Imaging optical system and imaging device

Abstract

To provide an image capturing optical system which has a view angle of 130° or greater, suppresses individual variations in performance with a minimum number of lenses, and offers stable recognition performance.SOLUTION: An image capturing optical system 10 comprises a first lens L1 with negative refractive power having a spherical shape, a second lens L2 with negative refractive power having an aspherical shape, and axial ray limiting aperture stop 12, a third lens L3 with positive refractive power having a spherical shape, a fourth lens L4 with positive refractive power having an aspherical shape, a fifth lens L5 with positive refractive power, and a sixth lens L6 with negative refractive power, arranged in order from the object side, and satisfies conditional expressions (1) through (3): 1.4<fL3 / f2G<2.6 ...(1), -1.0<(R3r+R3f) / (R3r-R3f)<-0.1 ...(2), 1.2<f2G / fa<1.7 ...(3).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an imaging optical system and an imaging device applicable to, for example, a sensing camera.

Background Art

[0002] In recent years, surveillance cameras and in-vehicle cameras have become widespread. The imaging optical systems mounted on surveillance cameras and in-vehicle cameras (hereinafter referred to as in-vehicle cameras, etc.) are required to be small and high-performance with the spread. In recent years, an in-vehicle imaging device is used as a sensing camera, and various driving supports are performed by analyzing an image acquired by the in-vehicle imaging device. The importance of the in-vehicle imaging device as a sensing camera is increasing for the realization of future automatic driving systems.

[0003] In an in-vehicle sensing camera, in order to stably recognize a person and an object, it is required to have good image quality, little individual variation, and little performance degradation against various environmental temperature changes. As an imaging optical system applicable to an in-vehicle imaging device or the like, various imaging optical systems having a relatively wide angle of view in which a lens having a negative refractive power on the object side (hereinafter referred to as a negative lens) is arranged have been proposed.

[0004] For example, Patent Document 1 proposes an imaging lens including six lenses of a negative lens, a negative lens, a lens having a positive refractive power (hereinafter referred to as a positive lens), a positive lens, a positive lens, and a negative lens in order from the object side. The imaging lens enables shooting with a total angle of view of around 120° and a relatively wide angle of view.

[0005] For example, Patent Document 3 proposes an imaging lens including six lenses of a negative lens, a negative lens, a positive lens, a positive lens, a negative lens, and a positive lens in order from the object side. The imaging lens achieves both an angle of view of 120° or more of the total angle of view and a large aperture with an F value of 2.0 or less.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-173347 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-037119 [Patent Document 3] Japanese Patent Application Laid-Open No. 2019-211598 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] Generally, for a sensing camera, a wide angle of view for shooting in a range equal to or greater than the human field of view and sufficient brightness for stably detecting people and objects even in low light are required.

[0008] In the imaging lens described in Patent Document 1, the overall angle of view is around 120°, achieving a relatively wide-angle shooting angle of view. However, the distance between the light passing position of the peripheral angle of view and the optical axis within the first lens is large, and the effective diameter of the first lens is large. Therefore, it is difficult to say that it is sufficiently miniaturized for in-vehicle use where installation in a limited space is required.

[0009] In the wide-angle imaging lens system described in Patent Document 2, the fifth lens and the sixth lens are plastic lenses. Plastic lenses have a larger linear expansion coefficient compared to glass lenses, and the refractive index changes due to changes in the environmental temperature. In addition, plastic lenses may be deteriorated or deformed in a high-temperature environment. Therefore, when the wide-angle imaging lens system described in Patent Document 2 is applied to an in-vehicle imaging device or the like, the focus fluctuates due to changes in the environmental temperature, and it becomes difficult to obtain good imaging performance in a high-temperature environment and a low-temperature environment. Replacing the plastic lenses described in Patent Document 2 with glass lenses makes it difficult to realize the imaging optical system at a low cost.

[0010] In the imaging lens described in Patent Document 3, miniaturization and wide-angleization have been achieved, but the refractive power of each lens in the rear group is strong. As a result, when assembling the lens unit, the performance degradation due to the relative optical axis deviation of each lens becomes large, and the performance variation for each individual imaging lens becomes large. Therefore, it is not suitable for a sensing camera that requires stable recognition performance.

[0011] In view of the above problems, an object of the present disclosure is to provide an imaging optical system and an imaging device that have a stable recognition performance by suppressing performance variations for each individual with a minimum number of lenses while achieving an angle of view of 130° or more.

Means for Solving the Problems

[0012] In order to solve the above problems, an imaging optical system according to an embodiment of the present disclosure includes: In order from the object side, a first lens group having a negative refractive power, an on-axis light beam restricting aperture, a second lens group having a positive refractive power, and is provided with The first lens group includes, in order from the object side, a first lens having a negative refractive power and a spherical shape, and a second lens having a negative refractive power and an aspherical shape and convex on the image side. The second lens group includes, in order from the object side, a third lens having a positive refractive power and a spherical shape, a fourth lens having a positive refractive power and an aspherical shape, and a cemented lens. The cemented lens includes, in order from the object side, a fifth lens having a positive refractive power and a sixth lens having a negative refractive power. Satisfies the following conditional expressions (1) to (3). 1.4 < fL3 / f2G < 2.6 (1) -1.0 < (R3r + R3f) / (R3r - R3f) < -0.1 (2) 1.2 < f2G / fa < 1.7 (3) However, fL3 is the focal length of the third lens on the d-line, f2G is the focal length of the second lens group on the d-line, R3f is the radius of curvature of the object-side surface of the third lens, R3r is the radius of curvature of the image-side surface of the third lens, and fa is the focal length of the entire lens system on the d-line.

[0013] To solve the above problems, an imaging device according to an embodiment of the present disclosure is equipped with the above imaging optical system.

Advantages of the Invention

[0014] According to the imaging optical system and the imaging device according to an embodiment of the present disclosure, while realizing an angle of view of 130° or more, the number of lenses is minimized, and performance variations between individuals are suppressed to have stable recognition performance.

Brief Description of the Drawings

[0015]

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Mode for Carrying Out the Invention

[0016] Hereinafter, the imaging optical system 10 and the imaging device 1 according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In each of the accompanying drawings showing the configurations of the imaging optical system 10 and the imaging device 1, the "object side" corresponds to the left side, and the "image side" corresponds to the right side.

[0017] FIG. 1 is a configuration diagram showing an overview of the imaging optical system 10 and the imaging device 1 according to an embodiment of the present disclosure.

[0018] The imaging optical system 10 includes a first lens group G1, an axial light beam restricting aperture, i.e., a second aperture 12 described later, and a second lens group G2, which are arranged in order from the object side. The first lens group G1 has a negative refractive power. The second lens group G2 has a positive refractive power.

[0019] The first lens group G1 includes, in order from the object side, a first lens L1 having a negative refractive power and a spherical shape, and a second lens L2 having a negative refractive power and an aspherical shape, convex on the image side. The second lens group G2 includes, in order from the object side, a third lens L3 having a positive refractive power and a spherical shape, a fourth lens L4 having a positive refractive power and an aspherical shape, and a cemented lens LJ. The cemented lens LJ includes, in order from the object side, a fifth lens L5 having a positive refractive power and a sixth lens L6 having a negative refractive power.

[0020] The imaging optical system 10 is substantially composed of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6. In the present disclosure, "substantially composed of" means that the optical elements substantially constituting the imaging optical system 10 are six lenses of the first lens L1 to the sixth lens L6, but in addition, the imaging optical system 10 may have lenses that do not substantially have power, and other optical elements such as apertures and cover glasses.

[0021] For example, the imaging optical system 10 has three apertures in addition to the first lens L1 to the sixth lens L6. The imaging optical system 10 has a first aperture 11 for flare cut disposed between the first lens L1 and the second lens L2. The imaging optical system 10 has a second aperture 12 for restricting the axial light beam disposed between the second lens L2 and the third lens L3. The imaging optical system 10 has a third aperture 13 for flare cut disposed between the third lens L3 and the fourth lens L4.

[0022] The imaging device 1 includes an imaging optical system 10 and an image sensor 20. The image sensor 20 has a cover glass 22 that protects the image plane 21. The imaging device 1 captures an object by the imaging optical system 10 forming an image of the object as a subject on the image plane 21 through the cover glass 22.

[0023] Hereinafter, each lens configuration of the imaging optical system 10 in FIG. 1 and the second aperture 12 will be described in more detail.

[0024] (First lens L1) The first lens L1 has a negative refractive power, and its object side is a convex surface. Since the object side of the first lens L1 is a convex surface, when the reflected light of the light incident on the imaging optical system 10 at the image plane 21 enters the object side surface of the first lens L1, the re-reflected light is suppressed from being re-imaged at the image plane 21. The smaller the radius of curvature of the object side surface of the first lens L1, the more the converging state of the re-reflected light at the image plane 21 is relaxed. If the object side surface of the first lens L1 is a concave surface, even if the imaging optical system 10 is to be widened, in order to ensure the peripheral light quantity, the diameter of the first lens L1 becomes large, and it becomes difficult to configure the imaging optical system 10 to be small.

[0025] (Second lens L2) The second lens L2 is an aspherical lens having a negative refractive power and a convex shape toward the image plane 21. The object side of the second lens L2 is a concave surface. The second lens L2 shares with the first lens L1 the refractive power required for widening the angle of view. Thereby, the occurrence of aberration in the peripheral portion of the screen is suppressed. Since the second lens L2 has a convex shape toward the image side, the incident angle of the on-axis marginal rays to the subsequent third lens L3 and the like is suppressed. Thereby, spherical aberration correction in the second lens group G2 is efficiently performed.

[0026] (Second aperture 12) The second aperture 12 is arranged so that the distance from the second aperture 12 to the object side surface of the first lens L1 becomes short. Thereby, it becomes possible to arrange the entrance pupil of the imaging optical system 10 as an imaging optical system on the object side, and it becomes possible to reduce the effective diameter of the first lens L1, that is, to miniaturize the first lens L1.

[0027] (Third lens L3) The third lens L3 is a spherical lens having a positive refractive power and a convex shape toward the image plane 21. The third lens L3 has a shape that suppresses the refraction angle with respect to the divergent light beam emitted from the first lens group G1. Thereby, the third lens L3 suppresses the occurrence of various aberrations.

[0028] (Fourth lens L4) The fourth lens L4 is a lens having a convex shape toward the image side and at least one aspherical surface. The fourth lens L4 has a positive refractive power and its image side is a convex surface. Since the on-axis light beam becomes high in the fourth lens L4, the aspherical surface is used to effectively correct spherical aberration and coma aberration. Different from the third lens L3, the fourth lens L4 is configured to have an optimal shape also for astigmatism because the passing positions of the on-axis light beam and the off-axis light beam are different.

[0029] (Bonded lens LJ) The bonded lens LJ includes a fifth lens L5 and a sixth lens L6. The bonded lens LJ has a fifth lens L5 having a positive refractive power together with a sixth lens L6 having a negative refractive power in order to minimize the influence on spherical aberration while arranging a lens having a large negative refractive power for suppressing the Petzval sum. Since the fifth lens L5 and the sixth lens L6 each have a large refractive power and need to be arranged close to each other, they are configured as a bonded lens. The bonded lens LJ suppresses the performance variation of the imaging optical system 10 while suppressing the overall length of the imaging optical system 10 by appropriately determining its combined refractive power.

[0030] The imaging optical system 10 satisfies the following conditional expressions (1) to (3). 1.4 < fL3 / f2G < 2.6 (1) -1.0 < (R3r + R3f) / (R3r - R3f) < -0.1 (2) 1.2 < f2G / fa < 1.7 (3) However, fL3 is the focal length of the third lens L3 at the d-line. f2G is the focal length of the second lens group G2 at the d-line. R3f is the radius of curvature of the object side surface of the third lens L3. R3r is the radius of curvature of the image side surface of the third lens L3. fa is the focal length of the entire lens system at the d-line.

[0031] The conditional expression (1) defines an appropriate ratio between the focal length of the third lens L3, which is the most important in determining the power arrangement within the second lens group G2, and the focal length of the second lens group G2.

[0032] When the ratio is below the lower limit of the conditional expression (1), the positive refractive power in the second lens group G2 concentrates on the object side of the second lens group G2. That is, the second lens group G2 has a strong telephoto-type refractive power arrangement. Therefore, while the height of the light rays after the fourth lens L4 rapidly decreases and the overall length can be shortened, the decentration sensitivity of the third lens L3 increases. As a result, when mass-producing the imaging optical system 10 as a lens unit, the performance variations of the imaging optical system 10 become large. Conversely, by the ratio being larger than the lower limit of the conditional expression (1), the performance variations of the imaging optical system 10 are suppressed.

[0033] When the ratio exceeds the upper limit of the conditional expression (1), the refractive power on the object side of the second lens group G2 is insufficient, and it becomes difficult to sufficiently reduce the height of the light rays after the fourth lens L4. For spherical aberration correction, the overall length after the fourth lens L4 becomes longer. In addition, the positive refractive power required after the fourth lens L4 increases, and both the positive and negative refractive powers of each lens increase. For example, the non-spherical aberration burden of the fourth lens L4 increases. As a result, it becomes difficult to stably manufacture the imaging optical system 10. Conversely, by the ratio being smaller than the upper limit of the conditional expression (1), it becomes easier to stably manufacture the imaging optical system 10.

[0034] Regarding the conditional expression (1), the lower limit value may be further set to 1.59 and the upper limit value may be further set to 2.42. Thereby, the above effects are more surely exerted.

[0035] The conditional expression (2) defines the shape factor of the third lens L3 for suppressing the decentration sensitivity of the third lens L3 and suppressing manufacturing variations in the entire lens system.

[0036] When the shape factor exceeds the upper limit of the conditional expression (2), the incident angles on the object side surface of the third lens L3 increase for both the F-number rays and the peripheral field angle rays emitted from the first lens group G1 having a negative refractive power as a whole. Therefore, the decentration sensitivity of the third lens L3 increases, and when mass-producing the imaging optical system 10 as a lens unit, the performance variations of the imaging optical system 10 increase. Conversely, when the shape factor becomes smaller than the upper limit of the conditional expression (2), the performance variations of the imaging optical system 10 are suppressed.

[0037] When the shape factor is below the lower limit of the conditional expression (2), the incident angle of the on-axis light beam on the object side surface of the third lens L3 is particularly suppressed. Thereby, it is possible to advantageously correct spherical aberration and coma aberration for the divergent light emitted from the first lens group G1, but it is necessary to increase the refractive index of the third lens L3 in order to ensure the refractive power required for the third lens L3 shown in the conditional expression (1). Therefore, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration. Conversely, when the shape factor becomes larger than the lower limit of the conditional expression (2), it becomes easier to correct axial chromatic aberration and lateral chromatic aberration.

[0038] Regarding the conditional expression (2), its lower limit value may be further set to -0.80 and its upper limit value may be further set to -0.20. Thereby, the above effects are more surely exhibited.

[0039] The conditional expression (3) defines the ratio between the focal length of the second lens group G2 and the focal length of the entire imaging optical system 10.

[0040] When this ratio is lower than the lower limit of conditional expression (3), since the refractive power of the second lens group G2 is large, the refractive power of each lens within the second lens group G2 becomes large. Accordingly, the radius of curvature of each lens surface becomes small. Thereby, the manufacturing error sensitivity becomes high. In addition, when configured with a limited number of lenses, it becomes difficult to correct various aberrations in a well-balanced manner. Conversely, by this ratio becoming larger than the lower limit of conditional expression (3), while reducing the manufacturing error sensitivity, it becomes easy to correct various aberrations in a well-balanced manner.

[0041] When this ratio exceeds the upper limit of conditional expression (3), since the refractive power of the second lens group G2 is small, the overall length of the imaging optical system 10 becomes long, and it becomes difficult to apply the imaging optical system 10 to the imaging device 1 which requires arrangement in a limited space. Conversely, by this ratio becoming smaller than the upper limit of conditional expression (3), miniaturization of the imaging optical system 10 becomes easy.

[0042] Regarding conditional expression (3), the lower limit value thereof may be further set to 1.30 and the upper limit value may be further set to 1.60. Thereby, the above-described effects are more surely exhibited.

[0043] The imaging optical system 10 may further satisfy the following conditional expressions (4) to (6). -1.6 < f1G / fa < -1.0 (4) 3.8 < R1f / fa < 8 (5) 0.19 < D1G / Da < 0.31 (6) However, f1G is the focal length of the first lens group G1 at d-line. R1f is the radius of curvature of the object side surface of the first lens L1. D1G is the distance on the optical axis Ax from the object side surface of the first lens L1 to the image side surface of the second lens L2. Da is the distance on the optical axis Ax from the object side surface of the first lens L1 to the image side surface of the sixth lens L6.

[0044] Conditional expression (4) appropriately defines the ratio of the focal length between the first lens group G1 and the entire lens system in order to prevent the enlargement of the first lens L1 accompanying the wide-angle conversion.

[0045] When the ratio exceeds the upper limit of conditional expression (4), since the refractive power of the first lens group G1 is large, it becomes possible to reduce the effective diameter of the first lens L1. However, as the aperture ratio of the first lens group G1 increases, it becomes difficult to correct aperture aberrations such as spherical aberration and coma aberration. In addition, the shape constraints of the third lens L3 increase, making it difficult to optimally arrange the refractive power of the second lens group G2. Conversely, when the ratio becomes smaller than the upper limit of conditional expression (4), it becomes easier to correct aperture aberrations such as spherical aberration and coma aberration, and it also becomes easier to optimally arrange the refractive power of the second lens group G2.

[0046] When the ratio is below the lower limit of conditional expression (4), since the refractive power of the first lens group G1 is small, the effective diameter of the first lens L1 tends to increase in order to ensure peripheral light quantity, making it difficult to apply the imaging optical system 10 to the imaging device 1 that requires arrangement in a limited space. Conversely, when the ratio becomes larger than the lower limit of conditional expression (4), miniaturization of the imaging optical system 10 becomes easier.

[0047] Regarding conditional expression (4), the lower limit value thereof may be further set to -1.50 and the upper limit value may be further set to -1.10. Thereby, the above effects are more surely exhibited.

[0048] Conditional expression (5) defines the ratio between the radius of curvature of the object side surface of the first lens L1 and the focal length of the entire lens system. Conditional expression (5) is for suppressing the re-imaging of the reflected light on the image surface 21 when the reflected light on the image surface 21 of the light incident on the imaging optical system 10 is incident on the object side surface of the first lens L1, and for suppressing the occurrence of field curvature accompanying wide-angle conversion.

[0049] When this ratio is lower than the lower limit of conditional expression (5), it is necessary to reduce the radius of curvature of the image-side surface of the first lens L1 in order to ensure the refractive power required for the first lens L1. At this time, in order to correct both the on-axis aberration such as spherical aberration and the off-axis aberration such as field curvature well, it is necessary to form an aspherical surface on the first lens L1. The effective diameter of the first lens L1 is large, and the cost increases due to aspherization. Therefore, it becomes difficult to apply the imaging optical system 10 to in-vehicle cameras and the like where cost requirements are strict. Conversely, when this ratio becomes larger than the lower limit of conditional expression (5), cost can be suppressed.

[0050] When this ratio exceeds the upper limit of conditional expression (5), when the reflected light on the image plane 21 of the light incident on the imaging optical system 10 is incident on the object-side surface of the first lens L1, the re-reflected light forms an image again on the image plane 21. As a result, a ghost with high illuminance is generated. Since a ghost with high illuminance causes misrecognition, it becomes difficult to apply the imaging optical system 10 to a sensing camera. Conversely, when this ratio becomes smaller than the upper limit of conditional expression (5), the generation of ghosts can be suppressed.

[0051] Regarding conditional expression (5), the lower limit value thereof may be further set to -4.0 and the upper limit value may be further set to -5.20. Thereby, the above effects are more surely exhibited.

[0052] Conditional expression (6) is an expression for optimally correcting various aberrations by appropriately setting the entrance pupil position, the light beam convergence action of the image-side surface of the second lens L2, and the light beam divergence action by the image-side surface of the first lens L1 and the object-side surface of the second lens L2.

[0053] When the ratio is below the lower limit of conditional expression (6), the distance on the optical axis Ax of the first lens group G1 becomes shorter. At this time, although the overall length of the imaging optical system 10 can be made compact, the optical path lengths of both the on-axis ray and the off-axis ray become shorter. As a result, it becomes difficult to perform optimal correction of various aberrations due to the light beam divergence action by the image-side surface of the first lens L1 and the object-side surface of the second lens L2, and the light beam convergence action by the image-side surface of the second lens L2. Conversely, by the ratio becoming larger than the lower limit of conditional expression (6), it becomes easier to perform optimal correction of various aberrations.

[0054] When the ratio exceeds the upper limit of conditional expression (6), the distance from the object-side surface of the first lens L1 to the entrance pupil becomes longer. At this time, when trying to make the F number smaller than 2.0, it is necessary to increase the effective diameter of the first lens L1 in order to secure the peripheral light quantity. Therefore, it is impossible to satisfy the miniaturization requirement for in-vehicle cameras etc. that need to be installed in a limited space. In addition, the deviation between the front principal point and the entrance pupil becomes large, and it becomes difficult to correct the field curvature well from the center to the periphery of the screen. Conversely, by the ratio becoming smaller than the upper limit of conditional expression (6), it becomes easier to miniaturize the imaging optical system 10, and it becomes easier to correct the field curvature well from the center to the periphery of the screen.

[0055] The imaging optical system 10 may further satisfy the following conditional expression (7). -5.8×10 -6 <f2G×(NR3 / fL3 + NR4 / fL4) < -4×10 -6 (7) However, fL4 is the focal length of the fourth lens L4 at the d line. NR3 is the relative refractive index temperature coefficient in the temperature range from 20°C to 40°C at the d line of the third lens L3. NR4 is the relative refractive index temperature coefficient in the temperature range from 20°C to 40°C at the d line of the fourth lens L4.

[0056] The conditional expression (7) is an expression that describes a conditional range determined by the focal lengths of the third lens L3 and the fourth lens L4 with large refractive powers and their respective temperature coefficients of relative refractive index. The conditional expression (7) is for obtaining good imaging performance even in a high-temperature environment of about 80°C and a low-temperature environment of about -40°C when the image sensor 20 is fixed with respect to the best image position of the lens under normal temperature environment during the manufacture of the imaging device 1.

[0057] When the value is below the lower limit of the conditional expression (7), a so-called over-temperature correction state occurs, and the distance from the image side surface of the sixth lens L6 to the best image surface 21 is farther than the photoelectric conversion surface of the image sensor 20 at high temperatures and closer at low temperatures. In any case, the imaging performance deteriorates compared to normal temperature. Conversely, by the value being larger than the lower limit of the conditional expression (7), the imaging performance is maintained.

[0058] When the value exceeds the upper limit of the conditional expression (7), a so-called under-temperature correction state occurs, and the distance from the image side surface of the sixth lens L6 to the best image surface 21 is closer than the photoelectric conversion surface of the image sensor 20 at high temperatures and farther at low temperatures. In any case, the imaging performance deteriorates compared to normal temperature. Conversely, by the value being smaller than the upper limit of the conditional expression (7), the imaging performance is maintained.

[0059] Regarding the conditional expression (7), the lower limit value may be further set to -5.5 and the upper limit value may be further set to -4.1. Thereby, the above effects are more surely exhibited.

[0060] (Example) Hereinafter, the lens configuration of the example related to the imaging optical system 10 of the present disclosure will be mainly described. In the following description, the lens configuration will be described in the order from the object side to the image side.

[0061] In the basic lens data of each of the following embodiments, the number i (i is a natural number) in the lens specifications is the surface number of the lens from the object side. R is the radius of curvature of the lens surface. D is the distance on the optical axis Ax between the i-th lens surface and the (i + 1)-th lens surface from the object side. N(d) is the refractive index of the d-line. νd is the Abbe number of the d-line. The effective diameter is the diameter of the lens in the direction perpendicular to the optical axis Ax, and is the diameter from the optical axis Ax to the end of the lens.

[0062] In the data of each of the following embodiments, for values derived from the lens specifications, including the focal length and back focus, etc., unless otherwise specified, they are values for the d-line (wavelength 587.56 nm).

[0063] In all the following values of the specifications, unless otherwise specified, the units of the described focal length f, radius of curvature R, lens surface interval D, effective diameter, and other lengths use millimeters (mm). However, since the imaging optical system 10 can obtain the same optical performance in both proportional enlargement and proportional reduction, it is not limited to this.

[0064] The aspherical data in each of the following embodiments shows the aspherical coefficients that give the aspherical shape of the lens surface marked with ※ in the basic lens data. For the aspherical shape, the coordinates of the aspherical surface are represented by the following formula.

Equation

[0065] However, h is the displacement from the optical axis Ax in the direction perpendicular to the optical axis Ax. z is the displacement (sag amount) in the direction of the optical axis Ax from the intersection of the aspherical surface and the optical axis Ax. r is the radius of curvature of the reference sphere. K is the conic coefficient. A is the 4th-order aspherical coefficient. B is the 6th-order aspherical coefficient. C is the 8th-order aspherical coefficient. D is the 10th-order aspherical coefficient. E is the 12th-order aspherical coefficient. F is the 14th-order aspherical coefficient.

[0066] As shown in the following lens configuration diagrams, the imaging optical system 10 according to each embodiment includes a first lens group G1 arranged in order from the object side, an axial light beam restricting aperture, i.e., a second aperture 12 described later, and a second lens group G2. The first lens group G1 has a negative refractive power. The second lens group G2 has a positive refractive power.

[0067] The first lens group G1 includes, in order from the object side, a first lens L1 having a negative refractive power and a spherical shape, and a second lens L2 having a negative refractive power and an aspherical shape and convex on the image side. The second lens group G2 includes, in order from the object side, a third lens L3 having a positive refractive power and a spherical shape, a fourth lens L4 having a positive refractive power and an aspherical shape, and a cemented lens LJ. The cemented lens LJ includes, in order from the object side, a fifth lens L5 having a positive refractive power and a sixth lens L6 having a negative refractive power.

[0068] The parallel plate disposed closest to the object side is the first aperture 11 as a filter and is not included in the first lens group G1. The first aperture 11 includes a cover glass, a UV cut filter, an IR cut filter, a low-pass filter, etc., and its characteristics are appropriately selected according to the imaging device 1 having the imaging optical system 10 according to the present disclosure.

[0069] The parallel plate disposed closest to the image side is the third aperture 13 as a filter and is not included in the second lens group G2. The third aperture 13 includes a cover glass, a UV cut filter, an IR cut filter, a low-pass filter, etc., and its characteristics are appropriately selected according to the imaging device 1 having the imaging optical system 10 according to the present disclosure.

[0070] (Example 1) FIG. 2 is a lens configuration diagram of the imaging optical system 10 according to Example 1 of the present disclosure. Table 1 shows basic lens data including the specifications of the imaging optical system 10 according to Example 1.

Table 1

[0071] Table 2 shows the aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 1. [Table 2]

[0072] Table 3 shows various data of the imaging optical system 10 according to Example 1. [Table 3]

[0073] FIG. 3 is a longitudinal aberration diagram of the imaging optical system 10 in the infinite focus state shown in FIG. 2. The longitudinal aberration diagram shown in FIG. 3 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0074] In the diagram representing spherical aberration, the vertical axis indicates the pupil coordinate with a maximum of 1. The solid line indicates the spherical aberration at the d-line (wavelength 587.56 nm). The dashed line indicates the spherical aberration at the C-line (wavelength 656.27 nm). The one-dot chain line indicates the spherical aberration at the g-line (435.84 nm).

[0075] In the diagram representing astigmatism, the vertical axis indicates the incident angle (°) on the object side. The solid line indicates the sagittal astigmatism at the d-line. The dashed line indicates the tangential astigmatism at the d-line.

[0076] In the diagram representing distortion, the vertical axis indicates the incident angle (°) on the object side. The solid line indicates the distortion at the d-line.

[0077] Since the above description of the longitudinal aberration diagram is the same for the longitudinal aberration diagrams shown in the other examples, the description will be omitted below.

[0078] (Example 2) FIG. 4 is a lens configuration diagram of the imaging optical system 10 according to Example 2 of the present disclosure. Table 4 shows the basic lens data including the specifications of the imaging optical system 10 according to Example 2. [Table 4] * indicates aspherical surface

[0079] Table 5 shows the aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 2.

Table 5

[0080] Table 6 shows various data of the imaging optical system 10 according to Example 2.

Table 6

[0081] Figure 5 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 4 at infinity focus. The longitudinal aberration diagram shown in Figure 5 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0082] (Example 3) Figure 6 is a lens configuration diagram of the imaging optical system 10 according to Example 3 of the present disclosure. Table 7 shows the basic lens data including the specifications of the imaging optical system 10 according to Example 3.

Table 7

[0083] Table 8 shows the aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 3.

Table 8

[0084] Table 9 shows various data of the imaging optical system 10 according to Example 3.

Table 9

[0085] FIG. 7 is a longitudinal aberration diagram when the imaging optical system 10 of FIG. 6 is focused at infinity. The longitudinal aberration diagram shown in FIG. 7 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0086] (Example 4) FIG. 8 is a lens configuration diagram of the imaging optical system 10 according to Example 4 of the present disclosure. Table 10 shows basic lens data including the specifications of the imaging optical system 10 according to Example 4.

Table 10

[0087] Table 11 shows aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 4.

Table 11

[0088] Table 12 shows various data of the imaging optical system 10 according to Example 4.

Table 12

[0089] FIG. 9 is a longitudinal aberration diagram when the imaging optical system 10 of FIG. 8 is focused at infinity. The longitudinal aberration diagram shown in FIG. 9 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%).

[0090] (Example 5) FIG. 10 is a lens configuration diagram of the imaging optical system 10 according to Example 5 of the present disclosure. Table 13 shows basic lens data including the specifications of the imaging optical system 10 according to Example 5.

Table 13

[0091] Table 14 shows aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 5.

Table 14

[0092] Table 15 shows various data of the imaging optical system 10 according to Example 5.

Table 15

[0093] FIG. 11 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 10 at infinity focus. The longitudinal aberration diagram shown in FIG. 11 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0094] (Example 6) FIG. 12 is a lens configuration diagram of the imaging optical system 10 according to Example 6 of the present disclosure. Table 16 shows basic lens data including the specifications of the imaging optical system 10 according to Example 6.

Table 16

[0095] Table 17 shows aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 6.

Table 17

[0096] Table 18 shows various data of the imaging optical system 10 according to Example 6.

Table 18

[0097] FIG. 13 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 12 at infinity focus. The longitudinal aberration diagram shown in FIG. 13 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%).

[0098] (Example 7) FIG. 14 is a lens configuration diagram of the imaging optical system 10 according to Example 7 of the present disclosure. Table 19 shows basic lens data including the specifications of the imaging optical system 10 according to Example 7. [Table 19] * indicates aspherical

[0099] Table 20 shows the aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 7. [Table 20]

[0100] Table 21 shows various data of the imaging optical system 10 according to Example 7. [Table 21]

[0101] FIG. 15 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 14 at infinity focus. The longitudinal aberration diagram shown in FIG. 15 is, in order from the left, spherical aberration (mm), coma aberration (mm), and distortion (%)

[0102] (Example 8) FIG. 16 is a lens configuration diagram of the imaging optical system 10 according to Example 8 of the present disclosure. Table 22 shows basic lens data including the specifications of the imaging optical system 10 according to Example 8. [Table 22] * indicates aspherical

[0103] Table 23 shows the aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 8. [Table 23]

[0104] Table 24 shows various data of the imaging optical system 10 according to Example 8.

Table 24

[0105] Figure 17 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 16 at infinity focus. The longitudinal aberration diagram shown in FIG. 17 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0106] (Example 9) Figure 18 is a lens configuration diagram of the imaging optical system 10 according to Example 9 of the present disclosure. Table 25 shows basic lens data including the specifications of the imaging optical system 10 according to Example 9

Table 25

[0107] Table 26 shows aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 9

Table 26

[0108] Table 27 shows various data of the imaging optical system 10 according to Example 9

Table 27

[0109] Figure 19 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 18 at infinity focus. The longitudinal aberration diagram shown in FIG. 19 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0110] (Example 10) Figure 20 is a lens configuration diagram of the imaging optical system 10 according to Example 10 of the present disclosure. Table 28 shows basic lens data including the specifications of the imaging optical system 10 according to Example 10

Table 28

[0111] Table 29 shows the aspherical data including the aspherical coefficients of the imaging optical system 10 according to Example 10.

Table 29

[0112] Table 30 shows various data of the imaging optical system 10 according to Example 10.

Table 30

[0113] FIG. 21 is a longitudinal aberration diagram of the imaging optical system 10 in FIG. 20 at infinity focus. The longitudinal aberration diagram shown in FIG. 21 is, in order from the left, spherical aberration (mm), astigmatism (mm), and distortion (%)

[0114] According to the imaging optical system 10 and the imaging device 1 according to one embodiment of the present disclosure as described above, while realizing an angle of view of 130° or more, the performance variation for each individual is suppressed with a minimum number of lenses, and stable recognition performance is achieved. According to the imaging optical system 10 and the imaging device 1 according to one embodiment of the present disclosure, the entire configuration can be made small with a minimum number of lenses. According to the imaging optical system 10 and the imaging device 1 according to one embodiment of the present disclosure, good imaging performance can be obtained in a high-temperature environment and a low-temperature environment.

[0115] It is obvious to those skilled in the art that the present disclosure can be realized in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, the foregoing description is illustrative and not restrictive. The scope of the disclosure is defined by the appended claims rather than the foregoing description. It is assumed that some changes within the equivalent scope of any change are included therein.

[0116] For example, the shapes, arrangements, orientations, and numbers of the respective components described above are not limited to the illustrated contents in the above description and drawings. The shapes, arrangements, orientations, and numbers of the respective components may be arbitrarily configured as long as their functions can be realized.

Explanation of Symbols

[0117] 1 Imaging device 10 Imaging optical system 20 Image sensor 21 Image plane 22 Cover glass Ax Optical axis L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens LJ Joining lens

Claims

1. In order from the object side, a first lens group having a negative refractive power, an axial light beam restricting aperture stop, a second lens group having a positive refractive power, and is composed of The first lens group is composed of, in order from the object side, a first lens having a negative refractive power and a spherical shape, and a second lens having a negative refractive power and an aspherical shape and convex on the image side. The second lens group is composed of, in order from the object side, a third lens having a positive refractive power and a spherical shape, a fourth lens having a positive refractive power and an aspherical shape, and a cemented lens. The cemented lens is composed of, in order from the object side, a fifth lens having a positive refractive power and a sixth lens having a negative refractive power. An imaging optical system that satisfies the following conditional expressions (1) to (3). 1.4 < fL3 / f2G < 2.6 (1) -1.0 < (R3r + R3f) / (R3r - R3f) < -0.1 (2) 1.2 < f2G / fa < 1.7 (3) However, fL3 is the focal length of the third lens at the d-line, f2G is the focal length of the second lens group at the d-line, R3f is the radius of curvature of the object side surface of the third lens, R3r is the radius of curvature of the image side surface of the third lens, and fa is the focal length of the entire lens system at the d-line.

2. The imaging optical system according to claim 1, An imaging optical system that satisfies the following conditional expressions (4) to (6). -1.6 < f1G / fa < -1.0 (4) 3.8 < R1f / fa < 8 (5) 0.19 < D1G / Da < 0.31 (6) However, f1G is the focal length of the first lens group on the d-line, R1f is the radius of curvature of the object-side surface of the first lens, D1G is the distance on the optical axis from the object-side surface of the first lens to the image-side surface of the second lens, and Da is the distance on the optical axis from the object-side surface of the first lens to the image-side surface of the sixth lens.

3. The imaging optical system according to claim 1 or 2, An imaging optical system that satisfies the following conditional expression (7). -5.8×10 －６ <f2G×(NR3 / fL3 + NR4 / fL4) < -4×10 －６ (7) However, fL4 is the focal length of the fourth lens on the d-line, NR3 is the relative refractive index temperature coefficient in the temperature range from 20°C to 40°C on the d-line of the third lens, and NR4 is the relative refractive index temperature coefficient in the temperature range from 20°C to 40°C on the d-line of the fourth lens.

4. An imaging device including the imaging optical system according to any one of claims 1 to 3.

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