Optical system, image capturing device, in-vehicle system, and mobile device

Abstract

To provide an optical system which offers a sufficient angle of view and central resolution, and can be used to constitute a compact image capturing device.SOLUTION: An optical system 100A provided herein consists of a front group 101A comprising multiple lenses, an aperture stop ST, and a rear group 102A comprising multiple lenses, arranged in order from the magnification conjugate side to the reduction conjugate side. Projection characteristics y(θ) of the optical system representing a relationship between a half view angle θ and an image height y on the image plane satisfy a condition expressed as: 1<f×sinθmax / y(θmax)≤1.9, where θmax represents the maximum half view angle of the optical system and f represents a focal length of the optical system. The differential value dy(θ) / dθ at the half view angle θ of the projection characteristics y(θ) has a maximum value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for an imaging device such as an in-vehicle camera. [Background technology]

[0002] In-vehicle cameras are used to obtain image data of the vehicle's surroundings and to recognize other vehicles and obstacles. For in-vehicle cameras used in place of rearview mirrors, which are primarily used to recognize other vehicles far behind, optical systems with projection characteristics close to y=f×tanθ, in which distortion aberration has been corrected, are suitable. On the other hand, for in-vehicle cameras used primarily to monitor a wide area near the vehicle, fisheye lenses with y=f×θ (equidistant projection), y=2f×sin(θ / 2) (equal solid angle projection), or y=f×sinθ (orthogonal projection) are suitable. However, fisheye lenses with these projection characteristics have low imaging magnifications, making them difficult to use as a replacement for a rearview mirror. For this reason, there is a demand for optical systems that have a wide angle of view equivalent to that of a fisheye lens and a large imaging magnification in the central angle of view region. Patent Document 1 discloses an optical system called a foveated lens having projection characteristics with a larger imaging magnification in the central angle of view region than the orthogonal projection method. Patent Document 2 discloses an optical system as a foveated lens having a larger maximum angle of view (half angle of view 90°) than the optical system of Patent Document 1, which has an insufficient maximum angle of view. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-354572 A [Patent Document 2] JP 2007-155976 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as the angle of view of the optical system of Patent Document 2 becomes wider, the size of the image sensor for acquiring image data becomes larger, resulting in a larger camera.

[0005] The present invention provides an optical system and the like that has a sufficient angle of view and imaging magnification in the central angle of view region, and that makes it possible to configure a small-sized imaging device. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention is an optical system having a plurality of lenses and an aperture stop, and when a projection characteristic of the optical system expressing a relationship between a half angle of view θ and an image height y on an image plane is defined as y(θ), a maximum half angle of view of the optical system is defined as θmax, and a focal length of the optical system is defined as f,

[0007]

number

[0008] The above condition is satisfied. Furthermore, the differential value dy(θ) / dθ of the projection characteristic y(θ) at a half angle of view θ has a maximum value. Note that an imaging device using the above optical system, and an in-vehicle system or a mobile device using the imaging device also constitute another aspect of the present invention. Effect of the Invention

[0009] According to the present invention, it is possible to realize an optical system that has a sufficient angle of view and imaging magnification in the central angle of view region and that can be used to configure a small-sized imaging device. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] FIG. 4 is a diagram showing the projection characteristic of the optical system of the first embodiment. [Diagram 3] FIG. 4 is a diagram showing the curvature of an aspheric surface of the optical system according to the first embodiment. [Figure 4] 4A to 4C are aberration diagrams of the optical system of Example 1. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 6] FIG. 11 is a diagram showing the projection characteristic of the optical system of the second embodiment. [Figure 7] FIG. 11 is a diagram showing the curvature of an aspheric surface of the optical system according to the second embodiment. [Figure 8] 6A to 6C are aberration diagrams of the optical system of Example 2. [Figure 9] FIG. 11 is a cross-sectional view of the optical system of the third embodiment. [Figure 10] FIG. 11 is a diagram showing the projection characteristic of the optical system of the third embodiment. [Figure 11] FIG. 11 is a diagram showing the curvature of an aspheric surface of the optical system according to the third embodiment. [Figure 12] 11A to 11C are aberration diagrams of the optical system of Example 3. [Figure 13] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 14] FIG. 13 is a diagram showing the projection characteristic of the optical system of the fourth embodiment. [Figure 15] FIG. 13 is a diagram showing the curvature of an aspheric surface of the optical system according to the fourth embodiment. [Figure 16] 11A to 11C are aberration diagrams of the optical system of Example 4. [Figure 17] FIG. 1 is a block diagram of an in-vehicle system using the optical system of each embodiment. [Figure 18] 1 is a schematic diagram of a vehicle equipped with an on-board system. [Figure 19] 4 is a flowchart showing an example of the operation of the in-vehicle system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] 1, 5, 9, and 13 show optical systems 100 (A, B, C, D) of Examples 1, 2, 3, and 4, respectively. The optical system 100 of each Example is suitable for imaging devices such as digital still cameras, digital video cameras, car-mounted cameras, mobile phone cameras, security cameras, wearable cameras, and medical cameras. In each figure, the left side is the magnification conjugate side (object side), and the right side is the reduction conjugate side (image side). The optical system 100 of each Example is an imaging (imaging) optical system that collects light beams from an object (not shown) located on the magnification conjugate side to form an object image on an image plane 300 on the reduction conjugate side. An imaging surface (light receiving surface) of an imaging element such as a CCD sensor or a CMOS sensor is arranged on the image plane. However, the optical system of each Example can also be used as a projection optical system of a projector that projects light beams from a spatial light modulation element such as a liquid crystal panel arranged on the reduction conjugate side onto a projection surface such as a screen arranged on the magnification conjugate side. In the following description, the optical system will be described as being used as an imaging optical system for an on-vehicle camera.

[0013] The optical system 100 in each embodiment is composed of a front group 101 (A to D) having a plurality of lenses, an aperture stop ST, and a rear group 102 (A to D) having a plurality of lenses, which are arranged in order from the enlargement conjugate side to the reduction conjugate side. An IR cut filter 201 and a cover glass 202 are arranged between the optical system 100 and an image plane 300. Furthermore, a low-pass filter or the like may be additionally arranged as necessary, and the IR cut filter 201 and the like may be omitted.

[0014] Furthermore, stops for limiting off-axis light beams may be disposed between the front group 101 and the aperture stop ST, and between the aperture stop ST and the rear group 102, respectively. EXAMPLES

[0015] 1, the front group 101A is made up of four lenses L1, L2, L3, and L4, and the rear group 102A is made up of four lenses L5, L6, L7, and L8.

[0016] The lens L1 closest to the magnification conjugate side in the front group 101A (optical system 100A) is an aspherical lens (first aspherical lens) whose both surfaces on the magnification conjugate side and the reduction conjugate side are aspheric, and whose paraxial refractive power (paraxial power) is negative.

[0017] The second lens L2 from the magnification conjugate side in front group 101A is an aspheric lens (second aspheric lens) whose both surfaces are aspheric, and has positive paraxial refractive power.

[0018] The third and fourth lenses L3 and L4 from the magnification conjugate side in front group 101A are both spherical lenses, and their refractive powers are negative and positive, respectively.

[0019] The lenses L5, L6, and L7 located closest to the magnification conjugate side, and the second and third lenses from the magnification conjugate side in the rear group 102A are all spherical lenses, and their refractive powers are negative, positive, and negative, respectively.

[0020] The lens (final lens) L8 on the most reduction conjugate side in rear group 102A (optical system 100A) is an aspheric lens (third aspheric lens) whose both surfaces are aspheric, and has positive paraxial refractive power.

[0021] The optical system 100A of this embodiment does not include a cemented lens and is entirely composed of single lenses. An on-vehicle camera may be placed in a high-temperature environment (e.g., 70°C or higher) exposed to direct sunlight in the summer and in a low-temperature environment below freezing in the winter, and a cemented lens may peel off due to the difference in linear expansion coefficient between the materials of the cemented lenses, so only single lenses are used.

[0022] Table 1 shows an example of values ​​for the optical system 100A of this embodiment. (A) shows the lens configuration, f shows the paraxial focal length (hereinafter, simply referred to as the focal length) (mm), and Fno shows the F-number. θmax shows the maximum half angle of view (°). In addition, from the magnification conjugate side, the radius of curvature r (mm) of the i-th surface, the distance d (mm) between the i-th surface and the (i+1)-th surface, the refractive index n for the d-line of each optical member, and the Abbe number ν based on the d-line are shown.

[0023] The Abbe number ν is given by the following equation, where Nd, NF, and NC are the refractive indices at the d line (587.6 nm), F line (486.1 nm), and C line (656.3 nm) of the Fraunhofer lines: It is expressed as ν=(Nd-1) / (NF-NC).

[0024] ST indicates the position of the aperture stop. Surfaces with an * on the left side have an aspheric shape expressed by the following formula (1). h is the coordinate in the radial direction from the optical axis, z is the coordinate in the optical axis direction (sag amount), r is the paraxial radius of curvature, and k is the conic constant. The sign of z is positive in the direction from the magnification conjugate side to the reduction conjugate side.

[0025]

number

[0026] (B) shows the conic constant k and aspheric coefficients B4, B6, B8, B10, B12, B14, and B16 of each aspheric surface. “E±x” is “10 ±x All aspheric coefficients that are not specifically indicated are 0. The explanation regarding the above-mentioned numerical example is the same for other examples described later.

[0027] The optical system 100A of this embodiment is an optical system in which the angle between the optical axis and the most off-axis chief ray, i.e., the maximum half angle of view θmax is π / 2 (=90°), and has the same maximum half angle of view as a fisheye lens. Moreover, the optical system 100A of this embodiment is an optical system in which the imaging magnification in the field angle region near the center (hereinafter referred to as the central field angle region) is larger than that of a fisheye lens.

[0028] 2A and 2B respectively show the projection characteristic and the resolution characteristic of the optical system 100A of this embodiment. Note that in Figs. 2A and 2B, the unit of the angle of view is ° (deg).

[0029] The projection characteristic y(θ) shown in FIG. 2(A) represents the relationship between the half angle of view (the angle between the optical axis and the incident light) θ and the imaging height (image height) y on the image plane 300. FIG. 2(B) represents the amount of change in the imaging height y with respect to a small change in the half angle of view θ, that is, the differential value dy(θ) / dθ at the half angle of view θ of the projection characteristic y(θ). The differential value dy(θ) / dθ corresponds to the local resolution at the imaging height y, and the larger this value is, the higher the local resolution is. Also, a higher local resolution means a larger local imaging magnification. In the following description, the resolution refers to this local resolution.

[0030] The optical system 100A of this embodiment is characterized in that its projection characteristic y(θ) satisfies the following conditional expression (2): f is the focal length of the optical system 100A, and θmax is the maximum half angle of view.

[0031]

number

[0032] The optical system 100A of this embodiment has a higher central resolution than that of an orthogonal projection type (y(θ)=f×sinθ) which has a high resolution in the central angle of view region (hereinafter referred to as central resolution) among the projection types of general fisheye lenses. If the value of conditional formula (2) falls below the lower limit, the central resolution will be lower than that of an orthogonal projection type fisheye lens having the same maximum imaging height, or the maximum imaging height will be larger, leading to an increase in the size of the optical system, which is not preferable.

[0033] If the upper limit of formula (2) is exceeded, the resolution near the center becomes too high, making it difficult to obtain an angle of view equivalent to that of a fisheye lens, or even if an angle of view equivalent to that of a fisheye lens is obtained, it becomes impossible to maintain good optical performance in the wide angle range, which is undesirable. It is more preferable to set the numerical range of conditional formula (2) as follows:

[0034]

number

[0035] It is even more preferable to set the numerical range of condition (2) as follows:

[0036]

number

[0037] Here, in order to obtain a wide angle of view equivalent to that of a fisheye lens, it is preferable that the maximum half angle of view θmax satisfies the following conditional expression (3): Note that in conditional expression (3), radians are used as the unit of the angle of view.

[0038]

number

[0039] Furthermore, if the following conditional expressions (3)' and (3)" are satisfied, a wide angle of view closer to that of a fisheye lens can be obtained.

[0040]

number

[0041]

number

[0042] The optical system 100A of this embodiment has a characteristic similar to the projection characteristic (y=f×tanθ) of an optical system for normal imaging so as to suppress optical distortion in a low angle of view region in order to prevent a decrease in the central resolution. As can be seen from FIG. 2B, a higher resolution can be obtained in a low angle of view region than on the optical axis (angle of view 0).

[0043] In addition, suppressing optical distortion in the low angle of view area reduces distortion near the center of the captured image, improving the detection accuracy of other vehicles, such as preceding and following vehicles. Furthermore, when the captured image in the low angle of view area is displayed on a monitor instead of a rearview mirror, a natural sense of perspective can be obtained by the naked eye, and electronic distortion correction is not necessary or the amount of correction can be reduced, suppressing deterioration of image quality and providing good visibility.

[0044] In the optical system 100A of this embodiment, the resolution increases as the angle of view increases from the optical axis in the low angle of view region, and decreases as the angle of view increases in the high angle of view region. Therefore, as shown in FIG. 2B, the resolution has a maximum value at a half angle of view θa, which is the boundary between the low angle of view region and the high angle of view region. Conversely, by configuring the optical system 100A so that the resolution has a maximum value at the half angle of view θa, it is possible to realize projection characteristics in which the resolution increases in low angle of view regions and decreases in high angle of view regions as the angle of view increases. It is preferable that the half angle of view θa at which the resolution (differential value dy(θ) / dθ) has a maximum value satisfies the following conditional expression (4).

[0045]

number

[0046] If the value of conditional expression (4) is below the lower limit, the low angle of view range in which high resolution is achieved becomes too narrow, which is not preferable, whereas if the value of conditional expression (4) is above the upper limit, the low angle of view range in which high resolution is achieved becomes too wide, which is not preferable, as it becomes difficult to obtain an angle of view equivalent to that of a fisheye lens, or it becomes difficult to maintain good optical performance in the high angle of view range even if an angle of view equivalent to that of a fisheye lens is obtained. It is more preferable that the numerical range of conditional expression (4) is as follows:

[0047]

number

[0048] It is even more preferable to set the numerical range of condition (4) as follows:

[0049]

number

[0050] Moreover, except on the optical axis (angle of view 0), at a half angle of view θ smaller than the half angle of view θa at which the resolution has a maximum value, the projection characteristic y(θ) of the optical system 100A preferably satisfies the following conditional expression (5).

[0051]

number

[0052] If conditional expression (5) is not satisfied, the resolution in the low angle of view region will decrease, which is not preferable. Here, the optical axis is excluded because, in principle, y(θ) / θ is equal to f on the optical axis regardless of the projection characteristics. In this embodiment, in the angle of view region where the half angle of view is smaller than θa, y(θ) ≒ f × tan θ, so conditional expression (5) is satisfied.

[0053] In order to obtain high resolution in the low angle range and a wide angle of view equivalent to that of a fisheye lens,

[0054]

number

[0055] It is preferable that the half angle of view θb satisfy the following conditional expression (7).

[0056]

number

[0057] The right side of conditional expression (6) is the maximum imaging height y(θmax) divided by the maximum half angle of view θmax, and represents the average resolution. Therefore, the half angle of view θb is the half angle of view at which the actual resolution is equal to the average resolution. By making the half angle of view θb that matches the average resolution approximately half the maximum half angle of view, it is possible to achieve a good balance between the resolution in the low angle of view region and the resolution in the high angle of view region, and to obtain a wide angle of view equivalent to that of a fisheye lens while also obtaining high resolution and good optical performance in the low angle of view region.

[0058] If the value of conditional expression (7) is below the lower limit, the low angle of view region having high resolution becomes too narrow, which is not preferable, and if the value of conditional expression (7) is above the upper limit, it becomes difficult to obtain a wide angle of view equivalent to that of a fisheye lens, or it becomes difficult to maintain good optical performance in the high angle of view region even if the same wide angle of view as that of a fisheye lens is obtained, which is also not preferable.

[0059] It is more preferable that the numerical range of conditional expression (7) be as follows:

[0060]

number

[0061] In the orthogonal projection method, which has a high central resolution among the projection methods of general fisheye lenses, when the maximum half angle of view θmax is π / 2 as in this embodiment, the resolution at the most peripheral angle of view (maximum half angle of view θmax) is 0. However, it is not preferable for the resolution at the most peripheral angle of view to be 0 in an in-vehicle camera used to monitor the periphery of a vehicle. In contrast, the optical system 100A of this embodiment is configured so that the resolution does not become 0 even at the most peripheral angle of view when the maximum half angle of view θmax is π / 2, and a certain level of resolution or higher can be ensured. Specifically, it is preferable that the resolution (differential value dy(θ) / dθ) at the angle of view (most peripheral angle of view) θ corresponding to the maximum half angle of view θmax satisfies the following conditional expression (8).

[0062]

number

[0063] If the value of conditional expression (8) is below the lower limit, the resolution at the most peripheral angle of view becomes too low, which is not preferable, whereas if the value of conditional expression (8) is above the upper limit, the resolution at the most peripheral angle of view becomes too high, and the range of angles of view in which high resolution is achieved becomes too narrow, which is also not preferable. It is more preferable that the numerical range of conditional expression (8) is as follows:

[0064]

number

[0065] It is even more preferable to set the numerical range of condition (8) as follows:

[0066]

number

[0067] In the optical system 100A of this embodiment, in order to realize the projection characteristics as described above, it is preferable that the front group 101A arranged on the magnification / reduction side of the aperture stop ST has a first aspherical lens L1. The first aspherical lens L1 can satisfactorily correct off-axis aberrations such as field curvature. Furthermore, it is preferable that the paraxial refractive power of the first aspherical lens L1 is negative. This makes it easier to correct off-axis aberrations while obtaining a wide angle of view equivalent to that of a fisheye lens.

[0068] In addition, in the optical system 100A of this embodiment, in order to more effectively correct off-axis aberrations, it is preferable to have a second aspherical lens L2 on the reduction conjugate side of the first aspherical lens L1. Furthermore, it is preferable that the paraxial refractive power of the second aspherical lens L2 is positive. This makes it easier to correct off-axis aberrations while increasing the central resolution.

[0069] Moreover, it is preferable that the first aspherical lens L1 and the second aspherical lens L2 are meniscus lenses with their convex surfaces facing the object side, which is advantageous in correcting the curvature of field.

[0070] Figure 3 shows the curvature for each radial position on the aspheric surfaces of lens L1 (surfaces 1 and 2) and lens L2 (surfaces 3 and 4). The points surrounded by dashed circles in each figure indicate the inflection points where the positive and negative curvatures are inverted (since they are radial positions, they are circles centered on the optical axis).

[0071] As described above, the optical system 100A of this embodiment suppresses optical distortion in the low angle of view region and has projection characteristics close to those of an optical system for normal imaging (y=f×tanθ). In this case, it is preferable that at least one aspheric surface in each of the lenses L1 and L2 has an inflection point, since this makes it easier to suppress optical distortion by bringing the projection characteristics in the low angle of view region closer to f×tanθ.

[0072] Furthermore, if at least one of these aspheric surfaces (for example, surfaces 1 and 2) has a plurality of inflection points, this is more preferable since it makes it easier to increase the resolution at the maximum half angle of view θmax.

[0073] It is preferable that the refractive index n1 of the lens L1 with respect to the d-line satisfies the following conditional expression (9).

[0074]

number

[0075] Since lens L1 has a meniscus shape with a convex surface on the magnification conjugate side, if the refractive index of lens L1 is low so as not to satisfy conditional formula (9), this leads to an increase in the amount of sag and the amount of asphericity of the meniscus shape, which increases the difficulty of processing, and is therefore undesirable. It is also undesirable from the viewpoint of miniaturization, such as shortening the optical path length and reducing the diameter of the optical system.

[0076] It is preferable that the refractive index n2 of the lens L2 with respect to the d-line satisfy the following conditional expression (10).

[0077]

number

[0078] As described above, the paraxial refractive power of the lens L1 is negative and the paraxial refractive power of the lens L2 is positive. Therefore, in order to reduce the Petzval sum, it is preferable that the refractive index n2 of the lens L2 is greater than the refractive index n1 of the lens L1.

[0079] Furthermore, in order to obtain an angle of view equivalent to that of a fisheye lens while improving the central resolution, it is preferable that the (paraxial) focal length fa of the front group 101A satisfies the following conditional expression (11).

[0080]

number

[0081] If the value of conditional expression (11) exceeds its upper limit, the central resolution will be lower than that of an orthogonal projection type fisheye lens, or it will be difficult to obtain a wide angle of view equivalent to that of a fisheye lens, or it will be difficult to maintain good optical performance in the wide angle of view range even if the same wide angle of view as that of a fisheye lens is obtained, which is not preferable.

[0082] In addition, it is preferable that the lens L4 closest to the reduction conjugate side in the front group 101A is a lens having a convex surface facing the reduction conjugate side. In an off-axis light beam with a wide angle of view, coma aberration occurs when the light beam is significantly bent by the lens L1, and it is preferable that the lens L4 be such a lens in order to more effectively correct this coma aberration.

[0083] In addition, it is preferable that the refractive power of the lens L8 closest to the reduction conjugate side in the rear group 102A is positive. Since the lens L8 is the lens closest to the reduction conjugate side with a large off-axis ray height, the positive refractive power of the lens L8 can reduce the angle of incidence of the ray with respect to the image plane 300 in the wide angle of view region. As a result, it is possible to easily obtain a wide angle of view equivalent to that of a fisheye lens while having good optical performance and high central resolution.

[0084] In addition, it is preferable to use an aspherical lens for lens L8, since this is effective in correcting off-axis aberrations such as field curvature, etc. However, when using an aspherical lens for lens L8, it is necessary to use an aspherical lens that has positive refractive power even in the peripheral portion in order to maintain the effect of reducing the angle of incidence of light rays with respect to image surface 300 in the wide angle of view region.

[0085] In addition, in the rear group 102A, it is preferable that the lenses L6 and L7 arranged on the enlargement conjugate side of the lens L8 have positive and negative refractive powers, respectively. In order to reduce the overall length of the optical system 100A that forms an object image on the image plane 300 and to make the optical system 100A compact, it is necessary that the focal length of the rear group 102A as a whole is positive. For this reason, the rear group 102A needs a lens with a positive refractive power. However, if the refractive power of all the lenses constituting the rear group 102A is positive, for example, spherical aberrations occurring in all the lenses constituting the rear group 102A are added. In addition, for off-axis aberrations such as coma aberrations, when the refractive power of the lens L8 is positive, it is more effective in correcting off-axis aberrations to arrange a lens with a negative refractive power at a position where the height of the off-axis light ray is large. Therefore, it is preferable that the refractive power of the lens L6 on the enlargement conjugate side is positive, and the refractive power of the lens L7 on the reduction conjugate side is negative.

[0086] In addition, it is preferable to determine the refractive power of the lens L5 according to the sign of the focal length fa of the front group 101A. In this embodiment, since the focal length fa of the front group 101A is positive, the refractive power of the lens L5 is negative. This allows the lens L5 to correct the residual spherical aberration of the front group 101A, making it easier to obtain better optical performance.

[0087] As described above, lens L8 has the effect of reducing the angle of incidence of light rays with respect to image plane 300 in the wide angle of view region. Therefore, when the distance on the optical axis from aperture stop ST to the surface on the reduction conjugate side of lens L8 is D and the total length of optical system 100A (the distance on the optical axis from the surface on the enlargement conjugate side of lens L1 to the surface on the reduction conjugate side of lens L8) is L, it is preferable to satisfy the following conditional expression (12).

[0088]

number

[0089] By satisfying this conditional expression (12), the optical system 100A can be made small in the radial direction while the height of off-axis rays at the lens L8 can be increased, which is preferable. If the value of the conditional expression (12) exceeds the upper limit, the aperture stop ST is located on the enlargement conjugate side, so it is easy to increase the height of off-axis rays at the lens L8, but the diameter of the lens L8 becomes large, which is not preferable. If the value of the conditional expression (12) falls below the lower limit, the aperture stop ST is located on the reduction conjugate side, so it is difficult to increase the height of off-axis rays at the lens L8, and the diameter of the lens L1 becomes large, which is not preferable. It is more preferable that the numerical range of condition (12) is as follows:

[0090]

number

[0091] FIG. 4 shows the longitudinal aberration (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) of the optical system 100A of this embodiment. 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), the two-dot chain line indicates the spherical aberration for the C-line (wavelength 656.3 nm), and the one-dot chain line indicates the spherical aberration for the F-line (486.1 nm). In the astigmatism diagram, the solid line S indicates the sagittal image surface, and the dashed line M indicates the meridional image surface. In the astigmatism diagram, the difference between the sagittal image surface and the meridional image surface is the astigmatism, and each waviness indicates the curvature of field. The distortion is shown for the d-line. The chromatic aberration diagram shows the lateral chromatic aberration for the C-line and the F-line. ω is the half angle of view (°). The horizontal axis of the spherical aberration diagram and the astigmatism diagram is ±0.2 mm, the horizontal axis of the distortion diagram is ±100%, and the horizontal axis of the chromatic aberration diagram is ±0.01 mm. The explanations of these aberration diagrams are the same for the other examples described later.

[0092] 4, in the optical system 100A of this embodiment, spherical aberration, field curvature, astigmatism, and lateral chromatic aberration are well corrected. Meanwhile, distortion is small in the low angle of view region, and increases as the image height increases in the high angle of view region, and has a characteristic close to y=f×tan θ in order to ensure high resolution in the low angle of view region.

[0093] Table 2 shows the parameter values ​​in this embodiment (numerical example) and the values ​​of each of the above-mentioned conditional expressions (except for conditional expression (5)). As can be seen from Table 2, the optical system 100A of this embodiment satisfies all of the conditional expressions. Therefore, the optical system 100A of this embodiment has good optical performance while having a high central resolution and a wide angle of view equivalent to a fisheye lens. EXAMPLES

[0094] The basic configuration of an optical system 100B of the second embodiment shown in FIG. 5 is the same as that of the optical system 100A of the first embodiment, and components corresponding to those of the optical system 100A of the first embodiment are denoted by the same reference numerals.

[0095] The front group 101B is composed of four lenses L1 to L4. The lens L1 is an aspherical lens (first aspherical lens) with aspherical surfaces on both sides and has negative paraxial refractive power. The lens L2 is an aspherical lens (second aspherical lens) with aspherical surfaces on both sides and has positive paraxial refractive power. The lenses L3 and L4 are spherical lenses with negative and positive refractive powers, respectively.

[0096] The rear group 102B is composed of four lenses L5 to L8. The lenses L5, L6, and L7 are spherical lenses, and have positive, positive, and negative refractive powers, respectively. The sign of the refractive power of the lens L5 is different from that of the first embodiment because the sign of the focal length fa of the front group 101A in this embodiment is opposite to that of the first embodiment.

[0097] The lens L8 is an aspherical lens (third aspherical lens) having aspherical surfaces on both sides and has a positive paraxial refractive power. Similarly to the first embodiment, the lens L8 also has a positive refractive power in the peripheral portion.

[0098] Table 3 shows an example of numerical values ​​of the optical system 100B of this embodiment. The optical system 100B of this embodiment is an optical system with a maximum half angle of view θmax of π / 2, which is equivalent to that of a fisheye lens.

[0099] 6A and 6B respectively show the projection characteristics and the resolution characteristics of the optical system 100B of this embodiment. As can be seen from these figures, the optical system 100B of this embodiment is an optical system that has a wide angle of view equivalent to that of a fisheye lens, but has a higher central resolution than a fisheye lens.

[0100] 7 shows the curvature for each radial position of the aspheric surfaces of lens L1 (surfaces 1 and 2) and the aspheric surfaces of lens L2 (surfaces 3 and 4). In this embodiment, surfaces 1, 2, and 3 have inflection points, and surfaces 2 and 3 have two inflection points. Although the surfaces with two inflection points are different from those in embodiment 1, the effect obtained is similar.

[0101] 8 shows the longitudinal aberration of the optical system 100B of this embodiment. As can be seen from this figure, the optical system 100B of this embodiment has excellent correction of spherical aberration, field curvature, astigmatism, and lateral chromatic aberration. On the other hand, the distortion is small in the low angle of view region, and increases as the image height increases in the high angle of view region, and has a characteristic close to y=f×tan θ in order to ensure high resolution in the low angle of view region.

[0102] Table 4 shows the parameter values ​​in this embodiment (numerical example) and the values ​​of the above-mentioned conditional expressions (except for conditional expression (5)). As can be seen from Table 4, the optical system 100B of this embodiment satisfies all of the conditional expressions. Therefore, the optical system 100B of this embodiment has good optical performance while having a high central resolution and a wide angle of view equivalent to a fisheye lens. EXAMPLES

[0103] The optical system 100C of Example 3 shown in FIG. 9 is different from Examples 1 and 2 in that the front group 101C is composed of a cover glass lens GL arranged on the most magnification conjugate side and three lenses L1 to L3. The cover glass lens GL plays the role of a cover glass for protecting the lens L1 and is also a lens with refractive power. Therefore, without the cover glass lens GL, the optical performance of the optical system 100C cannot be guaranteed. However, the cover glass lens GL is designed to be insensitive to positional errors so that it can be easily replaced if it is broken or scratched.

[0104] Lens L1 is an aspherical lens (first aspherical lens) with aspherical surfaces on both sides and has negative paraxial refractive power. Lens L2 is an aspherical lens (second aspherical lens) with aspherical surfaces on both sides and has positive paraxial refractive power. Lens L3 is a spherical lens with negative refractive power.

[0105] The rear group 102C is composed of four lenses L4 to L7. The lenses L4, L5, and L6 are spherical lenses, and have positive, positive, and negative refractive powers, respectively. The lens L7, which is the final lens, is an aspherical lens (third aspherical lens) with aspherical surfaces on both sides, and has positive paraxial refractive power. The lens L7 also has positive refractive power in the peripheral portion, similar to the lens L8 in the first and second embodiments.

[0106] In this embodiment, in order to suppress an increase in the overall length of the optical system 100C due to the provision of the cover glass lens GL, the front group 101C is composed of four lenses including the cover glass lens GL. Also, unlike the first and second embodiments, the lens L3 arranged on the most reduction conjugate side in the front group 101C has a negative refractive power, but has a convex surface on the reduction conjugate side, as in the first and second embodiments, which is preferable for better correction of coma aberration.

[0107] Table 5 shows an example of numerical values ​​of the optical system 100C of this embodiment. The optical system 100C of this embodiment is an optical system with a maximum half angle of view θmax of π / 2, which is equivalent to that of a fisheye lens.

[0108] 10A and 10B respectively show the projection characteristics and the resolution characteristics of the optical system 100C of this embodiment. As can be seen from these figures, the optical system 100C of this embodiment has a wide angle of view equivalent to that of a fisheye lens, but has a higher central resolution than a fisheye lens.

[0109] 11 shows the curvature for each radial position of the aspheric surfaces (surfaces 3 and 4) of lens L1 and the aspheric surfaces (surfaces 5 and 6) of lens L2. In this embodiment, surfaces 3, 4, and 5 have inflection points, and surfaces 4 and 5 have two inflection points. Although the surfaces with two inflection points are different from those in embodiment 1, the effect obtained is similar.

[0110] 12 shows the longitudinal aberration of the optical system 100C of this embodiment. As can be seen from this figure, the optical system 100C of this embodiment has excellent correction of spherical aberration, field curvature, astigmatism, and lateral chromatic aberration. On the other hand, the distortion is small in the low angle of view region, and increases as the image height increases in the high angle of view region, and has a characteristic close to y=f×tan θ in order to ensure high resolution in the low angle of view region.

[0111] Table 6 shows the parameter values ​​in this embodiment (numerical example) and the values ​​of the above-mentioned conditional expressions (except for conditional expression (5)). As can be seen from Table 6, the optical system 100C of this embodiment satisfies all of the conditional expressions. Therefore, the optical system 100C of this embodiment has good optical performance while having a high central resolution and a wide angle of view equivalent to a fisheye lens. EXAMPLES

[0112] An optical system 100D of Example 4 shown in FIG. 13 differs from the other examples in that it does not have a third aspherical lens, and a spherical lens L7 is disposed on the most reduction conjugate side of the rear group 102D.

[0113] The front group 101D is composed of three lenses L1 to L3. The lens L1 is an aspherical lens (first aspherical lens) with aspherical surfaces on both sides and has negative paraxial refractive power. The lens L2 is an aspherical lens (second aspherical lens) with aspherical surfaces on both sides and has positive paraxial refractive power. The lens L3 is a spherical lens with positive refractive power.

[0114] The rear group 102D is composed of four lenses L4 to L7. The lenses L4 to L7 are spherical lenses, and their respective refractive powers are positive, positive, negative and positive. In this embodiment, the front group 101D is composed of three lenses, and the rear group 102D has a spherical lens (last lens) L7 with a positive refractive power instead of the third aspherical lens.

[0115] Since the lens L7 is a spherical lens, it has a positive refractive power even in the peripheral portion. The provision of such a lens L7 is preferable in that it can reduce the angle of incidence of light rays with respect to the image plane 300 in the wide angle of view region and obtain a wide angle of view equivalent to that of a fisheye lens while maintaining a high central resolution.

[0116] Furthermore, the lens L3, which is disposed closest to the reduction conjugate side in the front group 101D, has a convex surface on the reduction conjugate side, which is preferable for better correction of coma aberration, as in the other embodiments.

[0117] Table 7 shows an example of numerical values ​​of the optical system 100D of this embodiment. The optical system 100D of this embodiment is an optical system with a maximum half angle of view θmax of π / 2, which is equivalent to that of a fisheye lens.

[0118] 14A and 14B respectively show the projection characteristics and the resolution characteristics of the optical system 100D of this embodiment. As can be seen from these figures, the optical system 100D of this embodiment has a wide angle of view equivalent to that of a fisheye lens, but has a higher central resolution than a fisheye lens.

[0119] 15 shows the curvature for each radial position of the aspheric surfaces (surfaces 1 and 2) of lens L1 and the aspheric surfaces (surfaces 3 and 4) of lens L2. In this embodiment, surfaces 1, 2, and 3 have inflection points, and surfaces 2 and 3 have two inflection points. Although the surfaces with two inflection points are different from those in embodiment 1, the effect obtained is similar.

[0120] 16 shows the longitudinal aberration of the optical system 100D of this embodiment. As can be seen from this figure, the optical system 100D of this embodiment has excellent correction of spherical aberration, field curvature, astigmatism, and lateral chromatic aberration. On the other hand, the distortion is small in the low angle of view region, and increases as the image height increases in the high angle of view region, and has characteristics close to y=f×tan θ in order to ensure high resolution in the low angle of view region.

[0121] Table 8 shows the parameter values ​​in this embodiment (numerical example) and the values ​​of each of the above-mentioned conditional expressions (except for conditional expression (5)). As can be seen from Table 8, the optical system 100D of this embodiment satisfies all of the conditional expressions. Therefore, the optical system 100D of this embodiment has good optical performance while having a high central resolution and a wide angle of view equivalent to a fisheye lens.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] [Table 4]

[0126] [Table 5]

[0127] [Table 6]

[0128] [Table 7]

[0129] [Table 8]

[0130] 15 shows the configuration of an in-vehicle camera 10 using the optical system of each of the above-mentioned embodiments as an imaging optical system, and an in-vehicle system (driving support device) 600 equipped with the in-vehicle camera 10. The in-vehicle system 600 is held by a movable body (moving device) such as an automobile (vehicle), and is a system for supporting the driving (operation) of the vehicle based on image information of the surroundings of the vehicle acquired by the in-vehicle camera 10.

[0131] Fig. 16 shows a vehicle 700 as a moving device equipped with an on-board system 600. Fig. 16 shows a case where the imaging range 50 of the on-board camera 10 is set in front of the vehicle 700, but the imaging range 50 may be set to the rear or side of the vehicle 700.

[0132] 16, the vehicle-mounted system 600 includes an in-vehicle camera 10, a vehicle information acquisition device 20, a control device (control unit, ECU: electronic control unit) 30, and a warning device (warning unit) 40. The vehicle-mounted camera 10 also includes an imaging unit 1, an image processing unit 2, a parallax calculation unit 3, a distance acquisition unit (acquisition unit) 4, and a collision determination unit 5. The image processing unit 2, the parallax calculation unit 3, the distance acquisition unit 4, and the collision determination unit 5 constitute a processing unit. The imaging unit 1 includes the optical system and the image sensor of each of the above-mentioned embodiments.

[0133] 17 shows an example of the operation of the in-vehicle system 600. In step S1, the imaging unit 1 captures images of objects (subjects) such as obstacles and pedestrians around the vehicle, and acquires a plurality of image data (parallax image data).

[0134] In step S2, vehicle information is acquired by the vehicle information acquisition device 20. The vehicle information includes the vehicle speed, yaw rate, steering angle, and the like.

[0135] In step S3, the image processing unit 2 performs image processing on the multiple image data acquired by the imaging unit 1. Specifically, image feature analysis is performed to analyze feature quantities such as the amount and direction of edges in the image data, and density values. Here, the image feature analysis may be performed on each of the multiple image data, or may be performed on only some of the multiple image data.

[0136] In step S4, disparity (image shift) information between the multiple image data acquired by the imaging unit 1 is calculated by the disparity calculation unit 3. As a method for calculating disparity information, a known method such as the SSDA method or the area correlation method can be used, and therefore a description thereof will be omitted here. Note that steps S2, S3, and S4 may be performed in the above order, or may be processed in parallel with each other.

[0137] In step S5, distance acquisition unit 4 acquires (calculates) distance information about the object captured by imaging unit 1. The distance information can be calculated based on the parallax information calculated by parallax calculation unit 3 and the internal and external parameters of imaging unit 1. Note that the distance information here refers to information about the relative position of the object, such as the distance from the object, the defocus amount, and the image shift amount, and may directly represent the distance value of the object in the image or indirectly represent information corresponding to the distance value.

[0138] Then, in step S6, the collision determination unit 5 uses the vehicle information acquired by the vehicle information acquisition device 20 and the distance information calculated by the distance acquisition unit 4 to determine whether the distance to the object is within a preset distance range. This makes it possible to determine whether an object exists within a set distance around the vehicle and to determine the possibility of a collision between the vehicle and the object. If an object exists within the set distance, the collision determination unit 5 determines that there is a "possibility of collision" (step S7), and if there is no object within the set distance, it determines that there is no "possibility of collision" (step S8).

[0139] Next, when the collision determination unit 5 determines that there is a "possibility of collision," it notifies (transmits) the determination result to the control device 30 and the warning device 40. At this time, the control device 30 controls the vehicle based on the determination result by the collision determination unit 5 (step S6), and the warning device 40 issues a warning to the vehicle user (driver, passengers) based on the determination result by the collision determination unit 5 (step S7). Note that the notification of the determination result may be sent to at least one of the control device 30 and the warning device 40.

[0140] The control device 30 can control the movement of the vehicle by outputting control signals to the driving parts (engine, motor, etc.) of the vehicle. For example, the control device 30 performs control such as applying the brakes on the vehicle, releasing the accelerator, turning the steering wheel, and generating control signals to generate braking forces on each wheel to suppress the output of the engine or motor. The warning device 40 also warns the user by, for example, issuing a warning sound (alarm), displaying warning information on the screen of a car navigation system, or applying vibrations to the seat belt or steering wheel.

[0141] According to the above-described in-vehicle system 600, the above-described processing can effectively detect an object, and it becomes possible to avoid a collision between the vehicle and the object. In particular, by applying the optical system of each of the above-described embodiments to the in-vehicle system 600, it becomes possible to detect an object and make a collision judgment over a wide angle of view while miniaturizing the entire in-vehicle camera 10 and increasing the degree of freedom of arrangement.

[0142] Note that, although various methods can be used for calculating the distance information, an example will be described in which a split-pupil type imaging element having a plurality of pixel units regularly arranged in a two-dimensional array is used as the imaging element of the imaging unit 1. In a split-pupil type imaging element, one pixel unit is composed of a microlens and a plurality of photoelectric conversion units, and can receive a pair of light beams passing through different regions in the pupil of the optical system and output a pair of image data from each photoelectric conversion unit.

[0143] Then, the image shift amount of each region is calculated by a correlation calculation between paired image data, and image shift map data representing the distribution of the image shift amount is calculated by the distance acquisition unit 4. Alternatively, the distance acquisition unit 4 may further convert the image shift amount into a defocus amount to generate defocus map data representing the distribution of the defocus amount (distribution on a two-dimensional plane of the captured image). The distance acquisition unit 4 may also acquire distance map data of the distance to the object converted from the defocus amount.

[0144] Furthermore, the in-vehicle system 600 and the moving device 700 may be provided with a notification device (notification unit) for notifying the manufacturer of the in-vehicle system or the dealer of the moving device, etc., of the collision of the moving device 700 with an obstacle. For example, the notification device may be one that transmits information (collision information) related to the collision between the moving device 700 and an obstacle to a preset external notification destination by e-mail or the like.

[0145] In this way, by adopting a configuration in which the notification device automatically notifies collision information, it is possible to promptly take measures such as inspection and repair after a collision occurs. The destination of the collision information may be an insurance company, a medical institution, the police, or any other party set by the user. The notification device may be configured to notify the destination of not only collision information but also failure information of each part and consumption information of consumables. The detection of the presence or absence of a collision may be performed using distance information acquired based on the output from the above-mentioned photoelectric conversion unit, or may be performed by another detection unit (sensor).

[0146] Although the application of the in-vehicle system 600 to driving assistance (collision damage reduction) has been described, the in-vehicle system 600 may be applied to cruise control (including full-speed following function) and automatic driving. The in-vehicle system 600 is not limited to vehicles such as automobiles, but may be applied to moving bodies such as ships, aircraft, and industrial robots. The in-vehicle system 600 is not limited to moving bodies, but may be applied to various devices that utilize object recognition such as an intelligent transport system (ITS). (Other Examples) The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0147] 100A~D optical system 101A~D front group 102A~D rear group 300 image plane ST aperture stop

Claims

1. An optical system having a plurality of lenses and an aperture stop, When the projection characteristic of the optical system, which indicates the relationship between the half angle of view θ and the image height y on the image plane, is y(θ), the maximum half angle of view of the optical system is θmax, and the focal length of the optical system is f, [0010] Satisfying the conditions, an optical system in which a differential value dy(θ) / dθ of the projection characteristic y(θ) at a half angle of view θ has a maximum value.

2. When the half angle of view at which the differential value dy(θ) / dθ becomes the maximum value is θa, [0025] 2. The optical system according to claim 1, which satisfies the following condition:

3. At a half angle of view θ that is smaller than a half angle of view θa at which the differential value dy(θ) / dθ becomes the maximum value and is larger than 0, [0030] 3. The optical system according to claim 1, wherein the following condition is satisfied: 【Request 4】 【Number 4】 When the half angle of view that satisfies the above is θb, [0050] 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. At the maximum half angle of view θmax, [006] 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. 6. The optical system according to claim 1, wherein the plurality of lenses includes a first aspheric lens disposed on the magnification conjugate side of the aperture stop.

7. 7. The optical system according to claim 6, wherein the sign of the paraxial refractive power of the first aspheric lens is negative.

8. 8. The optical system according to claim 6, wherein the first aspheric lens is a meniscus lens having a convex surface facing the magnification conjugate side.

9. The refractive index of the first aspherical lens with respect to the d line is n １ When [0070] 9. The optical system according to claim 6, wherein the following condition is satisfied:

10. 10. The optical system according to claim 6, wherein the plurality of lenses includes a second aspherical lens disposed on a reduction conjugate side of the first aspherical lens.

11. 11. The optical system according to claim 10, wherein the sign of the paraxial refractive power of the second aspheric lens is positive.

12. 12. The optical system according to claim 10, wherein the second aspheric lens is a meniscus lens having a convex surface facing the magnification conjugate side.

13. The refractive index of the first aspherical lens with respect to the d line is n １ The refractive index of the second aspheric lens with respect to the d line is n ２ When [0080] 13. The optical system according to claim 10, wherein the following condition is satisfied:

14. The optical system of claim 10 , wherein the first and second aspheric lenses each include an aspheric surface having an inflection point.

15. The optical system according to claim 14 , wherein the aspheric surface of at least one of the first and second aspheric lenses has a plurality of inflection points.

16. When the composite focal length of the lens disposed on the magnification conjugate side of the aperture stop is fa, [0097] 16. The optical system according to claim 1, wherein the following condition is satisfied:

17. 17. The optical system according to claim 1, wherein the lens closest to the reduction conjugate side among the plurality of lenses has a paraxial refractive power and a refractive power in a peripheral portion both of which have positive signs.

18. Let D be the distance on the optical axis from the aperture stop to the lens surface closest to the reduction conjugate side, and L be the distance on the optical axis from the lens surface closest to the enlargement conjugate side to the lens surface closest to the reduction conjugate side. [0089] 18. The optical system according to claim 1, wherein the following condition is satisfied: 【Request 19】 【Number 11】 19. The optical system according to claim 1, wherein the following condition is satisfied:

20. An optical system according to any one of claims 1 to 19; and an imaging element for imaging an object via the optical system.

21. An imaging device according to claim 20; and a determination unit that determines a possibility of a collision between the vehicle and the object based on distance information of the object acquired by the imaging device.

22. 22. The in-vehicle system according to claim 21, further comprising a control device that outputs a control signal to generate a braking force in a drive section of the vehicle when it is determined that there is a possibility of a collision between the vehicle and the object.

23. 23. The in-vehicle system according to claim 21, further comprising a warning device that issues a warning to a user of the vehicle when it is determined that there is a possibility of a collision between the vehicle and the object.

24. 24. The in-vehicle system according to claim 21, further comprising a notification device that notifies an outside party of information regarding a collision between the vehicle and the object.

25. A moving device comprising the imaging device according to claim 20, capable of holding and moving the imaging device.

26. 26. The moving device according to claim 25, further comprising a determination unit that determines a possibility of a collision with the object based on distance information of the object obtained by the imaging device.

27. 27. The moving device according to claim 26, further comprising a control unit that outputs a control signal for controlling movement when it is determined that there is a possibility of a collision with the object.

28. 27. The mobile device according to claim 25, further comprising a warning unit that issues a warning to a user of the mobile device when it is determined that there is a possibility of a collision with the object.

29. 29. The mobile device according to claim 25, further comprising a notification unit that notifies an outside source of information regarding the collision with the object.

Images