Stereo optical system and imaging device

Abstract

To provide a stereo optical system which secures a sufficient base line length and is wide-angle, compact, and well corrected for aberrations.SOLUTION: A stereo optical system 100 provided herein comprises two juxtaposed optical systems 101, 102. Each of the two optical systems comprises a front group L1 having negative refractive power, an intermediate group L2 with two reflective surfaces, and a rear group L3 arranged in order from the object side to the image side, where bending of light paths by the two reflective surfaces makes an optical axial distance between the rear groups smaller than an optical axial distance between the front groups. At least either of the intermediate group and the rear group has positive refractive power. Focal lengths f1, f2, f3 of the front group, intermediate group and rear group for the d-ray, and a focal length f of the optical system satisfy conditions expressed as: -4.00≤f1 / f≤-2.00, 0.55≤|f3 / f2|≤0.90.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a stereo optical system and an imaging device suitable for capturing stereoscopically viewable images (stereoscopic images). [Background technology]

[0002] As an imaging device capable of capturing a stereoscopic image by imaging, an imaging device in which two optical systems are arranged to have a parallax with respect to each other is used. Patent Document 1 discloses a stereo optical system that is compact while ensuring a baseline length between the two fisheye lenses by arranging two optical systems (fisheye lenses) in parallel and placing two reflecting members in each fisheye lens to bend the optical path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-8629 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, in a wide-angle optical system such as a fisheye lens, a front group with negative refractive power is arranged closer to the object side than the aperture stop, and a rear group with positive refractive power is arranged closer to the image side than the aperture stop. In such an optical configuration, the lens configuration is asymmetric with respect to the aperture stop, so it is difficult to achieve a wide angle of view while satisfactorily correcting various aberrations such as astigmatism and curvature of field.

[0005] In addition, in the stereo optical system disclosed in Patent Document 1, the distance from the intermediate group including two reflecting members and an aperture stop to the front group on the object side and the distance from the intermediate group to the rear group are both long, and the optical system tends to become large. In order to make the optical system compact, it is necessary to strengthen the refractive power of each group. However, if the refractive power of each group is simply strengthened, it is difficult to obtain an optical system with a wide angle of view while satisfactorily correcting various aberrations such as astigmatism and curvature of field.

[0006] The present invention provides a stereo optical system that can ensure a sufficient baseline length, has a wide angle of view, is compact, and yet has various aberrations well corrected, and an imaging device equipped with the same. [Means for solving the problem]

[0007] A stereo optical system according to one aspect of the present invention has two optical systems arranged in parallel. Each of the two optical systems includes a front group having a negative refractive power, and a Positive refractive power The intermediate group, Positive refractive power It consists of a rear group. The intermediate group includes two reflecting surfaces, Due to the bending of the optical path by the two reflecting surfaces, the optical axis distance between the rear group is narrower than the optical axis distance between the front groups in the two optical systems. One of the two reflecting surfaces, or a reflecting member having one of the two reflecting surfaces, is located at the most object side and the most image side of the intermediate group, respectively. . before Let f1, f2 and f3 be the focal lengths at the d-line of the first, middle and rear groups, respectively, and f be the focal length of the optical system. -4.00≦f1 / f≦-2. 303 0.55≦ | f3 / f2 | ≦0.90 The present invention is characterized in that the following conditions are satisfied: An imaging device including the above-described stereo optical system also constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, it is possible to ensure a sufficient baseline length, and to realize a stereo optical system that has a wide angle of view, is compact, and yet has various aberrations well corrected. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a horizontal cross-sectional view of the stereo optical system according to the embodiment. [Diagram 2] 3A and 3B are diagrams showing optical images formed by the stereo optical system of the embodiment. [Diagram 3]FIG. 2 is a horizontal cross-sectional view of one optical system that constitutes the stereo optical system of the first embodiment. [Figure 4] FIG. [Diagram 5] FIG. 11 is a horizontal cross-sectional view of an optical system that constitutes a stereo optical system according to a second embodiment. [Figure 6] FIG. 11 is an aberration diagram of the second embodiment. [Figure 7] FIG. 11 is a horizontal cross-sectional view of an optical system that constitutes a stereo optical system according to a third embodiment. [Figure 8] 11A to 11C are aberration diagrams of Example 3. [Figure 9] 1A and 1B are external views of an imaging device including a stereo optical system according to each embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, matters common to the following embodiments 1 to 3 will be described with reference to Figs. 1 to 4. The stereo optical system of each embodiment is used in imaging devices such as digital cameras, video cameras, broadcast cameras, surveillance cameras, and silver halide film cameras.

[0011] FIG. 1 shows a horizontal cross section of a stereo optical system 100 of the first embodiment. The stereo optical system 100 has two optical systems 101 and 102 arranged in parallel in the horizontal direction. In each figure, the left side is the object side (front side) and the right side is the image side (rear side). The optical systems 101 and 102 have the same configuration except for the direction of reflection of light by a reflecting member, which will be described later. The optical system 101 will be described below.

[0012] The optical system 101 has a first reflecting member 103 and a second reflecting member 105, each of which has two reflecting surfaces R1 and R2. The reflecting surfaces R1 and R2 each reflect light rays and bend the optical path. An aperture stop SP that determines (limits) the light flux of the open F-number (Fno) is provided between the first reflecting member 103 and the second reflecting member 105. An imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, or a film surface of a silver halide film is disposed on the image plane IP.

[0013] 2 is a schematic diagram showing an optical image (image circle) formed by the stereo optical system 100. Optical images IC1 and IC2 are formed by the optical systems 101 and 102, respectively, on an image plane IP. When the imaging surface of a single imaging element is disposed on the image plane IP, two optical images having a parallax between them can be captured by the imaging element. However, the two optical images formed by the two optical systems 101 and 102 may be captured by different imaging elements, respectively.

[0014] FIG. 3 shows a horizontal cross section of the optical system L0 (101). OA indicates the optical axis (reference ray) of the optical system L0. The optical system L0 has a first lens group L1 as a front group, a second lens group L2 as an intermediate group, and a third lens group L3 as a rear group, which are arranged in this order from the object side to the image side. The first lens group L1 has a negative refractive power as a whole. The second lens group L2 is composed of the above-mentioned reflecting surfaces R1 and R2 (first and second reflecting members 103 and 105), and an aperture stop SP and a positive lens arranged therebetween. The third lens group L3 has a positive refractive power as a whole. Due to the bending of the optical path by the above-mentioned reflecting surfaces R1 and R2, as shown in FIG. 1, the optical axis distance between the third lens group L3 (between the rear group) of the two optical systems 101 and 102 is narrower than the optical axis distance between the first lens group L1 (between the front group).

[0015] Between the third lens group L3 and the image surface IP, a glass block GB, such as a low-pass filter or an IR cut filter, is disposed.

[0016] In this embodiment, both the second lens group L2 and the third lens group L3 have positive refractive power, but it is sufficient that at least one of the second lens group L2 and the third lens group L3 has positive refractive power.

[0017] In addition, in each embodiment, a lens is disposed between the first and second reflecting members PR1, PR2 in the second lens group L2, but the entrance surfaces and exit surfaces of the first reflecting member PR1 and the second reflecting member PR2 may be formed as refractive surfaces instead of lenses.

[0018] FIG. 4 shows various aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system L0 of the first embodiment when focused at infinity. In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the dashed line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS indicates the sagittal image plane, and the dashed line ΔM indicates the meridional image plane. The distortion aberration is shown for the d-line. The chromatic aberration diagram shows the chromatic aberration of magnification at the g-line. ω is the half angle of view (°) obtained by ray tracing.

[0019] The optical system L0 in each embodiment employs an equiangular (equidistant) projection method. In the equiangular projection method, y is defined as y=fω, where y is the half image height, ω is the half angle of view, and f is the focal length. However, various projection methods, such as an equisolid angle projection method or a stereoscopic projection method, may be employed.

[0020] As described above, in the stereo optical system of each embodiment, a wide angle of view and high optical performance are achieved by providing an appropriate negative refractive power to the first lens group L1.

[0021] In addition, by disposing the first and second reflecting members 103 and 105 on the first and third lens group sides of the second lens group L2, respectively, it is possible to ensure a large baseline length while maintaining a small overall size. In a wide-angle lens such as that in each embodiment, the height of the light passing through the first and third lens groups tends to be higher than the height of the light passing through the second lens group. In addition, by using two reflecting members, it is possible to achieve a small configuration that can form two optical images formed by the stereo optical system on a single imaging element while ensuring a large baseline length.

[0022] Furthermore, by providing the third lens group L3 with an appropriate refractive power, it is possible to satisfactorily correct mainly off-axis aberrations occurring in the first lens group L1, and it is also possible for the third lens group L3 to correct mainly on-axis aberrations that could not be fully corrected by the second lens group L2.

[0023] In the following, specific conditions that should be satisfied in the above-mentioned optical configuration in order to ensure a sufficient base line length and to satisfactorily correct various aberrations while having a wide angle of view and a compact size will be described.

[0024] First, when the focal lengths of the first, second and third lens groups L1, L2 and L3 are f1, f2 and f3, respectively, and the focal length of the optical system L0 (entire system) is f, the following conditional expressions (1) and (2) must be satisfied.

[0025] -4.00≦f1 / f≦-2.00 (1) 0.55≦ | f3 / f2 | ≦0.90 (2) Conditional formula (1) shows the condition for realizing a wide angle of view, compactness, and high optical performance. If the focal length of the first lens group L1 is too long with respect to the focal length of the entire system so that f1 / f is below the lower limit of conditional formula (1), the negative refractive power of the first lens group L1 becomes too weak, making it difficult to achieve a wide angle of view and compactness of the entire system, which is not preferable. Also, if the focal length of the first lens group L1 is too short with respect to the focal length of the entire system so that f1 / f exceeds the upper limit of conditional formula (1), the negative refractive power of the first lens group L1 becomes too strong, making it difficult to correct various aberrations such as field curvature and astigmatism, which is not preferable.

[0026] Condition (2) represents a condition for realizing high optical performance. | f3 / f2 | If the focal length of the third lens group L3 becomes too short relative to the focal length of the second lens group L2 so that falls below the lower limit of conditional expression (2), the refractive power of the third lens group L3 becomes too strong, causing significant off-axis aberrations such as curvature of field and astigmatism. This is undesirable because it becomes difficult to obtain high optical performance. | f3 / f2 |If the focal length of the third lens group L3 becomes too long relative to the focal length of the second lens group L2 so that exceeds the upper limit of conditional expression (2), the refractive power of the third lens group L3 becomes too weak, which is undesirable because it becomes difficult to obtain high optical performance by correcting near-axial aberrations such as spherical aberration and coma aberration that could not be fully corrected by the second lens group L3.

[0027] It is more preferable that the numerical range of conditional expression (1) is as follows: -3.80≦f1 / f≦-2.10 (1a) It is even more preferable that the numerical range of conditional expression (1) is as follows: -3.50≦f1 / f≦-2.20 (1b) It is more preferable that the numerical range of conditional expression (2) is as follows:

[0028] 0.60≦ | f3 / f2 | ≦0.88 (2a) It is even more preferable that the numerical range of conditional expression (2) is as follows:

[0029] 0.65≦ | f3 / f2 | ≦0.86 (2b) In each embodiment, it is desirable to satisfy the following conditions.

[0030] In the second lens group L2, it is desirable that the refractive power of the lens provided between the reflecting surface R1 of the first reflecting member 103 and the reflecting surface R2 of the second reflecting member 105 is positive. In other words, it is desirable that the second lens group L2 has a positive refractive power. This makes it possible to converge the light beam diverged by the negative lens group in the first lens group L1, making it easier to make the entire system compact.

[0031] Furthermore, when the refractive index for the d-line of all the lenses constituting the first lens group L1 is taken as NdB1, it is desirable to satisfy the following conditional expression (3).

[0032] 1.70≦NdB1≦2.2 (3) Conditional formula (3) shows a condition for easily correcting various aberrations to obtain high optical performance. If NdB1 falls below the lower limit of conditional formula (3), the refractive index for the d-line of all the lenses in the first lens group L1 becomes too low, which is undesirable because it becomes difficult to correct various aberrations such as spherical aberration and curvature of field. If NdB1 exceeds the upper limit of conditional formula (3), the refractive index for the d-line of all the lenses in the first lens group L1 becomes too high, which is undesirable because it becomes difficult to manufacture the glass material for forming each lens. Moreover, this is undesirable because the correction balance of various aberrations such as spherical aberration and curvature of field in the entire system is lost.

[0033] It is more preferable that the numerical range of conditional expression (3) be as follows:

[0034] 1.75≦NdB1≦2.2 (3a) It is even more preferable that the numerical range of conditional expression (3) is as follows: 1.80≦NdB1≦2.2 (3b) Furthermore, when the refractive index for the d-line of at least one of the lenses constituting the third lens group L2 is NdB3, it is desirable to satisfy the following conditional expression (4). 1.70≦NdB3≦2.20 (4) Conditional formula (4) shows a condition for easily correcting various aberrations to obtain high optical performance. If NdB3 is below the lower limit of conditional formula (4), the refractive index of at least one lens constituting the third lens group L3 to the d-line becomes too low, which is undesirable because it becomes difficult to correct various aberrations such as astigmatism and curvature of field. If NdB3 is above the upper limit of conditional formula (4), the refractive index of at least one lens constituting the third lens group L3 to the d-line becomes too high, which is undesirable because it becomes difficult to manufacture the glass material constituting the lens.

[0035] It is more preferable that the numerical range of conditional expression (4) be as follows: 1.72≦NdB3≦2.2 (4a) It is even more preferable that the numerical range of condition (4) is as follows: 1.75≦NdB3≦2.2 (4b) In addition, in the second lens unit L2, it is desirable to place the aperture stop SP between the two reflecting surfaces R1, R2, which allows the effective diameters of the first lens unit L1 and the third lens unit L3 to be reduced in a well-balanced manner, thereby making it possible to reduce the size of the entire system.

[0036] Also, the distance on the optical axis from the lens surface closest to the image in the first lens group L1 to the aperture stop SP is defined as D1s, and the distance on the optical axis from the lens surface closest to the object (first surface) in the optical system L0 to the lens surface closest to the image (last surface) in the optical system L0 is defined as D1k. In this case, it is desirable to satisfy the following conditional expression (5).

[0037] 0.20≦D1s / D1k≦0.35 (5) Conditional formula (5) indicates a condition for making it easy to ensure a large base line length while miniaturizing the entire optical system. When D1s / D1k is below the lower limit of conditional formula (5), the axial distance from the lens surface closest to the image in the first lens group L1 to the aperture stop step SP becomes too small compared to the axial distance from the first surface to the final surface of the optical system. As a result, it becomes difficult to secure a sufficient base line length by disposing the first reflecting member 103, which is not preferable. Also, when D1s / D1k exceeds the upper limit of conditional formula (5), the axial distance from the lens surface closest to the image in the first lens group L1 to the aperture stop SP becomes too large compared to the axial distance from the first surface to the final surface of the optical system. As a result, it becomes difficult to miniaturize the entire system, which is not preferable.

[0038] It is more preferable that the numerical range of condition (5) be as follows: 0.23≦D1s / D1k≦0.32 (5a) It is even more preferable that the numerical range of condition (5) is as follows: 0.27≦D1s / D1k≦0.30 (5b) Furthermore, the distance on the optical axis from the aperture stop SP to the lens surface in the third lens group L3 closest to the object is denoted by Ds3, and the distance on the optical axis from the first surface to the final surface in the optical system L0 is denoted by D1k. In this case, it is desirable to satisfy the following conditional expression (6).

[0039] 0.10≦Ds3 / D1k≦0.35 (6) Conditional formula (6) indicates a condition for making it easy to ensure a large base line length while making the entire system compact. When Ds3 / D1k is below the lower limit of conditional formula (6), the distance on the optical axis from the aperture stop SP to the lens surface closest to the object in the third lens group L3 becomes too small compared to the distance on the optical axis from the first surface to the final surface of the optical system. As a result, it is difficult to ensure a sufficient base line length by disposing the second reflecting member 105, which is not preferable. When Ds3 / D1k exceeds the upper limit of conditional formula (6), the distance on the optical axis from the aperture stop SP to the lens surface closest to the object in the third lens group L3 becomes too large compared to the distance on the optical axis from the first surface to the final surface of the optical system. As a result, it is difficult to make the entire system compact, which is not preferable.

[0040] It is more preferable that the numerical range of condition (6) be as follows: 0.15≦Ds3 / D1k≦0.30 (6a) It is even more preferable that the numerical range of condition (6) is as follows: 0.18≦Ds3 / D1k≦0.28 (6b) Moreover, it is desirable that the focal length f1 of the first lens group L1 and the focal length f3 of the third lens group L3 satisfy the following conditional expression (7).

[0041] -0.60≦f1 / f3≦-0.35 (7) Conditional formula (7) indicates a condition for facilitating obtaining high optical performance while miniaturizing the entire system. If f1 / f3 falls below the lower limit of conditional formula (7), the focal length of the first lens group L1 becomes too long relative to the focal length of the third lens group L3, which is difficult to miniaturize the entire system, which is undesirable. If f1 / f3 exceeds the upper limit of conditional formula (7), the focal length of the first lens group L1 becomes too short relative to the focal length of the third lens group L3. As a result, various aberrations such as field curvature and distortion occurring in the first lens group L1 become large, which is undesirable because it is difficult to obtain high optical performance.

[0042] It is more preferable that the numerical range of condition (7) be as follows: -0.56≦f1 / f3≦-0.38 (7a) It is even more preferable that the numerical range of condition (7) be as follows: -0.52≦f1 / f3≦-0.40 (7b) Moreover, it is desirable that the half angle of view ω determined by ray tracing satisfies the following conditional expression (8).

[0043] 92.5°≦ω≦120.0° (8) Conditional formula (8) indicates a condition related to the angle of view. If ω is below the lower limit of conditional formula (8), it becomes difficult to achieve a wide angle of view exceeding 185°, which is undesirable. Also, if ω exceeds the upper limit of conditional formula (8), the diameter of the first lens unit L1 becomes too large, which is undesirable.

[0044] It is more preferable that the numerical range of conditional expression (8) be as follows: 94.0°≦ω≦115.0° (8a) It is even more preferable that the numerical range of conditional expression (8) be as follows: 94.5°≦ω≦110.0° (8b) Also, let Din be the base length, which is the distance between the vertices of the lens surfaces closest to the object in the two optical systems 101 and 102, in other words, the distance between the optical axes of the first lens group L1 in the two optical systems 101 and 102 (the optical axis distance between the front groups). Let Dout be the distance between the vertices of the lens surfaces closest to the image in the two optical systems 101 and 102, in other words, the optical axis distance between the third lens group L3 (between the rear groups) in the two optical systems 101 and 102. In this case, it is desirable to satisfy the following conditional expression (9). 0.05≦Dout / Din≦0.50 (9) Conditional formula (9) indicates a condition for making it easy to obtain a large baseline length while miniaturizing the stereo optical system. If Dout / Din is below the lower limit of conditional formula (9), the surface vertex distance of the lens surface closest to the object becomes too large compared to the surface vertex distance of the lens surface closest to the image, which is undesirable because the stereo optical system becomes large. Also, if Dout / Din exceeds the upper limit of conditional formula (9), the surface vertex distance of the lens surface closest to the object becomes too small compared to the surface vertex distance of the lens surface closest to the image, which is undesirable because it becomes difficult to obtain a large baseline length.

[0045] It is more preferable that the numerical range of condition (9) be as follows: 0.20≦Dout / Din≦0.40 (9a) It is even more preferable that the numerical range of condition (9) is as follows: 0.24≦Dout / Din≦0.35 (9b) The stereo optical system of each embodiment will be described below with specific numerical examples. EXAMPLES

[0046] 3, the optical system L0 is a fisheye lens having a focal length f of 4.77 mm, an F-number Fno of 2.8, and a half angle of view ω of 105.0°. The optical system L0 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power, arranged in this order from the object side to the image side.

[0047] The first lens group L1 is composed of, arranged in order from the object side to the image side, a negative meniscus lens convex on the object side, a negative meniscus lens convex on the object side, a negative meniscus lens convex on the image side, a positive meniscus lens convex on the image side, and a positive meniscus aspheric lens convex on the image side. This composition makes it possible to achieve a wide angle of view while effectively correcting various aberrations such as field curvature.

[0048] The second lens group L2 is composed of, in order from the object side to the image side, a reflecting surface R1 arranged on the first lens group L1 side, an aperture stop SP, a cemented lens consisting of a negative meniscus lens convex toward the object side and a positive lens having a biconvex shape, and a reflecting surface R2 arranged on the third lens group L3 side. This configuration ensures a long base length while being compact. In addition, by arranging the aperture stop SP between the reflecting surfaces R1 and R2, the effective diameters of the first lens group L1 and the third lens group L3 can be reduced in a well-balanced manner, and the entire system can be made compact. Furthermore, by arranging the cemented lens between the reflecting surfaces R1 and R2, various aberrations such as spherical aberration and axial chromatic aberration can be well corrected to obtain high optical performance.

[0049] The third lens group L3 is composed of, in order from the object side to the image side, a biconvex positive aspherical lens, a biconvex positive lens, a cemented lens consisting of a negative meniscus lens convex toward the object side and a biconvex positive lens, and a cemented lens consisting of a biconcave negative lens and a biconvex positive lens. This composition makes it possible to satisfactorily correct off-axis aberrations such as lateral chromatic aberration and curvature of field, thereby achieving high optical performance.

[0050] During focusing, the entire optical system L0 moves. This makes it possible to keep aberration fluctuations that accompany focusing small. However, it is also possible to move only a part of the optical system L0 during focusing. This also applies to other embodiments described below.

[0051] In the first embodiment, the surface vertex distance Dout of the lens surface closest to the image side is 18.5 mm. With this setting, two optical images formed by the stereo optical system can be captured by a single imaging element of a general full size (36 mm wide x 24 mm long). In this case, the surface vertex distance (baseline length) Din of the lens surface closest to the object side is 65 mm, which is close to the average human eye width. EXAMPLES

[0052] In the stereo optical system of Example 2 (Numerical Example 2) shown in Fig. 5, the optical system L0 is a fisheye lens with a focal length f of 4.99 mm, an F-number Fno of 2.8, and a half angle of view ω of 100.0°. The optical system L0 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power, arranged in this order from the object side to the image side. Fig. 6 shows various aberrations of the optical system L0 of this embodiment in an infinity focused state.

[0053] The first lens group L1 is composed of, arranged in order from the object side to the image side, a negative meniscus lens convex on the object side, a negative meniscus lens convex on the object side, a negative meniscus lens convex on the image side, a positive meniscus lens convex on the image side, and a positive meniscus aspheric lens convex on the image side. This composition makes it possible to achieve a wide angle of view and correct various aberrations such as field curvature.

[0054] The second lens group L2 is composed of a reflecting surface R1, an aperture stop SP, a cemented lens consisting of a negative meniscus lens convex toward the object side and a positive lens having a biconvex shape, and a reflecting surface R2, which are arranged in this order from the object side to the image side. This configuration ensures a long base length while being compact. Moreover, by arranging the aperture stop SP between the reflecting surfaces R1 and R2, the effective diameters of the first lens group L1 and the third lens group L3 can be reduced in a well-balanced manner, resulting in a compact optical system as a whole. Furthermore, by arranging the cemented lens between the reflecting surfaces R1 and R2, various aberrations such as spherical aberration and axial chromatic aberration can be well corrected to obtain high optical performance.

[0055] The third lens group L3 is composed of, from the object side to the image side, a biconvex positive aspherical lens, a biconvex positive lens, a cemented lens consisting of a negative meniscus lens convex toward the object side and a biconvex positive lens, and a cemented lens consisting of a biconcave negative lens and a biconvex positive lens. This composition makes it possible to satisfactorily correct off-axis aberrations such as lateral chromatic aberration and curvature of field, thereby achieving high optical performance.

[0056] In the second embodiment, the surface vertex distance Dout of the lens surface closest to the image side is 18.5 mm. With this setting, two optical images formed by the stereo optical system can be captured by a single imaging element of a general full size (36 mm wide x 24 mm long). In this case, the surface vertex distance (baseline length) Din of the lens surface closest to the object side is 63 mm, which is close to the average human eye width. EXAMPLES

[0057] In the stereo optical system of Example 3 (Numerical Example 3) shown in Fig. 7, the optical system L0 is a fisheye lens with a focal length f of 5.11 mm, an F-number Fno of 2.91, and a half angle of view ω of 95.2°. The optical system L0 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power. Fig. 8 shows various aberrations of the optical system L0 of this embodiment in an infinity focused state.

[0058] The first lens group L1 is composed of, arranged in order from the object side to the image side, a negative meniscus lens convex toward the object side, a negative meniscus lens convex toward the object side, a biconcave negative lens, and a positive meniscus lens convex toward the image side. This configuration makes it easy to achieve a wide angle of view and correct various aberrations such as field curvature.

[0059] The second lens group L2 is composed of a reflecting surface R1, an aperture stop SP, a cemented lens consisting of a negative meniscus lens convex toward the object side and a positive lens having a biconvex shape, and a reflecting surface R2, which are arranged in this order from the object side to the image side. This configuration ensures a long base line length while being compact. In addition, by arranging the aperture stop SP between the reflecting surfaces R1 and R2, the effective diameters of the first lens group L1 and the third lens group L3 can be reduced in a well-balanced manner, and a stereo optical system with a compact overall system can be obtained. Furthermore, by arranging the cemented lens between the reflecting surfaces R1 and R2, it is possible to easily correct various aberrations such as spherical aberration and axial chromatic aberration, and to obtain high optical performance.

[0060] The third lens group L3 is composed of, in order from the object side to the image side, a biconvex positive lens, a biconvex positive lens, and a cemented lens composed of a biconcave negative lens and a biconvex positive lens. This configuration makes it possible to effectively correct off-axis aberrations such as lateral chromatic aberration and curvature of field, and easily obtain high optical performance.

[0061] In the third embodiment, the surface vertex distance Dout of the lens surface closest to the image side is 18.5 mm. With this setting, two optical images formed by the stereo optical system can be captured by a single imaging element of a general full size (36 mm wide x 24 mm long). In this case, the surface vertex distance (baseline length) Din of the lens surface closest to the object side is 60 mm, which is close to the average human eye width.

[0062] Specific numerical data for Numerical Examples 1 to 3 are shown below. In each of the Numerical Examples, i indicates the order of the surface or optical member counted from the object side, r indicates the radius of curvature of the i-th optical surface (i-th surface), and d indicates the axial distance between the i-th surface and the (i+1)-th surface. In addition, nd is the refractive index at the d-line of the optical material between the i-th surface and the (i+1)-th surface, and νdi is the Abbe number based on the d-line of the optical material between the i-th surface and the (i+1)-th surface.

[0063] The Abbe number νd is given by the following equation, where Nd, NF, and NC are the refractive indices at the d line (587.6 nm), F line (486.1 nm), and C line (656.3 nm) of the Fraunhofer lines: νd=(Nd-1) / (NF-NC) It is expressed as:

[0064] The numerical data also shows the effective diameter (mm) of the i-th surface. BF stands for back focus (mm). Back focus is the distance on the optical axis from the final surface of the optical system (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. The total lens length is the distance on the optical axis from the foreground surface of the optical system (the lens surface closest to the object) to the final surface plus the back focus.

[0065] An "*" next to a surface number means that the surface is aspheric. The shape of an aspheric surface is expressed by the following formula, where the optical axis direction is the x-axis, the direction perpendicular to the optical axis is the h-axis, the direction of light travel is positive, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, and A8 are aspheric coefficients. The conic constant and the aspheric coefficient "eZ" are expressed as x10 -Z means...

[0066] x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ] +A4·h 4 +A6·h 6 +A8·h 8 The values ​​of conditional expressions (1) to (10) in Examples (Numerical Examples) 1 to 3 are shown in Table 1. [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd θ(°) Effective diameter 1 39.599 2.10 1.90043 37.4 46.27 2 13.205 9.00 25.68 3 31.760 1.00 1.95375 32.3 22.82 4 11.388 8.97 17.88 5 -12.544 0.95 1.81600 46.6 16.60 6 -37.460 1.71 17.84 7 -17.391 2.68 1.84666 23.8 17.94 8 -14.160 0.20 19.02 9* -21.888 2.35 1.88202 37.2 18.88 10 -15.223 7.85 19.46 11 ∞ 6.90 1.51633 64.1 12.71 12 (reflective surface) ∞ -6.90 45.0 17.60 13∞ -5.00 8.78 14 (Aperture) ∞ -1.25 9.43 15 -38.102 -0.45 1.90043 37.4 9.63 16 -14.825 -3.35 1.53172 48.8 9.58 17 19.760 -0.20 9.77 18 ∞ -6.10 1.51633 64.1 9.67 19(Reflective surface) ∞ 6.10 -45.0 15.55 20∞2.00 11.20 21 63.009 1.34 1.76450 49.1 12.41 22* -2089.595 0.20 12.63 23 21.844 4.06 1.43875 94.7 13.12 24 -21.621 0.20 13.30 25 274.552 0.85 1.83481 42.7 13.10 26 12.043 5.35 1.49700 81.5 12.82 27 -20.286 0.20 13.20 28 -31.128 0.75 1.90043 37.4 13.13 29 15.449 6.49 1.49700 81.5 13.58 30 -14.954 10.50 15.00 31(GB) ∞ 1.00 1.51633 64.1 32∞0.50 Image plane ∞ Aspheric Data 9th page K = 0.00000e+000 A 4=-2.49519e-005 A 6=-2.75892e-008 A 8=-1.71304e-010 Page 22 K = 0.00000e+000 A 4= 4.30985e-005 A 6= 1.27585e-007 A 8=-1.47051e-009 Various data Focal length 4.77 F-number 2.80 Half angle of view (°) 105.0 Image height 8.75 Lens length 106.16 BF 11.66 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -13.91 28.96 1.11 -39.88 L2 11 38.88 -10.25 17.67 -8.37 L3 21 33.03 19.44 6.30 -9.59 Single lens data Lens starting surface focal length 1 1 -22.87 2 3 -19.07 3 5 -23.51 4 7 65.25 5 9 48.66 6 15 -27.20 7 16 16.48 8 21 80.03 9 23 25.49 10 25 -15.11 11 26 16.09 12 28 -11.38 13 29 16.46 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd θ(°) Effective diameter 1 40.416 2.20 1.88100 40.1 43.90 2 12.438 9.53 24.16 3 62.468 1.05 1.95375 32.3 21.83 4 13.847 8.19 18.04 5 -12.415 1.00 1.81600 46.6 17.18 6 -21.150 1.23 18.43 7 -15.573 2.82 1.85478 24.8 18.49 8 -15.046 0.20 20.02 9* -24.848 2.60 1.88202 37.2 20.00 10 -15.967 10.87 20.59 11 ∞ 6.50 1.51633 64.1 12.00 12 (reflective surface) ∞ -6.50 45.0 16.64 13∞ -3.93 9.01 14 (Aperture) ∞ -1.26 9.47 15 -61.434 -0.47 1.90043 37.4 9.64 16 -15.285 -3.39 1.56732 42.8 9.62 17 20.271 -0.20 9.88 18 ∞ -6.50 1.51633 64.1 9.81 19(Reflective surface) ∞ 6.50 -45.0 6.67 20∞1.82 12.00 21 69.157 1.40 1.76450 49.1 13.14 22* -525.804 0.20 13.37 23 17.194 4.57 1.43875 94.7 14.06 24 -23.678 0.20 14.05 25 121.658 0.89 1.83481 42.7 13.63 26 10.245 5.48 1.53775 74.7 12.99 27 -28.806 0.20 13.13 28 -32.828 0.79 1.90043 37.4 13.08 29 12.667 6.83 1.53775 74.7 13.45 30 -16.339 10.50 14.91 31 ∞ 1.00 1.51633 64.1 32∞0.50 Image plane ∞ Aspheric Data 9th page K = 0.00000e+000 A 4=-2.20088e-005 A 6=-2.13895e-008 A 8=-1.55620e-010 Page 22 K = 0.00000e+000 A 4= 2.46058e-005 A 6= 6.99324e-008 A 8= 7.64111e-011 Various data Focal length 4.99 F-number 2.80 Half angle of view (°) 100.0 Image height 8.75 Lens length 108.98 BF 11.66 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -15.98 28.82 -0.55 -44.19 L2 11 47.05 -9.25 16.70 -8.23 L3 21 32.06 20.56 4.87 -11.73 Single lens data Lens starting surface focal length 1 1 -21.17 2 3 -18.85 3 5 -38.83 4 7 150.00 5 9 44.53 6 15 -22.71 7 16 15.91 8 21 80.03 9 23 23.50 10 25 -13.45 11 26 14.78 12 28 -10.07 13 29 14.46 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd θ(°) Effective diameter 1 37.835 1.90 1.85150 40.8 37.77 2 10.876 5.96 21.04 3 17.413 1.05 2.00100 29.1 19.44 4 10.527 7.09 16.28 5 -14.039 0.85 1.83481 42.7 15.27 6 94.650 1.60 15.83 7 -122.590 3.83 1.90366 31.3 16.29 8 -15.687 6.90 16.79 9 ∞ 6.70 1.51633 64.1 10.75 10 (reflective surface) ∞ -6.70 45.0 14.22 11∞ -2.05 7.75 12 (Aperture) ∞ -1.67 8.06 13 -31.669 -0.50 1.91082 35.3 8.36 14 -11.896 -2.98 1.54072 47.2 8.31 15 19.425 -0.15 8.53 16 ∞ -6.70 1.51633 64.1 8.49 17(Reflective surface) ∞ 6.70 -45.0 17.01 18∞2.07 12.30 19 39.406 2.06 1.80809 22.8 13.94 20 -89.544 0.15 14.12 21 18.103 4.36 1.43700 95.1 14.41 22 -25.920 0.30 14.11 23 -146.187 0.75 2.00069 25.5 13.54 24 9.713 6.79 1.49700 81.6 12.88 25 -22.914 12.00 14.03 26 ∞ 1.00 1.51633 64.1 27∞0.50 Image plane ∞ Various data Focal length 5.14 F-number: 2.91 Half angle of view (°) 95.2 Image height 8.55 Lens length 92.98 BF 13.16 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -11.83 22.29 1.57 -23.85 L2 9 39.02 -7.35 14.64 -9.12 L3 19 27.96 14.41 1.44 -9.13 Single lens data Lens starting surface focal length 1 1 -18.53 2 3 -28.79 3 5 -14.59 4 7 19.57 5 13 -21.17 6 14 14.12 7 19 34.11 8 21 25.15 9 23 -9.08 10 24 14.74

[0067] [Table 1]

[0068] 9 shows a digital still camera as an imaging device using the stereo optical system of each of the above-mentioned embodiments as an imaging optical system. Reference numeral 20 denotes a camera body, and 21 denotes an imaging optical system constituted by the stereo optical system of any of the embodiments 1 to 5. Reference numeral 22 denotes a solid-state imaging element such as a CCD sensor or a CMOS sensor that is built into the camera body 20 and captures an optical image (subject image) formed by the imaging optical system 21. Reference numeral 23 denotes a recording unit that records image data generated by processing an imaging signal from the imaging element 22, and 24 denotes a rear display that displays the image data.

[0069] By using the stereo optical system of each embodiment, a small-sized camera capable of stereoscopic viewing and having high optical performance can be obtained.

[0070] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0071] 100 Stereo Optical System 101, 102 Optical system R1,R2 reflective surface IP image plane L1 First lens group L2 Second lens group L3: Third lens group

Claims

1. A stereo optical system having two optical systems arranged in parallel, each of the two optical systems includes, arranged in order from the object side to the image side, a front group having negative refractive power, an intermediate group having positive refractive power, and a rear group having positive refractive power; The intermediate group includes two reflecting surfaces, a distance between the optical axes of the rear groups is narrower than a distance between the optical axes of the front groups in the two optical systems due to bending of the optical paths by the two reflecting surfaces, a reflecting member having one of the two reflecting surfaces or one of the two reflecting surfaces is disposed at a position closest to the object side and a position closest to the image side in the intermediate group, Let f1, f2 and f3 be the focal lengths of the front group, the intermediate group and the rear group with respect to the d-line, respectively, and f be the focal length of the optical system. −4.00≦f1 / f≦−2.303 0.55≦|f3 / f2|≦0.90 A stereo optical system characterized by satisfying the following conditions.

2. 2. The stereo optical system according to claim 1, wherein a lens is disposed between the two reflecting surfaces in the intermediate group.

3. 3. The stereo optical system according to claim 1, wherein an aperture stop is provided between the two reflecting surfaces in the intermediate group.

4. When the refractive index of each of the lenses constituting the front group with respect to the d-line is NdB1, 1.70≦NdB1≦2.20 4. The stereo optical system according to claim 1, wherein the following condition is satisfied:

5. When the refractive index of at least one of the lenses constituting the rear group with respect to the d-line is NdB3, 1.70≦NdB3≦2.20 5. The stereo optical system according to claim 1, wherein the following condition is satisfied:

6. Let D1s be the distance on the optical axis from the lens surface in the front group closest to the image side to the aperture stop, and D1k be the distance on the optical axis from the lens surface in the optical system closest to the object side to the lens surface in the optical system closest to the image side, 0.20≦D1s / D1k≦0.35 4. The stereo optical system according to claim 3, wherein the following condition is satisfied:

7. Let Ds3 be the distance on the optical axis from the aperture stop to the lens surface in the rear group closest to the object side. 0.10≦Ds3 / D1k≦0.35 7. The stereo optical system according to claim 6, wherein the following condition is satisfied:

8. the rear group has positive refractive power, −0.60≦f1 / f3≦−0.35 8. The stereo optical system according to claim 1, wherein the following condition is satisfied:

9. A stereo optical system having two optical systems arranged in parallel, each of the two optical systems includes, arranged in order from the object side to the image side, a front group having negative refractive power, an intermediate group having positive refractive power, and a rear group having positive refractive power; The intermediate group includes two reflecting surfaces, a distance between the optical axes of the rear groups is narrower than a distance between the optical axes of the front groups in the two optical systems due to bending of the optical paths by the two reflecting surfaces, a reflecting member having one of the two reflecting surfaces or one of the two reflecting surfaces is disposed at a position closest to the object side and a position closest to the image side in the intermediate group, Let f1, f2 and f3 be the focal lengths of the front group, the intermediate group and the rear group with respect to the d-line, respectively, and f be the focal length of the optical system. −4.00≦f1 / f≦−2.00 0.55≦|f3 / f2|≦0.90 −0.60≦f1 / f3≦−0.35 A stereo optical system characterized by satisfying the following conditions.

10. When the half angle of view at the d line is ω, 92.5°≦ω≦120.0° 10. The stereo optical system according to claim 1, wherein the following condition is satisfied:

11. In the two optical systems, the optical axis distance between the front groups is defined as Din, and the optical axis distance between the rear groups is defined as Dout. 0.05≦Dout / Din≦0.50 11. The stereo optical system according to claim 1, wherein the following condition is satisfied:

12. A stereo optical system according to any one of claims 1 to 11, and an image sensor for capturing an optical image formed by the two optical systems.

13. 13. The imaging device according to claim 12, wherein the two optical systems form the optical image on a single imaging element.

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