Stereo imaging system, stereo optical system, and imaging device

Abstract

[Problem] To downsize while avoiding interference between imaging elements when two optical systems are arranged in parallel. [Solution] In this stereo imaging system (10), two imaging devices (11, 12) each having an optical system including a first lens group (L1) are arranged such that the first lens groups are arranged in parallel. The optical system of each of the two imaging devices has: a first optical element (121) that splits an optical path from the first lens group into a first optical path extending in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path; a second lens group (L21) disposed on the first optical path and having positive refractive power toward a first imaging surface; a second optical element (122) that bends the second optical path; and a third lens group (L22) disposed on the second optical path bent by the second optical element and having positive refractive power toward a second imaging surface. The respective bending directions in which the second optical path is bent by the second optical element in each of the two imaging devices are different from each other.

Description

Stereo imaging system, stereo optical system, and imaging device

[0001] This invention relates to an optical system suitable for stereo imaging.

[0002] As an optical system used for imaging, Patent Document 1 discloses an optical system that uses an optical path separation element to guide light from a subject to multiple image sensors.

[0003] Japanese Patent Publication No. 2010-160312

[0004] When arranging two such optical systems in parallel for stereo imaging, miniaturization of the optical system is required while avoiding interference between the image sensors.

[0005] One aspect of the present invention is a stereo imaging system in which two imaging devices, each having an optical system including a first lens group, are arranged so that the first lens groups are in parallel. The optical system of each of the two imaging devices includes a first optical element that branches the optical path from the first lens group into a first optical path extending in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path, a second lens group arranged on the first optical path and having a positive refractive power toward the first imaging plane, a second optical element that bends the second optical path, and a third lens group arranged on the second optical path bent by the second optical element and having a positive refractive power toward the second imaging plane. A characteristic feature is that the bending direction of the second optical path by the second optical element in each of the two imaging devices is different from that of the other.

[0006] Another aspect of the present invention is a stereo imaging system in which two imaging devices, each having an optical system including a first lens group, are arranged so that the first lens groups are in parallel. The optical system of each of the two imaging devices includes a first optical element that branches the optical path from the first lens group into a first optical path extending toward a first imaging plane in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path, and a second optical element that bends the second optical path toward the second imaging plane. The bending direction of the second optical path by the second optical element in each of the two imaging devices is different from that of the other.

[0007] Another aspect of the present invention is that the stereo optical system has two optical systems, each including a first lens group, and the first lens groups are arranged in parallel. Each of the two optical systems includes a first optical element that branches the optical path from the first lens group into a first optical path extending in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path, a second lens group arranged on the first optical path and having a positive refractive power toward the first image plane, a second optical element that bends the second optical path, and a third lens group arranged on the second optical path bent by the second optical element and having a positive refractive power toward the second image plane. The bending direction of the second optical path by the second optical element in each of the two optical systems is different from that of the other.

[0008] Another aspect of the present invention is a stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel. Each of the two optical systems has a first optical element that branches the optical path from the first lens group into a first optical path extending toward a first image plane in a direction different from the optical axis direction of the first lens group, and a second optical element that extends in a direction different from the first optical path, and a second optical element that bends the second optical path toward the second image plane. A characteristic feature is that the bending direction of the second optical path by the second optical element in each of the two optical systems is different from that of the other. An imaging device having the above stereo optical system also constitutes another aspect of the present invention.

[0009] Another aspect of the present invention is a stereo imaging system in which two imaging devices, each having an optical system including a first lens group, are arranged so that the first lens groups are in parallel. The optical system of each of the two imaging devices includes a first optical element that bends the optical path from the first lens group, a second optical element positioned on the image side of the first optical element that branches the optical path into multiple optical paths, and a second lens group with positive refractive power, each positioned on the multiple optical paths branched by the second optical element toward multiple imaging planes. The first lens group of each of the two imaging devices is characterized by having an aperture diaphragm and a focus group that moves during focusing.

[0010] Another aspect of the present invention is a stereo imaging system in which two imaging devices, each having an optical system including a first lens group, are arranged so that the first lens groups are in parallel. The optical systems of the two imaging devices are characterized by each having a first optical element that bends the optical path from the first lens group, and a second optical element that is positioned closer to the image than the first optical element and branches the optical path into multiple optical paths toward multiple imaging surfaces.

[0011] Another aspect of the present invention is a stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel. Each of the two optical systems includes a first optical element that bends the optical path from the first lens group, a second optical element positioned on the image side of the first optical element that branches the optical path into multiple optical paths, and a second lens group with positive refractive power, each positioned on the multiple optical paths branched toward multiple image planes by the second optical element. Each of the two optical systems is characterized by having an aperture diaphragm and a focus group that moves during focusing.

[0012] Another aspect of the present invention is a stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel. Each of the two optical systems is characterized by having a first optical element that bends the optical path from the first lens group, and a second optical element that is positioned closer to the image than the first optical element and branches the optical path into multiple optical paths toward multiple image planes. An imaging device having the above stereo optical system also constitutes another aspect of the present invention.

[0013] Other objects and features of the present invention are described in the following examples.

[0014] According to the present invention, a compact stereo optical system and a stereo imaging device can be provided.

[0015] A diagram showing the configuration of a stereo imaging system as an example. A diagram showing the configuration of another stereo imaging system as an example. A cross-sectional view and aberration diagram of the optical system of Example 1. A cross-sectional view and aberration diagram of the optical system of Example 2. A diagram showing the configuration of an imaging device having the optical system of Example 3. A cross-sectional view and aberration diagram of the optical system of Example 3. A diagram showing the configuration of a stereo imaging system as Example 4. A diagram showing the configuration of another imaging system of Example 4.

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0017] Figures 1(A) and 1(B) show the configuration of a stereo imaging system (hereinafter simply referred to as the imaging system) 10 using the optical systems of Examples 1 to 3 described later. Figure 1(A) shows the imaging system viewed from a direction perpendicular to the optical axis of the first lens group, which will be described later, and Figure 1(B) shows the imaging system viewed from the object side in the direction of the sub-axis of the first lens group. The imaging system 10 is used for stereoscopic imaging and consists of imaging devices 11 and 12 arranged so that their respective optical systems form pairs with parallax to each other. This imaging system 10 is used for various imaging applications such as general-purpose imaging, broadcast imaging, cinema imaging, surveillance imaging, and in-vehicle imaging.

[0018] Each imaging device 11 and 12 simultaneously images the same subject by directing light from the subject to multiple image sensors via an optical system. By combining the multiple images obtained by simultaneously imaging the same subject in each imaging device, high-resolution composite images and composite images with a wide dynamic range can be generated. Because the images generated by imaging devices 11 and 12 have parallax with each other, these images can be viewed in 3D.

[0019] The optical system of each imaging device has a first lens group L1 closest to the object. The first lens groups L1 of imaging devices 11 and 12 are arranged in parallel so that their optical axes are parallel to each other at a predetermined interval (baseline length).

[0020] Furthermore, the optical system of each imaging device has one or more first optical elements 121 that branch the optical path from the first lens group L1 (i.e., the optical axis of the optical system) into a first optical path extending in a direction different from the optical axis direction of the first lens group L1 and a second optical path extending in a direction different from the first optical path. The second optical path may extend in the direction of the optical axis direction of the first lens group L1, or it may extend in a direction different from the optical axis direction.

[0021] Furthermore, the optical system of each imaging device includes a second-first lens group (second lens group) L21 arranged on the first optical path and having a positive refractive power toward the first image plane or first imaging plane (image sensor 131). The optical system also includes one or more second optical elements 122 that bend the second optical path, and a second-second lens group (third lens group) L22 arranged on the second optical path bent by the second optical elements 122 and having a positive refractive power toward the second image plane or second imaging plane (image sensor 132). One or more first optical elements include the first optical element closest to the object, and one or more second optical elements include the second optical element closest to the image. Figures 1(A) and (B) show an optical system having one (closest to the object) first optical element 121 and one (closest to the image) second optical element 122. The lens group includes one or more lenses.

[0022] In the first optical element, the surface that branches the optical path due to transmission, reflection, etc., is called the branching surface, and in the second optical element, the surface that bends the optical path due to reflection, etc., is called the bending surface. The branching direction of the first optical path at the branching surface and the bending direction of the second optical path at the bending surface may be perpendicular to the original optical path, or they may be in directions that deviate from the perpendicular.

[0023] The optical systems of imaging devices 11 and 12 have identical configurations, except for the direction of optical path branching by the first optical element 121 and the direction of optical path bending by the second optical element 122. In the optical systems of imaging devices 11 and 12, the first optical element 121 branches the first optical path toward the second optical path, and then the second optical element 122 bends the second optical path in different directions. This makes it possible to avoid interference between multiple (two) image sensors 131 and 132 in a compact imaging device.

[0024] Furthermore, the bending directions of the second optical path by the second optical element in each of the imaging devices 11 and 12 are different (for example, opposite directions as shown in Figure 1(B)). This allows for increased distances between the optical system portions on the image side of the second optical element 122 and between the imaging sensors 132 in the imaging devices 11 and 12, thereby avoiding interference.

[0025] Since the second-first lens group L21 and the second-second lens group L22 have positive refractive power, the optical path length from the first optical element 122 to the image sensors 131 and 132 can be increased, and as a result, the distance between the image sensors 131 and 132 can be increased to avoid interference between them.

[0026] The first optical element may be a beam splitter acting as a prism, as shown in Figure 1(A), or a half-mirror. Furthermore, it may be an element that branches the optical path according to wavelength, such as a color-separating prism or a dichroic mirror. By using an element that branches the optical path according to wavelength (color) and imaging with image sensors provided for each color, as in a so-called three-chip camera, a high-resolution color composite image can be obtained compared to imaging without separating wavelengths. The second optical element may be a prism with a reflective surface, or a mirror.

[0027] The optical path of light passing through the second-first lens group L21 and forming an image on the image sensor 131 is bent once by the first optical element 121. On the other hand, the optical path of light passing through the second-second lens group L22 and forming an image on the image sensor 132 is bent once by the second optical element 122. As a result, the subject image formed on the image sensor 131 and the subject image formed on the image sensor 132 are inverted horizontally or vertically from each other. Therefore, it is preferable to perform image processing to invert one of the captured images obtained by the image sensor 131 and the captured image obtained by the image sensor 132 to align the orientation of these captured images.

[0028] Figure 2 shows an imaging device 11A using an optical system with a different configuration than that of Figure 1(A), viewed from the same direction as in Figure 1(A) (a direction perpendicular to the optical axis of the first lens group L1). The optical system shown in Figure 2 has the same components as the optical systems in Figures 1(A) and (B), but the bending direction of the optical path of the second optical element 122 is different from that of Figures 1(A) and (B). As a result, the orientation of the optical axis of the second-second lens group L22 (the position of the image sensor 132) is different from that of Figures 1(A) and (B).

[0029] The configuration of the imaging device (not shown), which is paired with the imaging device 11A, is basically the same as that of the imaging device 11A, but the direction of bending of the optical path by the second optical element 122 (the second optical path from the second optical element 122 to the imaging device 132) is different from that of the imaging device 11A (opposite direction).

[0030] Furthermore, each imaging device preferably has the following configuration. First, the first lens group L1 preferably has an aperture diaphragm S and a first sub-lens group L1A as a focusing group that moves in the optical axis direction during focusing. A sub-lens group is a collection of one or more lenses that move in a way that changes the distance between adjacent sub-lens groups during focusing. By arranging the aperture diaphragm S and the focusing group (L1A) on the object side of the first optical element 121, it is not necessary to adjust the aperture or focus for each image sensor, and the configuration of the imaging device can be simplified.

[0031] Furthermore, it is preferable that the second-first lens group L21 includes a glass block 140 that does not have refractive power, such as a parallel plate. This is to make the optical path length from the first optical element 121 to the image sensor 131 and the optical path length from the second optical element 122 to the image sensor 132 the same, thereby making the aberrations in the image sensors 131 and 132 the same.

[0032] Furthermore, in the imaging device 11A with the configuration shown in Figure 2, it is preferable to arrange an intermediate lens group between the first optical element 121 and the second optical element 122 in order to increase the distance between the image sensors 131 and 132.

[0033] Furthermore, the optical axes of the second-first lens group L21 and the second-second lens group L22 may both extend perpendicular to the optical axis of the first lens group L1, as shown in Figures 1(A), (B) and 2, or they may extend at an angle other than perpendicular to the optical axis of the first lens group L1. Also, the optical axes of the second-first lens group L21 and the second-second lens group L22 may both be located in a plane parallel to the optical axis of the first lens group L1 and in a plane perpendicular to that plane, as shown in Figures 1(A) and (B), or both may be located in a plane parallel to the optical axis of the first lens group L1, as shown in Figure 2. Moreover, the optical axes of the second-first lens group L21 and the second-second lens group L22 may both be located in a plane perpendicular to the plane parallel to the optical axis of the first lens group L1. In any of these cases, the bending directions of the second optical path by the second optical element in each of the pair of imaging devices may be in different directions from each other.

[0034] Figure 3(A) shows a cross-section along the optical axis of the optical system of Example 1 when it is in focus on an object at infinity (hereinafter referred to as the infinity focus state). The optical system of Example 1 has a first lens group L1 with positive refractive power, a first optical element 121, a second optical element 122, and a second-first lens group L21 with positive refractive power on the first optical path bent by the first optical element 121, arranged in order from the object side to the image side. Light emitted from the second-first lens group L21 is imaged on the image sensor 131. Although not shown, the second-second lens group L22 with positive refractive power on the second optical path, which is bent by the second optical element 122 but not by the first optical element 121, has the same configuration as the second-first lens group L21. Light emitted from the second-second lens group L22 is imaged on the image sensor 132. The first lens group L1 includes an aperture diaphragm S and a first sub-lens group L1A.

[0035] Following the description of the optical system of Example 3, which will be discussed later, numerical examples 1 to 3 corresponding to Examples 1 to 3 are shown. Figure 3(B) shows the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system of numerical example 1 in the infinity focus state. In the spherical aberration diagram, Fno indicates the F number, the solid line indicates spherical aberration at the d line (wavelength 587.6 nm), and the dashed line indicates spherical aberration at the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S indicates astigmatism at the sagittal image plane, and the dashed line M indicates astigmatism at the meridional image plane. The distortion diagram shows distortion at the d line. The chromatic aberration diagram shows lateral chromatic aberration at the g line. ω is the half-angle of view (°).

[0036] Figure 4(A) shows a cross-section along the optical axis of the optical system of Embodiment 2 in the infinity focus state. The optical system of Embodiment 2 has, arranged in order from the object side to the image side, a first lens group L1 with positive refractive power, a first optical element 121, an intermediate lens group LM, a second optical element 122, and a second-first lens group L21 with positive refractive power on the first optical path bent by the first optical element 121. Light emitted from the second-first lens group L21 is imaged on the image sensor 131. Although not shown, a second-second lens group L22 with positive refractive power on the second optical path, which is bent by the second optical element 122 but not by the first optical element 121, has the same configuration as the second-first lens group L21. Light emitted from the second-second lens group L22 is imaged on the image sensor 132. The first lens group L1 includes an aperture diaphragm S and a first sub-lens group L1A. By arranging an intermediate lens group LM between the first optical element 121 and the second optical element 122, the second-first lens group L21 and the second-second lens group L22 can be miniaturized, and each imaging device can also be miniaturized.

[0037] Figure 4(B) shows the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system in numerical example 3 when it is in focus at infinity.

[0038] FIG. 5 shows the configuration of the imaging device 11B having the optical system of Example 3 as viewed from the same direction as FIG. 2. FIG. 6(A) shows a cross-section along the optical axis in the infinity-focus state of the optical system of Example 3. The optical system of Example 3 includes a first lens group L1 having a positive refractive power, a first optical element 121, another first optical element 123 disposed on a second optical path branched by the first optical element 121, and a second optical element 122 disposed on a first optical path branched by the first optical element 123, which are arranged in order from the object side to the image side. The optical system also has another second optical element 124 disposed on the second optical path branched by the first optical element 123.

[0039] The optical system of the present embodiment also has a second - 1 lens group L21 having a positive refractive power on the first optical path bent by the first optical element 121. The optical system also has another second - 1 lens group L21 having a positive refractive power on another first optical path that is bent by the first optical element 123 without being bent by the first optical element 121 and further bent by the second optical element 122. The light emitted from these two second - 1 lens groups L21 forms images on separate imaging elements 131, respectively. The second - 2 lens group L22 having a positive refractive power on the second optical path that is bent by the second optical element 124 without being bent by the first optical element 123 has the same configuration as the second - 1 lens group L21, and the light emitted from the second - 2 lens group L22 forms an image on the imaging element 132. The first lens group L1 includes an aperture stop S and a first sub - lens group L1A.

[0040] As in Example 3, the light incident from the first lens group L1 may be imaged by three imaging elements, and three captured images generated using these imaging elements may be combined to generate a combined image. The configuration of an imaging device (not shown) paired with the imaging device 11B is the same as the configuration of the imaging device 11B.

[0041] FIG. 6(B) shows the longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) in the infinity - focus state of the optical system of Numerical Example 3.

[0042] For the optical system of each embodiment (each numerical example), when the distance on the optical axis from the lens surface closest to the object side of the first lens group L1 to the lens surface closest to the image side of the first lens group L1 is D1 and the focal length of the entire optical system is f, it is preferable to satisfy the condition of the following formula (1).

[0043] 7.50 ≤ D1 / f ≤ 16.00 (1) If D1 / f is less than the lower limit of formula (1), it becomes difficult to arrange the aperture stop S and the first sub-lens group L1A which is a focus group in the first lens group L1, which is not preferable. If D1 / f exceeds the upper limit of formula (1), the diameter of the lens closest to the object side becomes large, and the lenses closest to the object side of the paired adjacent imaging devices interfere with each other, which is not preferable.

[0044] It is more preferable that the lower limit of formula (1) is 7.80, 8.00 or 8.20 (6.76 3.47). Also, it is more preferable that the upper limit of formula (1) is 15.00, 14.00 or 13.00 (19.35 21.59).

[0045] In addition, for the optical system of each embodiment, when the focal lengths of the second - 1 lens group L21 and the second - 2 lens group L22 are f2, it is preferable to satisfy the condition of the following formula (2).

[0046] 5.71 ≤ f2 / f ≤ 7.82 (2) If f2 / f is less than the lower limit of formula (2), the refractive powers of the second - 1 lens group L21 and the second - 2 lens group L22 become too large, making it difficult to correct the lateral chromatic aberration and field curvature generated in the first lens group L1, which is not preferable. If f2 / f exceeds the upper limit of formula (2), it becomes difficult to correct various aberrations generated in the first lens group L1, which is not preferable.

[0047] It is more preferable that the lower limit of formula (2) is 5.90, 6.10 or 6.30 (5.04 2.66). Also, it is more preferable that the upper limit of formula (2) is 7.40, 7.00 or 6.80 (8.91 9.64).

[0048] Furthermore, in each embodiment, it is preferable that the optical system satisfies the following condition (3), where D2 is the distance along the optical axis from the bending surface of the second optical element 122 to the first and second imaging surfaces (image planes).

[0049] 5.00 ≤ D2 / f ≤ 7.44 (3) If D2 / f falls below the lower limit of equation (3), the distance from the folding surface to each imaging surface (image plane) becomes too short, causing the image sensors 131 and 132 to interfere with each other, which is undesirable. If D2 / f exceeds the upper limit of equation (3), the distance from the folding surface to the imaging surface becomes too long, causing the imaging device to become larger, which is undesirable.

[0050] Furthermore, it is more preferable to set the lower limit of formula (3) to 5.20, 5.40, or 5.60 (4.37 2.19). Also, it is more preferable to set the upper limit of formula (3) to 7.30, 7.20, or 7.00 (7.89 8.19).

[0051] Furthermore, in each embodiment, it is preferable that the optical system satisfies the following condition (4), where DM is the distance along the optical axis from the branching surface of the first optical element 121 to the bending surface of the second optical element 122.

[0052] 2.47 ≤ DM / f ≤ 8.22 (4) If DM / f falls below the lower limit of equation (4), the first optical element 121 and the second optical element 122 interfere with each other, which is undesirable. If DM / f exceeds the upper limit of equation (4), the distance from the first optical element 121 to the second optical element 122 becomes too long, which is undesirable because the imaging device becomes larger.

[0053] Furthermore, it is more preferable to set the lower limit of formula (4) to 2.60, 2.80, or 2.90 (2.01 0.83). Also, it is more preferable to set the upper limit of formula (4) to 7.80, 7.50, 7.00, or 6.40 (10.30 11.69).

[0054] Furthermore, it is preferable that the optical system of each embodiment satisfies the following condition (5), where DS is the distance along the optical axis from the aperture diaphragm S to the first and second imaging planes, respectively.

[0055] 11.87 ≤ DS / f ≤ 20.01 (5) If DS / f falls below the lower limit of equation (5), it becomes difficult to position the aperture diaphragm S closer to the object than the first optical element 121, which is undesirable. If DS / f exceeds the upper limit of equation (5), the distance between the aperture diaphragm S and the second-first lens group L21 and the second-second lens group L22 becomes too long, causing the diameters of the second-first lens group L21 and the second-second lens group L22 to increase. As a result, the imaging device becomes larger, which is undesirable.

[0056] Furthermore, it is more preferable to set the lower limit of formula (5) to 12.00, 12.20, or 12.40 (11.27 7.97). Also, it is more preferable to set the upper limit of formula (5) to 18.00, 17.00, or 16.00 (23.53 25.89).

[0057] The above describes a case in which an imaging system is configured using two imaging devices, each having an optical system that satisfies the above configuration and conditions. However, it may also be configured as a stereo optical system and an integrated imaging device having the same, each containing two optical systems that satisfy the above configuration and conditions. In this case, the stereo optical system consists of two optical systems, each containing a first lens group, arranged so that the first lens groups are in parallel. Each of these two optical systems has one or more first optical elements that bend the optical path from the first lens group, and a second optical element that is positioned closer to the image than the first optical element closest to the image, and branches the optical path into multiple optical paths. Each first lens group includes an aperture diaphragm S and a focus group.

[0058] Numerical examples 1 to 3 are shown below. In each numerical example, the surface number i indicates the order of the surfaces when counted from the object side. r is the radius of curvature of the i-th surface from the object side (mm), d is the lens thickness or air gap on the optical axis between the i-th and (i+1)-th surfaces (mm), and nd is the refractive index of the optical material at the d-line between the i-th and (i+1)-th surfaces. νd is the Abbe number of the optical material at the d-line between the i-th and (i+1)-th surfaces. The Abbe number νd at the d-line is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer lines d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm), respectively.

[0059] d, focal length (mm), F number, and semi-field angle (°) are all values in the infinitely focused state. BF represents the back focus (mm). The back focus is the distance on the optical axis from the lens surface closest to the image side (the final surface) of the optical system to the paraxial image plane, expressed in terms of the air-equivalent length. The overall lens length is the length obtained by adding the back focus to the distance on the optical axis from the lens surface closest to the object side (the frontmost surface) of the optical system to the final surface.

[0060] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following formula when X is the displacement amount from the surface vertex in the optical axis direction, H is the height from the optical axis in the direction orthogonal to the optical axis, with the light propagation direction being positive, R is the paraxial curvature radius, K is the conic constant, and A4, A6, A8, A10 are the aspherical coefficients. The "e±xx" of the conic constant and the aspherical coefficients means ×10 ±xx is meant.

[0061] X = (H ２ / R) / [1 + {1 - (1 + K)(H / R) ２} １／２　 ] + A4 × h ４ + A6 × h ６ + A8 × h ８ + A10 × h １０ + A12 × h １２[Numerical Example 1] Unit: mm Surface Data Surface Number rd nd νd 1 58.960 2.50 2.00100 29.1 2 19.260 12.58 3 128.130 2.00 2.00069 25.5 4 35.789 7.47 5 -35.180 1.50 2.00100 29.1 6 35.840 1.88 7 70.612 13.31 1.74000 28.3 8 -15.913 1.50 1.75500 52.3 9 -29.744 1.57 10 96.467 10.75 1.51742 52.4 11 -25.100 1.50 2.00069 25.5 12 -29.032 9.44 13* -21.280 1.05 2.00100 29.1 14 35.263 6.79 1.51742 52.4 15 -21.761 9.61 16 (aperture) ∞ 2.00 17 182.035 4.21 1.71736 29.5 18 -39.049 2.00 19 ∞ 16.04 1.51633 64.1 20 ∞ 16.04 1.51633 64.1 21 ∞ 16.04 1.51633 64.1 22 ∞ 16.04 1.51633 64.1 23 ∞ 1.00 24 25.707 14.34 1.43875 94.7 25 -56.775 0.46 26 -66.697 1.70 2.00100 29.1 27 24.577 11.14 1.43875 94.7 28 -85.408 0.20 29 65.673 7.80 1.43875 94.7 30 -231.395 0.20 31 31.585 16.16 1.43875 94.7 32 -39.217 1.70 1.87070 40.7 33 -106.953 15.07 Image plane ∞ Aspherical data 13th plane K = 0.00000e+00 A 4 = 9.63772e-06 A 6 = 3.80437e-08 A 8 = 4.11555e-13 A10 = -3.99834e-14 Various Data Focal Length 10.90 F-number 2.91 Half Angle of View (°) 95.00 Image Height 18.00 Lens Length 225.60 BF 15.07 Lens Group Data Group Start Surface End Surface Focal Length L1 1 18 24.64 L1A 10 12 49.16 L2-1 24 33 69.68 [Numerical Example 2] Unit mm Surface Data Surface Number rd nd νd 1 43.749 1.95 2.00100 29.1 2 14.861 8.41 3* -174.867 1.30 2.00100 29.1 4 24.881 6.96 5 -16.683 1.30 2.00100 29.1 6 -296.826 0.37 7 -180.603 9.76 1.75211 25.0 8 -19.291 0.19 9 58.407 1.30 1.96300 24.1 10 29.267 1.80 11 32.899 11.99 1.53172 48.8 12 -17.423 1.30 1.49700 81.5 13 -46.042 0.65 14* 69.188 4.78 1.62041 60.3 15 -36.922 0.98 1.51633 64.1 16 49.355 24.47 17 (aperture) ∞ 1.95 18 ∞ 8.83 1.51633 64.1 19 ∞ 8.83 1.51633 64.1 20 ∞ 1.30 21 35.125 0.97 1.65160 58.5 22 15.583 3.28 1.49700 81.5 23 -49.533 0.19 24 ∞ 8.83 1.51633 64.1 25 ∞ 8.83 1.51633 64.1 26 ∞ 6.48 27 26.820 5.77 1.43875 94.7 28 -22.721 0.19 29 -75.166 4.18 1.43875 94.7 30 -16.807 1.30 1.87070 40.7 31 21.259 0.48 32 22.993 6.01 1.43875 94.7 33 -42.175 0.19 34 20.791 11.66 1.43875 94.7 35 -18.205 1.10 1.95375 32.3 36 -28.909 8.77 Image plane ∞ Aspherical data Third plane K = 0.00000e+00 A 4= 4.36079e-06 A 6=-5.43863e-08 A 8= 1.42166e-10 A10=-1.96625e-13 Fourteenth plane K = 0.00000e+00 A 4=-1.52652e-06 A 6 = 9.29124e-09 A 8 = -3.92721e-11 A10 = 8.37057e-14 Various data Focal length 7.05 F number 2.91 Half angle of view (°) 95.00 Image height 11.70 Lens length 166.71 BF 8.77 Lens group data group Start surface End surface Focal length L1 1 17 -45.66 L1A 14 16 622.90 LM 21 23 54.14 L2-1 27 36 47.41 [Numerical example 3] Unit mm Surface data surface number rd nd νd 1 61.892 2.50 2.00100 29.1 2 18.845 12.30 3 96.205 2.00 2.00100 29.1 4 33.863 9.08 5 -25.497 1.50 1.80400 46.5 6 55.942 1.39 7 107.758 10.22 1.84666 23.8 8 -28.587 5.75 9 1065.446 1.50 2.00100 29.1 10 22.701 8.60 1.53172 48.8 11 -107.956 4.29 12 4355.929 9.58 1.53172 48.8 13 -14.863 1.50 1.72916 54.7 14 -20.340 3.62 15* -17.902 1.05 2.00100 29.1 16 75.458 7.44 1.51742 52.4 17 -19.147 10.00 18 192.746 2.00 2.00069 25.5 19 60.263 10.13 1.72825 28.5 20 -37.726 2.00 21 (aperture) ∞ 2.00 22 ∞ 16.74 1.51633 64.1 23 ∞ 16.74 1.51633 64.1 24 ∞ 16.74 1.51633 64.1 25 ∞ 16.74 1.51633 64.1 26 ∞ 16.74 1.51633 64.1 27 ∞ 16.74 1.51633 64.1 28 ∞ 1.00 29 25.774 11.39 1.43875 94.7 30 -83.126 0.15 31 -144.020 2.00 2.00100 29.1 32 31.298 2.07 33 44.533 13.15 1.43875 94.7 34 -24.083 2.00 1.87070 40.7 35 -119.868 0.20 36 147.604 9.71 1.43875 94.7 37 -35.095 0.20 38 38.964 17.12 1.43875 94.7 39 -28.428 1.70 1.87070 40.7 40 -57.958 15.07 Image plane ∞ Aspherical data 15th plane K = 0.00000e+00 A 4= 4.41006e-06 A 6= 3.09378e-08 A 8= 2.42081e-11 A10= 5.76305e-13 Various data Focal length 10.90 F number 2.91 Half angle of view (°) 95.00 Image height 18.00 Lens length 284.68 BF 15.07 Lens group data group Start plane End plane Focal length L1 1 21 17.79 L1A 12 14 43.33 L2-1 29 40 73.36 Table 1 summarizes the values ​​of equations (1) to (5) for numerical examples 1 to 3. The optical systems in each numerical example satisfy all the conditions of equations (1) to (5).

[0062]

[0063] [Imaging System] Figure 7(A) shows the configuration of a stereo imaging system (hereinafter simply referred to as the imaging system) 210 as Example 4. The imaging system 210 is used for stereoscopic imaging and consists of imaging devices 211 and 212 arranged so that their respective optical systems have parallax with each other. This imaging system 210 is used for various imaging applications such as general-purpose imaging, broadcast imaging, cinema imaging, surveillance imaging, and in-vehicle imaging.

[0064] The imaging devices 211 and 212 each simultaneously image the same subject by directing light from the subject to multiple image sensors via an optical system. By combining the multiple images obtained by simultaneously imaging the same subject in each imaging device, high-resolution composite images and composite images with a wide dynamic range can be generated. Because the images generated by imaging devices 211 and 212 have parallax with each other, these captured images can be viewed in stereoscopic form.

[0065] The optical system of each imaging device has a first lens group L1 closest to the object. The first lens groups L1 of imaging devices 211 and 212 are arranged in parallel so that their optical axes are parallel to each other at a predetermined interval (baseline length).

[0066] Furthermore, the optical system of each imaging device includes one or more first optical elements 121 that bend the optical path (i.e., the optical axis of the optical system) from the first lens group, and one or more second optical elements 122 that are positioned closer to the image than all the first optical elements and branch the optical path (optical axis) to lead to multiple imaging surfaces (image sensors 131, 132). The one or more first optical elements include the first optical element closest to the object, and the one or more second optical elements include the second optical element closest to the image. Figure 7(A) shows an optical system having one (closest to the object) first optical element 121 and one (closest to the image) second optical element 122.

[0067] In the first optical element, the surface that bends the optical path due to reflection, etc., is called the bending surface, and in the second optical element, the surface that branches the optical path due to transmission, reflection, etc., is called the branching surface. The direction of bending of the optical path at the bending surface and the direction of branching of the optical path at the branching surface may be perpendicular to the original optical path, or they may be in directions that deviate from the perpendicular.

[0068] Each optical system also has a second-first lens group (second lens group) L21 with positive refractive power, positioned on a first optical path branched toward the image sensor 131 by the second optical element 122 closest to the image. Furthermore, the optical system has a second-second lens group (second lens group) L22 with positive refractive power, positioned on a second optical path branched toward the image sensor 132 by the second optical element 122 closest to the image. The image sensors 131 and 132 are positioned such that their imaging surfaces (light-receiving surfaces) are located on the image plane closer to the image than the second-first lens group L21 and the second-second lens group L22. Each lens group includes one or more lenses.

[0069] The optical systems of imaging devices 211 and 212 have identical configurations, except for the direction in which the optical path is bent by the first optical element 121 and the direction in which the optical path is branched by the second optical element 122. In the optical systems of imaging devices 211 and 212, interference between image sensors can be avoided by bending the optical path on the image side from the first optical element 121 in opposite directions and then branching the optical path with the second optical element 122. Furthermore, by branching a portion of the image side of each optical system, a compact imaging system can be constructed.

[0070] Since the second-first lens group L21 and the second-second lens group L22 have positive refractive power, the optical path length from the first optical element 122 to the image sensor 131 can be increased, and as a result, the distance between the image sensor 131 and the image sensor 132 can be increased to avoid interference between them.

[0071] The first lens group L1 includes an aperture diaphragm S and a first sub-lens group L1A, which acts as a focusing group that moves along the optical axis during focusing. A sub-lens group is a collection of one or more lenses that move in a manner that changes the distance between adjacent sub-lens groups during focusing. By arranging the aperture diaphragm S and the first sub-lens group L1A on the object side of the first optical element 121, aperture adjustment and focusing are not required for each image sensor, thus simplifying the configuration of the imaging device.

[0072] The first optical element may be a prism with a reflective surface, as shown in Figure 7(A), or a mirror. The second optical element may be a beam splitter acting as a prism, as shown in Figure 7(A), or a half-mirror. Furthermore, it may be an element that branches the optical path according to wavelength, such as a color-separating prism or a dichroic mirror. By using an element that branches the optical path according to wavelength (color) and imaging with image sensors provided for each color, as in a so-called three-chip camera, a high-resolution color composite image can be obtained compared to imaging without separating wavelengths.

[0073] The optical path of light passing through the second-first lens group L21 and forming an image on the image sensor 131 is bent a total of two times by the first optical element 121 and the second optical element 122. On the other hand, the optical path of light passing through the second-second lens group L22 and forming an image on the image sensor 132 is bent only once by the first optical element 121. As a result, the subject image formed on the image sensor 131 and the subject image formed on the image sensor 132 are inverted images of each other. Therefore, it is preferable to perform image processing to invert one of the captured images obtained by the image sensor 131 and the captured image obtained by the image sensor 132 to align the orientation of these captured images.

[0074] Figure 7(B) shows an imaging device 211A using an optical system with a different configuration than that of Figure 7(A), viewed from the same direction as in Figure 7(A) (a direction perpendicular to the optical axis of the first lens group L1). Figure 7(C) shows the imaging device 211A of Figure 7(B) viewed from the object side in the direction of the optical axis of the first lens group L1. The optical systems shown in Figures 7(B) and (C) have the same components as the optical system of Figure 7(A), but the branching (bending) direction of the optical path of the second optical element 122 is different from that of Figure 7(A), and as a result, the orientation of the optical axis of the second-second lens group L22 (position of the image sensor 132) is different from that of Figure 7(A).

[0075] Figure 8(A) shows an imaging device 211B using an optical system with a different configuration from that of Figure 7(A), viewed from the same direction as in Figure 7(A). Figure 8(B) shows the imaging device 211B of Figure 8(A) viewed from the object side in the optical axis direction of the first lens group L1.

[0076] The optical system shown in Figures 8(A) and 8(B) has one first optical element 121 and two second optical elements 122 and 123, which branch the optical path into three. Specifically, another second optical element 123 is placed between the first optical element 121 and the second optical element 122. In order to make the optical path lengths equal between the optical path passing through the second optical element 123 and the second optical element 122 and the optical path not passing through the second optical element 122, a glass block 124 is placed on the image side of the second optical element 122.

[0077] In Figures 8(A) and 8(B), the optical path branched by the second optical element 123 toward the second optical element 122 is further branched by the second optical element 122 into two optical paths toward the image sensor 132 and the image sensor 133.

[0078] Although Figures 8(A) and 8(B) show a configuration having multiple (two) second optical elements 122 and 123, a configuration with multiple first optical elements 121 may also be adopted.

[0079] The optical systems of the imaging devices 211 and 221A in this embodiment are basically the same as those of the optical systems of Embodiment 1 (numerical example 1) or Embodiment 2 (numerical example 2) described above. Furthermore, the optical system of the imaging device 211B in this embodiment is basically the same as those of the optical system of Embodiment 3 (numerical example 3) described above.

[0080] When the optical system of Embodiment 1 shown in Figure 3(A) is used in imaging devices 211 and 221A, the optical system has a first lens group L1 with positive refractive power, a first optical element 221, a second optical element 222, and a second-first lens group L21 with positive refractive power on the optical path not branched by the second optical element 122, arranged in order from the object side to the image side. Light emitted from the second-first lens group L21 is imaged on the image sensor 131. Although not shown, the second-second lens group L22 with positive refractive power on the optical path branched by the second optical element 122 has the same configuration as the second-first lens group L21, and light emitted from the second-second lens group L22 is imaged on the image sensor 132. The first lens group L1 has an aperture diaphragm S and a first sub-lens group L1A.

[0081] Furthermore, when the optical system of Embodiment 2 shown in Figure 4(A) is used in imaging devices 211 and 221A, the optical system has, arranged in order from the object side to the image side, a first lens group L1 with negative refractive power, a first optical element 121, an intermediate lens group LM with positive refractive power, a second optical element 122, and a second-first lens group L21 with positive refractive power on the optical path not branched by the second optical element 122. Light emitted from the second-first lens group L21 is imaged on the image sensor 131. Although not shown, the second-second lens group L22 with positive refractive power on the optical path branched by the second optical element 122 has the same configuration as the second-first lens group L21, and light emitted from the second-second lens group L22 is imaged on the image sensor 132. The first lens group L1 has an aperture diaphragm S and a first sub-lens group L1A.

[0082] By arranging the intermediate lens group LM between the first optical element 121 and the second optical element 122, the second-first lens group L21 and the second-second lens group L22 can be miniaturized, and an overall compact imaging device can be realized.

[0083] Furthermore, the optical system of the imaging device 211B is basically the same as the optical system of the above-described embodiment 3 (numerical example 3). When the optical system of embodiment 3 shown in Figure 6(A) is used in the imaging device 211B, the optical system has a first lens group L1 with positive refractive power arranged in order from the object side to the image side, a first optical element 121, a second optical element 123 arranged on the optical path bent by the first optical element 121, and another second optical element 122 arranged on the optical path branched by the second optical element 123. In addition, a glass block 125 is arranged on the optical path that was not branched by the second optical element 123.

[0084] The optical system has a second-first lens group L21 with positive refractive power on the optical path that passes through the glass block 125. Light emitted from the second-first lens group L21 forms an image on the image sensor 131. There is also a second-second lens group L22 with positive refractive power on the optical path that is branched by the second optical element 123 and further branched by the second optical element 122. Furthermore, there is a second-third lens group L23 with positive refractive power on the optical path that is not branched by the second optical element 122. Light emitted from the second-second lens group L22 and the second-third lens group L23 forms images on the image sensors 132 and 133, respectively. The second-second lens group L22 and the second-third lens group L23 have the same configuration as the second-first lens group L21. The first lens group L1 has an aperture diaphragm S and a first sub-lens group L1A.

[0085] Alternatively, the light incident from the first lens group L1 may be captured by three image sensors, and the three captured images generated using these image sensors may be combined to produce a composite image.

[0086] The configuration of the imaging device (not shown) paired with imaging device 211B is the same as that of imaging device 211B.

[0087] In this embodiment as well, it is preferable that the optical systems of numerical examples 1 to 3 satisfy the conditions of equation (1) described above. That is, it is preferable that the condition 7.50 ≤ D1 / f ≤ 16.00 is satisfied. The more preferable values ​​for the lower and upper limits of equation (1) are as described above.

[0088] Furthermore, in this embodiment, when f2 is the focal length of the second-first lens group L21 and the second-second lens group L22, respectively, it is preferable that the following conditions of equation (2A), similar to equation (2), are satisfied.

[0089] 5.71 ≤ f² / f ≤ 7.82 (2A) The explanation of what is undesirable when f² / f is below or above the lower limit of equation (2A), and the more preferable values ​​for the lower and upper limits of equation (2A), are the same as in equation (2).

[0090] Furthermore, in this embodiment, when D2 is the distance along the optical axis from the branching surface of the second optical element 122 to the imaging surfaces of the image sensors 131 and 132, it is preferable that the following conditions of equation (3A), similar to equation (3), are satisfied.

[0091] 5.00 ≤ D2 / f ≤ 7.44 (3A) If D2 / f falls below the lower limit of equation (3A), the distance from the bifurcation surface to the imaging surface becomes too short, causing the image sensors 131 and 132 to interfere with each other, which is undesirable. If D2 / f exceeds the upper limit of equation (3A), the distance from the bifurcation surface to the imaging surface becomes too long, causing the imaging device to become larger, which is also undesirable. The more preferable values ​​for the lower and upper limits of equation (3A) are the same as those in equation (3).

[0092] Furthermore, in this embodiment, when DM is defined as the distance along the optical axis from the bending surface of the first optical element 121 to the branching surface of the second optical element 122, it is preferable that the following condition of equation (4A), similar to equation (4), is satisfied.

[0093] 2.47 ≤ DM / f ≤ 8.22 (4A) The explanation of what is undesirable when DM / f is below or above the lower limit of equation (4A), and the more preferable values ​​for the lower and upper limits of equation (4A), are the same as in equation (4).

[0094] Furthermore, in this implementation, when DS is defined as the distance along the optical axis from the aperture diaphragm S to the imaging surface of the image sensor (131, 132), it is preferable that the following conditions of equation (5A), similar to equation (5), are satisfied.

[0095] 11.87 ≤ DS / f ≤ 20.01 (5A) The explanation of what is undesirable when DS / f is below or above the lower limit of equation (5A), and the more preferable values ​​for the lower and upper limits of equation (5A), are the same as in equation (5).

[0096] Furthermore, the optical systems of numerical examples 1 to 3 used in the imaging devices 211, 211A, and 211B of this embodiment satisfy all the conditions of equation (1) and equations (2A) to (5A). The values ​​of equation (1) and equations (2A) to (5A) are the same as the values ​​of equations (1) to (5) in Table 1.

[0097] The above describes a case in which an imaging system is configured using two imaging devices, each having an optical system that satisfies the above configuration and conditions. However, it is also possible to configure a stereo optical system and an integrated imaging device having the same, each including two optical systems that satisfy the above configuration and conditions. In this case, the stereo optical system consists of two optical systems, each including a first lens group, arranged so that the first lens groups are in parallel. Each of the two optical systems includes one or more first optical elements that bend the optical path from the first lens group, and a second optical element that is positioned closer to the image than the first optical element closest to the image, and that branches the optical path into multiple optical paths. Each first lens group includes an aperture diaphragm S and a focus group.

[0098] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention.

Claims

1. A stereo imaging system comprising two imaging devices, each having an optical system including a first lens group, arranged such that the first lens groups are in parallel, wherein the optical system of each of the two imaging devices comprises: a first optical element that branches the optical path from the first lens group into a first optical path extending in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path; a second lens group arranged on the first optical path and having a positive refractive power toward a first imaging plane; a second optical element that bends the second optical path; and a third lens group arranged on the second optical path bent by the second optical element and having a positive refractive power toward a second imaging plane, wherein the bending direction of the second optical path by the second optical element in each of the two imaging devices is different from that of the other.

2. The stereo imaging system according to claim 1, characterized in that the second optical path from the first optical element to the second optical element extends in the direction of the optical axis of the first lens group.

3. The stereo imaging system according to claim 1 or 2, characterized in that the bending direction of the second optical path by the second optical element in each of the two imaging devices is in opposite directions to each other.

4. The stereo imaging system according to any one of claims 1 to 3, characterized in that, when D1 is the distance on the optical axis from the lens surface closest to the object in the first lens group to the lens surface closest to the image in the first lens group, and f is the focal length of the optical system, the condition 7.50 ≤ D1 / f ≤ 16.00 is satisfied.

5. The stereo imaging system according to any one of claims 1 to 4, characterized in that, when the focal length of the second lens group and the third lens group is f2 and the focal length of the optical system is f, the condition 5.71 ≤ f2 / f ≤ 7.82 is satisfied.

6. The stereo imaging system according to any one of claims 1 to 5, characterized in that, when D2 is the distance along the optical axis from the surface that bends the second optical path in the second optical element to each of the first and second imaging surfaces, and f is the focal length of the optical system, the condition 5.00 ≤ D2 / f ≤ 7.44 is satisfied.

7. A stereo imaging system according to any one of claims 1 to 6, characterized in that, when DM is the distance on the optical axis from the surface that branches the optical path in the first optical element to the surface that bends the optical path in the second optical element, and f is the focal length of the optical system, the condition 2.47 ≤ DM / f ≤ 8.22 is satisfied.

8. A stereo imaging system according to any one of claims 1 to 7, characterized in that, when DS is the distance along the optical axis from the aperture diaphragm to each of the first and second imaging planes, and f is the focal length of the optical system, the condition 11.87 ≤ DS / f ≤ 20.01 is satisfied.

9. A stereo imaging system comprising two imaging devices, each having an optical system including a first lens group, arranged such that the first lens groups are in parallel, wherein the optical system of each of the two imaging devices includes a first optical element that branches the optical path from the first lens group into a first optical path extending toward a first imaging plane in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path, and a second optical element that bends the second optical path toward a second imaging plane, characterized in that the bending direction of the second optical path by the second optical element in each of the two imaging devices is different from that of the other.

10. A stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel, wherein each of the two optical systems includes: a first optical element that branches the optical path from the first lens group into a first optical path extending in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path; a second lens group arranged on the first optical path and having a positive refractive power toward a first image plane; a second optical element that bends the second optical path; and a third lens group arranged on the second optical path bent by the second optical element and having a positive refractive power toward a second image plane, wherein the bending direction of the second optical path by the second optical element in each of the two optical systems is different from that of the other.

11. The stereo optical system according to claim 10, characterized in that the second optical path from the first optical element to the second optical element extends in the direction of the optical axis of the first lens group.

12. The stereo optical system according to claim 10 or 11, characterized in that the bending directions of the second optical path by the second optical element in each of the two optical systems are in opposite directions to each other.

13. A stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel, wherein each of the two optical systems includes a first optical element that branches the optical path from the first lens group into a first optical path extending toward a first image plane in a direction different from the optical axis direction of the first lens group and a second optical path extending in a direction different from the first optical path, and a second optical element that bends the second optical path toward a second image plane, wherein the bending direction of the second optical path by the second optical element in each of the two optical systems is different from that of the other.

14. An imaging apparatus characterized by having a stereo optical system as described in any one of claims 10 to 13.

15. A stereo imaging system comprising two imaging devices, each having an optical system including a first lens group, arranged such that the first lens groups are in parallel, wherein the optical system of each of the two imaging devices includes a first optical element that bends the optical path from the first lens group, a second optical element positioned on the image side of the first optical element and branching the optical path into a plurality of optical paths, and a second lens group having positive refractive power, each positioned on a plurality of optical paths branched toward a plurality of imaging planes by the second optical element, and the first lens group of each of the two imaging devices includes an aperture diaphragm and a focus group that moves during focusing.

16. The stereo imaging system according to claim 15, characterized in that the two imaging devices are arranged such that the direction in which the first optical element in each optical system bends the optical path is opposite to that of the other.

17. The stereo imaging system according to claim 15 or 16, characterized in that, when D1 is the distance on the optical axis from the lens surface closest to the object in the first lens group to the lens surface closest to the image in the first lens group, and f is the focal length of the optical system, the condition 7.50 ≤ D1 / f ≤ 16.00 is satisfied.

18. The stereo imaging system according to any one of claims 15 to 17, characterized in that, when the focal length of the second lens group is f2 and the focal length of the optical system is f, the condition 5.71 ≤ f2 / f ≤ 7.82 is satisfied.

19. The stereo imaging system according to any one of claims 15 to 18, characterized in that, when D2 is the distance along the optical axis from the surface that branches the optical path toward the plurality of imaging surfaces in the second optical element to each of the plurality of imaging surfaces, and f is the focal length of the optical system, the condition 5.00 ≤ D2 / f ≤ 7.44 is satisfied.

20. A stereo imaging system according to any one of claims 15 to 19, characterized in that, when DM is the distance on the optical axis from the surface that bends the optical path in the first optical element to the surface that branches the optical path in the second optical element, and f is the focal length of the optical system, the condition 2.47 ≤ DM / f ≤ 8.22 is satisfied.

21. A stereo imaging system according to any one of claims 15 to 20, characterized in that, when DS is the distance on the optical axis from the aperture diaphragm to the imaging plane and f is the focal length of the optical system, the condition 11.87 ≤ DS / f ≤ 20.01 is satisfied.

22. A stereo imaging system comprising two imaging devices, each having an optical system including a first lens group, arranged such that the first lens groups are in parallel, wherein the optical systems of the two imaging devices each include a first optical element that bends the optical path from the first lens group, and a second optical element positioned on the image side of the first optical element that branches the optical path into multiple optical paths toward multiple imaging surfaces.

23. A stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel, wherein each of the two optical systems includes a first optical element that bends the optical path from the first lens group, a second optical element positioned on the image side of the first optical element and branching the optical path into a plurality of optical paths, and a second lens group having positive refractive power, each positioned on a plurality of optical paths branched toward a plurality of image planes by the second optical element, and each of the first lens groups of the two optical systems includes an aperture diaphragm and a focus group that moves during focusing.

24. The stereo optical system according to 23, characterized in that the direction in which the first optical element in each of the two optical systems bends the optical path is opposite to that of the other.

25. A stereo optical system having two optical systems, each including a first lens group, and arranged so that the first lens groups are in parallel, wherein each of the two optical systems includes a first optical element that bends the optical path from the first lens group, and a second optical element that is positioned closer to the image than the first optical element and branches the optical path into multiple optical paths toward multiple image planes.

26. An imaging apparatus characterized by having a stereo optical system as described in any one of claims 23 to 25.

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