Imaging lens and imaging device

Abstract

To realize a compact, bright, and stable imaging lens and imaging device. [Solution] The imaging lens of the imaging device (1) has a negative first lens (L1), a positive second lens (L2) having a meniscus shape, an aperture diaphragm (SP), a positive third lens (L3), and a positive cemented lens formed by a positive fourth lens (L4) and a negative fifth lens (L5), and satisfies a specific formula relating to the second and third lenses (L2, L3).

Description

[Technical Field]

[0001] This invention relates to an imaging lens and an imaging device. [Background technology]

[0002] Portable imaging devices such as SLR cameras, mirrorless cameras, and digital still cameras, as well as fixed imaging devices such as surveillance imaging devices and in-vehicle imaging devices, have long been in widespread use. These imaging devices utilize solid-state image sensors such as CCD (Charge Coupled Device) sensors or CMOS (Complementary Metal Oxide Semiconductor) sensors. The imaging lenses used in these imaging devices are required to be high-performance as the pixel count of solid-state image sensors increases.

[0003] Furthermore, in recent years, systems called ADAS (Advanced Driver Assistance Systems), which use in-vehicle imaging devices to perform sensing and provide appropriate driving assistance based on the analysis of images obtained from these devices, have begun to spread. The imaging lenses that make up these in-vehicle imaging devices are required to be small and inexpensive, yet capable of producing high-resolution images and having minimal performance changes due to eccentricity sensitivity.

[0004] An optical system is known for such imaging lenses, consisting of a negative lens with a concave shape facing the image plane, a positive lens, a biconvex lens, and a cemented lens having positive combined power, arranged in order from the object side to the image plane side (see, for example, Patent Document 1). Alternatively, an optical system is known for such imaging lenses, consisting of a negative lens with a concave shape facing the image plane side, a positive lens, a biconvex lens, a negative lens, and a positive lens, arranged in order from the object side to the image plane side (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-75141 [Patent Document 2] Japanese Patent Publication No. 2020-38401 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, there has been a demand for bright optical systems with large aperture ratios to accommodate high resolution, and when considering their use as imaging devices for in-vehicle sensing, even brighter imaging lenses are required.

[0007] However, in the optical system disclosed in Patent Document 1, the F-number is approximately 2.0, which may not ensure sufficient brightness. Furthermore, in the optical system disclosed in Patent Document 1, attempting to increase the aperture ratio makes it difficult to ensure optical performance because the power distribution of each lens is not appropriate. In addition, in the optical system disclosed in Patent Document 2, the power configuration of the lenses closer to the image plane is positive-negative-positive, which increases the eccentricity sensitivity of each lens, making it difficult to adjust the lens arrangement and thus difficult to ensure stable optical performance. Thus, there is still room for improvement in the prior art from the viewpoint of realizing an imaging lens that is compact, bright, and has stable optical performance.

[0008] One aspect of the present invention aims to realize an imaging lens and imaging device that are compact, bright, and have stable optical performance. [Means for solving the problem]

[0009] To solve the above problems, an imaging lens according to one aspect of the present invention comprises, in order from the object side toward the image plane side, a first lens having negative refractive power, a meniscus-shaped second lens having positive refractive power, an aperture diaphragm, a third lens having positive refractive power, and a cemented lens having positive combined refractive power formed by joining a fourth lens having positive refractive power and a fifth lens having negative refractive power, and satisfying the following formula. 0.825 ≦ D23 / f ≦ 1.850 (1-1) 0.48 ≦ L_D3 / f ≦ 1.20 (1-2) However, D23: The on-axis surface distance between the second lens and the third lens f: The focal length of the imaging lens L_D3: The center thickness of the third lens

[0010] Also, in order to solve the above problems, an imaging device according to an aspect of the present invention includes the above imaging lens and an imaging element that converts an optical image formed by the imaging lens on the image plane side into an electrical signal.

Effect of the Invention

[0011] According to an aspect of the present invention, an imaging lens and an imaging device that are small, bright, and have stable optical performance can be realized.

Brief Description of the Drawings

[0012] [Figure 1] It is a diagram schematically showing the lens configuration of the imaging lens of Example 1. [Figure 2] It is a diagram showing the longitudinal aberration of the imaging lens of Example 1. [Figure 3] It is a diagram schematically showing the lens configuration of the imaging lens of Example 2. [Figure 4] It is a diagram showing the longitudinal aberration of the imaging lens of Example 2. [Figure 5] It is a diagram schematically showing the lens configuration of the imaging lens of Example 3. [Figure 6] It is a diagram showing the longitudinal aberration of the imaging lens of Example 3. [Figure 7] It is a diagram schematically showing the lens configuration of the imaging lens of Example 4. [Figure 8] It is a diagram showing the longitudinal aberration of the imaging lens of Example 4. [Figure 9] It is a diagram schematically showing the lens configuration of the imaging lens of Example 5. [Figure 10]It is a diagram showing the longitudinal aberration of the imaging lens of Example 5. [Figure 11] It is a diagram schematically showing the lens configuration of the imaging lens of Example 6. [Figure 12] It is a diagram showing the longitudinal aberration of the imaging lens of Example 6. [Figure 13] It is a diagram schematically showing the configuration of an imaging device according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0013] In the following description, a "lens" does not include a parallel plate and can be a single lens. Examples of a single lens include a biconvex lens, a plano-convex lens, a convex meniscus lens, and a concave meniscus lens. The lens may be a spherical lens or an aspherical lens. An aspherical lens means a lens in which at least one lens surface is an aspherical surface. Examples of the aspherical lens include a composite lens having an aspherical resin layer on at least one lens surface of the lens, and a glass mold type aspherical lens made of glass material and having at least one lens surface with an aspherical shape. Also, a "cement lens" means a structure in which two or more single lenses are integrated without an air gap.

[0014] Also, in the following description, "refractive power" is also referred to as "power", a lens having a positive refractive power is also referred to as a "positive lens", and a lens having a negative refractive power is also referred to as a "negative lens".

[0015] 〔Imaging Lens〕 An imaging lens according to one embodiment of the present invention may have a configuration consisting of, in order from the object side to the image plane side, a first lens having negative power, a meniscus-shaped second lens having positive power, an aperture diaphragm, a third lens having positive power, and a cemented lens of a positive fourth lens having positive combined power and a negative fifth lens. This configuration is preferable in automotive camera applications from the viewpoint of achieving miniaturization and high-performance imaging. From the above viewpoint, it is preferable that the imaging lens has only the first to fifth lenses described above as its constituent lenses.

[0016] [Optical configuration] <First Lens> The first lens has negative refractive power. The first lens can be appropriately selected from known negative lenses.

[0017] <Second Lens> The second lens has a meniscus shape and positive refractive power. The second lens can be appropriately selected from known positive meniscus lenses.

[0018] The second lens is preferably a positive meniscus lens with its convex surface facing the image plane. By employing such a positive meniscus lens for the second lens, the principal point of the second lens can be positioned on the image plane side (rear) of the second lens. Therefore, the above configuration is preferable from the viewpoint of securing space on the image plane side (rear) of the second lens.

[0019] <Third Lens> The third lens has a positive refractive power. The third lens can be appropriately selected from known positive lenses.

[0020] <Bonded Lens> The imaging lens of this embodiment has a cemented lens formed by joining a fourth lens having positive refractive power and a fifth lens having negative refractive power, and having a positive combined refractive power. Having this cemented lens is preferable from the viewpoint of effectively correcting aberrations generated by the first and second lenses. Furthermore, in order to shorten the overall length of the imaging lens, it is desirable to have fewer lenses, and having this cemented lens is also preferable from the viewpoint of miniaturizing the imaging lens. Thus, having this cemented lens is preferable from the viewpoint of maintaining good spherical aberration correction and chromatic aberration correction, especially even with significant constraints on diameter and overall length, and is preferable from the viewpoint of realizing an imaging lens with good aberration performance.

[0021] The fourth lens has a positive refractive power. The positive refractive power of the fourth lens can be appropriately determined within the range in which the cemented lens, when combined with the fifth lens, has a positive combined refractive power. The fourth lens can be appropriately selected from known positive lenses within the range in which it can form a cemented lens with the fifth lens.

[0022] The fifth lens has a negative refractive power. The negative refractive power of the fifth lens can be appropriately determined within the range in which the cemented lens, when combined with the fourth lens, has a positive combined refractive power. The fifth lens can be appropriately selected from known negative lenses within the range in which it can form a cemented lens with the fourth lens.

[0023] <Opening diaphragm> The aperture diaphragm is positioned between the second and third lenses. The aperture diaphragm can be located anywhere in the optical path between the second and third lenses; any position is acceptable as long as sufficient brightness and optical performance can be achieved with the imaging lens. The position of the aperture diaphragm can be determined, for example, depending on the configuration of the lens barrel housing the imaging lens.

[0024] <Other optical elements> In addition to the lens and aperture diaphragm described above, the imaging lens of this embodiment may include other optical elements as further optical elements, to the extent that the effects of the present invention can be obtained. Examples of further optical elements include optical filters, faceplates, quartz low-pass filters, and infrared cut filters. For example, it is preferable for the imaging lens to include the above filters between the final lens and the image plane from the viewpoint of reducing the diameter of the entire lens system.

[0025] Furthermore, while it is preferable that there is an air gap between the second and third lenses from the viewpoint of obtaining the optical effects of the second and third lenses, other optical elements, such as the aforementioned additional optical elements, may be interposed between the second and third lenses. [Optical properties] From the viewpoint of realizing a compact, bright, and stable optical performance imaging lens, it is preferable that the imaging lens of this embodiment satisfies at least one of the following formulas.

[0026] <Formula (1-1)> 0.825 ≤ D23 / f ≤ 1.850 (1-1) however, D23: Distance between the planes of the second and third lenses on the axis. f: Focal length of the imaging lens

[0027] Equation (1-1) relates to the ratio of the distance between the second and third lenses to the focal length of the imaging lens. Note that D23 is the air-equivalent length. When D23 / f exceeds 1.850, the diameter of the light beam incident on the third lens increases, and the diameters of the third lens and the lenses closer to the image plane tend to increase. As a result, the radial and longitudinal dimensions of the imaging lens become larger, making it difficult to miniaturize the imaging lens. Also, if the imaging lens is a bright lens with a small F-number, the increased diameter of the light beam increases spherical aberration, which can make it difficult to correct aberrations in the entire imaging lens. When D23 / f is less than 0.825, the distance between the front group (first and second lenses) and the rear group (third to fifth lenses) is too close, making it difficult to adequately correct chromatic aberration and distortion generated in the front group with the rear group. Also, the increased power of the rear group to correct aberrations increases the eccentricity sensitivity, making it difficult to adjust the arrangement of each lens in the imaging lens, and making it difficult to ensure good optical performance.

[0028] From the viewpoint of miniaturization and good aberration correction, D23 / f is more preferably 1.750 or less, and even more preferably 1.200 or less. Furthermore, from the viewpoint of good aberration correction and ensuring good optical performance, D23 / f is more preferably 1.000 or more, and even more preferably 1.200 or more.

[0029] <Formula (1-2)> 0.48 ≤ L_D3 / f ≤ 1.20 (1-2) however, L_D3: Center thickness of the third lens f: Focal length of the imaging lens

[0030] Equation (1-2) relates to the ratio of the center thickness of the third lens to the focal length of the imaging lens. If L_D3 / f exceeds 1.20, the thickness of the third lens increases, axial chromatic aberration increases, and it becomes difficult to ensure the optical performance of the imaging lens, especially if it is a bright imaging lens with a small F-number. In addition, the overall length of the imaging lens increases, which is undesirable from the standpoint of miniaturization. If L_D3 / f is less than 0.48, the eccentricity sensitivity increases, making it difficult to adjust the arrangement of each lens in the imaging lens, and thus difficult to ensure good optical performance. Furthermore, it becomes difficult to secure the necessary edge material for manufacturing, which is undesirable from the standpoint of productivity.

[0031] From the viewpoint of ensuring optical performance and miniaturizing in the axial direction, L_D3 / f is more preferably 1.10 or less, and even more preferably 1.00 or less. Furthermore, from the viewpoint of suppressing changes in optical characteristics due to changes in eccentricity sensitivity and from the viewpoint of productivity, L_D3 / f is more preferably 0.53 or more, and even more preferably 0.55 or more.

[0032] <Formula (2)> -0.120≦f_L1 / f_L45≦-0.010 (2) however, f_L1: Focal length of the first lens f_L45: Focal length of the cemented lens

[0033] Equation (2) relates to an appropriate ratio of the refractive power of the first lens to the refractive power of the cemented lens. It is preferable for the imaging lens to satisfy equation (2) from the viewpoint of achieving both good correction of various aberrations and miniaturization of the imaging lens. If f_L1 / f_L45 is less than -0.120, the amount of aberration generated in the fourth and fifth lenses will increase, and astigmatism, coma aberration, and lateral chromatic aberration may worsen. If f_L1 / f_L45 exceeds -0.010, the amount of aberration generated in the first lens will increase, and coma aberration may worsen.

[0034] From the viewpoint of good aberration correction, f_L1 / f_L45 is more preferably -0.090 or higher, and even more preferably -0.080 or higher. Also, from the viewpoint of good coma aberration correction, f_L1 / f_L45 is more preferably -0.015 or lower.

[0035] <Formula (3)> 0.180 ≤ f_L3 / f_L2 ≤ 0.600 (3) however, f_L2: Focal length of the second lens f_L3: Focal length of the third lens

[0036] Equation (3) relates to the ratio of the focal length of the second lens to the focal length of the third lens. If f_L3 / f_L2 is less than 0.180, the error sensitivity corresponding to the eccentricity of the third lens relative to the optical axis tends to increase. If f_L3 / f_L2 exceeds 0.600, coma aberration and astigmatism tend to occur or become larger.

[0037] From the viewpoint of suppressing changes in optical characteristics due to changes in eccentricity sensitivity, f_L3 / f_L2 is more preferably 0.200 or higher, and even more preferably 0.250 or higher. Furthermore, from the viewpoint of suppressing the occurrence of aberrations, f_L3 / f_L2 is more preferably 0.550 or lower, and even more preferably 0.450 or lower.

[0038] <Formula (4)> 4.00 ≤ f_L2 / f ≤ 10.00 (4) however, f_L2: Focal length of the second lens f: Focal length of the imaging lens

[0039] Equation (4) relates to an appropriate ratio of the positive refractive power of the second lens to the refractive power of the imaging lens. It is preferable for the imaging lens to satisfy equation (4) from the viewpoint of achieving good correction of aberrations in the imaging lens and miniaturization. If f_L2 / f is less than 4.00, the positive refractive power of the second lens becomes too strong, which may cause coma and astigmatism. If f_L2 / f exceeds 10.00, the positive refractive power of the second lens becomes too weak, making it difficult to shorten the overall length of the imaging lens.

[0040] From the viewpoint of suppressing the occurrence of aberrations, f_L2 / f is more preferably 4.50 or higher, and even more preferably 5.00 or higher. Furthermore, from the viewpoint of miniaturizing the imaging lens in the axial direction, f_L2 / f is more preferably 9.50 or lower, and even more preferably 8.50 or lower.

[0041] <Formula (5)> -1.00 ≤ f_L1 / f_L3 ≤ -0.30 (5) however, f_L1: Focal length of the first lens f_L3: Focal length of the third lens

[0042] Equation (5) relates to the ratio of the focal length of the first lens to the focal length of the third lens. If f_L1 / f_L3 is less than -1.00, the image plane may be under-tilted, resulting in an image that is out of focus in both the center and the periphery of the screen. If f_L1 / f_L3 is greater than -0.30, the image plane may be over-tilted, also resulting in an image that is out of focus in both the center and the periphery of the screen.

[0043] From the viewpoint of suppressing under-tilting of the image plane, f_L1 / f_L3 is more preferably -0.95 or greater, and even more preferably -0.85 or greater. Also, from the viewpoint of suppressing over-tilting of the image plane, f_L1 / f_L3 is more preferably -0.40 or less, and even more preferably -0.50 or less.

[0044] <Formula (6)> 0.010≦f_L3 / f_L45≦0.150(6) however, f_L3: Focal length of the third lens f_L45: Focal length of the cemented lens

[0045] Equation (6) relates to the ratio of the focal length of the third lens to the combined focal length in a cemented lens of the fourth and fifth lenses. Preferably, the third lens has a positive refractive power mainly related to image formation. For this reason, it is preferable to set the ratio of the focal lengths of the third lens and the cemented lens to one that can effectively correct spherical aberration and coma aberration while considering miniaturization in the axial direction of the imaging lens or ensuring sufficient back focus.

[0046] If f_L3 / f_L45 is less than 0.010, the back focus of the imaging lens may be too short, making assembly impossible, or spherical aberration caused by the third lens may not be corrected. If f_L3 / f_L45 exceeds 0.150, the overall length of the imaging lens may become too large, or coma aberration caused by the cemented lens may not be corrected.

[0047] From the viewpoint of enabling assembly and good correction of aberrations, f_L3 / f_L45 is more preferably 0.012 or greater, and even more preferably 0.015 or greater. Furthermore, from the viewpoint of miniaturizing the imaging lens in the axial direction and good correction of spherical aberrations, f_L3 / f_L45 is more preferably 0.012 or greater, even more preferably 0.015 or greater, more preferably 0.125 or less, and even more preferably 0.098 or less.

[0048] <Formula (7)> -3.00 <G45L1SF<-1.20 (7) Equation (7) relates to the shape (shaping factor) of the cemented lens. In equation (7), "G45L1SF" is expressed by the following equation (7-1).

[0049] G45L1SF=(G4L1Lr+G5L1Rr) / (G4L1Lr-G5L1Rr) (7-1) In equation (7-1), "G4L1Lr" is the radius of curvature of the lens surface on the object side of the fourth lens, and "G5L1Rr" is the radius of curvature of the lens surface on the image side of the fifth lens. It is preferable for the imaging lens to satisfy equation (7) from the viewpoint of good correction of chromatic aberration and coma aberration.

[0050] If the G45L1SF is -3.00 or lower, the radius of curvature of the fourth lens may become too large, resulting in insufficient refractive power and potentially increasing the overall length of the imaging lens. Also, the radius of curvature of the fifth lens may become too small, leading to excessive correction of coma and astigmatism. If the G45L1SF is -1.20 or higher, the radius of curvature of the fourth lens may become too small, resulting in insufficient correction of spherical and coma. Also, the radius of curvature of the fifth lens may become too large, resulting in insufficient correction of coma and astigmatism.

[0051] From the viewpoint of miniaturizing the imaging lens in the axial direction and achieving good correction of coma and astigmatism, the G45L1SF is more preferably -2.50 or higher. Furthermore, from the viewpoint of achieving good correction of spherical and coma, the G45L1SF is more preferably -1.40 or lower, and even more preferably -1.50 or lower.

[0052] <Formula (8)> -3.00 ≤ f_L1 / f ≤ -1.00 (8) however, f_L1: Focal length of the first lens f: Focal length of the imaging lens

[0053] Equation (8) relates to an appropriate ratio of the refractive power of the first lens to the refractive power of the imaging lens. It is preferable for the imaging lens to satisfy equation (8) from the viewpoint of good correction of aberrations in the imaging lens and from the viewpoint of realizing a compact imaging lens with a deep depth of field.

[0054] If f_L1 / f is less than -3.00, the negative refractive power of the first lens becomes too weak, making it difficult to shorten the overall length of the imaging lens. If f_L1 / f exceeds -1.00, the negative refractive power of the first lens becomes too strong, making coma and astigmatism more likely to occur and more pronounced. Also, if f_L1 / f exceeds -1.00, the radius of curvature of the image-plane side of the first lens becomes too small, making it easier for the error sensitivity corresponding to the eccentricity of the first lens with respect to the optical axis to increase.

[0055] From the viewpoint of miniaturizing the imaging lens in the axial direction, f_L1 / f is more preferably -2.50 or higher, and even more preferably -1.74 or higher. Furthermore, from the viewpoint of suppressing the occurrence of coma aberration and astigmatism, and from the viewpoint of suppressing changes in optical characteristics due to changes in eccentricity sensitivity, f_L1 / f is more preferably -1.10 or lower, and even more preferably -1.20 or lower.

[0056] <Formula (9)> -0.400≦f_L1 / f_L2≦-0.200 (9) however, f_L1: Focal length of the first lens f_L2: Focal length of the second lens

[0057] Equation (9) relates to an appropriate ratio of the refractive power of the first lens to the refractive power of the second lens. It is preferable for the imaging lens to satisfy equation (9) from the viewpoint of good correction of various aberrations and from the viewpoint of miniaturization of the imaging lens.

[0058] If f_L1 / f_L2 is less than -0.400, the refractive power of the first lens becomes too weak, which can lead to an increased height of light rays entering the first lens, and consequently, an increase in the diameter of the first lens. Also, if f_L1 / f_L2 is less than -0.400, the refractive power of the second lens becomes too strong, resulting in insufficient performance against eccentricity, and it may become difficult to secure the desired optical characteristics of the imaging lens. Furthermore, if f_L1 / f_L2 exceeds -0.200, the refractive power of the first lens becomes too strong, causing the focal point of the first lens to shift towards the image plane. As a result, the overall length of the imaging device may increase. Moreover, if f_L1 / f_L2 exceeds -0.200, the Petzval sum becomes large, which may lead to excessive correction of field curvature.

[0059] From the viewpoint of miniaturizing the imaging lens in the radial direction and ensuring optical characteristics, f_L1 / f_L2 is more preferably -0.350 or greater, and even more preferably -0.300 or greater. Furthermore, from the viewpoint of miniaturizing the imaging lens in the axial direction and good correction of field curvature, f_L1 / f_L2 is more preferably -0.205 or less.

[0060] <Formula (10)> 1.00 <G1L1SF<3.00 (10) Equation (10) relates to the shape (shaping factor) of the first lens. In equation (10), "G1L1SF" is expressed by the following equation (10-1).

[0061] G1L1SF=(G1L1Lr+G1L1Rr) / (G1L1Lr-G1L1Rr) (10-1) In equation (10-1), "G1L1Lr" is the radius of curvature of the object-side lens surface of the first lens, and "G1L1Rr" is the radius of curvature of the image-side lens surface of the first lens. It is preferable for the imaging lens to satisfy equation (10) from the viewpoint of good correction of astigmatism and distortion.

[0062] If G1L1SF is 1.00 or less, the radius of curvature of the first lens becomes too large, resulting in insufficient refractive power and potentially increasing the overall length of the imaging lens. If the G1L1SF is set to 3.00 or higher, the radius of curvature of the first lens may become too small, resulting in insufficient correction of astigmatism and distortion.

[0063] From the viewpoint of good correction of astigmatism and distortion, the G1L1SF is more preferably 2.70 or less, and even more preferably 2.10 or less.

[0064] <Formula (11)> 0.500 ≤ D23 / BF ≤ 1.000 (11) however, D23: Distance between the planes of the second and third lenses on the axis. BF: Back focus of the imaging lens

[0065] Equation (11) relates to the ratio of the on-axial inter-plane distance between the second lens and the third lens to the back focus of the imaging lens. "Back focus" is the air-equivalent value of the distance from the lens surface on the image plane side of the fifth lens to the paraxial image plane. D23 is also an air-equivalent length.

[0066] If D23 / BF exceeds 1.000, the distance between the second and third lenses may become too large, potentially increasing the overall length of the imaging lens. Additionally, the increased light height entering the third lens can make spherical aberration correction difficult. If D23 / BF is less than 0.500, the back focus may become too large, potentially increasing the overall length of the imaging lens.

[0067] From the viewpoint of miniaturizing the imaging lens in the axial direction and achieving good correction of spherical aberration, D23 / BF is more preferably 0.900 or less, and even more preferably 0.850 or less. Furthermore, from the viewpoint of miniaturizing the imaging lens in the axial direction, D23 / BF is more preferably 0.600 or more, and even more preferably 0.700 or more.

[0068] [Imaging device] An imaging device according to one embodiment of the present invention has the optical system described above. The configuration of the imaging device of this embodiment is schematically shown in Figure 13. As shown in Figure 13, the imaging device 1 has a main body 20 and a lens barrel 10. The imaging device 1 is, for example, an in-vehicle imaging device.

[0069] The main body 20 includes an image sensor and a cover glass CG. The image sensor is a photoelectric conversion element that converts an optical image into an electrical signal, and is, for example, a solid-state image sensor. Examples of solid-state image sensors include CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors. The code IP represents the surface (image plane) of the image sensor.

[0070] The lens barrel 10 is detachably attached to the main body 20 and contains, in this order on the optical axis OA, a first lens L1, a second lens L2, a third lens L3, and a cemented lens formed by the fourth lens L4 and the fifth lens L5. The first lens L1 to the fifth lens L5 constitute the imaging lens of this embodiment as described above. The optical axis OA is the optical axis common to each lens of the lens barrel 10 and the image sensor of the main body 20.

[0071] In the imaging device 1, light incident on the object side of the imaging lens of this embodiment is ultimately formed as an image on the imaging surface of the image sensor. The image sensor then converts the received light into an electrical signal, generating a digital image corresponding to the image of the subject. The digital image can be recorded on a recording medium such as an HDD (Hard Disk Device), memory card, optical disc, or magnetic tape. When the imaging device 1 is a silver halide film camera, the image plane IP corresponds to the film plane.

[0072] Since the imaging device 1 is compact, bright, and equipped with the imaging lens of the above embodiment which has stable optical performance, it achieves the same effects as the imaging device. Therefore, the imaging device 1 can be applied to fixed imaging devices such as surveillance imaging devices and vehicle-mounted imaging devices.

[0073] 〔summary〕 A first aspect of the present invention is an imaging lens having, in order from the object side toward the image plane side, a first lens (L1) having negative refractive power, a meniscus-shaped second lens (L2) having positive refractive power, an aperture diaphragm (SP), a third lens (L3) having positive refractive power, and a cemented lens having positive combined refractive power formed by joining a fourth lens (L4) having positive refractive power and a fifth lens (L5) having negative refractive power, and satisfying the aforementioned formulas (1-1) and (1-2). According to the first aspect, an imaging lens that is compact, bright, and has stable optical performance can be realized.

[0074] A second aspect of the present invention satisfies formula (2) above in the first aspect. The second aspect is even more effective in terms of good aberration correction.

[0075] A third aspect of the present invention satisfies formula (3) above in the first or second aspect. The third aspect is even more effective in suppressing changes in optical properties due to changes in eccentricity sensitivity and in suppressing the occurrence of aberrations.

[0076] A fourth aspect of the present invention satisfies formula (4) above in any of the first to third aspects. The fourth aspect is even more effective from the viewpoint of suppressing the occurrence of aberrations and from the viewpoint of miniaturizing the imaging lens in the axial direction.

[0077] A fifth aspect of the present invention satisfies formula (5) above in any of the first to fourth aspects. The fifth aspect is even more effective in suppressing the tilt of the image plane.

[0078] A sixth aspect of the present invention satisfies formula (6) above in any of the first to fifth aspects. The sixth aspect is even more effective in terms of good aberration correction, miniaturization of the imaging lens in the axial direction, and good correction of spherical aberration.

[0079] A seventh aspect of the present invention satisfies formula (7) above in any of the first to sixth aspects. The seventh aspect is even more effective in terms of miniaturizing the imaging lens in the axial direction and providing good correction of coma aberration and astigmatism.

[0080] The eighth aspect of the present invention satisfies formula (8) above in any of the first to seventh aspects. The eighth aspect is even more effective in terms of miniaturizing the imaging lens in the axial direction, suppressing the occurrence of coma aberration and astigmatism, and suppressing changes in optical characteristics due to changes in eccentricity sensitivity.

[0081] The ninth aspect of the present invention satisfies formula (9) above in any of the first to eighth aspects. The ninth aspect is even more effective from the viewpoint of miniaturizing the imaging lens in the radial direction, ensuring optical characteristics, and providing good correction of field curvature.

[0082] The tenth aspect of the present invention satisfies formula (10) above in any of the first to ninth aspects. The tenth aspect is even more effective in terms of good correction of astigmatism and distortion.

[0083] An eleventh aspect of the present invention is an imaging device (1) comprising an imaging lens according to any of the first to tenth aspects, and an image sensor on the image plane side of the imaging lens that converts the optical image formed by the imaging lens into an electrical signal. According to the eleventh aspect, an imaging device that is compact, bright, and has stable optical performance can be realized.

[0084] As is clear from the above description, the imaging lens in the present invention achieves low cost and miniaturization with a small number of lenses, while enabling high-resolution imaging. Furthermore, the imaging device in the present invention, by incorporating the above-mentioned imaging lens, achieves miniaturization and enables high-resolution imaging.

[0085] Thus, the present invention can provide an imaging lens that achieves miniaturization of the entire imaging lens, particularly the diameter of the lens located closest to the object and the overall length of the imaging lens, while also providing a bright F-number of about 1.6 and good imaging performance that is less affected by eccentricity.

[0086] The imaging lens and imaging device of the present invention can be suitably used in surveillance cameras, security cameras, or in-vehicle cameras installed indoors or outdoors.

[0087] The imaging lens according to the present invention is compact, bright, and possesses stable optical performance. This invention, with its various advantages, is expected to contribute to achieving, for example, United Nations Sustainable Development Goal (SDG) 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0088] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0089] One embodiment of the present invention is described below.

[0090] The lens configuration of the imaging lens according to an embodiment of the present invention is shown in Figures 1, 3, 5, 7, 9, and 11. The imaging lens according to an embodiment of the present invention is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5, in order from the object side to the image plane side. The fourth lens L4 and the fifth lens L5 constitute a cemented lens. An optical aperture diaphragm SP is positioned between the second lens L2 and the third lens L3. The aperture diaphragm SP limits the diameter (amount of light) of the light beam incident from the object side to the image plane IP side. An optical block G is positioned between the fifth lens L5 and the image plane IP. The optical block G corresponds to an optical filter, faceplate, crystal low-pass filter, or infrared cut filter, etc. In an imaging device equipped with the imaging lens and a solid-state image sensor, the image plane IP corresponds to the imaging surface of the solid-state image sensor. As the solid-state image sensor, for example, a photoelectric conversion element such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor may be used.

[0091] The longitudinal aberration diagrams for the imaging lenses of the embodiments of the present invention are shown in Figures 2, 4, 6, 8, 10, and 12. The longitudinal aberration diagrams for each embodiment show, from left to right on the plane of the paper, spherical aberration (SA [mm]), astigmatism (AST [mm]), and distortion (DIS [%]). In the spherical aberration diagram, the vertical axis represents the F-number (Fno), the dashed line represents the spherical aberration at the d-line (wavelength 587.56 nm), the dotted line represents the spherical aberration at the C-line (wavelength 656.27 nm), and the solid line represents the spherical aberration at the g-line (wavelength 435.84 nm). In the astigmatism diagram, the vertical axis represents the image height (Y), the astigmatism of the sagittal ray ΔS at the d-line (wavelength 587.56 nm) is shown by a dashed line, and the astigmatism of the meridional ray ΔT is shown by a dashed line. In the distortion diagram, the vertical axis represents the image height (Y), and the distortion at the d line (wavelength 587.56 nm) is shown by a dashed line.

[0092] The surface data of all lenses in the imaging lens of the embodiment of the present invention are shown in Tables 1, 4, 7, 10, 13, and 16. In these tables, the "surface number" indicates the numbers of the lens surfaces that sequentially increase toward the image plane side, with the lens surface of the lens located closest to the object side among the lenses constituting the imaging lens being numbered 1. "R" shown in the same table indicates the radius of curvature [mm] of the lens surface corresponding to each surface number. However, a surface with an "R" value of INF indicates that the surface is a plane. "D" shown in the same table indicates the axial distance [mm] between the lens surface with surface number i (where i is a natural number) and the lens surface with surface number i + 1. "Nd" shown in the same table indicates the refractive index of each lens at the d-line (wavelength 587.56 nm). "ABV" shown in the same table indicates the Abbe number of each lens based on the d-line (wavelength 587.56 nm).

[0093] The surface data of the aspherical lenses in the imaging lens of the embodiment of the present invention are shown in Tables 2, 5, 8, 11, 14, and 17. In these tables, the surface numbers of the lenses that are aspherical and their aspherical coefficients are shown. The aspherical shape can be expressed by the following aspherical equation when the displacement z in the optical axis direction at the position of the distance h from the optical axis is based on the surface vertex. z = ch 2 / [1 + {1 - (1 + k)c 2 h 2} 1 / 2 1 / 2 +A4h 4 +A6h 6 +A8h 8 +A10h 10 ··· However, c: Curvature (1 / r) h: Height from the optical axis k: Conic coefficient (conic constant) A4, A6, A8, A10···: Aspherical coefficients of each order

[0094] In addition, the notation "E±m" (where m represents an integer) in the numerical values of the aspherical coefficients and the conic constant means "×10 ±m ".

[0095] The specifications of the imaging lens in the embodiment of the present invention are shown in Tables 3, 6, 9, 12, 15, and 18. These tables show the focal length [mm], F-number, half-angle of view (θ) [deg], image height [mm], total lens length [mm], and back focus (BF) of the entire imaging lens system. The "total lens length" is the sum of the distance from the object-side surface of the first lens to the image-plane-side surface of the fifth lens and the back focus (BF). The back focus (BF) is the distance from the image-plane-side surface of the fifth lens to the paraxial image plane, converted to an air-like value.

[0096] [Example 1] Figure 1 shows the lens configuration of the imaging lens of Example 1. Figure 2 shows the longitudinal aberration of the imaging lens of Example 1. Furthermore, Tables 1 to 3 show the surface data, aspherical data, and specifications for the imaging lens of Example 1, respectively.

[0097] [Table 1] No. RD Nd ABV 1 ASPH 10.0503 0.9000 1.85134 40.10 2 ASPH 3.2892 1.8906 3 -35.506 6.1983 1.80808 22.76 4 -15.1251 2.4231 5 STOP INF 3.6027 6 ASPH 16.1462 3.5902 1.61880 63.85 7 ASPH -8.4858 0.1044 8 10.8218 2.8335 1.60300 65.46 9 -9.1000 0.7000 1.85450 25.15 10 31.2674 2.9239 11 INF 1.0000 1.51680 64.20 12 INF 4.0750 13 INF 0.4000 1.51680 64.20 14 INF 0.1250

[0098] [Table 2] No. K *4 *6 *8 1 1.3497E+00 -2.3113E-03 9.4399E-05 -6.5235E-06 2 -2.1563E+00 3.6998E-03 3.3167E-05 -2.9930E-05 6 -1.4414E+00 4.9821E-05 -1.2638E-05 1.0875E-06 7 1.7865E-01 3.4206E-04 -7.4704E-06 7.5017E-07 No. *10 *12 1 3.4731E-07 -8.3167E-09 2 4.0519E-06 -1.6910E-07 6 -6.2593E-08 9.4360E-10 7 -3.9991E-08 5.2507E-10

[0099] [Table 3] Focal length [mm] 4.55 f-number 1.56 Half-angle [°] 45.9 Image height [mm] 3.46 Lens length [mm] 30.77 BF (in air) [mm] 8.05

[0100] [Example 2] Figure 3 shows the lens configuration of the imaging lens in Example 2. Figure 4 shows the longitudinal aberration of the imaging lens in Example 2. Furthermore, Tables 4 to 6 show the surface data, aspherical data, and specifications for the imaging lens in Example 2, respectively.

[0101] [Table 4] No. RD Nd ABV 1 ASPH 9.372 0.9599 1.85134 40.10 2 ASPH 3.2377 1.8932 3 -33.3111 6.2267 1.80808 22.76 4 -15.0193 2.5550 5 STOP INF 3.6365 6 ASPH 15.7293 3.5500 1.61880 63.85 7 ASPH -8.6262 0.1000 8 10.9732 2.8029 1.61800 63.40 9 -9.1000 0.7000 1.85450 25.15 10 29.3032 2.4741 11 INF 1.0000 1.51680 64.20 12 INF 4.0750 13 INF 0.4000 1.51680 64.20 14 INF 0.5250

[0102] [Table 5] No. K *4 *6 *8 1 8.9330E-01 -2.3822E-03 9.4784E-05 -6.5528E-06 2 -2.1775E+00 3.7395E-03 4.6605E-05 -3.6803E-05 6 -1.3374E+00 5.8460E-05 -1.2322E-05 1.0733E-06 7 2.0517E-01 3.5982E-04 -8.5966E-06 8.4878E-07 No. *10 *12 1 83.5705E-07 -8.7101E-09 2 4.9424E-06 -2.1056E-07 6 -5.9411E-08 9.2443E-10 7 -4.2185E-08 5.7222E-10

[0103] [Table 6] Focal distance [mm] 4.55 F value 1.56 Half-angle [°] 45.9 Image height [mm] 3.46 Lens length [mm] 30.90 BF (in air) [mm] 8.00

[0104] [Example 3] Figure 5 shows the lens configuration of the imaging lens of Example 3. Figure 6 shows the longitudinal aberration of the imaging lens of Example 3. Furthermore, Tables 7 to 9 show the surface data, aspherical data, and specifications for the imaging lens of Example 3, respectively.

[0105] [Table 7] No. RD Nd ABV 1 ASPH 9.0770 1.0454 1.85134 40.10 2 ASPH 3.1322 1.6302 3 -20.3736 5.8082 1.85450 25.15 4 -11.4812 1.8389 5 STOP INF 5.2634 6 ASPH 14.9711 2.6479 1.61880 63.85 7 ASPH -8.4333 0.1000 8 13.5980 2.1966 1.60300 65.46 9 -9.0000 0.7000 1.85450 25.15 10 52.6014 2.8507 11 INF 1.0000 1.51680 64.20 12 INF 4.0750 13 INF 0.4000 1.51680 64.20 14 INF 0.5250

[0106] [Table 8] No. K *4 *6 *8 1 6.1500E-01 -2.4076E-03 8.2079E-05 -6.6108E-06 2 -2.1265E+00 4.0129E-03 4.2326E-05 -4.1680E-05 6 -1.3425E+00 5.8747E-05 -1.6059E-05 1.1536E-06 7 1.3358E-01 3.9707E-04 -1.2497E-05 9.3719E-07 No. *10 *12 1 4.0662E-07 -1.0412E-08 2 5.0174E-06 -2.0168E-07 6 -4.1273E-08 -4.6812E-10 7 -2.8973E-08 -5.4993E-10

[0107] [Table 9] Focal length [mm] 4.55 f-number 1.56 Half-angle [°] 46.1 Image height [mm] 3.46 Lens length [mm] 30.08 BF (in air) [mm] 8.37

[0108] [Example 4] Figure 7 shows the lens configuration of the imaging lens of Example 4. Figure 8 shows the longitudinal aberration of the imaging lens of Example 4. Furthermore, Tables 10 to 12 show the surface data, aspherical data, and specifications for the imaging lens of Example 4, respectively.

[0109] [Table 10] No. RD Nd ABV 1 ASPH 9.0633 1.0030 1.85134 40.10 2 ASPH 3.1269 1.8418 3 -25.6945 5.9900 1.85450 25.15 4 -12.4668 1.7489 5 STOP INF 4.6939 6 ASPH 15.4202 2.7594 1.61880 63.85 7 ASPH -8.2813 0.1000 8 12.1918 2.3266 1.60300 65.46 9 -9.0000 0.7000 1.85450 25.15 10 36.8655 2.6120 11 INF 1.0000 1.51680 64.20 12 INF 4.0750 13 INF 0.4000 1.51680 64.20 14 INF 0.5250

[0110] [Table 11] No. K *4 *6 *8 1 7.3570E-01 -2.3601E-03 8.2883E-05 -6.7095E-06 2 -2.0092E+00 3.9243E-03 3.9918E-05 -3.9666E-05 6 -1.1979E+00 6.3584E-05 -1.6275E-05 1.1548E-06 7 1.1930E-01 3.9732E-04 -1.1196E-05 9.0139E-07 No. *10 *12 1 4.0268E-07 -1.0006E-08 2 5.1323E-06 -2.1196E-07 6 -4.2281E-08 -4.8373E-10 7 -3.2383E-08 -3.9298E-10

[0111] [Table 12] Focal length [mm] 4.55 f-number 1.56 Half-angle [°] 45.9 Image height [mm] 3.46 Lens length [mm] 29.78 BF (in air) [mm] 8.14

[0112] [Example 5] Figure 9 shows the lens configuration of the imaging lens of Example 5. Figure 10 shows the longitudinal aberration of the imaging lens of Example 5. Furthermore, Tables 13 to 15 show the surface data, aspherical data, and specifications for the imaging lens of Example 5, respectively.

[0113] [Table 13] No. RD Nd ABV 1 ASPH 9.4406 1.0756 1.85134 40.10 2 ASPH 3.2141 1.7693 3 -30.5121 6.1386 1.80808 22.76 4 -14.6312 2.4693 5 STOP INF 3.5557 6 ASPH 15.7812 3.9677 1.61880 63.85 7 ASPH -8.6535 0.1657 8 10.9639 2.7713 1.61800 63.40 9 -8.8478 0.7000 1.85450 25.15 10 34.2806 2.4247 11 INF 1.0000 1.51680 64.20 12 INF 4.0750 13 INF 0.4000 1.51680 64.20 14 INF 0.5250

[0114] [Table 14] No. K *4 *6 *8 1 8.4803E-01 -2.3921E-03 9.5423E-05 -6.6145E-06 2 -2.1965E+00 3.7362E-03 4.6959E-05 -3.7282E-05 6 -1.2932E+00 6.0130E-05 -1.2104E-05 1.0702E-06 7 2.3173E-01 3.5425E-04 -8.8335E-06 8.5513E-07 No. *10 *12 1 3.5973E-07 -8.6756E-09 2 4.9598E-06 -2.1078E-07 6 -6.0352E-08 1.0350E-09 7 -4.0164E-08 5.4213E-10

[0115] [Table 15] Focal length [mm] 4.55 f-number 1.57 Half-angle [°] 45.9 Image height [mm] 3.45 Lens length [mm] 31.04 BF (in air) [mm] 8.14

[0116] [Example 6] Figure 11 shows the lens configuration of the imaging lens of Example 6. Figure 12 shows the longitudinal aberration of the imaging lens of Example 6. Furthermore, Tables 16 to 18 show the surface data, aspherical data, and specifications for the imaging lens of Example 6, respectively.

[0117] [Table 16] No. RD Nd ABV 1 ASPH 10.0845 0.9000 1.85134 40.10 2 ASPH 3.2769 1.9851 3 -30.0543 6.7427 1.80808 22.76 4 -14.4587 2.2439 5 STOP INF 3.2937 6 ASPH 15.9250 4.3441 1.61880 63.85 7 ASPH -8.7149 0.1000 8 10.4903 2.5518 1.60300 65.46 9 -9.1000 0.7000 1.85450 25.15 10 32.8944 2.9234 11 INF 1.0000 1.51680 64.20 12 INF 4.0750 13 INF 0.4000 1.51680 64.20 14 INF 0.1250

[0118] [Table 17] No. K *4 *6 *8 1 1.2728E+00 -2.3268E-03 9.3441E-05 -6.3662E-06 2 -2.0921E+00 3.5486E-03 3.1201E-05 -2.7679E-05 6 -1.2326E+00 5.5466E-05 -1.2226E-05 1.0995E-06 7 2.1885E-01 3.2599E-04 -7.5081E-06 7.5850E-07 No. *10 *12 1 3.6605E-07 -9.9815E-09 2 4.0779E-06 -1.8992E-07 6 -6.2793E-08 1.0823E-09 7 -3.9103E-08 5.9504E-10

[0119] [Table 18] Focal length [mm] 4.40 f-number 1.56 Half-angle [°] 45.9 Image height [mm] 3.34 Lens length [mm] 31.38 BF (in air) [mm] 7.95

[0120] Table 19 shows the calculated values ​​of the aforementioned formulas in Examples 1 to 6.

[0121] [Table 19] Formula Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 (1-1) D23 / f 1.3240 1.361 1.561 1.416 1.217 1.370 (1-2) L_D3 / f 0.7890 0.780 0.582 0.606 0.872 0.987 (2) f_L1 / f_L45 -0.0397 -0.0433 -0.0180 -0.0134 -0.0622 -0.0552 (3) f_L3 / f_L2 0.3316 0.3245 0.3851 0.3886 0.3246 0.3378 (4) f_L2 / f 6.309 6.457 5.201 5.153 6.519 6.569 (5) f_L1 / f_L3 -0.6426 -0.6567 -0.6708 -0.6672 -0.6457 -0.6220 (6) f_L3 / f_L45 0.0617 0.0659 0.0269 0.0202 0.0963 0.0887 (7) G45L1SF -2.059 -2.197 -1.697 -1.988 -1.940 -1.936 (8) f_L1 / f -1.345 -1.376 -1.343 -1.336 -1.367 -1.380 (9) f_L1 / f_L2 -0.2131 -0.2131 -0.2583 -0.2593 -0.2096 -0.2101 (10) G1L1SF 1.973 2.056 2.054 2.053 2.032 1.963 (11) D23 / BF 0.749 0.774 0.849 0.791 0.740 0.697 [Explanation of Symbols]

[0122] 1. Imaging device 10 Telescope Tubes 20 Main unit L1~L5 First to Fifth Lenses SP aperture diaphragm G Optical Block IP image plane OA optical axis

Claims

1. An imaging lens having, in order from the object side to the image plane side, a first lens with negative refractive power, a meniscus-shaped second lens with positive refractive power, an aperture diaphragm, a third lens with positive refractive power, and a cemented lens formed by joining a fourth lens with positive refractive power and a fifth lens with negative refractive power, and having positive combined refractive power, and satisfying the following equation. 0.825 ≤ D23 / f ≤ 1.850 (1-1) 0.48≦L_D3 / f≦1.20 (1-2) however, D23: Distance between the axial surfaces of the second lens and the third lens f: Focal length of the imaging lens L_D3: Center thickness of the third lens

2. The imaging lens according to claim 1, satisfying the following formula. -0.120≦f_L1 / f_L45≦-0.010 (2) however, f_L1: Focal length of the first lens f_L45: Focal length of the cemented lens

3. The imaging lens according to claim 1, satisfying the following formula. 0.180≦f_L3 / f_L2≦0.600 (3) however, f_L2: Focal length of the second lens f_L3: Focal length of the third lens

4. The imaging lens according to claim 1, satisfying the following formula. 4.00≦f_L2 / f≦10.00 (4) however, f_L2: Focal length of the second lens

5. The imaging lens according to claim 1, satisfying the following formula. -1.00≦f_L1 / f_L3≦-0.30 (5) however, f_L1: Focal length of the first lens f_L3: Focal length of the third lens

6. The imaging lens according to claim 1, satisfying the following formula. 0.010≦f_L3 / f_L45≦0.150 (6) however, f_L3: Focal length of the third lens f_L45: Focal length of the cemented lens

7. The imaging lens according to claim 1, satisfying the following formula. -3.00<G45L1SF<-1.20 (7) however, G45L1SF: Expressed by the following formula G45L1SF=(G4L1Lr+G5L1Rr) / (G4L1Lr−G5L1Rr) (7-1) however, G4L1Lr: Radius of curvature of the object-side lens surface of the fourth lens. G5L1Rr: Radius of curvature of the lens surface on the image plane side of the fifth lens.

8. The imaging lens according to claim 1, satisfying the following formula. -3.00≦f_L1 / f≦-1.00 (8) however, f_L1: Focal length of the first lens

9. The imaging lens according to claim 1, satisfying the following formula. -0.400≦f_L1 / f_L2≦-0.200 (9) however, f_L1: Focal length of the first lens f_L2: Focal length of the second lens

10. The first lens is a concave meniscus lens, and The imaging lens according to claim 1, satisfying the following formula. 1.00<G1L1SF<3.00 (10) however G1L1SF: Expressed by the following formula G1L1SF=(G1L1Lr+G1L1Rr) / (G1L1Lr−G1L1Rr) (10-1) however, G1L1Lr: Radius of curvature of the object-side lens surface of the first lens. G1L1Rr: Radius of curvature of the lens surface on the image plane side of the first lens.

11. An imaging device comprising an imaging lens according to any one of claims 1 to 10, and an image sensor on the image plane side of the imaging lens that converts an optical image formed by the imaging lens into an electrical signal.

Images