Lens device and imaging apparatus

Abstract

To provide a stereo optical system that can easily reduce an error in a variable focal length between two optical systems.SOLUTION: A stereo optical system has two optical systems 101, 102 arranged in parallel, and the two optical systems form two optical images in areas different from each other on a single imaging surface arranged on an image surface. The two optical systems each have a plurality of lens groups L1 to L3, and move one movable lens group of the plurality of lens groups to change an interval between the movable lens group and a lens group adjacent thereto, thereby changing a focal length.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a stereo optical system for stereoscopic photography. [Background technology]

[0002] There is a demand for a stereo optical system for acquiring stereoscopically viewable images for virtual reality and other applications. Patent Document 1 discloses a stereo optical system in which two super-wide-angle lenses are arranged in parallel. Patent Document 2 discloses an imaging device in which two zoom lenses with variable focal lengths are arranged in parallel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-8629 A [Patent Document 2] JP 2013-57738 A Summary of the Invention [Problem to be solved by the invention]

[0004] The stereo optical system disclosed in Patent Document 1 allows for 3D imaging using a full-circle fisheye lens, but it is difficult to vary the focal length. In addition, in the imaging device disclosed in Patent Document 2, multiple movable groups move to change the focal length, so the error in the position (amount of movement) of the movable groups between the two zoom lenses, that is, the difference in focal length, becomes significant, and there is a risk that an appropriate stereoscopic effect cannot be obtained during imaging.

[0005] The present invention provides a stereo optical system that makes it easier to suppress errors in the variable focal lengths of two optical systems. [Means for solving the problem]

[0006] A stereo optical system according to one aspect of the present invention has two optical systems arranged in parallel, and the two optical systems form two optical images in different regions of a single imaging plane on which the image plane is arranged. Each of the two optical systems has a plurality of lens groups, and the focal length is changed by moving one of the plurality of lens groups, thereby changing the distance between the movable lens group and the adjacent lens group. Note that an imaging device equipped with the stereo optical system also constitutes another aspect of the present invention. Effect of the Invention

[0007] According to the present invention, it is possible to provide a stereo optical system that makes it easier to suppress errors in the variable focal lengths of two optical systems. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan sectional view of a lens device and a stereo optical system according to the embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the stereo optical system of the first embodiment. [Diagram 3] 4A to 4C are aberration diagrams of the stereo optical system of the first embodiment. [Figure 4] FIG. 11 is a cross-sectional view of a stereo optical system according to a second embodiment. [Diagram 5] 11A to 11C are aberration diagrams of the stereo optical system of the second embodiment. [Figure 6] FIG. 11 is a cross-sectional view of a stereo optical system according to a third embodiment. [Figure 7] 11A to 11C are aberration diagrams of the stereo optical system of the third embodiment. [Figure 8] FIG. 11 is a cross-sectional view of a stereo optical system according to a fourth embodiment. [Figure 9] 13A to 13C are aberration diagrams of the stereo optical system of the fourth embodiment. [Figure 10] FIG. 13 is a cross-sectional view of the stereo optical system according to the fifth embodiment. [Figure 11] 13A to 13C are aberration diagrams of the stereo optical system of the fifth embodiment. [Figure 12] FIG. 13 is a cross-sectional view of a stereo optical system according to a sixth embodiment. [Figure 13] 13A to 13C are aberration diagrams of the stereo optical system of the sixth embodiment. [Figure 14]FIG. 1 is a schematic diagram of an imaging device equipped with a stereo optical system according to Examples 1 to 6. [Figure 15] 4A to 4C are diagrams showing optical images formed on an image sensor in each embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0010] FIG. 1 shows a cross section of a lens device 100 having a stereo optical system of each embodiment described later, as viewed from above. FIG. 1 also shows a cross section of an imaging device 110 to which the lens device 100 as an interchangeable lens is detachably attached. The imaging device 110 includes a digital video camera, a digital still camera, a broadcast camera, a surveillance camera, a silver halide film camera, and the like. The imaging device 110 may also be a camera for a mobile terminal such as a smartphone or a tablet. In FIG. 1, the left side is the object side, the right side is the image side, the upper side is the right side in the horizontal direction, and the lower side is the left side.

[0011] The lens device 100 holds a stereo optical system consisting of two optical systems 101 and 102 arranged in parallel on the left and right sides within a housing. The two optical systems 101 and 102 have the same configuration, and these optical systems 101 and 102 form a right subject image and a left subject image as two optical images in different regions on the imaging surface (single imaging surface) of a single image sensor 111 arranged on the image surface IP of the optical systems 101 and 102.

[0012] FIG. 15 shows right and left subject images (image circles) 121, 122 formed on the imaging surface of the imaging element 111 by the stereo optical system of each embodiment. The right subject image 121 is formed in a half area on the right side (shown on the left side in the figure) in the longitudinal direction of the imaging surface, and the left subject image 122 is formed in a half area on the left side (shown on the right side in the figure). By photoelectrically converting (capturing) these two subject images 121, 122 by the imaging element 111, captured images (image for the right eye and image for the left eye) are obtained as two parallax images that have parallax with each other and can be viewed stereoscopically. These images for the right eye and the left eye are displayed on a display element such as a liquid crystal panel or an organic EL panel in a stereoscopic display device such as a VR goggle or a head mounted display. An observer can recognize an image with a sense of stereoscopic feeling by viewing the image for the right eye with the right eye and the image for the left eye with the left eye.

[0013] It should be noted that the film surface of a silver halide film in a film camera serving as an imaging device may be disposed as a single imaging surface on the image surface IP.

[0014] 2, 4, 6, 8, 10, and 12 each show a cross section at the wide-angle end of one of the two optical systems in the stereo optical systems of Examples 1 to 6. In these figures, the left side is the object side, and the right side is the image side.

[0015] Each of the two optical systems 101 and 102 is composed of a first lens group L1, a second lens group L2, and a third lens group L3, arranged in this order from the object side to the image side. Each optical system is a zoom lens with a variable focal length, and the focal length is changed by moving the second lens group L2, which is a single movable lens group, without moving the first and third lens groups L1 and L3. The arrows in each figure indicate the movement trajectory of the second lens group L2 toward the object side when the focal length changes from the wide-angle end to the telephoto end.

[0016] A lens group is a group of one or more lenses that move together when changing the focal length (zooming) between the wide-angle end and the telephoto end. In other words, the distance between adjacent lens groups changes when the focal length is changed. The wide-angle end and the telephoto end respectively indicate the maximum angle of view (shortest focal length) and the minimum angle of view (maximum focal length) when the movable lens group is located at both ends of the range that can be moved mechanically or controlled along the optical axis.

[0017] In addition, SP in each figure is an aperture stop, which adjusts the amount of light that passes through each optical system and reaches the image plane IP.

[0018] In addition, although the two optical systems 101 and 102 in each embodiment are each composed of three lens groups, the first to third lens groups L1 to L3, each optical system may be composed of two lens groups. In this case, too, it is preferable to have only one movable lens group that is moved to change the focal length.

[0019] Next, a characteristic configuration of the stereo optical system of each embodiment will be described. In a stereo optical system capable of stereoscopic imaging, an observer observes the captured images (images for the right eye and the left eye) obtained by stereoscopic imaging through a display device such as VR goggles. In this case, since humans are very sensitive to the deviation of the images seen by the left and right eyes, it is necessary to reduce the relative error of the two optical systems constituting the stereo optical system. In order to make the focal length of the two optical systems variable under such conditions, it is effective to reduce the number of movable lens groups in each optical system. Moreover, a driving member such as a cam ring is required to move the movable lens group. However, if a driving member is provided for each of the two optical systems, the base length, which is the distance between the optical axes of the two optical systems, increases, making it difficult to accommodate the two optical images formed by the two optical systems on the imaging surface of a single imaging element. For this reason, in the two optical systems 101 and 102 of each embodiment, the focal length is changed by moving only the second lens group L2, which is one movable lens group.

[0020] Moreover, it is preferable that the optical systems 101 and 102 in each embodiment have the following configuration.

[0021] It is preferable to move the two second lens groups in the two optical systems 101 and 102 as a unit by a single actuator. This eliminates the need for a driving member such as a cam ring for each optical system, making it possible to both miniaturize the stereo optical system and ensure a sufficient baseline length.

[0022] In each optical system, as described above, it is preferable to change the focus adjustment by moving the second lens group L2 as the movable lens group. In a small stereo optical system, it is required to reduce the number of lens groups and lenses as much as possible. In this case, if a lens group that is too close to the object or image plane is selected as the movable lens group, the optical performance will vary with the change in focal length of the optical system, and in particular the variation in spherical aberration and curvature of field will become large, which is not preferable.

[0023] It is also preferable to include an aperture stop SP in the movable lens group. In a compact stereo optical system, if the aperture stop and the movable lens group are separate, the optical performance will vary with changes in focal length, and in particular spherical aberration and field curvature will tend to increase, which is not preferable.

[0024] Each optical system preferably has 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 or negative refractive power, which allows for excellent correction of field curvature and astigmatism at the wide-angle and telephoto ends.

[0025] It is preferable that the first lens group L1 includes a first lens having negative refractive power and a second lens having negative refractive power, arranged in this order from the object side to the image side, so that the angle of view at the wide-angle end of each optical system can be made wider while favorably correcting the curvature of field, astigmatism, and distortion.

[0026] It is preferable to perform focus adjustment (focusing) by moving the two optical systems 101 and 102 as a whole. As described above, in a stereo optical system, it is necessary to reduce the relative error between the two optical systems, and it is not preferable to perform focus adjustment by only moving some of the lens groups in the two optical systems, as this tends to cause the above-mentioned relative error. Furthermore, it is preferable to move the optical systems 101 and 102 as a whole in focus adjustment. This makes it possible to reduce the above-mentioned relative error more effectively. In addition, in order to reduce the size of the lens device, it is preferable to move the optical systems 101 and 102 by a single actuator.

[0027] It is preferable that the stereo optical system of each embodiment satisfies at least one of the conditions of the following expressions (1) to (14).

[0028] 0.3≦Din / ft≦30.0 (1) 0.5≦Din / fw≦50.0 (2) 2.0≦TL / ft≦20.0 (3) 3.0≦TL / fw≦50.0 (4) -5.0≦f1 / fw≦-0.5 (5) 0.5≦f2 / fw≦10.0 (6) -0.5≦fw / f3≦0.2 (7) 2.0≦PeW / fw≦50.0 (8) 2.0≦PeT / ft≦50.0 (9) 0.2≦fm / ft≦5.0 (10) (0.2≦f2 / ft≦5.0) 0 <Dm / ft≦5.0 (11) (0 <D2 / ft≦5.0) 0.2≦Lb / fb≦10.0 (12) 2.0≦TDL / fw≦50.0 (13) 0.2≦BF / fw≦5.0 (14) In formulas (1) to (14), the optical axis distance (baseline length) between the lenses closest to the object of the two optical systems 101 and 102 is Din, the focal length of each optical system at the telephoto end is ft, and the focal length of each optical system at the wide-angle end is fw. The distance on the optical axis from the surface closest to the object of each optical system to the image plane IP is TL, the focal length of the first lens group L1 is f1, the focal length of the second lens group L2 is f2, and the focal length of the third lens group L3 is f3. The exit pupil distance of each optical system at the wide-angle end is PeW, and the exit pupil distance at the telephoto end is PeT. The exit pupil distance is the distance on the optical axis from the image plane IP to the exit pupil located at the position of the image of the aperture stop SP. The focal length of the movable lens group (second lens group L2) is fm (f2), and the movement amount of the movable lens group (second lens group L2) from the wide-angle end to the telephoto end is Dm (D2). The movement amount is positive when the movable lens group is located closer to the object side at the telephoto end than at the wide-angle end. The composite focal length of the portion of each optical system closer to the image side than the aperture stop SP at the wide-angle end is fb, the distance on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is Lb, and the distance on the optical axis from the surface closest to the object side to the surface closest to the image side in each optical system is TDL. The back focus of each optical system at the wide-angle end is BF. The back focus is the distance on the optical axis from the surface closest to the image side of the optical system to the image plane IP.

[0029] The condition of formula (1) shows the appropriate relationship between the base line length Din of the two optical systems 101 and 102 and the focal length ft at the telephoto end. If Din / ft falls below the lower limit of formula (1), the base line length becomes too small and the two optical systems 101 and 102 interfere with each other, which is not preferable. Also, if Din / ft exceeds the upper limit of formula (1), it is not preferable because a parallax image that can be viewed stereoscopically well cannot be obtained.

[0030] The condition of formula (2) shows the appropriate relationship between the base line length Din of the two optical systems 101 and 102 and the focal length fw at the wide-angle end. If Din / fw falls below the lower limit of formula (2), the base line length becomes too small and the two optical systems 101 and 102 interfere with each other, which is not preferable. Also, if Din / fw exceeds the upper limit of formula (2), it is not preferable because a parallax image that can be viewed stereoscopically well cannot be obtained.

[0031] The condition of formula (3) indicates the appropriate relationship between the total optical length TL of each optical system and the focal length ft at the telephoto end for miniaturizing the entire stereo optical system without the two optical systems 101, 102 interfering with each other at the telephoto end. If TL / ft falls below the lower limit of formula (3), the effective diameter of the object-side lens or image-side lens of each optical system becomes large, causing the two optical systems 101, 102 to interfere with each other, which is not preferable. If TL / ft exceeds the upper limit of formula (3), the entire stereo optical system becomes too large, which is not preferable.

[0032] The condition of formula (4) shows an appropriate relationship between the total optical length TL of each optical system and the focal length fw at the wide-angle end for miniaturizing the entire stereo optical system without the two optical systems 101, 102 interfering with each other at the wide-angle end. If TL / fw is below the lower limit of formula (4), the effective diameter of the object-side lens or image-side lens of each optical system becomes large, causing the two optical systems 101, 102 to interfere with each other, which is not preferable. If TL / fw is above the upper limit of formula (4), the entire stereo optical system becomes too large, which is not preferable.

[0033] The condition of formula (5) shows the appropriate relationship between the focal length f1 of the first lens group L1 and the focal length fw of each optical system at the wide-angle end. If f1 / fw is below the lower limit of formula (5), the power of the first lens group L1 becomes weak, making it difficult to make each optical system wide-angle, which is not preferable. If f1 / fw is above the upper limit of formula (5), the power of the first lens group L1 becomes too strong, making it difficult to correct the curvature of field, astigmatism, and distortion, which is not preferable.

[0034] The condition of formula (6) shows the appropriate relationship between the focal length f2 of the second lens group L2 and the focal length fw of each optical system at the wide-angle end. If f2 / fw is below the lower limit of formula (6), the magnification of the change in focal length from the wide-angle end to the telephoto end decreases, which is undesirable. If f2 / fw is above the upper limit of formula (6), the performance of the optical system changes with the change in focal length, and in particular the fluctuations in spherical aberration and curvature of field become large, which is undesirable.

[0035] The condition of formula (7) shows the appropriate relationship between the focal length f3 of the third lens group L3 and the focal length fw of each optical system at the wide-angle end. If fw / f3 is below the lower limit of formula (7), the back focus of each optical system becomes too short, which is undesirable since it becomes difficult to arrange the third lens group L3. If fw / f3 is above the upper limit of formula (7), the diameter of the third lens group increases, which causes the two optical systems 101 and 102 to interfere with each other, which is undesirable.

[0036] The condition of formula (8) shows the appropriate relationship between the exit pupil distance PeW at the wide-angle end of each optical system and the focal length fw at the wide-angle end. If PeW / fw is below the lower limit of formula (8), the back focus of each optical system becomes too short, making it difficult to arrange the third lens group L3, which is not preferable. If PeW / fw is above the upper limit of formula (8), the overall diameter of each optical system increases, causing the two optical systems 101 and 102 to interfere with each other, which is not preferable.

[0037] The condition of formula (9) shows the appropriate relationship between the exit pupil distance PeT at the telephoto end of each optical system and the focal length ft at the telephoto end. If PeT / ft falls below the lower limit of formula (9), the back focus of each optical system becomes too short, making it difficult to arrange the third lens group L3, which is undesirable. If PeT / ft exceeds the upper limit of formula (9), the diameter of each optical system increases, causing the two optical systems 101 and 102 to interfere with each other, which is undesirable.

[0038] The condition of formula (10) shows the appropriate relationship between the focal length fm of the movable lens group and the focal length ft at the telephoto end of each optical system. If fm / ft falls below the lower limit of formula (10), the power of the second lens group L2 becomes too strong, causing performance fluctuations as the focal length of the optical system changes, particularly as field curvature, astigmatism, and lateral aberration tend to increase, which is undesirable. If fm / ft exceeds the upper limit of formula (10), the power of the second lens group L2 becomes too weak, causing a decrease in the magnification of the change in focal length from the wide-angle end to the telephoto end, which is undesirable.

[0039] The condition of formula (11) shows the appropriate relationship between the amount of movement Dm of the movable lens group from the wide-angle end to the telephoto end and the focal length ft of each optical system at the telephoto end. If Dm / ft falls below the lower limit of formula (11), the power of the second lens group L2 becomes too strong, causing performance to vary with changes in the focal length of the optical system, and in particular, curvature of field, astigmatism, and lateral aberration tend to increase, which is undesirable. If Dm / ft exceeds the upper limit of formula (11), the amount of movement of the second lens group L2 increases, causing each optical system to become too large, which is undesirable.

[0040] The condition of formula (12) shows an appropriate relationship between the composite focal length fb of the portion of each optical system on the image side of the aperture stop SP at the wide-angle end and the distance Lb from the aperture stop SP to the image plane IP at the wide-angle end. If Lb / fb falls below the lower limit of formula (12), the back focus of each optical system becomes too short, making it difficult to arrange the third lens group L3, which is undesirable. If Lb / fb exceeds the upper limit of formula (12), the overall diameter of each optical system increases, causing the two optical systems 101 and 102 to interfere with each other, which is undesirable.

[0041] The condition of formula (13) shows the appropriate relationship between the distance TDL from the surface closest to the object to the surface closest to the image in each optical system and the focal length fw at the wide-angle end. If TDL / fw is below the lower limit of formula (13), it is difficult to increase the focal length of each optical system on the telephoto side, which is undesirable. If TDL / fw is above the upper limit of formula (13), each optical system as a whole becomes too large, which is undesirable.

[0042] Equation (14) shows the appropriate relationship between the back focus BF of each optical system and the focal length fw at the wide-angle end. If BF / fw is below the lower limit of equation (14), the back focus becomes too short, making it difficult to arrange the third lens group L3, which is not preferable. If BF / fw is above the upper limit of equation (14), the entire optical system becomes too large, which is not preferable.

[0043] It is more preferable to set the numerical ranges of the formulas (1) to (14) as follows:

[0044] 0.3≦Din / ft≦20.0 (1a) 0.5≦Din / fw≦25.0 (2a) 2.0≦TL / ft≦15.0 (3a) 3.0≦TL / fw≦30.0 (4a) -3.0≦f1 / fw≦-0.5 (5a) 0.5≦f2 / fw≦7.0 (6a) -0.4≦fw / f3≦0.2 (7a) 2.0≦PeW / fw≦40.0 (8a) 2.0≦PeT / ft≦40.0 (9a) 0.2≦fm / ft≦4.0 (10a) 0.2≦Dm / ft≦4.0 (11a) 0.2≦Lb / fb≦5.0 (12a) 2.0≦TDL / fw≦30.0 (13a) 0.2≦BF / fw≦3.0 (14a) It is more preferable to set the numerical ranges of the formulas (1) to (14) as follows:

[0045] 0.4≦Din / ft≦10.0 (1b) 0.7≦Din / fw≦15.0 (2b) 2.0≦TL / ft≦10.0 (3b) 5.0≦TL / fw≦20.0 (4b) -3.0≦f1 / fw≦-0.7 (5b) 1.0≦f2 / fw≦5.0 (6b) -0.3≦fw / f3≦0.2 (7b) 2.0≦PeW / fw≦30.0 (8b) 2.0≦PeT / ft≦30.0 (9b) 0.5≦fm / ft≦3.0 (10b) 0.5≦Dm / ft≦3.0 (11b) 0.5≦Lb / fb≦4.0 (12b) 3.0≦TDL / fw≦20.0 (13b) 0.5≦BF / fw≦2.0 (14b) Next, the configuration of the optical system (101, 102) in each embodiment will be described in detail. After the description of embodiment 6, numerical examples 1 to 6 corresponding to embodiments 1 to 6 are shown. The numerical examples will be described in detail later. EXAMPLES

[0046] The optical system of Example 1 (Numerical Example 1) shown in FIG. 2 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 negative refractive power.

[0047] In the optical system of this embodiment, only the second lens group L2 is moved as a movable lens group to change the focal length. In each optical system, the optical power arrangement is adjusted so that the position of the image plane IP does not change even if the second lens group L2 moves.

[0048] In the optical system of this embodiment, the focus is adjusted by moving the entire system. EXAMPLES

[0049] The optical system of Example 2 (Numerical Example 2) shown in Fig. 4 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, and the focal length is changed by moving only the second lens group L2. Since the third lens group L3 has positive refractive power, the variable range of the focal length is expanded to the wide angle side compared to Example 1. EXAMPLES

[0050] The optical system of Example 3 (Numerical Example 3) shown in FIG. 6 is, like Example 2, 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, and the focal length is changed by moving only the second lens group L2. Furthermore, in this embodiment, by including an aspherical lens, the variable range of the focal length is expanded to the wide-angle side and the telephoto side compared to embodiment 1. In addition, by widening the angle, the effective diameter and the base length of the optical system are larger than those of embodiment 2. EXAMPLES

[0051] The optical system of Example 4 (Numerical Example 4) shown in FIG. 8 is, like Example 1, 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 negative refractive power, and the focal length is changed by moving only the second lens group L2. In the optical system of this embodiment, the variable range of the focal length is shifted to the telephoto side compared to Example 1. In addition, by performing an appropriate power arrangement, the magnification of the change in focal length from the wide-angle end to the telephoto end is increased and the effective diameter of the optical system is suppressed. EXAMPLES

[0052] The optical system of Example 5 (Numerical Example 5) shown in FIG. 10, like Examples 2 and 3, 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, and the focal length is changed by moving only the second lens group L2. The optical system of this embodiment has an even wider angle than that of the third embodiment. EXAMPLES

[0053] The optical system of Example 6 shown in FIG. 12, like Examples 1 and 4, 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 negative refractive power, and the focal length is changed by moving only the second lens group L2.

[0054] The optical systems of the above-mentioned Examples 1 to 5 are coaxial optical systems whose optical axes extend straight from the object side to the image side, and therefore the optical axis distance between the lenses closest to the image side is also Din. In contrast, the optical system of this example is a folding optical system in which the optical axis (optical path) is folded twice.

[0055] Specifically, two reflecting prisms PR1 and PR2 are arranged in the second lens group L2 to bend the optical path by 90° each. This configuration ensures a base length Din greater than those in the first to fifth embodiments, making it possible to obtain parallax images that provide a stronger stereoscopic effect. Moreover, the distance between the optical axes of the lenses closest to the image side is set to Dout, which is shorter than Din, so that the two optical images formed by the two optical systems can be accommodated on the imaging surface of a single imaging element 111. The stereo optical system having the optical systems 101 and 102 of the respective embodiments may be used in an imaging device having a function for correcting various aberrations such as distortion and chromatic aberration of magnification by image processing.

[0056] Numerical examples 1 to 6 are shown below. In each numerical example, surface number m indicates the order of the surface when counted from the object side. r (mm) indicates the radius of curvature of the mth surface, and d (mm) indicates the distance (air gap) on the optical axis between the mth surface and the (m+1)th surface. In addition, nd indicates the refractive index at the d-line of the optical material between the mth surface and the (m+1)th surface, and νd indicates the Abbe number of the optical member based on the d-line. The Abbe number νd based on the d-line is given by Nd, NF, NC, and Ng, respectively, as the refractive indexes at the d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (wavelength 435.8 nm) of the Fraunhofer lines. νd=(Nd-1) / (NF-NC) The effective diameter is the radius (mm) of the area on the mth surface through which light rays that contribute to imaging pass.

[0057] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system is focused on an object at infinity. The back focus BF (mm) is as described above. The total lens length (mm) corresponds to the total optical length described above.

[0058] An asterisk (*) to the right of a surface number indicates that the surface is aspheric. When x is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A4 to A12 are the aspheric coefficients of each order, the aspheric shape is expressed as follows: x=(h2 / R) / [1+{1-(1+K)(h / R) 2}] 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A8×h 8 +A10×h 10 +A12×h 12 In the conic constant and aspheric coefficients, "e±XX" means "×10±XX."

[0059] The numerical values ​​related to the conditions of formulas (1) to (14) for each numerical example are shown together in Table 1. Each numerical example satisfies all of the conditions of formulas (1) to (14).

[0060] 3, 5, 7, 9, 11, and 13 respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of Numerical Examples 1 to 6 in (a) a state where the optical system is at the wide-angle end and focused on an object at infinity, and (b) a state where the optical system is at the telephoto end and focused on an object 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 S indicates the astigmatism on the sagittal image plane, and the dashed line M indicates the astigmatism on the meridional image plane. The distortion diagrams show distortion at the d-line. The chromatic aberration diagrams show chromatic aberration of magnification at the g-line. ω is the half angle of view (°). [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 54.702 0.70 1.80440 39.6 9.57 2 8.124 1.60 8.41 3 -117.593 0.60 1.60562 43.7 8.29 4 14.681 0.63 8.07 5 11.366 1.80 1.80000 29.8 8.12 6 18.121 (variable) 7.68 7 27.529 0.80 1.91082 35.2 6.24 8 7.657 3.54 1.80100 35.0 6.28 9 -36.508 5.52 6.53 10 (Aperture) ∞ 4.10 6.67 11 31.952 0.80 2.00069 25.5 6.77 12 13.980 0.00 1.49700 81.5 6.67 13 13.980 2.38 1.49700 81.5 6.67 14 -37.551 5.08 6.74 15 134.159 2.23 1.88300 40.8 7.27 16 -22.241 (variable) 7.60 17 63.573 2.32 1.49700 81.5 7.74 18 -15.677 0.80 2.00069 25.5 7.70 19 -81.180 (variable) 7.84 Image plane ∞ Various data Zoom ratio 1.50 Focal length 8.97 13.45 F-number 3.50 4.44 Half angle of view (°) 28.40 19.83 Image height 4.85 4.85 Lens length 62.24 62.24 BF 15.21 15.21 d6 10.26 2.72 d16 3.89 11.43 d19 15.21 15.21 Entrance pupil position 7.70 6.91 Exit pupil position -24.96 -28.51 Front principal point position 14.66 16.22 Back principal point position 6.25 1.76 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -9.35 5.32 1.01 -2.78 2 7 18.48 24.44 18.72 -14.71 3 17 -86.01 3.12 2.20 0.22 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 41.949 0.80 2.00100 29.1 10.63 2 7.086 2.83 8.71 3 -13.502 0.40 2.00100 29.1 8.39 4 -69.553 1.72 8.48 5 -13.025 1.96 1.94594 18.0 8.57 6 -9.329 (variable) 9.13 7 10.819 1.43 2.00100 29.1 5.92 8 8.522 1.80 5.64 9 11.175 2.97 1.59270 35.3 6.24 10 -45.024 1.81 6.21 11 (Aperture) ∞ 4.67 6.01 12 104.209 0.80 2.10420 17.0 5.54 13 19.269 2.05 1.43700 95.1 5.46 14 -24.364 2.00 5.50 15 30.202 2.17 1.59270 35.3 5.85 16 -34.028 (variable) 6.24 17 20.373 3.00 1.51742 52.4 6.56 18 -10.968 0.80 1.95375 32.3 6.64 19 -55.363 (variable) 6.85 Image plane ∞ Various data Zoom ratio 1.79 Focal length 5.94 10.64 F-number 3.50 5.03 Half angle of view (°) 39.22 24.51 Image height 4.85 4.85 Lens length 58.44 58.44 BF 13.92 13.92 d 6 12.29 2.00 d16 1.00 11.29 d19 13.92 13.92 Entrance pupil position 6.02 5.23 Exit pupil position -17.90 -29.25 Front principal point position 10.86 13.25 Back principal point position 7.98 3.29 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -8.85 7.72 -0.74 -8.99 2 7 17.44 19.72 10.63 -10.72 3 17 246.22 3.80 -9.09 -11.09 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* 23.045 0.80 1.98525 31.5 13.89 2* 7.577 4.03 11.04 3 -65.410 0.80 1.89043 41.6 9.90 4 19.704 1.00 9.43 5 -46.534 0.40 1.83835 46.0 9.40 6 22.127 0.80 9.42 7 20.289 2.73 1.93381 22.8 9.79 8 -39.413 (variable) 9.72 9 9.935 1.40 2.00100 29.1 5.84 10 7.673 1.87 5.52 11 10.635 6.02 1.59270 35.3 6.18 12 -40.659 1.80 6.13 13 (Aperture) ∞ 2.15 5.93 14 11.820 0.80 2.10420 17.0 5.67 15 7.376 2.24 1.43700 95.1 5.37 16 34.003 2.00 5.20 17 58.113 2.06 1.59270 35.3 5.07 18 -19.830 (variable) 4.97 19 -30.177 2.37 1.51742 52.4 6.06 20 -8.448 0.80 1.95375 32.3 6.50 21 -12.176 0.50 6.86 22* -27.244 1.00 1.53500 55.7 6.97 23* -34.502 (variable) 7.21 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-4.06825e-05 A 6= 4.08773e-07 A 8= 1.27474e-08 A10=-2.37008e-10 A12= 1.16807e-12 2nd side K = 0.00000e+00 A 4=-4.63543e-05 A 6=-9.53334e-07 A 8= 4.74624e-08 A10=-2.79488e-10 A12= 8.76211e-12 Page 22 K =-1.83630e+01 A 4=-8.07042e-04 A 6= 6.31020e-05 A 8=-4.51889e-06 A10= 1.23665e-07 Page 23 K =-8.11192e+01 A 4=-9.36175e-04 A 6= 6.56446e-05 A 8=-4.10436e-06 A10 = 1.02110e-07 Various data Zoom ratio 2.00 Focal length 5.42 10.83 F-number 3.50 5.67 Half angle of view (°) 41.85 24.13 Image height 4.85 4.85 Lens length 64.22 64.22 BF 13.99 13.99 d 8 13.67 2.00 d18 1.00 12.67 d23 13.99 13.99 Entrance pupil position 7.38 6.71 Exit pupil position -16.98 -35.79 Front principal point position 11.84 15.18 Back principal point position 8.57 3.16 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -8.15 10.56 0.87 -8.31 2 9 16.50 20.34 9.71 -10.11 3 19 121.24 4.67 9.20 6.61 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 19.037 0.80 2.09651 18.7 10.03 2 8.243 2.23 8.88 3 -21.227 0.40 1.89494 41.3 8.71 4 22.463 0.87 8.73 5 26.548 2.26 2.11847 16.8 9.06 6 -51.967 (variable) 9.07 7 11.681 1.39 2.00100 29.1 8.17 8 9.717 1.90 7.79 9 12.462 3.39 1.59270 35.3 8.46 10 -58.141 1.77 8.33 11 (Aperture) ∞ 2.67 8.02 12 11.990 0.80 2.10420 17.0 7.48 13 7.781 2.77 1.43700 95.1 7.04 14 31.156 2.00 6.70 15 68.856 2.33 1.59270 35.3 6.45 16 -22.043 (variable) 6.21 17 -9.207 2.00 1.51742 52.4 5.73 18 -7.284 0.80 1.95375 32.3 6.23 19 -9.267 (variable) 6.62 Image plane ∞ Various data Zoom ratio 2.50 Focal length 9.53 23.82 F-number 3.50 5.66 Half angle of view (°) 26.97 11.51 Image height 4.85 4.85 Lens length 68.05 68.05 BF 19.91 19.91 d 6 18.23 2.00 d16 1.54 17.77 d19 19.91 19.91 Entrance pupil position 8.83 6.77 Exit pupil position -16.37 -32.66 Front principal point position 15.86 19.80 Back principal point position 10.38 -3.91 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -12.34 6.56 -0.02 -5.29 2 7 17.11 19.01 8.31 -10.32 3 17 -203.44 2.80 -20.78 -25.11 [Numerical example 5] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 15.607 0.80 2.21347 22.2 11.11 2 5.580 3.07 8.45 3 -24.605 0.40 2.04882 33.2 7.74 4 15.976 3.05 7.50 5 21.517 2.12 1.95179 17.2 7.71 6 -64.252 (variable) 7.47 7 12.816 1.40 2.00100 29.1 5.10 8 8.513 1.92 4.94 9 15.713 3.14 1.59270 35.3 5.69 10 -13.106 1.38 5.97 11 (Aperture) ∞ 7.21 5.80 12 19.556 0.80 2.10420 17.0 5.09 13 9.487 2.67 1.43700 95.1 4.91 14 -21.597 2.00 5.63 15 -36.957 2.00 1.59270 35.3 6.50 16 -15.473 (variable) 7.07 17 -25.129 3.27 1.51742 52.4 7.35 18 -7.141 0.80 1.95375 32.3 7.97 19 -10.042 (variable) 8.50 Image plane ∞ Various data Zoom ratio 1.49 Focal length 4.62 6.89 F-number 3.50 4.48 Half angle of view (°) 46.40 35.16 Image height 4.85 4.85 Lens length 59.54 59.55 BF 13.71 13.71 d 6 8.80 2.00 d16 1.00 7.81 d19 13.71 13.71 Entrance pupil position 5.17 4.77 Exit pupil position -52.79 -90.27 Front principal point position 9.46 11.21 Back principal point position 9.09 6.83 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -6.78 9.44 -0.17 -10.10 2 7 16.92 22.53 11.89 -12.08 3 17 55.37 4.07 6.48 4.37 [Numerical example 6] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 124.377 0.77 1.80440 39.6 10.74 2 11.810 1.24 9.64 3 414.494 0.37 1.60562 43.7 9.54 4 10.989 0.82 9.14 5 10.309 1.72 1.80000 29.8 9.21 6 12.970 (variable) 8.67 7 94.558 0.59 1.91082 35.2 7.06 8 7.994 3.72 1.80100 35.0 6.91 9 -27.238 1.24 6.86 10 ∞ 13.40 1.51633 64.1 10.78 11 ∞ 0.99 7.83 12 (Aperture) ∞ 0.99 8.03 13 32.318 0.79 2.00069 25.5 8.15 14 21.444 0.00 1.49700 81.5 8.09 15 21.444 2.89 1.49700 81.5 8.09 16 -16.882 2.00 8.14 17 ∞ 13.40 1.51633 64.1 8.51 18∞2.00 12.24 19 37.036 2.00 1.88300 40.8 7.46 20 577.027 (variable) 7.51 21 35.011 2.52 1.49700 81.5 7.59 22 -15.682 0.80 2.00069 25.5 7.54 23 -160.018 (variable) 7.66 Image plane ∞ Various data Zoom ratio 1.49 Focal length 9.03 13.48 F-number 3.54 4.30 Half angle of view (°) 28.24 19.79 Image height 4.85 4.85 Lens length 78.34 78.34 BF 13.52 13.52 d 6 11.57 3.37 d20 1.00 9.20 d23 13.52 13.52 Entrance pupil position 8.81 8.23 Exit pupil position -22.00 -26.21 Front principal point position 15.54 17.13 Back principal point position 4.49 0.05 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -9.75 4.92 1.38 -2.06 2 7 20.35 44.01 21.83 -21.71 3 21 -90.85 3.32 3.72 1.55

[0061] [Table 1]

[0062] [Imaging device] Fig. 14 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 reference numeral 21 denotes an imaging optical system constituted by the stereo optical system of any of the embodiments 1 to 6, which is provided integrally with the camera body 20. Reference numeral 22 denotes an 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, and corresponds to the imaging element 111 in Fig. 1. Reference numeral 23 denotes a recording unit that records image data generated by processing an imaging signal from the imaging element 22, and reference numeral 24 denotes a rear display that displays the image data.

[0063] By using the stereo optical system of each embodiment, it is possible to provide an imaging device that is small and capable of stereoscopic imaging with a variable focal length. The imaging device may be a digital video camera, a digital still camera, a broadcast camera, a surveillance camera, a silver halide film camera, or the like.

[0064] The above embodiment includes the following configurations.

[0065] (Configuration 1) A stereo optical system having two optical systems arranged in parallel, the two optical systems forming two optical images in different regions on a single imaging plane arranged on the image plane, The two optical systems each include: A plurality of lens groups are included. A stereo optical system, characterized in that a focal length is changed by moving one movable lens group among the plurality of lens groups to change a distance between the movable lens group and an adjacent lens group. (Configuration 2) The two optical systems each include: The optical system has a first lens group, a second lens group, and a third lens group arranged in this order from the object side to the image side, 2. The stereo optical system according to configuration 1, wherein the focal length is changed by moving the second lens group as the movable lens group while the first and third lens groups are not moved. (Configuration 3) The stereo optical system according to configuration 2, wherein the first lens group has negative refractive power, the second lens group has positive refractive power, and the third lens group has positive or negative refractive power. (Configuration 4) 4. The stereo optical system according to any one of configurations 1 to 3, characterized in that the movable lens groups of the two optical systems are moved integrally. (Configuration 5) Let Din be the optical axis distance between the lenses closest to the object in the two optical systems, and ft be the focal length at the telephoto end of each of the two optical systems. 0.3≦Din / ft≦30.0 5. The stereo optical system according to any one of configurations 1 to 4, which satisfies the following condition: (Configuration 6) Let Din be the optical axis distance between the lenses closest to the object in the two optical systems, and fw be the focal length at the wide-angle end of each of the two optical systems. 0.5≦Din / fw≦50.0 6. The stereo optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) Let TL be the distance on the optical axis from the surface closest to the object in each of the two optical systems to the image plane, and ft be the focal length at the telephoto end of each of the two optical systems. 2.0≦TL / ft≦20.0 7. The stereo optical system according to any one of configurations 1 to 6, which satisfies the following condition: (Configuration 8) Let TL be the distance on the optical axis from the surface closest to the object in each of the two optical systems to the image plane, and fw be the focal length at the wide-angle end of each of the two optical systems. 3.0≦TL / fw≦50.0 8. The stereo optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) Let f1 be the focal length of the first lens group, and fw be the focal length of each of the two optical systems at the wide-angle end. When -5.0≦f1 / fw≦-0.5 4. The stereo optical system according to configuration 3, which satisfies the following condition: (Configuration 10) Let f2 be the focal length of the second lens group, and fw be the focal length of each of the two optical systems at the wide-angle end. 0.5≦f2 / fw≦10.0 10. The stereo optical system according to configuration 3 or 9, which satisfies the following condition: (Configuration 11) the third lens group has negative refractive power, When the focal length of each of the two optical systems at the wide-angle end is fw and the focal length of the third lens group is f3, -0.5≦fw / f3≦0.2 11. The stereo optical system according to configuration 3, 9 or 10, which satisfies the following condition: (Configuration 12) The stereo optical system according to configuration 3, 9, 10 or 11, characterized in that the first lens group includes a first lens having negative refractive power and a second lens having negative refractive power, arranged in that order from the object side to the image side. (Configuration 13) 13. The stereo optical system according to any one of configurations 1 to 12, wherein the movable lens group includes an aperture stop. (Configuration 14) The two optical systems are moved as a whole to adjust the focus. 14. The stereo optical system according to any one of configurations 1 to 13, characterized in that the two optical systems are moved together. (Configuration 15) When the exit pupil distance at the wide-angle end of each of the two optical systems is PeW and the focal length at the wide-angle end of each of the two optical systems is fw, 2.0≦PeW / fw≦50.0 15. The stereo optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) When the exit pupil distance at the telephoto end of each of the two optical systems is PeT, and the focal length at the telephoto end of each of the two optical systems is ft, 2.0≦PeT / ft≦50.0 16. The stereo optical system according to any one of configurations 1 to 15, wherein the following condition is satisfied: (Configuration 17) Let fm be the focal length of the movable lens group, and ft be the focal length at the telephoto end of each of the two optical systems. 0.2≦fm / ft≦5.0 17. The stereo optical system according to any one of configurations 1 to 16, wherein the following condition is satisfied: (Configuration 18) In each of the two optical systems, when the movable lens group is located closer to the object side at the telephoto end than at the wide-angle end, the amount of movement of the movable lens group from the wide-angle end to the telephoto end is defined as Dm, and the focal length of each of the two optical systems at the telephoto end is ft. 0 <Dm / ft≦5.0 18. The stereo optical system according to any one of configurations 1 to 17, wherein the following condition is satisfied: (Configuration 19) each of the two optical systems includes an aperture stop; Let Lb be the distance from the aperture stop to the image plane at the wide-angle end in each of the two optical systems, and fb be the composite focal length of the portion on the image side of the aperture stop at the wide-angle end. 0.2≦Lb / fb≦10.0 19. The stereo optical system according to any one of configurations 1 to 18, wherein the following condition is satisfied: (Configuration 20) When the distance on the optical axis from the surface closest to the object side to the surface closest to the image side in each of the two optical systems is TDL, and the focal length at the wide-angle end of each of the two optical systems is fw, 2.0≦TDL / fw≦50.0 20. The stereo optical system according to any one of configurations 1 to 19, which satisfies the following condition: (Configuration 21) When the back focus at the wide-angle end of each of the two optical systems is BF and the focal length at the wide-angle end is fw, 0.2≦BF / fw≦5.0 21. The stereo optical system according to any one of configurations 1 to 20, which satisfies the following condition: (Configuration 22) A stereo optical system according to any one of configurations 1 to 21; and a single image sensor that captures an image of a subject through the two optical systems.

[0066] 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]

[0067] 101,102 Optical system L1 First lens group L2 Second lens group L3: Third lens group 111 Image sensor

Claims

1. A stereo optical system having two optical systems arranged in parallel, the two optical systems forming two optical images in different regions on a single imaging plane arranged on the image plane, Each of the two optical systems is A lens group includes: A stereo optical system, characterized in that a focal length is changed by moving one of the plurality of lens groups to change a distance between the movable lens group and an adjacent lens group.

2. Each of the two optical systems is The optical system has a first lens group, a second lens group, and a third lens group arranged in this order from the object side to the image side, 2. The stereo optical system according to claim 1, wherein the focal length is changed by moving the second lens group as the movable lens group while the first and third lens groups are not moved.

3. 3. The stereo optical system according to claim 2, wherein the first lens group has a negative refractive power, the second lens group has a positive refractive power, and the third lens group has a positive or negative refractive power.

4. 2. The stereo optical system according to claim 1, wherein the movable lens groups of the two optical systems are moved integrally.

5. When the optical axis distance between the lenses closest to the object in the two optical systems is Din and the focal length at the telephoto end of each of the two optical systems is ft, 0.3≦Din / ft≦30.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

6. When the optical axis distance between the lenses closest to the object in the two optical systems is Din and the focal length at the wide-angle end of each of the two optical systems is fw, 0.5≦Din / fw≦50.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

7. Let TL be the distance on the optical axis from the surface closest to the object in each of the two optical systems to the image plane, and ft be the focal length at the telephoto end of each of the two optical systems. 2.0≦TL / ft≦20.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

8. When the distance on the optical axis from the surface closest to the object in each of the two optical systems to the image plane is TL, and the focal length at the wide-angle end of each of the two optical systems is fw, 3.0≦TL / fw≦50.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

9. When the focal length of the first lens group is f1 and the focal length of each of the two optical systems at the wide-angle end is fw, When -5.0≦f1 / fw≦-0.5 4. The stereo optical system according to claim 3, wherein the following condition is satisfied:

10. When the focal length of the second lens group is f2 and the focal length of each of the two optical systems at the wide-angle end is fw, 0.5≦f2 / fw≦10.0 4. The stereo optical system according to claim 3, wherein the following condition is satisfied:

11. the third lens group has a negative refractive power, When the focal length of each of the two optical systems at the wide-angle end is fw and the focal length of the third lens group is f3, −0.5≦fw / f3≦0.2 4. The stereo optical system according to claim 3, wherein the following condition is satisfied:

12. 4. The stereo optical system according to claim 3, wherein the first lens group includes a first lens having a negative refractive power and a second lens having a negative refractive power, arranged in this order from the object side to the image side.

13. The stereo optical system according to claim 1 , wherein the movable lens group includes an aperture stop.

14. The two optical systems are moved as a whole to adjust the focus; 2. The stereo optical system according to claim 1, further comprising a configuration in which the two optical systems are moved together.

15. When the exit pupil distance of each of the two optical systems at the wide-angle end is PeW and the focal length of each of the two optical systems at the wide-angle end is fw, 2.0≦PeW / fw≦50.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

16. When the exit pupil distance at the telephoto end of each of the two optical systems is PeT and the focal length at the telephoto end of each of the two optical systems is ft, 2.0≦PeT / ft≦50.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

17. When the focal length of the movable lens group is fm and the focal length of each of the two optical systems at the telephoto end is ft, 0.2≦fm / ft≦5.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

18. In each of the two optical systems, when the movable lens group is located closer to the object side at the telephoto end than at the wide-angle end, the amount of movement of the movable lens group from the wide-angle end to the telephoto end is defined as Dm, and the focal length of each of the two optical systems at the telephoto end is ft. 0<Dm / ft≦5.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

19. each of the two optical systems includes an aperture stop; Let Lb be the distance from the aperture stop to the image plane at the wide-angle end in each of the two optical systems, and fb be the composite focal length of the portion on the image side of the aperture stop at the wide-angle end. 0.2≦Lb / fb≦10.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

20. When the distance on the optical axis from the surface closest to the object side to the surface closest to the image side in each of the two optical systems is TDL, and the focal length at the wide-angle end of each of the two optical systems is fw, 2.0≦TDL / fw≦50.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

21. When the back focus at the wide-angle end of each of the two optical systems is BF and the focal length at the wide-angle end is fw, 0.2≦BF / fw≦5.0 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

22. A stereo optical system according to any one of claims 1 to 21; and a single image sensor for capturing an image of a subject through said two optical systems.

Images