Optical system

Abstract

To provide an optical system whose performance is less likely to fluctuate due to assembling.SOLUTION: An optical system 10 comprises a front group 13, a diaphragm 14 and a rear group 15. The front group 13 has negative power. The front group 13 includes a first lens 17 and a second lens 18. The first lens 17 has an image side which is a concave surface and is aspherical on both surfaces, and has negative power. The second lens 18 is positioned closer to the image side than the first lens 17, has an object side which is a concave surface, and has negative power. The diaphragm 14 is positioned closer to the image side than the front group 13. The rear group 15 is positioned closer to the image side than the diaphragm 14. The rear group 15 has positive power. The following conditional expressions (1), (2) are satisfied, where radius of curvature of the image side surface of the first lens 17 is denoted by R12; focal distance of the optical system 10 is denoted by f; and radius of curvature of the object side surface of the second lens 18 is denoted by R21. 0.56<R12 / f<0.67 ... (1) and -1.2≤R21 / f<-1 ... (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to optical systems. [Background technology]

[0002] Image sensors for surveillance cameras, in-vehicle cameras, and the like are becoming increasingly high-resolution. This trend toward higher pixel counts has led to a demand for higher-resolution optical systems. Furthermore, surveillance cameras, in-vehicle cameras, and the like are required to capture peripheral scenes with a wide angle of view. To achieve a wide-angle, high-resolution optical system, it has been proposed to use an aspherical lens in part of the optical system (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-126861 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for optical systems that use aspherical lenses in some parts but have low performance fluctuations due to assembly. [Means for solving the problem]

[0005] An optical system according to an embodiment of the present disclosure includes: a front group having negative power, the front group including a first lens having a concave surface on the image side, aspherical surfaces on both sides, and negative power, and a second lens located closer to the image side than the first lens, having a concave surface on the object side, aspherical surfaces on both sides, and negative power; a stop positioned closer to the image side than the front group; an optical system comprising: a third lens having convex surfaces on both sides; a fourth lens located closer to the image side than the third lens and having convex surfaces on both sides and aspherical surfaces on both sides; and a rear group having positive power located closer to the image side than the fourth lens and consisting of a cemented lens formed by cementing together a fifth lens which is a convex lens and a sixth lens which is a concave lens, When the radius of curvature of the image side surface of the first lens is R12, the focal length of the optical system is f, and the radius of curvature of the object side surface of the second lens is R21, conditional expressions (1) and (2) are satisfied. 0.56 <R12 / f<0.67 (1) -1.2≦R21 / f<-1 (2) [Effects of the Invention]

[0006] According to an optical system according to an embodiment of the present disclosure, performance variations due to assembly can be reduced. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a lens configuration diagram of an optical system according to an embodiment of the present disclosure, in Example 1. [Figure 2A] FIG. 2 is a graph showing spherical aberration of the optical system of FIG. [Figure 2B] FIG. 2 is a graph showing astigmatism of the optical system of FIG. [Figure 2C] FIG. 2 is a graph showing distortion of the optical system of FIG. [Figure 3] FIG. 10 is a lens configuration diagram of an optical system according to Example 2 of the present disclosure. [Figure 4A] FIG. 3 is a graph showing spherical aberration of the optical system of FIG. 2. [Figure 4B] FIG. 3 is a graph showing astigmatism of the optical system of FIG. 2. [Figure 4C] FIG. 3 is a graph showing distortion of the optical system of FIG. 2. [Figure 5] FIG. 10 is a lens configuration diagram of an optical system according to Example 3 of the present disclosure. [Figure 6A] FIG. 6 is a graph showing spherical aberration of the optical system of FIG. 5. [Figure 6B] FIG. 6 is a graph showing astigmatism of the optical system of FIG. 5. [Figure 6C] FIG. 6 is a graph showing distortion of the optical system of FIG. 5. [Figure 7] FIG. 10 is a lens configuration diagram of an optical system according to Example 4 of the present disclosure. [Figure 8A] FIG. 8 is a graph showing spherical aberration of the optical system of FIG. [Figure 8B] FIG. 8 is a graph showing astigmatism of the optical system of FIG. [Figure 8C] FIG. 8 is a graph showing distortion of the optical system of FIG. 7. [Figure 9] FIG. 10 is a lens configuration diagram of an optical system according to Example 5 of the present disclosure. [Figure 10A] FIG. 10 is a graph showing spherical aberration of the optical system of FIG. [Figure 10B] FIG. 10 is a graph showing astigmatism of the optical system of FIG. [Figure 10C] FIG. 10 is a graph showing distortion of the optical system of FIG. [Figure 11] FIG. 10 is a lens configuration diagram of an optical system according to Example 6 of the present disclosure. [Figure 12A] FIG. 12 is a graph showing spherical aberration of the optical system of FIG. [Figure 12B] FIG. 12 is a graph showing astigmatism of the optical system of FIG. [Figure 12C] FIG. 12 is a graph showing distortion of the optical system of FIG. [Figure 13] FIG. 10 is a lens configuration diagram of an optical system according to Example 7 of the present disclosure. [Figure 14A] FIG. 14 is a graph showing spherical aberration of the optical system of FIG. [Figure 14B] FIG. 14 is a graph showing astigmatism of the optical system of FIG. [Figure 14C] FIG. 14 is a graph showing distortion of the optical system of FIG. 13. [Figure 15] FIG. 13 is a lens configuration diagram of an optical system according to Example 8 of the present disclosure. [Figure 16A] FIG. 16 is a graph showing spherical aberration of the optical system of FIG. [Figure 16B] FIG. 16 is a graph showing astigmatism of the optical system of FIG. [Figure 16C] FIG. 16 is a graph showing distortion of the optical system of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0009] An optical system according to one embodiment will be described below with reference to the accompanying drawings. In each of the accompanying drawings showing the configuration of the optical system, the "object side" corresponds to the left side, and the "image side" corresponds to the right side. The drawings used in the following description are schematic, and the dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0010] As shown in FIG. 1 , an imaging device 11 including an optical system 10 according to an embodiment of the present disclosure may include an imaging element 12 and the optical system 10. The imaging device 11 according to an embodiment of the present disclosure may be mounted on a mobile object. Examples of mobile objects include automobiles, industrial vehicles, railroad vehicles, residential vehicles, and fixed-wing aircraft traveling on runways. Examples of automobiles include passenger cars, trucks, buses, motorcycles, and trolleybuses. Examples of industrial vehicles include agricultural and construction vehicles. Examples of industrial vehicles include forklifts and golf carts. Examples of agricultural industrial vehicles include tractors, cultivators, transplanters, binders, combines, and lawnmowers. Examples of construction industrial vehicles include bulldozers, scrapers, excavators, cranes, dump trucks, and road rollers. Examples of mobile objects include those powered by human power.

[0011] The imaging device 11 may capture moving images, for example, by continuously repeating imaging. The imaging device 11 may be used, for example, in a surveillance camera or an in-vehicle camera. In a configuration in which the imaging device 11 is used in an in-vehicle camera, the imaging device 11 may be located, for example, at least one of the side, front, and rear of a vehicle equipped with a control device that controls the imaging device 11. The imaging device 11 may capture images of at least one of the side, front, and rear of the vehicle.

[0012] The image sensor 12 may convert an optical image formed on an image plane is, where the optical system 10 forms an optical image of a subject, into an image signal. The image sensor 12 may include a solid-state image sensor such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS).

[0013] As described below, the optical system 10 may be a six-lens fixed focal length imaging lens. The optical system 10 may be located closer to the object than the image sensor 12. The optical system 10 includes a front group 13, an aperture stop 14, and a rear group 15. The optical system 10 may further include an optical element that has substantially no refractive power, such as a cover glass 16. The front group 13 has negative power. The aperture stop 14 is located closer to the image than the front group 13. The rear group 15 is located closer to the image than the aperture stop 14. The rear group 15 has positive power. The cover glass 16 may cover the image plane is of the image sensor 12. The cover glass 16 may be a parallel plate.

[0014] The front group 13 is made up of a first lens element 17 and a second lens element 18 .

[0015] The first lens 17 has a concave surface on the image side. The first lens 17 may have a convex surface on the object side. Both surfaces of the first lens 17 are aspheric. The radius of curvature of at least the object-side surface of the first lens 17 may be formed to increase with increasing distance from the optical axis ox. The first lens 17 has negative power.

[0016] The first lens 17 satisfies the condition of formula (1) on the image side surface. 0.56 <R12 / f<0.67 (1) In equation (1), R12 is the radius of curvature of the image-side surface of first lens 17. f is the focal length of optical system 10.

[0017] The second lens 18 is located closer to the image side than the first lens 17. The second lens 18 has a concave surface facing the object side. The second lens 18 may have a convex surface facing the image side. Both surfaces of the second lens 18 are aspheric. The second lens 18 has negative power.

[0018] The second lens 18 satisfies the condition of formula (2) on the object side surface. -1.2≦R21 / f<-1 (2) In equation (2), R21 is the radius of curvature of the object side surface of the second lens 18.

[0019] The diaphragm 14 may adjust the F-number of the optical system 10. The diaphragm 14 may be disposed close to the first lens 17 and the second lens 18. The diaphragm 14 may be provided between the second lens 18 and a third lens, which will be described later. By disposing the diaphragm 14 close to the first lens 17 and the second lens 18, the optical system 10 can have a wider angle of view while keeping the effective diameter of the first lens 17 small.

[0020] The rear group 15 is made up of a third lens element 19, a fourth lens element 20, and a cemented lens element 21.

[0021] The third lens 19 may be located closer to the image side than the aperture stop 14. The third lens 19 has convex surfaces on both sides. The third lens 19 may have positive power.

[0022] The fourth lens 20 is located closer to the image side than the third lens 19. The fourth lens 20 has convex surfaces on both sides. Both sides of the fourth lens 20 are aspherical. The focal length of the fourth lens 20 may be shorter than the focal lengths of other lenses having positive power in the optical system 10, in other words, the third lens 19 and a fifth lens (described later).

[0023] The fourth lens 20 may have a larger coefficient of linear expansion than the other lenses constituting the optical system 10, in other words, the first lens 17, the second lens 18, the third lens 19, and the cemented lens 21. The fourth lens 20 may be made of a glass material whose temperature coefficient of relative refractive index is a negative value. For example, the temperature coefficient of relative refractive index of the fourth lens 20 from 20°C to 40°C may be, for example, -6.2×10 -6 / °C.

[0024] The cemented lens 21 is located closer to the image side than the fourth lens 20. The cemented lens 21 is formed by cementing together a fifth lens 22 and a sixth lens 23. The fifth lens 22 and the sixth lens 23 may be cemented together with an adhesive, for example.

[0025] The fifth lens 22 is a convex lens having convex surfaces on both sides. The fifth lens 22 may be a spherical lens. The fifth lens 22 may have positive power.

[0026] The sixth lens 23 may be located closer to the object side than the fifth lens 22. The sixth lens 23 may be a concave lens having a concave surface on the object side. The sixth lens 23 may have a substantially flat surface on the image side. Specifically, the radius of curvature of the image side surface of the sixth lens 23 may be less than −200. The sixth lens 23 may be a spherical lens. The sixth lens 23 may have negative power.

[0027] The sixth lens 23 may be made of a glass material that satisfies the following formulas (3) and (4). 1.9 <nd6<2 (3) 16<νd6<20 (4) In equation (3), nd6 is the refractive index for the d-line of the glass material of the sixth lens 23. In equation (4), νd6 is the Abbe number for the d-line of the glass material.

[0028] An infrared cut coating may be provided on the image side surface of the sixth lens 23. The infrared cut coating may transmit visible light. The infrared cut coating may block electromagnetic waves in the near-infrared region, for example, in the range of 700 nm to 1200 nm. The infrared cut coating may be formed on the sixth lens 23 by, for example, vapor deposition. The infrared cut coating may also be provided on the sixth lens 23 by other known methods.

[0029] In the optical system 10, the first lens 17, the second lens 18, the diaphragm 14, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 may be positioned so as to satisfy the following formula (5). 0.45 <Df / Dr<0.65 (5) In equation (5), Df is the distance from the object side surface of the first lens 17 to the diaphragm 14 on the optical axis ox of the optical system 10. Also, Dr is the distance from the diaphragm 14 to the image side surface of the sixth lens 23 on the optical axis ox.

[0030] In the optical system 10, the first lens 17, the second lens 18, the diaphragm 14, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 may be positioned so as to satisfy the following formula (6). 0.23 <f / Dt / <0.27 (6) In equation (6), Dt is the distance from the object side surface of the first lens 17 to the image side surface of the sixth lens 23 on the optical axis ox of the optical system 10.

[0031] The first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 may be formed of a glass material. By forming the lenses from a glass material, yellowing due to ultraviolet rays and changes in optical properties due to temperature changes can be reduced. Alternatively, the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 may each be formed of a glass material with a different refractive index. The material of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 does not have to be limited to a glass material. For example, at least one of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 may be formed from a material other than a glass material, such as a resin material.

[0032] The optical system 10 of this embodiment, configured as described above, comprises a first lens 17 that has a concave surface on the image side, is aspherical on both sides, and has negative power; a second lens 18 that is located closer to the image side than the first lens 17, has a concave surface on the object side, is aspherical on both sides, and has negative power; a front group 13 that has negative power; a stop 14 that is located closer to the image side than the front group 13; a third lens 19 that has convex surfaces on both sides; and a second lens 18 that is located closer to the image side than the third lens 19, has convex surfaces on both sides. The optical system 10 includes a fourth lens 20 having aspherical surfaces on both sides, a cemented lens 21 positioned closer to the image side than the fourth lens 20 and formed by cementing together a fifth lens 22, which is a convex lens, and a sixth lens 23, which is a concave lens, and a rear group 15 positioned closer to the image side than the aperture stop 14 and having positive power, where R12 is the radius of curvature of the image-side surface of the first lens 17, f is the focal length of the optical system 10, and R21 is the radius of curvature of the object-side surface of the second lens 18, satisfying conditional expressions (1) and (2). With this configuration, the optical system 10 can have a large refractive power in the entire front group 13 because R12 / f and R21 / f have upper limits. Therefore, the optical system 10 can reduce aberrations. Furthermore, with this configuration, the optical system 10 can prevent the refractive powers of the first lens 17 and the second lens 18 from becoming excessively large because R12 and R21 have lower limits. This can reduce performance changes due to decentering. Therefore, the optical system 10 can increase the tolerance for assembly errors. In this way, the optical system 10 can reduce aberrations, in other words, reduce performance changes due to assembly while maintaining desired optical performance. Furthermore, since the optical system 10 has the cemented lens 21 formed by cementing the fifth lens 22 and the sixth lens 23 together, the optical system 10 can improve optical performance such as chromatic aberration correction while reducing the decentering sensitivity of the optical system 10, thereby improving productivity.

[0033] Furthermore, the optical system 10 satisfies conditional expression (5), where Df is the distance from the object-side surface of the first lens to the aperture stop 14 on the optical axis ox, and Dr is the distance from the aperture stop 14 to the image-side surface of the sixth lens 23. With this configuration, the optical system 10 prevents the front group 13 from becoming excessively long because Df / Dr has an upper limit. Therefore, the optical system 10 can reduce the height of light rays incident on the first lens 17 by adjusting the position of the aperture stop 14 so that it is closer to the object. Therefore, the optical system 10 can reduce the lens diameter of the first lens 17. With this configuration, the optical system 10 prevents the front group 13 from becoming excessively short because Df / Dr has a lower limit. Therefore, the optical system 10 maintains the position of the aperture stop 14 appropriately, preventing an excessive increase in the angle of light rays incident on each surface of the front group 13. In this way, the optical system 10 can correct aberrations.

[0034] Furthermore, the optical system 10 satisfies conditional expression (6), where Dt is the distance from the object-side surface of the first lens 17 to the image-side surface of the sixth lens 23 on the optical axis ox. With this configuration, the optical system 10 has an upper limit value for f / Dt, so its overall length is not excessively short compared to its focal length, facilitating mass production. Furthermore, the optical system 10 has a lower limit value for f / Dt, so its overall length is not excessively long compared to its focal length, allowing for overall miniaturization.

[0035] Furthermore, the optical system 10 satisfies conditional formula (3) when the refractive index of the glass material of the sixth lens 23 is nd6. With this configuration, the optical system 10 has an upper limit for nd6, allowing a material to be selected that can satisfy a desired internal transmittance for light with a wavelength of around 400 nm. With this configuration, the optical system 10 has a lower limit for nd6, allowing lateral chromatic aberration to be effectively corrected. With the Abbe number of the glass material of the sixth lens 23 is νd6, the optical system 10 satisfies conditional formula (4). With this configuration, the optical system 10 has an upper limit for νd6, allowing lateral chromatic aberration to be effectively corrected. With this configuration, the optical system 10 has a lower limit for νd6, allowing a material to be selected that can satisfy a desired internal transmittance for light with a wavelength of around 400 nm.

[0036] Furthermore, the optical system 10 is provided with an infrared-cutting coating on the image-side surface of the sixth lens 23. To capture a visible light image using a known image sensor, it is necessary to reduce the transmission of infrared light in the subject light flux formed by the optical system 10. To reduce the amount of infrared light transmitted, it is possible to provide an infrared-cutting filter on the light-receiving surface of the image sensor. However, a configuration with an infrared-cutting filter can cause multiple reflections between the sixth lens 23, a refractive element constituting the optical system 10, and thus generate a virtual image on the light-receiving surface of the image sensor. To address this issue, the optical system 10 having the above-described configuration provides an infrared-cutting coating on the sixth lens 23, which is a refractive element constituting the optical system 10, instead of providing an infrared-cutting filter, thereby reducing the number of optical elements that can generate multiple reflections. Therefore, the optical system 10 can form a subject image with reduced infrared light transmission while reducing the effect of virtual images. Furthermore, it is necessary to uniformly reduce the amount of infrared light transmitted across the entire light-receiving surface of the image sensor. Therefore, it is preferable that the infrared-cutting coating be provided on a surface with a large radius of curvature. To cope with such a situation, the optical system 10 having the above-described configuration satisfies the expressions (1) and (2), thereby making it possible to form a large radius of curvature for the image-side surface of the sixth lens 23, which is the refractive element located furthest to the image side in the optical system 10. Therefore, the optical system 10 provides an infrared cut coating on the image-side surface of the sixth lens 23, thereby making it possible to uniformly reduce the transmittance of infrared light.

[0037] Furthermore, in the optical system 10, the radius of curvature of the image-side surface of the sixth lens 23 is less than -200. With this configuration, the optical system 10 has an infrared-cutting coating provided on the surface with a large radius of curvature, which can reduce the difference in height of the infrared-cutting coating between the center and periphery of the sixth lens 23. Therefore, in the optical system 10, the difference in thickness of the infrared-cutting coating is reduced, which can reduce the influence of differences in the amount of infrared light transmitted on the subject image formed by the optical system 10.

[0038] In addition, in the optical system 10, the temperature coefficient of the relative refractive index of the fourth lens 20 at temperatures between 20°C and 40°C is a negative value. With this configuration, the optical system 10 has a function of temperature compensation for the entire lens. Therefore, the optical system 10 can also have a function of minimizing the amount of focus movement as a whole. [Example]

[0039] Next, a description will be given mainly of the lens configurations of examples of the optical system 10 of the present disclosure. More specifically, examples 1 to 8 will be shown using specific numerical values ​​of the optical system 10. Examples 1 to 8 have the characteristics of the optical system 10 described above with respect to the positive and negative powers of each lens, the surface shapes, and the parameters shown in conditional expressions (1) to (6).

[0040] In the basic lens data for each of the following examples, the number i (i is a natural number) in the lens specifications is a surface number assigned to each surface of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, sixth lens 23, aperture 14, and cover glass 16 included in the optical system 10, in order from the object side. Si indicates the i-th surface. Ri is the radius of curvature of the i-th surface. Di is the distance on the optical axis ox between the i-th surface Si and the (i+1)-th surface Si+1. Nd is the refractive index for the d-line. νd is the Abbe number for the d-line. The surface spacing Di is shown only in FIG. 1 for Example 1, and is not shown in the drawings for the other examples.

[0041] In all of the following specification values, the units of length such as the radius of curvature Ri and the surface spacing Di are millimeters (mm) unless otherwise specified, and are omitted in each table. In each table, "E" indicates an exponential notation (power of 10). The configuration of the optical system 10 is not limited to the configuration in the following examples, and equivalent optical performance can be obtained in both proportional magnification and proportional reduction.

[0042] Of the surfaces of the lenses in the following examples, the shape of the aspherical surface is expressed by the following formula (7): Formula (7) is an aspherical equation.

[0043]

number

[0044] Each numerical value in formula (7) is positive in the direction from the object side to the image side. K is a conic coefficient, and A is an aspherical coefficient of the i-th order. h is the height of the light ray, C is the reciprocal of the central radius of curvature, and Z is the depth from the tangent plane to the surface vertex. The aspherical data in each of the following examples indicates the aspherical coefficients and the like when the aspherical shape of the lens surface marked with an * in the basic lens data is expressed using formula 7.

[0045] In FIG. 1 , D1 is the thickness of the first lens 17 on the optical axis ox. D2 is the distance between the first lens 17 and the second lens 18 on the optical axis ox. D3 is the thickness of the second lens 18 on the optical axis ox. D4 is the distance between the second lens 18 and the diaphragm 14 on the optical axis ox. D5 is the distance between the diaphragm 14 and the third lens 19 on the optical axis ox. D6 is the thickness of the third lens 20 on the optical axis ox. D7 is the distance between the third lens 19 and the fourth lens 20 on the optical axis ox. D8 is the thickness of the fourth lens 20 on the optical axis ox. D9 is the distance between the fourth lens 20 and the cemented lens 21 on the optical axis ox. D10 is the thickness of the fifth lens 22 on the optical axis ox. D11 is the thickness of the sixth lens 23 on the optical axis ox. D12 is the distance between the cemented lens 21 and the cover glass 16 on the optical axis ox. D13 is the thickness of the cover glass 16. D14 is the distance between the cover glass 16 and the imaging element 12.

[0046] Example 1 FIG. 1 is a lens configuration diagram of an optical system 10 according to Example 1 of the present disclosure. FIG. 1 illustrates the lens configuration of the optical system 10 according to Example 1 in an optical cross section. As shown in FIG. 1, in the optical system 10 of Example 1, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above. The above description regarding the surface spacing Di similarly applies to the other examples below.

[0047] Table 1 shows basic lens data including specifications of the optical system 10 according to Example 1. In Table 1, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0048] [Table 1]

[0049] Table 2 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 1. The aspheric data shown in Table 2 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0050] [Table 2]

[0051] In the optical system 10 according to Example 1, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0052] [Table 3]

[0053] Figure 2A is a graph showing the spherical aberration of the optical system 10 of Figure 1. In Figure 2A, the vertical axis represents the entrance height on the entrance pupil normalized to a pupil diameter of 1, and the horizontal axis represents the deviation of the image position. Each line in the graph represents the spherical aberration (mm) for the C-line, d-line, and F-line shown on the right of the graph.

[0054] 2B is a graph showing the astigmatism of the optical system 10 of FIG. 1. In FIG. 2B, the vertical axis indicates the entrance height on the entrance pupil normalized to a pupil diameter of 1, and the horizontal axis indicates the deviation of the image position. Each line in the graph indicates astigmatism (mm) for the d-line. "Sagittal" refers to the value of the image plane in the sagittal direction, and "Tangential" refers to the value of the image plane in the vertical (hereinafter referred to as tangential) direction.

[0055] Fig. 2C is a graph showing distortion of the optical system 10 of Fig. 1. In Fig. 2C, the vertical axis represents the entrance height on the entrance pupil normalized to a pupil diameter of 1, and the horizontal axis represents the deviation of the image position. The line in the graph represents distortion (%) for the d-line.

[0056] As shown in FIGS. 2A, 2B, and 2C, according to the first embodiment, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance is obtained.

[0057] The above explanation regarding the aberration diagrams also applies to the aberration diagrams shown in the other examples, and therefore the explanation will be omitted below.

[0058] Example 2 Fig. 3 is a lens configuration diagram of an optical system 10 according to Example 2 of the present disclosure. Fig. 3 shows an optical cross section of the lens configuration of the optical system 10 according to Example 2. As shown in Fig. 3, in the optical system 10 of Example 2, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above.

[0059] Table 4 shows basic lens data including specifications of the optical system 10 according to Example 2. In Table 4, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0060] [Table 4]

[0061] Table 5 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 2. The aspheric data shown in Table 5 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0062] [Table 5]

[0063] In the optical system 10 according to Example 2, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0064] Fig. 4A is a graph showing the spherical aberration of the optical system 10 of Fig. 3. Fig. 4B is a graph showing the astigmatism of the optical system 10 of Fig. 3. Fig. 4C is a graph showing the distortion of the optical system 10 of Fig. 3. As shown in Figs. 4A, 4B, and 4C, according to Example 2, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0065] Example 3 Fig. 5 is a lens configuration diagram of an optical system 10 according to Example 3 of the present disclosure. Fig. 5 shows an optical cross section of the lens configuration of the optical system 10 according to Example 3. As shown in Fig. 5, in the optical system 10 of Example 3, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above.

[0066] Table 6 shows basic lens data including specifications of the optical system 10 according to Example 3. In Table 6, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0067] [Table 6]

[0068] Table 7 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 3. The aspheric data shown in Table 7 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0069] [Table 7]

[0070] In the optical system 10 according to Example 3, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0071] Fig. 6A is a graph showing the spherical aberration of the optical system 10 of Fig. 5. Fig. 6B is a graph showing the astigmatism of the optical system 10 of Fig. 5. Fig. 6C is a graph showing the distortion of the optical system 10 of Fig. 5. As shown in Figs. 6A, 6B, and 6C, according to Example 3, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0072] Example 4 Fig. 7 is a lens configuration diagram of an optical system 10 according to Example 4 of the present disclosure. Fig. 7 shows an optical cross section of the lens configuration of the optical system 10 according to Example 4. As shown in Fig. 7, in the optical system 10 of Example 4, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above.

[0073] Table 8 shows basic lens data including specifications of the optical system 10 according to Example 4. In Table 8, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0074] [Table 8]

[0075] Table 9 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 4. The aspheric data shown in Table 9 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0076] [Table 9]

[0077] In the optical system 10 according to Example 4, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0078] Fig. 8A is a graph showing the spherical aberration of the optical system 10 of Fig. 7. Fig. 8B is a graph showing the astigmatism of the optical system 10 of Fig. 7. Fig. 8C is a graph showing the distortion of the optical system 10 of Fig. 7. As shown in Figs. 8A, 8B, and 8C, according to Example 4, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0079] Example 5 Fig. 9 is a lens configuration diagram of an optical system 10 according to Example 5 of the present disclosure. Fig. 9 shows an optical cross section of the lens configuration of the optical system 10 according to Example 5. As shown in Fig. 9, in the optical system 10 of Example 5, the powers and shapes of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, and the sixth lens 23 are as described above.

[0080] Table 10 shows basic lens data including specifications of the optical system 10 according to Example 5. In Table 10, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0081] [Table 10]

[0082] Table 11 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 5. The aspheric data shown in Table 11 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0083] [Table 11]

[0084] In the optical system 10 according to Example 5, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0085] Fig. 10A is a graph showing the spherical aberration of the optical system 10 of Fig. 9. Fig. 10B is a graph showing the astigmatism of the optical system 10 of Fig. 9. Fig. 10C is a graph showing the distortion of the optical system 10 of Fig. 9. As shown in Figs. 10A, 10B, and 10C, according to Example 5, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0086] Example 6 Fig. 11 is a lens configuration diagram of an optical system 10 according to Example 6 of the present disclosure. Fig. 11 shows an optical cross section of the lens configuration of the optical system 10 according to Example 6. As shown in Fig. 11, in the optical system 10 of Example 6, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above.

[0087] Table 12 shows basic lens data including specifications of the optical system 10 according to Example 6. In Table 12, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0088] [Table 12]

[0089] Table 13 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 6. The aspheric data shown in Table 13 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0090] [Table 13]

[0091] In the optical system 10 according to Example 6, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0092] Fig. 12A is a graph showing the spherical aberration of the optical system 10 of Fig. 11. Fig. 12B is a graph showing the astigmatism of the optical system 10 of Fig. 11. Fig. 12C is a graph showing the distortion of the optical system 10 of Fig. 11. As shown in Figs. 12A, 12B, and 12C, according to Example 6, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0093] Example 7 Fig. 13 is a lens configuration diagram of an optical system 10 according to Example 7 of the present disclosure. Fig. 13 shows an optical cross section of the lens configuration of the optical system 10 according to Example 7. As shown in Fig. 13, in the optical system 10 of Example 7, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above.

[0094] Table 14 shows basic lens data including specifications of the optical system 10 according to Example 7. In Table 14, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0095] [Table 14]

[0096] Table 15 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 7. The aspheric data shown in Table 15 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0097] [Table 15]

[0098] In the optical system 10 according to Example 7, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0099] Fig. 14A is a graph showing the spherical aberration of the optical system 10 of Fig. 13. Fig. 14B is a graph showing the astigmatism of the optical system 10 of Fig. 13. Fig. 14C is a graph showing the distortion of the optical system 10 of Fig. 13. As shown in Figs. 14A, 14B, and 14C, according to Example 7, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0100] Example 8 Fig. 15 is a lens configuration diagram of an optical system 10 according to Example 8 of the present disclosure. Fig. 15 shows an optical cross section of the lens configuration of the optical system 10 according to Example 8. As shown in Fig. 15, in the optical system 10 of Example 8, the powers and shapes of the first lens 17, second lens 18, third lens 19, fourth lens 20, fifth lens 22, and sixth lens 23 are as described above.

[0101] Table 16 shows basic lens data including specifications of the optical system 10 according to Example 8. In Table 16, for aspherical surfaces S1, S2, S3, S4, S8, and S9 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0102] [Table 16]

[0103] Table 17 shows aspheric data including aspheric coefficients of the optical system 10 according to Example 8. The aspheric data shown in Table 17 is data for each of the surfaces S1 and S2 of the first lens 17, the surfaces S2 and S4 of the second lens 18, and the surfaces S8 and S9 of the fourth lens 20.

[0104] [Table 17]

[0105] In the optical system 10 according to Example 7, the focal lengths f1, f2, f3, f4, f5, f6, f56, and f of the first lens 17, the second lens 18, the third lens 19, the fourth lens 20, the fifth lens 22, the sixth lens 23, the cemented lens 21, and the optical system 10, the distance Df from the object side surface of the first lens 17 to the aperture 14, the distance Dr from the aperture 14 to the image side surface of the sixth lens 23, the distance Dt from the object side surface of the first lens 17 to the image side surface of the sixth lens 23, the refractive index nd6 and Abbe number vd6 of the glass material of the sixth lens 23, and the radii of curvature R62, R12 / f, R21 / f, Df / Dr, and f / Dt of the image side surface of the sixth lens 23 are as shown in Table 3.

[0106] Fig. 16A is a graph showing the spherical aberration of the optical system 10 of Fig. 15. Fig. 16B is a graph showing the astigmatism of the optical system 10 of Fig. 15. Fig. 16C is a graph showing the distortion of the optical system 10 of Fig. 15. As shown in Figs. 16A, 16B, and 16C, according to Example 8, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0107] In one embodiment, (1) the optical system comprises: a front group having negative power, the front group including a first lens having a concave surface on the image side, aspherical surfaces on both sides, and negative power, and a second lens located closer to the image side than the first lens, having a concave surface on the object side, aspherical surfaces on both sides, and negative power; a stop positioned closer to the image side than the front group; an optical system comprising: a third lens having convex surfaces on both sides; a fourth lens located closer to the image side than the third lens and having convex surfaces on both sides and aspherical surfaces on both sides; and a rear group having positive power located closer to the image side than the fourth lens and consisting of a cemented lens formed by cementing together a fifth lens which is a convex lens and a sixth lens which is a concave lens, When the radius of curvature of the image side surface of the first lens is R12, the focal length of the optical system is f, and the radius of curvature of the object side surface of the second lens is R21, conditional expressions (1) and (2) are satisfied. 0.56 <R12 / f<0.67 (1) -1.2≦R21 / f<-1 (2)

[0108] (2) In the optical system described in (1) above, If the distance on the optical axis from the object side surface of the first lens to the diaphragm is Df and the distance from the diaphragm to the image side surface of the sixth lens is Dr, then conditional expression (3) is satisfied. 0.45 <Df / Dr<0.65 (3)

[0109] (3) In the optical system of (1) or (2) above, If the distance on the optical axis from the object side surface of the first lens to the image side surface of the sixth lens is Dt, then conditional expression (4) is satisfied. 0.23 <f / Dt / <0.27 (4)

[0110] (4) In any of the optical systems (1) to (3) above, If the refractive index of the glass material of the sixth lens is nd6 and the Abbe number is νd6, then conditional expressions (5) and (6) are satisfied. 1.9 <nd6<2 (5) 16<νd6<20 (6)

[0111] (5) In any of the optical systems (1) to (3) above, An infrared cut coating is provided on the image side surface of the sixth lens.

[0112] (6) In the optical system of (5) above, The radius of curvature of the image side surface of the sixth lens is less than −200.

[0113] (7) In any of the optical systems (1) to (6) above, The diaphragm is provided between the second lens and the third lens.

[0114] (8) In any of the optical systems (1) to (7) above, The fourth lens has a negative temperature coefficient of relative refractive index in the temperature range of 20° C. to 40° C.

[0115] It will be apparent to those skilled in the art that the present disclosure may be embodied in other specific forms other than the above-described embodiments without departing from the spirit or essential characteristics thereof. Therefore, the foregoing description is illustrative and not limiting. The scope of the disclosure is defined not by the foregoing description but by the appended claims. All modifications within the range of equivalents of any modifications are intended to be embraced therein.

[0116] For example, the shape, size, arrangement, orientation, number, etc. of each of the above-described components are not limited to the above description and the illustrations in the drawings, and may be configured arbitrarily as long as the functions thereof can be realized.

[0117] Although the optical system 10 according to one embodiment has been described, the present disclosure is not limited to the optical system 10 of each of the above-described examples, and various modifications are possible without departing from the spirit of the invention. For example, the specifications of the optical system 10 of each example are merely examples, and various parameters can be changed within the scope of the present disclosure. [Explanation of symbols]

[0118] 10 Optical system 11 Imaging device 12 Image sensor 13 front group 14 Aperture 15 Rear group 16 cover slips 17 First lens 18 Second lens 19 Third lens 20 Fourth lens 21 cemented lens 22 5th lens 23 6th lens is image plane ox optical axis

Claims

1. a front group having negative power, the front group including a first lens having a concave surface on the image side, aspherical surfaces on both sides, and negative power, and a second lens located closer to the image side than the first lens, having a concave surface on the object side, aspherical surfaces on both sides, and negative power; a stop positioned closer to the image side than the front group; an optical system comprising: a third lens having convex surfaces on both sides; a fourth lens located closer to the image side than the third lens and having convex surfaces on both sides and aspherical surfaces on both sides; and a rear group having positive power located closer to the image side than the fourth lens and including a cemented lens formed by cementing together a fifth lens which is a convex lens and a sixth lens which is a concave lens, When the radius of curvature of the image side surface of the first lens is R12, the focal length of the optical system is f, and the radius of curvature of the object side surface of the second lens is R21, the conditional expressions (1) and (2) are satisfied. optical system. 0.56<R12 / f<0.67 (1) -1.2≦R21 / f<-1 (2)

2. 2. The optical system according to claim 1, When the distance on the optical axis from the object side surface of the first lens to the diaphragm is Df and the distance from the diaphragm to the image side surface of the sixth lens is Dr, conditional expression (3) is satisfied. optical system. 0.45<Df / Dr<0.65 (3)

3. 3. The optical system according to claim 1, If the distance on the optical axis from the object side surface of the first lens to the image side surface of the sixth lens is Dt, then conditional expression (4) is satisfied. optical system. 0.23<f / Dt / <0.27 (4)

4. 3. The optical system according to claim 1, When the refractive index of the glass material of the sixth lens is nd6 and the Abbe number is νd6, the conditional expressions (5) and (6) are satisfied. optical system. 1.9<nd6<2 (5) 16<νd6<20 (6)

5. 3. The optical system according to claim 1, An infrared cut coating is provided on the image side surface of the sixth lens. optical system.

6. 6. The optical system according to claim 5, The radius of curvature of the image side surface of the sixth lens is less than −200 optical system.

7. 3. The optical system according to claim 1, The diaphragm is provided between the second lens and the third lens. optical system.

8. 3. The optical system according to claim 1, The fourth lens has a negative temperature coefficient of relative refractive index in the temperature range from 20° C. to 40° C. optical system.

Images