Stereo optical system and imaging device

Abstract

To provide a compact stereo optical system which allows for capturing stereoscopic wide-angle images.SOLUTION: Each of two optical systems comprises a front group L1 having negative refractive power, an intermediate group having two reflective surfaces PR1, PR2, and a rear group L3 arranged in order from the object side to the image side. Bending of light paths by the reflective surfaces makes an optical axial distance Dout between the rear groups smaller than an optical axial distance Din between the front groups of the two optical systems. At least either of the intermediate group and the rear group has positive refractive power. The front group consists of a first sub group L1A consisting of one or more negative lenses disposed on the object side of a positive lens of the front group located on the most object side, and a second sub group L1B having positive refractive power, arranged in order form the object side to the image side. The optical system satisfies conditions expressed as: 0.20≤f1A / f1≤0.42, 0.61≤|f3 / f2|≤0.90, where f1, f2, f3, and f1A respectively represent focal lengths of the front group, intermediate group, rear group, and first sub group for the d-ray.SELECTED DRAWING: Figure 11

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 an imaging device in which the image circles of two fisheye lenses are housed in a single imaging element.

[0003] In order to obtain a realistic stereoscopic image, it is considered good to arrange the baseline length of the two optical systems to the width of a human eye (approximately 60 to 65 mm). However, since the size of an imaging element is generally smaller than the width of a human eye, simply arranging fisheye lenses will result in part of their image circles falling outside the imaging element. For this reason, in the imaging device of Patent Document 1, two reflecting members are arranged in each fisheye lens to bend the optical path, thereby fitting the image circles of the two fisheye lenses into a single imaging element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-8629 A Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses an embodiment in which the angle of view is 158° to 183°, but there is a demand for images with a wider angle of view to provide more realistic stereoscopic images.

[0006] However, in a fisheye lens including two reflecting members, the overall length is long in order to secure space for arranging the reflecting members. Therefore, the lens closest to the object side and the lens closest to the image side are farther away from the aperture, and when the angle of view is widened, the outer diameter of the lens closest to the object side is likely to become large. If the refractive power of the negative lens group closest to the object side including the lens closest to the object side is increased in order to reduce the outer diameter of the lens closest to the object side, the axial light rays are largely diverged and enter the aperture, so the aperture diameter becomes large.

[0007] The present invention provides a compact stereo optical system capable of capturing a stereoscopic image with a wide angle of view, and an imaging device including the same. [Means for solving the problem]

[0008] 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, in order from the object side to the image side, a front group having a negative refractive power, an intermediate group including two reflecting surfaces, and a rear group. Consists of Due to the bending of the optical path by the two reflecting surfaces, the optical axis distance between the rear groups is narrower than the optical axis distance between the front groups in the two optical systems. a reflecting member having one of two reflecting surfaces is disposed closest to the object side in the intermediate group, and a reflecting member having the other of the two reflecting surfaces is disposed closest to the image side in the intermediate group, At least one of the intermediate group and the rear group has positive refractive power. The front group is arranged in order from the object side to the image side. The first subgroup has a negative refractive power and the second subgroup has a positive refractive power, and the lens located closest to the object in the second subgroup is the positive lens located closest to the object among all the positive lenses located in the front group. Let f1, f2, f3 and f1A be the focal lengths of the front group, intermediate group, rear group and first subgroup at the d-line, respectively. 0.20≦f1A / f1≦0.42 0.61≦|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

[0009] According to the present invention, it is possible to realize a compact stereo optical system capable of capturing a stereoscopic image with a wide angle of view, and an imaging device including the same. [Brief description of the drawings]

[0010] [Figure 1]FIG. 2 is a vertical sectional view of the stereo optical system of the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of the stereo optical system of the first embodiment. [Diagram 3] FIG. 11 is a vertical sectional view of the stereo optical system according to the second embodiment. [Figure 4] 11A to 11C are aberration diagrams of the stereo optical system of the second embodiment. [Diagram 5] FIG. 11 is a vertical sectional view of the stereo optical system according to the third embodiment. [Figure 6] 11A to 11C are aberration diagrams of the stereo optical system of the third embodiment. [Figure 7] FIG. 11 is a vertical sectional view of the stereo optical system according to the fourth embodiment. [Figure 8] 13A to 13C are aberration diagrams of the stereo optical system of the fourth embodiment. [Figure 9] FIG. 13 is a vertical sectional view of the stereo optical system according to the fifth embodiment. [Figure 10] 13A to 13C are aberration diagrams of the stereo optical system of the fifth embodiment. [Figure 11] FIG. 2 is a horizontal cross-sectional view of the stereo optical system of the first embodiment. [Figure 12] 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

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The stereo optical system of the first to fifth embodiments has a configuration in which two optical systems are arranged in parallel with respect to a single imaging element in order to capture a stereoscopic image. 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.

[0012] 1, 3, 5, 7 and 9 respectively show vertical cross sections of the stereo optical system of Examples (numerical examples) 1, 2, 3, 4 and 5. Fig. 11 shows a horizontal cross section of the stereo optical system of Example 1.

[0013] In each diagram, the left side is the object side (front side) and the right side is the image side (rear side). Li (i=1, 2, 3) indicates the order of the lens groups when counting from the object side to the image side. SP is the aperture stop. IP is the image plane. The imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film camera is located on the image plane IP. Although not shown, optical blocks such as an optical filter, face plate, low-pass filter, and infrared cut filter can also be located on the object side of the image plane IP.

[0014] As shown in Fig. 11, the stereo optical system is composed of two optical systems arranged in parallel in the horizontal direction. In the first embodiment, the surface vertex distance (Din) between the lens surfaces closest to the object side of the two optical systems, in other words, the base length, which is the distance between the optical axes of the first lens group L1 in the two optical systems (the optical axis distance between the front groups), is set to 60 mm. The base length may be about 60 to 65 mm, which corresponds to the human eye width.

[0015] Each optical system includes two reflecting members PR1 and PR2 each having a reflecting surface, and the light beam is reflected twice by the reflecting surface to bend the optical path as shown in FIG. 11. FIGS. 1, 3, 5, 7, and 9 show the optical path in a developed form. In each embodiment, a prism is used as the first and second reflecting members PR1 and PR2, but a mirror may be used. Furthermore, as shown in the right part of FIG. 11, an image sensor (IP) viewed from the front side is shown, and the image circle of the two optical systems is formed to be contained within a single image sensor, and the two optical images formed by the two optical systems are captured by the image sensor. However, the two optical images formed by the two optical systems may be captured by different image sensors.

[0016] Figures 2, 4, 6, 8 and 10 respectively show various aberrations (spherical aberration, astigmatism, distortion and chromatic aberration) of the optical systems of Numerical Examples 1, 2, 3, 4 and 5 when focused at infinity. In the spherical aberration diagrams, 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 diagrams, 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 diagrams show the chromatic aberration of magnification at the g-line. ω is the half angle of view (°).

[0017] Numerical Example 1 is an example in which an imaging element with a short side length of 24 mm and a long side length of 36 mm is used. Since the baseline length is 60 mm and the long side length of the imaging element is 36 mm, which is longer than the baseline length, two reflecting members PR1 and PR2 are provided in each optical system and the two optical systems are brought closer to each other in the portion close to the imaging element, so that the image circles of both optical systems are contained on a single imaging element.

[0018] In this case, the image circle of one optical system needs to be within a range of 18 mm, which is half the length of the long side of the image sensor. In Numerical Example 1, the image circle diameter of each optical system is set to 17.5 mm, and a distance of 1 mm is set between the image circles of the two optical systems. In this case, the surface vertex distance (Dout) of the lens surfaces closest to the image side of the two optical systems, in other words, the optical axis distance between the third lens groups L3 (between the rear groups) in the two optical systems, is 18.5 mm. In this case, the distance on the optical axis between the two reflecting members (reflecting surfaces) in each optical system is 20.75 mm. In addition, the image circle of each optical system is formed so as to be inscribed in the short side of the image sensor.

[0019] The optical system in each embodiment employs a conformal projection method. In the conformal projection method, the half image height is defined as y=fω, where y is the half angle of view, ω is the half angle of view, and f is the focal length. In Numerical Example 1, the image circle diameter is 17.5 mm, so the half image height is y=8.75 mm, the focal length is f=4.78 mm, and the half angle of view is ω=104.88°.

[0020] Numerical Example 2 is also an example in which an image sensor with a base length of 60 mm, a short side length of 24 mm, and a long side length of 36 mm is used. The image circle diameter of each optical system is set to 17.1 mm, and a distance of 1.4 mm is set between the image circles of the two optical systems. In this case, the surface vertex distance (Dout) of the lens surfaces closest to the image side of the two optical systems is 18.5 mm. In addition, the image circle of each optical system is 0.2 mm away from the short side of the image sensor so that the image circle does not deviate from the image sensor even if the position of the optical axis is shifted due to manufacturing error. In Numerical Example 2, the half image height y=8.55 mm, the focal length f=5.13 mm, and the half angle of view ω=95.49°.

[0021] The base line length, the size of the imaging element, and the diameter and interval of the image circle in Numerical Example 3 are the same as those in Numerical Example 1. The focal length f is 4.74 mm, and the half angle of view ω is 105.75°.

[0022] Numerical Example 4 is an example in which an imaging element with a base length (Din) of 65 mm, a short side length of 24 mm, and a long side length of 36 mm is used. The surface vertex distance (Dout) of the lens surfaces closest to the image side of the two optical systems is set to 18.5 mm, and the distance on the optical axis between the two reflecting members of each optical system is 23.25 mm. In this numerical example, the image circle diameter is 17.5 mm, the half image height y=8.75 mm, the focal length f=4.89 mm, and the half angle of view ω=102.44°.

[0023] Numerical example 5 is an example in which an imaging element with a base length (Din) of 60.5 mm, a short side length of 15 mm, and a long side length of 22.5 mm is used. The image circle diameter of each optical system is set to 10.5 mm, and a distance of 1 mm is set between the image circles of the two optical systems. In this case, the surface vertex distance (Dout) of the lens surfaces closest to the image side of the two optical systems is 11.5 mm. The image circles of each optical system are 0.25 mm away from the short side of the imaging element. In this numerical example, the half image height y=5.25 mm, the focal length f=3.02 mm, and the half angle of view ω=99.67°.

[0024] Although the optical system in each embodiment employs a conformal projection system, various projection systems, such as a conformal solid angle projection system or a stereoscopic projection system, may be employed.

[0025] Next, the specific configuration of the optical system of each embodiment will be described. The optical system of each embodiment has a first lens group (front group) L1 with negative refractive power, a first reflecting member PR1, a second lens group L2 with positive refractive power having an aperture stop SP, an intermediate group composed of the second reflecting member PR2, and a third lens group (rear group) L3 with positive refractive power, which are arranged in order from the object side to the image side. The front group with negative refractive power and the rear group with positive refractive power arranged on either side of the aperture stop SP form a retrofocus type refractive power arrangement, thereby realizing an optical system that is compact overall but has a wide angle of view.

[0026] In each 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 them has positive refractive power.

[0027] In addition, in each embodiment, the second lens group L2 is disposed between the first and second reflecting members PR1, PR2 in the intermediate group, 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 the second lens group L2.

[0028] In the optical system of each embodiment, an aperture stop SP is disposed between two reflecting members PR1 and PR2. In order to form the image circles of the two optical systems on a single image sensor as shown in Fig. 11, the lenses after the second reflecting member PR2 of the two optical systems must be placed close to each other. In other words, by bending the optical path by the first and second reflecting members PR1 and PR2, the optical axis distance between the third lens group L3 (between the rear groups) of the two optical systems must be narrower than the optical axis distance between the first lens group L1 (between the front groups).

[0029] For this reason, if the aperture stop SP is located closer to the object side than the first reflecting member PR1, the lens diameter of the lens closest to the image side will increase, which may cause interference with the lens closest to the image side of the other optical system. On the other hand, if the aperture stop SP is located closer to the image side than the second reflecting member PR2, the lens diameter of the lens closest to the object side will increase, which may cause an increase in the weight of the optical system or cause interference with the lens closest to the object side of the other optical system.

[0030] When two reflecting members are included in each optical system, as in the optical systems of the respective embodiments, the overall optical length becomes long. For this reason, the first lens group L1 and the third lens group L3 are positioned away from the aperture stop SP. If the angle of view is simply increased in this configuration, the lens diameters of the lenses closest to the object and closest to the image, whose effective diameter is determined by off-axis rays, will increase, causing interference between the lenses and an increase in weight.

[0031] Therefore, in order to suppress the increase in the effective diameter of the lens closest to the object side due to the wide angle, it is advisable to increase the refractive power of the first lens group L1, which has a negative refractive power. However, since the distance between the first lens group L1 and the aperture stop SP is wide, if the refractive power of the first lens group L1 is increased, the axial light rays are largely diverged by the first lens group L1, and as a result, the aperture stop SP becomes large. In addition, the first reflecting member PR1 also becomes large, so the weight increases. This tendency becomes even stronger when the diameter of the optical system is increased. Therefore, in order to suppress the increase in the effective diameter and the aperture diameter of the lens closest to the object side, it is necessary to appropriately set the refractive power arrangement of the lenses constituting the first lens group L1.

[0032] For this reason, in the optical system of each embodiment, the first lens group L1 is composed of a 1A lens group (first subgroup) L1A and a 1B lens group (second subgroup) L1B arranged from the object side to the image side. The 1A lens group L1A has a negative refractive power as a whole and is composed of one or more lenses from the negative lens closest to the object in the first lens group L1 to a negative lens on the object side of the positive lens closer to the image side. That is, the 1A lens group L1A is composed of one or more negative lenses arranged on the object side of the positive lens arranged closest to the object side among the positive lenses included in the first lens group L1. The 1B lens group L1B has a positive refractive power as a whole and is composed of at least one lens after the positive lens.

[0033] The optical system of each embodiment is characterized in that it satisfies the following conditional expression (1).

[0034] 0.20≦f1A / f1≦0.42 (1) In conditional formula (1), f1A represents the focal length of the first lens group L1A, and f1 represents the focal length of the first lens group L1.

[0035] Conditional formula (1) shows a condition for achieving both a small diameter of the lens closest to the object side and a small size of the intermediate group consisting of the first reflecting member PR1, the second lens group, and the second reflecting member PR2. In each embodiment, the first lens group L1 is composed of the first A lens group L1A with strong negative refractive power and the first B lens group L1B with strong positive refractive power, so that the first lens group L1 as a whole has a weak negative refractive power. The first A lens group L1A with strong negative refractive power reduces the diameter of the lens closest to the object side, and the first B lens group L1B with strong positive refractive power reduces the divergence effect of the on-axis light beam passing through the first lens group L1, thereby realizing a small size of the intermediate group.

[0036] If f1A / f1 falls below the lower limit of conditional formula (1), the refractive power of the 1A lens group L1A becomes too strong, causing the intermediate group to become large and increasing off-axis aberrations such as curvature of field and distortion, which is undesirable. Also, if f1A / f1 exceeds the upper limit of conditional formula (1), the refractive power of the 1A lens group L1A becomes too weak, causing the lens closest to the object to have a large diameter, which is undesirable.

[0037] It is more preferable that the numerical range of conditional expression (1) is as follows:

[0038] 0.22≦f1A / f1≦0.40 (1a) It is even more preferable that the numerical range of conditional expression (1) is as follows:

[0039] 0.23≦f1A / f1≦0.35 (1b) In addition, in the optical system of each embodiment, the second lens group L2 with positive refractive power is disposed between the first and second reflecting members (reflecting surfaces), and off-axis light rays after passing through the aperture stop SP are converged toward the optical axis, thereby suppressing an increase in the effective lens diameter of the third lens group L3. However, the second lens group L2 is disposed near the aperture stop SP, and has a large effect on on-axis aberrations such as spherical aberration and coma aberration. Therefore, in order to achieve both high performance of the optical system and a small diameter of the third lens group L3, it is necessary to appropriately set the refractive powers of the second lens group L2 and the third lens group L3.

[0040] Therefore, when the focal length of the second lens group L2 with respect to the d-line is f2 and the focal length of the third lens group L3 with respect to the d-line is f3, the optical system of each embodiment satisfies the following conditional expression (2).

[0041] 0.61≦|f3 / f2|≦0.90 (2) Conditional formula (2) indicates a condition related to the optical performance of the optical system and the reduction in the diameter of the third lens group L3. If |f3 / f2| falls below the lower limit of conditional formula (2), the refractive power of the second lens group L2 becomes too small, reducing the convergence of off-axis rays as described above, and the diameter of the third lens group L3 becomes too large, which may cause interference with the other lenses, which is undesirable. If |f3 / f2| exceeds the upper limit of conditional formula (2), the refractive power of the second lens group L2 becomes too large, which increases on-axis aberrations such as spherical aberration and coma aberration, and reduces optical performance, which is undesirable.

[0042] It is more preferable to set the numerical range of condition (2) as follows:

[0043] 0.63≦|f3 / f2|≦0.88 (2a) It is even more preferable to set the numerical range of condition (2) as follows:

[0044] 0.64≦|f3 / f2|≦0.85 (2b) By adopting the above configuration and satisfying the above conditional expressions, it is possible to achieve a wide angle of view, a large aperture, and a compact size in a stereo optical system in which two optical systems are arranged horizontally to form their respective image sensors on a single imaging element.

[0045] Furthermore, when the focal length of the 1B lens unit L1B with respect to the d-line is f1B, it is desirable to satisfy the following conditional expression (3).

[0046] -1.95≦f1B / f1≦-1.10 (3) Conditional formula (3) indicates a condition related to the size and optical performance of the first reflecting member PR1 and the aperture stop SP. If f1B / f1 falls below the lower limit of conditional formula (3), the refractive power of the first-B lens group L1B becomes too small, making it impossible to converge the axial light beam diverging from the first-A lens group L1A, and the first reflecting member PR1 and the aperture stop SP become large, which is undesirable. Also, if f1B / f1 exceeds the upper limit of conditional formula (3), off-axis aberrations such as curvature of field and distortion occurring in the first-B lens group L1B become large, which is undesirable because it degrades the optical performance.

[0047] It is more preferable to set the numerical range of condition (3) as follows:

[0048] -1.80≦f1B / f1≦-1.15 (3a) It is even more preferable to set the numerical range of condition (3) as follows:

[0049] -1.66≦f1B / f1≦-1.20 (3b) Furthermore, when the focal length of the optical system with respect to the d-line is f and the focal length of the second lens unit L2 with respect to the d-line is f2, it is desirable to satisfy the following conditional expression (4).

[0050] 6.10≦f2 / f≦10.90 (4) Conditional formula (4) shows the condition related to the optical performance of the optical system and the small diameter of the third lens group L3. If f2 / f is below the lower limit of conditional formula (4), the refractive power of the second lens group L2 becomes too large, and on-axis aberrations such as spherical aberration and coma aberration increase, which is not preferable. If f2 / f is above the upper limit of conditional formula (4), the refractive power of the second lens group L2 becomes too weak, and the convergence action of off-axis rays toward the optical axis after passing through the aperture stop SP becomes small. As a result, the effective diameter of the third lens group L3 increases, which is not preferable because it may interfere with the third lens group L3 of the other optical system.

[0051] It is more preferable to set the numerical range of condition (4) as follows:

[0052] 6.60≦f2 / f≦10.40 (4a) It is even more preferable to set the numerical range of condition (4) as follows:

[0053] 7.10≦f2 / f≦9.90 (4b) Furthermore, when the focal length of the third lens group with respect to the d-line is f3, it is desirable to satisfy the following conditional expression (5).

[0054] 4.40≦f3 / f≦9.60 (5) Conditional formula (5) shows the condition related to the optical performance of the optical system and the reduction in the diameter of the third lens group L3. If f3 / f is below the lower limit of conditional formula (5), the refractive power of the third lens group L3 becomes too large, which increases off-axis aberrations such as curvature of field and distortion, which is not preferable. If f3 / f exceeds the upper limit of conditional formula (5), the refractive power of the third lens group L3 becomes too weak, which reduces the convergence action of off-axis rays toward the optical axis after passing through the aperture stop SP. As a result, the effective diameter of the third lens group L3 increases, which is not preferable because it may interfere with the third lens group L3 of the other optical system.

[0055] It is more preferable to set the numerical range of condition (5) as follows:

[0056] 4.70≦f3 / f≦9.20 (5a) It is even more preferable to set the numerical range of condition (5) as follows:

[0057] 5.00≦f3 / f≦8.80 (5b) In addition, when the surface vertex distance (baseline length) of the lens surfaces closest to the object in the two optical systems is Din and the surface vertex distance of the lens surfaces closest to the image is Dout, it is desirable to satisfy the following conditional expression (6).

[0058] 0.05≦Dout / Din≦0.50 (6) Conditional formula (6) is a conditional formula related to the sense of three-dimensionality and discomfort felt by the viewer when viewing a three-dimensional image. If Dout / Din falls below the lower limit of conditional formula (6), the baseline length becomes much wider than the human eye width, which is undesirable since the parallax between the images obtained through the two optical systems becomes too large, which may cause discomfort or fatigue to the viewer. If Dout / Din exceeds the upper limit of conditional formula (6), the parallax becomes too small and no sense of three-dimensionality can be obtained, which is undesirable.

[0059] It is more preferable to set the numerical range of condition (6) as follows:

[0060] 0.10≦Dout / Din≦0.45 (6a) It is even more preferable to set the numerical range of condition (6) as follows:

[0061] 0.15≦Dout / Din≦0.40 (6b) Furthermore, when the average value of the refractive index for the d-line of the plurality of negative lenses constituting the 1A lens group L1A is taken as N1Aave, it is desirable to satisfy the following conditional expression (7).

[0062] 1.80≦N1Aave≦2.20 (7) Conditional formula (7) shows a condition related to the optical performance of the optical system. As described above, the first-A lens group L1A has a strong negative refractive power in order to reduce the diameter of the first lens group L1. Therefore, off-axis aberrations such as field curvature and distortion are likely to occur, and in order to achieve high image quality, it is advisable to use a glass material with a high refractive index. If N1Aave falls below the lower limit of conditional formula (7), the refractive index of the negative lens in the first-A lens group L1A is too low, which increases off-axis aberrations, which is undesirable. Also, if N1Aave exceeds the upper limit of conditional formula (7), the workability of the lens decreases, which is undesirable.

[0063] It is more preferable to set the numerical range of condition (7) as follows:

[0064] 1.85≦N1Aave≦2.10 (7a) It is even more preferable to set the numerical range of condition (7) as follows:

[0065] 1.88≦N1Aave≦2.05 (7b) Furthermore, when the refractive index for the d-line of the positive lens having the greatest refractive power among at least one positive lens constituting the 1B lens subgroup L1B is set to N1Bp, it is desirable to satisfy the following conditional expression (8).

[0066] 1.78≦N1Bp≦2.20 (8) Conditional formula (8) indicates the condition regarding the optical performance of the optical system and the miniaturization of the first reflecting member PR1 and the aperture stop SP. As described above, the 1B lens group L1B converges the axial light beam that is strongly diverged by the 1A lens group L1A, and the subsequent 1st reflecting member PR1 and the aperture stop SP are miniaturized. If N1Bp is below the lower limit of conditional formula (8), the refractive power of the 1B lens group becomes too strong, and the aberration generated by the 1B lens group becomes large, which is undesirable as it degrades the optical performance. If N1Bp is above the upper limit of conditional formula (8), it is undesirable as it degrades the workability of the lens.

[0067] It is more preferable to set the numerical range of condition (8) as follows:

[0068] 1.80≦N1Bp≦2.10 (8a) It is even more preferable to set the numerical range of condition (8) as follows:

[0069] 1.83≦N1Bp≦2.05 (8b) Furthermore, when the half angle of view determined by ray tracing of the optical system is denoted by ω, it is desirable to satisfy the following conditional expression (9):

[0070] 85.0°≦ω≦120.0° (9) If ω is below the lower limit of conditional expression (9), the angle of view is insufficient when viewing a stereoscopic image, making it difficult to obtain a sufficient sense of realism, which is undesirable.If ω exceeds the upper limit of conditional expression (9), the number of pixels per incident angle on the imaging element decreases, making the resolution of the stereoscopic image insufficient, which is undesirable.

[0071] It is more preferable to set the numerical range of condition (9) as follows:

[0072] 87.5≦ω≦115.0 (9a) It is even more preferable to set the numerical range of condition (9) as follows:

[0073] 90.0≦ω≦110.0 (9b) Furthermore, when the F-number of the optical system is Fno, it is desirable to satisfy the following conditional expression (10):

[0074] 2.00≦Fno≦4.50 (10) If Fno is below the lower limit of conditional expression (10), the first and second reflecting members PR1 and PR2 and the aperture stop SP will become large, which is undesirable, and if Fno exceeds the upper limit of conditional expression (10), image quality will deteriorate due to increased noise during imaging, which is undesirable.

[0075] It is more preferable to set the numerical range of condition (10) as follows:

[0076] 2.20≦Fno≦4.10 (10a) It is even more preferable to set the numerical range of condition (10) as follows:

[0077] 2.40≦Fno≦3.60 (10b) Next, the configuration of each lens group in each embodiment will be described. In embodiments 1, 2, 4, and 5, the first A lens group L1A is composed of a negative meniscus lens with a convex surface on the object side, a negative meniscus lens with a convex surface on the object side, and a biconcave lens, which are arranged in this order from the object side to the image side. In addition, in embodiment 4, the image side surface of the biconcave lens is aspheric to correct off-axis aberrations such as curvature of field and distortion. In embodiment 3, the first A lens group L1A is composed of a negative meniscus lens with a convex surface on the object side, a biconcave lens, and a negative meniscus lens with a convex surface on the image side, which are arranged in this order from the object side to the image side.

[0078] In the first embodiment, the first lens group L1B is composed of a positive meniscus lens with a convex surface on the image side and a negative meniscus lens with a convex surface on the image side, which are arranged in order from the object side to the image side. In addition, the image side surface of the negative meniscus lens is aspheric to correct off-axis aberrations such as curvature of field and distortion. In the second and fourth embodiments, the first lens group L1B is composed of a positive meniscus lens with a convex surface on the image side. In the third embodiment, the first lens group L1B is composed of a cemented lens of a positive meniscus lens with a convex surface on the image side and a negative meniscus lens with a convex surface on the image side, which are arranged in order from the object side to the image side. In addition, the image side surface of the negative meniscus lens is aspheric to correct off-axis aberrations such as curvature of field and distortion. In the fifth embodiment, the first lens group L1B is composed of a biconvex lens.

[0079] In addition, in the first to fifth embodiments, prisms are used as the first and second reflecting members PR1, PR2.

[0080] In Examples 1 to 4, the second lens group L2 is composed of an aperture stop SP, a cemented lens of a negative meniscus lens convex on the object side, and a biconvex lens, arranged in that order from the object side to the image side. In Example 5, the second lens group L2 is composed of an aperture stop SP, a negative meniscus lens convex on the object side, and a biconvex lens, arranged in that order from the object side to the image side.

[0081] Furthermore, in Examples 1 and 3, the third lens group L3 is composed of a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a cemented lens of a negative meniscus lens with a convex surface on the object side and a biconvex lens, which are arranged in this order from the object side to the image side. In Example 2, the third lens group L3 is composed of a biconvex lens, a biconvex lens, and a cemented lens of a biconcave lens and a biconvex lens, which are arranged in this order from the object side to the image side. In Example 4, the third lens group L3 is composed of a cemented lens of a biconvex lens and a negative meniscus lens with a convex surface on the image side, a biconvex lens, and a cemented lens of a negative meniscus lens with a convex surface on the object side and a biconvex lens, which are arranged in this order from the object side to the image side. In Example 5, the third lens group L3 is composed of a biconvex lens, a cemented lens of a negative meniscus lens with a convex surface on the object side and a biconvex lens, which are arranged in this order from the object side to the image side.

[0082] Specific numerical data for Numerical Examples 1 to 5 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.

[0083] 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:

[0084] 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.

[0085] The first and second reflecting members in each numerical example are described as one block of material. In reality, each reflecting member is arranged so as to bend the light beam by 45 degrees with respect to the center of the block of material.

[0086] In addition, in each numerical example, a method is adopted in which the entire optical system is moved in the direction of the optical axis when focusing from an object at infinity to an object at a close distance. In order to reduce the weight of the drive unit that drives the optical system, it is also possible to drive a part of the optical system for focusing. 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, A8, A10 (, A12) are aspheric coefficients. The "ex" of the conic constant and aspheric coefficients is x 10 -x means...

[0087]

number

[0088] The values ​​of conditional expressions (1) to (10) in Examples (Numerical Examples) 1 to 5 are summarized in Table 1. [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 34.245 1.75 2.00100 29.1 38.55 2 10.727 8.36 21.09 3 40.942 0.95 1.95375 32.3 19.57 4 17.998 5.62 17.39 5 -14.473 0.95 1.88300 40.8 16.55 6 485.400 2.55 17.39 7 -30.711 4.23 2.00069 25.5 17.94 8 -13.665 0.59 18.90 9 -12.726 1.55 1.58313 59.4 18.41 10* -13.253 6.90 18.95 11 ∞ 13.00 1.51633 64.1 12.30 12∞3.00 8.43 13 (Aperture) ∞ 0.50 8.81 14 34.485 0.70 1.90043 37.4 8.91 15 12.617 3.80 1.54072 47.2 8.84 16 -19.342 0.25 9.09 17 ∞ 12.00 1.51633 64.1 9.01 18 ∞ 1.63 10.41 19 13.588 3.89 1.43875 94.7 12.17 20 -19.839 0.20 12.25 21 -41.411 0.85 1.83481 42.7 12.09 22 9.542 5.12 1.49700 81.5 12.15 23 -25.605 0.30 13.08 24 23.211 0.75 1.90043 37.4 13.98 25 13.141 4.61 1.49700 81.5 13.83 26 -73.713 13.51 14.32 Image plane ∞ Aspheric Data Side 10 K = 0.00000e+000 A 4= 3.30939e-005 A 6=-1.46934e-008 A 8= 8.65575e-010 A10=-1.57365e-012 Various data Focal length 4.78 F-number 2.80 Half angle of view (°) 104.88 Image height 8.75 Lens length 97.55 BF 13.51 Entrance pupil position 10.45 Exit pupil position -50.46 Front principal point position 14.87 Back principal point position 8.73 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -14.49 26.54 -1.19 -40.65 L2 13 38.90 5.00 3.20 -0.17 L3 19 30.52 15.71 4.44 -7.19 Single lens data Lens starting surface focal length 1 1 -16.21 2 3 -34.37 3 5 -15.90 4 7 21.89 5 9 6615.95 6 11 0.00 7 14 -22.44 8 15 14.74 9 17 0.00 10 19 19.06 11 21 -9.22 12 22 14.70 13 24 -34.87 14 25 22.84 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 37.835 1.90 1.85150 40.8 38.26 2 11.044 5.89 21.36 3 16.936 1.05 2.00100 29.1 19.71 4 10.396 7.26 16.44 5 -14.348 0.85 1.85150 40.8 15.40 6 78.512 1.83 15.94 7 -171.522 3.90 1.91650 31.6 16.52 8 -16.120 6.99 17.01 9 ∞ 13.40 1.51633 64.1 10.84 10∞2.05 7.72 11 (Aperture) ∞ 1.65 8.01 12 32.437 0.50 1.90043 37.4 8.29 13 11.736 3.00 1.54072 47.2 8.25 14 -19.189 0.15 8.46 15 ∞ 13.40 1.51633 64.1 8.42 16 ∞ 2.17 12.34 17 40.449 2.00 1.80809 22.8 14.04 18 -112.028 0.15 14.23 19 19.706 4.25 1.49700 81.6 14.55 20 -26.991 0.32 14.29 21 -125.299 0.75 2.00069 25.5 13.72 22 9.886 6.90 1.49700 81.6 13.06 23 -22.112 13.21 14.22 Image plane ∞ Various data Focal length 5.13 F-number: 2.91 Half angle of view (°) 95.49 Image height 8.55 Lens length 93.57 BF 13.21 Entrance pupil position 10.91 Exit pupil position -54.55 Front principal point position 15.66 Back principal point position 8.08 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -12.41 22.68 1.27 -25.53 L2 11 39.29 5.15 3.80 -0.08 L3 17 27.80 14.37 1.87 -8.65 Single lens data Lens starting surface focal length 1 1 -18.93 2 3 -29.24 3 5 -14.19 4 7 19.18 5 9 0.00 6 12 -20.66 7 13 13.94 8 15 0.00 9 17 36.99 10 19 23.63 11 21 -9.13 12 22 14.81 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 32.204 1.75 2.00100 29.1 38.50 2 10.699 10.58 21.07 3 -78.044 0.95 2.00100 29.1 18.41 4 24.653 4.81 16.60 5 -14.061 0.95 1.91082 35.3 16.18 6 -60.746 1.47 17.36 7 -43.270 4.57 2.00069 25.5 17.96 8 -13.755 1.50 1.58313 59.4 18.81 9* -14.442 7.07 19.10 10 ∞ 13.00 1.51633 64.1 12.30 11∞3.00 8.29 12 (Aperture) ∞ 0.50 8.64 13 40.250 0.70 1.87070 40.7 8.72 14 12.989 3.80 1.54072 47.2 8.67 15 -20.730 0.25 8.94 16 ∞ 12.00 1.51633 64.1 8.88 17 ∞ 1.50 10.86 18 18.363 3.55 1.43875 94.7 12.39 19 -20.988 0.20 12.62 20 -78.396 0.85 1.83481 42.7 12.58 21 13.807 3.95 1.49700 81.5 12.71 22 -74.957 0.30 13.35 23 15.313 0.75 2.00100 29.1 14.22 24 9.426 6.50 1.49700 81.5 13.58 25 -65.349 13.51 14.31 Image plane ∞ Aspheric Data 9th page K = 0.00000e+000 A 4= 3.82080e-005 A 6= 1.00161e-007 A 8=-1.70767e-010 A10= 4.27075e-012 Various data Focal length 4.74 F-number 2.80 Half angle of view (°) 105.75 Image height 8.75 Lens total length 98.00 BF 13.51 Entrance pupil position 10.62 Exit pupil position -49.18 Front principal point position 15.01 Back principal point position 8.77 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -15.82 26.58 -2.05 -45.04 L2 12 44.37 5.00 3.39 0.03 L3 18 28.89 16.09 3.69 -7.86 Single lens data Lens starting surface focal length 1 1 -16.69 2 3 -18.63 3 5 -20.28 4 7 18.70 5 8 -2533.25 6 10 0.00 7 13 -22.29 8 14 15.38 9 16 0.00 10 18 22.95 11 20 -14.00 12 21 23.81 13 23 -26.16 14 24 17.07 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 32.204 1.75 2.00100 29.1 38.51 2 10.624 7.72 20.97 3 24.232 0.95 2.00100 29.1 19.34 4 12.748 6.79 16.60 5 -12.957 0.95 1.85400 40.4 15.34 6* 278.285 2.15 16.29 7 -48.376 4.10 2.00100 29.1 17.03 8 -14.676 6.90 17.92 9 ∞ 13.00 1.51633 64.1 12.30 10 ∞ 1.50 8.64 11 (Aperture) ∞ 1.50 8.87 12 44.079 0.70 1.83481 42.7 9.13 13 13.067 3.80 1.54072 47.2 9.11 14 -17.531 3.25 9.41 15 ∞ 12.00 1.51633 64.1 9.00 16∞1.50 11.20 17 33.445 3.77 1.49700 81.5 12.40 18 -12.867 0.85 1.80400 46.6 12.76 19 -34.227 0.00 13.48 20 27.869 4.13 1.49700 81.5 14.06 21 -22.810 0.30 14.20 22 148.722 0.75 1.95375 32.3 13.82 23 10.283 6.47 1.49700 81.5 13.32 24 -27.769 13.51 14.32 Image plane ∞ Aspheric Data Side 6 K = 0.00000e+000 A 4= 3.25358e-005 A 6= 2.20598e-007 A 8=-6.10712e-009 A10= 3.74834e-011 A12=-7.69846e-014 Various data Focal length 4.89 F-number 2.80 Half angle of view (°) 102.44 Image height 8.75 Lens length 98.35 BF 13.51 Entrance pupil position 10.31 Exit pupil position -85.68 Front principal point position 14.97 Back principal point position 8.62 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -12.10 24.42 0.63 -31.44 L2 11 36.40 6.00 4.41 0.04 L3 17 30.57 16.27 4.35 -7.37 Single lens data Lens starting surface focal length 1 1 -16.51 2 3 -28.03 3 5 -14.48 4 7 19.84 5 9 0.00 6 12 -22.48 7 13 14.48 8 15 0.00 9 17 19.22 10 18 -26.11 11 20 25.94 12 22 -11.61 13 23 16.00 [Numerical example 5] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 21.335 1.10 2.00100 29.1 26.01 2 7.424 6.76 14.61 3 286.662 0.60 2.00100 29.1 13.07 4 12.363 4.48 11.49 5 -12.962 0.60 1.88300 40.8 10.31 6 18.337 1.15 10.60 7 31.801 3.11 1.84666 23.9 11.39 8 -12.417 3.47 11.69 9 ∞ 10.00 1.51633 64.1 9.50 10∞6.85 6.62 11 (Aperture) ∞ 0.15 7.03 12 26.581 0.80 1.88300 40.8 7.10 13 8.264 0.15 7.04 14 8.470 4.38 1.54072 47.2 7.20 15 -13.128 2.17 7.70 16 ∞ 10.00 1.51633 64.1 7.50 17 ∞ 1.03 8.13 18 9.163 2.19 1.43875 94.7 9.07 19 -230.699 0.13 9.00 20 23.408 0.50 2.00100 29.1 8.93 21 6.789 3.52 1.49700 81.5 8.52 22 -14.303 0.15 8.78 23 -50.245 0.50 2.00100 29.1 8.76 24 11.044 2.70 1.80810 22.8 8.88 25 -33.265 13.50 9.14 Image plane ∞ Various data Focal length 3.02 F-number 2.80 Half angle of view(°) 99.67 Image height 5.25 Lens total length 80.00 BF 13.50 Entrance pupil position 7.33 Exit pupil position -46.97 Front principal point position 10.19 Back principal point position 10.48 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 -6.61 17.81 1.75 -19.10 L2 11 29.80 5.48 4.14 0.62 L3 18 25.05 9.69 1.71 -5.04 Single lens data Lens starting surface focal length 1 1 -11.85 2 3 -12.92 3 5 -8.52 4 7 10.90 5 9 0.00 6 12 -13.86 7 14 10.25 8 16 0.00 9 18 20.14 10 20 -9.70 11 21 9.81 12 23 -9.01 13 24 10.55

[0089] [Table 1]

[0090] 12 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.

[0091] 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.

[0092] 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]

[0093] L1 First lens group L2 Second lens group L3: Third lens group L1A 1A lens group L1B 1Bth lens group IP image plane PR1 First reflector PR2 Second reflector

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 including two reflecting surfaces, and a rear group, 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 is disposed closest to the object side in the intermediate group, and a reflecting member having the other of the two reflecting surfaces is disposed closest to the image side in the intermediate group, At least one of the intermediate group and the rear group has positive refractive power, the front group includes, in order from the object side to the image side, a first sub-group having negative refractive power and a second sub-group having positive refractive power, the lens disposed closest to the object side in the second subgroup is a positive lens disposed closest to the object side among all the positive lenses disposed in the front group, Let f1, f2, f3 and f1A be the focal lengths of the front group, the intermediate group, the rear group and the first partial group with respect to the d-line, respectively. 0.20≦f1A / f1≦0.42 0.61≦|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 the intermediate group and the rear group both have positive refractive power.

3. When the focal length of the second subgroup with respect to the d-line is f1B, −1.95≦f1B / f1≦−1.10 3. The stereo optical system according to claim 1, wherein the following condition is satisfied:

4. the intermediate group has a positive refractive power, When the focal length of each of the two optical systems with respect to the d-line is f, 6.10≦f2 / f≦10.90 4. The stereo optical system according to claim 1, wherein the following condition is satisfied:

5. the rear group has positive refractive power, When the focal length of each of the two optical systems with respect to the d-line is f, 4.40≦f3 / f≦9.60 5. The stereo optical system according to claim 1, wherein the following condition is satisfied:

6. 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 6. The stereo optical system according to claim 1, wherein the following condition is satisfied:

7. When the average value of the refractive index for the d line of the negative lenses constituting the first subgroup is N1Aave, 1.80≦N1Aave≦2.20 7. The stereo optical system according to claim 1, wherein the following condition is satisfied:

8. When the refractive index of the positive lens having the largest refractive power among the positive lenses constituting the second subgroup is N1Bp for the d-line, 1.78≦N1Bp≦2.20 8. The stereo optical system according to claim 1, wherein the following condition is satisfied:

9. When the half angle of view of each of the two optical systems is ω, 85.0°≦ω≦120.0° 9. The stereo optical system according to claim 1, wherein the following condition is satisfied:

10. When the F-number of each of the two optical systems is Fno, 2.00≦Fno≦4.50 10. The stereo optical system according to claim 1, wherein the following condition is satisfied:

11. 11. The stereo optical system according to claim 1, further comprising a lens disposed between the two reflecting surfaces in the intermediate group.

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

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

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

Images