Stereo optical system and imaging apparatus

Abstract

To maximize an image circle formed on one imaging element by two optical systems arranged in parallel.SOLUTION: A stereo optical system forms image circles 103 and 105 on one imaging element IP by two optical systems 101 and 102 arranged in parallel. Each of the optical systems has an angle of view in which other optical system is reflected in first regions 104 and 106 outside in a parallel arrangement direction in the image circles, and a field stop RC so as to lower a light amount of second regions 107 and 108 inside in the image circles. A distance between optical axes of the two optical systems and image circle diameters are set so that a distance between centers of the image circles on the imaging element is shorter than the image circle diameters, third regions 103a and 105a between the first regions and the second regions in the image circles are brought into close contact with each other or adjacent to each other, and the first region is out of the imaging element.SELECTED DRAWING: Figure 17

Description

[Technical Field]

[0001] The present invention relates to an optical system and an imaging device used for stereo imaging. [Background technology]

[0002] When capturing left and right parallax images that a user can view stereoscopically with both eyes through an image display device such as a head-mounted display, a stereo imaging optical system having two parallel optical systems is used. Patent Document 1 discloses a stereo optical system that can capture left and right parallax images through two optical systems, each of which is a fisheye lens. In this stereo optical system, the optical paths of the left and right optical systems are bent so that the distance between the optical axes of the image-side portions of the left and right optical systems is narrower than the distance between the optical axes of the object-side portions of the left and right optical systems so that the image circles of the left and right optical systems can be contained within a single image sensor. Attaching this stereo optical system to a regular lens-interchangeable imaging device having a single image sensor enables stereo imaging. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-008629 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in order to fit the image circles of the left and right optical systems into one image sensor, as in the stereo optical system of Patent Document 1, it is necessary to reduce the size of the image circle of each optical system compared to when one image sensor is provided for one optical system. As a result, the number of pixels in the image obtained by imaging is reduced, limiting the improvement in image quality.

[0005] Furthermore, if each of the left and right optical systems is a fisheye lens, stray light generated in one optical system may be reflected in the image circle of the other optical system, degrading image quality.

[0006] The present invention provides a stereo optical system in which the image circle formed on one imaging element by each of two parallel-arranged optical systems is made as large as possible, thereby improving the quality of the image obtained by imaging. [Means for solving the problem]

[0007] One aspect of the present invention provides a stereo optical system having two optical systems arranged in parallel, forming an image circle of the two optical systems on a single image sensor. Each of the two optical systems has an angle of view such that the other optical system is reflected in a first region of the image circle that is located on the outside in the direction of parallel arrangement of the two optical systems, and a field stop for reducing the amount of light in a second region of the image circle that is located on the inside in the direction of parallel arrangement. The distance between the optical axes of the two optical systems and the diameter of the image circle are set so that the distance between the centers of the image circles of the two optical systems on the image sensor is shorter than the image circle diameter, so that third regions between the first and second regions of the image circles of the two optical systems are close to or adjacent to each other, and at least a portion of the first region is outside the image sensor. An imaging device including the stereo optical system and an image sensor also constitutes another aspect of the present invention. [Effects of the Invention]

[0008] According to the present invention, the image circle (third area) formed on one imaging element by each of two optical systems arranged in parallel can be made as large as possible, thereby improving the quality of the image obtained by imaging. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of one optical system in the stereo optical system of the first embodiment. [Figure 2]FIG. 10 is a longitudinal aberration diagram of Example 1 (Numerical Example 1). [Figure 3] FIG. 10 is a graph showing a peripheral light amount ratio in Numerical Example 1. [Figure 4] FIG. 2 is a diagram illustrating a field stop in the first embodiment. [Figure 5] FIG. 10 is a cross-sectional view of one optical system in the stereo optical system of the second embodiment. [Figure 6] FIG. 10 is a longitudinal aberration diagram of Example 2 (Numerical Example 2). [Figure 7] 10A and 10B are graphs showing peripheral light amount ratios in Numerical Example 2. [Figure 8] FIG. 11 is a cross-sectional view of one optical system in the stereo optical system of the third embodiment. [Figure 9] FIG. 10 is a longitudinal aberration diagram of Example 3 (Numerical Example 3). [Figure 10] 10A and 10B are graphs showing peripheral light amount ratios in Numerical Example 3. [Figure 11] FIG. 2 is a diagram showing an area of ​​the image circle of one optical system into which stray light from the other optical system is captured. [Figure 12] FIG. 10 is a diagram showing an area of ​​the image circle that is not suitable for viewing. [Figure 13] Diagram showing the field stop [Figure 14] FIG. 2 is a diagram showing an image circle on an imaging element. [Figure 15] FIG. 10 is another diagram showing an image circle on an imaging element. [Figure 16] FIG. 10 is yet another diagram showing an image circle on an imaging element. [Figure 17] FIG. 10 is another diagram showing the image circle on the imaging element. [Figure 18] 1A and 1B are external views of an imaging device including a stereo optical system according to each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to describing specific embodiments 1 to 3, matters common to all embodiments will be described.

[0011] The stereo optical system of each embodiment is provided in an interchangeable lens that is detachably attached to various imaging devices equipped with an imaging element, such as a digital camera, a video camera, a broadcast camera, a surveillance camera, etc. Note that the stereo optical system of each embodiment may be provided integrally with the imaging device.

[0012] As shown in FIG. 11, the stereo optical system of each embodiment has two optical systems (a right-eye optical system and a left-eye optical system) 101, 102 arranged side by side in the Z direction. In the figure, the left side is the object side (front side) and the right side is the image side (rear side). The X direction indicates the optical axis direction in which the optical axis of each optical system (shown by a dashed line) extends. The right side of FIG. 11 shows an image plane IP as seen from the object side. One image sensor (image sensor surface), shown by a rectangular frame in the figure, is disposed on the image plane IP. The image sensor has a rectangular shape with its long side extending in the Z direction and its short side extending in the Y direction. Image circles 103, 105 of the two optical systems 101, 102 are formed on the image sensor. In each embodiment, the image circle is defined as the area from the position (center) on the optical axis of each optical system where the light amount is 1 to the peripheral edge where the light amount is 0.

[0013] Each of the two optical systems 101 and 102 has an angle of view in which the other (adjacent) optical system is reflected in outer first regions 104 and 106 of the image circles 103 and 105 in the Z direction (parallel arrangement direction). Specifically, the angle of view is 180° or more. This makes it possible to obtain an image of an imaging region that covers the field of view of an observer who observes the image generated from the output of the imaging element through an image display device such as a head-mounted display, thereby providing the observer with a high sense of presence.

[0014] Furthermore, the two optical systems 101 and 102 each have a field stop RC. The field stop RC is provided to reduce the amount of light in second regions 107 and 108 on the inside of the image circles 103 and 105 in the Z direction. The field stop RC only needs to reduce the amount of light in the second regions compared to when the field stop RC is not provided, and does not necessarily have to reduce the amount of light in the second regions to zero. The regions of the image circles 103 and 105 between the first regions 104 and 106 and the second regions 107 and 108 are third regions 103a and 105a that are suitable for capturing images (viewing images).

[0015] In each embodiment, the distance Dout between the optical axes of the two optical systems 101 and 102 at the image side and the image circle diameter IH are set to satisfy the following conditions: First, as shown in Fig. 16 or 17, the distance CD between the centers of the image circles 103 and 105 of the two optical systems 101 and 102 on the image sensor is set to be shorter than the image circle diameter IH, so that the third regions 103a and 105a are close to or adjacent to each other. Second, at least a portion of the first regions 104 and 106 is set to be outside the image sensor.

[0016] Each of the optical systems 101 and 102 includes a first lens group (object-side 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. A reflecting member PR1 is disposed between the first lens group L1 and the second lens group L2, and a reflecting member PR2 is disposed between the second lens group L2 and the third lens group L2c. The reflecting member PR1 bends the optical path of the optical system 101 in the Z direction, and the reflecting member PR2 bends the optical path in the X direction. As a result, the distance Dout between the optical axes of the third lens group L3 is shorter than the distance Din (baseline length) between the optical axes of the first lens group L1 of the two optical systems 101 and 102. The baseline length is set to approximately the distance between a human's left and right eyes (60 to 65 cm). This allows two captured images with a parallax that enables stereoscopic vision to be obtained from the output of a single image sensor. Prisms, mirrors, etc. can be used as the reflecting members PR1 and PR2. SP is the aperture stop.

[0017] Although not shown, an optical block such as an optical filter (a low-pass filter, an infrared cut filter, or the like) or a face plate can be disposed between the third lens group L3 and the image plane IP.

[0018] 11 shows light rays reaching a first region 104 in an image circle 103 of an optical system 101 from an adjacent optical system 102. When these light rays reach the first region 104, the optical system 102 is captured in the first region 104. Solid lines indicate light rays from the front surface of the lens closest to the object in the optical system 102, and dashed lines indicate light rays from the side surface of the lens. Similarly, when light rays reach a first region 106 in an image circle 105 of the optical system 102 from the optical system 101, the optical system 101 is captured in the first region 106.

[0019] When an image is captured through each optical system in such a state, there will be areas in the resulting image where the adjacent optical system is reflected, and in those areas the image that should be viewed cannot be viewed.

[0020] 12, a first region 104 in which the left-eye optical system 102 is reflected exists near the right end of the image circle 103 of the right-eye optical system 101, while the right-eye optical system 101 is not reflected in a second region 108 in which the right-eye optical system 101 is reflected near the right end of the image circle 105 of the left-eye optical system 102. Similarly, a first region 106 in which the right-eye optical system 101 is reflected exists near the left end of the image circle 105 of the left-eye optical system 102, while the left-eye optical system 102 is not reflected in a second region 107 in which the left-eye optical system 102 is reflected near the left end of the image circle 103 of the right-eye optical system 101.

[0021] For this reason, the images of the regions near the right and left ends in the right-eye image obtained by imaging through the right-eye optical system 101 and the images of the regions near the right and left ends in the left-eye image obtained by imaging through the left-eye optical system 102 are different from each other. Such regions of different images are not suitable for viewing with both eyes. Therefore, the first region (104, 106) of the image circle of each optical system, in which the adjacent optical system is reflected, and the second region (107, 108) not suitable for image viewing are regions that do not need to be imaged in the first place.

[0022] The stereo optical system of each embodiment removes the first and second regions (hereinafter collectively referred to as unnecessary image circle regions) of the image circle of each optical system from the imaging target, and then enlarges the third region (hereinafter referred to as the viewing image circle region) suitable for viewing on the imaging element. This increases the number of pixels in the image region (hereinafter referred to as the viewing image region) of the captured image that corresponds to the viewing image circle region, thereby achieving high image quality.

[0023] Figure 14 shows image circles 103 and 105 when unnecessary image circle regions are not removed. The upper part of the figure shows the distribution of light intensity on the image circles 103 and 105. In this case, unnecessary image circle regions 104, 106, 107, and 108 exist on the imaging element, so the areas of the viewable image circle regions 103a and 105a are smaller. As a result, the number of pixels in the viewable image region in the captured image decreases, and image quality deteriorates.

[0024] 15 shows a case where the arrangement (i.e., the distance between the optical axes of the optical systems 101 and 102) and size (diameter) of the image circles 103 and 105 are set so that the second regions 107 and 108 are overlapped and the first regions 104 and 106 are positioned outside the image sensor. The upper part of the figure shows the distribution of the light intensity of the image circles 103 and 105. In this case, the areas of the ornamental image circle regions 103a and 105a become larger, and the number of pixels in the ornamental image region in the captured image can be increased, thereby improving image quality.

[0025] Furthermore, in each embodiment, the arrangement and size of the image circles 103 and 105 are set as shown in Figure 15, and a field stop RC is provided between the optical systems 101 and 102 and the image sensor to cut off second regions 107 and 108 from the image circles 103 and 105 on the image sensor. Figure 13(A) shows effective light rays that pass through the optical system and reach the image plane when no field stop is provided. The light rays shown by solid lines in the figure are light rays that reach an image height at the edge of the viewing image circle region. The second region extends from this image height to the image height reached by unwanted light rays shown by dashed lines.

[0026] Figure 13(B) shows the effective light rays that pass through the optical system and reach the image plane when a field stop RC is provided. The unnecessary light rays shown in Figure 13(A) are blocked by the field stop RC, thereby reducing the amount of light in the second region. Hereinafter, reducing the amount of light in the second region by the field stop RC is also referred to as cutting the second region of the image circle.

[0027] Figure 16 shows image circles 103 and 105 that have the arrangement and size shown in Figure 15, with second regions 107 and 108 cut out by field stop RC. The upper part of the figure shows the distribution of light intensity in the image circles 103 and 105. The D-cut ends of the image circles 103 and 105, where parts of the second regions 107 and 108 have been D-cut, are adjacent to each other. This makes it possible to reduce (eliminate) the area where the image circles 103 and 105 overlap.

[0028] 17, the sizes of the image circles 103 and 105 may be enlarged to the extent that the ornamental image circle regions 103a and 105a of the image circles 103 and 105 do not overlap with the other image circle. In this case, the D-cut edges of the image circles 103 and 105 overlap with the second region of the other image circle and are close to each other. As a result, the inner edges of the ornamental image circle regions 103a and 105a are close to each other (preferably adjacent).

[0029] By setting the arrangement and size of the image circles 103 and 105 in this way, the area of ​​the viewing image region in the captured image can be made larger, and the image quality of the viewing image region can be further improved.

[0030] The stereo optical system of each embodiment is an optical system that enables two optical images formed by two optical systems 101 and 103 to be captured by a single image sensor. The viewing image circle regions 103a and 105a of the two optical systems 101 and 103 are brought as close as possible to each other while the size of each image circle is increased. For this reason, a field stop RC is provided to prevent light rays from one optical system from entering the image circle of the other optical system and degrading the image quality of the image captured through each optical system.

[0031] Furthermore, because the angle of view of each optical system is large, there are many imaging scenes in which stray light from light sources such as the sun enters each optical system. The optical path of such stray light is often different from the optical path of effective light. For this reason, even if stray light is limited by a field stop placed within the optical system, the effect of reducing stray light is small. For this reason, in each embodiment, stray light can be effectively blocked by providing a field stop RC immediately before the image sensor (between the optical system and the image sensor).

[0032] Note that light rays at different image heights at least partially overlap with each other at the lenses behind the aperture stop SP. For example, the light rays shown by the solid lines and the light rays shown by the dashed lines in Fig. 11 partially overlap with each other at all lenses behind the aperture stop SP, and are completely separated on the image side of the lens closest to the image side in the optical system. For this reason, when reducing the amount of light in the second region with the field stop RC, in order to minimize the reduction in light amount in the viewing image circle region, it is preferable to place the field stop RC between the optical system where the light rays are separated and the image sensor.

[0033] The stereo optical system of each embodiment satisfies the condition of the following equation (1), where the distance between the optical axes of the image-side portions of the two optical systems 101 and 102 (i.e., the third lens group L3) is Dout and the image circle diameter of each optical system is IH. 0.75≦Dout / IH≦0.99 (1) If Dout / IH falls below the lower limit of equation (1), the amount of light in the viewing image circle area will be too low, which is undesirable. Correcting the reduced amount of light through image processing will increase noise and degrade image quality. Furthermore, if Dout / IH exceeds the upper limit of equation (1), the viewing image circle area cannot be sufficiently enlarged on the imaging element, making it impossible to obtain a high-quality image, which is also undesirable.

[0034] It is more preferable to set the numerical range of the formula (1) as follows. 0.77≦Dout / IH≦0.97 (1a) It is more preferable that the numerical range of the formula (1) is as follows: 0.79≦Dout / IH≦0.94 (1b) By satisfying the condition of formula (1), the size of the viewing image circle area formed on one image sensor by each of the two parallel-arranged optical systems 101 and 103 can be made as large as possible, thereby improving the quality of the image obtained by imaging.

[0035] It is desirable that the stereo optical system of each embodiment satisfies at least one of the conditions of the following expressions (2) to (6).

[0036] When the half angle of view of each optical system is ω, it is desirable that the condition of formula (2) be satisfied. 160.0°≦2ω≦220.0° (2) If 2ω is below the lower limit of equation (2), the view angle that can be displayed on the image display device becomes small, making it impossible to provide a realistic image, which is undesirable.If 2ω is above the upper limit of equation (2), the view angle that can be displayed becomes too wide, reducing the number of pixels per unit view angle and degrading image quality, which is undesirable.

[0037] It is more preferable to set the numerical range of the formula (2) as follows. 170.0°≦2ω≦215.0° (2a) It is more preferable that the numerical range of the formula (2) is as follows: 175.0°≦2ω≦210.0° (2b) In the stereo optical system of each embodiment, when the distance between the optical axes of the first lens group L1, which is the object-side lens group of the two optical systems 101 and 103, is Din and the distance between the optical axes of the third lens group L3, which is the image-side lens group, is Dout, it is preferable that the condition of the following formula (3) be satisfied: 0.05≦Dout / Din≦0.50 (3) If Dout / Din falls below the lower limit of equation (3), the baseline length becomes much wider than the human interpupillary distance, which is undesirable because the left-eye image and right-eye image will have too much parallax, causing the viewer to feel fatigued.If Dout / Din exceeds the upper limit of equation (3), the left-eye image and right-eye image will not have enough parallax, preventing the viewer from experiencing a three-dimensional effect, which is undesirable.

[0038] It is more preferable to set the numerical range of the formula (3) as follows. 0.10≦Dout / Din≦0.45 (3a) It is more preferable to set the numerical range of the formula (3) as follows. 0.15≦Dout / Din≦0.40 (3b) It is preferable that the stereo optical system of each embodiment satisfies the condition of the following formula (4), where Fno is the F-number of each optical system. 2.40≦Fno≦6.50 (4) If Fno is below the lower limit of formula (4), the reflecting members PR1 and PR2 and the aperture stop SP will become large, which is undesirable.If Fno is above the upper limit of formula (4), noise will increase during imaging, which will degrade image quality, which is undesirable. It is more preferable to set the numerical range of the formula (4) as follows. 2.55≦Fno≦5.90 (4a) It is more preferable that the numerical range of the formula (4) is as follows: 2.70≦Fno≦4.50 (4b) Figure 4 shows a schematic diagram of the field stop RC provided in each optical system. The field stop RC blocks light rays at a light-shielding portion (hatched portion) outside the position at a distance RCa from the optical axis of each optical system to reduce the amount of light in the second region. The maximum opening diameter of the portion of the field stop RC where no light-shielding portion is provided is RCb (>RCa). In this case, RCa and RCb satisfy the condition shown in the following equation (5). 0.25≦RCa / RCb≦0.48 (5) If RCa / RCb is below the lower limit of formula (5), the amount of light in the visual image circle region becomes too low, which is undesirable.If RCa / RCb is above the upper limit of formula (5), the amount of light in the unnecessary image circle region cannot be sufficiently reduced, the visual image circle region cannot be enlarged, and high image quality cannot be achieved, which is undesirable.

[0039] It is more preferable to set the numerical range of the formula (5) as follows: 0.28≦RCa / RCb≦0.47 (5a) It is more preferable that the numerical range of the formula (5) is as follows:

[0040] 0.30≦RCa / RCb≦0.46 (5b) The shape of the field stop RC may be a straight line extending from the optical axis through the position of RCa as shown in FIG. 4, or may be a curved line extending through the position of RCa.

[0041] In the stereo optical system of each embodiment, it is preferable that the condition of the following equation (6) be satisfied, where dRC is the distance on the optical axis from the field stop RC to the image plane IP, and sk is the distance on the optical axis from the image-side surface of the lens (final lens) having refractive power closest to the image in each optical system to the image plane IP. 0.20≦dRC / sk<1.00 (6) In each embodiment, as described above, a field stop RC is placed between the final lens of the optical system and the image plane IP in order to minimize the reduction in light intensity in the viewing image circle area while reducing the amount of light in the unnecessary image circle area. If the lower limit of equation (6) is exceeded, the amount of light in the area suitable for viewing will be significantly reduced, which is undesirable. If dRC / sk exceeds the upper limit of equation (6), interference with optical components such as a low-pass filter or infrared cut filter located on the object side of the image sensor will occur, which is undesirable.

[0042] It is more preferable to set the numerical range of the formula (6) as follows: 0.35≦dRC / sk≦0.95 (6a) It is more preferable that the numerical range of the formula (6) is as follows: 0.50≦dRC / sk≦0.90 (6b) The stereo optical systems of Examples 1 to 3 will be described below together with corresponding numerical examples. [Example]

[0043] The stereo optical system of Example 1 (Numerical Example 1) has two optical systems with an image height of 10.00 mm, a focal length of 5.59 mm, and a half angle of view of 102.50°, as shown in FIG. 1 , and is used in an imaging device equipped with an image sensor measuring 36 mm horizontally and 24 mm vertically. The optical axes of the third lens groups L3 of the two optical systems are located at positions +9 mm and −9 mm in the Z direction from the center of the image sensor, respectively. The distance Dout between the optical axes of the third lens groups L3 is 18.0 mm. The base length (Din) of the two optical systems is 63.6 mm.

[0044] The first lens group L1 of each optical system is composed of, arranged in order from the object side to the image side, a negative meniscus lens convex toward the object side, a negative meniscus lens convex toward the object side, and a cemented lens consisting of a negative meniscus lens convex toward the object side and a positive meniscus lens convex toward the object side. The image-side surface of the second negative meniscus lens from the object side is made aspheric to correct field curvature and astigmatism.

[0045] The second lens unit L2 of each optical system is composed of, arranged in order from the object side to the image side, a cemented lens of a negative meniscus lens convex on the object side and a biconvex lens, and an aperture stop SP.

[0046] The third lens group L3 of each optical system is composed of, arranged in order from the object side to the image side, a cemented lens consisting of a negative meniscus lens convex toward the object side and a biconvex lens, and a cemented lens consisting of a biconvex lens, a positive meniscus lens convex toward the image side, and a negative meniscus lens convex toward the image side.

[0047] The solid line in Figure 3 shows the marginal illumination ratio for each image height relative to the amount of light on the optical axis in the direction (Y direction) in which the field stop RC is not provided in the optical system of Numerical Example 1. The dashed line in Figure 3 shows the marginal illumination ratio in the Z direction reduced by the field stop RC in the optical system of Numerical Example 1. The optical system of Numerical Example 1 has an image height of 10.00 mm, but because a certain amount of light is required for image viewing, the light intensity ratio at an image height of 10.00 mm is set to 18.7%. For this reason, there is light even at image heights of 10.00 mm or more, and the image height at which the light intensity ratio is 0% is 10.18 mm.

[0048] In this way, it is necessary to set the image height to be limited by the field stop RC so that the area having a light amount exceeding the set image height of 10.00 mm does not overlap with the area in which the image generated by imaging through the adjacent optical system is viewed.

[0049] In this numerical example, the highest image height in the Z direction in the viewing image circle area is 8.20 mm (10.18 mm in the Y direction), and field stop RC is provided so that the amount of light decreases from an image height of 8.20 mm in the Z direction, as shown by the dashed line. Specifically, in Figure 4, field stop RC is provided so that the area in the Z direction equal to or greater than RCa6.60 mm of the original effective diameter RCb of 15.45 mm is light-reduced, and the light intensity ratio decreases from an image height of 8.20 mm, as shown by the dashed line in Figure 3, to 0% at an image height of 9.70 mm.

[0050] As mentioned above, the optical axis distance between the third lens unit L3 of the two optical systems is 18.0 mm, the viewing image circle area extends up to an image height of 8.20 mm, and the image height at which the peripheral illumination ratio is 0% is 9.70 mm. For this reason, the viewing image circle area of ​​each of the two optical systems is set so that it does not overlap with the viewing image circle area of ​​the adjacent optical system.

[0051] Furthermore, while the distance from the center to the edge of the image sensor in the Z direction is 9.0 mm, the first region into which the adjacent optical system is captured is a region starting from an image height of 8.20 mm, and the viewing image circle region is contained within the image sensor. In this way, it is important to set the optical axis distance, image circle diameter, and field stop RC of the third lens unit L3 so that the viewing image circle regions of the two optical systems are secured toward the center of the image sensor, and only the first region into which the adjacent optical system is captured is outside the image sensor toward the periphery.

[0052] Figure 2 shows the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system of Numerical Example 1. In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the dashed line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS indicates the sagittal image plane, and the dashed line ΔM indicates the meridional image plane. The distortion diagram shows distortion for the d-line. The chromatic aberration diagram shows the chromatic aberration of magnification for the g-line. ω is the half angle of view (°). The explanations for these longitudinal aberration diagrams are the same for the other numerical examples described below.

[0053] Numerical values ​​for Numerical Example 1 are shown after Example 3. In the numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the ith surface from the object side, d is the lens thickness or air gap (mm) between the ith and (i+1)th surfaces, and nd is the refractive index at the d-line of the optical material between the ith and (i+1)th surfaces. νd is the Abbe number based on the d-line of the optical material between the ith and (i+1)th surfaces. The Abbe number νd is given by Nd, NF, and NC, respectively, 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. νd=(Nd-1) / (NF-NC) It is expressed as:

[0054] BF represents back focal length (mm). Back focal length is the distance on the optical axis from the final surface of the optical system (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length, and corresponds to sk in equation (6). The total lens length (mm) is the distance on the optical axis from the foremost surface of the optical system (the lens surface closest to the object) to the final surface, plus the back focal length.

[0055] An "*" next to a surface number indicates that the surface has 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 the aspherical coefficient "eM" are multiplied by 10. -M means.

[0056]

number

[0057] Moreover, values ​​corresponding to the above-mentioned conditional expressions (1) to (6) in Numerical Example 1 are summarized in Table 1. [Example]

[0058] The stereo optical system of Example 2 (Numerical Example 2) has two optical systems with an image height of 9.70 mm, a focal length of 5.74 mm, and a half angle of view of 96.82°, as shown in FIG. 5, and is used in an imaging device equipped with an image sensor measuring 36 mm horizontally and 24 mm vertically. The optical axes of the third lens groups L3 of the two optical systems are located at positions +9.25 mm and −9.25 mm vertically from the center of the image sensor, respectively. The distance Dout between the optical axes of the third lens groups L3 is 18.5 mm. The base length (Din) of the two optical systems is 60.75 mm.

[0059] The first lens group L1 of each optical system is composed of, arranged from the object side to the image side, a negative meniscus lens convex toward the object side, a negative meniscus lens convex toward the object side, a negative meniscus lens convex toward the object side, and a positive meniscus lens convex toward the object side. The object-side surface of the third negative meniscus lens from the object side is aspheric, thereby correcting field curvature and astigmatism. The configurations of the second and third lens groups L2 and L3 of each optical system are the same as in Example 1.

[0060] The solid line in Figure 7 shows the marginal illumination ratio for each image height relative to the amount of light on the optical axis in the Y direction when no field stop RC is provided in the optical system of Numerical Example 2. The dashed line in Figure 7 shows the marginal illumination ratio in the Z direction reduced by the field stop RC in the optical system of Numerical Example 2. The second region in this numerical example is the region with an image height of 8.18 mm or more, but the field stop RC is set so that the amount of light is reduced from an image height of 7.59 mm in the Z direction. This setting reduces the amount of light in the viewing image circle region, but also reduces the image height at which the amount of light becomes zero. This makes it possible to increase the distance between the viewing image circle regions of the two optical systems, further expanding the image circle. In other words, higher image quality can be achieved in captured images.

[0061] It is desirable that the reduction in the amount of light in the viewing image circle region by the field stop RC be within a range that does not interfere with viewing of the captured image, but the reduction in the amount of light may be compensated for by image processing of the captured image.

[0062] In this numerical example, the field stop RC is provided so as to attenuate the area of ​​the effective diameter RCb of 15.83 mm shown in FIG. 4 that is equal to or greater than RCa 6.60 mm in the Z direction. As shown by the dashed line in FIG. 7, the light intensity ratio is reduced from an image height of 7.59 mm, and becomes 0% at an image height of 9.72 mm.

[0063] As mentioned above, the optical axis distance between the third lens unit L3 of the two optical systems is 18.5 mm, the viewing image circle area extends up to an image height of 8.18 mm, and the image height at which the peripheral illumination ratio is 0% is 9.72 mm. For this reason, the viewing image circle area of ​​each of the two optical systems is set so that it does not overlap with the viewing image circle area of ​​the adjacent optical system.

[0064] In addition, while the distance from the center to the edge of the image sensor in the Z direction is 8.75 mm, the first region into which the adjacent optical system is captured is the region from an image height of 8.18 mm, and the viewing image circle region is contained within the image sensor.

[0065] 6 shows the longitudinal aberration of the optical system of Numerical Example 2. Table 1 shows the values ​​corresponding to the above-mentioned conditional expressions (1) to (6) in Numerical Example 2. [Example]

[0066] The stereo optical system of Example 3 (Numerical Example 3) has two optical systems with an image height of 7.00 mm, a focal length of 3.85 mm, and a half angle of view of 104.18°, as shown in FIG. 8, and is used in an imaging device equipped with an image sensor measuring 22.5 mm horizontally and 15 mm vertically. The optical axes of the third lens groups L3 of the two optical systems are located at positions +5.70 mm and −5.70 mm vertically from the center of the image sensor, respectively. The distance Dout between the optical axes of the third lens groups L3 is 11.4 mm. The base length (Din) of the two optical systems is 55.0 mm.

[0067] The configurations of the first, second and third lens units L1, L2 and L3 of each optical system are the same as those in the first embodiment.

[0068] The solid line in Fig. 10 shows the marginal illumination ratio for each image height relative to the amount of light on the optical axis in the Y direction when no field stop RC is provided in the optical system of Numerical Example 3, and the image height at which the light intensity ratio is 0% is 7.06 mm. The dashed line in Fig. 10 shows the marginal illumination ratio in the Z direction reduced by the field stop RC in the optical system of Numerical Example 3. The second region in this numerical example is the region of image heights of 5.40 mm and above, but the field stop RC is set so that the amount of light is reduced from an image height of 4.00 mm in the Z direction.

[0069] In this embodiment as well, it is desirable that the reduction in the amount of light in the viewing image circle area by the field stop RC be within a range that does not interfere with viewing the captured image, but the reduction in light amount may be compensated for by image processing of the captured image.

[0070] In this numerical example, the field stop RC is provided so as to attenuate the area of ​​the effective diameter RCb of 10.86 mm shown in FIG. 4 that is equal to or greater than RCa3.71 mm in the Z direction. As shown by the dashed line in FIG. 10, the light intensity ratio is reduced from an image height of 4.00 mm, and the light intensity ratio is set to 0% at an image height of 5.95 mm.

[0071] As mentioned above, the optical axis distance between the third lens unit L3 of the two optical systems is 11.4 mm, the viewing image circle area extends up to an image height of 5.40 mm, and the image height at which the peripheral illumination ratio is 0% is 5.95 mm. For this reason, the viewing image circle area of ​​each of the two optical systems is set so that it does not overlap with the viewing image circle area of ​​the adjacent optical system.

[0072] Also, while the distance from the center to the edge of the image sensor in the Z direction is 5.55 mm, the first region into which the adjacent optical system is captured is the region from an image height of 5.40 mm, and the viewing image circle region is contained within the image sensor.

[0073] 9 shows the longitudinal aberration of the optical system of Numerical Example 3. Table 1 shows the values ​​corresponding to the above-mentioned conditional expressions (1) to (6) in Numerical Example 3.

[0074] According to each of the embodiments described above, the image circle formed on one image sensor by each of the two parallel-arranged optical systems can be made as large as possible, thereby improving the quality of the image obtained by imaging.

[0075] In the above embodiments, the projection method of the optical system is the equiangular projection method, but other projection methods such as the equisolid angle projection method or the stereoscopic projection method may also be used.

[0076] Furthermore, the sizes of the image pickup elements given in the above embodiments are merely examples, and image pickup elements of other sizes may also be used. [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 40.212 2.00 1.91082 35.3 48.01 2 12.305 9.23 24.54 3 23.956 1.09 1.85400 40.4 22.96 4* 12.069 3.85 19.19 5 32.411 1.09 1.90043 37.4 18.31 6 9.048 4.18 1.85478 24.8 15.10 7 14.719 7.49 13.66 8 ∞ 13.00 1.51633 64.1 10.15 9∞2.00 6.56 10 14.807 0.80 2.00100 29.1 7.15 11 9.141 4.00 1.62004 36.3 7.01 12 -32.731 1.00 7.11 13 (Aperture) ∞ 2.00 7.01 14 ∞ 13.00 1.51633 64.1 6.85 15 ∞ 1.97 9.52 16 50.909 0.97 2.00100 29.1 11.20 17 19.691 3.01 1.49700 81.5 11.56 18 -30.051 0.00 12.38 19 12.552 6.53 1.43875 94.7 14.12 20 -16.148 0.30 13.99 21 -17.940 3.21 1.59522 67.7 13.70 22 -11.478 0.86 2.00100 29.1 13.69 23 -80.041 2.05 14.50 24 ∞ 11.46 15.45 Image plane ∞ Aspheric data Side 4 K =-9.46957e-002 A 4=-2.00280e-005 A 6= 1.39815e-007 A 8=-2.65465e-009 Various data Focal length 5.59 F-number 4.10 Half angle of view (°) 102.50 Image height 10.00 Lens total length 95.08 BF 11.46 Entrance pupil position 12.15 Exit pupil position -24.35 Front principal point position 16.86 Back principal point position 5.87 Rca 6.60 Rcb 15.45 Single lens data Lens starting surface focal length 1 1 -20.15 2 3 -29.73 3 5 -14.25 4 6 20.51 5 8 0.00 6 10 -25.68 7 11 11.96 8 14 0.00 9 16 -32.59 10 17 24.43 11 19 17.30 12 21 45.17 13 22 -13.47 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 32.477 1.94 1.95375 32.3 45.69 2 13.390 10.10 26.47 3 36.545 1.05 1.83481 42.7 24.20 4 20.546 3.00 21.22 5* 61.673 1.05 1.85400 40.4 19.54 6 9.845 2.09 15.42 7 11.893 3.50 1.85478 24.8 15.29 8 14.071 6.90 13.43 9 ∞ 13.25 1.51633 64.1 10.71 10 ∞ 1.00 9.22 11 18.144 0.75 1.91082 35.3 9.78 12 10.520 4.25 1.59270 35.3 9.65 13 -33.345 1.00 9.89 14 (Aperture) ∞ 1.00 9.84 15 ∞ 13.00 1.51633 64.1 9.80 16 ∞ 1.72 10.39 17 44.257 0.94 1.95375 32.3 11.88 18 18.233 3.15 1.49700 81.5 12.20 19 -35.627 0.00 12.97 20 14.043 6.91 1.43875 94.7 14.50 21 -17.502 0.30 14.46 22 -37.189 4.08 1.49700 81.5 13.93 23 -10.631 0.83 2.00100 29.1 13.56 24 -54.546 4.27 14.36 25 ∞ 11.46 15.83 Image plane ∞ Aspheric data 5th page K = 0.00000e+000 A 4= 9.42786e-006 A 6=-1.81797e-007 A 8= 2.60380e-009 A10=-9.79910e-012 Various data Focal length 5.74 F-number 2.91 Half angle of view (°) 96.82 Image height 9.70 Lens length 97.55 BF 11.46 Entrance pupil position 13.53 Exit pupil position -28.20 Front principal point position 18.44 Back principal point position 5.72 RCa 6.60 RCb 15.83 Single lens data Lens starting surface focal length 1 1 -25.14 2 3 -57.96 3 5 -13.85 4 7 51.64 5 9 0.00 6 11 -28.84 7 12 14.00 8 15 0.00 9 17 -33.10 10 18 24.75 11 20 19.03 12 22 28.50 13 23 -13.32 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 26.681 1.40 2.00100 29.1 42.54 2 12.236 11.23 24.42 3 54.814 0.76 1.85400 40.4 20.83 4* 9.538 4.71 15.28 5 91.244 0.76 1.88300 40.8 14.48 6 8.241 5.63 1.85478 24.8 12.87 7 36.217 7.12 11.59 8 ∞ 14.41 1.51633 64.1 8.15 9∞ 1.90 5.60 10 28.260 0.78 1.91082 35.3 5.99 11 11.944 2.80 1.59270 35.3 5.98 12 -26.153 0.70 6.20 13 (Aperture) ∞ 1.21 6.22 14 ∞ 14.41 1.95375 32.3 6.24 15 ∞ 1.51 6.37 16 16.501 0.68 1.90043 37.4 7.29 17 12.163 2.20 1.43875 94.7 7.35 18 -58.748 1.76 7.80 19 21.262 3.26 1.43875 94.7 8.68 20 -14.448 0.30 8.95 21 -50.926 3.13 1.49700 81.5 8.87 22 -10.135 0.60 1.95375 32.3 8.85 23 -59.880 6.03 9.16 24 ∞ 11.46 10.86 Image plane ∞ Aspheric data Side 4 K = 7.88130e-002 A 4=-3.19820e-005 A 6= 6.69832e-007 A 8=-4.82627e-009 Focal length 3.85 F-number 4.10 Half angle of view (°) 104.18 Image height 7.00 Lens length 98.74 BF 11.46 Entrance pupil position 12.17 Exit pupil position -29.90 Front principal point position 15.66 Back principal point position 7.61 Rca 3.71 Rcb 10.86 Single lens data Lens starting surface focal length 1 1 -23.73 2 3 -13.63 3 5 -10.30 4 6 11.42 5 8 0.00 6 10 -23.24 7 11 14.22 8 14 0.00 9 16 -55.50 10 17 23.19 11 19 20.17 12 21 24.83 13 22 -12.87

[0077] [Table 1]

[0078] 18 shows a digital still camera as an imaging device that uses the stereo optical system of each of the above-described embodiments as an imaging optical system. 20 denotes the camera body, and 21 denotes an imaging optical system configured with the stereo optical system of any of the embodiments 1 to 3. 22 denotes an imaging element such as a CCD sensor or CMOS sensor that is built into the camera body 20 and captures an optical image (subject image) formed by the imaging optical system 21. 23 denotes a recording unit that records image data generated by processing the imaging signal from the imaging element 22, and 24 denotes a rear display that displays the image data.

[0079] By using the stereo optical system of each embodiment in this camera, it is possible to obtain high-quality images that can be viewed stereoscopically.

[0080] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of symbols]

[0081] 101 Right eye optical system 102 Left eye optical system 103, 105 Image Circle 103a, 105a Third Region 104, 106 First Area 107, 108 Second Area RC field stop IP image plane (image sensor)

Claims

1. A stereo optical system having two optical systems arranged in parallel and forming an image circle of the two optical systems on one image sensor, Each of the two optical systems is an angle of view in which the other optical system is reflected in a first region on the outer side of the image circle in a direction in which the two optical systems are arranged in parallel; a field stop for reducing the amount of light in a second region on the inside of the image circle in the parallel arrangement direction; A stereo optical system characterized in that the distance between the optical axes of the two optical systems and the image circle diameters are set so that the center-to-center distance between the image circles of the two optical systems on the imaging element is shorter than the image circle diameter, so that third areas between the first and second areas of the image circles of the two optical systems are close to or adjacent to each other, and so that at least a portion of the first area is outside the imaging element.

2. When the distance between the optical axes is Dout and the image circle diameter is IH, 0.75≦Dout / IH≦0.99 2. The stereo optical system according to claim 1, wherein the following condition is satisfied:

3. When the half angle of view of each of the two optical systems is ω, 160.0°≦2ω≦220.0° 3. The stereo optical system according to claim 1, wherein the following condition is satisfied:

4. Each of the two optical systems has an object-side lens group and an image-side lens group, a distance between the optical axes of the image-side lens groups is shorter than a distance between the optical axes of the object-side lens groups in the two optical systems by bending an optical path between the object-side lens and the image-side lens groups, 4. The stereo optical system according to claim 1, wherein the distance between the optical axes of the two optical systems is the distance between the optical axes of the image side lens groups.

5. When the optical axis distance of the object-side lens group is Din and the optical axis distance of the image-side lens group is Dout, 0.05≦Dout / Din≦0.50 5. The stereo optical system according to claim 4, wherein the following condition is satisfied:

6. When the F-number of each of the two optical systems is Fno, 1.40≦Fno≦6.50 6. The stereo optical system according to claim 1, wherein the following condition is satisfied:

7. In each of the two optical systems, when a distance from an optical axis of the optical system to a light-shielding portion for reducing the amount of light in the field stop is RCa, and a maximum aperture diameter of a portion of the field stop where the light-shielding portion is not provided is RCb, 0.25≦RCa / RCb≦0.48 7. The stereo optical system according to claim 1, wherein the following condition is satisfied:

8. In each of the two optical systems, when a distance on the optical axis from the field stop to an image plane is dRC, and a distance on the optical axis from an image side surface of a lens having refractive power and located closest to the image side in the optical system to the image plane is sk, 0.20≦dRC / sk<1.00 8. The stereo optical system according to claim 1, wherein the following condition is satisfied:

9. A stereo optical system according to any one of claims 1 to 8; An imaging device comprising the imaging element.

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