Imaging lens and imaging device

Abstract

This imaging lens comprises, in order from the object side toward the image side, a first lens group, a diaphragm, and a second lens group having a positive refractive power. The first lens group includes three or more Ln lenses arranged continuously, and the Ln lenses are negative lenses in which the surface on the image side is a concave surface. With regard to two of the Ln lenses selected from the lenses having the strongest refractive power among the three or more Ln lenses arranged continuously in the first lens group, when the average of the Abbe number ν is denoted by νave and the average of the partial dispersion ratio θ is denoted by θave, νave and θave are included within a predetermined region in an orthogonal coordinate system in which ν is the horizontal axis and θ is the vertical axis.

Description

[Technical Field]

[0001] The present disclosure relates to an imaging lens and an imaging device. [Background technology]

[0002] Near-infrared light has traditionally been used in imaging applications such as factory automation (FA) cameras, machine vision (MV) cameras, surveillance cameras, and in-vehicle cameras. For example, near-infrared light is used for object identification and inspection in FA and MV applications, and for surveillance applications, near-infrared light is used for imaging at night and in poor visibility conditions such as fog or smoke. Note that near-infrared here refers to the wavelength band of 700 nm to 2500 nm.

[0003] As an imaging lens designed with near-infrared light in mind, for example, the lens system described in Japanese Patent No. 6309478 is known. Summary of the Invention [Problem to be solved by the invention]

[0004] Among near-infrared light, SWIR (Short Wave Infra-Red) light, which can be classified as a wavelength band from 1000 nm to 2500 nm, is highly useful. In recent years, there has been a demand for imaging lenses that can achieve high performance and are compatible with wavelengths from the visible range to the near-infrared range, especially the SWIR range, while preventing the lens system from becoming too large.

[0005] The present disclosure provides an imaging lens that can accommodate wavelength ranges from the visible range to the SWIR range and achieve high performance while suppressing an increase in the size of the lens system, and an imaging device that includes this imaging lens. [Means for solving the problem]

[0006] An imaging lens according to a first aspect of the present disclosure includes, in order from the object side to the image side, a first lens group, a stop, and a second lens group having positive refractive power. The first lens group includes three or more Ln lenses arranged in succession. The Ln lenses are negative lenses with concave surfaces on the image side. For each lens in the first lens group and the second lens group, the refractive index at a wavelength of 435.83 nm is defined as ng, the refractive index at a wavelength of 1529.58 nm as na, and the refractive index at a wavelength of 2325.42 nm as nb. The Abbe number ν and the partial dispersion ratio θ are defined as ν=(na-1) / (ng-nb), Define θ=(na-nb) / (ng-nb), and for two Ln lenses selected from the two with the strongest refractive power among three or more consecutively arranged Ln lenses included in the first lens group, let the average of ν be νave and the average of θ be θave. In an orthogonal coordinate system with the horizontal axis being ν and the vertical axis being θ, A first region represented by θ>0.0250×ν-0.1300; A second region represented by θ<0.0250×ν-0.0075; The third region, represented by θ>0.0225, The fourth region, represented by θ<0.1650, The common area of ​​these four areas includes νave and θave.

[0007] The imaging lens according to the first aspect has, in the orthogonal coordinate system, The fifth region is represented by θ>0.0250×ν-0.1000. The sixth region is represented by θ<0.0250×ν-0.0375. The seventh region, represented by θ>0.0500, The eighth region, represented by θ<0.1500, It is preferable that ν ave and θ ave are included in the common area of ​​the four areas.

[0008] In a second aspect of the present disclosure, when the average of v of all positive lenses in the imaging lens is vPave, the average of v of all negative lenses in the imaging lens is vNave, the average of θ of all positive lenses in the imaging lens is θPave, and the average of θ of all negative lenses in the imaging lens is θNave, it is preferable that the following conditional expressions (1) and (2) be satisfied. Furthermore, in addition to satisfying the following conditional expressions (1) and (2), it is more preferable that at least one of the following conditional expressions (1-1) and (2-1) be satisfied. 6<νPave-νNave<12 (1) 0.01<θPave-θNave<0.1 (2) 6.5<νPave-νNave<11.5 (1-1) 0.015<θPave-θNave<0.095 (2-1)

[0009] In a third aspect of the present disclosure, in the above-mentioned aspect, when the angle between the chief ray incident on the image plane at the maximum image height and an axis parallel to the optical axis is defined as CRA and the unit of CRA is degrees, it is preferable to satisfy the following conditional expression (3), and it is more preferable to satisfy the following conditional expression (3-1): 0≦|CRA|<10 (3) 0≦|CRA|<9 (3-1)

[0010] In a fourth aspect of the present disclosure, in the above-mentioned aspect, when the sum of the distance on the optical axis from the lens surface of the imaging lens closest to the object side to the lens surface of the imaging lens closest to the image side and the back focus of the imaging lens in terms of the air equivalent distance at a wavelength of 1529.58 nm is TL, and the focal length of the imaging lens at a wavelength of 1529.58 nm is f, it is preferable to satisfy the following conditional formula (4), and it is more preferable to satisfy the following conditional formula (4-1): 29 <TL / f<38 (4) 29.5 <TL / f<37.6 (4-1)

[0011] In a fifth aspect of the present disclosure, in the above-mentioned aspect, it is preferable that the first lens group has positive refractive power.

[0012] A sixth aspect of the present disclosure is that, in the above-mentioned aspect, when the focal length of the first lens group at a wavelength of 1529.58 nm is fG1 and the focal length of the second lens group at a wavelength of 1529.58 nm is fG2, it is preferable to satisfy the following conditional formula (5), and it is more preferable to satisfy the following conditional formula (5-1): 0.4 <fG2 / fG1<2 (5) 0.5 <fG2 / fG1<1.9 (5-1)

[0013] A seventh aspect of the present disclosure is such that, in the above-mentioned aspect, when the focal length of the first lens group at a wavelength of 1529.58 nm is fG1 and the focal length of the lens in the first lens group located closest to the image at a wavelength of 1529.58 nm is fLp, it is preferable that the following conditional expression (6) be satisfied: 1.3 <fLp / fG1<3.1 (6)

[0014] As for an eighth aspect of the present disclosure, in the above-mentioned aspect, when the effective diameter of the lens surface of the imaging lens closest to the object side is φt and the effective diameter of the lens surface of the imaging lens closest to the image side is φe, it is preferable that the following conditional expression (7) is satisfied: 2.5<φt / φe<8 (7)

[0015] A ninth aspect of the present disclosure, in the above-mentioned aspect, preferably, the first lens group includes four or less Ln lenses arranged in succession.

[0016] In a tenth aspect of the present disclosure, in the above aspect, when v of the lens closest to the image side of the imaging lens is vE, it is preferable that the following conditional expression (8) be satisfied. 17<νE (8)

[0017] An eleventh aspect of the present disclosure is such that, in the above-mentioned aspect, at least one of the three or more Ln lenses arranged successively in the first lens group is preferably an aspherical lens.

[0018] A twelfth aspect of the present disclosure is such that, in the above-mentioned aspect, the lens of the imaging lens closest to the image side is preferably an aspherical lens having positive refractive power.

[0019] A thirteenth aspect of the present disclosure is such that, in the above-mentioned aspects, it is preferable that the number of lenses included in the first lens group is seven or less.

[0020] In a fourteenth aspect of the present disclosure, in the above-mentioned aspect, it is preferable that the number of lenses included in the second lens group is seven or less.

[0021] An imaging device according to another aspect of the present disclosure includes the imaging lens according to the above aspect.

[0022] In this specification, the terms "consisting of" and "consisting of" are intended to mean that, in addition to the listed components, other components may also be included, such as a lens that has substantially no refractive power, optical elements other than lenses, such as an aperture, a filter, and a cover glass, and mechanical parts, such as a lens flange, a lens barrel, an image sensor, and an image stabilization mechanism.

[0023] In this specification, "a group having positive refractive power" means that the group as a whole has positive refractive power. "A lens having positive refractive power" and "a positive lens" are synonymous. "A lens having negative refractive power" and "a negative lens" are synonymous. The "lens group" is not limited to a configuration consisting of multiple lenses, and may be a configuration consisting of only one lens.

[0024] A compound aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrated together to function as a single aspherical lens as a whole) is not considered a cemented lens, but is treated as a single lens. The sign of the refractive power and the surface shape of a lens that includes an aspherical surface are considered in the paraxial region.

[0025] The "focal length" used in the conditional expressions is the paraxial focal length. Unless otherwise specified, the values ​​used in the conditional expressions are values ​​based on a wavelength of 1529.58 nm when focused on an object at infinity. "Higher order" in relation to aberrations means fifth order or higher. In this specification, "near infrared" refers to the wavelength band of 700 nm to 2500 nm, and "SWIR" refers to the wavelength band of 1000 nm to 2500 nm. The "nm" used as the unit of wavelength is nanometer. [Effects of the Invention]

[0026] According to the above aspect, the imaging lens of the present disclosure and the imaging device including this imaging lens can accommodate wavelength ranges from the visible range to the SWIR range while suppressing an increase in the size of the lens system, and can achieve high performance. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a cross-sectional view showing the configuration of an imaging lens according to an exemplary embodiment and a light beam, which corresponds to the imaging lens of Example 1. FIG. [Figure 2] FIG. 2 is a diagram for explaining materials of a negative lens. [Figure 3] FIG. 1 is a diagram for explaining CRA. [Figure 4] 3A to 3C are diagrams showing various aberrations of the imaging lens of Example 1. [Figure 5] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a second embodiment. [Figure 6] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 2. [Figure 7] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a third embodiment. [Figure 8] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 3. [Figure 9] 10 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a fourth embodiment. [Figure 10] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 4. [Figure 11] 10 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a fifth embodiment. [Figure 12] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 5. [Figure 13] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a sixth embodiment. [Figure 14] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 6. [Figure 15] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a seventh embodiment. [Figure 16] 10A to 10C are diagrams showing various aberrations of the imaging lens of Example 7. [Figure 17] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to an eighth embodiment. [Figure 18] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 8. [Figure 19] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a ninth embodiment. [Figure 20] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 9. [Figure 21] FIG. 20 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a tenth embodiment. [Figure 22] 20A to 20C are diagrams showing various aberrations of the imaging lens of Example 10. [Figure 23] FIG. 20 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to an eleventh embodiment. [Figure 24] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 11. [Figure 25] FIG. 22 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a twelfth embodiment. [Figure 26] 13A to 13C are diagrams showing various aberrations of the imaging lens of Example 12. [Figure 27] FIG. 22 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a thirteenth embodiment. [Figure 28] 20A to 20C are diagrams showing various aberrations of the imaging lens of Example 13. [Figure 29] FIG. 22 is a cross-sectional view showing the configuration of an imaging lens and a light beam according to a fourteenth embodiment. [Figure 30] 20A to 20C are diagrams showing various aberrations of the imaging lens of Example 14. [Figure 31] 1 is a schematic configuration diagram of an imaging device according to an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 1 shows the configuration of an imaging lens according to an exemplary embodiment of the present disclosure in a cross section including an optical axis Z. The example shown in FIG. 1 corresponds to the imaging lens of Example 1, which will be described later. In FIG. 1, the left side is the object side and the right side is the image side, and the image is shown in focus on an object at infinity. FIG. 1 also shows an axial light beam 2 and a light beam 3 at the maximum image height as light beams.

[0029] 1 shows an example in which a parallel-plate-shaped optical member PP is arranged on the image side of the imaging lens, assuming that the imaging lens is applied to an imaging device. The optical member PP is a member that is assumed to include various filters and / or cover glass, etc. Examples of various filters include a low-pass filter, an infrared cut filter, and a filter that cuts off specific wavelength ranges. The optical member PP is a member that does not have refractive power, and a configuration in which the optical member PP is omitted is also possible.

[0030] The imaging lens of the present disclosure comprises, in order from the object side to the image side, a first lens group G1, an aperture stop St, and a second lens group G2 having positive refractive power. As an example, in the example shown in Fig. 1, the first lens group G1 comprises, in order from the object side to the image side, seven lenses, L11 to L17, and the second lens group G2 comprises, in order from the object side to the image side, seven lenses, L21 to L27. Note that the aperture stop St shown in Fig. 1 does not indicate the shape, but rather its position on the optical axis.

[0031] The first lens group G1 preferably has positive refractive power. In FA and MV applications, close-range photography is emphasized. By making the refractive power of the first lens group G1 positive, the spread of the light beam emitted from the first lens group G1 during close-range photography can be reduced compared to when the refractive power of the first lens group G1 is negative, thereby preventing the second lens group G2 from becoming larger in diameter and weight. Furthermore, because the spread of the light beam from the first lens group G1 can be reduced, the refractive power of the lenses in the second lens group G2 does not need to be strong in order to converge the spread light beam, thereby reducing the amount of various aberrations.

[0032] The first lens group G1 includes three or more consecutively arranged Ln lenses Ln. The Ln lenses Ln are negative lenses with a concave image-side surface. In the example shown in FIG. 1, the lenses L11 to L14 each correspond to an Ln lens Ln. This configuration allows the negative refractive power to be distributed to the three or more Ln lenses Ln, thereby reducing the absolute value of the angle of incidence of light rays on each lens surface and suppressing an increase in astigmatism. Furthermore, the absolute value of the radius of curvature of each Ln lens Ln can be increased, which is advantageous for lens workability. If two or more of the three or more consecutively arranged Ln lenses Ln are meniscus lenses, an increase in astigmatism can be further suppressed.

[0033] The first lens group G1 preferably includes four or fewer consecutively arranged Ln lenses Ln. By limiting the number of Ln lenses Ln to four or fewer, it is possible to prevent the lens system from becoming larger and heavier, and this is advantageous for reducing costs.

[0034] In the imaging lens of the present disclosure, the lens materials are selected taking into consideration the wavelength ranges of the visible and SWIR regions, and in particular the Abbe number and partial dispersion ratio are set as described below. For each lens of the first lens group G1 and the second lens group G2, the refractive index at a wavelength of 435.83 nm (g-line) is set to ng, the refractive index at a wavelength of 1529.58 nm to na, and the refractive index at a wavelength of 2325.42 nm to nb. Then, for each lens, the Abbe number ν and partial dispersion ratio θ are respectively set to ν=(na-1) / (ng-nb), θ=(na-nb) / (ng-nb) It is defined as:

[0035] Of the three or more consecutively arranged Ln lenses Ln included in the first lens group G1, the average of v is vave and the average of θ is θave for the two Ln lenses Ln selected from those with the strongest refractive power. Specifically, when there is only one Ln lens Ln with the strongest refractive power, "two Ln lenses Ln selected from those with the strongest refractive power" refers to the Ln lens Ln with the strongest refractive power and the Ln lens Ln with the second strongest refractive power among the three or more Ln lenses Ln. Furthermore, the refractive powers of the "two Ln lenses Ln selected from those with the strongest refractive power" may be the same.

[0036] In this case, in an orthogonal coordinate system with the horizontal axis as ν and the vertical axis as θ, A first region represented by θ>0.0250×ν-0.1300; A second region represented by θ<0.0250×ν-0.0075; The third region, represented by θ>0.0225, The fourth region, represented by θ<0.1650, Of the three or more Ln lenses Ln, the materials of the two Ln lenses Ln selected from those with stronger refractive power are selected so that νave and θave are included in the common area of ​​the four areas. Figure 2 shows an example of the above-mentioned orthogonal coordinate system. The rectangular area surrounded by solid lines in Figure 2 corresponds to the common area of ​​the four areas, the first to fourth areas. The plots shown in Figure 2 correspond to νave and θave of Examples 1 to 14, which will be described later.

[0037] By selecting a material for the common region of the first to fourth regions, it becomes easy to correct first-order axial chromatic aberration, second-order chromatic aberration, lateral chromatic aberration, spherical aberration, astigmatism, and distortion in a well-balanced manner over a wide wavelength range from the visible region to the SWIR region, which is advantageous for achieving high performance. If a material not included in the common region of the first to fourth regions were selected, it would be difficult to correct first-order chromatic aberration and residual second-order spectrum, and attempting to correct these in this case would result in increased spherical aberration.

[0038] Furthermore, by selecting a material for the common region of the first to fourth regions, it is possible to correct chromatic aberration well without increasing the number of lenses, and the size of the lens system can be prevented from increasing. If a material not included in the common region of the first to fourth regions were selected, correcting axial chromatic aberration in a wide wavelength range from the visible region to the SWIR region would require an increased number of lenses, resulting in an increase in the size of the lens system.

[0039] In order to obtain better characteristics, in the above orthogonal coordinate system, The fifth region is represented by θ>0.0250×ν-0.1000. The sixth region is represented by θ<0.0250×ν-0.0375. The seventh region, represented by θ>0.0500, The eighth region, represented by θ<0.1500, It is preferable to select the materials of the two Ln lenses Ln that have the strongest refractive power among the three or more Ln lenses Ln so that νave and θave are included in the common area of ​​the four areas. The rectangular area surrounded by the dashed line in Figure 2 corresponds to the common area of ​​the four areas, the fifth to eighth areas.

[0040] Furthermore, it is preferable that the imaging lens of the present disclosure has at least one of the following configurations. If the average of v of all positive lenses in the imaging lens is vPave and the average of v of all negative lenses in the imaging lens is vNave, it is preferable that the imaging lens satisfies the following conditional formula (1). Satisfying conditional formula (1) is advantageous for correcting first-order chromatic aberrations related to the g-line and light with a wavelength of 2325.42 nm. Furthermore, if the configuration satisfies the following conditional formula (1-1), even better characteristics can be achieved. 6<νPave-νNave<12 (1) 6.5<νPave-νNave<11.5 (1-1)

[0041] If the average of θ of all positive lenses in the imaging lens is θPave and the average of θ of all negative lenses in the imaging lens is θNave, it is preferable that the imaging lens satisfy the following conditional expression (2). Satisfying conditional expression (2) is advantageous for correcting residual secondary spectrum. Furthermore, if the configuration satisfies the following conditional expression (2-1), even better characteristics can be achieved. 0.01<θPave-θNave<0.1 (2) 0.015<θPave-θNave<0.095 (2-1)

[0042] It is more preferable that the imaging lens simultaneously satisfy conditional expressions (1) and (2). It is even more preferable that the imaging lens simultaneously satisfy conditional expressions (1) and (2) and then satisfy at least one of conditional expressions (1-1) and (2-1).

[0043] If the angle between the chief ray 3c incident at the maximum image height on the image plane Sim and an axis Zp parallel to the optical axis Z is defined as CRA, and the CRA is expressed in degrees, it is preferable that the imaging lens satisfy the following conditional formula (3). As an example, FIG. 3 shows a partial enlarged view including the chief ray 3c at the maximum image height, the axis Zp parallel to the optical axis Z, and CRA. Conditional formula (3) relates to the telecentricity of light rays emerging from the lens system. By satisfying conditional formula (3), the absolute value of the angle of incidence with respect to the light-receiving surface of the sensor located on the image plane Sim can be reduced, thereby suppressing a decrease in the peripheral illumination ratio. Furthermore, a configuration that satisfies the following conditional formula (3-1) can achieve even better characteristics. 0≦|CRA|<10 (3) 0≦|CRA|<9 (3-1)

[0044] If TL is the sum of the distance on the optical axis from the lens surface closest to the object of the imaging lens to the lens surface closest to the image of the imaging lens and the back focus of the imaging lens in terms of the air equivalent distance at a wavelength of 1529.58 nm, and f is the focal length of the imaging lens at a wavelength of 1529.58 nm, it is preferable that the imaging lens satisfy the following conditional expression (4). By ensuring that the corresponding value of conditional expression (4) is not below the lower limit, the overall length of the lens system does not become too short, preventing the refractive power of each lens from becoming too strong. This makes it possible to suppress the occurrence of high-order spherical aberrations at each wavelength and facilitates correction of chromatic aberrations over a wide wavelength range. By ensuring that the corresponding value of conditional expression (7) is not above the upper limit, the overall length of the lens system can be prevented from becoming too long. Furthermore, if a configuration is adopted that satisfies the following conditional expression (4-1), even better characteristics can be achieved. 29 <TL / f<38 (4) 29.5 <TL / f<37.6 (4-1)

[0045] If the focal length of the first lens group G1 at a wavelength of 1529.58 nm is fG1 and the focal length of the second lens group G2 at a wavelength of 1529.58 nm is fG2, it is preferable that the imaging lens satisfy the following conditional expression (5). By satisfying conditional expression (5), the refractive powers of the first lens group G1 and the second lens group G2 can be well balanced, making it easy to correct lateral chromatic aberration and distortion. Furthermore, if the configuration satisfies the following conditional expression (5-1), even better characteristics can be achieved. 0.4 <fG2 / fG1<2 (5) 0.5 <fG2 / fG1<1.9 (5-1)

[0046] If the focal length of the first lens group G1 at a wavelength of 1529.58 nm is fG1 and the focal length of the lens in the first lens group G1 located closest to the image at a wavelength of 1529.58 nm is fLp, it is preferable that the imaging lens satisfy the following conditional expression (6). By satisfying conditional expression (6), it is possible to suppress the longitudinal chromatic aberration that occurs in the first lens group G1 over a wide wavelength range from the visible region to the SWIR region, which is advantageous for achieving high performance. Furthermore, if the configuration satisfies the following conditional expression (6-1), even better characteristics can be achieved. 1.3 <fLp / fG1<3.1 (6) 1.4 <fLp / fG1<3.0 (6-1)

[0047] Assuming that the effective diameter of the lens surface of the imaging lens closest to the object side is φt and the effective diameter of the lens surface of the imaging lens closest to the image side is φe, it is preferable that the imaging lens satisfy the following conditional expression (7). By ensuring that the corresponding value of conditional expression (7) is not equal to or less than the lower limit, the absolute value of the angle of incidence with respect to the light-receiving surface of the sensor arranged on the image plane Sim can be reduced, thereby suppressing a decrease in the peripheral illumination ratio. By ensuring that the corresponding value of conditional expression (7) is not equal to or greater than the upper limit, it is possible to suppress an increase in the size and weight of the lens system, which is also advantageous for cost reduction. Furthermore, by satisfying the following conditional expression (6-1), even better characteristics can be achieved. Note that the "effective diameter" refers to the diameter of a circle formed by the point farthest from the optical axis Z in the radial direction, when considering the point at which all light rays contributing to image formation intersect with the lens surface. 2.5<φt / φe<8 (7) 3.0<φt / φe<7.5 (7-1)

[0048] When the v of the lens closest to the image side of the imaging lens is vE, it is preferable that the imaging lens satisfy the following conditional expression (8). By ensuring that the corresponding value of conditional expression (8) is not below the lower limit, it is possible to suppress lateral chromatic aberration in a wide wavelength range from the visible range to the SWIR range, which is advantageous for achieving high performance. Furthermore, by ensuring that the corresponding value of conditional expression (8-1) is not above the upper limit, it is possible to suppress axial chromatic aberration in a wide wavelength range from the visible range to the SWIR range, which is advantageous for achieving high performance. Furthermore, if the configuration satisfies conditional expression (8-2), even better characteristics can be achieved. 17<νE (8) 17<νE<28 (8-1) 18.5<νE<26.5 (8-2)

[0049] While Fig. 1 shows an example in which the first lens group G1 is composed of seven lenses and the second lens group G2 is composed of seven lenses, the number of lenses constituting each lens group can be different from the example shown in Fig. 1. However, if the number of lenses included in the first lens group G1 is seven or less, the size and weight of the lens system can be suppressed, and this is advantageous for cost reduction. Similarly, if the number of lenses included in the second lens group G2 is seven or less, the size and weight of the lens system can be suppressed, and this is advantageous for cost reduction.

[0050] To improve design flexibility and achieve good aberration correction, any surface of the imaging lens may be aspherical. The aspherical surface may be formed by grinding or molding. Furthermore, a hybrid aspherical lens may be used as the lens having an aspherical surface.

[0051] Specifically, it is preferable that at least one of the three or more consecutively arranged Ln lenses Ln included in the first lens group G1 is an aspherical lens, which is advantageous for effectively correcting distortion and astigmatism.

[0052] Specifically, it is preferable that the lens closest to the image side of the imaging lens is an aspherical lens with positive refractive power. This is advantageous for correcting distortion and astigmatism well. It also makes it easier to adjust the CRA so that it satisfies conditional expression (3).

[0053] To correct chromatic aberration, any of the lens groups in the imaging lens may be configured to include a gradient index lens such as a diffractive optical element or a gradient index lens (GRIN lens), or an organic optical material with anomalous dispersion.

[0054] The imaging lens preferably has a focusing function. When focusing, the imaging lens may be configured so that the entire imaging lens moves as a unit, so that at least one lens group moves, or so that a part of the imaging lens consisting of at least one lens moves.

[0055] To maintain transmittance over a wide wavelength range from the visible to the SWIR range, the imaging lens may be coated with an anti-reflection coating. The anti-reflection coating may suppress reflection over the entire wavelength range used, or may suppress reflection over only a selected few wavelength ranges used. The anti-reflection coating may be a special coating that suppresses reflection by forming nano-level structures in a moth-eye pattern on the lens surface.

[0056] When manufacturing the imaging lens, a mechanism for adjusting the flange focal distance may be provided to adjust the imaging position. Also, when manufacturing the imaging lens, the imaging position may be adjusted by moving a part of the imaging lens consisting of at least one lens, or a lens group.

[0057] The above-described preferred and possible configurations, including those relating to the conditional expressions, can be combined in any desired manner, and are preferably selectively adopted as appropriate according to the required specifications.

[0058] Next, examples of the imaging lens of the present disclosure will be described. The following Examples 1 to 7, 9 to 10, and 13 to 14 are examples of the present disclosure, and Examples 8 and 11 to 12 are reference examples of the present disclosure. [Example 1] A cross-sectional view of the configuration of the imaging lens of Example 1 is shown in Figure 1, and since the illustration method is as described above, some overlapping explanations will be omitted here. The imaging lens of Example 1 is composed of, in order from the object side to the image side, a first lens group G1, an aperture stop St, and a second lens group G2. The first lens group G1 is composed of, in order from the object side to the image side, lenses L11 to L17. The second lens group G2 is composed of, in order from the object side to the image side, lenses L21 to L27. This concludes the overview of the imaging lens of Example 1.

[0059] For the imaging lens of Example 1, basic lens data is shown in Table 1, specifications in Table 2, and aspherical coefficients in Table 3. In Table 1, the Sn column shows the surface numbers, with the surface closest to the object being surface 1 and the numbers increasing by one toward the image side. The R column shows the radius of curvature of each surface. The D column shows the surface spacing on the optical axis between each surface and its adjacent surface on the image side. The na column shows the refractive index of each component at a wavelength of 1529.58 nm. The ν, θ, and material name columns show the ν, θ, and material name of each component, respectively. The φ column shows the effective diameter of each surface.

[0060] In Table 1, the sign of the radius of curvature of a surface with a convex surface facing the object side is positive, and the sign of the radius of curvature of a surface with a convex surface facing the image side is negative. Table 1 also lists the aperture stop St and optical element PP, and the surface number column for the surface corresponding to the aperture stop St is accompanied by the surface number and the term (St). The value in the bottom column of D in Table 1 is the distance between the surface closest to the image side in the table and the image plane Sim. For each material listed in the material name column, if the manufacturer is specified, the manufacturer's name is listed between the material name and a period. Manufacturer names are listed in general terms, with "OHARA" representing Ohara Corporation and "SCHOTT" representing SCHOTT. In the material name column, "CAF2" represents fluorite, "ZNSE" represents zinc selenide, and "ZNS_MS" represents zinc sulfide multispectral.

[0061] Table 2 shows the focal length f, back focal length Bf in air equivalent distance, F-number FNo., and maximum full angle of view 2ω. The (°) in the 2ω column indicates that the unit is degrees. The values ​​shown in Tables 1 and 2 are based on a wavelength of 1529.58 nm when focused on an object at infinity.

[0062] In Table 1, the aspherical surface numbers are marked with an *, and the column for the radius of curvature of the aspherical surface lists the numerical value of the paraxial radius of curvature. In Table 3, the column for Sn lists the aspherical surface numbers, and the columns for KA and Am (m = 3, 4, 5, ..., 20) list the numerical values ​​of the aspherical coefficients for each aspherical surface. The numerical values ​​of the aspherical coefficients in Table 3, "E±n" (n: integer), are expressed as "×10 ±n" KA and Am are aspherical coefficients in the aspherical formula given below. Zd=C×h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×h m however, Zd: Aspheric depth (length of the perpendicular line drawn from a point on the aspheric surface at height h to a plane perpendicular to the optical axis where the vertex of the aspheric surface touches) h: Height (distance from the optical axis to the lens surface) C: Reciprocal of paraxial radius of curvature KA, Am: aspherical coefficients In the aspherical formula, Σ means the summation over m.

[0063] In the data in each table, the angle unit is degrees and the length unit is mm (millimeters), but since the optical system can be used with proportional enlargement or reduction, other appropriate units can also be used. Also, in each table below, the values ​​are rounded to a predetermined number of decimal places.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] FIG. 4 shows aberration diagrams of the imaging lens of Example 1 when focused on an object at infinity. From left to right, FIG. 4 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration. In the spherical aberration diagram, aberrations at wavelengths of 1529.58 nm, g-line, and 2325.42 nm are shown by solid lines, long-dashed lines, and short-dashed lines, respectively. In the astigmatism diagram, aberrations at wavelengths of 1529.58 nm in the sagittal direction are shown by solid lines, and aberrations at wavelengths of 1529.58 nm in the tangential direction are shown by dashed lines. In the distortion diagram, aberrations at wavelengths of 1529.58 nm based on the equidistant projection method are shown by solid lines. In the lateral chromatic aberration diagram, aberrations at wavelengths of 1529.58 nm are shown by long-dashed lines and short-dashed lines, respectively. The maximum F-number is written next to "FNo.=" on the spherical aberration diagram, and the maximum half angle of view is written next to "ω=" on the other aberration diagrams.

[0068] The symbols, meanings, notation methods, and illustration methods of each data item related to the above-mentioned first embodiment are the same in the following embodiments unless otherwise specified, and therefore, redundant explanations will be omitted below.

[0069] [Example 2] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 2 is shown in Fig. 5. The imaging lens of Example 2 has a configuration similar to that of the imaging lens of Example 1, except that the first lens group G1 is made up of six lenses, lenses L11 to L16, in that order from the object side to the image side. For the imaging lens of Example 2, basic lens data is shown in Table 4, specifications in Table 5, and aspherical coefficients in Table 6, and each aberration diagram is shown in Fig. 6.

[0070] [Table 4]

[0071] [Table 5]

[0072] [Table 6]

[0073] [Example 3] Fig. 7 shows a cross-sectional view illustrating the configuration and light beam of the imaging lens of Example 3. The imaging lens of Example 3 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 3, basic lens data is shown in Table 7, specifications are shown in Table 8, and aspherical coefficients are shown in Table 9, and each aberration diagram is shown in Fig. 8.

[0074] [Table 7]

[0075] [Table 8]

[0076] [Table 9]

[0077] [Example 4] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 4 is shown in Fig. 9. The imaging lens of Example 4 has a configuration similar to that of the imaging lens of Example 1, except that the first lens group G1 is made up of six lenses, lenses L11 to L16, in that order from the object side to the image side. For the imaging lens of Example 4, basic lens data is shown in Table 10, specifications in Table 11, and aspherical coefficients in Table 12, and each aberration diagram is shown in Fig. 10.

[0078] [Table 10]

[0079] [Table 11]

[0080] [Table 12]

[0081] [Example 5] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 5 is shown in Fig. 11. The imaging lens of Example 5 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 5, basic lens data is shown in Table 13, specifications in Table 14, and aspherical coefficients in Table 15, and each aberration diagram is shown in Fig. 12.

[0082] [Table 13]

[0083] [Table 14]

[0084] [Table 15]

[0085] [Example 6] Fig. 13 is a cross-sectional view showing the configuration and light beam of the imaging lens of Example 6. The imaging lens of Example 6 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 6, basic lens data is shown in Table 16, specifications in Table 17, and aspherical coefficients in Table 18, and each aberration diagram is shown in Fig. 14.

[0086] [Table 16]

[0087] [Table 17]

[0088] [Table 18]

[0089] [Example 7] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 7 is shown in Fig. 15. The imaging lens of Example 7 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 7, basic lens data is shown in Table 19, specifications in Table 20, and aspherical coefficients in Table 21, and each aberration diagram is shown in Fig. 16.

[0090] [Table 19]

[0091] [Table 20]

[0092] [Table 21]

[0093] [Example 8] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 8 is shown in Fig. 17. The imaging lens of Example 8 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 8, basic lens data is shown in Table 22, specifications in Table 23, and aspherical coefficients in Table 24, and each aberration diagram is shown in Fig. 18.

[0094] [Table 22]

[0095] [Table 23]

[0096] [Table 24]

[0097] [Example 9] Fig. 19 is a cross-sectional view showing the configuration and light beam of the imaging lens of Example 9. The imaging lens of Example 9 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 9, basic lens data is shown in Table 25, specifications in Table 26, and aspherical coefficients in Table 27, and each aberration diagram is shown in Fig. 20.

[0098] [Table 25]

[0099] [Table 26]

[0100] [Table 27]

[0101] [Example 10] Fig. 21 shows a cross-sectional view illustrating the configuration and light beam of the imaging lens of Example 10. The imaging lens of Example 10 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 10, basic lens data is shown in Table 28, specifications in Table 29, and aspherical coefficients in Table 30, and each aberration diagram is shown in Fig. 22.

[0102] [Table 28]

[0103] [Table 29]

[0104] [Table 30]

[0105] [Example 11] Fig. 23 is a cross-sectional view showing the configuration and light beam of the imaging lens of Example 11. The imaging lens of Example 11 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 11, basic lens data is shown in Table 31, specifications are shown in Table 32, and aspherical coefficients are shown in Table 33, and each aberration diagram is shown in Fig. 24.

[0106] [Table 31]

[0107] [Table 32]

[0108] [Table 33]

[0109] [Example 12] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 12 is shown in Fig. 25. The imaging lens of Example 12 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 12, basic lens data is shown in Table 34, specifications in Table 35, and aspherical coefficients in Table 36, and each aberration diagram is shown in Fig. 26.

[0110] [Table 34]

[0111] [Table 35]

[0112] [Table 36]

[0113] [Example 13] Fig. 27 is a cross-sectional view showing the configuration and light beam of the imaging lens of Example 13. The imaging lens of Example 13 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 13, basic lens data is shown in Table 37, specifications in Table 38, and aspherical coefficients in Table 39, and each aberration diagram is shown in Fig. 28.

[0114] [Table 37]

[0115] [Table 38]

[0116] [Table 39]

[0117] [Example 14] A cross-sectional view showing the configuration and light beam of the imaging lens of Example 14 is shown in Fig. 29. The imaging lens of Example 14 has a configuration similar to the outline of the imaging lens of Example 1. For the imaging lens of Example 14, basic lens data is shown in Table 40, specifications in Table 41, and aspherical coefficients in Table 42, and each aberration diagram is shown in Fig. 30.

[0118] [Table 40]

[0119] [Table 41]

[0120] [Table 42]

[0121] Table 43 shows the corresponding values ​​of conditional expressions (1) to (8) for the imaging lenses of Examples 1 to 14.

[0122] [Table 43]

[0123] From the above data, it can be seen that the imaging lenses of Examples 1 to 14 suppress an increase in the size of the lens system, and also effectively correct various aberrations over a wide wavelength range from the visible range to the SWIR range, thereby achieving high optical performance.

[0124] SWIR light can penetrate fog and smoke better than light with wavelengths of 700 nm to 1000 nm, so imaging with SWIR light can obtain a lot of information. An optical system with a small F-number that is compatible with SWIR light also enables imaging using night airglow, which has a peak wavelength around 1600 nm. Furthermore, because SWIR light has the property of penetrating silicon, it can also be used to inspect silicon wafers, solar cells, and the like. Furthermore, if the spectrum of an object can be obtained from the visible to SWIR range, advanced analysis becomes possible in infrastructure deterioration investigations such as concrete, and in the inspection of agricultural products and soil. As described above, the imaging lens of the present disclosure, which is compatible with the SWIR wavelength range, is highly useful.

[0125] Although the technology of the present disclosure has been described above using exemplary embodiments and examples, the technology of the present disclosure is not limited to the exemplary embodiments and examples and can be modified in various ways. For example, the radius of curvature, surface spacing, refractive index, Abbe number, partial dispersion ratio, effective diameter, etc. of each lens are not limited to the values ​​shown in the examples and can take other values.

[0126] Furthermore, the aberration diagrams in the above examples are shown for a wavelength range of 435.83 nm (g-line) to 2325.42 nm, but the technology of the present disclosure is not limited to this wavelength range and can also be applied to imaging lenses with expanded or narrowed wavelength ranges.

[0127] Next, an imaging device according to an exemplary embodiment of the present disclosure will be described. Fig. 31 shows a schematic configuration diagram of an imaging device 10 using an imaging lens 1 according to an exemplary embodiment of the present disclosure, as an imaging device according to an exemplary embodiment of the present disclosure. Examples of the imaging device 10 include factory automation cameras, music video cameras, digital cameras, surveillance cameras, in-vehicle cameras, and cinema cameras. The imaging device 10 is a camera capable of supporting the visible and SWIR ranges.

[0128] The imaging device 10 includes an imaging lens 1, a filter 4 arranged on the image side of the imaging lens 1, an imaging element 5, and a signal processing unit 6 that performs arithmetic processing on an output signal from the imaging element 5. FIG. 31 conceptually illustrates a first lens group G1, an aperture stop St, and a second lens group G2 of the imaging lens 1. The imaging element 5 captures an image of a subject formed by the imaging lens 1 and converts it into an electrical signal, and may be, for example, a CMOS (Complementary Metal-Oxide Semiconductor) sensor or a CCD (Charge Coupled Device) sensor. The imaging element 5 is arranged so that its imaging surface coincides with the image plane Sim of the imaging lens 1.

[0129] 31 shows only one image sensor 5, the image sensor 10 may be configured to include multiple image sensors. The image sensor 10 may be configured such that a spectroscopic prism and / or a dichroic mirror is inserted somewhere on the optical axis of the optical system, so that light is split into wavelengths and captured by separate image sensors.

[0130] Furthermore, the imaging device according to the exemplary embodiment of the present disclosure is not limited to a camera compatible with the visible and SWIR ranges, and the technology of the present disclosure can also be applied to a visible range camera, a SWIR range camera, a multispectral camera, a hyperspectral camera, a thermography camera, etc.

[0131] The disclosure of Japanese Patent Application No. 2020-195483, filed on November 25, 2020, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. The lens comprises, in order from the object side to the image side, a first lens group, a stop, and a second lens group having positive refractive power, the first lens group includes three or more Ln lenses arranged in series, The Ln lens is a negative lens having a concave surface on the image side, For each lens of the first lens group and the second lens group, the refractive index at a wavelength of 435.83 nm is defined as ng, the refractive index at a wavelength of 1529.58 nm as na, and the refractive index at a wavelength of 2325.42 nm as nb, The Abbe number ν and the partial dispersion ratio θ are respectively ν=(na-1) / (ng-nb), θ is defined as (nan−nb) / (ng−nb), With respect to two Ln lenses selected from the two Ln lenses having stronger refractive powers among the three or more Ln lenses arranged successively in the first lens group, when the average of the Abbe numbers ν is νave and the average of the partial dispersion ratios θ is θave, In an orthogonal coordinate system with the Abbe number ν on the horizontal axis and the partial dispersion ratio θ on the vertical axis, A fifth region represented by θ>0.0250×ν−0.1000; A sixth region represented by θ<0.0250×ν−0.0375; A seventh region represented by θ>0.0500; A tenth region represented by θ≦0.1137; The common area of ​​the four areas includes νave and θave. Imaging lens.

2. The lens comprises, in order from the object side to the image side, a first lens group, a stop, and a second lens group having positive refractive power, the first lens group includes three or more Ln lenses arranged in series, The Ln lens is a negative lens having a concave surface on the image side, For each lens of the first lens group and the second lens group, the refractive index at a wavelength of 435.83 nm is defined as ng, the refractive index at a wavelength of 1529.58 nm as na, and the refractive index at a wavelength of 2325.42 nm as nb, The Abbe number ν and the partial dispersion ratio θ are respectively ν=(na-1) / (ng-nb), θ is defined as (nan−nb) / (ng−nb), With respect to two Ln lenses selected from the two Ln lenses having stronger refractive powers among the three or more Ln lenses arranged successively in the first lens group, when the average of the Abbe numbers ν is νave and the average of the partial dispersion ratios θ is θave, In an orthogonal coordinate system with the Abbe number ν on the horizontal axis and the partial dispersion ratio θ on the vertical axis, A fifth region represented by θ>0.0250×ν−0.1000; A sixth region represented by θ<0.0250×ν−0.0375; A seventh region represented by θ>0.0500; A ninth region represented by θ≦0.1338; The common area of ​​the four areas includes ν and θ, The first lens group includes four or less of the Ln lenses arranged in succession. Imaging lens.

3. The average of the Abbe numbers ν of all the positive lenses of the imaging lens is νPave, The average of the Abbe numbers ν of all the negative lenses of the imaging lens is νNave, The average of the partial dispersion ratios θ of all the positive lenses of the imaging lens is θ ave, When the average of the partial dispersion ratios θ of all the negative lenses of the imaging lens is θNave, 6<νPave−νNave<12 (1) 0.01<θPave−θNave<0.1 (2) The conditional expressions (1) and (2) are satisfied. The imaging lens according to claim 1 or 2.

4. The angle between the chief ray incident on the image plane at the maximum image height and an axis parallel to the optical axis is defined as CRA, If the unit of CRA is degrees, 0≦|CRA|<10 (3) Satisfying conditional expression (3) expressed as The imaging lens according to any one of claims 1 to 3.

5. TL is the sum of the distance on the optical axis from the lens surface of the imaging lens closest to the object side to the lens surface of the imaging lens closest to the image side and the back focus of the imaging lens at a wavelength of 1529.58 nm in terms of the air-equivalent distance; When the focal length of the imaging lens at a wavelength of 1529.58 nm is f, 29<TL / f<38 (4) Satisfying conditional expression (4) expressed as The imaging lens according to any one of claims 1 to 4.

6. The first lens group has a positive refractive power. The imaging lens according to any one of claims 1 to 5.

7. The focal length of the first lens group at a wavelength of 1529.58 nm is fG1, When the focal length of the second lens group at a wavelength of 1529.58 nm is fG2, 0.4<fG2 / fG1<2 (5) Satisfying conditional expression (5) expressed as The imaging lens according to any one of claims 1 to 6.

8. The focal length of the first lens group at a wavelength of 1529.58 nm is fG1, When the focal length of the lens in the first lens group arranged closest to the image at a wavelength of 1529.58 nm is fLp, 1.3<fLp / fG1<3.1 (6) Satisfying conditional expression (6) expressed as The imaging lens according to any one of claims 1 to 7.

9. The effective diameter of the lens surface of the imaging lens closest to the object is φt, When the effective diameter of the lens surface of the imaging lens closest to the image side is φe, 2.5<φt / φe<8 (7) Satisfying conditional expression (7) The imaging lens according to any one of claims 1 to 8.

10. When the Abbe number ν of the lens closest to the image side of the imaging lens is νE, 17<νE (8) Satisfying conditional expression (8) The imaging lens according to any one of claims 1 to 9.

11. At least one of the three or more Ln lenses arranged successively in the first lens group is an aspherical lens. The imaging lens according to any one of claims 1 to 10.

12. The lens closest to the image side of the imaging lens is an aspherical lens having positive refractive power. The imaging lens according to any one of claims 1 to 11.

13. The number of lenses included in the first lens group is seven or less. The imaging lens according to any one of claims 1 to 12.

14. The number of lenses included in the second lens group is seven or less. The imaging lens according to any one of claims 1 to 13.

15. 6.5<νPave−νNave<11.5 (1-1) 0.015<θPave-θNave<0.095 (2-1) The conditional expressions (1-1) and (2-1) are satisfied. The imaging lens according to claim 3 .

16. 0≦|CRA|<9 (3-1) Satisfy the conditional expression (3-1) expressed by The imaging lens according to claim 4 .

17. 29.5<TL / f<37.6 (4-1) Satisfy the conditional expression (4-1) expressed by The imaging lens according to claim 5 .

18. 0.5<fG2 / fG1<1.9 (5-1) Satisfy the conditional expression (5-1) expressed by The imaging lens according to claim 7 .

19. An imaging device comprising the imaging lens according to any one of claims 1 to 18.

Images