WO2011077988A1

WO2011077988A1 - Imaging optical system

Info

Publication number: WO2011077988A1
Application number: PCT/JP2010/072361
Authority: WO
Inventors: 恵子山田
Original assignee: コニカミノルタオプト株式会社
Priority date: 2009-12-23
Filing date: 2010-12-13
Publication date: 2011-06-30
Also published as: JPWO2011077988A1

Abstract

An imaging optical system has at least three reflective surfaces as optical surfaces with power, and an intermediate image is formed in the optical system. Along the optical path, the reflective surface nearest the object and the reflective surface nearest the image are both concave, and at least one of the reflective surfaces has a non-rotationally symmetric shape having a single plane of symmetry, and the condition 1.1<L/F<3.0 is fulfilled (where L is the width of the effective region of the reflective surface nearest the image in the yz plane, and F is the width of the effective region of the reflective surface (S1) nearest the object in the yz plane).

Description

Imaging optical system

The present invention relates to an imaging optical system having a reflecting surface, and more specifically, for example, an imaging optical system that forms an optical image of a subject with infrared rays (particularly far infrared rays), an imaging optical device including the imaging optical system, and an image input function It relates to digital equipment.

Research on imaging optical systems that perform imaging using infrared rays has been actively conducted. For example, Patent Document 1 proposes an imaging optical system having a configuration in which a reflective surface and a refractive surface are combined, and realizes a bright F number necessary for an infrared imaging optical system. Patent Document 2 proposes an imaging optical system consisting only of a reflecting surface, and has an intermediate image in the optical path. Patent Document 3 proposes an imaging optical system in which a surface having power is configured by only a reflecting surface. Patent Document 4 proposes an imaging optical system that forms an intermediate image using a reflecting surface, although infrared rays are not intended for imaging.

JP-A-10-206986 International Publication No. 2002/084364 JP 2009-180752 A JP 2000-2331060 A

Since the influence of diffraction is larger in the infrared region than in the visible region, it is necessary to brighten the F-number of the imaging optical system in order to reduce the imaged spot. In Patent Document 1, a bright F number is realized by a combination of a reflecting surface and a refracting surface. However, materials that can be transmitted with respect to wavelengths in the infrared region are limited to Ge, Si, ZnS, and the like. There is a problem that these materials are expensive, and there is also a problem that a shape that can be manufactured is limited because processing is difficult. In addition, since any material that transmits the infrared region has a refractive index of 2 or more, there is a problem that a ghost caused by reflection of light rays on the optical surface is large.

On the other hand, when the imaging optical system is configured with only the reflective surface, the cost can be reduced compared with the configuration where the imaging optical system is configured only with the refracting surface. It is difficult to realize a bright imaging optical system. For example, Patent Document 2 proposes an imaging optical system that forms an intermediate image. However, since the imaging optical system is composed of two reflecting surfaces, the F-number differs between the long side direction and the short side direction on the imaging screen. The F number in the long side direction is dark.

Patent Document 3 proposes an imaging optical system that includes three reflecting surfaces and does not form an intermediate image. However, a configuration with an F number of 2 or less cannot be realized. Patent Document 4 proposes an imaging optical system that includes a reflecting prism and forms an image using visible light, and realizes a compact configuration by folding light rays, but a configuration when the F-number becomes brighter. Is not mentioned. Further, in an optical system using a reflecting prism (such as Patent Document 4), chromatic aberration occurs in the reflected light path. Furthermore, it is difficult to manufacture a prism having a rotationally asymmetric curved surface using a material such as germanium or silicon from the viewpoint of processing difficulty, cost, and transmittance.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a high-performance and compact reflective imaging optical system having a bright F number suitable for infrared imaging and an imaging optical system having the same. It is to provide an apparatus and a digital device.

To achieve the above object, the imaging optical system of the first invention is an imaging optical system having at least three reflecting surfaces as optical surfaces having power, and having an intermediate image in the optical system, The reflection surface closest to the object side and the reflection surface closest to the image side along the optical path are both concave surfaces, and at least one reflection surface is a non-rotationally symmetric reflection surface having a single symmetry surface. When the yz plane in the orthogonal coordinate system (x, y, z) is satisfied, the following conditional expression (1) is satisfied.
1.1 <L / F <3.0 (1)
However,
L: effective area width of the most image-side reflecting surface in the yz section,
F: effective area width of the reflecting surface closest to the object in the yz section,
It is.

The imaging optical system according to a second aspect of the present invention is the imaging optical system according to the first aspect, wherein the principal ray incident on the center of the effective area of the screen is the screen center principal ray, the screen center principal ray exists on the yz plane, and Conditional expression (2) is satisfied.
0.3 <Ro_y / Ri_y <0.8 (2)
However,
Ro_y: curvature in the y direction that the most object-side reflecting surface in the yz section has at the intersection with the screen center principal ray,
Ri_y: curvature in the y direction that the most image-side reflecting surface in the yz section has at the intersection with the screen center principal ray,
It is.

The imaging optical system according to a third aspect of the present invention is the imaging optical system according to the first or second aspect, wherein the non-rotationally symmetric reflecting surface has a positive power in the x direction over the entire effective area on the yz cross section. It is characterized in that the curvature in the x direction is larger than the curvature.

An imaging optical system according to a fourth aspect of the present invention includes the at least one surface satisfying the following conditional expression (3) as the non-rotationally symmetric reflecting surface in any one of the first to third aspects. It is characterized by that.
0 <| Ry / Rx | <0.8 (3)
However,
Rx: curvature in the x direction at the center of the effective region in the yz section,
Ry: curvature in the y direction at the center of the effective region in the yz section,
It is.

The imaging optical system according to a fifth aspect of the present invention is the imaging optical system according to any one of the first to fourth aspects, wherein two or more reflecting surfaces having power are positioned on the optical path closer to the image side than the position of the intermediate image. The second reflecting surface counted from the image side is the non-rotationally symmetric reflecting surface, and in the yz section, the power in the y direction at the center of the effective area of the reflecting surface closest to the image side is counted from the image side. It is characterized by being stronger than the power in the y direction at the center of the effective area of the second reflecting surface.

An imaging optical system according to a sixth invention is characterized in that, in any one of the first to fifth inventions, the intermediate image does not have an intersection with a reflecting surface.

An imaging optical system according to a seventh invention is characterized in that, in any one of the first to sixth inventions, the following conditional expressions (4A) and (4B) are satisfied.
0.4 <Dx1 / Dx2 <0.7 (4A)
0.4 <Dy1 / Dy2 <0.8 (4B)
However,
Dx1: the maximum effective area width in the x direction of the reflecting surface located adjacent to the object side of the intermediate image,
Dx2: the maximum effective area width in the x direction of the reflecting surface located adjacent to the image side of the intermediate image,
Dy1: Maximum effective area width on the yz section of the reflecting surface located adjacent to the object side of the intermediate image, Dy2: Maximum effective area on the yz section of the reflecting surface located adjacent to the image side of the intermediate image width,
It is.

The imaging optical system according to an eighth aspect of the present invention is the imaging optical system according to any one of the first to seventh aspects, wherein the light beam reflected by the second reflecting surface counting from the object side in the yz section is the most object side. The reflection surface is bent in a direction approaching a light beam incident from the object side.

The imaging optical system of the ninth invention has an intermediate image in the optical system, and has two or more non-rotationally symmetric reflecting surfaces having only one symmetry plane on the object side of the position of the intermediate image. If the plane of symmetry is the yz plane in the Cartesian coordinate system (x, y, z), and the principal ray incident on the center of the effective area of the screen is the screen center principal ray, the screen center principal ray exists on the yz plane. The following conditional expression (5) is satisfied.
0.3 <Ro_x / Ro2_x <0.8 (5)
However,
Ro_x: curvature in the x direction that the reflecting surface closest to the object side in the yz section has at the intersection with the screen center principal ray,
Ro2_x: curvature in the x direction that the second reflecting surface from the object side in the yz section has at the intersection with the screen center principal ray,
It is.

The imaging optical system according to a tenth aspect of the present invention is characterized in that, in any one of the first to ninth aspects of the invention, the optical surface having power has only a reflecting surface.

An imaging optical system according to an eleventh aspect of the present invention is the optical system according to any one of the first to tenth aspects of the invention, having only four reflecting surfaces as optical surfaces having power, and three from the second reflecting surface from the object side. An intermediate image is located in the optical path to the second reflecting surface.

An imaging optical device according to a twelfth aspect of the invention is an imaging optical system according to any one of the first to eleventh aspects of the invention, an imaging element that converts an optical image formed on the light receiving surface into an electrical signal, The imaging optical system is provided so that an optical image of a subject is formed on the light receiving surface of the imaging device.

The imaging optical device according to a thirteenth invention is characterized in that, in the twelfth invention, the imaging optical system forms an optical image of a subject with infrared rays.

The imaging optical device according to a fourteenth invention is characterized in that, in the thirteenth invention, the infrared wavelength region is 5 μm to 11 μm.

The digital apparatus according to the fifteenth aspect of the invention is characterized in that at least one of a still picture shooting and a moving picture shooting of a subject is added by including the imaging optical device according to the twelfth aspect of the invention.

According to the present invention, since the reflection surface is effectively used, a high-performance and compact reflection-type imaging optical system having a bright F number suitable for infrared imaging, and imaging provided with the same An optical device can be realized. By using the imaging optical device according to the present invention in a digital device such as a digital camera or an in-vehicle camera, a high-performance infrared image input function can be added to the digital device in a compact manner.

1 is an optical path diagram showing an optical configuration of a first embodiment (Example 1). The optical path figure which shows the optical structure of 2nd Embodiment (Example 2). The optical path figure which shows the optical structure of 3rd Embodiment (Example 3). 2 is a spot diagram of Example 1. FIG. 10 is a spot diagram of Example 2. FIG. FIG. 6 is a spot diagram of Example 3. FIG. The figure which shows the example of schematic structure of the digital device carrying an imaging optical device in a typical cross section.

Hereinafter, an imaging optical system, an imaging optical device, a digital device, and the like according to the present invention will be described. An imaging optical system according to the present invention is an imaging optical system having at least three reflecting surfaces as optical surfaces having power, and having an intermediate image in the optical system, and is most reflective on the object side along the optical path. The surface and the most image-side reflecting surface are both concave, and at least one reflecting surface is a non-rotationally symmetric reflecting surface having a single symmetric surface. The symmetric surface is represented by an orthogonal coordinate system (x, y, z). Yz plane in (1)), the following conditional expression (1) is satisfied (power: an amount defined by the reciprocal of the focal length).
1.1 <L / F <3.0 (1)
However,
L: effective area width of the most image-side reflecting surface in the yz section,
F: effective area width of the reflecting surface closest to the object in the yz section,
It is.

When constructing an imaging optical system suitable for infrared imaging, the use of a refractive surface limits the materials. Materials that can be used for refraction in the infrared region have problems in terms of cost, increased processing difficulty, ghost effects, etc., so at least three reflective surfaces are used as optical surfaces having power. It is preferable.

Also, since the influence of diffraction is larger in the infrared region than in the visible region, it is necessary to brighten the F number. For example, assuming that the infrared wavelength band is 8 to 16 μm and the pixel pitch of the image sensor is 20 μm, a bright F number of about 1 to 2 is required. If the imaging optical system is configured with a reflecting surface, it is not affected by the wavelength and can support a wide wavelength band. However, it is necessary to lengthen the back focus in order to avoid interference of the optical path. If the back focus is lengthened, it becomes difficult to make the system compact. Therefore, it becomes a problem to achieve both a bright F number and compactness.

When a configuration having an intermediate image in the optical system is used, the light flux width is once reduced in the optical system, so that both brightness and a reduction in the size of the optical system can be achieved. In other words, once the image is formed so as to form an intermediate image in the optical system, the degree of freedom at the time of re-imaging increases, so that it is possible to easily achieve both a bright F number and compactness.

If the reflecting surface closest to the object side is concave, the width of the light beam incident on the imaging optical system is reduced in the vicinity of the entrance aperture, so that it is possible to effectively reduce the size of the optical system. Further, when the reflecting surface closest to the image side is concave, a bright F number can be realized while preventing interference between the light beam and the optical member (for example, the substrate of the image sensor disposed at the image surface position). .

When the imaging optical system is provided with a non-rotationally symmetric reflecting surface having a single symmetric surface, various aberrations generated in the optical system can be favorably corrected. Examples of non-rotationally symmetric shapes with a single symmetric surface include free-form surface shapes and anamorphic surface shapes, but from the viewpoint of aberration correction in imaging optical systems using reflective surfaces, free-form surface shapes with a single symmetric surface It is preferable to provide a reflective surface. For example, on the most object-side reflecting surface and the most image-side reflecting surface, a free-form surface is effective for correcting field curvature. Further, in the case of a configuration having only four reflecting surfaces as optical surfaces having power, it is effective for correcting astigmatism to use a free curved surface as the second reflecting surface from the object side.

Conditional expression (1) defines a preferable condition range regarding the ratio of the effective area width between the most object-side reflecting surface (first reflecting surface) and the most image-side reflecting surface (final reflecting surface). The effective area widths F and L are, for example, as shown in the optical path diagram of FIG. 7, when the only symmetry plane of the non-rotationally symmetric reflection plane is the yz plane in the orthogonal coordinate system (x, y, z). The effective area widths of the first and fourth reflecting surfaces S1 and S4 in the yz section are shown. By limiting the magnification between the intermediate image and the image so as to satisfy the conditional expression (1), the F-number can be reduced. Since the size of the effective area width F is determined to some extent by the aperture ST and the size of the field angle, exceeding the upper limit of the conditional expression (1) means that the effective area width L is increased. Therefore, if the upper limit of conditional expression (1) is exceeded, the optical system size will increase. On the other hand, if the lower limit of conditional expression (1) is exceeded, interference between the image plane and the light flux occurs, or it becomes difficult to correct curvature of field that occurs on the most image-side reflecting surface.

According to the above characteristic configuration, the reflection surface is effectively used, and thus a high-performance and compact reflection type imaging optical system having a bright F number suitable for infrared photography and the same are provided. An imaging optical device can be realized. In addition, since the imaging optical device is lighter and smaller, if the imaging optical device is used in a digital device such as a digital camera or an in-vehicle camera, a high-performance infrared image input function is added to the digital device in a lightweight and compact manner. Is possible. Therefore, it can contribute to the downsizing, high performance, high functionality, etc. of digital equipment. The conditions for achieving such effects in a well-balanced manner and achieving higher optical performance, downsizing, etc. will be described below.

If the principal ray incident on the center of the effective area of the screen is the screen center principal ray, it is desirable that the screen center principal ray exists on the yz plane and satisfies the following conditional expression (2).
0.3 <Ro_y / Ri_y <0.8 (2)
However,
Ro_y: curvature in the y direction that the most object-side reflecting surface in the yz section has at the intersection with the screen center principal ray,
Ri_y: curvature in the y direction that the most image-side reflecting surface in the yz section has at the intersection with the screen center principal ray,
It is.

Conditional expression (2) defines a preferable range of conditions for realizing a compact reflective optical system having a small F-number. The curvatures Ro_y and Ri_y represent the curvatures in the y direction that the first and fourth reflecting surfaces S1 and S4 have at the intersections with the screen center principal ray PR in the yz section, for example, as shown in the optical path diagram of FIG. . When the lower limit of conditional expression (2) is exceeded, the power of the most image-side reflecting surface (for example, the fourth reflecting surface S4) becomes strong, and astigmatism generated there increases. It is difficult to correct this with another reflecting surface (for example, the third reflecting surface S3), and it is also difficult to prevent interference between the light beam and the image surface. On the other hand, when the upper limit of conditional expression (2) is exceeded, the power of the most object-side reflecting surface (first reflecting surface S1) becomes strong, leading to an increase in the size of the optical system. In addition, since the intermediate image IS approaches the second reflecting surface S2, if the astigmatism is corrected by the second reflecting surface S2, it is necessary to apply power to the second reflecting surface S2, and astigmatism is reduced. Incorrect correction. As a result, it becomes difficult to prevent the intermediate image plane IS from having an intersection with the reflecting surface, and dust on the reflecting surface greatly affects the optical performance.

In order to achieve a bright F number, it is important to have a configuration that cancels out aberrations that occur before and after the intermediate image. In this configuration, positive / negative, intermediate image, and negative / positive configurations are taken from the object side, and astigmatism that becomes noticeable when the F-number is brightened by taking a symmetrical power arrangement with respect to the intermediate image. The configuration is effective for correction. In the conditional expressions (1) and (2), the magnification relationship across the intermediate image is defined by defining the size and power of the surface having positive power before and after the intermediate image. By appropriately arranging the magnification relationship, it is possible to effectively cancel out aberrations occurring before and after the intermediate image.

In the optical path diagram of FIG. 7, all of the four reflecting surfaces S1 to S4 have a free-form surface shape, and light rays incident on the imaging optical system OP from the object side pass through the aperture stop ST, and then first to first 4 is sequentially reflected by the four reflecting surfaces S1 to S4 and reaches the image surface IM. In this four-surface reflection configuration, the intermediate image IS is formed in the optical path between the second reflection surface S2 and the third reflection surface S3, and both the first reflection surface S1 and the fourth reflection surface S4 have positive power. It has a free-form surface shape. Since the power of the fourth reflection surface S4 is stronger than that of the first reflection surface S1 at the intersection with the screen center principal ray PR, the intermediate image IS is reduced by the fourth reflection surface S4, and a bright F number is obtained. Achieved. Further, since the light flux is once converged by forming the intermediate image IS, the size of the reflecting surface can be reduced as compared with the case where the intermediate image IS is not formed.

It is desirable that the non-rotationally symmetric reflecting surface has a positive power in the x direction over the entire effective area on the yz section, and has a larger curvature in the x direction than the curvature in the y direction. In an imaging optical system using a reflective surface, the reflective surface is decentered to prevent interference between the light beam and the optical member. This leads to an increase in astigmatism. Astigmatism can be satisfactorily corrected by setting the power and curvature of the non-rotationally symmetric reflecting surface as described above. Such a reflective surface is preferably disposed between the concave reflective surface closest to the object side and the concave reflective surface closest to the image side.

In the optical path diagram of FIG. 7, the second reflecting surface S2 and the third reflecting surface S3 are free-form curved reflecting surfaces having positive power in the direction perpendicular to the yz plane (x direction), and the power in the x direction is the yz plane. It is stronger than the power in the direction parallel to. By increasing the power in the x direction, it is possible to correct astigmatism generated on the first reflecting surface S1 and the fourth reflecting surface S4 and to realize good optical performance on the image plane IM. When the focal length is determined to some extent by the first reflecting surface S1 and the fourth reflecting surface S4, the curvature in the y direction becomes stronger than the curvature in the x direction. In order to correct the astigmatism generated there, the curvature in the x direction is made stronger than the curvature in the y direction on the second reflecting surface S2 and the third reflecting surface S3.

It is desirable that the non-rotationally symmetric reflecting surface has at least one surface satisfying the following conditional expression (3).
0 <| Ry / Rx | <0.8 (3)
However,
Rx: curvature in the x direction at the center of the effective region in the yz section,
Ry: curvature in the y direction at the center of the effective region in the yz section,
It is.

Conditional expression (3) defines a preferable range of conditions for satisfactorily correcting astigmatism generated in the reflective optical system. When the conditional expression (3) is satisfied, the power in the x direction becomes stronger than the power in the y direction, so that astigmatism can be corrected satisfactorily. If the upper limit of conditional expression (3) is exceeded, it will be difficult to correct astigmatism occurring on the most object-side reflecting surface and the most image-side reflecting surface.

Two or more reflecting surfaces having power are positioned on the optical path on the image side with respect to the position of the intermediate image, and the second reflecting surface counted from the image side is the non-rotationally symmetric reflecting surface, yz In the cross section, it is desirable that the y-direction power at the center of the effective area of the reflecting surface closest to the image side is stronger than the y-direction power at the center of the effective area of the second reflecting surface counted from the image side.

By arranging two or more reflective surfaces with power closer to the image side than the intermediate image formation position, astigmatism that occurs on the concave reflective surface closest to the image can be corrected with other reflective surfaces. It becomes. In addition, by making the power of the reflecting surface closest to the image side stronger than the power of the second reflecting surface from the image side, a bright F number can be obtained while ensuring the distance from the reflecting surface closest to the image side to the image surface. It can be realized. Even in a normal coaxial optical system, in order to lengthen the lens back, an optical element having the strongest positive power may be disposed on the most image side. Similarly, the distance to the light receiving surface of the image sensor is ensured by disposing the reflecting surface having the strongest power on the most image side. Large astigmatism generated when the power of the reflecting surface is increased can be corrected by the second reflecting surface from the image surface.

It is desirable that the intermediate image does not have an intersection with the reflecting surface. By disposing the intermediate image formation position at a position away from the reflecting surface, it is possible to reduce the influence of dust on the reflecting surface and the roughness of the reflecting surface on the optical performance.

It is desirable to satisfy the following conditional expressions (4A) and (4B).
0.4 <Dx1 / Dx2 <0.7 (4A)
0.4 <Dy1 / Dy2 <0.8 (4B)
However,
Dx1: the maximum effective area width in the x direction of the reflecting surface located adjacent to the object side of the intermediate image,
Dx2: the maximum effective area width in the x direction of the reflecting surface located adjacent to the image side of the intermediate image,
Dy1: Maximum effective area width on the yz section of the reflecting surface located adjacent to the object side of the intermediate image, Dy2: Maximum effective area on the yz section of the reflecting surface located adjacent to the image side of the intermediate image width,
It is.

Conditional expressions (4A) and (4B) are the ratios of the maximum effective area widths of the reflecting surfaces (for example, the second and third reflecting surfaces S2 and S3 in FIG. 7) located before and after the intermediate image, A preferable condition range for the intermediate image position in the y direction is defined. When the lower limit of conditional expression (4A) or (4B) is exceeded, the distance from the intermediate image position to the reflecting surface position becomes close, and the influence of dust on the reflecting surface and roughness of the reflecting surface on the optical performance increases. Conversely, when the upper limit of conditional expression (4A) or (4B) is exceeded, the size of the intermediate image increases, making it difficult to brighten the F number while preventing interference between the light beam and the image plane.

In the yz section, the light beam reflected by the second reflecting surface counted from the object side is bent in a direction approaching the light beam incident from the object side (that is, the intersecting direction) on the reflecting surface closest to the object side. It is desirable that That is, it is desirable to bend the light beam into a four-letter shape by reflection on the first and second reflecting surfaces counted from the object side.

For example, as shown in the optical path diagram of FIG. 7, when the light beam is bent into a shape of 4 on the first and second reflecting surfaces S <b> 1 and S <b> 2, the distance for separating the light beam from the optical member can be shortened, A bright F number can be realized. Further, by bending the light beam into a four-letter shape, it becomes possible to reduce the optical path length difference at each angle of view, so that a configuration with a small field curvature can be realized. Since the screen shape of the light receiving surface of a general image sensor is a rectangle, the yz section is a section parallel to the screen short side direction. When the light beam is bent in the long side direction corresponding to the x direction, the optical system size becomes larger than when the light beam is bent in the short side direction of the screen, and the optical path length necessary for the light beam separation becomes longer. It becomes difficult to realize. Therefore, it is desirable to have an optical path that is bent into a four-letter shape in a cross section parallel to the short side direction of the screen.

When the principal ray incident on the center of the effective area of the screen is the screen center principal ray, it is desirable that the screen center principal ray exists on the yz plane and satisfies the following conditional expression (5). However, the configuration that satisfies the following conditional expression (5) is independent of the configuration that satisfies the conditional expression (1) described above, and may be a configuration that satisfies only the conditional expression (5). The preferable conditions may be satisfied. Therefore, the imaging optical system according to the present invention has an intermediate image in the optical system, and has two or more non-rotationally symmetric reflecting surfaces having only one symmetry plane on the object side from the position of the intermediate image. If the symmetric plane is the yz plane in the Cartesian coordinate system (x, y, z) and the principal ray incident on the center of the effective area of the screen is the screen center principal ray, the screen center principal ray exists on the yz plane. The following conditional expression (5) is satisfied.
0.3 <Ro_x / Ro2_x <0.8 (5)
However,
Ro_x: curvature in the x direction that the reflecting surface closest to the object side in the yz section has at the intersection with the screen center principal ray,
Ro2_x: curvature in the x direction that the second reflecting surface from the object side in the yz section has at the intersection with the screen center principal ray,
It is.

Conditional expression (5) defines a preferable condition range for satisfactorily correcting astigmatism generated in the reflection optical system. When the optical performance is secured to some extent on the first and second reflecting surfaces counted from the object side, if the power is determined on the first reflecting surface, the curvature in the x direction is larger than the curvature in the y direction on the first reflecting surface. Get smaller. As power in the x direction of the first reflecting surface becomes weak, astigmatism generated on the first reflecting surface increases. In conditional expression (5), the curvature of the second reflecting surface is increased in the x direction in order to correct it.

If the lower limit of conditional expression (5) is exceeded, the power in the x direction of the reflecting surface closest to the object side becomes weak, and astigmatism occurring on the reflecting surface closest to the object side becomes large. Therefore, the correction by the second reflecting surface becomes insufficient. On the contrary, if the upper limit of conditional expression (5) is exceeded, the power in the x direction of the reflecting surface closest to the object side becomes strong and correction of astigmatism becomes easy, but correction of field curvature becomes difficult.

It is desirable to have only a reflective surface as an optical surface with power. If the surface having power is composed of only the reflecting surface, no ghost caused by surface reflection on the refracting surface will occur. Further, it is not necessary to use an expensive material with high processing difficulty (such as Ge) that transmits far-infrared wavelengths. Since only the reflecting surface is configured, no chromatic aberration occurs.

It is desirable that the optical surface having power has only four reflecting surfaces, and the intermediate image is located in the optical path from the second reflecting surface to the third reflecting surface from the object side. By arranging the reflecting surfaces symmetrically with respect to the intermediate image forming position, it is possible to cancel out aberrations generated on the reflecting surfaces. Therefore, good optical performance can be obtained.

In the infrared region, especially in the wavelength band of 5 μm or more, the transmittance of the glass material is very small, making it difficult to construct an imaging optical system using ordinary glass materials, and configuring the imaging optical system only with a reflective surface. This is advantageous. On the other hand, since the wavelength of far-infrared light generated from a person or animal is about 10 μm, when an optical image is formed using a wavelength up to 11 μm, it is possible to capture a person or animal even at night.

The imaging optical system according to the present invention is suitable for use in a digital device with an infrared image input function (for example, an in-vehicle camera). By combining this with an imaging device or the like, an image of a subject is optically captured and electrically An imaging optical device that outputs as a simple signal can be configured. The imaging optical device is an optical device that constitutes a main component of a camera used for still image shooting and moving image shooting of a subject. For example, an imaging optical system that forms an optical image of an object in order from the object (that is, subject) side, and And an imaging device that converts an optical image formed by the imaging optical system into an electrical signal. Then, by arranging the imaging optical system having the above-described characteristic configuration so that the optical image of the subject is formed on the light receiving surface of the imaging element, the imaging optical device having high performance at low cost and the A digital device can be realized.

Examples of the camera include a digital camera, a video camera, an in-vehicle camera, a surveillance camera, a video phone camera, a door phone camera, etc., and a personal computer, a portable information device (for example, a mobile computer, a cellular phone, a portable information). Small and portable information device terminals such as terminals), peripheral devices (mouse, scanner, printer, memory, etc.), cameras incorporated in or external to other digital devices, and the like. As can be seen from these examples, it is possible not only to configure a camera by using an imaging optical device, but also to add a camera function by mounting the imaging optical device on various digital devices. For example, a digital device with an image input function such as a mobile phone with a camera can be configured.

FIG. 7 is a schematic cross-sectional view showing a schematic configuration example of a digital device having an image input function. The imaging optical device mounted on the digital device illustrated in FIG. 7 includes an imaging optical system OP that forms an optical image (image plane) IM of an object in order from the object (ie, subject) side, and a light receiving surface by the imaging optical system OP. And an image sensor SR that converts an optical image IM formed on the SS into an electrical signal. When a digital device with an image input function is configured with this imaging optical device, the imaging optical device is usually arranged inside the body, but when realizing the camera function, it is possible to adopt a form as necessary. Is possible. For example, the unitized imaging optical device can be configured to be detachable or rotatable with respect to the main body of the digital device.

As the image sensor SR, for example, a solid-state image sensor such as a CCD image sensor or a CMOS image sensor having a plurality of pixels is used. Since the imaging optical system OP is provided so that the optical image IM of the subject is formed on the light receiving surface SS of the imaging element SR, the optical image IM formed by the imaging optical system OP is electrically generated by the imaging element SR. Converted to a typical signal.

The digital apparatus includes a signal processing unit 1, a control unit 2, a memory 3, an operation unit 4, a display unit 5 and the like in addition to the imaging optical device. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, and the like as required by the signal processing unit 1 and recorded as a digital video signal in the memory 3 (semiconductor memory, optical disk, etc.) In some cases, it is transmitted to other devices via a cable or converted into an infrared signal or the like (for example, a communication function of a mobile phone). The control unit 2 is composed of a microcomputer, and performs control of functions such as a photographing function (still image photographing function, moving image photographing function, etc.), an image reproduction function, etc .; control of a driving mechanism for focusing, and the like. For example, the control unit 2 controls the imaging optical device so that at least one of still image shooting and moving image shooting of a subject is performed. The display unit 5 includes a display such as a liquid crystal monitor, and displays an image using an image signal converted by the image sensor SR or image information recorded in the memory 3. The operation unit 4 is a part including operation members such as an operation button (for example, a release button) and an operation dial (for example, a shooting mode dial), and transmits information input by the operator to the control unit 2.

As described above, the imaging optical system OP shown in FIG. 7 has four reflecting surfaces S1 to S4 as optical surfaces having power, and after the intermediate image IS is once formed in the optical system, the imaging device The optical image IM is formed on the SR light receiving surface SS. The first reflecting surface S1 closest to the object side and the fourth reflecting surface S4 closest to the image side along the optical path are both concave surfaces, and the reflecting surfaces are non-rotationally symmetric reflecting surfaces having only one symmetry surface. .

FIGS. 1 to 3 show optical cross sections of first to third embodiments as specific optical configurations of the imaging optical system OP. The imaging optical systems OP of the first to third embodiments are all single-focus imaging optical systems for photographing infrared images that form an optical image IM with respect to the imaging element SR (FIG. 7). In the first and second embodiments (FIGS. 1 and 2), the stop ST, the first reflecting surface S1, the second reflecting surface S2, and the third reflecting surface S3 are sequentially arranged along the optical path from the object side. And the fourth reflecting surface S4, the optical path is bent in a letter 4 shape by the first reflecting surface S1 and the second reflecting surface S2, and the optical path is formed by the third reflecting surface S3 and the fourth reflecting surface S4. Is folded into a figure 4 shape. In the third embodiment (FIG. 3), the diaphragm ST, the first reflecting surface S1, the second reflecting surface S2, and the third reflecting surface S3 are sequentially formed along the optical path from the object side. Thus, the optical path is bent in a W shape at the first reflecting surface S1 to the third reflecting surface S3.

Hereinafter, the configuration and the like of the imaging optical system embodying the present invention will be described more specifically with reference to the construction data of the examples. Examples 1 to 3 (EX1 to 3) listed here are numerical examples corresponding to the first to third embodiments, respectively, and represent the optical configurations of the first to third embodiments. The optical path diagrams (FIGS. 1 to 3) show the optical arrangements, optical paths, and the like of the corresponding Examples 1 to 3, respectively.

The surface data 1, surface data 2, free-form surface data, and various data are shown as construction data of each example. Table 1 shows correspondence data and related data of each conditional expression for each example. In the

surface data

1 and 2, i (i = 1, 2, 3,...) Is a surface number. Therefore, the i-th surface counted from the object side is the i-th surface. The surface data 1 indicates the type and shape of the i-th surface, and the surface data 2 indicates the arrangement data of the i-th surface.

The arrangement of the i-th surface is specified by each surface data of surface vertex coordinates (x, y, z) and rotation angle (Tilt) in the surface data 2. The surface vertex coordinates of the i-th surface are the local orthogonal coordinate system (X, y, z) in the global orthogonal coordinate system (x, y, z) with the surface vertex as the origin of the local orthogonal coordinate system (X, Y, Z). Y, Z) is represented by the coordinates (x, y, z) of the origin (unit: mm), and the inclination of the i-th surface is represented by the rotation angle (Tilt) around the X axis about the surface vertex. (Unit: °; counterclockwise with respect to the positive direction of the X axis is the positive direction of the rotation angle of the X rotation). However, the coordinate systems are all defined by the right-handed system, and the global orthogonal coordinate system (x, y, z) is an absolute coordinate system that matches the local orthogonal coordinate system (X, Y, Z) of the aperture stop ST. ing. The X direction and the Y direction are coordinate axis directions in an orthogonal coordinate system (X, Y, Z) in which the surface vertex of the i-th surface is the origin and the normal line at the surface vertex is the Z axis. Individual data (curvature, length, etc.) on the surface is appropriately expressed in the coordinate axis direction of the coordinate system (x, y, z) before rotation (the same applies to FIG. 7).

Regarding the free-form surface data of each embodiment, the i-th surface composed of a free-form surface (XY polynomial surface) is expressed by the following equation (FS) using a local orthogonal coordinate system (X, Y, Z) having the surface vertex as the origin. ). In the free-form surface data of the i-th surface, RDY indicates the radius of curvature (unit: mm) in the Y-direction of the i-th surface, and the reciprocal thereof is the curvature C0 at the surface vertex. It should be noted that the coefficient of the term not described in the free-form surface data of each embodiment is 0, and ^En = × 10 ⁻ⁿ for all data.
Z = (C0 · h ² ) / [1 + √ {1- (1 + K) · C0 ² · h ² }] + ΣΣ {A (j, k) · X ^j · Y ^k } (FS)

However, in the formula (FS),
Z: Displacement amount in the Z-axis direction at the position of height h (based on the surface vertex),
h: height in the direction perpendicular to the Z axis (h ² = X ² + Y ² ),
C0: curvature at the top of the surface (= 1 / radius of curvature),
K: Conic constant,
A (j, k): j-th order of X, k-th order polynomial free-form surface coefficient of Y,
It is.

As various data, the angle of view (°) in the x direction (screen long side direction) and y direction (screen short side direction), the diameter (mm) of the aperture stop ST, the F number, the focal length (mm) of the entire system, the total length ( mm), height (mm), and sensor size (H: screen long side size, V: screen short side size, D: diagonal size; mm).

The optical performance of each example is shown by spot diagrams (FIGS. 4 to 6). The spot diagram indicates the imaging characteristics (mm) on the image plane IM, and the field position of each spot indicates the field angle and relative value in the X and Y directions.

Example 1
Surface data 1
i Surface type Surface shape
1 Aperture (ST) -----
2 First reflective surface (S1) Free curved surface (XY polynomial surface)
3 Second reflecting surface (S2) Free curved surface (XY polynomial surface)
4 Third reflective surface (S3) Free curved surface (XY polynomial surface)
5 4th reflective surface (S4) Free curved surface (XY polynomial surface)
6 Image plane (IM)

Surface data 2

Free-form data for the second surface

3rd surface free-form surface data

4th surface free-form surface data

Fifth surface free-form surface data

Various data x direction angle of view [degree]: ± 8.5
y-direction angle of view [degree]: ± 6.4
Diaphragm diameter [mm]: 38.6
F number: 1.32
Focal length [mm]: -52.0
Total length [mm]: 120.0
Height [mm]: 150.0
Sensor size H [mm]: 16
Sensor size V [mm]: 12
Sensor size D [mm]: 20

Example 2
Surface data 1
i Surface type Surface shape
1 Aperture (ST) -----
2 First reflective surface (S1) Free curved surface (XY polynomial surface)
3 Second reflecting surface (S2) Free curved surface (XY polynomial surface)
4 Third reflective surface (S3) Free curved surface (XY polynomial surface)
5 4th reflective surface (S4) Free curved surface (XY polynomial surface)
6 Image plane (IM)

Surface data 2

Free-form data for the second surface

3rd surface free-form surface data

4th surface free-form surface data

Fifth surface free-form surface data

Various data x direction angle of view [degree]: ± 8.5
y-direction angle of view [degree]: ± 6.4
Diaphragm diameter [mm]: 38.8
F number: 1.33
Focal length [mm]: -52.0
Total length [mm]: 96.0
Height [mm]: 160.0
Sensor size H [mm]: 16
Sensor size V [mm]: 12
Sensor size D [mm]: 20

Example 3
Surface data 1
i Surface type Surface shape
1 Aperture (ST) -----
2 First reflective surface (S1) Free curved surface (XY polynomial surface)
3 Second reflecting surface (S2) Free curved surface (XY polynomial surface)
4 Third reflective surface (S3) Free curved surface (XY polynomial surface)
5 Image plane (IM)

Surface data 2

Free-form data for the second surface

3rd surface free-form surface data

4th surface free-form surface data

Various data x direction angle of view [degree]: ± 8.5
y-direction angle of view [degree]: ± 6.4
Diaphragm diameter [mm]: 37.6
F number: 1.35
Focal length [mm]: -52.0
Total length [mm]: 122.4
Height [mm]: 199.7
Sensor size H [mm]: 16
Sensor size V [mm]: 12
Sensor size D [mm]: 20

OP Imaging optical system ST Aperture S1 to S4 First to fourth reflecting surfaces IS Intermediate image IM Image surface (optical image)
SR image sensor SS light-receiving surface PR screen center principal ray 1 signal processing unit 2 control unit 3 memory 4 operation unit 5 display unit

Claims

An imaging optical system having at least three reflecting surfaces as optical surfaces having power and having an intermediate image in the optical system, wherein the most object-side reflecting surface and the most image-side reflecting surface along the optical path Both are concave surfaces, and at least one reflection surface is a non-rotationally symmetric reflection surface having a single symmetry surface. When the symmetry surface is a yz plane in an orthogonal coordinate system (x, y, z), An imaging optical system characterized by satisfying conditional expression (1);
1.1 <L / F <3.0 (1)
However,
L: effective area width of the most image-side reflecting surface in the yz section,
F: effective area width of the reflecting surface closest to the object in the yz section,
It is.
2. The chief ray incident on the center of the effective area of the screen is defined as a screen chief ray, and the chief ray at the center of the screen is present on the yz plane and satisfies the following conditional expression (2). Imaging optical system;
0.3 <Ro_y / Ri_y <0.8 (2)
However,
Ro_y: curvature in the y direction that the most object-side reflecting surface in the yz section has at the intersection with the screen center principal ray,
Ri_y: curvature in the y direction that the most image-side reflecting surface in the yz section has at the intersection with the screen center principal ray,
It is.
2. The non-rotationally symmetric reflecting surface has a positive power in the x direction and a larger curvature in the x direction than the curvature in the y direction over the entire effective region on the yz section. Imaging optical system.
The imaging optical system according to claim 1, wherein the non-rotationally symmetric reflecting surface has at least one surface satisfying the following conditional expression (3):
0 <| Ry / Rx | <0.8 (3)
However,
Rx: curvature in the x direction at the center of the effective region in the yz section,
Ry: curvature in the y direction at the center of the effective region in the yz section,
It is.
Two or more reflecting surfaces having power are positioned on the optical path on the image side with respect to the position of the intermediate image, and the second reflecting surface counted from the image side is the non-rotationally symmetric reflecting surface, yz The power in the y direction at the center of the effective area of the reflecting surface closest to the image side in the cross section is stronger than the power in the y direction at the center of the effective area of the second reflecting surface counted from the image side. The imaging optical system according to Item 1.
The imaging optical system according to claim 1, wherein the intermediate image does not have an intersection with the reflecting surface.
The imaging optical system according to claim 1, wherein the following conditional expressions (4A) and (4B) are satisfied:
0.4 <Dx1 / Dx2 <0.7 (4A)
0.4 <Dy1 / Dy2 <0.8 (4B)
However,
Dx1: the maximum effective area width in the x direction of the reflecting surface located adjacent to the object side of the intermediate image,
Dx2: the maximum effective area width in the x direction of the reflecting surface located adjacent to the image side of the intermediate image,
Dy1: Maximum effective area width on the yz section of the reflecting surface located adjacent to the object side of the intermediate image, Dy2: Maximum effective area on the yz section of the reflecting surface located adjacent to the image side of the intermediate image width,
It is.
In the yz section, the light beam reflected by the second reflecting surface counted from the object side is bent in a direction approaching the light beam incident from the object side to the reflecting surface closest to the object side. The imaging optical system according to claim 1.
There is an intermediate image in the optical system, and there are two or more non-rotationally symmetric reflecting surfaces having a single symmetric surface closer to the object side than the position of the intermediate image, and the symmetric surface is an orthogonal coordinate system (x , Y, z), and the principal ray incident on the center of the effective area of the screen is the screen center principal ray, the screen center principal ray exists on the yz plane and satisfies the following conditional expression (5): An imaging optical system characterized by:
0.3 <Ro_x / Ro2_x <0.8 (5)
However,
Ro_x: curvature in the x direction that the reflecting surface closest to the object side in the yz section has at the intersection with the screen center principal ray,
Ro2_x: curvature in the x direction that the second reflecting surface from the object side in the yz section has at the intersection with the screen center principal ray,
It is.
10. The imaging optical system according to claim 1, wherein the optical surface having power has only a reflecting surface.
10. The optical surface having power includes only four reflecting surfaces, and an intermediate image is located in an optical path from the second reflecting surface to the third reflecting surface from the object side. The imaging optical system according to any one of the above.
An image pickup optical system according to any one of claims 1 to 9 and an image pickup device that converts an optical image formed on the light receiving surface into an electrical signal, the light receiving surface of the image pickup device being provided on the light receiving surface. An imaging optical apparatus, wherein the imaging optical system is provided so that an optical image of a subject is formed.
13. The imaging optical apparatus according to claim 12, wherein the imaging optical system forms an optical image of a subject with infrared rays.
14. The imaging optical apparatus according to claim 13, wherein the infrared wavelength region is 5 μm to 11 μm.
13. A digital apparatus comprising the imaging optical device according to claim 12 to which at least one function of still image shooting and moving image shooting of a subject is added.