Wide-angle lens unit, camera module, image-capturing system, and moving body

Abstract

To provide a wide-angle lens unit, camera module, image-capturing system and moving body that can reduce intensity of a ring ghost.SOLUTION: A second lens L2 in which a lens surface peripheral part directing toward an object side is a concave curved surface is arranged on an image side of a first lens L1 in which a lens surface directing toward the image side is a concave curved surface, and a multilayer film is formed on the concave curved surface of the second lens L2, and a film thickness Ti of the multilayer film is designed by a following (1) expression. Ti=T0i*1 / cos(sin-1((sin θ2)*N0 / Ni)) ...(1), However, 35°≤θ2<60°, Ti is the film thickness of an i-th (i is a natural number) layer of the multilayer film, T0i is a design film thickness of an i-th layer of the multilayer film, θ2 is an incidence angle when ghost intensity of an optical system as a whole is minimum, N0 is a refractive index of a medium, and Ni is the refractive index of the i-th layer.SELECTED DRAWING: Figure 17

Description

[Technical field]

[0001] The present invention particularly relates to a wide-angle lens unit constituting an on-board camera mounted on a vehicle such as an automobile, a camera module, an imaging system, and a moving body equipped with an imaging system. [Background technology]

[0002] Vehicles are equipped with on-board cameras to support parking and prevent collisions through image recognition, and attempts are also being made to apply them to autonomous driving. The camera module of such on-board cameras generally includes a lens unit having a lens group consisting of multiple lenses arranged along an optical axis, a lens barrel that houses and holds the lens group, and an aperture member that is arranged between at least one of the lenses in the lens group (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-231993 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the development of advanced driver-assistance systems (ADAS) has been progressing toward the realization of autonomous driving, but ghosting is a problem with ADAS. A ghost is a so-called "false image" in which an image of a non-existent object is formed on the sensor surface. Ghosts occur when light that enters a lens unit is reflected by the lens or other components and forms an image on the sensor surface. Humans can recognize ghosts as objects that do not exist, but ADAS mistakenly recognize ghosts as objects that do exist. If an ADAS makes a mistake in recognition, it will make incorrect decisions and control accordingly, which could lead to an accident. Various types of in-vehicle cameras are used depending on the ADAS function. For example, for automatic parking, an (ultra) wide-angle camera that can capture a wide range is installed at the rear of the vehicle. (Ultra) wide-angle cameras require (ultra) wide-angle lenses with good resolution performance, but (ultra) wide-angle lenses are prone to ghosting. Therefore, the inventors designed and analyzed a lens coating to combat ghosting, with a view to applying (ultra) wide-angle cameras to ADAS. Generally, a wide-angle lens supports a focal length of 38 to 24 mm and an angle of view of 60 to 84 degrees, an ultra-wide-angle lens supports a focal length of 20 to 13 mm and an angle of view of 94 to 118 degrees, and a fisheye lens supports an angle of view of about 180 degrees. In the following, wide-angle lenses, ultra-wide-angle lenses, and fisheye lenses will be described as wide-angle lenses.

[0005] An example of the configuration of a (super) wide-angle lens for a view camera is shown in Figure 1. This wide-angle lens is composed of five lenses. For convenience in the following explanation, the lenses are defined as follows. That is, from the object side to the image (sensor) side, the lenses are respectively called the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5. In addition, the lens surface on the object side of each lens is called lens surface R1, and the lens surface on the image side is called lens surface R2. As shown in Figure 1, a first lens L1 with a deep concave surface facing the image side is positioned to capture light with a wide angle of view. A second lens L2 with a convex curved surface is positioned on the object side to obtain a bright image all the way to the periphery. This configuration is typical of an ultra-wide-angle lens. With this configuration, strong ring-shaped ghosts (ring ghosts) can occur near the periphery of the image on the sensor.

[0006] Figure 2 shows an actual image taken with an (ultra) wide-angle lens for a view camera. This image was taken of a fiber optic light source in a darkroom. In this image, the only object that actually exists is the image of the light source in the center. However, a ring-shaped image can be seen near the periphery of the image. This is a ring ghost. Figure 3 shows the optical path where the ring ghost occurs with a solid line. The ring ghost is caused by reflected light that occurs between the opposing surfaces of the lens surface R1 of the second lens L2 and the lens surface R2 of the first lens L1 at the lens periphery. To deal with ghost caused by such inter-surface reflection, the reflected light is prevented from forming an image on the image plane of the sensor, or the reflected light is weakened to reduce the ghost intensity below the sensitivity of the sensor so that the sensor does not recognize it. In order to prevent the reflected light from forming an image, the shape and spacing of the lens surfaces are changed. In order to weaken the reflected light, an anti-reflection coating (AR coating) (hereinafter referred to as coating) is applied to the lens surface. Changing the lens shape has a significant effect on the imaging performance, so it is necessary to reduce the intensity of the reflected light by using a coating.

[0007] When a coating is applied to the lens surface, light that enters the lens from the air is reflected by the coating and the lens surface. The principle by which the coating reduces reflectivity is that these two reflected lights cancel each other out, reducing the intensity of the reflected light. When light is perpendicularly incident on a lens, the intensity of the reflected light is reduced according to the following condition: n1T=((2m-1)λ0) / 4 Here, n1 is the refractive index of the coating, T is the thickness of the coating, λ0 is the wavelength of the incident light, and m is a natural number. As shown in this conditional expression, the reflectance on the lens surface (lens surface) can be reduced by designing the film thickness. Furthermore, there are two types of coating: a single layer coating made up of one layer and a multilayer coating made up of multiple layers.

[0008] Before the design lens is prototyped, a ghost simulation (hereafter referred to as Ghost SIM) is performed to check for ghosts. Ghost SIM is performed by creating a lens model that takes into account the reflectance characteristics of the coating. After verifying that the strength of the lens is acceptable for practical use based on the Ghost SIM results, a prototype lens unit is produced. Figure 4 shows the results of a simulation of ring ghosting for a certain model. The graph on the left is a distribution of intensity. The point in the center of the graph is the light source. It can be seen that the area of ​​strong ghost intensity is ring-shaped. The graph on the right shows the cross-sectional intensity at line S on the left on a logarithmic scale. The ghost intensity is evaluated using the ratio of ghost intensity when the intensity of the light source image is set to 1 as an index. The intensity ratio of the ring ghost is 7.9 x 10 -5 The ghost intensity requirement for this model was 1.8×10 -4 Therefore, ring ghosting was not expected to be a problem in practical use. However, despite the preliminary ghost SIM test confirming that there were no problems, the ring ghost in the prototype lens was stronger than expected and became a problem. -4 A strong ring ghost was observed on the platform.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide a wide-angle lens unit, a camera module, an imaging system, and a moving object that can reduce the intensity of ring ghosts. [Means for solving the problem]

[0010] Normally, the thickness of the coating on the lens surface R1 of the second lens L2 is designed so that the reflectance is at its best when the angle of incidence is 0°. However, when the angle of incidence on the lens surface R1 of the second lens L2 is large, the reflectance becomes higher than when the angle of incidence is 0° due to incidence angle dependency. This is one of the causes of strong ghosting. Figure 15 shows the optical path of the ring ghost and an enlarged view of the light beam incident on lens surface R1 of second lens L2. The average angle of incidence of the light beam on the coating on lens surface R1 of second lens L2 is approximately 57°. This 57° is the angle of incidence value for a certain model where ghosting was a problem, and is merely one example.

[0011] The reflectance of the coating changes depending on the angle of incidence of the light. Figure 16 shows a graph of the calculated reflectance when the angles of incidence on the coating on lens surface R1 of second lens L2 are (a) 0°, (b) 45°, and (c) 57°. Normally, the coating thickness is designed so that the reflectance is at its best when the angle of incidence is 0°. As shown in Figure 16, the reflectance increases as the angle of incidence increases. To reduce ring ghosts, it is necessary to design the film thickness so that the reflectance is low at an incident angle of 57°. However, if the film thickness is optimized at an incident angle of 57°, the reflectance will be high at an incident angle of 0°. To achieve a balance between incident angles of 0° and 57°, the film thickness was designed to be optimized at an incident angle of 45°.

[0012] The film thickness conversion formula is shown below. Since the slope of the peripheral portion of lens surface R1 of second lens L2 is small and the film thickness does not differ much from the center, it is possible to use a multilayer film on lens surface R1 of second lens L2. Also, this conversion formula does not take into account differences in film thickness on the periphery. T i =T 0i ×1 / cos(sin -1 ((sinθ2)×N0 / N i )) Here, T i is the thickness of the i-th layer of the multilayer after conversion, T 0i is the thickness of the i-th layer before conversion (the thickness at which the reflectance is low at 0° incidence), θ2 is the angle of incidence to the coating at which the ghost intensity of the entire optical system is minimized, N0 is the refractive index of the medium, and N i is the refractive index of the i-th layer. Here, θ2 can be, for example, 45°.

[0013] In the following description, the design optimized at an incidence angle of 0° will be referred to as the "0° best design," and the design optimized at an incidence angle of θ2 will be referred to as the "best incidence angle design."

[0014] Figure 18 shows graphs of the reflectance for the 0° best designed coat and the best incident angle designed coat at incident angles of (a) 0°, (b) 45°, and (c) 57°. The graph for the best incident angle designed coat is shifted overall to the longer wavelength side as indicated by the arrows compared to the best 0° design. At an incident angle of 0°, the best incident angle designed coat had a higher reflectance on the shorter wavelength side and a lower reflectance on the longer wavelength side compared to the best 0° designed coat. At incident angles of 45° and 57°, the best incident angle designed coat had a lower reflectance on the longer wavelength side compared to the best 0° designed coat. A ghost SIM was performed by applying an incident angle best design coating to the lens surface R1 of the second lens L2. As a result, the ghost intensity ratio was 7.9×10 -5 It was confirmed that the intensity of ghosts in the entire optical system was reduced by approximately 0.8 times compared to the model in which the 0° best design coating was applied to the lens surface R1 of the second lens L2 shown in Figure 19(a). After verification with several models, it was found that the ghost intensity in the entire optical system was minimized when the angle of incidence θ2 was set to 35° or more and less than 60°.

[0015] A multilayer film is formed on the lens surface R1 of the second lens L2. 1. As shown in Figure 17, the multilayer film has different thicknesses T1, T2, .... First, this thickness is the thickness when the incident angle is 0°. If this thickness is used, ghosts will occur. 2. Then, for each film, the film thickness is calculated from 0° to 90° using the incident angle θ2 as a parameter. 3. Perform ghost simulation for each film thickness for each calculated incident angle to determine θ2 that minimizes the ghost intensity of the entire optical system. 4. After checking with several optical systems, it was found that the ghost intensity was minimized when θ2 was between 35° and 60°.

[0016] As described above, the lens unit according to the present invention is a lens unit in which a coating is deposited with a thickness converted to take into account the incidence angle dependency, that is, a coating designed to optimize the incidence angle is applied to the lens surface R1 of the image-side lens (e.g., the second lens L2). A multilayer film is formed on the convex curved surface of the second lens, The thickness Ti of the multilayer film is designed according to the following formula (1). T i =T 0i ×1 / cos(sin -1 ((sinθ2)×N0 / N i ))…(1) however, 35°≦θ2<60°, T i is the thickness of the ith layer (i is a natural number) of the multilayer film, T 0i is the design thickness of the ith layer of the multilayer. θ2 is the angle of incidence to the coating when the ghost intensity of the entire optical system is at a minimum, N0 is the refractive index of the medium, and N i is the refractive index of the i-th layer.

[0017] The present invention also provides a camera module having the lens unit, an imaging system having the camera module, and a moving body equipped with the imaging system. The camera module, imaging system, and moving body can achieve the same effects as the wide-angle lens unit described above. Note that the term "moving body" refers to any object that can move, such as a vehicle. Effect of the Invention

[0018] According to the present invention, the intensity of the ring ghost can be reduced. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing a schematic configuration of a wide-angle lens unit according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing an actual image of a ring ghost. [Diagram 3] FIG. 2 is a diagram showing an optical path in which a ring ghost occurs. [Figure 4] FIG. 13 is a diagram showing a simulation result of a ring ghost. [Diagram 5] 1A shows a first lens having a deposited film with a thickness that was assumed in ghost analysis, and FIG. 1B shows a first lens having a deposited film with an actual thickness. [Figure 6] FIG. 4 is a diagram showing the film thickness of the peripheral portion of the first lens. [Figure 7] FIG. 13 is a diagram showing a film thickness changing ghost SIM model taking into account the film thickness of the peripheral part of the first lens. [Figure 8] 13A and 13B show the results of a ring ghost simulation using a uniform film thickness SIM model, and FIG. 13B shows the results of a variable film thickness SIM model. [Figure 9] 1A shows a first lens having an evaporated film with a central best design, and FIG. 1B shows a first lens having an evaporated film with a peripheral best design according to the first embodiment. [Figure 10] 1 shows the reflectance of the lens surface of the first lens, where (a) is a graph showing the reflectance at the center of the lens surface, and (b) is a graph showing the reflectance of the reflective portion of the lens surface. [Figure 11] 10A and 10B show simulation results of a ring ghost, in which FIG. 10A shows the results of a center best design model, and FIG. 10B shows the results of a peripheral best design model according to the first embodiment. [Figure 12] 1A shows an actual image of a ring ghost caused by a central best design coat, and FIG. 1B shows an actual image of a ring ghost caused by a peripheral best design coat according to the first embodiment. [Figure 13] 1 is a diagram showing a schematic configuration of a wide-angle lens unit according to an embodiment of the present invention. [Figure 14] 1A and 1B show the results of a ring ghost simulation using the center best design model, and FIG. 1B shows the results of a peripheral best design model. [Figure 15] FIG. 2 is a diagram showing the optical path where a ring ghost occurs and an enlarged light beam incidence area. [Figure 16]14 shows the calculated values ​​of the reflectance of the lens surface of the second lens, where (a) is a graph of the calculated values ​​when the incident angle is 0°, (b) is a graph of the calculated values ​​when the incident angle is 45°, and (c) is a graph of the calculated values ​​when the incident angle is 57°. [Figure 17] 4 is a diagram showing a schematic diagram of a multilayer film (evaporated film) provided on the lens surface of a second lens. FIG. [Figure 18] The graphs show the reflectance of the lens surface of the second lens, where (a) is a graph when the incident angle is 0°, (b) is a graph when the incident angle is 45°, and (c) is a graph when the incident angle is 57°. [Figure 19] 13A and 13B show simulation results of a ring ghost, in which FIG. 13A shows the results of a best design model, and FIG. 13B shows the results of a best design model for the incident angle according to the second embodiment. [Figure 20] 1 is a diagram illustrating a schematic configuration of a camera module according to an embodiment of the present invention. [Figure 21] 1 is a schematic diagram of a vehicle as a moving body on which an imaging system (on-vehicle system) including a camera module according to an embodiment of the present invention is mounted. [Figure 22] 22 is a block diagram showing a configuration of an imaging device that constitutes the imaging system shown in FIG. 21. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiment contributes to "9. Industry, innovation and infrastructure" of the Sustainable Development Goals (SDGs) advocated by the United Nations, which states, "9.1 Develop quality, reliable, sustainable and resilient infrastructure, including regional and transborder infrastructure, to support economic development and human well-being, with a focus on affordable and equitable access for all." It should be noted that the (ultra) wide-angle lens unit of this embodiment described below is intended particularly for use as a camera module for an in-vehicle camera or the like, and is fixedly installed, for example, on the outer surface of a vehicle, with wiring being pulled into the vehicle and connected to a display or other device.

[0021] FIG. 1 is a diagram showing a schematic configuration of a (super) wide-angle lens unit 11 according to an embodiment of the present invention. As shown in the figure, the wide-angle lens unit 11 of this embodiment includes a cylindrical lens barrel (not shown) made of, for example, resin, a plurality of lenses arranged in the lens barrel, for example, five lenses consisting of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5 from the object side, and an aperture. In this embodiment, the aperture is interposed between the third lens L3 and the fourth lens L4, and is an "aperture aperture" that limits the amount of transmitted light and determines the F-number that is an index of brightness, or a "light blocking aperture" that blocks light rays that cause ghosts and light rays that cause aberrations. An in-vehicle camera equipped with such a wide-angle lens unit 11 includes the wide-angle lens unit 11, a board having an image sensor (imaging element), and an installation member (not shown) that installs the board on a vehicle such as an automobile.

[0022] The multiple lenses L1, L2, L3, L4, and L5 assembled and housed within the lens barrel are stacked and arranged with their optical axes aligned, and constitute a group of lenses used for imaging, with the lenses L1, L2, L3, L4, and L5 lined up along a single optical axis O. In this case, the first lens L1, which is located closest to the object and constitutes the lens group, has a convex lens surface facing the object side and a concave lens surface facing the image side, and the second lens L2 has a convex lens surface facing the object side. The first lens L1 is a glass lens, and the other lenses L2, L3, L4, and L5 are plastic lenses, but are not limited to this (for example, the first lens L1 may be a plastic lens).

[0023] The object-side lens surface R1 of the first lens L1 has a spherical shape with a positive curvature, and the image-side lens surface R2 of the first lens L1 has a spherical shape with a positive curvature. The object-side lens surface R1 faces the convex surface toward the object side, and the image-side lens surface R2 has a concave curved portion toward the image side. The object-side lens surface R1 of the second lens L2 is an aspheric shape with a positive curvature, but may be an aspheric shape with a negative curvature in the center and a positive curvature in the periphery. The image-side lens surface R2 of the second lens L2 is an aspheric shape with a positive curvature. The object-side lens surface R1 faces the convex surface toward the object side, and the image-side lens surface R2 has a curved portion with a concave shape toward the image side.

[0024] The object-side lens surface of the third lens L3 has an aspheric shape with a positive curvature, and the image-side lens surface of the third lens L3 has an aspheric shape with a negative curvature. The object-side lens surface faces the object side convexly, and the image-side lens surface faces the image side convexly. The fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens. The object-side lens surface of the fourth lens L4 has an aspheric shape with a positive curvature, and the image-side lens surface has an aspheric shape with a positive curvature. The object-side lens surface faces the object side with a convex surface, and the image-side lens surface faces the image side with a concave surface. The object-side lens surface of the fifth lens L5 has an aspheric shape with a positive curvature, and the image-side lens surface has an aspheric shape with a negative curvature. The object-side lens surface faces the object side with a convex surface, and the image-side lens surface faces the image side with a convex surface.

[0025] The cover glass is a glass plate for protecting the imaging element (image sensor). In addition, an IR cut filter (infrared cut filter) for cutting light in the infrared region may be disposed between the cover glass and the fifth lens L5. When designing a wide-angle lens system, the IR cut filter and the cover glass are treated as an integral part of the wide-angle lens system. However, the IR cut filter and the cover glass are not essential components of the wide-angle lens system.

[0026] As shown in FIG. 9(b), in this embodiment, an anti-reflection film m1 (hereinafter, referred to as coat m1) is provided by vapor deposition on the lens surface R2 of the first lens L1. When coating m1 is deposited on lens surface R2, the coating is formed uniformly in the direction of incidence of the deposition particles on the first lens L1 set in a jig, as shown by the arrow. At the lens periphery of the first lens L1, lens surface R2 is inclined with respect to the deposition direction. For this reason, the film thickness in the normal direction of lens surface R2 is thinner at the periphery. In the past, with uniform film thickness SIM models, differences in film thickness at the periphery of the lens surface were not taken into account, as they were considered to be manufacturing errors. However, at the periphery of a lens surface with a small radius of curvature, such as lens surface R2 of the first lens L1 of an ultra-wide-angle lens, the inclination is large and the difference in film thickness becomes noticeable.

[0027] Fig. 9(a) shows a conventional example in which a coating m0 is formed on the lens surface R2 of the first lens L1. As shown in Fig. 9(a), the coating m0 is designed to have a thickness T0 at the center C of the lens surface R2 of the first lens L1, and the thickness is thinner at the periphery of the lens surface R2 than at the center C. In contrast, in this embodiment, as shown in FIG. 9(b), the coating m1 has a thickness designed to be T0 at the periphery of the lens surface R2, resulting in a well-balanced coating thickness. In FIG. 9(a), θ0 is θ(h0) when the effective diameter (height of the outermost periphery) of the lens surface R2 of the first lens L1 is h0. In FIG. 9(b), θ1 is θ(h1) when the height from the center C of the lens surface R2 of the first lens L1 is h1. Based on the above, the conversion formula for calculating the central film thickness T when the film thickness becomes T0 at a height h1 from the center C is shown below. T = T0 / cosθ1(1) θ1=sin -1 (h1 / h0×sinθ0) 0.45≦h1 / h0≦0.75 T0 is the thickness of the coating m0 at the center C of the lens surface R2 before conversion, and T is the thickness of the coating m1 at the center C of the lens surface R2 after conversion. In addition, a single-layer film is used because the change in reflectance due to the change in film thickness is smaller in a single-layer film than in a multi-layer film.

[0028] If the conventional coating design before conversion is called the "best center design" and the new coating design of this embodiment after conversion is called the "best peripheral design," as shown in Figure 10(b), the best peripheral design coating has a thicker overall film thickness than the best central design, resulting in a graph that is shifted overall to the long wavelength side, as indicated by the arrow. The best peripheral design coating has a low reflectance on the long wavelength side at the center and a high reflectance on the short wavelength side. The reflectance of the best peripheral design coating is reduced in the L1 reflective area. As shown in FIG. 11, in the peripheral best design coating of this embodiment, the ghost intensity ratio is 4.0×10 -5 In addition, when an actual image was evaluated on a lens unit with the peripheral best design coating, it was confirmed that the ghost intensity was reduced compared to the conventional central best design, as shown in Figure 12.

[0029] Next, the reason why the ratio of h1 to h0 is set to 0.45≦h1 / h0≦0.75 will be explained. For the film thickness (T = T0) model before conversion, ghost SIM was performed taking into account the reflectance of all lens surfaces. The results are shown in Tables 1 and 2. In the model shown in Table 1, h1 / h0 is changed from 0.5 to 0.80 when the angle of incidence of the light on the lens unit (the angle of incidence of the light on the first lens located closest to the object) is 10° and 80°.

[0030] [Table 1]

[0031] When the light incidence angle to the lens unit is 80°, the strongest ghost is observed, with an intensity ratio of 1.0×10 -4 It was. In order to examine the value of h1 / h0, ghost SIM was performed with the coating thickness converted by changing the value of h1 / h0. As shown in Table 1, it was confirmed that the ghost intensity when the light incident angle on the lens unit was 80° was reduced when h1 / h0 = 0.55 or more.

[0032] However, when the film thickness is optimized so that the reflectance is low near the periphery of the lens, the reflectance is high near the center of the lens, and the intensity of the ghost caused by the reflection at the center of the lens becomes strong. In the model shown in Table 1, when h1 / h0 = 0.8, the ghost intensity ratio of the ghost generated when the light incident angle to the lens unit is 10° is 1.0 × 10 -4 It was confirmed that the ghost intensity becomes stronger when the film thickness is changed. In this case, the maximum ghost intensity seen overall becomes the same as that before the film thickness change. In this way, it was confirmed that the ghost intensity is reduced when h1 / h0 is 0.55 to 0.75 in the model shown in Table 1.

[0033] Next, in the model shown in Table 2, h1 / h0 is changed from 0.4 to 0.60 when the angle of incidence of the light beam on the lens unit (the angle of incidence of the light beam on the first lens located closest to the object) is 10° and 100°. .

[0034] [Table 2]

[0035] Like the model shown in Table 1, the model shown in Table 2 has a trade-off in ghost strength due to h1 / h0. As shown in Table 2, it was confirmed that the ghost intensity was reduced when the value of h1 / h0 was 0.45 to 0.55.

[0036] From the models shown in Tables 1 and 2, it was confirmed that there is an effect of reducing ghost intensity when 0.45≦h1 / h0≦0.75.

[0037] In this embodiment, in addition to the peripheral best designed coating on the lens surface R2 of the first lens L1, a new design (the present invention) was also made for the coating on the lens surface R1 of the second lens. Note that, in this embodiment, the new design is made on the wide-angle lens unit 12 as shown in Fig. 13, but the new design may be made on the wide-angle lens unit 12 as shown in Fig. 1, or the new design may be made on a lens unit having a first lens L1 with a normal central best designed coating, without a peripheral best designed coating on the lens surface R2 of the first lens L1.

[0038] As shown in FIG. 13, the (ultra) wide-angle lens unit 12 of this embodiment is for ADAS applications, and includes, for example, a cylindrical lens barrel (not shown) made of resin, a plurality of lenses arranged in the lens barrel, for example, seven lenses consisting of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 from the object side, and an aperture. In this embodiment, the aperture is interposed between the third lens L3 and the second lens L4, and is an "aperture aperture" that limits the amount of transmitted light and determines the F-number, which is an index of brightness, or a "light blocking aperture" that blocks light rays that cause ghosts and light rays that cause aberrations. An in-vehicle camera equipped with such an ultra-wide-angle lens unit 12 includes the ultra-wide-angle lens unit 12, a board having an image sensor (imaging element), and an installation member (not shown) that installs the board on a vehicle such as an automobile.

[0039] The object-side lens surface R1 of the first lens L1 has a spherical shape with a positive curvature, and the image-side lens surface R2 of the first lens L1 has a spherical shape with a positive curvature. The object-side lens surface R1 faces the convex surface toward the object side, and the image-side lens surface R2 has a concave curved portion toward the image side. The object-side lens surface R1 of the second lens L2 is an aspheric shape with a positive curvature, but may be an aspheric shape with a negative curvature in the center and a positive curvature in the periphery. The image-side lens surface R2 of the second lens L2 is an aspheric shape with a positive curvature. The object-side lens surface R1 faces the convex surface toward the object side, and the image-side lens surface R2 faces the concave surface toward the image side.

[0040] The object-side lens surface of the third lens L3 has an aspheric shape with a positive curvature, and the image-side lens surface of the third lens L3 has an aspheric shape with a negative curvature. The object-side lens surface faces the object side convexly, and the image-side lens surface faces the image side convexly. The object-side lens surface of the fourth lens L4 is aspheric with a negative curvature, and the image-side lens surface of the fourth lens L4 is aspheric with a negative curvature. The object-side lens surface faces the concave surface toward the object side, and the image-side lens surface faces the convex surface toward the image side. The object side lens surface of the fifth lens L5 is an aspheric surface having a positive curvature. 5 The image-side lens surface of has an aspheric shape with a positive curvature. The object-side lens surface faces a convex surface toward the object side, and the image-side lens surface faces a concave surface toward the image side. The object-side lens surface of the sixth lens L6 has an aspheric shape with a positive curvature, and the image-side lens surface has an aspheric shape with a negative curvature. The object-side lens surface faces the object side with a convex surface, and the image-side lens surface faces the image side with a convex surface. The sixth lens L6 and the seventh lens L7 are cemented together to form a cemented lens. The seventh lens L7 has an object-side lens surface that is aspheric with a negative curvature, and an image-side lens surface that is aspheric with a negative curvature. The object-side lens surface faces the object side with a concave surface, and the image-side lens surface faces the image side with a convex surface.

[0041] The cover glass is a glass plate for protecting the imaging element (image sensor). In addition, an IR cut filter (infrared cut filter) for cutting light in the infrared region may be disposed between the seventh lens L7 and the cover glass. When designing an ultra-wide-angle lens system, the IR cut filter and the cover glass are treated as an integral part of the ultra-wide-angle lens system. However, the IR cut filter and the cover glass are not essential components of the ultra-wide-angle lens system.

[0042] 15 shows the optical path of the ring ghost and an enlarged view of the portion where the light rays are incident on the lens surface R1 of the second lens L2. The average angle of incidence of the light rays on the coating on the lens surface R1 of the second lens L2 is approximately 57°. The reflectivity of the coating varies depending on the angle of incidence of the light; the best reflectivity is achieved when the angle of incidence is 0°, and the reflectivity increases as the angle of incidence increases. To reduce ring ghosts, it is necessary to design the film thickness so that the reflectance is low at an incident angle of 57°. However, if the film thickness is optimized at an incident angle of 57°, the reflectance will be high at an incident angle of 0°. To achieve a balance between incident angles of 0° and 57°, the film thickness was designed to be optimized at an incident angle of 45°.

[0043] The film thickness conversion formula is shown below. Since the slope of the peripheral portion of lens surface R1 of second lens L2 is small and the film thickness does not differ much from the center, it is possible to use a multilayer film on lens surface R1 of second lens L2. Also, this conversion formula does not take into account differences in film thickness on the periphery. T i =T 0i ×1 / cos(sin -1 ((sinθ2)×N0 / N i )) 35°≦θ2<90° Here, T i is the thickness of the i-th layer of the multilayer after conversion, T 0i is the thickness of the i-th layer before conversion (the thickness at which the reflectance is low at 0° incidence), θ2 is the angle of incidence to the coating at which the ghost intensity of the entire optical system is minimized, N0 is the refractive index of the medium, and N i is the refractive index of the i-th layer. Here, θ2 is 45°. In addition, T 0i The material of the film and the total number of films are determined, and the film thickness is optimized using thin film calculation software (for example, "Essential Macleod" by Sigma Koki Co., Ltd.).

[0044] A multilayer film is formed on the lens surface R1 of the second lens L2. 1. As shown in Figure 17, the multilayer film has different thicknesses T1, T2, .... First, this thickness is the thickness when the incident angle is 0°. If this thickness is used, ghosts will occur. 2. Then, for each film, the film thickness is calculated from 0° to 90° using the incident angle θ2 as a parameter. 3. Perform ghost simulation for each film thickness for each calculated incident angle to determine θ2 that minimizes the ghost intensity of the entire optical system. 4. After checking with several optical systems, it was found that the ghost intensity was minimized when θ2 was between 35° and 90°.

[0045] If the conventional design optimized at an incidence angle of 0° is called the "0° best design" and the design optimized at an incidence angle θ2 in this embodiment is called the "best incidence angle design," as shown in Fig. 18, the best incidence angle design coat is generally shifted toward the long wavelength side as indicated by the arrow compared to the best 0° design. At an incidence angle of 0°, the best incidence angle design coat has a higher reflectance on the short wavelength side and a lower reflectance on the long wavelength side compared to the best 0° design coat. At incidence angles of 45° and 57°, the best incidence angle design coat has a lower reflectance on the long wavelength side compared to the best 0° design coat. In a model in which a peripheral best design coat is applied to the lens surface R2 of the first lens L1, a ghost SIM was performed by applying an incident angle best design coat to the lens surface R1 of the second lens L2. As shown in FIG. 19(b), the ghost intensity ratio was 7.9×10 -5 It was confirmed that the loss was reduced to approximately 0.8 times that of the model in which the 0° best design coating was applied to the lens surface R1 of the second lens L2 shown in FIG. 19(a).

[0046] In this embodiment, in a lens unit in which a peripheral best designed coat is not applied to the lens surface R2 of the first lens L1, an incident angle best designed coat is applied to the lens surface R1 of the second lens L2. The conversion formula for the thickness of the film formed on the lens surface R1 of the second lens L2 is shown below. Since the inclination of the lens surface R1 of the second lens L2 is small at the periphery and the film thickness does not change much from the center, a multilayer film can be used on the lens surface R1 of the second lens L2. Also, this conversion formula does not take into account the difference in film thickness at the periphery. T i =T 0i ×1 / cos(sin -1 ((sinθ2)×N0 / N i )) 35°≦θ2<60° Here, T i is the thickness of the i-th layer of the multilayer after conversion, T 0i is the thickness of the i-th layer before conversion (the thickness at which the reflectance is low at 0° incidence), θ2 is the angle of incidence to the coating at which the ghost intensity of the entire optical system is minimized, N0 is the refractive index of the medium, and N i is the refractive index of the i-th layer. Here, θ2 is 45°.

[0047] Next, the reason why the angle of incidence onto the coating when the ghost intensity of the entire optical system is at a minimum is set to 35°≦θ2<60° will be explained. For the film thickness (T = T0) model before conversion, ghost SIM was performed taking into account the reflectance of all lens surfaces. The results are shown in Tables 3 and 4. In the model shown in Table 3, θ2 is changed from 30° to 45° when the angle of incidence of the light beam on the lens unit (the angle of incidence of the light beam on the first lens L1 located closest to the object) is 10° and 100°.

[0048] [Table 3]

[0049] As shown in Table 3, when the incident angle of the light to the lens unit is 100°, the ghost with the maximum intensity is confirmed, and the intensity ratio is 1.6 × 10 -4 It was. In order to study the value of θ2, ghost SIM was performed with the film thickness of the coating converted by changing the value of θ2. As shown in Table 3, when the incident angle of the light beam on the lens unit is 100°, the ghost intensity is maximum when θ2 = 30° (intensity ratio: 1.6 × 10 -4 ) and it was confirmed that the effect was reduced when θ2 was 35° or more.

[0050] However, if the reflectivity is optimized to be low when the angle of incidence on the coating is large, the reflectivity will be high when the angle of incidence on the coating is around 0°, and the intensity of the ghost caused by the reflection of light rays at an angle of incidence on the coating around 0° will become strong. In the model shown in Table 3, when θ2 = 45°, the ghost intensity ratio of the ghost generated when the light incident angle to the lens unit is 10° is 1.6 × 10 -4 It was confirmed that the ghost intensity becomes stronger when the film thickness is changed. In this case, the maximum ghost intensity seen overall becomes the same as the intensity before the film thickness change. In this way, it was confirmed that the ghost intensity is reduced when θ2 is between 35° and 40° in the model shown in Table 3.

[0051] Next, in the model shown in Table 4, θ2 is changed from 35° to 65° when the angle of incidence of the light beam on the lens unit (the angle of incidence of the light beam on the first lens L1, which is located closest to the object) is 10° and 40°.

[0052] [Table 4]

[0053] Like the model shown in Table 3, the model shown in Table 4 has a trade-off in ghost intensity depending on θ2. As shown in Table 4, it was confirmed that the ghost intensity was reduced when the value of θ2 was between 40° and 60°.

[0054] From the models shown in Tables 3 and 4, it was confirmed that there is an effect of reducing ghost intensity when 35°≦θ2<60°.

[0055] Fig. 20 is a diagram showing a schematic configuration of a camera module 300 of this embodiment having the lens unit 11 or the lens unit 12 configured as described above. Although Fig. 20 shows the camera module 300 having the lens unit 11, the camera module 300 may have the lens unit 12. As shown in the figure, the camera module 300 includes a mount (base) 302 that holds the lens unit 11. The camera module 300 also includes a package sensor (imaging element; image sensor) 304.

[0056] The mount 302 has a female thread 302 a that screws into the male thread 11 a of the lens units 11 and 12 . Package sensor 304 is disposed inside mount 302 facing infrared cut filter 301, and is disposed at a position where it receives an image of an object formed by lens unit 11. Package sensor 304 also includes a CCD, CMOS, or the like, and converts light that is collected through lens unit 11 and reaches it into an electrical signal. The converted electrical signal is converted into analog data or digital data, which is a component of image data captured by the camera.

[0057] FIG. 21 shows a vehicle 240 as a moving body equipped with an in-vehicle system (imaging system) equipped with an imaging device 250 including the camera module 300 shown in FIG. 20. As shown in the figure, the imaging device 250 can be mounted on the vehicle 240, and FIG. 21 shows an example of an arrangement illustrating the mounting position of the imaging device 250 on the vehicle 240. The imaging device 250 mounted on the vehicle 240 can also be called an in-vehicle camera, and can be installed in various places on the vehicle 240. For example, the first imaging device 250a may be disposed on or near the front bumper as a camera that monitors the front when the vehicle 240 is traveling. The second imaging device 250b that monitors the front may be disposed near the room mirror (inner rearview mirror) in the vehicle interior of the vehicle 240. The third imaging device 250c may be disposed on the dashboard or in the instrument panel as a camera that monitors the driving situation of the driver. The fourth imaging device 250d may be installed at the rear of the vehicle 240 for rear monitoring of the vehicle 240. The imaging devices 250a and 250b may be called front cameras. The third imaging device 250c may be called an in-camera. The fourth imaging device 250d may be called a rear camera. The imaging device 250 is not limited to these, and may include imaging devices installed at 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.

[0058] An image signal of an image captured by the imaging device 250 may be output to an information processing device 242 and / or a display device 243 in the vehicle 240. The information processing device 242 and the display device 243, together with the imaging device 250, constitute an in-vehicle system. The information processing device 242 in the vehicle 240 includes a device that processes an image signal acquired by the imaging device 250, recognizes the image, and assists the driver in driving. The information processing device 242 includes, but is not limited to, a navigation device, a collision damage mitigation brake device, a vehicle distance control device, and a lane departure warning device. The display device 243 displays an image processed and output by the information processing device 242, but can also receive an image signal directly from the imaging device 250. The display device 243 may employ, but is not limited to, a liquid crystal display (LCD), an organic EL (Electro-Luminescence) display, and an inorganic EL display. The display device 243 can display to the driver (can output information to passengers) an image signal output from an imaging device 250 that captures an image from a position that is difficult for the driver to view, such as a rear camera.

[0059] Fig. 22 shows the configuration of an imaging device constituting the in-vehicle system shown in Fig. 21. As shown in the figure, an imaging device 250 according to the embodiment includes a control unit 252, a storage unit 254, and the camera module 300 shown in Fig. 21 described above.

[0060] The control unit 252 controls the camera module 300 and processes an electrical signal output from the image sensor 304 of the camera module 300. The control unit 252 may be configured as a processor, for example. The control unit 252 may include one or more processors. The processor may include a general-purpose processor that loads a specific program to execute a specific function, and a dedicated processor specialized for a specific process. The dedicated processor may include an application-specific integrated circuit (IC). The application-specific IC may be an application specific integrated circuit (ASIC). The processor may include a programmable logic device, which is also called a programmable logic device (PLD). A PLD is a field-programmable gate array (FPGA). The control unit 252 may be either a System-on-a-Chip (SoC) or a System In a Package (SiP) in which one or more processors work together.

[0061] The storage unit 254 stores various information or parameters related to the operation of the imaging device 250. The storage unit 254 may be composed of, for example, a semiconductor memory or the like. The storage unit 254 may function as a work memory for the control unit 252. The storage unit 254 may store captured images. The storage unit 254 may store various parameters and the like for the control unit 252 to perform detection processing based on the captured images. The storage unit 254 may be included in the control unit 252.

[0062] As described above, the camera module 300 captures an object image formed via the lens unit 11 with the image sensor 304, and outputs the captured image. The image captured by the camera module 300 is also called a captured image.

[0063] The image sensor 304 is, for example, a CMOS (Complementary Metal Oxide The image sensor 304 may be a CCD (Charge Coupled Device) or a CCD (Crystal Semiconductor) image sensor. The image sensor 304 has an imaging surface on which a number of pixels are arranged. Each pixel outputs a signal specified by a current or voltage according to the amount of incident light. The signal output by each pixel is also called imaging data.

[0064] The imaging data may be read by the camera module 300 for all pixels and taken into the control unit 252 as a captured image. The captured image read out for all pixels is also referred to as a maximum captured image. The imaging data may be read by the camera module 300 for some pixels and taken into the control unit 252 as a captured image. In other words, the imaging data may be read out from pixels in a predetermined capture range. The imaging data read out from pixels in the predetermined capture range may be taken into the control unit 252 as a captured image. The predetermined capture range may be set by the control unit 252. The camera module 300 may obtain the predetermined capture range from the control unit 252. The imaging element 304 may capture an image of a predetermined capture range of a subject image formed through the lens unit 11.

[0065] The present invention is not limited to the above-mentioned embodiment, and can be modified in various ways without departing from the scope of the present invention. For example, the shapes of the lenses, lens barrels, etc., in the present invention are not limited to those in the above-mentioned embodiment. Furthermore, the above-mentioned embodiments may be combined in part or in whole, or a part of the configuration may be omitted from one of the above-mentioned embodiments, without departing from the scope of the present invention. [Explanation of symbols]

[0066] 1 Wide-angle lens unit 12 Ultra-wide-angle lens unit L1 First lens L2 Second lens R1, R2 lens surface m1 Evaporation film 300 Camera Module 240 Vehicles (mobile)

Claims

1. A lens unit including a lens group in which a plurality of lenses are arranged along the optical axis of the lenses, and a lens barrel that houses and holds the lens group, The lens surface facing the image side is a concave curved surface. The present invention includes a configuration in which an image-side lens is arranged, the peripheral portion of which faces the object side and has a convex curved surface, a multilayer film is formed on the convex curved surface of the image-side lens, A lens unit characterized in that the thickness Ti of the multilayer film is designed according to the following formula (1): T ｉ =T ０ｉ ×1 / cos(sin －１ ((sinθ ２ )×N ０ / N ｉ ))…(1) however, 35°≦θ ２ <60°、 T ｉ is the thickness of the i-th layer (i is a natural number) of the multilayer film, T ０ｉ is the design thickness of the ith layer of the multilayer film, θ ２ is the angle of incidence when the ghost intensity of the entire optical system is at a minimum, N ０ is the refractive index of the medium, N ｉ is the refractive index of the i-th layer.

2. 13. A camera module comprising: the lens unit according to claim 1; and an image sensor that converts light collected through the lens group of the lens unit into an electrical signal.

3. an imaging device comprising: the camera module according to claim 2; and a control unit that controls the camera module and processes an electrical signal output from the imaging element of the camera module; a processing device that processes an image signal acquired by the imaging device; a display device that displays an image that has been processed and output by the processing device; An imaging system comprising:

4. 4. A vehicle equipped with the imaging system according to claim 3, wherein information is output to a passenger by the display device.

Images