Wide-angle lens and imaging device

Abstract

To provide a wide-angle lens and an imaging device the temperature characteristics of which are good, and which are compact and low cost.SOLUTION: A wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a prism P, and a second lens group G2 having positive refractive power, the first lens group G1 including, in order from the object side, a first negative lens L1 and a second negative lens L2, the prism P deflecting a beam having entered from the first lens group G1 and presenting it to the second lens group G2 and satisfying the expression below. The imaging device comes equipped with the wide-angle lens. Expression (1): 8.0<fp / f<13.0, where fp represents the focal distance of the prism P, f represents the focal distance of the wide-angle lens.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wide-angle lens and an imaging device, and particularly to a wide-angle lens and an imaging device suitable for various imaging devices using solid-state imaging elements (such as CCDs and CMOSs) such as cameras mounted on moving bodies such as video cameras, digital still cameras, single-lens reflex cameras, mirrorless single-lens cameras, and drones.

Background Art

[0002] In recent years, due to the spread of SNS (Social networking service) and video distribution services, individuals have been sharing their experiences and the like with others through photos, videos, and the like. In addition, in recent years, the spread of imaging devices mounted on moving bodies such as drones has also been progressing. Under such a background, as an optical system of an imaging device, the need for a wide-angle lens capable of acquiring an image with a large amount of information has been increasing.

[0003] The miniaturization of imaging devices has been progressing, and in addition, when mounted on a moving body, the imaging device is required to be small and lightweight. Therefore, the wide-angle lens is required to be further miniaturized while maintaining a wide angle of view. For example, in Patent Document 1 and Patent Document 2, wide-angle lenses that achieve overall miniaturization by bending the optical path with a prism have been proposed. All of these wide-angle lenses arrange a lens group having a negative refractive power on the object side, and by bending the optical path of the light rays incident from the lens group having the negative refractive power with a prism, a configuration that facilitates overall miniaturization is adopted.

[0004] By the way, imaging devices mounted on moving bodies are mainly used outdoors. Therefore, as a wide-angle lens for imaging devices for moving bodies, in addition to the requirements for a wide angle of view and miniaturization, an optical system with good temperature characteristics with little variation in the focal position and the like even when the ambient temperature fluctuates is required. Also, it is required to be low-cost while satisfying these requirements.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-030436 [Patent Document 2] Japanese Patent Publication No. 2002-169088 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the wide-angle lens described in Patent Document 1, a larger diameter glass aspherical lens is placed on the object side than the prism, making it difficult to reduce costs. Furthermore, in the wide-angle lens described in Patent Document 2, a plastic prism is used, and the refractive power of the prism is not optimized, making it difficult to suppress changes in the focal position due to fluctuations in ambient temperature.

[0007] Therefore, the object of the present invention is to provide a wide-angle lens and imaging device that have good temperature characteristics, are compact, and are low cost. [Means for solving the problem]

[0008] To solve the above problems, the wide-angle lens according to the present invention is composed of, in order from the object side, a first lens group having negative refractive power, a prism, and a second lens group having positive refractive power, wherein the first lens group has, in order from the object side, a first negative lens and a second negative lens, and the prism bends the light rays incident from the first lens group and causes them to incident on the second lens group, satisfying the following equation. 8.0 < fp / f < 13.0 (1) however, fp: focal length of the prism f: Focal length of the wide-angle lens

[0009] Furthermore, in order to solve the above problems, the imaging device according to the present invention is characterized by comprising the wide-angle lens and an image sensor that converts the optical image formed by the wide-angle lens into an electrical signal. [Effects of the Invention]

[0010] The present invention aims to provide a wide-angle lens and imaging device that have good temperature characteristics, are compact, and are low cost. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of the wide-angle lens according to Embodiment 1 of the present invention. [Figure 2] These are the spherical aberration diagram, astigmatism diagram, and distortion diagram of the wide-angle lens of Example 1 in the state of focusing on an object at infinity. [Figure 3] This is a cross-sectional view of the wide-angle lens according to Embodiment 2 of the present invention. [Figure 4] These are the spherical aberration diagram, astigmatism diagram, and distortion diagram for the wide-angle lens of Example 2 in the state of focusing on an object at infinity. [Figure 5] This is a cross-sectional view of the wide-angle lens according to Embodiment 3 of the present invention. [Figure 6] These are the spherical aberration diagram, astigmatism diagram, and distortion diagram for the wide-angle lens of Example 3 when an object at infinity is in focus. [Figure 7] This is a cross-sectional view of the wide-angle lens according to Embodiment 4 of the present invention. [Figure 8] These are the spherical aberration diagram, astigmatism diagram, and distortion diagram of the wide-angle lens of Example 4 in the state of focusing on an object at infinity. [Modes for carrying out the invention]

[0012] The following describes embodiments of the wide-angle lens and imaging device according to the present invention. However, the wide-angle lens and imaging device described below are only one embodiment of the wide-angle lens and imaging device according to the present invention, and the wide-angle lens and imaging device according to the present invention are not limited to the following embodiments.

[0013] 1. Wide-angle lens 1-1.Optical configuration The wide-angle lens is composed of, in order from the object side, a first lens group having a negative refractive power, a prism, and a second lens group having a positive refractive power. Hereinafter, a detailed description will be given in order from the object side.

[0014] (1) First lens group The first lens group has a negative refractive power. By arranging a negative refractive power in the first lens group, it is possible to realize a wide angle of view and facilitate miniaturization of the wide-angle lens.

[0015] Here, the first lens group is assumed to include a first negative lens having a negative refractive power and a second negative lens in order from the object side. By configuring the first lens group using at least two negative lenses in this way, while arranging a strong negative refractive power in the first lens group, it is possible to suppress the curvature of each lens from becoming too large, suppress the occurrence of various aberrations such as field curvature, and easily realize a wide-angle lens with high optical performance using a small number of lens elements.

[0016] As long as the first lens group has a negative refractive power and includes the first negative lens and the second negative lens, the other configuration is not particularly limited. For example, a further negative lens may be provided on the image side of the second negative lens. By configuring the first lens group with three negative lenses, it becomes easier to arrange a strong negative refractive power in the first lens group, realize a wide angle of view, suppress the occurrence of aberrations, and reduce the size of the first lens group in the radial direction.

[0017] (2) Prism In this wide-angle lens, a prism is placed between the first and second lens groups, and the prism bends the light rays incident from the first lens group before they enter the second lens group. Generally, achieving a wide angle of view tends to increase the diameter of the front element and the overall optical length. However, in this wide-angle lens, the overall optical length can be shortened by using a prism to shorten the optical path length. Furthermore, by bending the optical path, not only the optical elements but also various other elements constituting the wide-angle lens can be arranged efficiently, allowing for overall space saving (reduction in volume) including the lens barrel, and thus enabling the overall miniaturization of the wide-angle lens.

[0018] The prism has an incident surface into which light rays enter from the first lens group, a reflective surface that reflects the light rays that entered through the incident surface in a predetermined angular direction, and an exit surface from which the light rays reflected by the reflective surface exit. The incident surface is positioned on the optical axis of the first lens group, and the exit surface is positioned on the optical axis of the second lens group. There are no particular limitations on the angle at which the light rays are bent by the reflective surface, but it is preferably 75° or more, 80° or more, or 85° or more, preferably 105° or less, 100° or less, or 95° or less, and more preferably 90°.

[0019] Furthermore, it is preferable that the incident surface of the prism has a positive refractive power. By making the incident surface of the prism a curved surface rather than a flat surface and arranging it to have a positive refractive power, the optical length of the second lens group can be shortened, making it easier to miniaturize the entire wide-angle lens.

[0020] Furthermore, it is preferable that the incident surface of the prism be aspherical. By making the incident surface of the prism aspherical, a wide-angle lens with high imaging performance can be realized without placing an aspherical lens in the first lens group. The lenses constituting the first lens group have a larger diameter than the lenses constituting the second lens group. Therefore, by making the incident surface of the prism aspherical, it becomes unnecessary to place an aspherical lens in the first lens group, which is advantageous in terms of cost reduction. Furthermore, since the first lens group is located on the object side, it is susceptible to ambient temperature changes, so it is preferable to use glass lenses. On the other hand, since the first lens group of the prism is located on the object side, it is less susceptible to ambient temperature changes compared to the first lens group. In this case, by appropriately setting the refractive power of the incident surface of the prism, it becomes easier to suppress fluctuations in the focal position even when using a plastic prism, and further cost reduction can be achieved.

[0021] (3) Second lens group By placing a second lens group with positive refractive power on the image plane side of the prism, the overall optical length after the prism can be shortened, thereby reducing the overall size of the wide-angle lens.

[0022] As long as the second lens group has positive refractive power, its specific optical configuration is not particularly limited, but for example, it is preferable that the lens positioned closest to the object in the second lens group is a positive lens. By positioning the positive lens closest to the object in the second lens group, it becomes easier to shorten the overall optical length. In this case, it is even more preferable for shortening the overall optical length if the side surface of the object is convex.

[0023] Furthermore, it is preferable that the lens positioned closest to the image plane in the second lens group is also a positive lens. By positioning a positive lens closest to the image plane, a beam of light that converges to the image plane can be incident, making it easier to shorten the overall optical length of the wide-angle lens.

[0024] (4) Aperture diaphragm In this wide-angle lens, the arrangement of the aperture diaphragm is not particularly limited. Here, the aperture diaphragm refers to the aperture diaphragm that defines the diameter of the light beam of the wide-angle lens, that is, the aperture diaphragm that defines the Fno of the optical system. However, it is preferable to place the aperture diaphragm within the second lens group or between the prism and the second lens group in order to miniaturize the wide-angle lens. Furthermore, when the positive lens is placed on the object side of the second lens group, it is preferable to place the aperture diaphragm on the image side of that positive lens in order to obtain a wide-angle lens with better optical performance and a smaller size.

[0025] 1-3.Formula The optical system preferably satisfies one or more of the following equations.

[0026] 1-3-1. Formula (1) 8.0 < fp / f < 13.0 (1) however, fp: Focal length of the prism f: Focal length of the wide-angle lens

[0027] Equation (1) above defines the ratio of the focal length of the prism to the focal length of the wide-angle lens. When equation (1) is satisfied, an appropriate positive refractive force is provided for the prism, and fluctuations in the focal position can be suppressed even when the ambient temperature changes, and good imaging performance can be maintained regardless of the ambient temperature. In other words, a wide-angle lens with good temperature characteristics can be obtained.

[0028] Conversely, if the value in equation (1) falls below the lower limit, the refractive power of the prism becomes too strong, making it difficult to suppress the shift in focal position due to changes in ambient temperature. In other words, it becomes difficult to obtain a wide-angle lens with good temperature characteristics, which is undesirable. On the other hand, if the value in equation (1) exceeds the upper limit, the refractive power of the prism becomes too weak, making it difficult to shorten the overall optical length. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0029] To obtain the above effect, the lower limit of equation (1) is more preferably 9.0, and even more preferably 9.5. Furthermore, the upper limit of equation (1) is more preferably 12.5, and even more preferably 12.0. However, the inequality sign (<) in equation (1) may be replaced with an equality sign (≦).

[0030] 1-3-2. Formula (2) 1.2 < |f1| / f < 1.7 (2) however, f1: Focal length of the first lens group

[0031] Equation (2) above defines the ratio of the focal length of the first lens group to the focal length of the wide-angle lens. When equation (2) is satisfied, it is possible to correct various aberrations and miniaturize the optical system at the same time, making it easier to miniaturize the wide-angle lens.

[0032] Conversely, if the value in equation (2) falls below the lower limit, the refractive power of the first lens group becomes too strong, making it difficult to correct field curvature and astigmatism, which is undesirable. On the other hand, if the value in equation (2) exceeds the upper limit, the refractive power of the first lens group becomes too weak, making it difficult to reduce the diameter of each lens constituting the first lens group. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0033] To obtain the above effect, the lower limit of equation (2) is more preferably 1.3, and even more preferably 1.4. Furthermore, the upper limit of equation (2) is more preferably 1.6, and even more preferably 1.5.

[0034] 1-3-3. Formula (3) 1.5 < f2 / f < 4.5 (3) however, f2: Focal length of the second lens group

[0035] Equation (3) above defines the ratio of the focal length of the second lens group to the focal length of the wide-angle lens. When equation (3) is satisfied, it is possible to correct various aberrations and miniaturize the optical system at the same time, making it easier to miniaturize the wide-angle lens.

[0036] Conversely, if the value in equation (3) falls below the lower limit, the refractive power of the second lens group becomes too strong, making it difficult to correct spherical aberration and axial chromatic aberration, which is undesirable. On the other hand, if the value in equation (3) exceeds the upper limit, the refractive power of the second lens group becomes too weak, making it difficult to shorten the overall length. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0037] To obtain the above effect, the lower limit of equation (3) is more preferably 2.0, and even more preferably 2.5. Furthermore, the upper limit of equation (3) is more preferably 4.0, and even more preferably 3.5.

[0038] 1-3-4. Formula (4) 0.2 < |f1| / f2 < 0.8 (4) however, f1: Focal length of the first lens group f2: Focal length of the second lens group

[0039] Equation (4) above defines the ratio of the focal length of the first lens group to the focal length of the second lens group. When equation (4) is satisfied, it is possible to correct various aberrations and miniaturize the optical system at the same time, making it easier to miniaturize the wide-angle lens.

[0040] Conversely, if the value in equation (4) falls below the lower limit, the refractive power of the first lens group becomes too strong, making it difficult to correct field curvature and astigmatism, or the refractive power of the second lens group becomes too weak, making it difficult to shorten the overall optical length, which is undesirable. On the other hand, if the value in equation (4) exceeds the upper limit, the refractive power of the first lens group becomes too weak, making it difficult to reduce the diameter of each lens constituting the first lens group, or the refractive power within the second lens group becomes too strong, making it difficult to correct spherical aberration and axial chromatic aberration, which is undesirable.

[0041] To obtain the above effect, the lower limit of equation (4) is more preferably 0.3, and even more preferably 0.4. Furthermore, the upper limit of equation (4) is more preferably 0.7, and even more preferably 0.6.

[0042] 1-3-5. Formula (5) 0.2 < R12 / |f11| < 0.8 (5) however, R12: Radius of curvature of the image surface of the first negative lens f11: Focal length of the first negative lens

[0043] Equation (5) above defines the refractive power of the image side of the first negative lens. By satisfying equation (5), it is possible to correct various aberrations and miniaturize the optical system, making it easier to miniaturize the wide-angle lens.

[0044] Conversely, if the value in equation (5) falls below the lower limit, the refractive power of the image side of the first negative lens becomes too strong, making it difficult to correct field curvature and astigmatism, which is undesirable. On the other hand, if the value in equation (5) exceeds the upper limit, the refractive power of the image side of the first negative lens becomes too weak, making it difficult to reduce the diameter of each lens constituting the first lens group. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0045] To obtain the above effect, the lower limit of equation (5) is more preferably 0.3, and even more preferably 0.4. Furthermore, the upper limit of equation (5) is more preferably 0.7, and even more preferably 0.6.

[0046] 1-3-6. Formula (6) 2.0 < f2f / f < 5.0 (6) however, f2f: The focal length of the lens in the second lens group that is closest to the object.

[0047] Equation (6) above defines the ratio between the focal length of the lens located closest to the object in the second lens group and the focal length of the wide-angle lens. When equation (6) is satisfied, it is possible to correct various aberrations and miniaturize the optical system at the same time, making it easier to miniaturize the wide-angle lens.

[0048] Conversely, if the value in equation (6) falls below the lower limit, the refractive power of the lens closest to the object in the second lens group becomes too strong, making it difficult to correct spherical aberration, which is undesirable. On the other hand, if the value in equation (6) exceeds the upper limit, the refractive power of the lens closest to the object in the second lens group becomes too weak, making it difficult to shorten the overall optical length. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0049] To obtain the above effect, the lower limit of equation (6) is more preferably 2.5, and even more preferably 3.0. Furthermore, the upper limit of equation (6) is more preferably 4.5, and even more preferably 4.0.

[0050] 1-3-7. Formula (7) 2.50 < f2r / f < 5.50 (7) however, f2r: The focal length of the lens located closest to the image sensor in the second lens group.

[0051] Equation (7) above defines the ratio between the focal length of the lens located closest to the image in the second lens group and the focal length of the wide-angle lens. Satisfying equation (7) makes it possible to correct various aberrations and miniaturize the optical system, which is preferable as it enables miniaturization of the wide-angle lens.

[0052] Conversely, if the value in equation (7) falls below the lower limit, the refractive power of the lens located closest to the image in the second lens group becomes too strong, making it difficult to correct field curvature and astigmatism, which is undesirable. On the other hand, if the value in equation (7) exceeds the upper limit, the refractive power of the lens located closest to the image in the second lens group becomes too weak, making it difficult to shorten the overall optical length. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0053] To obtain the above effect, the lower limit of equation (7) is more preferably 3.0, and even more preferably 3.5. Furthermore, the upper limit of equation (7) is more preferably 5.0, and even more preferably 4.4.

[0054] 1-3-8. Equations (8) and (9) 1.80 < N1 ·····(8) 20 < ν1 ·····(9) however, N1: Refractive index of the first negative lens with respect to the d line ν1: Abbe number for the d line of the first negative lens

[0055] Equations (8) and (9) above define the lower limit of the refractive index of the first negative lens with respect to the d line and the Abbe number with respect to the d line. When the first negative lens satisfies equations (8) and (9), it is possible to correct various aberrations and miniaturize the optical system at the same time, making it easier to miniaturize the wide-angle lens.

[0056] In contrast, if the value in equation (8) falls below the lower limit, in order to miniaturize the wide-angle lens, it becomes necessary to increase the curvature of the lens surface of the first negative lens and strengthen the refractive power of the first negative lens. In that case, it becomes difficult to correct off-axis aberrations, making it difficult to achieve both correction of various aberrations and miniaturization of the optical system, which is undesirable.

[0057] Furthermore, if the value in equation (9) falls below the lower limit, the chromatic aberration increases, making it difficult to correct the chromatic aberration with the lens on the image side of the first negative lens, which is undesirable as it makes it difficult to achieve miniaturization of the optical system.

[0058] To obtain the above effect, the lower limit of equation (8) is more preferably 1.90, and even more preferably 1.95. Also, the lower limit of equation (9) is more preferably 23, and even more preferably 25.

[0059] 1-3-9. Equations (10) and (11) 1.80 < N2 ·····(10) 20 < ν2 ·····(11) however, N2: Refractive index of the second negative lens with respect to the d line ν2: Abbe number for the d line of the second negative lens

[0060] Equations (10) and (11) above define the lower limit of the refractive index of the second negative lens with respect to the d line and the Abbe number with respect to the d line. When the second negative lens satisfies equations (10) and (11), it is possible to correct various aberrations and miniaturize the optical system at the same time, making it easier to miniaturize the wide-angle lens.

[0061] In contrast, if the value in equation (10) falls below the lower limit, in order to achieve miniaturization, it becomes necessary to increase the curvature of the lens surface of the second negative lens and strengthen the refractive power of the second negative lens. In that case, it becomes difficult to correct off-axis aberrations, making it difficult to achieve both correction of various aberrations and miniaturization of the optical system, which is undesirable.

[0062] Furthermore, if the value in equation (11) falls below the lower limit, the chromatic aberration becomes larger, making it difficult to correct chromatic aberration with the image lens on the image side of the second negative lens. This makes it difficult to achieve both correction of various aberrations and miniaturization of the optical system, which is undesirable.

[0063] To obtain the above effect, the lower limit of equation (10) is more preferably 1.90, and even more preferably 1.95. Also, the lower limit of equation (11) is more preferably 23, and even more preferably 25.

[0064] 1-3-10. Formula (12) 1.60 < Np ·····(12) however, Np: Refractive index of the prism with respect to the d line.

[0065] Equation (12) above defines the lower limit of the refractive index of a prism with respect to the d line. If equation (12) is satisfied, it becomes easier to miniaturize the wide-angle lens. In contrast, if the value in equation (12) falls below the lower limit, the optical path shortening within the prism becomes insufficient, making it difficult to shorten the overall optical length. Therefore, this is undesirable from the standpoint of miniaturizing the wide-angle lens.

[0066] To obtain the above effect, the lower limit of equation (12) is more preferably 1.63, and even more preferably 1.64.

[0067] 2. Imaging device Next, the imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the wide-angle lens according to the present invention and an image sensor that converts the optical image formed by the wide-angle lens into an electrical signal. It is preferable that the image sensor is provided on the image side of the optical system.

[0068] There are no particular limitations on the image sensor, and solid-state image sensors such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also be used. The imaging device according to the present invention is suitable for imaging devices using these solid-state image sensors, such as digital cameras and video cameras. Furthermore, the imaging device can be applied to various imaging devices such as single-lens reflex cameras, mirrorless cameras, digital still cameras, surveillance cameras, in-vehicle cameras, and drone-mounted cameras. These imaging devices may be interchangeable-lens imaging devices or fixed-lens imaging devices in which the lens is fixed to the housing. In particular, the wide-angle lens is suitable for the optical system of an imaging device mounted on a mobile body such as a drone. Because the wide-angle lens provides a wide field of view, it can acquire a lot of information necessary for autonomous navigation and monitoring the surroundings in a single image.

[0069] Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples. [Examples]

[0070] (1) Optical configuration Figure 1 is a cross-sectional view of a wide-angle lens according to Embodiment 1 of the present invention. As shown in Figure 1, the wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a prism P, and a second lens group G2 having positive refractive power.

[0071] The first lens group G1 consists of a negative meniscus lens L1 with a convex shape toward the object, a negative meniscus lens L2 with a convex shape toward the object, and a biconcave lens L3. Negative meniscus lenses L1 and L2 are the first negative lens and the second negative lens as referred to in this invention.

[0072] The incident surface of prism P has a convex shape toward the object and possesses positive refractive power. Furthermore, this incident surface is aspherical. The reflective surface of prism P bends the light rays incident from the first lens group G1 by 90° and causes them to incident on the second lens group G2.

[0073] The second lens group G2 consists, in order from the object side, of a positive lens L4 with a convex surface on the object side, an aperture diaphragm S, a cemented lens formed by joining a biconvex lens L5 and a biconcave lens L6, and a biconvex lens L7.

[0074] On the image plane side of the second lens group G2, an infrared cut filter IR, a cover glass CG, and an image plane IP are arranged in order from the object side. The image plane IP is, for example, the imaging surface of a solid-state image sensor such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. The configuration of the second lens group G2 and subsequent components is the same in other embodiments, so a further explanation will be omitted.

[0075] (2) Numerical Examples Next, we will describe a numerical example of the wide-angle lens. The lens data, various data, and aspherical data of the wide-angle lens are shown below. In the "(Lens Data)" column, "No." indicates the order of the lens surfaces counted from the object side (surface number), "R" indicates the radius of curvature of the lens surface, "D" indicates the distance between the lens surfaces on the optical axis, "Nd" indicates the refractive index for the d line (wavelength λ=587.6nm), and "ABV" indicates the Abbe number for the d line. In the "No." column, "STOP" displayed in the column following the surface number indicates an aperture diaphragm, and "ASPH" indicates an aspherical surface. Also, "0.0000" in the radius of curvature column indicates a plane. Note that in the numerical examples shown below, the unit of length is "mm" and the unit of field of view is "°".

[0076] In the "(Various Data)" section, "F" represents the focal length of the wide-angle lens, "Fno" is the F-number, and "W" is the half-angle of view.

[0077] "(Aspherical Data)" indicates the aspherical coefficient for each aspherical surface. However, an aspherical surface is defined by the following equation, where Z is the displacement from the vertex of the surface in the optical axis direction.

number

[0078] Furthermore, the values ​​of equations (1) to (12), the focal length f1 of the first lens group G1, the focal length fp of the prism, and the focal length f2 of the second lens group G2 are shown in Table 1 (discussed later). Since the details regarding these values ​​are the same in other embodiments, explanations are omitted below.

[0079] Figure 2 shows the longitudinal aberration diagrams for the wide-angle lens in the state of focus on an object at infinity. Each longitudinal aberration diagram, from left to right in the diagram, represents spherical aberration, astigmatism, and distortion. In the diagram representing spherical aberration, the vertical axis is the ratio to the maximum aperture, and the horizontal axis is defocus. The solid line represents the d line (wavelength λ=587.56nm), the short dashed line represents the C line (wavelength λ=656.28nm), and the long dashed line represents the F line (wavelength λ=486.13nm). In the diagram representing astigmatism, the vertical axis is the half-angle of view (W), and the horizontal axis is defocus. The solid line represents the sagittal image plane (X) relative to the d line, and the dashed line represents the meridional image plane (Y) relative to the d line. In the diagram representing distortion, the vertical axis is the half-angle of view (W), and the horizontal axis is the percentage. Since the same applies to the longitudinal aberration diagrams shown in other embodiments, the explanations for each of these figures will be omitted below.

[0080] (Lens data) No. RD Nd ABV 1 21.4690 1.1000 2.00100 29.13 2 10.7147 3.2840 3 18.4909 1.0000 2.00069 25.46 4 8.1302 5.1934 5 -19.2431 0.8000 1.49700 81.61 6 8.0756 2.6644 7ASPH 16.5336 11.9251 1.66134 20.37 8 0.0000 0.4239 9ASPH 7.9763 2.2096 1.85135 40.10 10ASPH -386.0510 1.2475 11STOP 0.0000 0.8696 12ASPH 6.6259 1.8793 1.80139 45.45 13 -7.0902 0.6500 1.92286 20.88 14 5.7333 1.9461 15ASPH 7.8592 2.1595 1.69350 53.20 16ASPH -66.1740 0.6476 17 0.0000 0.3000 1.51680 64.20 18 0.0000 1.0000 19 0.0000 0.5000 1.51680 64.20 20 0.0000 1.2000

[0081] (Various data) F 2.5400 Fno 2.0606 W 100.0000

[0082] (Aspherical data) No. K A4 A6 A8 A10 7 0.00000E+00 -9.67880E-05 -7.77733E-09 0.00000E+00 0.00000E+00 9 0.00000E+00 -6.65145E-05 -4.11614E-06 1.73634E-07 -2.79011E-09 10 0.00000E+00 -2.51737E-04 7.83045E-06 1.49524E-08 -2.89684E-09 12 -2.19884E+00 -5.14777E-06 3.66404E-05 -9.18442E-06 5.44024E-07 15 0.00000E+00 -1.63854E-04 1.02941E-05 -3.43640E-07 1.36595E-09 16 0.00000E+00 4.28676E-04 8.48339E-06 -1.09210E-06 1.09415E-08 [Examples]

[0083] (1) Optical configuration Figure 3 is a cross-sectional view of a wide-angle lens according to Embodiment 2 of the present invention. As shown in Figure 3, the wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a prism P, and a second lens group G2 having positive refractive power.

[0084] The first lens group G1 consists of a negative meniscus lens L1 with a convex shape toward the object, a negative meniscus lens L2 with a convex shape toward the object, and a biconcave lens L3. Negative meniscus lenses L1 and L2 are the first negative lens and the second negative lens as referred to in this invention.

[0085] The incident surface of prism P has a convex shape toward the object and possesses positive refractive power. Furthermore, this incident surface is aspherical. The reflective surface of prism P bends the light rays incident from the first lens group G1 by 90° and causes them to incident on the second lens group G2.

[0086] The aperture diaphragm S is located on the object side of the second lens group G2. The second lens group G2 consists of, in order from the object side, a positive lens L4 with a convex surface on the object side, a cemented lens formed by joining a biconvex lens L5 and a biconcave lens L6, and a biconvex lens L7.

[0087] (2) Numerical Examples Next, a numerical example of the wide-angle lens will be described. The lens data, various data, and aspherical data of the wide-angle lens are shown below. Figure 4 shows the longitudinal aberration diagram of the wide-angle lens when an object at infinity is in focus.

[0088] (Lens data) No. RD Nd ABV 1 21.4690 1.1000 2.00100 29.13 2 10.7148 3.2500 3 18.2944 1.0000 2.00069 25.46 4 8.1470 5.1725 5 -19.7190 0.8000 1.49700 81.61 6 8.0108 2.7675 7ASPH 17.6380 11.6724 1.66134 20.37 8 0.0000 0.2247 9STOP 0.0000 0.2000 10ASPH 8.0049 2.1099 1.85135 40.10 11ASPH -393.1684 1.3622 12 0.0000 0.9536 13ASPH 6.7114 1.9275 1.80139 45.45 14 -6.8347 0.6500 1.92286 20.88 15 5.8772 1.8820 16ASPH 7.8082 2.1690 1.69350 53.20 17ASPH -70.5918 0.6468 18 0.0000 0.3000 1.51680 64.20 19 0.0000 1.0000 20 0.0000 0.5000 1.51680 64.20 21 0.0000 1.2000

[0089] (Various data) F 2.5400 Fno 2.0659 W 100.0000

[0090] (Aspherical data) No. K A4 A6 A8 A10 7 0.00000E+00 -9.86212E-05 -3.33240E-08 0.00000E+00 0.00000E+00 10 0.00000E+00 -6.92420E-05 -4.33854E-06 1.69251E-07 -3.24773E-09 11 0.00000E+00 -2.25842E-04 5.87276E-06 4.23273E-08 -2.93111E-09 13 -2.14719E+00 -1.88289E-05 3.10465E-05 -7.97798E-06 4.47046E-07 16 0.00000E+00 -1.86404E-04 1.06672E-05 -3.56452E-07 8.72385E-10 17 0.00000E+00 4.14516E-04 8.45879E-06 -1.11082E-06 1.07027E-08 [Examples]

[0091] (1) Optical configuration Figure 5 is a cross-sectional view of the wide-angle lens of Embodiment 3 according to the present invention. As shown in Figure 5, the wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a prism P, and a second lens group G2 having positive refractive power.

[0092] The first lens group G1 consists of a negative meniscus lens L1 with a convex shape toward the object, a negative meniscus lens L2 with a convex shape toward the object, and a biconcave lens L3. Negative meniscus lenses L1 and L2 are the first negative lens and the second negative lens as referred to in this invention.

[0093] The incident surface of prism P has a convex shape toward the object and possesses positive refractive power. Furthermore, this incident surface is aspherical. The reflective surface of prism P bends the light rays incident from the first lens group G1 by 90° and causes them to incident on the second lens group G2.

[0094] The second lens group G2 consists of, in order from the object side, a positive lens L4 with a convex surface on the object side, an aperture diaphragm S, a biconvex lens L5, a biconcave lens L6, and a biconvex lens L7.

[0095] (2) Numerical Examples Next, a numerical example of the wide-angle lens will be described. The lens data, various data, and aspherical data of the wide-angle lens are shown below. Figure 6 shows the longitudinal aberration diagram of the wide-angle lens when an object at infinity is in focus.

[0096] (Lens data) No. RD Nd ABV 1 20.6909 1.1000 2.00100 29.13 2 10.2863 2.8454 3 16.0498 1.2787 2.00100 29.13 4 8.0555 4.4480 5 -25.3158 1.0000 1.49700 81.61 6 6.5814 4.4517 7ASPH 18.8598 9.1819 1.65096 21.51 8 0.0000 0.4570 9ASPH 9.4585 1.4020 1.85135 40.10 10ASPH -77.4121 0.8278 11STOP 0.0000 0.8723 12ASPH 4.3062 1.8548 1.49710 81.56 13ASPH -7.4700 0.2457 14 -15.2389 0.6500 1.92286 20.88 15 5.0914 2.1071 16ASPH 8.0323 2.2777 1.61881 63.85 17ASPH -69.2233 0.4000 18 0.0000 0.3000 1.51680 64.20 19 0.0000 1.0000 20 0.0000 0.5000 1.51680 64.20 21 0.0000 1.2000

[0097] (Various data) F 2.6000 Fno 2.5986 W 100.0000

[0098] (Aspherical data) No. K A4 A6 A8 A10 7 0.00000E+00 -3.15926E-04 -1.42160E-07 -2.01921E-07 8.79845E-09 9 0.00000E+00 9.10979E-05 1.85750E-05 1.06188E-06 1.20499E-07 10 0.00000E+00 -4.67436E-04 8.74141E-05 -1.46293E-06 2.19000E-07 12 -7.34431E-01 -9.99925E-04 2.63119E-04 -3.27812E-05 5.23012E-06 13 -8.06981E+00 9.67344E-05 1.51352E-04 -1.65739E-05 5.19462E-06 16 0.00000E+00 1.61436E-04 -2.76380E-05 1.14352E-06 -3.15725E-08 17 0.00000E+00 4.50619E-04 -1.58960E-05 -8.44948E-07 5.00151E-09 [Examples]

[0099] (1) Optical configuration Figure 7 is a cross-sectional view of the wide-angle lens of Embodiment 4 according to the present invention. As shown in Figure 7, the wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a prism P, and a second lens group G2 having positive refractive power.

[0100] The first lens group G1 consists of a negative meniscus lens L1 with a convex shape toward the object, a negative meniscus lens L2 with a convex shape toward the object, and a biconcave lens L3. Negative meniscus lenses L1 and L2 are the first negative lens and the second negative lens as referred to in this invention.

[0101] The incident surface of prism P has a convex shape toward the object and possesses positive refractive power. Furthermore, this incident surface is aspherical. The reflective surface of prism P bends the light rays incident from the first lens group G1 by 90° and causes them to incident on the second lens group G2.

[0102] The second lens group G2 consists, in order from the object side, of a positive lens L4 with a convex surface on the object side, an aperture diaphragm S, a cemented lens formed by joining a biconvex lens L5 and a biconcave lens L6, and a biconvex lens L7.

[0103] (2) Numerical Examples Next, a numerical example of the optical system will be described. Below are the lens data, various data, and aspherical data for the wide-angle lens. Figure 8 shows the longitudinal aberration diagram of the wide-angle lens when an object at infinity is in focus.

[0104] (Lens data) No. RD Nd ABV 1 21.4690 1.1000 2.00069 25.46 2 10.7145 3.1049 3 17.5054 1.0000 2.00069 25.46 4 8.2223 5.0947 5 -21.8175 1.0530 1.49700 81.61 6 7.5575 3.0568 7ASPH 18.7839 11.1983 1.65096 21.51 8 0.0000 0.4291 9ASPH 8.1735 1.9235 1.85135 40.10 10ASPH -366.9752 1.1395 11STOP 0.0000 1.5883 12ASPH 7.1645 2.3484 1.80139 45.45 13 -5.3434 0.6500 1.92286 20.88 14 6.3639 1.4482 15ASPH 7.6747 2.2173 1.69350 53.20 16ASPH -73.6406 0.5631 17 0.0000 0.3000 1.51680 64.20 18 0.0000 1.0000 19 0.0000 0.5000 1.51680 64.20 20 0.0000 1.2000

[0105] (Various data) F 2.5400 Fno 2.1398 W 100.0000

[0106] (Aspherical data) No. K A4 A6 A8 A10 7 0.00000E+00 -1.17225E-04 -9.19720E-09 0.00000E+00 0.00000E+00 9 0.00000E+00 -2.80797E-05 -7.09233E-06 3.78978E-07 -1.03341E-08 10 0.00000E+00 -1.31366E-04 -4.51656E-07 2.88881E-07 -9.15915E-09 12 -1.99006E+00 -4.92482E-05 5.79976E-06 -2.09607E-06 4.41940E-08 15 0.00000E+00 -2.11360E-04 1.15851E-05 -3.71257E-07 7.05605E-10 16 0.00000E+00 3.86371E-04 1.17588E-05 -1.32278E-06 1.42628E-08

[0107] [Table 1] Example 1 Example 2 Example 3 Example 4 Equation (1) fp / f 9.84 10.50 11.14 11.36 Equation (2) |f1| / f 1.42 1.43 1.41 1.45 Equation (3) f2 / f 3.02 3.02 2.91 2.99 Equation (4) |f1| / f2 0.47 0.47 0.49 0.49 Equation (5) R12 / |f11| 0.48 0.48 0.48 0.48 Equation (6) f2f / f 3.62 3.64 3.84 3.71 Equation (7) f2r / f 4.04 4.04 4.52 3.99 Equation (8) N1 2.00 2.00 2.00 2.00 Equation (9) ν1 29.1 29.1 29.1 25.46 Equation (10) N2 2.00 2.00 2.00 2.00 Equation (11) ν2 25.5 25.5 29.1 25.46 Equation (12) Np 1.66 1.66 1.65 1.65 f1 -3.60 -3.63 -3.68 -3.68 fp 25.00 26.67 28.97 28.86 f2 7.66 7.67 7.56 7.59

[0108] [summary] A wide-angle lens according to a first aspect of the present invention is composed of, in order from the object side, a first lens group having negative refractive power, a prism, and a second lens group having positive refractive power. The first lens group comprises, in order from the object side, a first negative lens and a second negative lens. The prism bends the light rays incident from the first lens group and causes them to enter the second lens group. The following equation is satisfied. 8.0 < fp / f < 13.0 (1) however, fp: focal length of the prism f: Focal length of the wide-angle lens

[0109] In the first embodiment, a wide-angle lens according to a second aspect of the present invention may satisfy the following formula. 1.2 < |f1| / f < 1.7 (2) however, f1: Focal length of the first lens group

[0110] A wide-angle lens according to a third aspect of the present invention may satisfy the following formula in the first or second aspect. 1.5 < f2 / f < 4.5 (3) however, f2: Focal length of the second lens group

[0111] A wide-angle lens according to the fourth aspect of the present invention may satisfy the following formula in any of the first to third aspects. 0.2 < |f1| / f2 < 0.8 (4) however, f1: Focal length of the first lens group f2: Focal length of the second lens group

[0112] A wide-angle lens according to the fifth aspect of the present invention may satisfy the following formula in any of the first to fourth aspects. 0.2 < R12 / |f11| < 0.8 (5) however, R12: Radius of curvature of the image surface of the first negative lens. f11: Focal length of the first negative lens

[0113] A wide-angle lens according to the sixth aspect of the present invention may satisfy the following formula in any of the first to fifth aspects. 2.0 < f2f / f < 5.0 (6) however, f2f: The focal length of the lens in the second lens group that is closest to the object.

[0114] A wide-angle lens according to the seventh aspect of the present invention may satisfy the following formula in any of the first to sixth aspects. 2.5 < f2r / f < 5.5 (7) however, f2r: The focal length of the lens located closest to the image sensor in the second lens group.

[0115] A wide-angle lens according to the eighth aspect of the present invention may satisfy the following formula in any of the first to seventh aspects. 1.80 < N1 ·····(8) 20 < ν1 ·····(9) however, N1: Refractive index of the first negative lens with respect to the d line. ν1: Abbe number of the first negative lens with respect to the d line.

[0116] A wide-angle lens according to the ninth aspect of the present invention may satisfy the following formula in any of the first to eighth aspects. 1.80 < N2 ·····(10) 20 < ν2 ·····(11) however, N2: Refractive index of the second negative lens with respect to the d line. ν2: Abbe number of the second negative lens with respect to the d line.

[0117] A wide-angle lens according to the tenth aspect of the present invention may satisfy the following formula in any of the first to ninth aspects. 1.60 < Np ·····(12) however, Np: Refractive index of the prism with respect to the d line.

[0118] In the wide-angle lens according to the eleventh aspect of the present invention, the incident surface of the prism may be aspherical in any of the first to tenth aspects.

[0119] An imaging device according to the twelfth aspect of the present invention comprises a wide-angle lens according to any of the first to eleventh aspects described above, and an image sensor that converts an optical image formed by the wide-angle lens into an electrical signal.

[0120] The wide-angle lens and imaging device described in the above embodiments and examples are one aspect of the wide-angle lens and imaging device according to the present invention, and correspond to the wide-angle lens according to the first to eleventh embodiments and the imaging device according to the twelfth embodiment. The wide-angle lens and imaging device according to each of the above embodiments will produce the same effects as those described in the above embodiments and examples. The wide-angle lens and imaging device according to the present invention are not limited to the wide-angle lens and imaging device described in the embodiments and examples, and can be appropriately modified within the range of the wide-angle lens and imaging device according to each of the above embodiments. [Industrial applicability]

[0121] According to the present invention, it is possible to provide a wide-angle lens and imaging device that have good temperature characteristics, are compact, and are low cost. [Explanation of symbols]

[0122] G1 First Lens Group G2 Second Lens Group CG cover glass IP image plane IR infrared cut filter P Prism

Claims

1. Starting from the object side, it consists of a first lens group with negative refractive power, a prism, and a second lens group with positive refractive power. Starting from the object side, the first lens group consists of a negative lens, a negative lens, and a negative lens, and the second lens group consists of a positive lens, a positive lens, a negative lens, and a positive lens. The first lens group comprises, in order from the object side, a first negative lens and a second negative lens. The prism is made of plastic material, The refractive index of the d-line of the aforementioned plastic material is set to 1.65096 or higher. The prism bends the light rays incident from the first lens group and causes them to enter the second lens group. A wide-angle lens characterized by satisfying the following equation. 8.0 < fp / f < 13.0 (1) 1.2 < |f1| / f < 1.7 (2) 1.5 < f2 / f < 4.5 (3) however, fp: Focal length of the prism f: Focal length of the wide-angle lens f1: Focal length of the first lens group f2: Focal length of the second lens group

2. A wide-angle lens according to claim 1, satisfying the following formula. 0.2 < |f1| / f2 < 0.8 (4) however, f1: Focal length of the first lens group f2: Focal length of the second lens group

3. A wide-angle lens according to claim 1, satisfying the following formula. 0.2 < R12 / | f11 | < 0.8 (5) however, R12: Radius of curvature of the image surface of the first negative lens. f11: Focal length of the first negative lens

4. A wide-angle lens according to claim 1, satisfying the following formula. 2.0 < f2f / f < 5.0 (6) however, f2f: The focal length of the lens located closest to the object in the second lens group.

5. A wide-angle lens according to claim 1, satisfying the following formula. 2.5 < f2r / f < 5.5 (7) however, f2r: The focal length of the lens located furthest towards the image in the second lens group.

6. A wide-angle lens according to claim 1, satisfying the following formula. 1.80 < N1 (8) 20 < ν1 (9) however, N1: Refractive index of the first negative lens with respect to the d line ν1: Abbe number of the first negative lens with respect to the d line.

7. A wide-angle lens according to claim 1, satisfying the following formula. 1.80 < N2 (10) 20 < ν2 (11) however, N2: Refractive index of the second negative lens with respect to the d line ν²: Abbe number of the second negative lens with respect to the d line.

8. A wide-angle lens according to claim 1, satisfying the following formula. 1.60 < Np (12) however, Np: Refractive index of the prism with respect to the d line.

9. The wide-angle lens according to claim 1, wherein the incident surface of the prism is aspherical.

10. An imaging device comprising a wide-angle lens according to any one of claims 1 to 9, and an image sensor that converts an optical image formed by the wide-angle lens into an electrical signal.

Images