Imaging lens system, camera module, vehicle-mounted system, and mobile object

Abstract

Provided are an imaging lens system that can achieve high resolution and a compact size, a camera module, a vehicle-mounted system, and a mobile object. This imaging lens system comprises, in order from the object side to the image side: a first lens (L1) that has negative power and has an image-side surface having a concave surface facing the image side; a second lens (L2) that has negative power, has an object-side surface being an aspherical shape having an infection point with a central portion having a concave surface facing the object side and a peripheral portion having a convex surface facing the object side, and has an image-side surface having a concave surface facing the image side; a third lens (L3) that has positive power, and has an image-side surface having a convex surface facing the image side; an aperture STOP; a fourth lens (L4) that has positive power, and has an object-side surface having a convex surface facing the object side; and a fifth lens (L5) and a sixth lens (L6) that constitute a cemented lens, one having negative power and the other having positive power.

Description

Imaging lens system, camera module, vehicle-mounted system, mobile body

[0001] The present invention relates to an imaging lens system, a camera module, a vehicle-mounted system, and a mobile body.

[0002] In recent years, vehicle-mounted cameras have been required to have a sensing function for detecting people and objects, and the resolution of image sensors has been increasing and they are becoming larger. Along with this, the imaging lens systems mounted on vehicle-mounted cameras and the like also tend to become larger. On the other hand, due to the requirement for omnidirectional sensing around the vehicle, vehicle-mounted cameras are increasingly being mounted at spatially restricted positions such as side mirrors. Therefore, miniaturization of vehicle-mounted cameras is being demanded. Also, in order to realize the sensing function, high imaging performance of the imaging lens system is required. Patent Document 1 describes an imaging lens system composed of six lenses mounted on a vehicle-mounted camera or the like.

[0003] Japanese Patent Application Laid-Open No. 2016-057562

[0004] In the imaging lens system described in Patent Document 1, since the power of the fifth lens is large, large chromatic aberration occurs and the imaging performance is not sufficient. Therefore, it is difficult to achieve high resolution. Also, in the imaging lens system described in Patent Document 1, the ratio of the overall optical length to the focal length is relatively large, and the aperture (effective diameter) of the first lens is also about three times the diagonal length of the image sensor. Therefore, the imaging lens system described in Patent Document 1 is a relatively large optical system and it is difficult to meet the requirement for miniaturization of vehicle-mounted cameras.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide an imaging lens system, a camera module, a vehicle-mounted system, and a mobile body that can achieve high resolution and are miniaturized.

[0006] One embodiment of the imaging lens system comprises, in order from the object side toward the image side, a first lens having negative power with its image side surface facing concave toward the image side; a second lens having an aspherical shape with an inflection point on its object side, with a concave surface facing toward the object side in the center and a convex surface facing toward the object side in the periphery, and having negative power with its image side surface facing concave toward the image side; a third lens having positive power with its image side surface facing convex toward the image side; an aperture; a fourth lens having positive power with its object side surface facing convex toward the object side; and a fifth and sixth lens forming a cemented lens, one of which has negative power and the other has positive power.

[0007] According to the present invention, it is possible to achieve high resolution and provide a miniaturized imaging lens system, camera module, in-vehicle system, and mobile device.

[0008] This is a cross-sectional view showing the configuration of the camera module and imaging lens system according to Example 1. This is a spherical aberration diagram (longitudinal aberration diagram) of the imaging lens system of Example 1. This is an image field curvature diagram of the imaging lens system of Example 1. This is a distortion aberration diagram of the imaging lens system of Example 1. This is a magnification chromatic aberration diagram of the imaging lens system of Example 1. This is a cross-sectional view showing the configuration of the camera module and imaging lens system according to Example 2. This is a spherical aberration diagram (longitudinal aberration diagram) of the imaging lens system of Example 2. This is an image field curvature diagram of the imaging lens system of Example 2. This is a distortion aberration diagram of the imaging lens system of Example 2. This is a magnification chromatic aberration diagram of the imaging lens system of Example 2. This is a cross-sectional view showing the configuration of the camera module and imaging lens system according to Example 3. This is a spherical aberration diagram (longitudinal aberration diagram) of the imaging lens system of Example 3. This is an image field curvature diagram of the imaging lens system of Example 3. This is a distortion aberration diagram of the imaging lens system of Example 3. This is a magnification chromatic aberration diagram of the imaging lens system of Example 3. This is a cross-sectional view showing the configuration of the camera module and imaging lens system according to Example 4. This is a spherical aberration diagram (longitudinal aberration diagram) of the imaging lens system of Example 4. This is an image field curvature diagram of the imaging lens system of Example 4. This is a distortion aberration diagram of the imaging lens system of Example 4. This is a magnification chromatic aberration diagram of the imaging lens system of Example 4. This is a cross-sectional view showing the configuration of the camera module and imaging lens system according to Example 5. This is a spherical aberration diagram (longitudinal aberration diagram) of the imaging lens system of Example 5. This is an image field curvature diagram of the imaging lens system of Example 5. This is a distortion aberration diagram of the imaging lens system of Example 5. This is a magnification chromatic aberration diagram of the imaging lens system of Example 5. This is a schematic diagram of a vehicle equipped with an in-vehicle system comprising a camera module according to one embodiment of the present invention. This is a block diagram showing the configuration of the imaging device constituting the in-vehicle system of Figure 11.

[0009] The embodiments of the present invention will be described below with reference to the drawings. These embodiments can realize highly reliable systems, particularly in sensing systems, and contribute to the development of resilient infrastructure. They target "9. Build resilient infrastructure, including local and transboundary infrastructure, to support economic development and human well-being, with a focus on affordable and equitable access for all," which is part of the United Nations Sustainable Development Goals (SDGs). Furthermore, these embodiments can reduce the volume of glass material used in the first lens and correct aberrations caused by reducing the aperture of the first lens without increasing the number of lenses constituting the imaging lens system. These embodiments target "12. Ensure sustainable consumption and production patterns," specifically "12.8 By 2030, ensure that people everywhere have the information and awareness necessary to understand sustainable development and livelihoods in harmony with nature." (Embodiment 1: Imaging Lens System) The imaging lens system according to Embodiment 1 comprises, in order from the object side toward the image side, a first lens having negative power with its image side surface facing concave toward the image side; a second lens having an aspherical shape with an inflection point on its object side, with a concave surface facing toward the object side in the center and a convex surface facing toward the object side in the periphery, and having negative power with its image side surface facing concave toward the image side; a third lens having positive power with its image side surface facing convex toward the image side; an aperture; a fourth lens having positive power with its object side surface facing convex toward the object side; and a fifth and sixth lens forming a cemented lens, one of which has negative power and the other has positive power.

[0010] This makes it possible to achieve high resolution and provide a miniaturized imaging lens system. Specifically, by having the object side surface of the second lens have the shape described above, the negative power of the second lens can be made to weaken from the center towards the periphery. Reducing the aperture of the first lens has the disadvantage that it becomes difficult to adjust the relationship between the angle of view and the image height of the image formed on the image sensor (hereinafter referred to as "angle of view characteristics"), but the above-described features of the object side surface of the second lens make it possible to control the angle of view characteristics. Specifically, within the effective circular image of the imaging lens system, the rate of change in image height can be gradually reduced as the angle of view increases. Here, "within the effective circular image" means "within the range of the circular image formed on the image plane". This makes it possible to deliberately compress the image at the periphery on the image plane of the image sensor, and the effect of aberrations that occur towards the periphery can be reduced. Specifically, the effect of image displacement such as coma aberration that occurs towards the periphery can be reduced by compressing the image when forming it. Furthermore, it becomes possible to suppress the decrease in peripheral light intensity, which is a problem in wide-angle imaging lens systems. Therefore, it is possible to achieve high resolution and provide an imaging lens system that is also miniaturized.

[0011] Furthermore, when the focal length of the first lens is defined as f1, the focal length of the fourth lens as f4, the Abbe number of the d line of the fourth lens as νd4, the focal length of the third lens as f3, and the focal length of the entire optical system as f, the following conditions (1) to (4) are satisfied: -5.0 < f1 / f < -3.0 ... (1) 2.7 < f4 / f < 3.1 ... (2) νd4 > 60 ... (3) 6.0 < f3 / f < 10.0 ... (4)

[0012] By making the power of the first lens relatively strong enough to satisfy condition (1), it is possible to reduce the aperture of the first lens and thus miniaturize the optical system. More specifically, if the value of f1 / f is greater than -3.0, the focal length of the first lens is too long relative to the focal length of the entire optical system; in other words, the power of the first lens is too weak, the aperture of the first lens becomes large, and it is not possible to reliably miniaturize the imaging lens system. On the other hand, if the value of f1 / f is less than -5.0, the focal length of the first lens is too short relative to the focal length of the entire optical system; in other words, the power of the first lens is too strong, and although it is possible to reduce the aperture of the first lens, the chromatic aberration generated in the first lens becomes too large, and the imaging performance of the imaging lens system deteriorates. The value of f1 / f is more preferably -3.15 or greater and -3.70 or less. Furthermore, by making the power of the fourth lens satisfy condition (2), higher resolution can be achieved more reliably. Specifically, if the value of f4 / f is greater than 3.1, the focal length of the fourth lens is too long relative to the overall focal length of the optical system; in other words, the power of the fourth lens is too weak, the overall length of the optical system becomes long, and it becomes impossible to reliably miniaturize the imaging lens system. On the other hand, if the value of f4 / f is less than 2.7, the focal length of the fourth lens is too short relative to the overall focal length of the optical system; in other words, the power of the fourth lens is too strong, the overall length of the optical system becomes short, the error sensitivity of the imaging performance increases, and manufacturing errors are more likely to occur. The value of f4 / f is more preferably 2.75 or greater and 2.95 or less. Furthermore, by satisfying condition (3) with the Abbe number νd4 of the fourth lens, chromatic aberration occurring in the first lens can be corrected, and high resolution can be achieved. Specifically, if the Abbe number νd4 of the fourth lens is less than 60, chromatic aberration occurring in the first lens cannot be sufficiently corrected. The Abbe number νd4 of the fourth lens is more preferably greater than 63, and even more preferably greater than 68. Furthermore, by satisfying condition (4) with respect to the power of the third lens, the distance from the entrance pupil to the aperture (the distance along the optical axis from the side of the object of the first lens to the aperture) can be shortened, and the optical system can be miniaturized.Specifically, if the f3 / f value is greater than 10.0, the focal length of the third lens is too long relative to the overall focal length of the optical system; in other words, the power of the third lens is too weak, the gap between the first lens and the aperture widens, requiring a larger aperture for the first lens, and preventing miniaturization of the imaging lens system. On the other hand, if the f3 / f value is less than 6.0, the focal length of the third lens is too short relative to the overall focal length of the optical system; in other words, the power of the third lens is too strong, the gap between the first lens and the aperture narrows, allowing for a smaller aperture for the first lens, but the chromatic aberration occurring in the first lens becomes too large, degrading the imaging performance of the imaging lens system. The f3 / f value is more preferably 6.5 or higher and 9.5 or lower, and even more preferably 8.0 or higher and 9.0 or lower.

[0013] Furthermore, the imaging lens system preferably satisfies the following condition (5), where TTL is defined as the distance along the optical axis from the object side of the first lens to the image plane of the image sensor, and f is defined as the focal length of the entire optical system: 9 < TTL / f < 11 ... (5) By satisfying the above condition (5), the imaging lens system can be reliably miniaturized. Specifically, if the value of TTL / f is greater than 11, the imaging lens system cannot be reliably miniaturized. On the other hand, if the value of TTL / f is less than 9, each lens needs to be miniaturized, which increases the difficulty of manufacturing, worsens the manufacturing yield, and increases the cost of parts. The value of TTL / f is more preferably 9.3 or more and 10.5 or less, and even more preferably 9.5 or more and 10.0 or less.

[0014] Furthermore, the imaging lens system preferably satisfies the following condition (6) when the focal length of the fifth lens is defined as f5 and the focal length of the entire optical system as f: 10.0 < |f5 / f| < 30.0 ... (6) By satisfying the above condition (6), axial chromatic aberration that occurs when using glass material that satisfies conditions (2) and (3) for the fourth lens can be suitably corrected. Specifically, if the value of |f5 / f| is greater than 30.0, the power of the fifth lens is too weak, and axial chromatic aberration cannot be sufficiently corrected, resulting in a deterioration of the resolution performance of the imaging lens system. On the other hand, if the value of |f5 / f| is less than 10.0, the power of the fifth lens is too strong, resulting in excessive correction of axial chromatic aberration, and a deterioration of the resolution performance of the imaging lens system. The value of |f5 / f| is more preferably 13.0 or more and 28.5 or less, and even more preferably 14.5 or more and 22.0 or less.

[0015] Furthermore, when the d-line refractive index of the first lens is defined as nd1, it is preferable that the following condition (7) is satisfied: nd1 > 1.8 ... (7) By satisfying the above condition (7), the aperture of the first lens can be reduced. Specifically, if the value of nd1 is less than 1.8, the power of the first lens is too weak, and it is not possible to reduce the aperture of the first lens. The value of nd1 is more preferably 1.83 or higher, and even more preferably 1.84 or higher.

[0016] Furthermore, it is preferable that the first and fourth lenses are glass lenses, and the second, third, fifth, and sixth lenses are plastic lenses. By using a glass lens for the first lens, an imaging lens system with excellent weather resistance can be provided. Also, by using a glass lens for the fourth lens, an imaging lens system with reduced focus shift due to changes in ambient temperature can be provided. Specifically, by using a glass lens for the fourth lens, a glass material with a relative refractive index temperature coefficient dnd4 / dT for the d line of less than 0 can be selected as the glass material for the fourth lens. As a result, the amount of focus shift due to temperature changes of the fourth lens itself can offset the change in distance (amount of focus shift) from the lens surface on the object side of the first lens to the image plane of the image sensor caused by expansion and contraction of the lens barrel in the optical axis direction due to changes in ambient temperature. In particular, in imaging lens systems for automotive use, when the lens barrel expands in the optical axis direction at high temperatures, the image plane of the image sensor moves away from the imaging lens system. However, when the fourth lens becomes hot, the focal point of the fourth lens shifts toward the image side, thereby maintaining the imaging performance of the imaging lens system. On the other hand, manufacturing costs can be reduced by using plastic lenses for the second, third, fifth, and sixth lenses.

[0017] (Embodiment 2: Camera Module) The camera module according to Embodiment 2 comprises the above-described imaging lens system and an image sensor positioned at the focal point of the imaging lens system, which converts the light collected through the imaging lens system into an electrical signal. This makes it possible to achieve high resolution and provide a miniaturized camera module.

[0018] Next, embodiments corresponding to the imaging lens system according to Embodiment 1 and the camera module according to Embodiment 2 will be described with reference to the drawings. (Embodiment 1) Figure 1 is a cross-sectional view showing the configuration of the camera module 10 of Embodiment 1. Specifically, the camera module 10 comprises an imaging lens system 11 and an image sensor 12. The imaging lens system 11 and the image sensor 12 are housed in a housing (not shown).

[0019] The image sensor 12 is an element that converts received light into an electrical signal, and for example, a CCD image sensor or a CMOS image sensor is used. The image sensor 12 is positioned at the imaging position (focal position) of the imaging lens system 11.

[0020] The imaging lens system 11 according to Embodiment 1 comprises, in order from the object side to the image side, a front group Gf consisting of a first lens L1, a second lens L2, and a third lens L3, an aperture diaphragm (STOP), and a rear group Gr consisting of a fourth lens L4, a fifth lens L5, and a sixth lens L6. The imaging plane of the imaging lens system 11 is indicated by IMG. The first lens L1 and the fourth lens L4 are glass lenses. The second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6 are plastic lenses. An optical filter (infrared cut filter, visible / infrared bandpass filter, etc.) is placed between the imaging lens system 11 and the image sensor 12 as needed. In this specification, an example in which an infrared cut filter (IRCF) is placed between the imaging lens system 11 and the image sensor 12 will be described.

[0021] The first lens L1 is a glass lens with negative power. The object side S1 of the first lens L1 has a spherical shape with a convex surface facing the object. The image side S2 of the first lens L1 has a spherical shape with a concave surface facing the image.

[0022] The second lens L2 is a plastic lens with negative power. The object side surface S3 of the second lens L2 has an aspherical shape with an inflection point. Specifically, the object side surface S3 of the second lens L2 has a concave surface facing the object in the central part and a convex surface facing the object in the peripheral part. In addition, the image side surface S4 of the second lens L2 has an aspherical shape with a concave surface facing the image.

[0023] The third lens L3 is a plastic lens with positive power. The object side S5 of the third lens L3 has an aspherical shape with a concave surface facing the object. The image side S6 of the third lens L3 has an aspherical shape with a convex surface facing the image.

[0024] The aperture stop is the aperture that determines the F-number (F-number, Fno) of the lens system. The aperture stop is located between the third lens L3 and the fourth lens L4.

[0025] The fourth lens L4 is a glass lens with positive power. The object side S9 of the fourth lens L4 has a spherical shape with a convex surface facing the object. The image side S10 of the fourth lens L4 also has a spherical shape with a convex surface facing the image.

[0026] The fifth lens L5 is a plastic lens with negative power. The object side S11 of the fifth lens L5 has an aspherical shape with a convex surface facing the object. The image side S12 of the fifth lens L5 has an aspherical shape with a concave surface facing the image.

[0027] The sixth lens L6 is a plastic lens with positive power. The object side S13 of the sixth lens L6 has an aspherical shape with a convex surface facing the object. The image side S14 of the sixth lens L6 also has an aspherical shape with a convex surface facing the image.

[0028] The fifth lens L5 and the sixth lens L6 constitute a cemented lens. That is, the image side S12 of the fifth lens L5 and the object side S13 of the sixth lens L6 are in contact. The fifth lens L5 and the sixth lens L6 are joined by an adhesive layer with an axial thickness of 0.020 mm.

[0029] An infrared cut filter (IRCF) is a filter used to cut out light in the infrared region. When designing the imaging lens system 11, the infrared cut filter is treated as an integral part of the imaging lens system 11. However, the infrared cut filter is not an essential component of the imaging lens system 11. The infrared cut filter is located on the image side of the sixth lens L6. In addition, a sensor cover glass may be placed between the infrared cut filter and the image sensor 12 to prevent dust from adhering to the image sensor 12.

[0030] Table 1 shows the lens data for each lens surface in the imaging lens system 11 of Example 1. In Table 1, the lens data for each surface includes the radius of curvature (mm), interplanar spacing (mm) at the central optical axis, effective diameter (mm), refractive index nd for the d line, and Abbe number νd for the d line. In Table 1, surfaces marked with an asterisk (*) indicate that they are aspherical surfaces.

[0031]

[0032] The aspherical shape used on the lens surface is determined by using α, where z is the sag amount, c is the reciprocal of the radius of curvature, k is the conicity coefficient, and r is the height from the optical axis OA, with 4th, 6th, 8th, 10th, 12th, 14th, and 16th order aspherical coefficients respectively. ４ , α ６ , α ８ , α １０ , α １２ , α １４ , α １６ When this is the case, it can be expressed by the following equation.

[0033] Table 2 shows the aspheric coefficients for defining the aspheric shape of the aspheric lens surface in the imaging lens system 11 of Example 1. Note that in Table 2, for example, "-2.843E-03" is equivalent to "-2.843×10 －３ This means "[...]." The numerical representation is the same for the following table.

[0034]

[0035] Next, aberrations will be described with reference to the drawings. FIGS. 2A to 2D show spherical aberration diagrams (longitudinal aberration diagrams), field curvature diagrams, distortion aberration diagrams, and chromatic aberration of magnification diagrams in the imaging lens system 11 of Example 1. As shown in FIGS. 2A to 2D, in the imaging lens system 11 of Example 1, the F number is 2.0 and the semi-field angle is 103°. Also, in the longitudinal aberration diagram of FIG. 2A, the horizontal axis indicates the position where the light ray intersects the optical axis OA, and the vertical axis indicates the passing height of the light ray on the entrance pupil. Further, FIG. 2A shows the simulation results for the d-line, C-line, and F-line. Also, in the field curvature diagram of FIG. 2B, the horizontal axis indicates the distance in the direction of the optical axis OA, and the vertical axis indicates the image height (field angle). Also, in the field curvature diagram of FIG. 2B, Sag indicates the imaging position in the sagittal ray bundle, and Tan indicates the imaging position in the tangential ray bundle. Further, FIG. 2B shows the simulation result for the d-line. Also, in the distortion aberration diagram of FIG. 2C, the horizontal axis indicates the distortion aberration (%) of the image, and the vertical axis indicates the image height (field angle). Further, FIG. 2C shows the simulation result for the d-line light ray. Also, in the chromatic aberration of magnification diagram of FIG. 2D, the horizontal axis indicates the amount of chromatic aberration of magnification, and the vertical axis indicates the image height (field angle). Further, FIG. 2D shows the simulation results for the d-line, C-line, and F-line.

[0036] (Example 2) FIG. 3 is a cross-sectional view showing the camera module 10 according to Example 2. Since the imaging lens system 11 according to Example 2 has the same lens configuration as that of Example 1, its description will be omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 2 will be described.

[0037] Table 3 shows the lens data of each lens surface of the imaging lens system 11 according to Example 2. Since the items shown in Table 3 are the same as those in Table 1, their description will be omitted.

[0038]

[0039] Table 4 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 2. In Table 4, the aspherical shape adopted for the lens surface is represented by the same formula as that in Example 1.

[0040]

[0041] FIGS. 4A to D show spherical aberration diagrams (vertical aberration diagrams), field curvature diagrams, distortion aberration diagrams, and chromatic aberration of magnification diagrams in the imaging lens system 11 of Example 2. Since the explanations for each aberration diagram shown in FIGS. 4A to D are the same as those in FIGS. 2A to D, the explanations are omitted.

[0042] (Example 3) FIG. 5 is a cross-sectional view showing the camera module 10 according to Example 3. Since the imaging lens system 11 according to Example 3 has the same lens configuration as that of Example 1, the explanation thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 3 will be described.

[0043] Table 5 shows the lens data of each lens surface of the imaging lens system 11 according to Example 3. Since the items shown in Table 5 are the same as those in Table 1, the explanation thereof is omitted.

[0044]

[0045] Table 6 shows the aspherical coefficients for defining the aspherical shape of the lens surface that is an aspherical surface in the imaging lens system 11 of Example 3. In Table 6, the aspherical shape adopted for the lens surface is represented by the same formula as that in Example 1.

[0046]

[0047] FIGS. 6A to D show spherical aberration diagrams (vertical aberration diagrams), field curvature diagrams, distortion aberration diagrams, and chromatic aberration of magnification diagrams in the imaging lens system 11 of Example 3. Since the explanations for each aberration diagram shown in FIGS. 6A to D are the same as those in FIGS. 2A to D, the explanations are omitted. (Example 4) FIG. 7 is a cross-sectional view showing the camera module 10 according to Example 4. Since the imaging lens system 11 according to Example 4 has the same lens configuration as that of Example 1, the explanation thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 4 will be described.

[0048] Table 7 shows the lens data of each lens surface of the imaging lens system 11 according to Example 4. Since the items shown in Table 7 are the same as those in Table 1, the explanation thereof is omitted.

[0049]

[0050] Table 8 shows the aspheric coefficients used to define the aspherical shape of the lens surface in the imaging lens system 11 of Example 4. In Table 8, the aspherical shape adopted for the lens surface is expressed by the same formula as in Example 1.

[0051]

[0052] Figures 8A to 8D show the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, distortion diagram, and chromatic aberration diagram of the imaging lens system 11 of Example 4. The explanation of each aberration diagram shown in Figures 8A to 8D is the same as that of Figures 2A to 2D, so the explanation is omitted. (Example 5) Figure 9 is a cross-sectional view showing the camera module 10 according to Example 5. The imaging lens system 11 according to Example 5 differs from Example 1 in that the object side surface S3 of the second lens L2 has a convex shape toward the object. The other configurations of the imaging lens system 11 according to Example 5 have the same lens configuration as Example 1, so the explanation is omitted. The characteristic data of the imaging lens system 11 according to Example 5 will be described below.

[0053] Table 9 shows the lens data for each lens surface of the imaging lens system 11 according to Example 5. The items shown in Table 9 are the same as those in Table 1, so their explanation is omitted.

[0054]

[0055] Table 10 shows the aspheric coefficients for defining the aspheric shape of the lens surface in the imaging lens system 11 of Example 5. In Table 10, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1.

[0056]

[0057] Figures 10A to 10D show the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, distortion diagram, and chromatic aberration diagram for the imaging lens system 11 of Example 5. The explanation of each aberration diagram shown in Figures 10A to 10D is the same as that for Figures 2A to 10D, so the explanation is omitted.

[0058] Table 11 shows the optical total length TTL of the imaging lens system 11, the focal length f of the entire optical system of the imaging lens system 11, the focal length f1 of the first lens L1, the focal length f2 of the second lens L2, the focal length f3 of the third lens L3, the focal length f4 of the fourth lens L4, the focal length f5 of the fifth lens L5, the focal length f6 of the sixth lens L6, the values ​​of f1 / f, f2 / f, f3 / f, f4 / f, f5 / f, f6 / f, the TTL / f value, the d-line refractive index nd1 of the first lens L1, and the d-line Abbe number νd4 of the fourth lens. In Table 11, the units for focal length and optical total length are all in mm. The focal length and total length shown in 11 were calculated using light rays with a wavelength of 550 nm.

[0059]

[0060] In Examples 1 to 5, the object side surface S3 of the second lens L2 has an aspherical shape with an inflection point, and has a concave surface facing the object in the central part and a convex surface facing the object in the peripheral part. This allows control of the angle of view characteristics, and within the effective image circle of the imaging lens system, the rate of change in image height can be gradually reduced as the angle of view increases. As a result, the image can be deliberately compressed at the peripheral part of the imaging plane of the image sensor 12, and the effect of aberrations that occur towards the periphery can be reduced. In fact, as shown in Figures 2A to D, 4A to D, 6A to D, 8A to D, and 10A to D, the imaging lens system 11 according to Examples 1 to 5 has a suitable reduction in spherical aberration, field curvature, and distortion, and has excellent imaging performance and high resolution. Furthermore, it is possible to suppress the decrease in peripheral light intensity, which is a problem in wide-angle imaging lens systems. In fact, in Examples 1 to 5, the F value is 2.0, and a bright imaging lens system 11 has been realized.

[0061] Furthermore, in Examples 1 to 5, the power of the first lens L1 is relatively strong, satisfying condition (1), which enables a smaller aperture for the first lens L1 and thus a smaller optical system. Specifically, because the value of f1 / f is less than -3.0, the aperture of the first lens can be reduced, and the imaging lens system can be reliably miniaturized. Also, because the value of f1 / f is greater than -5.0, the chromatic aberration occurring in the first lens L1 is kept within a suitable range, and deterioration of the imaging performance of the imaging lens system 11 can be avoided. In fact, in Examples 1 to 5, as shown in Figures 2D, 4D, 6D, 8D, and 10D, chromatic aberration can be suitably reduced.

[0062] Furthermore, by satisfying the condition (2) with respect to the power of the fourth lens L4, higher resolution can be achieved more reliably. Specifically, because the value of f4 / f is greater than 2.7, it is possible to prevent the error sensitivity of the imaging performance from becoming high and to avoid the occurrence of manufacturing errors. Also, because the value of f4 / f is less than 3.1, it is possible to avoid increasing the overall length of the optical system, and the imaging lens system 11 can be reliably miniaturized.

[0063] Furthermore, by satisfying the Abbe number νd4 of the fourth lens L4 in condition (3), the chromatic aberration occurring in the first lens L1 can be corrected, thereby achieving high resolution. In fact, in Examples 1 to 5, as shown in Figures 2D, 4D, 6D, 8D, and 10D, chromatic aberration can be suitably reduced.

[0064] Furthermore, by satisfying the condition (4) with respect to the power of the third lens L3, the distance from the entrance pupil to the aperture can be shortened, and the optical system can be miniaturized. Specifically, since the value of f3 / f is less than 10.0, the gap between the first lens L1 and the aperture does not widen, enabling a smaller aperture for the first lens L1 and miniaturizing the imaging lens system 11. Also, since the value of f3 / f is greater than 6.0, it is possible to suppress excessive chromatic aberration occurring in the first lens L1, thus avoiding deterioration of the imaging performance of the imaging lens system 11. Therefore, it is possible to achieve high resolution and provide a miniaturized imaging lens system 11. In fact, in the imaging lens systems 11 according to Examples 1 to 5, the aperture (effective diameter) of the first lens L1 is approximately slightly less than twice the diagonal length of the image sensor 12, thus achieving miniaturization of the imaging lens system 11. Furthermore, as shown in Figures 2A-D, 4A-D, 6A-D, 8A-D, and 10A-D, the imaging lens systems 11 according to Examples 1 to 5 effectively reduce spherical aberration, field curvature, distortion, and chromatic aberration, resulting in excellent imaging performance and high resolution.

[0065] Furthermore, in Examples 1 to 5, the imaging lens system 11 satisfies the above condition (5). This makes it possible to reliably miniaturize the imaging lens system.

[0066] Furthermore, in Examples 1 to 5, the imaging lens system 11 satisfies the above conditional equation (6). This allows for suitable correction of axial chromatic aberration generated by the fourth lens L4. In fact, as shown in Figures 2A to D, 4A to D, 6A to D, 8A to D, and 10A to D, the imaging lens system 11 according to Examples 1 to 5 effectively reduces spherical aberration, field curvature, and distortion, resulting in excellent imaging performance and high resolution.

[0067] Furthermore, in Examples 1 to 5, the imaging lens system 11 satisfies the above conditional equation (7). This makes it possible to reduce the aperture of the first lens L1.

[0068] Furthermore, in Examples 1 to 5, the first lens L1 and the fourth lens L4 are glass lenses, while the second lens L2, third lens L3, fifth lens L5, and sixth lens L6 are plastic lenses. By using a glass lens for the first lens L1, an imaging lens system 11 with excellent weather resistance can be provided. Also, by using a glass lens for the fourth lens L4, an imaging lens system 11 with reduced focus shift due to changes in ambient temperature can be provided. Table 12 shows the amount of focus shift (μm) of the imaging lens system 11 of Examples 1 to 5 with respect to changes in ambient temperature at focal length f. Table 12 shows the amount of focus shift from focal length f at room temperature of 25°C. The material of the barrel and housing used to calculate the amount of focus shift at focal length f shown in Table 10 is RenyXL1027U manufactured by Mitsubishi Engineering Plastics Corporation. Furthermore, by using plastic lenses for the second lens L2, third lens L3, fifth lens L5, and sixth lens L6, manufacturing costs can be reduced.

[0069] Furthermore, the camera module 10 is equipped with an imaging lens system 11, and the imaging lens system 11 is miniaturized and has sufficient resolution for image recognition in autonomous driving, thereby enabling miniaturization of the camera module 10 and high-precision sensing.

[0070] (Embodiment 3) Figure 11 is a schematic diagram of a vehicle 40 equipped with an in-vehicle system comprising an imaging device 50 including an imaging lens system 11 according to Embodiment 1 or Embodiment 2 and an image sensor 12 that converts the light focused through thereon into an electrical signal. As shown in the figure, the imaging device 50 can be mounted on the vehicle 40, and Figure 11 is an example of an arrangement illustrating the mounting position of the imaging device 50 on the vehicle 40. The imaging device 50 mounted on the vehicle 40 can also be called an in-vehicle camera and can be installed in various locations on the vehicle 40. For example, the first imaging device 50a may be placed on or near the front bumper as a camera that monitors the area in front of the vehicle 40 when it is in motion. The second imaging device 50b that monitors the area in front may be placed near the rearview mirror inside the vehicle 40. The third imaging device 50c may be placed on the dashboard or inside the instrument panel as a camera that monitors the driver's driving conditions. The fourth imaging device 50d may be installed at the rear of the vehicle 40 for use as a rear monitor. The imaging devices 50a and 50b can be called front cameras. The third imaging device 50c can be called an in-camera. The fourth imaging device 50d can be called a rear camera. The imaging device 50 is not limited to these, and includes imaging devices installed in various positions, such as a left side camera that images the left rear side and a right side camera that images the right rear side.

[0071] The image signal of the image captured by the imaging device 50 can be output to an information processing device 42 and / or a display device 43, etc., within the vehicle 40. These information processing devices 42 and 43 together with the imaging device 50 constitute an in-vehicle system. The information processing device 42 within the vehicle 40 includes a device that processes the image signal acquired by the imaging device 50 and recognizes various objects in the captured image to assist the driver in driving. The information processing device 42 also includes, but is not limited to, a navigation device, a collision damage mitigation braking device, a vehicle distance control device, and a lane departure warning device. The display device 43 displays the image processed and output by the information processing device 42, but can also receive the image signal directly from the imaging device 50. The display device 43 may employ, but is not limited to, a liquid crystal display (LCD), an organic electro-luminescence (EL) display, or an inorganic EL display. The display device 43 can display the image signal output from the imaging device 50, which captures images from positions that are difficult for the driver to see, such as a rear camera, to the driver or other occupants.

[0072] Figure 12 shows the configuration of the imaging device 50 that constitutes the in-vehicle system shown in Figure 11. As shown in the figure, the imaging device 50 according to one embodiment comprises a control unit 52, a storage unit 54, and a camera module 10.

[0073] The control unit 52 controls the camera module 10 and processes the electrical signals output from the image sensor 12 of the camera module 10. This control unit 52 may be configured as a processor, for example. The control unit 52 may also include one or more processors. The processors may include general-purpose processors that load specific programs and execute specific functions, and dedicated processors specialized for specific processing. Dedicated processors may include application-specific integrated circuits (ICs). Application-specific integrated circuits are also called ASICs (Application Specific Integrated Circuits). The processors may also include programmable logic devices. Programmable logic devices are also called PLDs (Programmable Logic Devices). PLDs may include field-programmable gate arrays (FPGAs). The control unit 52 may be either a system-on-a-chip (SoC) or a system-in-a-package (SiP) in which one or more processors cooperate.

[0074] The storage unit 54 stores various information or parameters related to the operation of the imaging device 50. The storage unit 54 may be composed of, for example, a semiconductor memory. The storage unit 54 may function as a work memory for the control unit 52. The storage unit 54 may store captured images. The storage unit 54 may store various parameters, etc., for the control unit 52 to perform detection processing based on the captured images. The storage unit 54 may be included in the control unit 52.

[0075] As described above, the camera module 10 captures the subject image formed via the imaging lens system 11 with the image sensor 12 and outputs the captured image. The image captured by the camera module 10 is also called the captured image.

[0076] The image sensor 12 may be composed of, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device). The image sensor 12 has an imaging surface in which multiple pixels are arranged. Each pixel outputs a signal that is specified by current or voltage according to the amount of incident light. The signal output by each pixel is also called imaging data.

[0077] The imaging data may be read out by the camera module 10 for all pixels and taken into the control unit 52 as an image. The image obtained by reading out all pixels is also called the maximum image. The imaging data may be read out by the camera module 10 for some pixels and taken into the image. In other words, the imaging data may be read out from pixels within a predetermined acquisition range. The imaging data read out from pixels within a predetermined acquisition range may be taken into the image. The predetermined acquisition range may be set by the control unit 52. The camera module 10 may obtain the predetermined acquisition range from the control unit 52. The image sensor 12 may capture an image within a predetermined acquisition range from the subject image formed via the imaging lens system 11.

[0078] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. For example, the applications of the imaging lens system of the present invention are not limited to in-vehicle cameras and surveillance cameras, but can also be used for other applications such as mounting on small electronic devices such as mobile phones.

[0079] This application claims priority based on Japanese Patent Application No. 2024-174313, filed on 3 October 2024, and incorporates all of its disclosures herein. Potential for industrial use

[0080] This enables the achievement of high resolution and provides miniaturized imaging lens systems, camera modules, in-vehicle systems, and mobile devices.

[0081] 10 Camera module 11 Imaging lens system 12 Image sensor 40 Vehicle (mobile body) 42 Information processing device (processing device) 43 Display device (output device) 50 Imaging device 52 Control unit L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens STOP Aperture Gf Front group Gr Rear group IRCF Infrared cut filter IMG Image plane OA Optical axis

Claims

1. An imaging lens system characterized by comprising, in order from the object side toward the image side, a first lens having negative power with its image side surface facing concave toward the image side; a second lens having an aspherical shape with an inflection point on its object side, with a concave surface facing toward the object side in the center and a convex surface facing toward the object side in the periphery, and having negative power with its image side surface facing concave toward the image side; a third lens having positive power with its image side surface facing convex toward the image side; an aperture; a fourth lens having positive power with its object side surface facing convex toward the object side; and a fifth and sixth lens forming a cemented lens, one of which has negative power and the other has positive power.

2. The imaging lens system according to claim 1, wherein, within the effective circular image area of ​​the imaging lens system, the rate of change in image height gradually decreases as the angle of view increases.

3. The imaging lens system according to claim 1, characterized in that it satisfies the following conditions (1) to (4), when the focal length of the first lens is defined as f1, the focal length of the fourth lens as f4, the Abbe number of the d line of the fourth lens as νd4, the focal length of the third lens as f3, and the focal length of the entire optical system as f: -5.0 < f1 / f < -3.0 ... (1) 2.7 < f4 / f < 3.1 ... (2) νd4 > 60 ... (3) 6.0 < f3 / f < 10.0 ... (4) 4. The imaging lens system according to claim 1, characterized in that when the distance along the optical axis from the object side of the first lens to the image plane of the image sensor is defined as TTL and the focal length of the entire optical system is defined as f, the following condition (5) is satisfied: 9 < TTL / f < 11 ... (5) 5. The imaging lens system according to claim 1, characterized in that, when the focal length of the fifth lens is defined as f5 and the focal length of the entire optical system is defined as f, the following condition (6) is satisfied: 10.0 < |f5 / f| < 30.0 ... (6) 6. The imaging lens system according to claim 1, characterized in that, when the d-line refractive index of the first lens is defined as nd1, the following condition (7) is satisfied: nd1 > 1.8 ... (7) 7. The imaging lens system according to claim 1, wherein the first lens and the fourth lens are glass lenses, and the second lens, the third lens, the fifth lens, and the sixth lens are plastic lenses.

8. A camera module comprising an imaging lens system according to any one of claims 1 to 7, and an image sensor that converts light focused through the imaging lens system into an electrical signal.

9. An in-vehicle system mounted on a vehicle, comprising: a camera module as described in claim 8; and an information processing device that processes an image captured by the image sensor of the camera module and recognizes an object in the image captured.

10. A mobile body equipped with the in-vehicle system described in claim 9, wherein the in-vehicle system further comprises an output device that outputs information to the occupants, and the information processing device is configured to output recognition information of the object to the output device.

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