JPH10333040A - Image pickup optical system and image pickup device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact image pickup optical system in which a clear image whose distortion is reduced is provided even at a wide viewing angle and to provide an image pickup device using the system. SOLUTION: This image pickup optical system is for forming an object image on an image pickup element surface 8 and provided with a back-side optical group 4 at least on a more image side than a pupil surface 1. The back- side optical group 4 is provided with a prism member 4 having at least three surfaces arranged eccentrically so that the whole surfaces are inclined toward an axial main light beam 2 when a light beam emitting the center of an object, passing through the center of a pupil and reaching the center of an image is made as the axial main light beam 2. Then, at least these three surfaces are constituted of a surface 5 having a transmitting action, a rotation symmetric surface-shaped curved surface 6 having both of a reflecting action and the transmitting action and a rotation asymmetric surface-shaped curved surface 7 having the reflecting action and for correcting a rotation asymmetric eccentric aberration caused by the eccentricity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup optical system and an image pickup apparatus using the same, and more particularly, to an image pickup power necessary for at least one image formation which is optimal for an image pickup apparatus in which an image to be formed is relatively small. The present invention relates to an optical system and an imaging apparatus in which a reflection surface of the optical system is decentered.

[0002]

2. Description of the Related Art A conventional well-known compact decentered optical system is disclosed in Japanese Patent Application Laid-Open No. Sho 59-84201. However, this is an invention of a one-dimensional light receiving lens using a cylindrical reflecting surface, and two-dimensional imaging cannot be performed. Japanese Patent Application Laid-Open No. Sho 62-144127 uses the same cylindrical surface for two-time reflection in order to reduce the spherical aberration of the above invention.

Japanese Patent Application Laid-Open No. Sho 62-205547 discloses that an aspherical reflecting surface is used as the shape of the reflecting surface, but does not mention the shape of the reflecting surface. Further, U.S. Pat. No. 3,810,221 and U.S. Pat.
In both cases of No. 31, there is shown an example in which a lens system having a rotationally symmetric aspherical mirror and a surface having only one plane of symmetry is used for a finder optical system of a reflex camera.
However, a plane having only one plane of symmetry is used for correcting the inclination of the observed virtual image.

Further, Japanese Patent Application Laid-Open No. 1-257834 (US Pat. No. 5,274,406) discloses that a rear projection television has a reflecting mirror which has only one plane of symmetry in order to correct image distortion. Although an example of use is shown, a projection lens system is used for projection onto a screen, and a plane having only one plane of symmetry is used for correcting image distortion. Also, an example of a rear-view mirror type decentered optical system using an anamorphic surface and a toric surface is shown as an observation optical system. However, correction of aberrations including image distortion is insufficient.
It should be noted that none of the above prior arts uses a surface having only one symmetric surface and uses it as a back mirror for a folded optical path.

[0005] Also, JP-A-8-292368, JP-A-8-292371 and JP-A-8-292372 disclose:
An imaging optical system (single focus optical system, zoom optical system) using a surface having only one symmetric surface as a reflecting surface is shown. However, the optical path length from the rotationally asymmetric surface on the most object side to the rotationally asymmetric surface on the most image side is long until the light enters and exits the optical component including the rotationally asymmetric surface (an example in which an image is formed once in the middle). Yes), there is no merit of using a rotationally asymmetric surface, which is difficult to manufacture, because the optical system becomes large.

[0006]

In a conventional rotationally symmetric optical system, since a transmission rotationally symmetric lens having a refractive power bears a refractive power, many components are required for aberration correction. However, in these decentering optical systems of the prior art, if the aberration of the formed image is properly corrected, and especially if the rotationally asymmetric distortion is not properly corrected, the formed figure or the like is distorted. As a result, the correct shape could not be recorded.

In a rotationally symmetric optical system in which the refractive lens constituting the optical system is constituted by a rotationally symmetric surface about the optical axis, the optical system becomes long in the optical axis direction because the optical path is straight. As a result, there is a problem that the imaging device becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a small-sized image pickup optical system which provides an image which is clear and has little distortion even at a wide angle of view, and uses the same. The purpose of the present invention is to provide an imaging device that has been used.

[0009]

According to the present invention, there is provided an imaging optical system for forming an object image on an imaging element surface, wherein the imaging optical system has at least a rear optical element located closer to the image side than the pupil plane. The rear optical group has an eccentric so that the entire surface is inclined with respect to the principal ray when a ray exiting from the object center and passing through the center of the pupil and reaching the image center is defined as an axial principal ray. An optical system with at least three surfaces arranged,
The at least three surfaces have a permeable effect;
It consists of a curved surface with a rotationally symmetric surface shape that shares the reflection and transmission functions, and a curved surface with a rotationally asymmetric surface shape that has a reflection effect and corrects rotationally asymmetric eccentric aberration caused by eccentricity. is there.

In this case, it is desirable that a curved surface having a rotationally symmetric surface shape that shares the reflection function and the transmission function is formed by a total reflection surface or a semi-transmission reflection surface. Further, it is desirable that the reflecting surface is formed by a coated mirror surface.

A surface having a reflecting action is disposed opposite to a face sharing a reflecting action and a transmitting action, and a direction in which an axial principal ray reaches an incident surface of the optical system is defined as a Z-axis direction. When the axis constituting the orthogonal coordinate system with the Y-axis direction, the Y-axis, and the Z-axis is defined as the X-axis within the eccentric plane of the surface, a small amount of d is separated from the incident surface side of the optical system in the Y direction with the axial principal ray. A value obtained by dividing the sin of the angle formed between the two light rays in the YZ plane by NA'yi and NA'yi by the width d of the parallel light beam on the side where the parallel light beam is incident and exiting from the optical system. If / d is the power Py in the Y direction of the optical system and p is the optical path length of the axial principal ray from the entrance surface of the prism member to the exit surface of the prism member, then 0.1 <p × Py <8 ·・ ・ It is desirable to satisfy (1).

First, a coordinate system used in the following description will be described. As shown in FIG.
A ray that passes through the center of the aperture 1 and reaches the center of the image plane 8 is defined as an axial principal ray 2, an optical axis defined by a straight line that intersects the first surface of the optical system is defined as a Z axis, and the Z axis is An axis that is orthogonal and within the eccentric plane of each surface constituting the imaging optical system is defined as a Y axis, and an axis that is orthogonal to the Z axis and orthogonal to the Y axis is an X axis.

In general, in a spherical lens system composed of only spherical lenses, spherical aberration caused by a spherical surface and aberrations such as coma and curvature of field are mutually corrected on several planes, so that the aberration is reduced as a whole. Configuration.
On the other hand, an aspherical surface or the like is used to satisfactorily correct aberrations with a small number of surfaces. 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 configuration and operation of the present invention will be described below. When the rotationally symmetric optical system is decentered, rotationally asymmetric aberration occurs, and it is impossible to correct this by only the rotationally symmetric optical system. Rotationally asymmetric aberrations caused by this eccentricity include image distortion, field curvature, and astigmatism and coma which also occur on the axis. FIG. 6 shows the field curvature generated by the concave mirror M arranged eccentrically, FIG. 7 shows the astigmatism generated by the concave mirror M arranged eccentrically, and FIG. 8 shows the axial coma generated by the concave mirror M arranged eccentrically. It is a figure showing an aberration. According to the present invention, a rotationally asymmetric surface is arranged in an optical system to correct the rotationally asymmetric aberration caused by the eccentricity as described above.

The rotationally asymmetric aberration generated by the concave mirror disposed eccentrically includes rotationally asymmetric field curvature. For example, a light ray incident on a concave mirror decentered from an object point at infinity hits the concave mirror and is reflected and imaged.After the light ray hits the concave mirror, the rear focal length to the image plane is the curvature of the part hit by the light ray. Halve. Then, as shown in FIG. 6, an image plane inclined with respect to the axial principal ray is formed. Correction of such rotationally asymmetric field curvature has not been possible with rotationally symmetric optical systems. In order to correct the tilted curvature of field, the concave mirror M is constituted by a rotationally asymmetric surface. In this example, the curvature is increased (the refractive power is increased) in the positive Y-axis direction (upward in the figure). , Y axis negative direction ((downward in the figure)
Can be corrected by weakening the curvature (reducing the refractive power). Further, 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.

Next, rotationally asymmetric astigmatism will be described. As described above, the eccentrically arranged concave mirror M
In this case, astigmatism as shown in FIG. This 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.

Further, when the imaging optical system of the present invention is configured to have a bent optical path, it is possible to give power to the reflecting surface, and it is possible to omit the transmission type lens. Further, the optical system can be made compact by bending the optical path.

Further, the reflection surface can be made to have a high reflectivity by forming a total reflection surface inclined with respect to the light beam so that the light beam enters beyond the critical angle. In addition, it is possible to have both a reflecting action and a transmitting action. Further, it is preferable that the reflection surface is formed of a reflection surface having a metal thin film such as aluminum or silver formed on the surface, or a reflection surface or a semi-transmission reflection surface formed of a dielectric multilayer film. 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.

More preferably, when a rotationally asymmetric surface is used for the reflecting surface, no chromatic aberration occurs at all, as compared with the case where the reflecting surface is used. Further, since the light beam can be bent even if the inclination of the surface is small, other aberrations are less likely to occur. That is, when the same refracting power is to be obtained, the occurrence of aberration is smaller on the reflecting surface than on the refracting surface.

Further, as in the case of the image pickup optical system of the present invention, when the formed image is small, the image pickup optical system can be reduced in size according to the so-called coefficient multiplication principle in the drawing.
In consideration of actual manufacturing, it is preferable to reduce the size of the imaging optical system unnecessarily, because the thickness of the edge of the lens, the thickness at the center is reduced, and the lens diameter is too small, which rather increases the manufacturing cost and is preferable. Absent. On the other hand, if the optical system is configured with a manufacturable size, in the conventional optical system using a refractive lens, since the optical axis is straight, there is a spatial waste in the interval between the refractive surfaces having power. . Therefore, if the optical axis is spatially folded using the reflecting surface,
An optical path required for image formation can be secured by effectively using a relatively small space. At this time, if the optical path length of the imaging optical system is unnecessarily increased, the configuration is decentered and the optical axis is turned back, so that not only the size is increased against the purpose of effectively using the space, but also the optical path length is larger than the image to be formed. Is too long, there arises a problem that it becomes difficult to secure a back focus necessary for arranging a member for capturing an optical image, such as a film or an image sensor.

In the present invention, a folded optical path is employed, and at the same time, the following conditions are satisfied, whereby a small optical system is successfully constructed.

That is, in the imaging optical system of the present invention,
The rear optical group has at least a second reflecting surface arranged opposite to the reflecting surface, and the direction until the axial principal ray reaches the first surface of the optical system is defined as a Z-axis direction. Assuming that an axis constituting a rectangular coordinate system with the Y-axis direction, the Y-axis, and the Z-axis in the eccentric plane is the X-axis, a parallel light beam slightly separated by d in the Y-direction from the axial principal ray from the entrance surface side of the optical system. And the angle sin formed by the two rays in the YZ plane on the side exiting from the optical system is represented by N
A′yi, a value NA′yi / d obtained by dividing the NA′yi by the width d of the parallel light flux, is defined as the power Py in the Y direction of the optical system, and the axial principal ray is arranged closest to the object side of the optical system. When an optical path length from the time when the light enters the optical system component having the rotationally asymmetric surface to the time when the light passes through the optical system component having the rotationally asymmetric surface disposed closest to the image side of the optical system is p, 0.1 <P × Py <8 (1)

First, the power of the optical system is defined in the present invention. As shown in FIG. 9, when the eccentric direction of the optical system is set in the Y-axis direction, a light beam with a minute height d in the YZ plane parallel to the axial principal ray 2 is incident on the optical system from the object side. And the angle sin formed by the two light rays in the YZ plane on the side exiting from the optical system is defined as NA′yi, and NA′yi / d
Is the power Py of the entire optical system in the Y direction, and similarly, a light beam having a minute height d in the XZ plane parallel to the axial principal ray 2 is made incident on the optical system from the object side and emitted from the optical system. The angle sin formed in the plane including the on-axis principal ray orthogonal to the YZ plane of the two rays on the side is defined as NA′xi, and NA′xi
/ D is the power Px of the entire optical system in the X direction.

Then, after the axial chief ray is incident on an optical system component having a rotationally asymmetric surface located closest to the object side of the optical system, a rotationally asymmetric surface located closest to the image side of the optical system is removed. The optical path length until the optical system component is emitted is p (in FIG. 9, since both are the same decentered prism optical system 4, the optical path length of the axial chief ray 2 therein).
Then, it is desirable to configure the optical system so as to satisfy the above equation (1) in order to reduce the size of the optical system.

More preferably, if 0.5 <p × Py <5.0 (1) ′ is satisfied, a small lens system can be achieved.

More preferably, if 0.5 <p × Py <0.7 (1) ”is satisfied, a smaller lens system can be achieved.

Further, when the optical system component having a rotationally asymmetric surface of the image pickup optical system of the present invention is constituted by the first and second reflection operation surfaces and the first and second transmission operation surfaces, the optical axis becomes two. The optical system can be folded down on the reflecting surface, and the size of the optical system can be reduced. Furthermore, since there are two transmission surfaces, better results can be obtained for the principal point position and the field curvature. Further, better aberration performance can be obtained by using two reflecting surfaces as back mirrors.

If the pupil is not projected to the object side, the size of the optical system becomes large, and the optical path length p becomes too large. Or, it becomes difficult to secure the back focus. Furthermore, if you rely too much on the eccentric rotationally asymmetric surface,
It becomes difficult to correct asymmetric aberrations caused by eccentricity, especially eccentric coma. Therefore, arranging the optical system on the object side from the rotationally asymmetric surface and sharing the power is also an effective means for improving the optical performance.

When a stop is disposed on the object side of an optical system component having a rotationally asymmetric surface, an optical member is further disposed on the object side to protect the stop member and to provide a reflecting surface with a surface mirror. In the case of the configuration, it is also useful for measures such as dust prevention.

Further, in the imaging optical system of the present invention, the eccentric aberration can be corrected by the decentered rotationally asymmetric surface. However, an optical member is arranged on the object side, and the eccentric rotationally asymmetric reflective surface and the decentered rotationally asymmetric reflective surface are integrated. It is preferable to correct aberration. At that time, it is preferable that the optical member be decentered in order to favorably correct the asymmetric aberration because uniform correction can be performed.

In the image pickup optical system of the present invention, when the number of optical system components having a decentered rotationally asymmetric reflective surface is reduced, or when the optical system component having the reflective surface is formed by a prism block, the stop can be set to an object. Otherwise, the optical system will be large. At that time, all the powers are biased toward the image side with respect to the aperture. To correct distortion, both negative and positive powers are required. However, if the negative power is too high, the size of the optical system increases and the optical path length increases, which is not preferable. Therefore, it is preferable to dispose a positive lens on the object side of the stop to correct distortion. Further, when an optical system component having an eccentric rotationally asymmetric reflecting surface is constituted by a prism block, it is difficult to correct some chromatic aberration generated on the transmitting surface, but it is also effective in correcting chromatic aberration. It is. In particular, it is more preferable to decenter the positive lens in order to correct asymmetric aberration.

In particular, when a wide-angle lens having a wide angle of view is formed, the focal length becomes short, so that it is difficult to secure the back focus. In that case, it is preferable to adopt a so-called retrofocus type in which negative and positive powers are sequentially arranged from the object side. Moreover, it is better to increase the negative power and increase the interval between the negative group and the positive group as much as possible. However, if negative power is given to an eccentric rotationally asymmetric surface, eccentric aberration becomes too large and it is difficult to correct it, and it is particularly difficult to correct coma asymmetry.

Therefore, a concave lens should be placed on the object side, negative power should be given to a normal refracting lens, a negative group and a positive group should be spaced apart, and the optical axis should be folded back to make it compact. .

When an optical system component having an eccentric rotationally asymmetric reflecting surface is constituted by a single block and a stop is provided, it is better to provide a stop on the object side of the block without increasing the size of the block. preferable. At this time, it is preferable to dispose an optical member having an optical power of approximately zero, which also serves as a stop protection means, on the object side. Further, as another effect, when an electronic image pickup device is used, a function of dividing an in-plane region, giving a slight inclination to the surface for each region, and changing a traveling direction of light by a small amount is provided. If an optical low-pass filter function is provided according to the method, it is effective to shorten the back focus.

When an axial principal ray enters and exits a front optical unit disposed on the object side of an optical system component having an eccentric rotationally asymmetric reflecting surface, the amount of angular displacement is Δ
When θ and the displacement amount of the position are Δh, at least one of 0.1 ° <Δθ <45 ° (2) or 0 <Δh × Py <1.0 (3) Is desirable. Where P
y is the power of the optical system in the Y direction.

If both equations (2) and (3) take a small value exceeding the lower limit, there is no point in eccentricity. If both values exceed the upper limit and take a large value, the eccentric aberration in each part becomes too large, and it becomes difficult to correct.

More preferably, at least one of 1 ° <Δθ <30 ° (2) ′ or 0.005 <Δh × Py <0.5 (3) ′ is satisfied. .

By the way, when the first reflecting surface and the second transmitting surface of the optical system component having the decentered rotationally asymmetric reflecting surface are the same, three surfaces are formed, and the manufacturability is improved.

Further, when the first reflection surface is configured to utilize total reflection for reflection, a high reflectivity can be obtained as described above, light loss can be minimized, and the reflection surface and the transmission surface can be reduced. When they are the same, manufacturing becomes easy.

Further, as described above, by forming the optical system components having the decentered rotationally asymmetric reflection surface in a single block and reducing the number of constituent members, it is possible to expect a reduction in the size and cost of the optical system.

Further, the rotationally asymmetric reflecting surface is constituted as a back mirror of an optical material having a function of a wavelength selecting means, and the wavelength selecting means has a so-called infrared cut function, and has a mole% a of CuO contained in the optical material. However, it is desirable to satisfy the following conditions.

A <1 (4) A so-called infrared cut filter or the like can be manufactured by mixing impurities such as copper. However, it is difficult to control the wavelength selectivity as the impurities increase. Manufacturing becomes easier. Further, in order to improve the resistance of glass containing a large amount of copper and the like, it is common to use a fluorophosphoric acid-based network, but if the content can be reduced,
A highly resistant network structure can be adopted and is effective. However, if impurities are reduced, the thickness of the filter must be increased in order to ensure wavelength selectivity, and there is a problem that the lens system is enlarged in order to secure space.

In an optical system that folds the optical axis as in the present invention, an optical path length longer than the actual thickness can be obtained, so that an effective wavelength selection characteristic can be achieved with a small impurity content. The content of copper may be adjusted according to the optical path length of the designed optical system. However, when a is defined as mol% of CuO, it is preferable that a <1 (4) is satisfied.

It is more preferable that 1 × 10 ⁻⁵ <a <1 (4) ′.

It is more preferable that 1 × 10 ⁻⁵ <a <0.5 (4) ”.

In the image pickup optical system according to the present invention, it is preferable that at least one of the reflecting surfaces having an eccentric rotationally asymmetric surface is a plane-symmetric free-form surface having only one symmetric surface. Here, the free-form surface used in the present invention is defined by the following equation.

Z = C ₂ + C ₃ y + C ₄ x + C ₅ y ² + C ₆ yx + 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 yx 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 yx 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 ····· ··· (a) provided that, C _m (m 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 ₄ , C ₆ , C ₉ ,
_{C 11, C 13, C 15} , C 18, C 20, C 22, C 24, C 26, C
_{28, C 31, C 33,} C 35, C 37, 0 the coefficients of each term of ...
Is possible.

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 definition formula (a),
C ₃ , C ₆ , C ₈ , C ₁₀ , C ₁₃ , C ₁₅ , C ₁₇ , C ₁₉ , C
_{21, C 24, C 26,} C 28, C 30, C 32, C 34, C 36, ··
It is possible by setting the coefficient of each term of 0 to 0, and it is possible to improve the manufacturability by having the above-mentioned plane of symmetry.

By setting one of the symmetry plane parallel to the YZ plane and the symmetry plane parallel to the XZ plane as the symmetry plane,
It is possible to effectively correct rotationally asymmetric aberrations caused by eccentricity.

The above definition is shown as one example, and the feature of the present invention is to correct rotationally asymmetric aberrations caused by eccentricity on a rotationally asymmetric surface having only one symmetric surface. It goes without saying that the same effect can be obtained for any other defining formula.

In general, it is difficult to manufacture an optical system component having an eccentric rotationally asymmetric reflecting surface (eccentric prism optical system) by polishing, and it is preferable to form one by one by grinding, injection molding of plastic or glass molding. It will be produced by molding. At this time, it is necessary to confirm whether the surface of the decentered prism optical system is formed in a predetermined shape. A three-dimensional coordinate measuring device is generally used for measuring such a three-dimensional rotationally asymmetric shape, but it takes a long measurement time and is not practical.

In the present invention, it is important that at least one of the at least three surfaces constituting the decentered prism optical system 4 be a rotationally symmetric surface.

More preferably, the effective area is widest,
An eccentric prism that can easily evaluate the finished shape of the surface shape in a short time by configuring the surface having the transmission function and the internal reflection function on the side close to the pupil where the aberration degradation is relatively large as a rotationally symmetric surface The optical system has been successfully constructed.

Further, the decentered prism optical system of the rear optical unit has a first transmitting surface, a first reflecting surface, a second reflecting surface, and a second transmitting surface. The second reflecting surface has a rotationally asymmetric surface shape, is a plane-symmetric free-form surface having only one symmetric surface, and the first reflecting surface is common to the second transmitting surface. In the case of a surface, if this surface is given a strong power, the occurrence of chromatic aberration becomes large. In addition, it is sufficient that the area used as the first reflection operation surface and the region used as the second transmission operation surface can be substantially separated. However, this causes an increase in the size of the prism block constituting the rear optical unit. The area that overlaps with the second transmission action surface increases. Therefore, in order to achieve both the operation on the first reflection operation surface and the operation on the second transmission operation surface, it is easier to control without giving a strong power. That is, the only plane of symmetry of the plane-symmetric free-form surface is the YZ plane, the direction orthogonal to the plane is the X axis, and the intersection of the axial principal ray with the first and second reflection operation surfaces. When the powers in the nearby X direction are Px1 and Px2, respectively, it is desirable that | Px1 | <| Px2 | (5)

Further, it is desirable to satisfy the following condition: 1 <| Px2 / Px1 | <20 (6) If the upper limit of the condition 20 is exceeded, the power of the second reflecting surface becomes extremely strong,
Back focus cannot be ensured, and the complexity of the surface shape increases for aberration correction, which is not preferable. Further, it is more preferable to satisfy the following condition: 1.1 <| Px2 / Px1 | <10 (6) '.

Further, it is more preferable to satisfy the following condition: 2.0 <| Px2 / Px1 | <5 (6) ".

When the power in the X direction near the intersection of the axial principal ray with the second transmission action surface is Px3, the following expression may be satisfied: | Px3 / Px2 | <0.5 (7) desirable. That is, if the second transmission surface has a strong power, distortion and chromatic aberration are increased, which is not preferable. Therefore, it is desirable to satisfy the condition (7).

It is even more preferable to satisfy | Px3 / Px2 | <0.2 (7) '.

In the above description, the only plane of symmetry of the plane-symmetric free-form surface is the YZ plane, and the direction orthogonal to the plane is X
Axis, and the value of tan in the YZ plane of the normal of the surface at the position where the maximum angle of view in the X direction of the surface hits, and the value of the surface at the position where the axial chief ray hits the surface Assuming that the difference from the value of tan in the YZ plane of the normal is DY, it is preferable to satisfy the following condition: 0 ≦ | DY | <0.1 (8)

This conditional expression relates to, for example, a bow-shaped rotationally asymmetric image distortion that curves like a bow when a horizontal line is captured. As shown in the perspective view of FIG. 10A and the projection onto the YZ plane of FIG. 10B, the rotational asymmetry at the point where the principal ray having the maximum angle of view in the X direction intersects the rotationally asymmetric plane A is shown. The value of tan in the YZ plane of the normal n 'of the surface and the tan in the YZ plane of the normal n of the rotationally asymmetric surface at the point where the axial chief ray intersects the rotationally asymmetric surface A It is important that the condition (8) is satisfied when the difference from the value of is DY. Exceeding the lower limit of 0 to the above conditional expression makes it impossible to correct bow-shaped image distortion. If the upper limit of 0.1 is exceeded, bow-shaped image distortion will be overcorrected, and in both cases, the image will be bowed.

More preferably, it is preferable to satisfy the following condition: 0 ≦ | DY | <0.01 (8) ′.

The direction in which the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the only symmetrical surface of the plane-symmetric free-form surface is the YZ plane, and the direction orthogonal to the surface is the YZ plane. X axis, Y
The difference in curvature in the X direction between the principal ray having the maximum principal angle of view in the positive direction and the principal ray having the maximum angle of view in the negative Y direction is represented by Cx.
n, where Pxn is the power in the X direction of the portion where the axial principal ray hits the surface, it is important to satisfy the following condition: 0 ≦ | Cxn / Pxn | <10 (9) This conditional expression relates to image distortion generated in a trapezoid. If the upper limit of the above conditional expression (10) is exceeded, trapezoidal distortion will occur significantly, making it difficult to correct on other surfaces.

More preferably, it is preferable to satisfy the following condition: 0 ≦ | Cxn / Pxn | <1 (9) ′

The rotationally asymmetric surface is disposed in an optical system configured eccentrically, and is formed as a plane symmetric free-form surface such that a plane substantially identical to the eccentric surface of each eccentrically arranged surface becomes a symmetrical surface. The left and right sides can be made symmetrical with respect to the symmetry plane, so that aberration correction and manufacturability can be greatly improved.

Next, the power of the entire optical system in the X direction is represented by Px
When the power in the X direction of the portion of the rotationally asymmetric surface on which the axial chief ray hits is Pxn, the following conditional expression is satisfied: 0 <| Pxn / Px | <100 (10) It is preferable for correction. If the upper limit of the above conditional expression (100) is exceeded, the power of the rotationally asymmetric surface becomes too strong compared to the power of the entire optical system, and the rotationally asymmetric surface has too strong a refracting power. Cannot be corrected in other aspects. If the lower limit of 0 is exceeded, the power in the X-axis direction of the rotationally asymmetric surface is lost, and the power in the X-axis direction must be arranged as another surface, increasing the number of required surfaces. The use of the surface is contrary to the purpose of miniaturizing the optical system.

More preferably, if the condition of 0.05 <| Pxn / Px | <10 (10) 'is satisfied, rotationally asymmetric aberration can be favorably corrected, which is preferable in terms of aberration correction.

The power of the entire optical system in the Y direction is Py
Assuming that the power Pyn in the Y direction at the portion of the rotationally asymmetric surface on which the axial chief ray hits, the following conditional expression is satisfied: 0 <| Pyn / Py | <100 (11) Above. The meaning of the lower limit 0 and the upper limit 100 of the above conditional expression is determined by the conditional expression (1
0).

More preferably, if the condition of 0 <| Pyn / Py | <10 (11) ′ is satisfied, rotationally asymmetric aberration can be favorably corrected, which is preferable in terms of aberration correction.

Next, assuming that the powers of the entire optical system in the X and Y directions are Px and Py, the following conditional expression is satisfied: 0.3 <| Px / Py | <2 (12) Is preferable for aberration correction. If the lower limit of 0.3 and the upper limit of 2 in the above conditional expression are exceeded, the focal length of the entire optical system will be too different in the X and Y directions, making it difficult to obtain good image distortion and distorting the image.

More preferably, satisfying the following condition: 0.8 <| Px / Py | <1.2 (12) ′ enables rotationally asymmetric aberrations to be favorably corrected, which is preferable in terms of aberration correction.

Further, in the imaging optical system of the present invention, it is desirable that the lateral aberration of the optical system is 200 μm or less. In the present invention, when the lateral aberration of the optical system is 200 μm or less, the aberration can be sufficiently ignored, and good imaging performance can be obtained. Further, the image distortion of the imaging optical system of the present invention is 20% or less. It is desirable. In the present invention, when the image distortion of the optical system is 20% or less, the aberration can be sufficiently neglected, and good image forming performance can be obtained. In the case of a lens having positive power, the spread of light rays on the first reflecting surface can be suppressed, and the first reflecting surface can be reduced in size.

Further, the first reflection function surface is configured as a back mirror by arranging the light beam to travel in the order of the first transmission function surface, the first reflection function surface, and the second transmission function surface. It becomes possible. When the first reflecting surface is constituted by a back mirror, better results can be obtained with respect to the field curvature aberration than by a front mirror.

Further, by giving one or both of the first transmission action surface and the second transmission action surface the power of the same sign as that of the first reflection action surface, the field curvature is almost completely corrected. It becomes possible.

On the other hand, by setting the powers of the first transmitting action surface and the second transmitting action surface to substantially zero, a good result can be obtained with respect to chromatic aberration. This is because, in principle, chromatic aberration does not occur on the first reflecting surface, so that it is not necessary to correct chromatic aberration with other surfaces. Therefore, the power is set to approximately 0 so that chromatic aberration does not occur on the first transmission operation surface and the second transmission operation surface.
By doing so, it is possible to configure an optical system with less chromatic aberration in the entire optical system.

More preferably, the rear optical unit includes at least a first transmissive surface from the object side to the image side,
When the first reflection operation surface, the second reflection operation surface, and the second transmission operation surface are formed, and the second reflection operation surface is formed in a rotationally asymmetric surface shape, the two reflection operation surfaces are formed. The power can be changed, and the principal point position can be set in front of or behind the optical system in a combination of positive and negative or negative and positive. This can also give good results for field curvature.

Further, by forming the two reflecting surfaces as back mirrors, it is possible to almost eliminate curvature of field.
In particular, in the case of an electronic imaging optical system that requires a large back focus compared to the focal length, it is preferable to arrange negative power on the object side or set the first reflecting surface to negative power. However, when the power is increased in the latter case, the distortion becomes worse. Further, at this time, if the first reflection operation surface and the second transmission operation surface are the same, the negative power of the transmission operation surface is also increased, which causes deterioration of chromatic aberration. Therefore, the first
The reflection action surface is preferably shaped such that the area used as the reflection action surface is negative, and the power becomes weaker as it approaches the area used as the second transmission action surface, and the power becomes weaker as the second transmission action surface. In the case where negative power is disposed on the object side as in the former case, the first reflecting surface may be configured with weak positive or negative power.

When the image pickup optical system of the present invention is used as a photographing lens of an electronic image pickup device for forming an image on an electronic image pickup device, information of distortion and chromatic aberration of magnification of the optical system is processed in a processing section of the image pickup device. Pre-stored in memory etc.,
With the function of correcting using digital image processing technology based on that information, and correcting the distortion and chromatic aberration of magnification that occur in the optical system, the allowable amount of aberration to be corrected in the optical system increases, This is particularly effective when a small photographic lens that satisfies optical performance with a small number of lens components as in the present invention is used. Furthermore, even if the processing unit of the camera does not hold the information, it can be installed in a processing device such as a personal computer as data of image processing software and configured to perform image processing on the device, and the same function can be obtained. It goes without saying that you can have it.

The present invention includes an image pickup apparatus having an image pickup device arranged to receive an object image formed by the above-described image pickup optical system. In this case, it is preferable that the image sensor is formed by an electronic image sensor having a function of converting light received by the image sensor into electric information, and an observation unit for observing an object image received by the electronic image sensor. It is desirable to have.

[0081]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 of the imaging optical system according to the present invention will be described below. The configuration parameters of the first embodiment will be described later. In the configuration parameters, as shown in FIG. 1, the surface of the diaphragm 1 is set as the origin of the eccentric surface, and the axial principal ray 2 is set at the object center (omitted in the figure). A direction passing along the axial principal ray 2 from the center of the object to the first surface of the optical system is defined as a Z-axis.
A plane including the center is defined as a YZ plane, a Y axis is set in a direction orthogonal to the Z axis in the YZ plane, a direction from the object point to the first surface of the optical system is defined as a positive direction of the Z axis, and a Y axis is defined. Is defined as the upward direction in the drawing (the direction in which the light is reflected by the first reflecting surface 6). And
An axis constituting the right-handed orthogonal coordinate system with the Y axis and the Z axis is defined as an X axis.

In the first embodiment shown in FIG. 1, each plane is decentered in the YZ plane, and the only symmetric plane of each rotationally asymmetric free-form surface is formed as the YZ plane. For the eccentric surface, the amount of eccentricity (x, y, z, respectively) in the X-axis direction, the Y-axis direction, and the Z-axis direction from the center of the origin of the optical system at the top of the surface, and the center of the surface X-axis, Y-axis, and Z-axis (for a free-form surface, the Z-axis in the above-described equation (a))
Angle of inclination (°) about each axis (α,
β, γ) are given. In this case, α and β
Is positive counterclockwise with respect to the positive direction of each axis,
Positive γ means clockwise with respect to the positive direction of the Z axis.

Among the optical surfaces constituting the optical system according to the first embodiment, the spherical surface has a radius of curvature, and when a specific surface and a surface following the specific surface constitute a coaxial system, the surface spacing is reduced. In addition, the refractive index and Abbe number of the medium are given according to a conventional method.

The shape of the surface of the free-form surface is defined by the equation (a), and the Z axis of the definition expression is the axis of the free-form surface. Note that the term relating to the aspheric surface for which no data is described is zero. Regarding the refractive index, d-line (wavelength 58
7.56 nm). The unit of the length is mm.

As another definition of the free-form surface, Zer
There is a nice polynomial. The shape of this surface is given by the following equation (b)
Defined by The Z axis of the defining equation is the axis of the Zernike polynomial. X = R × cos (A) Y = R × sin (A) Z = D ₂ + D ₃ R cos (A) + D ₄ R sin (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) (b) FIG. 1 shows a YZ sectional view including the axial chief ray 2 of the first embodiment. In the figure, 1 is an aperture, 2 is an axial principal ray, 4 is an eccentric prism optical system constituting the rear group on the image side of the aperture 1, 5 is a first surface of the eccentric prism optical system, 6 is a second surface, 7 Denotes a third surface, 8 denotes an image surface, and 9 denotes filters such as an infrared cut filter, an optical low-pass filter, and a cover glass. The first surface 5 of the decentered prism optical system 4 has a first transmission (operation) surface of the rear unit, the second surface 6 has a first reflection (operation) surface and a second transmission (operation) surface, and a third surface. Surface 7 constitutes a second reflecting (working) surface. In the first embodiment, the front unit is not arranged on the object side of the stop 1.

Then, a light beam emitted from an object not shown is
The light passes through the first surface 5 of the decentered prism optical system 4 of the rear group, passes through the opening of the diaphragm 1, enters the inside, is reflected by the second surface 6, and then is reflected by the third surface 7, and this time the second surface The transmitted light 6 passes through the decentered prism optical system 4 to form an object image on an image plane 8 via filters 9.

The size of the image is １ ／ of about 4 × 3 mm.
Although the size is optimized assuming the inch size, it goes without saying that other sizes can be applied by multiplying the whole by a coefficient. Further, the present invention includes not only an imaging optical system but also an imaging device incorporating the optical system.

The specifications of the first embodiment are based on a horizontal half angle of view of 21.32.
°, vertical half angle of view 16.31 °, entrance pupil diameter 2.061m
m, the size of the image is 3.90 × 2.93 mm. This embodiment has no front unit on the object side with respect to the stop 1, and is an embodiment in which the imaging optical system is constituted only by the eccentric prism optical system 4.

This embodiment is an example in which two rotationally asymmetric free-form surfaces having one symmetric surface are used, and the stop 1, the first transmitting surface 5, the first reflecting surface 6, The first reflection surface and the second transmission surface are composed of the same surface 6, and the first reflection surface uses total reflection. It is composed of few faces. In this embodiment, a rotationally symmetric spherical surface is used for the first reflection surface 6 (second transmission surface 6), and it is also possible to use a rotationally symmetric aspheric surface.

Although the constituent parameters will be described later, the amount of eccentricity is expressed as the amount of eccentricity from the first surface, and the sixth surface is a virtual surface. The seventh and subsequent surfaces represent various optical members (filters 9) such as an infrared cut filter, an optical low-pass filter, and a cover glass.

FIG. 2 shows the state of lateral aberration for each angle of view in this embodiment, and FIG. 3 shows the state of distortion. FIG. 2 showing lateral aberration
In the figure, the numbers in parentheses indicate (horizontal (X direction) angle of view, vertical (Y direction) angle of view), and show lateral aberration diagrams at the angle of view. Hereinafter, the configuration parameters of the first embodiment will be described.

Example 1 Surface Number Curvature Radius Interval Eccentricity Refractive Index Abbe Number Object Surface ∞ ∞ 1 ∞ (aperture) 2 Free-form surface [1] Eccentricity (1) 1.8061 40.9 3 25.588 Eccentricity (2) 1.8061 40.9 4 Free-form surface [2 ] Eccentricity (3) 1.8061 40.9 5 25.588 Eccentricity (2) 6 ∞ 0.00 Eccentricity (4) 7 ∞ 1.00 1.5163 64.1 8 ０．４ 0.40
1.5163 64.1 Image surface ∞ Free-form surface [1] C ₅ -1.2542 × 10 ^-2 C ₇ -4.2947 × 10 ^-2 C ₁₀ 2.5821 × 10 ^-3 C ₁₄ 6.6025 × 10 ^-3 C ₁₉ -3.0926 × 10 ^-4 C ₂₁ -6.0066 × 10 ^-4 Free-form surface [2] C ₅ -4.3080 × 10 ^-2 C ₇ -4.2205 × 10 ^-2 C ₈ 6.5283 × 10 ^-4 C ₁₀ 2.0953 × 10 ^-4 C ₁₂ -1.8831 × 10 ^-4 C ₁₄ -1.1569 × 10 ^-4 C ₁₆ -1.0976 × 10 ^-4 C ₁₇ 2.0676 × 10 ^-5 C ₁₉ 3.1183 × 10 ^-5 C ₂₁ 1.7044 × 10 ^-5 Eccentricity (1) x 0.000 y 0.000 z 1.768 α 14.63 β 0.00 γ 0.00 Eccentricity (2) x 0.000 y 0.318 z 4.518 α -41.57 β 0.00 γ eccentricity (3) x 0.000 y 3.086 z 4.506 α 109.22 β 0.00 γ 0.00 Eccentricity (4) x 0.000 y -2.821 z 8.493 α -54.38 β 0.00 γ 0.00.

It is to be noted that each of the conditional expressions (1) and
The values for (5) to (12) are as shown in the table below.
However, some values relating to the first reflecting surface 6 which is a spherical surface are also shown. Here, DY1 and DY2 are the first reflecting surface 6, the second
DY, Px1 and Px2 of the reflecting surface 7 are the first reflecting surface 6 and the second
Pxn, Py1, and Py2 of the reflection surface 7 are the first reflection surface 6, and Pyn, Cx1, and Cx2 of the second reflection surface 7 are the first reflection surface 6,
Cxn of the second reflection surface 7. DTx and DTy are the maximum values (%) of the distortion in the X and Y directions, respectively.

[0094]

The imaging optical system of the present invention as described above is used for an imaging device such as a small TV camera using a CCD as an imaging device. FIG. 4 shows a conceptual diagram of a configuration in which the imaging optical system 10 of the present invention is incorporated in an imaging device using a CCD 11 as an electronic imaging device. In this imaging apparatus, an object image is formed by an imaging optical system 10 on a CCD 11 disposed on an image plane via filters 9 such as an infrared cut filter and an optical low-pass filter, and the object image is converted into a video signal by the CCD 11. The converted video signal is directly displayed on the CRT 13 acting as an electronic finder by the processing means 12, and is recorded in the recording medium 14 built in the imaging device. Further, the imaging device includes a microphone 15, and performs audio information recording simultaneously with video signal recording. Further, as described above, in the processing unit 12, information on the distortion and the chromatic aberration of magnification of the imaging optical system 10 is stored in the recording medium 14 or a memory attached to the processing unit 12 in advance, and based on the information, The distortion and the chromatic aberration of magnification generated in the optical system 10 may be corrected by using a digital image processing technique.

In such an image pickup apparatus, the number of components of the image pickup optical system 10 is reduced and the size of the image pickup optical system 10 is reduced according to the present invention, so that the apparatus can be reduced in size and cost.

The above-described image pickup optical system of the present invention and an image pickup apparatus using the same can be constituted, for example, as follows. [1] In an imaging optical system for forming an object image on an imaging element surface, the imaging optical system has a rear optical unit at least on an image side of a pupil plane, and the rear optical unit emits a pupil by projecting an object center. When the ray that reaches the image center through the center is the axial chief ray,
A prism member having at least three surfaces eccentrically arranged so that the entire surface is inclined with respect to the principal ray, wherein the at least three surfaces have a surface having a transmission function, and a reflection function and a transmission function. An imaging optical system comprising: a curved surface having a rotationally symmetrical surface shape and a rotationally asymmetrical surface shape that has a reflecting action and corrects rotationally asymmetrical eccentric aberration caused by eccentricity.

[2] In the above item [1], the curved surface having a rotationally symmetric surface shape that shares the reflection function and the transmission function is formed by a total reflection surface or a semi-transmission reflection surface. Optical system.

[3] The imaging optical system according to the above [1], wherein the reflecting surface is formed by a coated mirror surface.

[4] In the above item [1], the surface having the reflection function is arranged to face the surface sharing the reflection function and the transmission function, and the axial principal ray is incident on the optical system. When the direction up to is the Z-axis direction, the eccentric plane of the surface is the Y-axis direction, the Y-axis, the axis constituting the orthogonal coordinate system with the Z-axis is the X-axis, from the incident surface side of the optical system, A parallel luminous flux slightly separated by d in the Y direction from the on-axis principal ray is made incident, and the angle sin formed by the two rays in the YZ plane on the side exiting from the optical system is NA′yi, NA′yi. The value NA′yi / d obtained by dividing yi by the width d of the parallel light flux is calculated as Y ′ of the optical system.
0.1 <p × Py <8 (1) where p is the optical power in the direction and p is the optical path length of the axial principal ray from the entrance surface of the prism member to the exit surface of the prism member. An imaging optical system characterized by satisfying the following.

[5] Any one of the above [1] to [4]
In the above item, the prism member is composed of a first surface having a transmission function sandwiching a medium having a refractive index of more than 1, a second surface having a reflection function and a transmission function, and a third surface having a reflection function. Light from an object is incident on the first surface, is reflected on the second surface, is reflected on the third surface, and is transmitted through the second surface and is emitted. Imaging optical system.

[6] The imaging optical system according to the above [5], wherein the prism member is formed as a single unitary block.

[7] Any one of the above [1] to [6]
9. The imaging optical system according to item 1, wherein an infrared cut filter having an action of cutting an infrared component of an object image formed by the optical system is disposed in the optical system.

[8] Any one of the above [1] to [6]
In the above item, at least one of the surfaces having the reflecting action described above.
An imaging optical system, wherein the surface is constituted by a back mirror of a wavelength selection optical member having an action of transmitting or blocking a specific wavelength.

[0105]

[9] The imaging optical system according to the above [8], wherein the wavelength selection optical member has an infrared cut function.

[10] The imaging optical system according to the above [6], wherein the medium of the prism member has an infrared cut function.

[11] The imaging optical system according to [10], wherein the medium of the prism member satisfies the following condition (4). a <1 (4) where is the mole% of CuO contained in the prism member.

[12] The imaging optical system according to [11], wherein the following condition (4) ′ is satisfied.

1 × 10 ⁻⁵ <a <1 (4) ′ [13] In any one of the above items [1] to [12], the reflection action surface having the rotationally asymmetric surface shape is symmetric. An imaging optical system comprising a plane-symmetric free-form surface having only one surface.

[14] In the above [13], the only plane of symmetry of the plane symmetric free-form surface is the YZ plane, the direction orthogonal to the plane is the X axis, and the first principal axis of the axial principal ray is the first axis. | Px1 | <| Px2 | (5) where the powers in the X direction near the intersection with the reflection action surface and the second reflection action face are Px1 and Px2, respectively. Optical system.

[15] The imaging optical system according to the above [14], wherein 1 <| Px2 / Px1 | <20 (6).

[16] In the above [13], the only plane of symmetry of the plane-symmetric free-form surface is the YZ plane, the direction orthogonal to the plane is the X axis, and the second axis of the axial principal ray is the second axis. When the power in the X direction near the intersection with the reflection action surface is Px2 and the power in the X direction near the intersection of the axial principal ray with the second transmission action surface is Px3, | Px3 / Px2 | < 0.5 (7) An imaging optical system, wherein:

[17] In the above [13], the only plane of symmetry of the plane-symmetric free-form surface is the YZ plane, the direction orthogonal to the plane is the X axis, and the maximum angle of view of the plane in the X direction is The tan in the YZ plane of the normal to the surface at the position where the ray hits
Is the difference between the value of tan and the value of tan in the YZ plane of the normal to the surface at the position where the on-axis chief ray hits the surface, where 0 ≦ | DY | <0.1 (8) An imaging optical system characterized by satisfying the following.

[18] In the above [13], the direction in which the axial chief ray reaches the first surface of the optical system is the Z-axis direction, and the only plane of symmetry of the plane-symmetric free-form surface is YZ. The direction orthogonal to the surface is defined as the X axis, and the difference between the curvature in the X direction of the portion where the principal ray having the maximum angle of view in the Y positive direction and the principal ray having the maximum angle of view in the Y negative direction is in contact with the surface. Cxn, where Pxn is the power in the X direction of the portion where the on-axis principal ray hits the surface, 0 ≦ | Cxn / Pxn | <10 (9).

[19] In any one of the above items [13] to [18], at least one of the eccentric surfaces of the prism member may be such that a surface including the eccentric direction substantially coincides with the symmetric surface. An imaging optical system which is eccentrically arranged.

[20] In the above [19], the eccentric directions of all the eccentric surfaces of the prism member are all on the same plane, and the plane including the eccentric directions substantially coincides with the symmetric plane. An imaging optical system characterized by being formed.

[21] In the above [18] or [19], the direction in which the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the eccentric plane is the Y-axis direction, Y axis, Z
When the axis constituting the orthogonal coordinate system with the axis is the X axis, the axis chief ray and the minute amount d in the X direction from the incident surface side of the optical system.
The divergent parallel light beam is incident, and the angle sin formed in the plane including the axial principal ray perpendicular to the YZ plane of the two rays on the side exiting from the optical system is defined as NA′xi, N
The value NA'xi / A'xi / A'xi divided by the width d of the parallel light flux
When d is the power Px in the X direction of the optical system and Pxn is the power in the X direction of the portion of the rotationally asymmetric surface that the axial chief ray impinges, 0 <| Pxn / Px | <100. (10) An imaging optical system characterized by satisfying the following.

[22] An imaging optical system according to [21], wherein the following condition is satisfied: 0.05 <| Pxn / Px | <10 (10) '.

[23] In the above item [18] or [19], the direction in which the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the eccentric plane is the Y-axis direction, Y axis, Z
When the axis constituting the orthogonal coordinate system with the axis is the X axis, the axis chief ray and the minute amount d in the Y direction from the incident surface side of the optical system.
The sine of the angle formed between the two light rays in the YZ plane on the side where the separated parallel light beams are incident and emitted from the optical system is represented by N
A′yi, a value obtained by dividing the NA′yi by the width d of the parallel light flux, NA′yi / d is a power Py of the optical system in the Y direction.
When the power in the Y direction of the portion of the rotationally asymmetric surface where the axial principal ray falls is defined as Pyn, 0 <| Pyn / Py | <100 (11) is satisfied. Optical system.

[24] The imaging optical system according to [23], wherein 0 <| Pyn / Py | <10 (11) 'is satisfied.

[25] In the above-mentioned [19] or [20], the direction in which the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the eccentric plane is the Y-axis direction, Y axis, Z
When the axis constituting the orthogonal coordinate system with the axis is the X axis, the axis chief ray and the minute amount d in the Y direction from the incident surface side of the optical system.
The sine of the angle formed between the two light rays in the YZ plane on the side where the separated parallel light beams are incident and emitted from the optical system is represented by N
A′yi, a value obtained by dividing the NA′yi by the width d of the parallel light flux, NA′yi / d is a power Py of the optical system in the Y direction.
The direction in which the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the eccentric plane is the Y-axis direction, the Y-axis
When the axis constituting the orthogonal coordinate system with the axis is the X axis, the axis chief ray and the minute amount d in the X direction from the incident surface side of the optical system.
The divergent parallel light beam is incident, and the angle sin formed in the plane including the axial principal ray perpendicular to the YZ plane of the two rays on the side exiting from the optical system is defined as NA′xi, N
The value NA'xi / A'xi / A'xi divided by the width d of the parallel light flux
When d is the power Px in the X direction of the optical system, 0.3 <| Px / Py | <2 (12) is satisfied.

[26] An imaging optical system according to [25], wherein 0.8 <| Px / Py | <1.2 (12) 'is satisfied.

[27] The imaging optical system according to any one of [1] to [26], wherein the optical system has a lateral aberration of 200 μm or less.

[28] The imaging optical system according to any one of [1] to [26], wherein the image distortion of the optical system is 20% or less.

[29] The imaging apparatus according to any one of [1] to [27], further including an imaging element arranged to receive an object image formed by the optical system.

[30] The imaging apparatus according to [29], wherein the imaging apparatus is formed of an electronic imaging element having a function of converting light received by the imaging element into electrical information.

[31] The imaging apparatus according to [30], further comprising an observation unit for observing the object image received by the electronic imaging element.

[0128]

As is apparent from the above description, according to the present invention, it is possible to provide an image pickup optical system which is small in size and generates less aberration as compared with a rotationally symmetric transmission optical system.

[Brief description of the drawings]

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

FIG. 2 is a lateral aberration diagram of the first embodiment.

FIG. 3 is a distortion diagram of the first embodiment.

FIG. 4 is a conceptual diagram of a configuration in which the imaging optical system of the present invention is incorporated in an imaging device.

FIG. 5 is a diagram for explaining an axial principal ray and a coordinate system according to the present invention.

FIG. 6 is a conceptual diagram for explaining field curvature caused by an eccentric reflecting surface.

FIG. 7 is a conceptual diagram for explaining astigmatism generated by a decentered reflecting surface.

FIG. 8 is a conceptual diagram for explaining coma generated by a decentered reflecting surface.

FIG. 9 is a diagram for explaining the power of the imaging optical system of the present invention.

FIG. 10 is a diagram for explaining a parameter DY used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Stop 2 ... On-axis principal ray 3 ... Front group 4 ... Rear group (eccentric prism optical system) 5 ... 1st surface of eccentric prism optical system 6 ... 2nd surface of eccentric prism optical system 7 ... eccentric prism optical system Third surface 8 ... Image surface 9 ... Filters 10 ... Imaging optical system 11 ... CCD 12 ... Processing means 13 ... CRT 14 ... Recording medium 15 ... Microphone

Claims (4)

[Claims] 1. An imaging optical system for forming an object image on an imaging element surface, comprising: a rear optical group at least on an image side of a pupil plane; When a ray reaching the image center through the center of the pupil is defined as an axial principal ray, the prism member having at least three surfaces eccentrically arranged so that the entire surface is inclined with respect to the principal ray, At least three surfaces having a permeable effect;
An imaging optics characterized by comprising a curved surface having a rotationally symmetric surface shape that shares a reflection function and a transmission function, and a curved surface having a rotationally asymmetric surface shape having a reflection effect and correcting rotationally asymmetrical eccentric aberration caused by eccentricity. system. 2. The imaging optical system according to claim 1, wherein the curved surface having a rotationally symmetric surface shape that shares the reflection function and the transmission function is formed by a total reflection surface or a semi-transmission reflection surface. . 3. The imaging optical system according to claim 1, wherein said reflection surface is formed by a coated mirror surface. 4. The optical system according to claim 1, wherein the surface having the reflection function is arranged to face a surface sharing the reflection function and the transmission function, and the axial chief ray reaches the incident surface of the optical system. When the axis of the optical system is X-axis, the Z-axis direction is the direction up to the axis, and the X-axis is the Y-axis direction within the eccentric plane of the surface, and the X-axis is the axis forming the orthogonal coordinate system with the Z-axis. A principal ray and a parallel light beam separated by a small amount d in the Y direction are made incident, and the angle sin formed by the two rays in the YZ plane on the exit side from the optical system is NA′yi, and the NA′yi is The value NA′yi / d divided by the width d of the parallel light flux is defined as the power Py in the Y direction of the optical system, and the optical path length of the axial principal ray from the entrance surface of the prism member to the exit surface of the prism member. To p
Where 0.1 <p × Py <8 (1).