size and thickness by folding an optical path using a reflection surface having a small number of reflections.

[0014]

According to the present invention, there is provided an imaging optical system for forming an object image having a positive refractive power as a whole, wherein the imaging optical system has a refractive index. (N) having a first prism and a second prism formed of a medium larger than 1.3 (n> 1.3), wherein the second prism is disposed closer to the image side than the first prism;
The first prism is formed by an imaging system that does not form an intermediate image, and the first prism has three optically active surfaces that transmit or reflect a light beam. And the second surface reflects the light beam incident from the first surface in the prism and emits the light beam reflected on the third surface out of the prism, and the third surface is reflected on the second surface. A rotation configured to reflect a light beam, wherein at least one of the second surface and the third surface has a curved surface shape that gives power to the light beam, and the curved surface shape corrects aberration generated by eccentricity. The second prism has an asymmetric surface shape, and the second prism has a reflecting surface for reflecting a light beam in at least one prism, and the reflecting surface gives power to the light beam, and corrects aberration caused by eccentricity. To have a rotationally asymmetric surface shape That it is configured in which the features.

Hereinafter, the reason and operation of the above-described configuration in the present invention will be described in order. In order to achieve the above object, the first imaging optical system of the present invention has a refractive index (n) of 1.3.
A first prism and a second prism formed of a medium larger than (n> 1.3), wherein the second prism is disposed closer to the image side than the first prism and does not form an intermediate image. An imaging optical system characterized by being formed by a system.

A refractive optical element such as a lens can have power only by giving a curvature to its boundary surface. Therefore, when a light beam is refracted at the boundary surface of the lens, chromatic aberration due to the chromatic dispersion characteristics of the refractive optical element is inevitably generated. As a result, another refractive optical element is generally added for the purpose of correcting chromatic aberration.

On the other hand, a reflecting optical element such as a mirror or a prism does not generate chromatic aberration in principle even if its reflecting surface has power, and another optical element is used only for the purpose of correcting chromatic aberration. No need to add. Therefore, in the optical system using the reflective optical element, the number of constituent optical elements can be reduced from the viewpoint of chromatic aberration correction, as compared with the optical system using the refractive optical element.

At the same time, since the reflection optical system using the reflection optical element folds the optical path, the size of the optical system itself can be reduced as compared with the refractive optical system.

Further, since the reflection surface has a higher sensitivity to eccentricity error than the refraction surface, high accuracy is required for assembly adjustment.
However, among the reflective optical elements, since the relative positional relationship between the surfaces of the prisms is fixed, the eccentricity may be controlled as a single prism, and unnecessary assembly accuracy and adjustment man-hours are unnecessary.

Further, the prism has an entrance surface, an exit surface, which are refraction surfaces, and a reflection surface, and has a greater degree of freedom for aberration correction than a mirror having only a reflection surface. In particular, by allowing the reflection surface to share most of the desired power and reducing the power of the entrance surface and the exit surface, which are refraction surfaces, the degree of freedom in correcting aberrations is larger than that of a mirror, while maintaining the degree of freedom for aberrations. Compared with such a refractive optical element, the occurrence of chromatic aberration can be extremely reduced. Further, since the inside of the prism is filled with a transparent body having a higher refractive index than air, the optical path length can be made longer than that of air. Thinning and miniaturization are possible.

Further, the imaging optical system is required to have good imaging performance not only at the center but also at the periphery. In the case of a general coaxial optical system, the sign of the ray height of the off-axis light beam is reversed before and after the stop, and thus the off-axis aberration is worsened due to the loss of symmetry of the optical element with respect to the stop. Therefore, by arranging the refracting surface with the diaphragm interposed therebetween, it is general to sufficiently satisfy the symmetry with respect to the diaphragm and correct the off-axis aberration.

Accordingly, in the present invention, not only the center but also off-axis aberrations can be satisfactorily corrected by arranging two prisms and taking a configuration in which symmetry with respect to the stop is sufficiently considered. If only one prism is arranged, asymmetry with respect to the stop increases, and deterioration of off-axis aberration is inevitable.

For the above reason, the present invention has a first prism and a second prism, and the second prism is disposed closer to the image side than the first prism, and is used in an imaging system which does not form an intermediate image. It is preferable that the image forming optical system be substantially telecentric on the image side.

Next, a configuration that is substantially telecentric on the image side will be described in detail. As described above, since the reflection surface has a higher eccentricity error sensitivity than the refraction surface, a configuration of an optical system which is hardly affected by the influence is desired. In the case of a general coaxial optical system, since the off-axis chief ray is substantially parallel to the optical axis in the almost telecentric configuration on the image side, the position of the off-axis ray on the image plane is maintained even when defocused. It has the property of Therefore, the position accuracy of the off-axis light beam is improved by reflecting the property in the imaging optical system of the present invention, and in particular, in order to prevent performance deterioration due to focusing of the optical system using the reflection surface having relatively high eccentric sensitivity. It is desirable to adopt a configuration that is substantially telecentric on the image side that is kept.

By adopting such a configuration, in particular, C
It is also optimal for an imaging optical system using an imaging device such as a CD.
Further, by adopting this configuration, the influence of the COS fourth power rule is reduced, and the shading can be reduced.

As described above, by adopting the basic structure of the present invention, it is possible to obtain a small-sized image-forming optical system which has a smaller number of optical elements than the refractive optical system and has good performance from the center to the periphery. Is possible.

By the way, the first prism of the present invention has three optical working surfaces for transmitting or reflecting a light beam, the first surface of which receives a light beam from an object into the prism, and
The surface reflects the light beam incident from the first surface in the prism, emits the light beam reflected on the third surface out of the prism, and the third surface reflects the light beam reflected on the second surface. At least one of the second surface and the third surface has a curved surface shape that gives power to a light beam, and the curved surface shape has a rotationally asymmetric surface shape that corrects aberrations caused by eccentricity. Things.

Here, assuming that a ray passing through the center of the object point and passing through the center of the stop and reaching the center of the image plane is an axial principal ray,
If at least one reflecting surface is not decentered with respect to the axial chief ray, the incident ray and the reflected ray of the axial chief ray take the same optical path, and the axial chief ray is blocked in the optical system. . As a result, an image is formed only by the light flux whose central portion is shielded, and the center becomes dark or the image is not formed at the center at all.

It is also possible to decenter the powered reflecting surface with respect to the axial principal ray. When the reflecting surface with power is decentered with respect to the axial chief ray,
It is desirable that at least one of the surfaces constituting the prism used in the present invention is a rotationally asymmetric surface.
Among them, it is particularly preferable to make at least one reflection surface a rotationally asymmetric surface for aberration correction.

The reason will be described in detail below. First, a coordinate system to be used and a rotationally asymmetric surface will be described. An optical axis defined by a straight line until the on-axis principal ray intersects the first surface of the optical system is defined as a Z axis, and is orthogonal to the Z axis and within an eccentric plane of each surface constituting the imaging optical system. Is defined as the Y axis,
An axis orthogonal to the optical axis and orthogonal to the Y axis is defined as an X axis. The ray tracing direction will be described in terms of forward ray tracing from the object to the image plane.

In general, in a spherical lens system composed only of spherical lenses, spherical aberration caused by a spherical surface and aberrations such as coma and field curvature are mutually corrected on several planes, so that the aberration is reduced as a whole. Configuration.

On the other hand, in order to satisfactorily correct aberrations with a small number of surfaces, a rotationally symmetric aspherical surface or the like is used. This is to reduce various aberrations generated on the spherical surface. However, in a decentered optical system, it is impossible to correct rotationally asymmetric aberration generated by decentering by a rotationally symmetric optical system. The rotationally asymmetric aberrations caused by this eccentricity include distortion, field curvature, astigmatism and coma which also occur on the axis.

First, the rotationally asymmetric field curvature will be described. For example, light rays incident on a concave mirror decentered from an object point at infinity are reflected and imaged on the concave mirror, but after the light rays hit the concave mirror, the rear focal length to the image plane is
When the image field side is air, the radius of curvature becomes half of the radius of curvature of the portion hit by the light beam. Then, as shown in FIG. 17, an image plane inclined with respect to the axial principal ray is formed. As described above, it is impossible to correct rotationally asymmetric curvature of field with a rotationally symmetric optical system.

In order to correct the tilted curvature of field by the concave mirror M itself, which is the source, the concave mirror M is constituted by a rotationally asymmetric surface. In this example, the curvature is strong in the positive Y-axis direction ( If the refractive power is increased) and the curvature is decreased (the refractive power is decreased) in the negative direction of the Y axis, the correction can be made. In addition, by arranging a rotationally asymmetric surface having the same effect as the above configuration in the optical system separately from the concave mirror M, a flat image surface can be obtained with a small number of components. In addition, the rotationally asymmetric surface is preferably a rotationally asymmetric surface shape having no rotationally symmetric axis both inside and outside the surface, which is preferable in terms of increasing the degree of freedom and correcting aberrations.

Next, rotationally asymmetric astigmatism will be described. As described above, the eccentrically arranged concave mirror M
In this case, astigmatism as shown in FIG. 18 also occurs for axial rays. Astigmatism can be corrected by appropriately changing the curvature in the X-axis direction and the curvature in the Y-axis direction of the rotationally asymmetric surface, as described above.

Further, rotationally asymmetric coma will be described. Similarly to the above description, in the concave mirror M arranged eccentrically, coma as shown in FIG. To correct the coma aberration, the inclination of the surface can be changed as the distance from the origin of the X axis of the rotationally asymmetric surface increases, and the inclination of the surface can be appropriately changed depending on the sign of the Y axis.

In the image forming optical system according to the present invention, it is also possible that at least one surface having the above-mentioned reflecting action is decentered with respect to the axial principal ray, and has a rotationally asymmetric surface having power. With such a configuration, it becomes possible to correct the eccentric aberration caused by giving power to the reflecting surface by the surface itself, and by relaxing the power of the refracting surface of the prism, the occurrence of chromatic aberration itself can be reduced. Can be smaller.

The rotationally asymmetric surface used in the present invention is preferably a plane-symmetric free-form surface having only one plane of symmetry. Here, the free-form surface used in the present invention is:
It is defined by the following equation (a). Note that the Z axis of the definition formula is the axis of the free-form surface.

[0039] Here, the first term of the equation (a) is a spherical term, and the second term is a free-form surface term.

In the spherical term, c: curvature of the vertex k: conic constant (conical constant) r = √ (X ² + Y ² ).

The free-form surface term is Here, C _j (j is an integer of 2 or more) is a coefficient.

The free-form surface generally includes an XZ plane,
Although neither YZ plane has a plane of symmetry, in the present invention, X
By setting all the odd-order terms to 0, a free-form surface having only one symmetry plane parallel to the YZ plane is obtained. For example, in the above definition formula (a), C ₂ , C ₅ , C ₇ ,
_{C 9, C 12, C 14} , C 16, C 18, C 20, C 23, C 25, C
₂₇ , C ₂₉ , C ₃₁ , C ₃₃ , C ₃₅ ...

By setting all odd-numbered terms of Y to 0, a free-form surface having only one symmetry plane parallel to the XZ plane is obtained. For example, in the above definition formula, C ₃ ,
_{C 5, C 8, C 10} , C 12, C 14, C 17, C 19, C 21, C
₂₃ , C ₂₅ , C ₂₇ , C ₃₀ , C ₃₂ , C ₃₄ , C ₃₆ ...

One of the directions of the symmetry plane is a symmetry plane, and the eccentricity in the corresponding direction, for example, the eccentricity direction of the optical system with respect to the symmetry plane parallel to the YZ plane is in the Y-axis direction. By making the eccentric direction of the optical system the X-axis direction with respect to the symmetric plane parallel to the XZ plane, it is possible to effectively correct rotationally asymmetric aberrations caused by the eccentricity while improving the productivity. Becomes possible.

Further, the above-mentioned definition expression (a) is shown as one example as described above, and the present invention uses a rotationally asymmetric surface having only one symmetric surface to produce a rotation caused by eccentricity. It is characterized by correcting asymmetric aberrations and at the same time improving productivity, and it goes without saying that the same effect can be obtained for any other definitional expressions.

If the first prism is of the type that shares the first reflecting surface and the second transmitting surface as described above, the incident light beam is largely bent at the first reflecting surface, and the second reflecting surface has a small bending angle. Thus, since the light is reflected to the second transmission surface, the thickness in the vertical direction with respect to the incident optical axis of the entire optical system can be reduced.

Further, by making the first prism a prism having a negative refractive power, it is possible to obtain a wide imaging angle of view. This is because it is possible to converge a light beam having a wide angle of view by negative power and converge the light beam when the light beam enters the second group constituted by the second prism. This is a preferable configuration from the viewpoint of aberration correction when an optical system having a short distance is configured.

When the prism having such a configuration is used for the first prism, more preferably, the second prism is arranged at a position facing the second reflection surface with respect to the optical axis incident on the first prism. It is possible to reduce the vertical height of the entire optical system.

Further, both the second surface and the third surface of the first prism can be configured so as to apply power to the light beam and have a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity.

Further, at least one of the second surface and the third surface of the first prism may be formed as a rotationally asymmetric surface shape having a plane symmetric free-form surface having only one symmetric surface.

Further, the rotationally asymmetric surface shape of both the second surface and the third surface of the first prism can be constituted by a plane-symmetric free-form surface shape having only one plane of symmetry.

In this case, only the symmetrical free-form surface of the second surface of the first prism and the only symmetrical free-form surface of the third surface are formed in the same plane. In addition, the first prism can be configured.

Further, the first surface of the first prism may be configured so as to have a rotationally asymmetric surface shape that applies power to the light beam and corrects aberration generated by eccentricity. It is effective to take such a surface shape on the refraction surface in order to correct aberrations caused by eccentricity.

In this case, the rotationally asymmetric surface shape of the first surface of the first prism can be constituted by a plane-symmetric free-form surface shape having only one plane of symmetry.

Further, the rotationally asymmetric surface shape arranged in the second prism can be constituted by a plane-symmetric free-form surface shape having only one symmetrical surface.

In this case, it is preferable that the first prism and the second prism are configured so that at least one surface and only one symmetric surface are arranged on the same plane. Arranging the pupil between the two prisms and arranging the second prism between the pupil and the image plane is effective in improving the symmetry and favorably correcting the off-axis aberration. In that case, it is desirable to dispose an aperture on the pupil.

In the present invention, the second prism is
It can be configured to have two or more curved reflecting surfaces that give power to the light flux.

In the present invention, as the second prism,
It is possible to use an optical system having three optically active surfaces, ie, an incident surface that also serves as a reflecting surface and a transmitting surface, a reflecting surface, and an emitting surface.

This prism type, which shares the second reflecting surface and the first transmitting surface, largely bends the light beam at the second reflecting surface, and the first reflecting surface reflects the light beam to the second reflecting surface with a small bending angle. Therefore, the thickness of the prism optical system in the incident light beam direction can be reduced.

More preferably, by setting the first reflecting surface of the second prism to a positive power, a good result in aberration correction can be obtained. This is because by applying power to the first reflecting surface having a small bending angle of the light beam, it is possible to apply power to a surface with less occurrence of decentering aberration. More preferably, by setting the second reflecting surface to negative power,
The principal point position of the second prism can be set to the object side, and the back focus of the second prism can be shortened.

In the present invention, as the second prism, a prism composed of three optically active surfaces, that is, a reflecting surface that gives power to a light beam, an incident surface, and an exit surface can be used.

In this case, since the number of reflections is one, only one reflection surface requiring particularly high accuracy is required, which is superior in manufacturing.

More preferably, it is preferable that the reflecting surface has a positive power. When the reflecting surface has a positive power, the generation of aberrations is smaller than when power is added to the transmitting surface.

Further, in the present invention, the second prism may be composed of two reflecting surfaces for giving power to a light beam, an entrance surface, and an exit surface.

This shape of the second prism increases the degree of freedom in correcting aberrations, and causes less occurrence of aberrations. Further, since the relative eccentricity of the two reflecting surfaces is small, the aberrations occurring on the two reflecting surfaces are corrected by the two reflecting surfaces, so that the occurrence of the aberration is small. More preferably, when the two reflecting surfaces have powers of different signs, it is possible to increase the mutual correction effect of aberrations, and to obtain high resolution.

More preferably, the smaller the relative eccentricity at the point where the optical axis of the first reflecting surface and the second reflecting surface reflects, the less the occurrence of eccentric aberration and the more the occurrence of rotationally asymmetric aberration Is reduced.

Further, in the present invention, the second prism is composed of three optical working surfaces: an entrance surface, an exit surface which also serves as a reflection surface and a transmission surface, and a reflection surface which gives power to a light beam. Can be used.

This has the same shape as the first prism,
This prism type, which shares the first reflecting surface and the second transmitting surface, largely bends the light beam at the first reflecting surface, and the second reflecting surface reflects the light beam to the second transmitting surface with a small bending angle. In addition, the thickness of the entire optical system in the vertical direction with respect to the incident optical axis can be reduced.

Since the second reflecting surface having a small bending angle has a positive power, the principal point of the second prism can be arranged on the image side, and a large back focus can be obtained. , A filter and the like are preferably arranged immediately before the image forming plane.

In the present invention, the second prism has three reflecting surfaces, one of which is formed by an incident surface also serving as a transmitting surface, and the other reflecting surface is formed by a transmitting surface. What is formed by an exit surface which also serves as a surface can be used.

This prism is composed of three surfaces, and
Since there are three reflecting surfaces, it is possible to disperse the power to three reflecting surfaces, and it is possible to reduce the occurrence of aberration. Further, since the optical paths intersect within the prism, the optical path length can be made longer than that of a prism having a structure in which the optical path is simply folded.

When this prism is a second prism, a positive power is given to the second reflecting surface having a small bending angle, so that the second reflecting surface having a relatively long optical path length from the second transmitting surface of the second prism. In this case, it is possible to arrange a surface having main power, and to reduce the back focus.

In the prism of the present invention, on the optically active surface having both a transmitting action and a reflecting action, it is desirable that the reflecting action is based on total reflection. If the condition for total reflection is not satisfied, both the reflecting action and the transmitting action cannot be achieved, and it is difficult to reduce the size of the prism itself.

The reflecting surface other than the total reflecting surface is preferably constituted by a reflecting surface having a thin metal film such as aluminum or silver formed on the surface or a reflecting surface having a dielectric multilayer film formed thereon. When the metal thin film has a reflecting action, it is possible to easily obtain a high reflectance. In the case of a dielectric reflection film, it is advantageous when a reflection film having low wavelength selectivity and low absorption is formed. As a result, it is possible to obtain a low-cost, compact imaging optical system in which the manufacturing accuracy of the prism is reduced.

In the present invention, it is desirable that a first prism having a diverging function be provided on the object side with respect to the stop, a second prism having a converging function be provided on the image side, and be substantially telecentric on the image side.

In an image forming optical system using a refractive optical element, the power arrangement differs depending on the application. For example, in a telephoto system having a narrow angle of view, a configuration is generally adopted in which the entire system is a positive or negative telephoto type, and the overall length of the optical system is made smaller than the focal length. In a wide-angle system having a wide angle of view, a configuration is generally adopted in which the back focus is made larger than the focal length by making the entire system a negative and positive retrofocus type.

In particular, in the case of an image forming optical system using an image pickup device such as a CCD, an optical low-pass filter for removing moiré and eliminating the influence of infrared light is provided between the image forming optical system and the image pickup device. It is necessary to arrange a cut filter.
Therefore, in order to secure a space for disposing these optical members, it is desirable to adopt a retrofocus type as the configuration of the imaging optical system.

In a retrofocus type imaging optical system, it is particularly important to correct off-axis aberrations, which greatly depends on the aperture position. As described above, in the case of a general coaxial optical system, off-axis aberrations are worsened because the symmetry of the optical element with respect to the stop is lost. Therefore, by arranging optical elements of the same sign with the stop interposed therebetween, it is common to sufficiently satisfy the symmetry with respect to the stop and correct the off-axis aberration. In the case of the negative and positive retrofocus types, since the power arrangement is originally asymmetric, the performance of off-axis aberration greatly changes depending on the stop position.

Therefore, by disposing a stop between the first prism having a diverging function on the object side and the second prism having a converging function on the image side, deterioration of off-axis aberration due to asymmetry of the power arrangement is minimized. It is possible to suppress it. If the stop is arranged on the object side of the diverging prism or on the image side of the image-side convergence prism, asymmetry with respect to the stop is further increased, and it becomes difficult to correct the stop.

In this case, the first prism having a diverging function on the object side with respect to the stop and the second prism having a converging function on the image side may be provided, and only the prism may be provided.

In the imaging optical system of the present invention,
An imaging optical system having one imaging plane throughout the entire system. As described above, the sensitivity of the decentering error of the reflecting surface is larger than that of the refracting surface, and the reflecting optical member composed of one block like a prism is transferred by integrating the surface accuracy error and the decentering error of each surface. The smaller the number of reflecting surfaces, the less the manufacturing accuracy. Therefore, it is not desirable to increase the number of reflections more than necessary.For example, in an imaging optical system that forms an intermediate image and relays the image, the number of reflections increases more than necessary,
Manufacturing errors on each surface become severe, leading to increased costs.

In the image forming optical system according to the present invention, it is needless to say that focusing of the image forming optical system can be performed by moving the whole prism or moving only one prism. Focusing can be performed by moving the imaging plane in the direction of the principal ray. Accordingly, even if the direction of incidence of the axial chief ray from the object and the direction of the axial chief ray that emerges from the most image-side surface do not match due to the decentering of the imaging optical system, the axial chief ray due to focusing can be used. It is possible to prevent the shift of the incident side of the principal ray. Further, it is also possible to divide the parallel plane plate into a plurality of wedge-shaped prisms and perform focusing by moving the prism in a direction perpendicular to the Z axis. Also in this case, focusing is possible regardless of the eccentricity of the imaging optical system.

In the imaging optical system of the present invention, if at least one of the prisms is made of an organic material such as plastic, the cost can be reduced. Also,
It is desirable to use a low moisture absorption material such as amorphous polyolefin since the change in imaging performance is small even with a change in humidity.

In the present invention, temperature compensation can be performed by using a diverging prism and a converging prism. In particular, in order to prevent a focus shift due to a temperature change, which is a problem when plastic is used as the material of the prism, it is possible to make the prism have a power having a different sign.

Further, in the present invention, it is desirable that the plurality of prisms are provided with respective relative positioning portions on a surface having no optical action. In particular, when a plurality of prisms having power on the reflecting surface as in the present invention are arranged, the relative positional accuracy shift causes performance degradation. Therefore, in the present invention, by providing the relative positioning portion on the surface of the prism having no optical action, it is possible to secure positional accuracy and secure desired performance. In particular, if a plurality of prisms are integrated by a connecting member using the positioning portion, assembly adjustment becomes unnecessary, and the cost can be further reduced.

The optical path may be folded in a direction different from the eccentric direction of the imaging optical system of the present invention by using a reflecting optical member such as a mirror on the object side of the incident surface of the imaging optical system of the present invention. It is possible. Thereby, the degree of freedom of the layout of the imaging optical system is further increased, and the size of the entire imaging optical device can be reduced.

In the present invention, the image forming optical system can be composed of only a prism. As a result, the number of parts is reduced, and the cost is reduced. Further, it is of course possible to integrate a plurality of prisms before and after the stop to form one prism. Thereby, further cost reduction is possible.

In the present invention, in addition to the first prism and the second prism, the object side, between the two prisms,
Alternatively, another lens (positive lens, negative lens) may be included as a component at any or a plurality of positions on the image side of the two prisms.

Further, the image forming optical system of the present invention can be a bright single focus lens. Also, a zoom lens (magnification image forming optical system) can be formed by combining one or a plurality of refractive optical systems on the distance between two prisms, the object side of the two prisms, or the image side.

In the present invention, it is also possible to form the refracting surface and the reflecting surface of the imaging optical system with a spherical surface or a rotationally symmetric aspherical surface.

When the above-described image forming optical system of the present invention is arranged in the image pickup section of the image pickup apparatus, or when the image pickup apparatus has a camera mechanism, the prism member arranged in the front group is optically connected. A cover that is arranged closest to the object side among the optical elements having an effect, the entrance surface of the prism member is eccentrically arranged with respect to the optical axis, and is arranged perpendicular to the optical axis on the object side with respect to the prism member. The prism member disposed in the front group may be configured to include an incident surface eccentrically arranged with respect to the optical axis on the object side, and the incident surface and the air gap may be arranged. , A cover lens having power arranged coaxially with the optical axis with respect to the optical axis can be arranged closer to the object side than the entrance surface.

As described above, when the prism member is disposed closest to the object and the eccentric incident surface is provided on the front surface of the photographing apparatus,
Since the incident surface obliquely seen from the subject can be seen, an uncomfortable feeling may be given as if the photographing was performed around a position shifted from the subject. Therefore, by arranging a cover member or a cover lens perpendicular to the optical axis, it is possible to perform imaging without feeling uncomfortable with the object to be imaged, similarly to a general imaging device.

Any of the imaging optical systems of the present invention as described above is arranged as a finder objective optical system, and further, an image erecting optical system for erecting an object image formed by the finder objective optical system. A finder optical system can be configured from the eyepiece optical system.

Further, a camera device can be constructed by including the finder optical system and a photographing objective optical system provided therewith.

Further, an imaging optical system comprising any one of the above-described imaging optical systems of the present invention and an imaging device arranged on an image plane formed by the imaging optical system is provided. Can be.

Further, any one of the above-described imaging optical systems of the present invention is arranged as a photographing objective optical system, and an optical path different from the photographing optical system or an optical path of the photographing objective optical system. The camera device can be provided with a finder optical system disposed in any of the optical paths divided from the camera.

Further, any one of the above-described image forming optical systems of the present invention, an image pickup device arranged on an image plane formed by the image forming optical system, and image information received by the image pickup device. An electronic camera device can be configured to include a recording medium that records the image data, and an image display element that forms an observation image by receiving image information from the recording medium or the image sensor.

An observation system having any one of the above-described imaging optical systems according to the present invention and an image transmission member that transmits an image formed by the imaging optical system along a long axis direction.
An endoscope apparatus can be configured to include an illumination light source and an illumination system having an illumination light transmission member that transmits illumination light from the illumination light source along the long axis direction.

[0099]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 5 of the imaging optical system of the present invention will be described below. The configuration parameters of each embodiment will be described later. In each embodiment, as shown in FIG. 1, the axial principal ray 1 is defined as a ray that exits the center of the object, passes through the center of the stop 2, and reaches the center of the image plane 3. Then, the axial principal ray 1 and the incident surface (first surface) 11 of the first prism 10, the exit surface (fourth surface) 14, and the incident surface of the second prism 20 (first surface)
Surface) 21 and the intersection with the exit surface (fourth surface) 24, and the incident surface is perpendicular to the axial principal ray 1 incident on that surface.
With respect to the emission surface, virtual surfaces are respectively taken perpendicular to the axial principal ray 1 emitted from the surface. The intersection of each virtual plane is defined as the origin of an eccentric optical surface between the optical surface passing through the intersection and the next virtual surface (the image plane for the last virtual surface), and the axial principal ray 1 (the intersection of the incident surface is defined). In the case of a given virtual surface, the direction along the incident axial principal ray 1) is defined as the Z-axis direction along the emitting axial principal ray 1). Ray 1 and first prism 10
For the first virtual surface passing through the intersection with the incident surface (first surface) 11, the direction along the traveling direction of the axial principal ray 1 is defined as the positive direction of the Z-axis, and for the other virtual surfaces, the first virtual surface is defined as the first virtual surface. When the number of reflections in the optical path from the surface to the virtual surface is an even number, the direction along the traveling direction of the axial principal ray 1 is defined as the positive direction of the Z-axis. The direction opposite to the traveling direction of the principal ray 1 is defined as the positive direction of the Z axis, the plane including the Z axis and the center of the image plane is defined as the YZ plane, and passes through the origin and is orthogonal to the YZ plane. Is defined as a positive X-axis direction, and an axis constituting a right-handed orthogonal coordinate system with the X-axis and Z-axis is defined as a Y-axis. FIG. 1 illustrates a coordinate system related to the first virtual surface, which is defined at the intersection of each virtual surface and the entrance surface 11 of the first prism 10. FIG. 2 does not show these virtual planes and coordinate systems in the following.

In Examples 1 to 5, each surface is decentered in the YZ plane, and the only symmetrical plane of each rotationally asymmetric free-form surface is the YZ plane.

For the eccentric surface, the amount of eccentricity (X, Y, and Z in the X-axis, Y-axis, and Z-axis directions) at the top of the surface from the origin of the corresponding coordinate system, and the X-axis, Y-axis, Z
Angle of inclination about each axis (α, β, γ, respectively)
(°)). In this case, α and β
Is counterclockwise with respect to the positive direction of each axis, γ
Positive means clockwise with respect to the positive direction of the Z axis.

In the case where a specific surface (including a virtual surface) and a surface following the specific surface (including a virtual surface) form a coaxial optical system in the optical system of each embodiment, the surface spacing is given. In addition, the refractive index of the medium and the Abbe number are given according to a conventional method.

Further, the shape of the surface of the free-form surface used in the present invention is defined by the above equation (a), and the Z axis of the definition equation is the axis of the free-form surface.

The aspherical surface is a rotationally symmetric aspherical surface given by the following equation. ^{Z = (y 2 / R)} / [1+ {1- (1 + K) y 2 / R 2} 1/2] + Ay 4 + By 6 + Cy 8 + Dy 10 + ...... ··· (b) However, the light of Z An optical axis (on-axis principal ray) with the traveling direction being positive, and y is taken in a direction perpendicular to the optical axis. Here, R is a paraxial radius of curvature, K is a conic constant, and A, B, C, D,... Are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.
The Z axis of this definition expression is the axis of the rotationally symmetric aspherical surface.

Note that terms relating to free-form surfaces and aspheric surfaces for which no data is described are zero. Regarding the refractive index,
The values for the d-line (wavelength 587.56 nm) are shown. The unit of the length is mm.

As another definition of the free-form surface, there is a Zernike polynomial given by the following expression (c).
The shape of this surface is defined by the following equation. The Z axis of the defining equation is the axis of the Zernike polynomial. The definition of the rotationally asymmetric surface is defined by polar coordinates of the height of the Z axis with respect to the XY plane, A is the distance from the Z axis in the XY plane, R is the azimuth around the Z axis, and the Z axis It can be expressed by the rotation angle measured from.

X = R × cos (A) y = R × sin (A) Z = D ₂ + D ₃ Rcos (A) + D ₄ Rsin (A) + D ₅ R ² cos (2A) + D ₆ (R ² −1 ^{_{) + D 7 R 2 sin (}} 2A) + D 8 R 3 cos (3A) + D 9 (3R 3 -2R) cos (A) + D 10 (3R 3 -2R) sin (A) + D 11 R 3 sin (3A) + D ^{_{12 R 4 cos (4A) +}} D 13 (4R 4 -3R 2) cos (2A) + D 14 (6R 4 -6R 2 +1) + D 15 (4R 4 -3R 2) sin (2A) + D 16 R 4 sin (4A ^{_{) + D 17 R 5 cos (}} 5A) + D 18 (5R 5 -4R 3) cos (3A) + D 19 (10R 5 -12R 3 + 3R) cos (A) + D 20 (10R 5 -12R 3 + 3R) sin (A) ^{_{+ D 21 (5R 5 -4R 3}} ) sin (3A) + D 22 R 5 sin (5A) + D 23 R 6 cos (6A) + D 24 (6R 6 -5R 4) cos (4A) + D 25 (15R 6 -20R 4 ^{+ 6R 2) cos (2A)} + D 26 (20R 6 -30R 4 + 12R 2 -1) + D 27 (15R 6 -20R 4 + 6R 2) sin (2A) ^{_{D 28 (6R 6 -5R 4)}} sin (4A) + D 29 R 6 sin (6A) ····· ··· (c) In addition, to design an optical system symmetric with respect to the X-axis direction, D
_{4, D 5, D 6,} D 10 0, D 11, D 12, D 13, D 14, D
_20, D _21, D ₂₂ ... to use.

As another example, the following definition formula (d)
Is raised. Z = ΣΣC _nm XY As an example, when k = 7 (seventh-order term) is considered, when expanded, it can be expressed by the following equation. _{Z = C 2 + C 3 y} + C 4 | x | + C 5 y 2 + C 6 y | x | + C 7 x 2 + C 8 y 3 + C 9 y 2 | x | + C 10 yx 2 + C 11 | x 3 | + C 12 y 4 ^{_{+ C 13 y 3 | x |}} + C 14 y 2 x 2 + C 15 y | x 3 | + C 16 x 4 + C 17 y 5 + C 18 y 4 | x | + C 19 y 3 x 2 + C 20 y 2 | x 3 | + C ^{_{21 yx 4 + C 22 | x}} 5 | + C 23 y 6 + C 24 y 5 | x | + C 25 y 4 x 2 + C 26 y 3 | x 3 | + C 27 y 2 x 4 + C 28 y | x 5 | + C 29 x ^{_{6 + C 30 y 7 + C}} 31 y 6 | x | + C 32 y 5 x 2 + C 33 y 4 | x 3 | + C 34 y 3 x 4 + C 35 y 2 | x 5 | + C 36 yx 6 + C 37 | x 7 | (D) In the embodiment of the present invention, the surface shape is represented by a free-form surface using the above equation (a).
It goes without saying that the same operation and effect can be obtained by using the equation (d).

In each of the first to fifth embodiments, the photographing angle of view is 26.3 ° in the horizontal half angle of view, 20.3 ° in the vertical half angle of view, and the image height is 1.0.
6 × 1.2 mm, entrance pupil diameter 1.15 mm, F-number 2.8, focal length 3.24 mm, 35 m
It is equivalent to 35 mm when converted to an m-silver camera. Of course, it goes without saying that it can be applied to other sizes. Further, the present invention includes not only an imaging optical system using the imaging optical system of the present invention but also an imaging device incorporating the optical system.

Embodiment 1 FIG. 1 is a sectional view of Embodiment 1 taken along the line YZ including the axial principal ray. The configuration parameters of this embodiment will be described later, but the free-form surface is represented by FFS, the aspheric surface is represented by ASS, and the virtual surface is represented by HRP (virtual reference plane). The same applies to other embodiments. In the first embodiment, the first prism 10, the stop 2, the second prism 20, and the image plane (imaging plane) 3 are arranged in the order in which light passes from the object side. 14, the first surface 11 of which is a first transmission surface,
The second surface 12 is a first reflection surface, the third surface 13 is a second reflection surface, and the fourth surface 14 is a second transmission surface.
The light passes through the transmitting surface 11, the first reflecting surface 12, the second reflecting surface 13, and the second transmitting surface 14 in this order.
The first surface 21 is a first transmission surface, the second surface 22 is a first reflection surface, and the third surface 23 is a second surface.
The reflection surface and the fourth surface 24 are second transmission surfaces, and light rays from the object are transmitted through the first transmission surface 21, the first reflection surface 22, and the second reflection surface 2.
Third, the light is transmitted in the order of the second transmission surface 24. The first reflecting surface 12 and the second transmitting surface 14 of the first prism 10 and the first transmitting surface 21 and the second reflecting surface 23 of the second prism 20 are the same optically active surfaces having both transmitting and reflecting functions. I have.

The second to sixth planes of the constituent parameters described later are represented by the amount of eccentricity with respect to the virtual plane 1 of the first plane, and the top positions of the seventh and eighth planes are as follows. The ninth to thirteenth surfaces are represented by the amount of eccentricity with respect to the imaginary surface 3 of the eighth surface, only by the surface interval along the axial principal ray from the virtual surface 2 of the sixth surface. The image plane is represented only by the plane interval along the axial principal ray from the virtual plane 4 of the thirteenth plane.

Embodiment 2 FIG. 2 is a sectional view taken along the line YZ of FIG. In the second embodiment, the first prism 10, the stop 2, the second prism 20, and the image plane (imaging plane) 3 are arranged in the order in which light passes from the object side.
And the first prism 10 extends from the first surface 11 to the fourth surface 1
4, the first surface 11 of which is a first transmission surface and the second surface 1
2 is a first reflecting surface, 3rd surface 13 is a 2nd reflecting surface, and 4th surface 14
Is a second transmission surface, and light rays from the object are transmitted through the first transmission surface 1
1, first reflection surface 12, second reflection surface 13, second transmission surface 14
, And the second prism 20 is composed of a first surface 21 to a third surface 23, the first surface 21 is a first transmission surface, the second surface 22 is a first reflection surface, and the third surface 23. Denotes a second transmission surface, and a light beam from the object passes through the first transmission surface 21, the first reflection surface 22, and the second transmission surface 23 in this order. And the first
The first reflecting surface 12 and the second transmitting surface 14 of the prism 10 are the same optically active surface having both a transmitting effect and a reflecting effect.

The second to sixth surfaces of the constituent parameters described later are represented by the eccentricity with respect to the virtual surface 1 of the first surface, and the top positions of the seventh and eighth surfaces are The ninth to twelfth surfaces are represented by the amount of eccentricity based on the eighth imaginary surface 3 only by the surface interval along the axial principal ray from the imaginary surface 2 of the sixth surface. The image plane is represented only by the surface interval along the axial principal ray from the virtual surface 4 of the twelfth surface.

Embodiment 3 FIG. 3 is a sectional view of Embodiment 3 taken along the line YZ including the axial principal ray. In the third embodiment, the first prism 10, the stop 2, the second prism 20, the image plane (imaging plane) 3
And the first prism 10 extends from the first surface 11 to the fourth surface 1
4, the first surface 11 of which is a first transmission surface and the second surface 1
2 is a first reflecting surface, 3rd surface 13 is a 2nd reflecting surface, and 4th surface 14
Is a second transmission surface, and light rays from the object are transmitted through the first transmission surface 1
1, first reflection surface 12, second reflection surface 13, second transmission surface 14
, And the second prism 20 is composed of a first surface 21 to a fourth surface 24, the first surface 21 being a first transmission surface, the second surface 22 being a first reflection surface, and a third surface 23. Is a second reflecting surface, and the fourth surface 24 is a second transmitting surface, and light rays from an object pass through the first transmitting surface 21, the first reflecting surface 22, and the second reflecting surface 2.
Third, the light is transmitted in the order of the second transmission surface 24. The first reflecting surface 12 and the second transmitting surface 14 of the first prism 10 are the same optically active surface having both a transmitting effect and a reflecting effect.

Further, the second to sixth planes of the constituent parameters described later are represented by the amount of eccentricity with respect to the virtual plane 1 of the first plane, and the top positions of the seventh and eighth planes are The ninth to thirteenth surfaces are represented by the amount of eccentricity with respect to the imaginary surface 3 of the eighth surface, only by the surface interval along the axial principal ray from the virtual surface 2 of the sixth surface. The image plane is represented only by the plane interval along the axial principal ray from the virtual plane 4 of the thirteenth plane.

Embodiment 4 FIG. 4 is a sectional view taken along the line YZ of Embodiment 4 and including the axial principal ray. In the fourth embodiment, the first prism 10, the stop 2, the second prism 20, and the image plane (imaging plane) 3 are arranged in the order in which light passes from the object side.
And the first prism 10 extends from the first surface 11 to the fourth surface 1
4, the first surface 11 of which is a first transmission surface and the second surface 1
2 is a first reflecting surface, 3rd surface 13 is a 2nd reflecting surface, and 4th surface 14
Is a second transmission surface, and light rays from the object are transmitted through the first transmission surface 1
1, first reflection surface 12, second reflection surface 13, second transmission surface 14
, And the second prism 20 is composed of a first surface 21 to a fourth surface 24, the first surface 21 being a first transmission surface, the second surface 22 being a first reflection surface, and a third surface 23. Is a second reflecting surface, and the fourth surface 24 is a second transmitting surface, and light rays from an object pass through the first transmitting surface 21, the first reflecting surface 22, and the second reflecting surface 2.
Third, the light is transmitted in the order of the second transmission surface 24. Then, the first reflection surface 12 and the second transmission surface 14 of the first prism 10 and the first reflection surface 22 and the second transmission surface 24 of the second prism 20 are the same optically active surface having both a reflective effect and a transmissive effect. I have.

Further, the second to sixth surfaces of the constituent parameters described later are represented by the eccentricity with respect to the virtual surface 1 of the first surface, and the top positions of the seventh and eighth surfaces are The ninth to thirteenth surfaces are represented by the amount of eccentricity with respect to the imaginary surface 3 of the eighth surface, only by the surface interval along the axial principal ray from the virtual surface 2 of the sixth surface. The image plane is represented only by the plane interval along the axial principal ray from the virtual plane 4 of the thirteenth plane.

Fifth Embodiment FIG. 5 is a sectional view taken along the line YZ of the fifth embodiment including the axial chief ray. In the fifth embodiment, the first prism 10, the stop 2, the second prism 20, and the image plane (imaging plane) 3 are arranged in the order in which light passes from the object side.
And the first prism 10 extends from the first surface 11 to the fourth surface 1
4, the first surface 11 of which is a first transmission surface and the second surface 1
2 is a first reflecting surface, 3rd surface 13 is a 2nd reflecting surface, and 4th surface 14
Is a second transmission surface, and light rays from the object are transmitted through the first transmission surface 1
1, first reflection surface 12, second reflection surface 13, second transmission surface 14
, And the second prism 20 is composed of a first surface 21 to a fifth surface 25, the first surface 21 being a first transmission surface, the second surface 22 being a first reflection surface, and a third surface 23. Is a second reflecting surface, a fourth surface 24 is a third reflecting surface, and a fifth surface 25 is a second transmitting surface. Light rays from an object pass through the first transmitting surface 21, the first reflecting surface 22, and the second reflecting surface. 23, the third reflecting surface 24, and the second transmitting surface 25 in this order. Then, the first prism 10
The reflection surface 12, the second transmission surface 14, the first prism 20
The transmission surface 21 and the third reflection surface 24, and the first reflection surface 22 and the second transmission surface 25 are the same optically active surfaces having both transmission and reflection.

Further, the second to sixth planes of the constituent parameters to be described later are represented by the amount of eccentricity with respect to the virtual plane 1 of the first plane, and the top positions of the seventh and eighth planes are The ninth to fourteenth surfaces are represented by the amount of eccentricity with respect to the eighth imaginary surface 3 as represented by only the surface interval along the axial principal ray from the sixth imaginary surface 2. The image plane is represented only by the surface interval along the axial principal ray from the virtual surface 4 of the fourteenth surface.

The following is a description of the constituent parameters of the first to fifth embodiments. "FFS" in these tables is a free-form surface, "AS
“S” indicates an aspherical surface, and “HRP” indicates a virtual surface.

Example 1 Surface Number Curvature Radius Surface Distance Eccentricity Refractive Index Abbe Number Object Surface ∞ ∞ 1 ∞ (HRP1) 2 187.08 Eccentricity (1) 1.4924 57.6 3 FFS Eccentricity (2) 1.4924 57.6 4 FFS Eccentricity (3) 1.4924 57.6 5 FFS eccentricity (2) 6 ∞ (HRP2) 3.12 Eccentricity (4) 7 ∞ (diaphragm surface) 1.12 8 ∞ (HRP3) 9 FFS eccentricity (5) 1.4924 57.6 10 FFS eccentricity (6) 1.4924 57.6 11 FFS eccentricity (5) 1.4924 57.6 12 32.37 Eccentricity (7) 13 ∞ (HRP4) 1.83 Eccentricity (8) Image plane ＦＦ FFS C ₄ -2.3809 × 10 ^-3 C ₆ 3.2334 × 10 ^-3 FFS C ₄ -1.8702 × 10 ^-2 C ₆ -2.0254 × 10 ^-4 FFS C ₄ -3.9504 × 10 ^-3 C ₆ 5.1588 × 10 ^-3 FFS C ₄ -4.0315 × 10 ^-2 C ₆ -2.6088 × 10 ^-2 FFS C ₄ -3.9505 × 10 ^-3 C ₆ 5.1587 × 10 ^-3 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α 39.02 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 1.72 Z 6.85 α -39.10 β 0.00 γ 0.00 Eccentricity (3) X 0.00 Y 5.84 Z 7.01 α -76.56 β 0.00 γ 0.00 Eccentricity (4) X 0.00 Y 3.50 Z 8. 32 α -72.13 β 0.00 γ 0.00 Eccentricity (5) X 0.00 Y -1.92 Z -0.62 α -17.15 β 0.00 γ 0.00 Eccentricity (6) X 0.00 Y -0.28 Z 2.63 α 10.31 β 0.00 γ 0.00 Eccentricity (7) X 0.00 Y -4.19 Z 0.64 α -83.27 β 0.00 γ 0.00 Eccentricity (8) X 0.00 Y -4.19 Z 0.64 α -48.98 β 0.00 γ 0.00.

Example 2 Surface Number Curvature Radius Surface Distance Eccentricity Refractive Index Abbe Number Object Surface ∞ ∞ 1 ∞ (HRP1) 2 FFS Eccentricity (1) 1.4924 57.6 3 FFS Eccentricity (2) 1.4924 57.6 4 FFS Eccentricity (3) 1.4924 57.6 5 FFS eccentricity (2) 6 ∞ (HRP2) 0.79 eccentricity (4) 7 ∞ (throttle surface) 0.76 8 ∞ (HRP3) 9 FFS eccentricity (5) 1.4924 57.6 10 FFS eccentricity (6) 1.4924 57.6 11 FFS eccentricity (7) 12 ∞ (HRP4) 1.66 Eccentricity (8) Image plane ＦＦ FFS C ₄ 1.3453 × 10 ^-2 C ₆ -8.2513 × 10 ^-3 FFS C ₄ 1.8876 × 10 ^-3 C ₆ -1.6029 × 10 ^-3 FFS C ₄ -7.8452 × 10 ^-3 C ₆ -2.4788 × 10 ^-3 FFS C ₄ 3.2783 × 10 ^-2 C ₆ 7.3318 × 10 ^-3 FFS C ₄ -4.6255 × 10 ^-2 C ₆ -4.0306 × 10 ^-2 FFS C ₄ 2.5719 × 10 ^-2 C ₆ -4.2508 × 10 ^-2 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α 9.19 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 0.47 Z 8.79 α -53.19 β 0.00 γ 0.00 Eccentricity (3) X 0.00 Y 5.59 Z 10.59 α -89.43 β 0.00 γ 0.00 Eccentricity (4) 0.00 Y 2.67 Z 11.69 α -78.28 β 0.00 γ 0.00 Eccentricity (5) X 0.00 Y 0.00 Z 0.00 α 32.49 β 0.00 γ 0.00 Eccentricity (6) X 0.00 Y 0.70 Z 3.47 α -8.20 β 0.00 γ 0.00 Eccentricity (7) X 0.00 Y 2.07 Z 0.85 α-46.92 β 0.00 γ 0.00 Eccentricity (8) X 0.00 Y 2.07 Z 0.85 α -17.65 β 0.00 γ 0.00.

Example 3 Surface Number Curvature Radius Surface Distance Eccentricity Refractive Index Abbe Number Object Surface ∞ ∞ 1 ∞ (HRP1) 2 67.95 Eccentricity (1) 1.4924 57.6 3 FFS Eccentricity (2) 1.4924 57.6 4 FFS Eccentricity (3) 1.4924 57.6 5 FFS eccentricity (2) 6 ∞ (HRP2) 1.00 eccentricity (4) 7 ∞ (diaphragm surface) 1.00 8 ∞ (HRP3) 9 ASS eccentricity (5) 1.4924 57.6 10 FFS eccentricity (6) 1.4924 57.6 11 FFS eccentricity (7) 1.4924 57.6 12 FFS Eccentricity (8) 13 ∞ (HRP4) 2.33 Eccentricity (9) Image plane ＳＳ ASS R 23.11 K 0.0000 A -3.5108 × 10 ^-4 FFS C ₄ 1.1724 × 10 ^-2 C ₆ -1.7916 × 10 ^-3 FFS C ₄ -1.4625 × 10 ^-2 C ₆ -2.4137 × 10 ^-2 FFS C ₄ -2.1370 × 10 ^-2 C ₆ -1.4068 × 10 ^-2 FFS C ₄ 2.0820 × 10 ^-2 C ₆ 2.1408 × 10 ^-2 FFS C ₄ 1.5105 × 10 ^-2 C ₆ 4.9343 × 10 ^-2 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α 38.78 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 2.88 Z 11.57 α -42.06 β 0.00 γ 0.00 Eccentricity (3) X 0.00 Y 7.99 Z 12.30 α -79. 11 β 0.00 γ 0.00 Eccentricity (4) X 0.00 Y 5.38 Z 13.80 α -70.07 β 0.00 γ 0.00 Eccentricity (5) X 0.00 Y 0.00 Z 0.00 α 14.37 β 0.00 γ 0.00 Eccentricity (6) X 0.00 Y 0.42 Z 5.06 α- 17.53 β 0.00 γ 0.00 Eccentricity (7) X 0.00 Y 4.16 Z 0.59 α -15.78 β 0.00 γ 0.00 Eccentricity (8) X 0.00 Y 4.74 Z 4.57 α 34.63 β 0.00 γ 0.00 Eccentricity (9) X 0.00 Y 4.74 Z 4.57 α- 6.82 β 0.00 γ 0.00.

Example 4 Surface Number Curvature Radius Surface Distance Eccentricity Refractive Index Abbe Number Object Surface ∞ ∞ 1 ∞ (HRP1) 2 40.48 Eccentricity (1) 1.4924 57.6 3 FFS Eccentricity (2) 1.4924 57.6 4 FFS Eccentricity (3) 1.4924 57.6 5 FFS eccentricity (2) 6 ∞ (HRP2) 3.12 Eccentricity (4) 7 ∞ (throttle surface) 0.70 8 ∞ (HRP3) 9 12.11 Eccentricity (5) 1.4924 57.6 10 FFS Eccentricity (6) 1.4924 57.6 11 FFS Eccentricity (7) 1.4924 57.6 12 FFS Eccentricity (6) 13 ∞ (HRP4) 5.00 Eccentricity (8) Image plane ∞ FFS C ₄ -4.5625 × 10 ^-3 C ₆ 4.5402 × 10 ^-3 FFS C ₄ -2.7516 × 10 ^-2 C ₆ -5.0048 × 10 ^-3 FFS C ₄ 1.0894 × 10 ^-2 C ₆ 5.5 128 × 10 ^-3 FFS C ₄ 3.6901 × 10 ^-2 C ₆ 3.2000 × 10 ^-2 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α -1.46 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y -0.06 Z 7.06 α -57.27 β 0.00 γ 0.00 Eccentricity (3) X 0.00 Y 7.23 Z 10.31 α -99.94 β 0.00 γ 0.00 Eccentricity (4) X 0.00 Y 2.18 Z 10.68 α -100.93 β 0.00 γ 0.00 Eccentricity (5) X 0.00 Y 0.00 Z 0.00 α 22.62 β 0.00 γ 0.00 Eccentricity (6) X 0.00 Y 0.24 Z 1.81 α 60.38 β 0.00 γ 0.00 Eccentricity (7) X 0.00 Y -3.37 Z 3.35 α 92.80 β 0.00 γ 0.00 Eccentricity (8) X 0.00 Y- 1.01 Z 4.09 α 77.81 β 0.00 γ 0.00.

Example 5 Surface Number Curvature Radius Surface Distance Eccentricity Refractive Index Abbe Number Object Surface ∞ ∞ 1 ∞ (HRP1) 2 94.61 Eccentricity (1) 1.4924 57.6 3 FFS Eccentricity (2) 1.4924 57.6 4 FFS Eccentricity (3) 1.4924 57.6 5 FFS eccentricity (2) 6 ∞ (HRP2) 4.01 eccentricity (4) 7 ∞ (diaphragm surface) 0.70 8 ∞ (HRP3) 9 FFS eccentricity (5) 1.4924 57.6 10 FFS eccentricity (6) 1.4924 57.6 11 FFS eccentricity (7) 1.4924 57.6 12 FFS eccentricity (8) 1.4924 57.6 13 FFS eccentricity (6) 14 ∞ (HRP4) 1.16 Eccentricity (9) Image plane ＦＦ FFS C ₄ -2.0123 × 10 ^-3 C ₆ 1.2182 × 10 ^-3 FFS C ₄ -1.6483 × 10 ^-2 C ₆ -8.2183 × 10 ^-3 FFS C ₄ 8.5811 × 10 ^-3 C ₆ 4.3592 × 10 ^-3 FFS C ₄ -6.3609 × 10 ^-3 C ₆ -3.1335 × 10 ^-3 FFS C ₄ 2.9782 × 10 ^-2 C ₆ 2.6081 × 10 ^-2 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α 24.60 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 1.78 Z 12.04 α -48.01 β 0.00 γ 0.00 Eccentricity (3) X 0.00 Y 6.54 Z 13.26 α -88.77 β 0.00 γ 0 .00 Eccentricity (4) X 0.00 Y 3.66 Z 14.14 α -87.01 β 0.00 γ 0.00 Eccentricity (5) X 0.00 Y -1.85 Z 0.48 α 14.92 β 0.00 γ 0.00 Eccentricity (6) X 0.00 Y 0.20 Z 2.50 α 58.36 β 0.00 γ 0.00 Eccentricity (7) X 0.00 Y -4.40 Z 4.36 α 129.40 β 0.00 γ 0.00 Eccentricity (8) X 0.00 Y -1.85 Z 0.48 α 14.92 β 0.00 γ 0.00 Eccentricity (9) X 0.00 Y 0.66 Z 1.75 α -114.72 β 0.00 γ 0.00.

Next, FIG. 6 shows a lateral aberration diagram of the first embodiment. In this transverse aberration diagram, the numbers shown in parentheses represent (horizontal (X direction) angle of view, vertical (Y direction) angle of view),
The lateral aberration at the angle of view is shown.

As the second prism 20 constituting the imaging optical system of the present invention in the above embodiment, the prism of the first to fifth embodiments having the number of internal reflections of 1 to 3 is used. The prism used as the second prism 20 in the imaging optical system of the present invention is not limited to this. 12 to 16 show examples thereof. Note that any of them will be described as a prism P that forms an image on the image plane 36. However, the light path from the subject is incident from the image plane 36 by reversing the optical path, and the prism P is also used as the prism P that forms an image on the pupil 31 side. Can be.

In the case of FIG. 12, the prism P is the first surface 3
The light incident through the entrance pupil 31 is refracted by the first surface 32 and enters the prism P, and the light enters the prism P at the second surface 33. The light is reflected, is incident on the third surface 34, is totally reflected, is incident on the fourth surface 35, is internally reflected, is again incident on the third surface 34, is refracted, and forms an image on the image surface 36.

In the case of FIG. 13, the prism P is
The light incident through the entrance pupil 31 is refracted by the first surface 32 and enters the prism P, and the light enters the prism P at the second surface 33. The light is reflected, enters the third surface 34, is internally reflected, is again incident on the second surface 33, is internally reflected, is incident on the fourth surface 35, is refracted, and is refracted.
6 is formed.

In the case of FIG. 14, the prism P is the first surface 3
The light incident through the entrance pupil 31 is refracted by the first surface 32 and enters the prism P, and the light enters the prism P at the second surface 33. The light is reflected, is incident on the third surface 34, is internally reflected, is again incident on the second surface 33, is internally reflected, is incident on the fourth surface 35, is internally reflected, is again incident on the second surface 33, and is now Is refracted to form an image on the image plane 36.

In the case of FIG. 15, the prism P is the first surface 3
2, the light incident through the entrance pupil 31 is refracted by the first surface 32, enters the prism P, is internally reflected by the second surface 33, and is reflected again by the second surface 33. The light is incident on the first surface 32 and is now totally reflected, internally reflected on the third surface 34, and is again incident on the first surface 32 and totally reflected, and is incident again on the third surface 34 and is now refracted. , On the image plane 36.

In the case of FIG. 16, the prism P is the first surface 3
2, the light incident through the entrance pupil 31 is refracted by the first surface 32, enters the prism P, is internally reflected by the second surface 33, and is reflected again by the second surface 33. The light enters the first surface 32, is totally reflected this time, is internally reflected by the third surface 34, is again incident on the first surface 32, is totally reflected, is again incident on the third surface 34, is internally reflected, and Each time the light enters the first surface 32 and is refracted this time, an image is formed on the image plane 36.

The imaging optical system according to the present invention as described above can be used in a photographing apparatus, in particular, a camera, which forms an object image and receives the image with an image pickup device such as a CCD or a silver halide film to perform photographing. it can. It can also be used as an observation device for observing an object image through an eyepiece, particularly as an objective optical system for a finder section of a camera. Further, it can also be used as an imaging optical system for an optical device using a small imaging element such as an endoscope. less than,
The embodiment is illustrated.

FIGS. 7 to 9 are conceptual diagrams showing a configuration in which the imaging optical system of the present invention is incorporated in an objective optical system of a finder section of an electronic camera. 7 is a front perspective view showing the appearance of the electronic camera 40, FIG. 8 is a rear perspective view of the same, and FIG.
It is sectional drawing which shows a structure of. In this case, the electronic camera 40 includes a photographic optical system 41 having a photographic optical path 42, a finder optical system 43 having a finder optical path 44,
Shutter 45, flash 46, LCD monitor 4
7 and the like, and when the shutter 45 disposed above the camera 40 is pressed, the photographing objective optical system 4
Photographing is performed through 8. An object image formed by the photographing objective optical system 48 is transmitted to a CCD 49 through a filter 51 such as a low-pass filter or an infrared cut filter.
Is formed on the imaging surface 50. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 52. Further, a memory or the like is arranged in the processing means 52,
A captured electronic image can also be recorded. This memory may be provided separately from the processing means 52, or may be configured to perform electronic recording and writing using a floppy disk or the like. Further, the camera may be configured as a silver halide camera in which a silver halide film is arranged instead of the CCD 49.

Further, on the optical path 44 for the finder,
For example, an image forming optical system similar to that of the fourth embodiment is arranged as the finder objective optical system 53. In this case, a cover lens 54 having a positive power is arranged as a cover member to form a part of the objective optical system 53 for a finder, thereby expanding the angle of view. The front group of the finder objective optical system 53 is formed by the cover lens 54 and the prism 10 on the object side of the diaphragm 2 of the imaging optical system, and the finder objective lens is formed by the prism 20 on the image side of the diaphragm 2 of the imaging optical system. The rear group of the optical system 53 is configured. The object image formed by the finder objective optical system 53 is formed on a field frame 57 of a Porro prism 55 which is an image erecting member. In addition, the field of view frame 5
Numeral 7 separates the first reflection surface 56 and the second reflection surface 58 of the Porro prism 55 from each other and is disposed therebetween. Behind the polyprism 55, an eyepiece optical system 59 for guiding the erect image into the observer's eyeball E is disposed.

In the camera 40 configured as described above, the finder objective optical system 53 can be configured with a small number of optical members, high performance and low cost can be realized, and the optical path itself of the objective optical system 53 can be bent. Therefore, the degree of freedom of arrangement inside the camera increases, which is advantageous in design.

Although the configuration of the photographing objective optical system 48 has not been mentioned in the configuration of FIG. 9, the photographing objective optical system 48 is not limited to the refraction type coaxial optical system, but also includes two prisms of the present invention. It is of course possible to use any type of imaging optical system consisting of 10, 20.

Next, FIG. 10 is a conceptual diagram of a configuration in which the image forming optical system of the present invention is incorporated in the objective optical system 48 of the photographing section of the electronic camera 40. In the case of this example, the imaging objective optical system 48 arranged on the imaging optical path 42 uses the same imaging optical system as in the fifth embodiment. The object image formed by the objective optical system for photographing is formed on the imaging surface 50 of the CCD 49 via a filter 51 such as a low-pass filter or an infrared cut filter. The object image received by the CCD 49 is passed through a processing unit 52 to a liquid crystal display (LC).
D) Displayed on 60 as an electronic image. The processing unit 52 also controls a recording unit 61 that records an object image captured by the CCD 49 as electronic information. LCD60
Is guided to the observer's eyeball E via the eyepiece optical system 59. The eyepiece optical system 59 is composed of an eccentric prism having the same form as that used in the imaging optical system of the present invention. In this example, the entrance surface 62 and the reflection surface 6 are used.
3 and a surface 64 for both reflection and refraction. Also, in the surfaces 63 and 64 having two reflecting actions,
At least one surface, desirably both surfaces, is constituted by a plane-symmetric free-form surface having only one plane of symmetry for applying power to the light beam and correcting eccentric aberration. The only plane of symmetry is the prism 1 of the photographing objective optical system 48.
It is formed on substantially the same plane as the only plane of symmetry of the plane-symmetric free-form surface included in 0 and 20. Further, the photographing objective optical system 48 may include another lens (positive lens, negative lens) as a constituent element on the object side of the two prisms 10 and 20, between them, or on the image side.

In the camera 40 thus configured, the photographing objective optical system 48 can be composed of a small number of optical members, high performance and low cost can be realized, and the entire optical system can be arranged on the same plane. Thus, it is possible to realize the thickness of the thickness in the direction perpendicular to the arrangement plane.

In this example, a parallel flat plate is arranged as the cover member 65 of the photographing objective optical system 48, but a lens having power may be used as in the previous example.

Here, without providing the cover member, the surface of the image forming optical system according to the present invention which is disposed closest to the object can also be used as the cover member. In this example, the surface closest to the object is the incident surface of the prism 10. However, since this incident surface is eccentrically arranged with respect to the optical axis, if this surface is arranged in front of the camera, the photographing center of the camera 40 is shifted from itself when viewed from the subject side. This is an illusion (similar to a general camera, it is usual to sense that the image is taken in the vertical direction of the incident surface), giving a sense of incongruity. Therefore, when the surface closest to the object side of the imaging optical system is an eccentric surface as in the present example, providing the cover member 65 (or the cover lens 54) may cause an uncomfortable feeling when viewed from the subject side. It is desirable to be able to receive photography with the same feeling as an existing camera without feeling.

Next, FIG. 11 is a conceptual diagram showing a configuration in which the image forming optical system of the present invention is incorporated in an objective optical system 80 of an observation system of an electronic endoscope. In the case of this example, the objective optical system 80 of the observation system
Uses the imaging optical system shown in the third embodiment. This electronic endoscope is, as shown in FIG.
1, a light source device 72 that supplies illumination light, and a video processor 73 that performs signal processing corresponding to the electronic endoscope 71.
A monitor 74 for displaying a video signal output from the video processor 73; and a video processor 73
And a VTR deck 75 for recording video signals and the like, a video disk 76, and a video printer 77 for printing out the video signals as video. Figure 1
It is configured as shown in FIG. The light beam illuminated from the light source device 72 passes through the light guide fiber bundle 86 and illuminates the observation site by the illumination objective optical system 85. Then, light from this observation site is transmitted to the cover member 84.
Is formed as an object image by the observation objective optical system 80 via the. This object image is transmitted to a CCD 8 through a filter 81 such as a low-pass filter or an infrared cut filter.
It is formed on the second imaging surface 83. Further, this object image is converted into a video signal by a CCD 82, and the video signal is directly displayed on a monitor 74 by a video processor 73 shown in FIG. And printed out from the video printer 77 as a video.

The endoscope thus configured can be configured with a small number of optical members, can realize high performance and low cost, and can realize the two prisms 10 of the objective optical system 80 of the observation system.
Since the 20s are arranged in the long axis direction of the endoscope, the above-described effect can be obtained without hindering the reduction in diameter.

Next, FIG. 20 shows a desirable configuration when the imaging optical system according to the present invention is disposed in front of an image pickup device such as a CCD or a filter. In the figure, an eccentric prism P is a prism included in the imaging optical system of the present invention. Now, when the imaging surface C of the imaging device forms a square as shown in the figure,
Symmetry plane D of a plane-symmetric free-form surface arranged on eccentric prism P
Is at least one of the sides forming the square of the imaging surface C.
Arrangement so as to be parallel to each other is desirable for beautiful image formation.

Further, when the imaging surface C has four interior angles of approximately 90 °, such as a square and a rectangle, the plane of symmetry D of the plane-symmetric free-form surface is parallel to the imaging surface C. It is arranged in parallel to a certain two sides, more preferably, is arranged in the middle of the two sides, and the configuration is such that the symmetry plane D coincides with the position where the imaging plane C is symmetrical left and right or up and down. preferable. With this configuration, it is easy to obtain the accuracy of assembling into the device,
It is effective for mass production.

Further, among the optical surfaces constituting the decentered prism P, the first surface, the second surface, the third surface, etc., when a plurality of surfaces or all surfaces are plane-symmetric free-form surfaces, a plurality of surfaces are used. Alternatively, it is desirable from the viewpoint of design and aberration performance that the symmetrical surfaces of all surfaces are arranged on the same surface D. It is desirable that the relationship between the symmetry plane D and the imaging plane C has the same relation as described above.

The above-described imaging optical system of the present invention can be constituted, for example, as follows. [1] In an image forming optical system having a positive refractive power as a whole for forming an object image, the image forming optical system has a refractive index (n).
Has a first prism and a second prism formed of a medium larger than 1.3 (n> 1.3), wherein the second prism is disposed closer to the image side than the first prism, and The first prism is formed by an imaging system that does not form an image, and the first prism has three optically active surfaces that transmit or reflect a light beam,
The first surface in which the light beam from the object enters the prism, the second surface reflects the light beam incident from the first surface in the prism, and emits the light beam reflected on the third surface out of the prism. The third surface is configured to reflect the light beam reflected by the second surface, and at least one of the second surface and the third surface has a curved surface shape that gives power to the light beam. The curved surface shape has a rotationally asymmetric surface shape that corrects aberrations caused by eccentricity, and the second prism includes:
At least one prism has a reflecting surface for reflecting the light beam in the prism, and the reflecting surface is configured to apply power to the light beam and to have a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity. An imaging optical system, characterized in that:

[2] The second surface of the first prism and the third surface
2. The imaging optical system according to claim 1, wherein both surfaces are configured to apply power to the light beam and to have a rotationally asymmetric surface shape for correcting aberrations generated by decentering.

[3] The second surface of the first prism and the third surface
2. The imaging optical system according to claim 1, wherein at least one of the rotationally asymmetric surfaces has a plane-symmetric free-form surface having only one plane of symmetry.

[4] The second surface of the first prism and the third surface
3. The imaging optical system according to claim 2, wherein both rotationally asymmetric surface shapes of the surfaces are configured as a plane-symmetric free-form surface shape having only one plane of symmetry.

[5] The only symmetrical surface of the plane-symmetric free-form surface of the second surface of the first prism and the third surface of the first prism
5. The imaging optical system according to claim 4, wherein the first prism is configured such that only one symmetric surface of a plane-symmetric free-form surface is formed in the same plane.

[6] The first surface of the first prism is characterized in that it has a rotationally asymmetric surface shape that gives power to a light beam and corrects aberration caused by eccentricity. 6. The imaging optical system according to any one of the above items 1 to 5.

[7] The method according to the above item 6, wherein the rotationally asymmetric surface shape of the first surface of the first prism is a plane-symmetric free-form surface shape having only one plane of symmetry. Imaging optics.

[8] The rotationally asymmetric surface arranged in the second prism is a plane-symmetric free-form surface having only one plane of symmetry. 8. The imaging optical system according to any one of items 7 to 7.

[0155]

[9] The above-mentioned [8], wherein the first prism and the second prism are provided with a plane-symmetric free-form surface configured such that at least one surface at a time has only one plane of symmetry arranged on the same plane. An imaging optical system as described in the above.

[10] The pupil is arranged between the first prism and the second prism, and the second prism is arranged between the pupil and the image plane. 10. The imaging optical system according to any one of items 1 to 9.

[11] The imaging optical system according to the above item 10, wherein a stop is arranged on the pupil.

[12] The lens according to any one of items 1 to 11, wherein the second prism is configured to have at least two curved reflecting surfaces for giving power to the light beam. Image optics.

[13] The optically active surface of the second prism has an incident surface serving as both a reflecting surface and a transmitting surface, a reflecting surface,
12. The imaging optical system according to any one of the above items 1 to 11, wherein the imaging optical system is constituted by three optical working surfaces of an exit surface.

[14] Any one of the above items 1 to 11, wherein the second prism is constituted by three optical working surfaces of a reflecting surface for giving power to the light beam, an incident surface, and an exit surface. 2. The imaging optical system according to claim 1.

[15] The second prism according to any one of the above items 1 to 11, wherein the second prism comprises four reflecting surfaces for giving power to the light beam, an entrance surface, and an exit surface. An imaging optical system according to claim 1.

[16] The second prism is characterized in that the second prism is composed of three optically active surfaces: an entrance surface, an exit surface that also serves as a reflection surface and a transmission surface, and a reflection surface that gives power to a light beam. 12. The imaging optical system according to any one of the above items 1 to 11.

[17] The second prism has three reflecting surfaces, one of which is formed as an incident surface also serving as a transmitting surface, and the other reflecting surface also serving as a transmitting surface. Characterized in that it is formed by a set exit surface.
12. The imaging optical system according to any one of items 1 to 11.

[18] The image forming optical system according to any one of the above items 1 to 17 is arranged as a finder objective optical system, and further, an image corrector for erecting an object image formed by the finder objective optical system. A finder optical system comprising a vertical optical system and an eyepiece optical system.

[19] A camera device comprising: the finder optical system according to the above item 18, and a photographing objective optical system provided in parallel with the finder optical system.

[20] An image forming optical system according to any one of the above items 1 to 17, and an image pickup device arranged on an image plane formed by the image forming optical system. An imaging optical system characterized by the above-mentioned.

[21] The imaging optical system according to any one of 1 to 17 above is arranged as a photographing objective optical system, and an optical path different from the photographing optical system or the photographing objective optical system. And a finder optical system disposed in any one of the optical paths divided from the optical path.

[22] The imaging optical system according to any one of the above items 1 to 17, an imaging device arranged on an image plane formed by the imaging optical system, and light received by the imaging device. An electronic camera apparatus, comprising: a recording medium for recording image information; and an image display element for forming an observation image by receiving image information from the recording medium or the imaging element.

[23] An observation system including the imaging optical system according to any one of the above items 1 to 17, and an image transmitting member that transmits an image formed by the imaging optical system along a long axis direction. An endoscope apparatus comprising: an illumination light source; and an illumination system having an illumination light transmission member that transmits illumination light from the illumination light source along the long axis direction.

[0170]

As is apparent from the above description, according to the present invention, a high-performance and low-cost imaging optical system can be provided with a small number of optical elements. In addition, by folding the optical path using a reflection surface with a small number of reflections, it is possible to provide a high-performance imaging optical system that is reduced in size and thickness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an imaging optical system according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of an imaging optical system according to a second embodiment of the present invention.

FIG. 3 is a sectional view of an imaging optical system according to a third embodiment of the present invention.

FIG. 4 is a sectional view of an imaging optical system according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of an imaging optical system according to a fifth embodiment of the present invention.

FIG. 6 is a lateral aberration diagram of the imaging optical system of the first embodiment.

FIG. 7 is a front perspective view showing the appearance of an electronic camera to which the imaging optical system of the present invention is applied.

FIG. 8 is a rear perspective view of the electronic camera of FIG. 7;

9 is a cross-sectional view illustrating a configuration of the electronic camera in FIG.

FIG. 10 is a conceptual diagram of another electronic camera to which the imaging optical system of the present invention is applied.

FIG. 11 is a conceptual diagram of an electronic endoscope to which the imaging optical system of the present invention is applied.

FIG. 12 is a diagram showing an example of an eccentric prism applicable to the present invention.

FIG. 13 is a diagram showing another example of an eccentric prism applicable to the present invention.

FIG. 14 is a diagram showing another example of an eccentric prism applicable to the present invention.

FIG. 15 is a diagram showing another example of the eccentric prism applicable to the present invention.

FIG. 16 is a diagram showing another example of an eccentric prism applicable to the present invention.

FIG. 17 is a conceptual diagram for explaining field curvature caused by an eccentric reflecting surface.

FIG. 18 is a conceptual diagram for explaining astigmatism generated by a decentered reflecting surface.

FIG. 19 is a conceptual diagram for explaining coma generated by a decentered reflecting surface.

FIG. 20 is a diagram showing a desirable configuration when an imaging optical system according to the present invention is arranged in front of an image sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... On-axis principal ray 2 ... Stop 3 ... Image surface 10 ... 1st prism 11 ... 1st surface 12 ... 2nd surface 13 ... 3rd surface 14 ... 4th surface 20 ... 2nd prism 21 ... 1st surface 22 ... 2nd surface 23 ... 3rd surface 24 ... 4th surface 25 ... 5th surface 31 ... pupil 32 ... 1st surface 33 ... 2nd surface 34 ... 3rd surface 35 ... 4th surface 36 ... image surface 40 ... electronic camera 41 ... Shooting optical system 42 ... Shooting optical path 43 ... Finder optical system 44 ... Finder optical path 45 ... Shutter 46 ... Flash 47 ... Liquid crystal display monitor 48 ... Shooting objective optical system 49 ... CCD 50 ... Imaging surface 51 ... Filter 52 ... Processing Means 53 ... Objective optical system for viewfinder 54 ... Cover lens 55 ... Porro prism 56 ... First reflecting surface 57 ... Field frame 58 ... Second reflecting surface 59 ... Eyepiece optical system 60 ... Liquid crystal display element (LCD) 61 ... Recording means 62 Incident surface 63 ... Reflective surface 64 ... Combined surface for reflection and refraction 65 ... Cover member 71 ... Electron endoscope 72 ... Light source device 73 ... Video processor 74 ... Monitor 75 ... VTR deck 76 ... Video disk 77 ... Video printer 78 ... Insert Part 79 ... Tip part 80 ... Observation objective optical system 81 ... Filter 82 ... CCD 83 ... Imaging surface 84 ... Cover member 85 ... Illumination objective optical system 86 ... Light guide fiber bundle M ... Concave mirror P ... Prism E ... Observer eyeball C: imaging plane D: symmetry plane

Claims (6)

[Claims] 1. An imaging optical system having an overall positive refractive power for forming an object image, wherein said imaging optical system is a medium having a refractive index (n) greater than 1.3 (n> 1.3). A first prism and a second prism formed of the first prism, the second prism is disposed closer to the image side than the first prism, and is formed by an imaging system that does not form an intermediate image; The prism has three optically active surfaces for transmitting or reflecting a light beam, a first surface among which a light beam from an object enters the prism, and a second surface for reflecting the light beam incident from the first surface. The light reflected at the inside and the light reflected at the third surface are emitted to the outside of the prism, and the third surface is configured to reflect the light reflected at the second surface. At least one of the three surfaces has a curved shape that gives power to the light beam; The curved surface has a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity, the second prism has a reflecting surface for reflecting a light beam in at least one prism, and the reflecting surface has a power for the light beam. And an imaging optical system configured to have a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity. 2. The optical system according to claim 1, wherein the optically active surface of the second prism comprises three optically active surfaces, namely, an incident surface which also serves as a reflection surface and a transmission surface, a reflection surface, and an emission surface. The imaging optical system according to claim 1. 3. The imaging optics according to claim 1, wherein said second prism comprises three reflecting surfaces for giving power to the light beam, an entrance surface, and an exit surface. system. 4. The connection according to claim 1, wherein said second prism comprises two reflecting surfaces for applying power to the light beam, an entrance surface, and an exit surface. Image optics. 5. The optical system according to claim 1, wherein the second prism is composed of an entrance surface, an exit surface that also serves as a reflection surface and a transmission surface, and a reflection surface that gives power to the light beam. 2. The imaging optical system according to claim 1, wherein: 6. The second prism has three reflecting surfaces, one of which is formed as an incident surface that also serves as a transmitting surface, and the other reflecting surface also serves as a transmitting surface. 2. The image forming optical system according to claim 1, wherein the image forming optical system is formed on an exit surface.