Stereo optical system and imaging apparatus

Abstract

To provide a small-sized stereo optical system that can perform high-speed, silent focusing and perform stereoscopic imaging with high image quality.SOLUTION: A stereo optical system has two optical systems OSR, OSL arranged in parallel. Each optical system is a coaxial optical system, and includes an aperture stop SP and a focus lens group Lfc that is arranged closer to an image side than the aperture stop SP and moves to change the interval between adjacent lenses or lens groups for focusing. When the distance between optical axes of the two optical systems is defined as D, the focal distance of each optical system as f, and the maximum half angle of view of each optical system as ω, the condition of 1.80≤D / f tanω≤5.50 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] There is a demand for a stereoscopic optical system for capturing stereoscopically visible images for virtual reality and other applications. Patent Document 1 discloses a stereoscopic optical system in which two optical systems, each including a reflective surface that bends the optical path midway, are arranged in parallel, ensuring a sufficient distance between the optical axes (baseline length) on the object side while reducing the distance between the optical axes on the image side, enabling stereoscopic imaging using a single image sensor. Patent Document 2 discloses a compact stereoscopic optical system in which two coaxial optical systems, whose optical axes extend straight from the object side to the image side, are arranged in parallel, and which is a pan-focus type optical system without a focusing mechanism. Patent Document 3 discloses an optical system that is not a stereoscopic optical system but moves the entire optical system for focusing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-008629 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-003022 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-085429 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] The stereo optical system of Patent Document 1 tends to be large in size in the base length direction because each of the two optical systems includes a reflecting surface.

[0005] On the other hand, the stereo optical system of Patent Document 2 uses two coaxial optical systems that do not include reflecting surfaces, which is advantageous for miniaturization. However, the baseline length (i.e., the amount of parallax) is insufficient, which weakens the three-dimensional effect obtained from the captured image. Moreover, a large F-number is set for deep focus, which further weakens the three-dimensional effect obtained from the captured image.

[0006] Furthermore, if the number of lenses is reduced to reduce weight, as in the stereo optical system of Patent Document 2, the angle of incidence of off-axis light rays on the image sensor placed on the image plane becomes larger, and the coloring of the image (hereinafter referred to as color shading) generated by the image sensor becomes noticeable, resulting in a deterioration in the image quality of the captured video.

[0007] If an optical system that moves the entire optical system for focusing, as in Patent Document 3, is used as two optical systems of a stereo optical system, the load on the actuator that drives the entire two optical systems becomes large, making it difficult to perform high-speed, quiet focusing.

[0008] The present invention provides a compact stereo optical system that is capable of high-speed, quiet focusing and high-quality stereoscopic imaging. [Means for solving the problem]

[0009] 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 is a coaxial optical system, and includes an aperture stop and a focus lens group that is arranged on the image side of the aperture stop and moves to change the spacing between adjacent lenses or lens groups for focusing. When the distance between the optical axes of the two optical systems is D, the focal length of each of the two optical systems is f, and the maximum half angle of view of each of the two optical systems is ω, 1.80≦D / f·tanω≦5.50 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. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a compact stereo optical system that is capable of high-speed and quiet focusing and capable of performing high-quality stereoscopic imaging. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view of one optical system of the stereo optical system of the first embodiment. [Figure 2] 4A to 4C are aberration diagrams of the stereo optical system of Example 1. [Figure 3] FIG. 10 is a cross-sectional view of one optical system of the stereo optical system according to the second embodiment. [Figure 4] 10A to 10C are aberration diagrams of the stereo optical system of Example 2. [Figure 5] FIG. 11 is a cross-sectional view of one optical system of the stereo optical system according to the third embodiment. [Figure 6] 10A to 10C are aberration diagrams of the stereo optical system of Example 3. [Figure 7] FIG. 10 is a cross-sectional view of one optical system of the stereo optical system according to the fourth embodiment. [Figure 8] 10A to 10C are aberration diagrams of the stereo optical system of Example 4. [Figure 9] FIG. 13 is a cross-sectional view of one optical system of the stereo optical system according to the fifth embodiment. [Figure 10] 10A to 10C are aberration diagrams of the stereo optical system of Example 5. [Figure 11] FIG. 13 is a cross-sectional view of one optical system of the stereo optical system according to the sixth embodiment. [Figure 12] 13A to 13C are aberration diagrams of the stereo optical system of Example 6. [Figure 13] FIG. 13 is a cross-sectional view of one optical system of the stereo optical system according to the seventh embodiment. [Figure 14] 13A to 13C are aberration diagrams of the stereo optical system of Example 7. [Figure 15] FIG. 1 is a plan view showing a stereo optical system according to Examples 1 to 7. [Figure 16] FIG. 2 is a diagram showing two image circles formed on a single imaging element by the stereo optical systems of Examples 1 to 7. [Figure 17] FIG. 1 is a diagram showing an imaging device equipped with a stereo optical system according to Examples 1 to 7. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to describing specific embodiments 1 to 7, matters common to all embodiments will be described.

[0013] 1, 3, 5, 7, 9, 11, and 13 each show the configuration of one of the two optical systems arranged side by side in the stereo optical systems of Examples 1 to 7 when it is focused on an object at infinity (hereinafter referred to as the infinity focused state). In each figure, the left side is the object side (front side) and the right side is the image side (rear side). SP indicates the aperture stop, and IP indicates the image plane. The imaging surface (light receiving surface) of an imaging element or the film surface (photosensitive surface) of a silver halide film is located on the image plane IP.

[0014] 15 shows the stereo optical system of Examples 1 to 7 as viewed from above. The stereo optical system has a right optical system OSR and a left optical system OSL as two optical systems arranged side by side in the left-right direction. Both the right optical system OSR and the left optical system OSL are coaxial optical systems that do not include a reflecting surface.

[0015] FIG. 16 shows a right image circle ICR and a left image circle ICL formed side by side in left and right regions on an image plane (imaging plane of a single imaging element) IP by the right optical system OSR and the left optical system OSL, respectively.

[0016] The right optical system OSR and the left optical system OSL of the stereo optical system in each embodiment each include an aperture stop SP and a focus lens group Lfc that is positioned closer to the image than the aperture stop SP and moves to change the spacing between adjacent lenses or lens groups for focusing. A lens group is a group of one or more lenses that may or may not move during focusing. In each figure, the solid arrow indicates the direction of movement of the focus lens group Lfc during focusing from infinity to close range.

[0017] As described above, the stereo optical system of each embodiment employs a configuration in which the focus lens group Lfc is positioned closer to the image side than the aperture diaphragm SP (the aperture diaphragm SP and the front lens group Lf, which is closer to the object than the aperture diaphragm SP, do not move during focusing). This configuration reduces the weight of the focus lens group Lfc by the weight of the aperture diaphragm SP, which includes the front lens group Lf and the actuator that changes the diaphragm diameter. This enables high-speed, quiet focusing.

[0018] In each embodiment, the distance (baseline length) between the optical axes of the right optical system OSR and the left optical system OSL is D, the focal length of each of the right optical system OSR and the left optical system OSL (hereinafter simply referred to as the optical system) is f, and the maximum half angle of view of the optical system is ω. In this case, the stereo optical system of each embodiment satisfies the condition of the following formula (1).

[0019] 1.80≦D / f·tanω≦5.50 (1) The condition in equation (1) indicates the appropriate relationship between the baseline length of the stereo optical system and the size of the image sensor to ensure high image quality while maintaining the three-dimensional effect of the captured image. If the baseline length is increased so that D / f tan ω exceeds the upper limit of equation (1), the size of the image circle on the image sensor becomes too small, degrading the image quality, which is undesirable. If the baseline length is reduced so that D / f tan ω falls below the lower limit of equation (1), the three-dimensional effect of the captured image becomes too weak, and the two image circles overlap on the image sensor, preventing an appropriate captured image from being obtained, which is also undesirable.

[0020] It is more preferable to set the numerical range of the formula (1) as follows.

[0021] 1.90≦D / f·tanω≦4.50 (1a) Furthermore, it is more preferable to set the numerical range of the formula (1) as follows.

[0022] 2.00≦D / f·tanω≦3.50 (1b) By using the above configuration and satisfying the condition of formula (1), it is possible to realize a stereo optical system that provides a natural three-dimensional effect, enables the capture of images with good image quality, and facilitates fast and quiet focusing.

[0023] Moreover, it is preferable that the optical system of each embodiment has at least one of the following configurations.

[0024] First, in the optical systems of each embodiment, it is preferable to position a negative lens closest to the object side, which brings the image-side principal point position of the entire front lens unit Lf, which is closer to the object side than the aperture stop SP, closer to the focus lens unit Lfc, which is closer to the image side than the aperture stop SP, and makes it possible to increase the imaging magnification for close objects.

[0025] Furthermore, the stereo optical system of each embodiment is assumed to capture two optical images formed by two optical systems, one on the left and one on the right, with a single image sensor. In this case, two image circles formed by the two optical systems are formed in regions on both the left and right sides of the center of the image sensor. In this case, in the region from the center of the image sensor to the center of each image circle, light rays are incident at an angle opposite to the angle of incidence of light rays expected when using a normal single optical system, which makes it easy for significant color shading to occur on the image sensor.

[0026] For this reason, in the optical systems of each embodiment, it is preferable to place a positive lens element closest to the image. In this embodiment, the term "lens" refers to a single lens, and the term "lens element" refers to an optical element that functions as a lens, such as a single lens or a cemented lens formed by cementing together multiple single lenses. By placing a positive lens element closest to the image, the angle of incidence of off-axis light rays on the image sensor becomes smaller, making it possible to reduce color shading.

[0027] As mentioned above, it is preferable that all lenses (front lens group Lf) on the object side of the aperture stop SP in each optical system and the aperture stop SP do not move during focusing.

[0028] Furthermore, it is preferable that each optical system have three or fewer lenses on the object side of the aperture stop SP. To suppress stripe noise, which will be described later, it is necessary to ensure a wide distance between the aperture stop SP and the image sensor in each optical system. For this reason, the number of lenses constituting the front lens group Lf is reduced, and any insufficient aberration correction effectiveness is compensated for by lenses positioned in a wide space on the image side of the aperture stop SP. This makes it possible to reduce the overall optical length while suppressing stripe noise.

[0029] Furthermore, it is preferable that each optical system has a positive lens element (a cemented lens of a positive lens Grp1 and a negative lens Grn) closest to the object on the image side of the aperture stop SP. By locating a positive lens close to the aperture stop SP and at a position where the width of the incident light beam is wide, light beams are converged well, spherical aberration is corrected well while the overall optical length is shortened, and a large aperture optical system is achieved. When a negative lens is cemented to a positive lens, axial chromatic aberration can be corrected well.

[0030] Furthermore, when the size of the two optical systems of each embodiment is reduced proportionally to form a compact stereo optical system, the aperture stop SP and the image sensor are brought closer together, which can cause electromagnetic interference between the aperture stop drive actuator and the image sensor. As a result, stripe-like noise (hereinafter referred to as stripe noise) occurs in the captured image. For this reason, in the optical systems of each embodiment, it is preferable to ensure that the distance from the aperture stop SP to the image plane IP is relatively large compared to the size of the stereo optical system. This can reduce stripe noise.

[0031] It is also preferable to arrange two or more positive lenses in the focus lens group Lfc. Sharing the refractive power among two or more positive lenses prevents the curvature of each lens surface from becoming large, thereby suppressing the occurrence of high-order aberrations. It is also preferable to arrange a negative lens in the focus lens group Lfc. This makes it possible to suppress the occurrence of various aberrations in the two positive lenses. With the above-mentioned configuration, it is possible to suppress fluctuations in various aberrations during focusing.

[0032] It is also preferable that the optical system of each embodiment satisfies at least one of the conditions of the following expressions (2) to (14).

[0033] Here, the focal length of the focus lens group Lfc is defined as fLfc, and the distance on the optical axis from the lens surface closest to the object in the rear lens group Lr, which includes all lenses on the image side of the aperture stop SP in the optical system, to the lens surface closest to the image in the rear lens group Lr is defined as TLr. The focal length of the positive lens element Grp2 closest to the image in the focus lens group Lfc is defined as fGrp2, and the focal length of the positive lens Grp1 closest to the object in the focus lens group Lfc is defined as fGrp1. The focal length of the negative lens Grn with the strongest negative refractive power among the lenses in the focus lens group Lfc that are closer to the object than the positive lens element Grp2 closest to the image is defined as fGn. The Abbe number, based on the d-line of the material of the positive lens included in the positive lens element Grp2 closest to the image in the focus lens group Lfc is defined as νdGrp2.

[0034] Let o1Lfc be the axial distance from the lens surface of the focus lens group Lfc closest to the object to the object-side principal point position of the focus lens group Lfc, TLfc be the axial distance from the lens surface of the focus lens group Lfc closest to the object to the lens surface of the focus lens group Lfc closest to the image, fLr be the focal length of the rear lens group Lr, fLf be the focal length of the front lens group Lf including all lenses on the object side of the aperture stop SP, and TLf be the axial distance from the lens surface of the front lens group Lf closest to the object to the lens surface of the front lens group Lf closest to the image.

[0035] Let R1 be the radius of curvature of the object-side lens surface of the negative lens Gfn closest to the object in the optical system, and R2 be the radius of curvature of the image-side lens surface of the negative lens Gfn closest to the object. Let fGfp be the focal length of the positive lens Gfp closest to the object in the optical system, and fGfn be the focal length of the negative lens Gfn closest to the object in the optical system. Let Lpi be the distance on the optical axis from the aperture stop SP of the optical system to the image plane IP. Let TL be the distance on the optical axis from the lens surface closest to the object in the optical system to the image plane IP, and t1 be the distance on the optical axis from the lens surface closest to the object in the optical system to the exit pupil position.

[0036] 1.00≦fLfc / f≦2.40 (2) 0.30≦TLr / fGrp2≦1.60 (3) 0.10≦fGrp1 / fGrp2≦1.00 (4) -1.60≦fGrn / fGrp1≦-0.30 (5) 55.00≦νdGrp2≦100.00 (6) 0.10≦o1Lfc / TLfc≦0.85 (7) -0.50≦fLr / fLf≦1.40 (8) 0.10≦TLf / TLr≦1.00 (9) -3.50≦(R2+R1) / (R2-R1)≦-0.50 (10) -1.60≦fGfp / fGfn≦-0.30 (11) 1.60≦Lpi / D≦3.60 (12) 0.70≦TL / f≦4.50 (13) 0.14≦t1 / f≦0.80 (14) The condition of formula (2) indicates an appropriate relationship between the focal length of the focus lens group Lfc and the focal length of the entire optical system for suppressing fluctuations in various aberrations during focusing. If the refractive power of the focus lens group Lfc becomes weak so that fLfc / f exceeds the upper limit of formula (2), the amount of movement of the focus lens group Lfc during focusing increases, and the overall length of the optical system (hereinafter referred to as the overall lens length) becomes long, which is undesirable. If the refractive power of the focus lens group Lfc becomes strong so that fLfc / f falls below the lower limit of formula (2), it becomes difficult to suppress fluctuations in various aberrations during focusing, which is also undesirable.

[0037] The condition of formula (3) indicates an appropriate relationship between the axial thickness of the rear lens unit Lr and the focal length of the positive lens element Grp2, which is the positive lens element closest to the image side of the rear lens unit Lr, in order to reduce color shading while suppressing distortion occurring in the positive lens element Grp2. If the refractive power of the positive lens element Grp2 becomes strong enough that TLr / fGrp2 exceeds the upper limit of formula (3), it becomes difficult to correct the distortion occurring in the positive lens element Grp2, which is undesirable. Also, if the refractive power of the positive lens element Grp2 becomes weak enough that TLr / fGrp2 falls below the lower limit of formula (3), the angle of incidence of light rays to the image sensor increases, which is undesirable because it causes significant color shading.

[0038] The condition of formula (4) indicates an appropriate relationship between the focal length of the positive lens element Grp1 and the focal length of the positive lens element Grp2, which is necessary to reduce the size of the focus lens group Lfc while suppressing spherical aberration occurring in the positive lens element Grp1 closest to the object in the focus lens group Lfc and increase the imaging magnification for close objects. If the refractive power of the positive lens element Grp1 becomes weak so that fGrp1 / fGrp2 exceeds the upper limit of formula (4), the focus lens group Lfc becomes large, and the entire optical system becomes large, which is undesirable. Furthermore, an increase in the size of the focus lens group Lfc makes fast and quiet focusing difficult, which is undesirable. If the refractive power of the positive lens element Grp1 becomes strong so that fGrp1 / fGrp2 falls below the lower limit of formula (4), it becomes difficult to correct the spherical aberration occurring in the positive lens element Grp1, which is undesirable.

[0039] The condition of formula (5) indicates an appropriate relationship between the focal length of the negative lens Grn and the focal length of the positive lens Grp1 for suppressing fluctuations in various aberrations during focusing while satisfactorily correcting spherical aberrations occurring in the positive lens Grp1. If the refractive power of the negative lens Grn becomes weak so that fGrn / fGrp1 exceeds the upper limit of formula (5), it becomes difficult to correct the spherical aberrations occurring in the positive lens Grp1, which is undesirable. If the refractive power of the negative lens Grn becomes strong so that fGrn / fGrp1 falls below the lower limit of formula (5), it becomes difficult to suppress fluctuations in various aberrations during focusing, which is also undesirable.

[0040] The condition of formula (6) indicates the appropriate range of the Abbe number for the d-line of the positive lens included in the positive lens element Grp2 to suppress the occurrence of lateral chromatic aberration in the positive lens element Grp2. If the positive lens has low dispersion so that νdGrp2 exceeds the upper limit of formula (6), the refractive index of the glass material that can be selected generally becomes low, and the radius of curvature of the positive lens must be small to ensure the necessary refractive power. As a result, it becomes difficult to suppress high-order aberrations, which is undesirable. If the positive lens has high dispersion so that νdGrp2 falls below the lower limit of formula (6), it becomes difficult to correct the lateral chromatic aberration occurring in the positive lens element Grp2, which is undesirable.

[0041] The condition of formula (7) indicates an appropriate relationship between the distance from the lens surface of the focus lens group Lfc closest to the object to the object-side principal point of the focus lens group Lfc and the thickness of the focus lens group Lfc, in order to increase the imaging magnification for close objects. If the object-side principal point of the focus lens group Lfc is located on the image side so that o1Lfc / TLfc exceeds the upper limit of formula (7), it becomes difficult to ensure an imaging magnification suitable for stereoscopic vision when imaging close objects, which is undesirable. If the object-side principal point of the focus lens group Lfc is located on the object side so that o1Lfc / TLfc falls below the lower limit of formula (7), the focus lens group Lfc will be positioned closer to the image, making it difficult to ensure back focus, which is undesirable.

[0042] The condition of formula (8) indicates an appropriate relationship between the focal length of the front lens group Lf and the focal length of the rear lens group Lr for suppressing distortion and lateral chromatic aberration while reducing the overall lens length. If the refractive power of the rear lens group Lr is weakened so that fLr / fLf exceeds the upper limit of formula (8), the principal point position of the entire optical system moves toward the image side, thereby increasing the overall lens length, which is undesirable. If the negative refractive power of the front lens group Lf is strengthened so that fLr / fLf falls below the lower limit of formula (8), the asymmetry in the refractive power distribution before and after the aperture stop SP increases, making it difficult to correct distortion and lateral chromatic aberration, which is also undesirable.

[0043] The condition of formula (9) indicates the appropriate relationship between the axial thickness of the front lens group Lf and the thickness of the rear lens group Lr for suppressing the occurrence of stripe noise while reducing the overall lens length. If the thickness of the rear lens group Lr is reduced so that TLf / TLr exceeds the upper limit of formula (9), the lens configuration on the image side of the aperture stop SP will shrink, narrowing the distance between the aperture stop SP and the image plane IP, making it difficult to suppress stripe noise, which is undesirable. If the thickness of the rear lens group Lr is increased so that TLf / TLr falls below the lower limit of formula (9), the overall lens length will increase, which is undesirable.

[0044] The condition of equation (10) indicates an appropriate range for the shape factor of the negative lens Gfn closest to the object for correcting spherical aberration occurring in the front lens group Lf. If the radius of curvature of the image-side lens surface of the negative lens Gfn becomes small enough that (R2+R1) / (R2-R1) exceeds the upper limit of equation (10), it becomes difficult to suppress high-order aberrations, which is undesirable. If the radius of curvature of the image-side lens surface of the negative lens Gfn becomes small enough that (R2+R1) / (R2-R1) falls below the lower limit of equation (10), it becomes difficult to correct spherical aberration occurring in the negative lens Gfp, which is undesirable.

[0045] The condition of equation (11) indicates the appropriate relationship between the focal length of the positive lens Gfp closest to the object and the focal length of the negative lens Gfn closest to the object, which are used to correct spherical aberration occurring in the front lens group Lf. If fGfp / fGfn exceeds the range of equation (11), it becomes difficult to correct the spherical aberration occurring in the front lens group Lf, which is undesirable.

[0046] The condition of equation (12) shows the appropriate relationship between the distance from the aperture stop SP to the image plane IP and the base length to reduce the overall lens length while suppressing the generation of stripe noise. If the aperture stop SP is farther away from the image plane IP so that Lpi / D exceeds the upper limit of equation (12), the overall lens length increases, which is not preferable. If the aperture stop SP is closer to the image plane IP so that Lpi / D falls below the lower limit of equation (12), it becomes difficult to suppress stripe noise, which is also not preferable.

[0047] The condition in equation (13) indicates the appropriate relationship between the total lens length and the focal length of the entire optical system to achieve both compactness and high performance in the optical system. If the total lens length is increased so that TL / f exceeds the upper limit of equation (13), the optical system will become larger, which is undesirable. If the total lens length is decreased so that TL / f falls below the lower limit of equation (13), the aperture stop SP will be too close to the image plane IP, making it difficult to suppress stripe noise, which is also undesirable. Furthermore, the angle of incidence of light rays on the image sensor will increase, which is undesirable, resulting in significant color shading.

[0048] The condition of equation (14) indicates an appropriate relationship between the distance from the lens surface closest to the object to the exit pupil position and the focal length of the entire optical system, which is necessary to reduce the size of the optical system while suppressing distortion. If the entrance pupil position is located on the image side so that t1 / f exceeds the upper limit of equation (14), the diameter of the lens closest to the object in the optical system increases, which is undesirable. If the entrance pupil position is located on the object side so that t1 / f falls below the lower limit of equation (14), the negative refractive power of the front lens unit Lf becomes strong, which increases the asymmetry in the refractive power distribution before and after the aperture stop SP, making it difficult to suppress distortion and chromatic aberration of magnification, which is also undesirable.

[0049] It is more preferable that the numerical ranges of the formulas (2) to (14) be as follows:

[0050] 1.10≦fLfc / f≦2.20 (2a) 0.40≦TLr / fGrp2≦1.50 (3a) 0.15≦fGrp1 / fGrp2≦0.90 (4a) -1.40≦fGrn / fGrp1≦-0.40 (5a) 60.00≦νdGrp2≦90.00 (6a) 0.15≦o1Lfc / TLfc≦0.80 (7a) -0.45≦fLr / fLf≦1.20 (8a) 0.15≦TLf / TLr≦0.90 (9a) -3.00≦(R2+R1) / (R2-R1)≦-0.70 (10a) -1.40≦fGfp / fGfn≦-0.40 (11a) 1.70≦Lpi / D≦3.50 (12a) 0.80≦TL / f≦3.00 (13a) 0.16≦t1 / f≦0.70 (14a) Furthermore, it is more preferable to set the numerical ranges of the formulas (2) to (14) as follows.

[0051] 1.20≦fLfc / f≦2.00 (2b) 0.50≦TLr / fGrp2≦1.40 (3b) 0.20≦fGrp1 / fGrp2≦0.80 (4b) -1.20≦fGrn / fGrp1≦-0.50 (5b) 65.00≦νdGrp2≦85.00 (6b) 0.20≦o1Lfc / TLfc≦0.75 (7b) 0.10≦fLr / fLf≦0.80 (8b) 0.20≦TLf / TLr≦0.80 (9b) -2.60≦(R2+R1) / (R2-R1)≦-0.90 (10b) -1.20≦fGfp / fGfn≦-0.50 (11b) 1.80≦Lpi / D≦3.40 (12b) 0.90≦TL / f≦2.00 (13b) 0.18≦t1 / f≦0.60 (14b) Below, we will explain in detail Examples 1 to 7. First, we will explain the configuration of the front lens unit Lf on the object side of the aperture stop SP in the optical system of each Example.

[0052] The front lens unit Lf in Examples 1, 2, 3 and 4 is composed of a negative lens Gfn and a positive lens Gfp, arranged in this order from the object side to the image side.

[0053] The front lens group Lf of the fifth embodiment is composed of, arranged in order from the object side to the image side, a negative lens Gfn and a cemented lens in which a negative lens and a positive lens Gfp are cemented together.

[0054] The front lens group Lf of the sixth embodiment is composed of a negative lens Gfn, a negative lens, and a positive lens Gfp, arranged in this order from the object side to the image side.

[0055] The front lens group Lf of Example 7 is composed of a cemented lens in which a negative lens Gfn and a positive lens Gfp are cemented together, in order from the object side to the image side.

[0056] Next, the configuration of the rear lens unit Lr located on the image side of the aperture stop SP in the optical system of each embodiment will be described.

[0057] The rear lens group Lr in Example 1 is composed of, arranged in order from the object side to the image side, a positive lens Grp1, a negative lens Grn, a negative lens, and a positive lens element Grp2 as a cemented lens in which a positive lens and a negative lens are cemented together.

[0058] The rear lens group Lr in Examples 2 and 6 is composed of, arranged in order from the object side to the image side, a cemented lens formed by cementing a positive lens Grp1 and a negative lens Grn, a negative lens, and a positive lens element Grp2 as a single lens.

[0059] The rear lens unit Lr in Examples 3 and 7 is composed of, arranged in order from the object side to the image side, a positive lens Grp1, a negative lens Grn, a negative lens, and a positive lens element Grp2 as a single lens.

[0060] The rear lens group Lr in Example 4 is composed of, arranged in order from the object side to the image side, a cemented lens formed by cementing a positive lens Grp1 and a negative lens Grn, and a positive lens element Grp2 as a cemented lens formed by cementing a positive lens, a positive lens, and a negative lens.

[0061] The rear lens group Lr in Example 5 is composed of, arranged in order from the object side to the image side, a positive lens, a positive lens Grp1, a negative lens Grn, and a positive lens element Grp2 as a cemented lens formed by cementing a positive lens and a negative lens together.

[0062] In Examples 1, 2, 3, 4, 6 and 7, during focusing from infinity to a close distance, the entire rear lens unit Lr moves toward the object side as the focus lens unit Lfc.

[0063] In the fifth embodiment, the focus lens group Lfc is made up of a positive lens element Grp1, a negative lens element Grn, and a positive lens element Grp2, which are part of the rear lens group Lr. The focus lens group Lfc moves toward the object side during focusing from infinity to a close distance.

[0064] Numerical Examples 1 to 7 corresponding to Examples 1 to 7, respectively, are shown below. In each numerical example, the surface number indicates the order of the surface from the object side. r is the radius of curvature (mm) of the ith surface, and d is the lens thickness or air gap (mm) on the optical axis between the ith surface and the (i+1)th surface. nd is the refractive index at the d-line of the optical material between the ith surface and the (i+1)th surface. νd is the Abbe number based on the d-line of the optical material. When 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 are nd, nF, and nC, respectively, the Abbe number νd based on the d-line is given by νd=(nd-1) / (nF-nC) θgF is the partial dispersion ratio, and when the refractive index at the g-line (wavelength 435.8 nm) is Ng, θgF=(Ng-NF) / (NF-NC) The effective diameter is the radius (mm) of the area through which light rays that contribute to image formation on the i-th surface pass.

[0065] BF represents back focus (mm). Back focus is the distance on the optical axis from the lens surface closest to the image (final surface) of the optical system to the paraxial image plane, expressed as the air-equivalent length. The total lens length (mm) is the distance on the optical axis from the lens surface closest to the object (front surface) of the optical system to the final surface, plus the back focus (total optical length).

[0066] An "*" next to a surface number indicates that the surface is a lens surface with an aspherical shape. The aspherical shape is expressed by the following formula, where x is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, the direction of light travel is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, and A10 are aspherical coefficients. The conic constant and aspherical coefficient "e±M" are multiplied by x10 ±M means.

[0067] x=(h 2 / 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 Moreover, the values ​​of the conditions of the above-mentioned formulas (1) to (14) in Numerical Examples 1 to 7 are summarized in Table 1. The optical systems of each Numerical Example satisfy all of the conditions of formulas (1) to (14).

[0068] Furthermore, Figures 2, 4, 6, 8, 10, 12, and 14 respectively show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of Numerical Examples 1 to 7. In each diagram, (A) shows the longitudinal aberration when focused on an object at infinity, and (B) shows the longitudinal aberration when focused on a close object. 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 two-dot chain 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 diagrams show distortion for the d-line. The chromatic aberration diagrams show lateral chromatic aberration for the g-line. ω is the half angle of view (°). [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 ∞ 1.50 1.51742 52.43 0.5564 5.60 2 9.221 0.96 5.60 3 10.548 4.60 1.49700 81.61 0.5386 5.93 4 -28.057 0.84 6.04 5 (Aperture) ∞ (Variable) 5.97 6 10.047 4.00 2.00100 29.14 0.5997 5.75 7 29.335 0.64 4.55 8 32.956 0.95 1.85896 22.73 0.6284 4.24 9 5.974 1.60 4.01 10 -7.308 1.70 1.76200 40.10 0.5765 4.58 11 -8.125 1.49 5.60 12 18.218 4.00 1.55200 70.70 0.5421 6.98 13 -5.070 1.50 1.51823 58.90 0.5457 7.43 14 -27.727 (variable) 7.94 Image plane ∞ Various data Focal length 22.42 F-number 4.00 Half angle of view (°) 12.21 Image height 4.85 Lens length 40.40 BF 13.81 Infinity Close (-0.05x) d 5 2.80 1.62 d14 13.81 14.99 Single lens data Lens starting surface focal length 1 1 -17.82 2 3 16.06 3 6 13.83 4 8 -8.64 5 10 -958.35 6 12 7.65 July 13 -12.25 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 29.770 1.01 1.58313 59.38 0.5434 7.57 2 11.365 1.59 7.43 3 12.118 2.00 1.49700 81.61 0.5386 7.86 4 -118.280 3.41 7.78 5 (Aperture) ∞ (Variable) 7.37 6 9.369 5.50 1.61800 63.33 0.5441 7.05 7 -17.653 1.05 1.54814 45.79 0.5686 5.35 8 6.532 5.60 4.79 9 -5.000 1.63 1.78880 28.43 0.6009 6.05 10 -6.698 0.10 7.29 11 77.565 3.78 1.49700 81.61 0.5386 7.86 12 -14.393 (variable) 8.64 Image plane ∞ Various data Focal length 30.26 F-number 4.00 Half angle of view (°) 9.11 Image height 4.85 Lens length 42.19 BF 13.29 Infinity Close (-0.05x) d 5 3.24 1.41 d12 13.29 15.12 Single lens data Lens starting surface focal length 1 1 -32.17 2 3 22.23 3 6 10.74 4 7 -8.57 5 9 -43.38 6 11 24.76 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 24.985 1.50 1.53172 48.84 0.5631 8.41 2 9.910 0.49 8.17 3 10.134 4.01 1.49700 81.61 0.5386 8.32 4 134.664 4.00 8.01 5 (Aperture) ∞ (Variable) 7.54 6 8.759 2.76 1.59522 67.74 0.5442 7.29 7 -68.528 0.90 6.54 8 -35.144 2.00 1.51602 56.86 0.5480 5.92 9 6.866 6.53 4.90 10 -5.283 1.15 1.95906 17.47 0.6598 6.31 11 -6.464 0.10 7.22 12 24.729 3.57 1.49700 81.61 0.5386 7.82 13 -38.858 (variable) 8.27 Image plane ∞ Various data Focal length 33.62 F-number 4.00 Half angle of view (°) 8.21 Image height 4.85 Lens length 42.50 BF 11.97 Infinity Close (-0.05x) d 5 3.53 1.50 d13 11.97 14.00 Single lens data Lens starting surface focal length 1 1 -31.99 2 3 21.82 3 6 13.22 4 8 -10.95 5 10 -57.74 6 12 30.98 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 205.606 1.50 1.59522 67.74 0.5442 6.51 2 8.229 3.98 5.73 3 19.264 2.50 1.49700 81.61 0.5386 5.04 4 -14.271 3.09 5.25 5 (Aperture) ∞ (Variable) 5.14 6 11.655 3.98 1.90366 31.34 0.5963 4.99 7 -12.847 1.92 1.78470 26.29 0.6135 5.02 8 6.395 2.67 4.98 9 -19.517 1.70 1.59522 67.74 0.5442 6.38 10 -11.819 0.20 7.20 11 17.530 4.12 1.59522 67.74 0.5442 7.85 12 -5.894 1.22 1.51742 52.43 0.5564 8.16 13 176.184 (variable) 8.34 Image plane ∞ Various data Focal length 15.69 F-number 4.00 Half angle of view (°) 17.18 Image height 4.85 Lens length 42.25 BF 11.21 Infinity Close (-0.05x) d 5 4.16 3.35 d13 11.21 12.02 Single lens data Lens starting surface focal length 1 1 -14.44 2 3 16.91 3 6 7.33 4 7 -5.21 5 9 46.51 6 11 7.93 7 12 -11.00 [Numerical example 5] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 ∞ 0.70 1.80000 29.84 0.6017 5.43 2 6.329 1.27 4.88 3 -13.660 1.50 1.54814 45.79 0.5686 4.78 4 9.401 2.05 1.89190 37.13 0.5780 4.80 5 -13.344 3.48 4.67 6 (Aperture) ∞ 3.43 5.01 7 44.010 3.00 1.49700 81.61 0.5386 5.33 8 -42.280 (variable) 5.99 9 11.818 4.00 1.52841 76.46 0.5396 8.14 10 -27.624 0.32 8.20 11 26.737 0.90 1.60342 38.03 0.5835 8.08 12 7.842 1.17 7.76 13 16.984 3.89 1.52841 76.46 0.5396 8.00 14 -6.667 0.50 1.87400 35.26 0.5827 8.16 15 -14.476 (variable) 8.58 Image plane ∞ Various data Focal length 11.20 F-number 3.50 Half angle of view (°) 23.41 Image height 4.85 Lens length 41.63 BF 11.41 Infinity Close (-0.05x) d 8 4.00 3.40 d15 11.41 12.01 Single lens data Lens starting surface focal length 1 1 -7.91 2 3 -9.93 3 4 6.46 4 7 43.90 5 9 16.23 6 11 -18.73 7 13 9.61 8 14 -14.57 [Numerical example 6] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 114.658 1.50 1.53775 74.70 0.5392 7.00 2 6.574 1.00 5.78 3 -25.778 1.09 1.52841 76.46 0.5396 5.72 4 12.827 1.72 5.47 5 12.959 4.40 1.67000 57.33 0.5438 5.65 6 -14.908 3.19 6.31 7 (Aperture) ∞ (Variable) 6.32 8 7.961 4.00 1.49700 81.61 0.5386 6.34 9 -9.696 2.00 1.59551 39.24 0.5803 5.69 10 7.710 1.86 6.04 11* -12.334 -0.90 1.53110 55.91 0.5684 6.56 12* -12.928 0.10 7.35 13 27.534 5.50 1.49700 81.61 0.5386 8.33 14 -7.997 (variable) 10.00 Image plane ∞ Aspheric data Page 11 K = 0.00000e+000 A 4=-1.15050e-003 A 6=-1.44404e-005 A 8=-8.01224e-007 A10= 4.36928e-008 Side 12 K = 0.00000e+000 A 4=-4.25982e-004 A 6= 2.13474e-006 A 8=-9.98293e-008 A10= 4.36622e-008 Various data Focal length 11.20 F-number 2.85 Half angle of view (°) 23.41 Image height 4.85 Lens length 45.41 BF 14.10 Infinity Close (-0.05x) d 7 4.04 3.44 d14 14.10 14.71 Single lens data Lens starting surface focal length 1 1 -13.03 2 3 -16.05 3 5 11.05 4 8 9.51 5 9 -6.92 6 11 -1066.00 7 13 13.14 [Numerical example 7] Unit: mm Surface Data Surface number rd nd νd θgF Effective diameter 1 32.134 1.22 1.54072 47.23 0.5651 8.01 2 13.698 4.78 1.49700 81.61 0.5386 7.87 3 6910.736 4.00 7.56 4 (Aperture) ∞ (Variable) 7.13 5 8.038 3.77 1.49700 81.61 0.5386 7.08 6 -26.698 0.72 6.03 7 -21.989 2.00 1.67000 57.33 0.5438 5.51 8 12.753 8.02 4.78 9 -5.168 1.70 1.55200 70.70 0.5421 5.33 10 -10.299 5.15 6.29 11 21.954 3.63 1.59522 67.74 0.5442 8.81 12 -66.587 (variable) 9.10 Image plane ∞ Various data Focal length 44.83 F-number 5.60 Half angle of view (°) 6.17 Image height 4.85 Lens total length 47.00 BF 8.00 Infinity Close (-0.05x) d 4 4.00 0.73 d12 8.00 11.27 Single lens data Lens starting surface focal length 1 1 -45.21 2 2 27.61 3 5 12.90 4 7 -11.78 May 9 -21.30 6 11 28.17

[0069] [Table 1]

[0070] [Imaging device] FIG. 17 shows an imaging device such as a digital camera equipped with the stereo optical system according to any one of the first to seventh embodiments.

[0071] ID denotes a camera body. The camera body ID is equipped with a stereo optical system (image pickup optical system) according to any one of Examples 1 to 7, which has a right optical system OSR and a left optical system OSL. S denotes a single image pickup element, such as a CCD sensor or CMOS sensor, which is built into the camera body ID and photoelectrically converts (captures) two optical images formed by the stereo optical system. The camera body ID processes the image pickup signal from the image pickup element S to generate image data, which is then recorded on a recording medium (not shown).

[0072] By using the stereo optical system of each embodiment, it is possible to realize a small-sized imaging device that can generate high-quality captured images.

[0073] The imaging device may be a single-lens reflex camera with a quick-turn mirror or a mirrorless camera without a quick-turn mirror. The stereo optical system may be detachable from the camera body or may be integrated into the camera body.

[0074] The above embodiment includes the following configurations.

[0075] (Configuration 1) A stereo optical system having two optical systems arranged in parallel, Each of the two optical systems is a coaxial optical system, and includes an aperture stop and a focus lens group that is disposed closer to the image side than the aperture stop and moves to change the spacing between adjacent lenses or lens groups for focusing; When the distance between the optical axes of the two optical systems is D, the focal length of each of the two optical systems is f, and the maximum half angle of view of each of the two optical systems is ω, 1.80≦D / f·tanω≦5.50 A stereo optical system characterized by satisfying the following conditions: (Configuration 2) When the focal length of the focus lens group is fLfc, 1.00≦fLfc / f≦2.40 2. The stereo optical system according to configuration 1, wherein the following condition is satisfied: (Configuration 3) Let TLr be the distance on the optical axis from the lens surface closest to the object in a rear lens group including all lenses on the image side of the aperture stops in each of the two optical systems to the lens surface closest to the image side in the rear lens group, and let fGrp2 be the focal length of the positive lens element closest to the image side in the focus lens group. 0.30≦TLr / fGrp2≦1.60 3. The stereo optical system according to configuration 1 or 2, wherein the following conditions are satisfied: (Configuration 4) When the focal length of the positive lens closest to the object side in the focus lens group is fGrp1, 0.10≦fGrp1 / fGrp2≦1.00 4. The stereo optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) Let fGrp1 be the focal length of the positive lens element closest to the object side in the focus lens group, and fGn be the focal length of the negative lens element with the strongest negative refractive power that is located closer to the object side than the positive lens element closest to the image side in the focus lens group. -1.60≦fGrn / fGrp1≦-0.30 5. The stereo optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the Abbe number of the material of the positive lens included in the positive lens element closest to the image side in the focus lens group is νdGrp2, the Abbe number is based on the d-line, 55.00≦νdGrp2≦100.00 6. The stereo optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) Let o1Lfc be the distance on the optical axis from the lens surface closest to the object in the focus lens group to the object-side principal point position of the focus lens group, and TLfc be the distance on the optical axis from the lens surface closest to the object in the focus lens group to the lens surface closest to the image in the focus lens group. 0.10≦o1Lfc / TLfc≦0.85 7. The stereo optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) When the focal length of a rear lens group including all lenses on the image side of the aperture stop in each of the two optical systems is defined as fLr, and the focal length of a front lens group including all lenses on the object side of the aperture stop is defined as fLf, -0.50≦fLr / fLf≦1.40 8. The stereo optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) Let TLf be the distance on the optical axis from the lens surface closest to the object in a front lens group including all lenses on the object side of the aperture stop in each of the two optical systems to the lens surface closest to the image side in the front lens group, and TLr be the distance on the optical axis from the lens surface closest to the object in a rear lens group including all lenses on the image side of the aperture stop in each of the two optical systems to the lens surface closest to the image side in the rear lens group, 0.10≦TLf / TLr≦1.00 9. The stereo optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) When the radius of curvature of the object-side lens surface of the negative lens closest to the object in each of the two optical systems is R1 and the radius of curvature of the image-side lens surface of the negative lens closest to the object is R2, -3.50≦(R2+R1) / (R2-R1)≦-0.50 10. The stereo optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) When the focal length of the positive lens closest to the object in each of the two optical systems is fGfp and the focal length of the negative lens closest to the object in each of the two optical systems is fGfn, -1.60≦fGfp / fGfn≦-0.30 11. The stereo optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied: (Configuration 12) When the distance on the optical axis from the aperture stop of each of the two optical systems to the image plane is Lpi, 1.60≦Lpi / D≦3.60 12. The stereo optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) When the distance on the optical axis from the lens surface closest to the object in each of the two optical systems to the image plane is TL, 0.70≦TL / f≦4.50 13. The stereo optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) When the distance on the optical axis from the lens surface closest to the object in each of the two optical systems to the exit pupil position is t1, 0.14≦t1 / f≦0.80 14. The stereo optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) 15. The stereo optical system according to any one of configurations 1 to 14, wherein all lenses on the object side of the aperture stop in each of the two optical systems do not move for focusing. (Configuration 16) 16. The stereo optical system according to any one of configurations 1 to 15, wherein the aperture stops in each of the two optical systems do not move during focusing. (Configuration 17) 17. The stereo optical system according to any one of configurations 1 to 16, wherein each of the two optical systems has three or less lenses on the object side of the aperture stop. (Configuration 18) 18. The stereo optical system according to any one of configurations 1 to 17, wherein each of the two optical systems has a positive lens element closest to the image side of the aperture stop. (Configuration 19) 19. The stereo optical system according to any one of configurations 1 to 18, wherein each of the two optical systems has a positive lens element closest to the object on the image side of the aperture stop. (Configuration 20) The stereo optical system according to any one of configurations 1 to 19, and a single imaging element that captures the two optical images formed by the two optical systems.

[0076] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0077] OSR right optical system OSL left optical system SP aperture stop Lf Front lens group Lr rear lens group Lfc focus lens group

Claims

1. A stereo optical system having two optical systems arranged in parallel, Each of the two optical systems is a coaxial optical system, and includes an aperture stop and a focus lens group that is disposed on the image side of the aperture stop and moves to change the spacing between adjacent lenses or lens groups for focusing; When the distance between the optical axes of the two optical systems is D, the focal length of each of the two optical systems is f, and the maximum half angle of view of each of the two optical systems is ω, 1.80≦D / f・tanω≦5.50 A stereo optical system characterized by satisfying the following conditions:

2. When the focal length of the focus lens group is fLfc, 1.00≦fLfc / f≦2.40 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

3. Let TLr be the distance on the optical axis from the lens surface closest to the object in a rear lens group including all lenses on the image side of the aperture stops in each of the two optical systems to the lens surface closest to the image side in the rear lens group, and let fGrp2 be the focal length of the positive lens element closest to the image side in the focus lens group. 0.30≦TLr / fGrp2≦1.60 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the positive lens closest to the object side in the focus lens group is fGrp1, 0.10≦fGrp1 / fGrp2≦1.00 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

5. Let fGrp1 be the focal length of the positive lens element closest to the object side in the focus lens group, and fGn be the focal length of the negative lens element with the strongest negative refractive power that is located closer to the object side than the positive lens element closest to the image side in the focus lens group. −1.60≦fGrn / fGrp1≦−0.30 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

6. When the Abbe number of the material of the positive lens included in the positive lens element closest to the image side in the focus lens group is νdGrp2, the Abbe number is based on the d-line, 55.00≦νdGrp2≦100.00 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

7. Let o1Lfc be the distance on the optical axis from the lens surface closest to the object in the focus lens group to the object-side principal point position of the focus lens group, and TLfc be the distance on the optical axis from the lens surface closest to the object in the focus lens group to the lens surface closest to the image in the focus lens group. 0.10≦o1Lfc / TLfc≦0.85 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

8. When the focal length of a rear lens group including all lenses on the image side of the aperture stop in each of the two optical systems is defined as fLr, and the focal length of a front lens group including all lenses on the object side of the aperture stop is defined as fLf, −0.50≦fLr / fLf≦1.40 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

9. Let TLf be the distance on the optical axis from the lens surface closest to the object in a front lens group including all lenses on the object side of the aperture stop in each of the two optical systems to the lens surface closest to the image side in the front lens group, and TLr be the distance on the optical axis from the lens surface closest to the object in a rear lens group including all lenses on the image side of the aperture stop in each of the two optical systems to the lens surface closest to the image side in the rear lens group, 0.10≦TLf / TLr≦1.00 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

10. When the radius of curvature of the object-side lens surface of the negative lens closest to the object in each of the two optical systems is R1 and the radius of curvature of the image-side lens surface of the negative lens closest to the object is R2, -3.50≦(R2+R1) / (R2-R1)≦-0.50 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

11. When the focal length of the positive lens closest to the object side in each of the two optical systems is fGfp and the focal length of the negative lens closest to the object side in each of the two optical systems is fGfn, −1.60≦fGfp / fGfn≦−0.30 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

12. When the distance on the optical axis from the aperture stop of each of the two optical systems to the image plane is Lpi, 1.60≦Lpi / D≦3.60 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

13. When the distance on the optical axis from the lens surface closest to the object in each of the two optical systems to the image plane is denoted by TL, 0.70≦TL / f≦4.50 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

14. When the distance on the optical axis from the lens surface closest to the object side in each of the two optical systems to the exit pupil position is t1, 0.14≦t1 / f≦0.80 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

15. 2. The stereo optical system according to claim 1, wherein all lenses on the object side of said aperture stop in each of said two optical systems do not move for focusing.

16. 2. The stereo optical system according to claim 1, wherein the aperture stops in each of the two optical systems do not move during focusing.

17. 2. The stereo optical system according to claim 1, wherein each of the two optical systems has three or fewer lenses on the object side of the aperture stop.

18. 2. The stereo optical system according to claim 1, wherein each of the two optical systems has a positive lens element closest to the image side of the aperture stop.

19. 2. The stereo optical system according to claim 1, wherein each of the two optical systems has a positive lens element closest to the object side on the image side of the aperture stop.

20. A stereo optical system according to any one of claims 1 to 19; and a single image sensor for capturing two optical images formed by the two optical systems.

Images