Optical system

Abstract

The optical system has a front group, a diaphragm, and a rear group. The front group comprises a first lens, a second lens, a third lens, and a fourth lens. The first lens has negative power. The second lens has negative power. The third lens has positive power. The fourth lens has positive power. The rear group comprises a fifth lens and a cemented lens. Both surfaces of the fifth lens are aspherical. The fifth lens has positive power. In the cemented lens, a sixth lens and a seventh lens are cemented. The sixth lens has positive power. The seventh lens has negative power. When the focal length of the fifth lens is f5 and the focal length of the optical system is f, conditional expression (1) is satisfied.　Conditional expression (1): 1.68 ≤ f 5 / f ≤ 8.76

Description

optical system CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2024-098323, filed on June 18, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an optical system.

[0003] Image sensors for surveillance cameras, in-vehicle cameras, and the like are becoming increasingly high-resolution. This trend has led to a demand for high-resolution optical systems. To achieve this, it has been proposed to use multiple aspherical lenses in the optical system (see Patent Document 1).

[0004] JP 2018-159898 A

[0005] An optical system according to an embodiment of the present disclosure includes a front group including a first lens having negative power, a second lens located closer to the image than the first lens and having negative power, a third lens located closer to the image than the second lens and having positive power, and a fourth lens located closer to the image than the third lens and having positive power, a stop located closer to the image than the front group, and a rear group including a fifth lens having aspherical surfaces on both sides and having positive power, and a cemented lens formed by cementing together a sixth lens located closer to the image than the fifth lens and having positive power with a seventh lens located closer to the image than the sixth lens and having negative power, wherein the optical system satisfies conditional expression (1): 1.68≦f5 / f≦8.76 (1)

[0006] FIG. 1 is a lens configuration diagram of an optical system according to an embodiment of the present disclosure, showing a first example; FIG. 2 is a graph showing spherical aberration of the optical system of FIG. 1; FIG. 3 is a graph showing astigmatism of the optical system of FIG. 1; FIG. 4 is a graph showing distortion of the optical system of FIG. 1; FIG. 5 is a lens configuration diagram of an optical system according to a second example of the present disclosure; FIG. 6 is a graph showing spherical aberration of the optical system of FIG. 3; FIG. 7 is a graph showing astigmatism of the optical system of FIG. 3; FIG. 8 is a lens configuration diagram of an optical system according to a third example of the present disclosure; FIG. 9 is a graph showing spherical aberration of the optical system of FIG. 5; FIG. 10 is a graph showing astigmatism of the optical system of FIG. 9; FIG. 11 is a lens configuration diagram of an optical system according to a fourth example of the present disclosure; FIG. 12 is a graph showing spherical aberration of the optical system of FIG. 7; FIG. 13 is a graph showing astigmatism of the optical system of FIG. 7; FIG. 14 is a lens configuration diagram of an optical system according to a fifth example of the present disclosure; FIG. 15 is a graph showing spherical aberration of the optical system of FIG. 9; FIG. 16 is a graph showing astigmatism of the optical system of FIG. 9; FIG. 11 is a graph showing distortion of the optical system of FIG. 9 . FIG. 12 is a lens configuration diagram of an optical system according to Example 6 of the present disclosure. FIG. 13 is a graph showing spherical aberration of the optical system of FIG. 11 . FIG. 14 is a graph showing astigmatism of the optical system of FIG. 11 . FIG. 15 is a lens configuration diagram of an optical system according to Example 7 of the present disclosure. FIG. 16 is a graph showing spherical aberration of the optical system of FIG. 13 . FIG. 16 is a graph showing astigmatism of the optical system of FIG. 13 . FIG. 17 is a lens configuration diagram of an optical system according to Example 8 of the present disclosure. FIG. 18 is a graph showing spherical aberration of the optical system of FIG. 15 . FIG. 18 is a graph showing astigmatism of the optical system of FIG. 15 . FIG. 19 is a lens configuration diagram of an optical system according to Example 9 of the present disclosure. FIG. 19 is a graph showing spherical aberration of the optical system of FIG. 17 . FIG. 19 is a graph showing astigmatism of the optical system of FIG. 17 . FIG. 19 is a lens configuration diagram of an optical system according to Example 10 of the present disclosure. Fig. 20 is a graph showing spherical aberration of the optical system of Fig. 19. Fig. 21 is a graph showing astigmatism of the optical system of Fig. 19. Fig. 22 is a graph showing distortion of the optical system of Fig. 19. Fig. 23 is a lens configuration diagram of an optical system according to Comparative Example 1 of the present disclosure.FIG. 22 is a graph showing spherical aberration of the optical system of FIG. 21. FIG. 23 is a graph showing astigmatism of the optical system of FIG. 21. FIG. 24 is a graph showing distortion of the optical system of FIG. 21. FIG. 25 is a lens configuration diagram of an optical system according to Comparative Example 2 of the present disclosure. FIG. 26 is a graph showing spherical aberration of the optical system of FIG. 23. FIG. 27 is a graph showing astigmatism of the optical system of FIG. 23. FIG. 28 is a graph showing distortion of the optical system of FIG. 23.

[0007] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0008] 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.

[0009] 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 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.

[0010] The imaging device 11 may capture moving images, for example, by continuously repeating imaging. The imaging device 11 may be used, for example, in 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 that includes 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.

[0011] 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).

[0012] As described below, the optical system 10 may be a seven-lens fixed focal length imaging lens. The optical system 10 may be located closer to the object side than the image sensor 12. The optical system 10 includes a front group 13, a diaphragm 14, and a rear group 15. The optical system 10 may further include optical elements that have substantially no refractive power, such as an infrared cut filter 16 and a cover glass 17.

[0013] The front group 13 is made up of a first lens 18 , a second lens 19 , a third lens 20 , and a fourth lens 21 .

[0014] The first lens 18 has negative power. The first lens 18 may have a convex surface on the object side. The first lens 18 may have a concave surface on the image side. The first lens 18 may be a spherical lens.

[0015] The second lens 19 is located closer to the image side than the first lens 18. The second lens 19 has negative power. The second lens 19 may have a concave surface on the object side. The second lens 19 may have a concave surface on the image side. The second lens 19 may be a spherical lens.

[0016] The second lens 19 may satisfy the condition of formula (2): −1.04≦R21 / f2<−0.31 (2) In formula (2), R21 is the radius of curvature of the object-side surface of the second lens 19. f2 is the focal length of the second lens 19.

[0017] The third lens 20 is located closer to the image side than the second lens 19. The third lens 20 has positive power. The third lens 20 may have a convex surface facing the image side. The third lens 20 may be a spherical lens.

[0018] The fourth lens 21 is located closer to the image side than the third lens 20. The fourth lens 21 has positive power. The fourth lens 21 may have a convex surface facing the object side. The fourth lens 21 may be a spherical lens.

[0019] The third lens 20 and the fourth lens 21 may satisfy the condition of formula (3): 1.22≦f34 / f≦2.42 (3) In formula (3), f34 is the combined focal length of the third lens 20 and the fourth lens 21. f is the focal length of the optical system 10.

[0020] The diaphragm 14 is located closer to the image side than the front group 13. The diaphragm 14 may adjust the F-number of the optical system 10. The diaphragm 14 may be provided between the fourth lens 21 and a fifth lens 22, which will be described later.

[0021] The rear group 15 is made up of a fifth lens element 22 and a cemented lens element 23 .

[0022] The fifth lens 22 may be located closer to the image side than the aperture stop 14. The fifth lens 22 has positive power. Both surfaces of the fifth lens 22 are aspherical. The fifth lens 22 satisfies the condition of formula (1): 1.68≦f5 / f≦8.76 (1) In formula (1), f5 is the focal length of the fifth lens 22.

[0023] The cemented lens 23 is formed by cementing a sixth lens 24 and a seventh lens 25 together.

[0024] The sixth lens 24 may be located closer to the image side than the fifth lens 22. The sixth lens 24 has positive power. The sixth lens 24 may have a convex surface on the image side. The sixth lens 24 may be a spherical lens.

[0025] The fourth lens 21, the fifth lens 22, and the sixth lens 24 may satisfy the condition of the following formula (5): 9.21≦(ν4+ν5) / f46≦15.22 (5) In formula (5), ν4 is the Abbe number of the glass material of the fourth lens 21. ν5 is the Abbe number of the glass material of the fifth lens 22. f46 is the composite focal length of the fourth lens 21, the fifth lens 22, and the sixth lens 24.

[0026] The seventh lens 25 may be located closer to the image side than the sixth lens 24. The seventh lens 25 has negative power. The seventh lens 25 may have a concave surface on the object side. The seventh lens 25 may be a spherical lens.

[0027] The infrared cut filter 16 may be located closer to the image side than the rear group 15. The infrared cut filter 16 may transmit visible light. The infrared cut filter 16 may block electromagnetic waves in the near-infrared region, for example, in the range of 700 nm to 1200 nm. The infrared cut filter 16 may be a parallel plate.

[0028] The cover glass 17 may cover the image surface is of the imaging element 12. The cover glass 17 may be a parallel plate.

[0029] The optical system 10 of this embodiment configured as described above includes a front group 13 consisting of a first lens 18 having negative power, a second lens 19 located closer to the image than the first lens 18 and having negative power, a third lens 20 located closer to the image than the second lens 19 and having positive power, and a fourth lens 21 located closer to the image than the third lens 20 and having positive power, an aperture stop 14 located closer to the image than the front group 13, and a rear group 15 consisting of a fifth lens 22 having aspherical surfaces on both sides and having positive power, and a cemented lens 23 formed by cementing together a sixth lens 24 located closer to the image than the fifth lens 22 and having positive power, and a seventh lens 25 located closer to the image than the sixth lens 24 and having negative power, where f5 is the focal length of the fifth lens 22 and f is the focal length of the optical system 10, and the optical system 10 satisfies conditional expression (1). With this configuration, the optical system 10 can correct spherical aberration by using aspherical lenses. Furthermore, because the optical system 10 satisfies conditional expression (1), the angle of incidence of the light ray leaving the fifth lens 22 with respect to the normal to the sixth lens 24 can be reduced. Therefore, the optical system 10 suppresses coma aberration, thereby achieving sufficient resolution performance. Furthermore, because the optical system 10 uses an aspherical lens only for the fifth lens 22, manufacturing costs can be reduced compared to configurations using multiple aspherical lenses. Furthermore, because the optical system 10 uses an aspherical lens only for the fifth lens 22, the tolerance for centering accuracy is greater than in configurations using multiple aspherical lenses, making it easier to manufacture the optical system to meet the designed specifications.

[0030] Furthermore, the optical system 10 satisfies conditional expression (5) when the Abbe number of the fourth lens 21 is v4, the Abbe number of the fifth lens 22 is v5, and the composite focal length of the fourth lens 21, the fifth lens 22, and the sixth lens 24 is f46. With this configuration, the optical system 10 corrects chromatic aberration of magnification in the rear group 15, thereby achieving good resolution over the entire angle of view.

[0031] Furthermore, the optical system 10 satisfies (3) when the composite focal length of the third lens element 20 and the fourth lens element 21 is f34. By satisfying f34 / f≦2.42, the optical system 10 can ensure that the front group 13 has sufficient power relative to the rear group 15, making it possible to shorten the overall length of the optical system 10. Furthermore, by satisfying 1.22≦f34 / f, the optical system 10 can prevent the front group 13 from exerting excessively strong power relative to the rear group 15, making it possible to easily correct aberrations in the rear group 15.

[0032] Furthermore, the optical system 10 satisfies conditional expression (2) when the radius of curvature of the object-side surface of the second lens 19 is R21 and the focal length of the second lens 19 is f2. In the optical system 10, the first lens 18 and the second lens 19 have negative power, and therefore spherical aberration, field distortion, and the like are adjusted by the two subsequent lenses, the third lens 20 and the fourth lens 21, which have positive power. Since the optical system 10 satisfies R21 / f2≦−0.31, the second lens 19 has sufficient power, facilitating aberration correction by the subsequent third lens 20 and the fourth lens 21, which have positive power. Furthermore, since the optical system 10 satisfies −1.04≦R21 / f2, the power of the second lens 19 is prevented from becoming excessively strong, and therefore there is no need to make the powers of the third lens 20 and the fourth lens 21 extremely strong. As a result, the optical system 10 does not need to make the curvatures of the second lens 19, the third lens 20, and the fourth lens 21 extremely small, and therefore the occurrence of coma aberration can be easily suppressed.

[0033] 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 10 using specific numerical values ​​of the optical system 10 will be shown along with comparative examples 1 and 2. Examples 1 to 10 have the characteristics of the optical system 10 described above with respect to the positive and negative powers of each lens, the surface shapes, the parameters shown in conditional formula (1), and the like.

[0034] In the basic lens data in 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 18, second lens 19, third lens 20, fourth lens 21, fifth lens 22, sixth lens 24, seventh lens 25, aperture 14, infrared cut filter 16, and cover glass 17 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. The surface spacing Di is shown only in FIG. 1 for Example 1, and is omitted in the drawings for the other examples.

[0035] 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.

[0036] Of the surfaces of the lenses in the following examples, the shape of the aspherical surface is expressed by the following equation (6): Equation (6) is an aspherical equation.

[0037]

[0038] Each numerical value in formula (6) 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 order i. h is the height of the 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 "*" in the basic lens data is expressed using formula (6).

[0039] In FIG. 1 , D1 is the thickness of the first lens 18 on the optical axis ox. D2 is the distance between the first lens 18 and the second lens 19 on the optical axis ox. D3 is the thickness of the second lens 19 on the optical axis ox. D4 is the distance between the second lens 19 and the third lens 20 on the optical axis ox. D5 is the thickness of the third lens 19 on the optical axis ox. D6 is the distance between the third lens 20 and the fourth lens 21 on the optical axis ox. D7 is the thickness of the fourth lens 20 on the optical axis ox. D8 is the distance between the fourth lens 20 and the diaphragm 14 on the optical axis ox. D9 is the distance between the diaphragm 14 and the fifth lens 22 on the optical axis ox. D10 is the thickness of the fifth lens 22 on the optical axis ox. D11 is the distance between the fifth lens 22 and the cemented lens 23 on the optical axis ox. D12 is the thickness of the sixth lens 24 on the optical axis ox. D13 is the thickness of the seventh lens 25 on the optical axis ox. D14 is the distance between the cemented lens 23 and the infrared cut filter 16 on the optical axis ox. D15 is the thickness of the infrared cut filter 16. D16 is the distance between the infrared cut filter 16 and the cover glass 17 on the optical axis ox. D17 is the thickness of the cover glass 17. D18 is the distance between the cover glass 17 and the image sensor 12.

[0040] Example 1 Fig. 1 is a lens configuration diagram of an optical system 10 according to Example 1 of the present disclosure. Fig. 1 shows 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 18, second lens 19, third lens 20, fourth lens 21, fifth lens 22, sixth lens 24, and seventh lens 25 are as described above. The above description regarding the surface spacing Di applies similarly to the other examples below.

[0041] Table 1 shows basic lens data including specifications of the optical system 10 according to Example 1. In Table 1, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0042]

[0043] 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 S10 and S11 of the fifth lens 22.

[0044]

[0045] In the optical system 10 according to Example 1, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 3.

[0046]

[0047] 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 formation position. Each line in the graph represents the spherical aberration (mm) for the C-line (656.2725 nm), e-line (546.0740 nm), and g-line (435.8343 nm) shown in the upper right corner of the graph.

[0048] Fig. 2B is a graph showing astigmatism of the optical system 10 of Fig. 1. In Fig. 2B, the vertical axis represents the angle of view, and the horizontal axis represents the deviation of the image position. S represents the value of the image surface is in the sagittal direction, and T represents the value of the image surface is in the tangential direction.

[0049] Fig. 2C is a graph showing distortion of the optical system 10 of Fig. 1. In Fig. 2C, the vertical axis represents the angle of view, and the horizontal axis represents the amount of distortion.

[0050] As shown in FIGS. 2A, 2B, and 2C, according to Example 1, spherical aberration, astigmatism, distortion, and the like are well corrected, and an optical system 10 with excellent imaging performance is obtained.

[0051] The above explanation regarding the aberration diagrams also applies to the aberration diagrams shown in the other examples, and therefore will not be repeated below.

[0052] 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 the lens configuration of the optical system 10 according to Example 2 in an optical cross section. As shown in Fig. 3, in the optical system 10 of Example 2, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0053] Table 4 shows basic lens data including specifications of the optical system 10 according to Example 2. In Table 4, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0054]

[0055] Table 5 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 2. The aspherical data shown in Table 5 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0056]

[0057] In the optical system 10 according to Example 2, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 3.

[0058] 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.

[0059] 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 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0060] Table 6 shows basic lens data including specifications of the optical system 10 according to Example 3. In Table 6, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0061]

[0062] Table 7 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 3. The aspherical data shown in Table 7 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0063]

[0064] In the optical system 10 according to Example 3, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 3.

[0065] 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.

[0066] 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 the lens configuration of the optical system 10 according to Example 4 in an optical cross section. As shown in Fig. 7, in the optical system 10 of Example 4, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0067] Table 8 shows basic lens data including specifications of the optical system 10 according to Example 4. In Table 8, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0068]

[0069] 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 S10 and S11 of the fifth lens 22.

[0070]

[0071] In the optical system 10 according to Example 4, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 3.

[0072] 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.

[0073] 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 the lens configuration of the optical system 10 according to Example 5 in an optical cross section. As shown in Fig. 9, in the optical system 10 of Example 5, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0074] Table 10 shows basic lens data including specifications of the optical system 10 according to Example 5. In Table 10, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0075]

[0076] Table 11 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 5. The aspherical data shown in Table 11 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0077]

[0078] In the optical system 10 according to Example 5, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 3.

[0079] 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.

[0080] 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 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0081] Table 12 shows basic lens data including specifications of the optical system 10 according to Example 6. In Table 12, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0082]

[0083] Table 13 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 6. The aspherical data shown in Table 13 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0084]

[0085] In the optical system 10 according to Example 6, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 3.

[0086] 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.

[0087] 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 the lens configuration of the optical system 10 according to Example 7 in an optical cross section. As shown in Fig. 13, in the optical system 10 of Example 7, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0088] Table 14 shows basic lens data including specifications of the optical system 10 according to Example 7. In Table 14, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0089]

[0090] Table 15 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 7. The aspherical data shown in Table 15 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0091]

[0092] In the optical system 10 according to Example 7, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 16.

[0093]

[0094] 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.

[0095] 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 the lens configuration of the optical system 10 according to Example 8 in an optical cross section. As shown in Fig. 15, in the optical system 10 of Example 8, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0096] Table 17 shows basic lens data including specifications of the optical system 10 according to Example 8. In Table 17, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0097]

[0098] Table 18 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 8. The aspherical data shown in Table 18 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0099]

[0100] In the optical system 10 according to Example 8, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 16.

[0101] 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.

[0102] Example 9 Fig. 17 is a lens configuration diagram of an optical system 10 according to Example 9 of the present disclosure. Fig. 17 shows the lens configuration of the optical system 10 according to Example 9 in an optical cross section. As shown in Fig. 17 , in the optical system 10 of Example 9, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0103] Table 19 shows basic lens data including specifications of the optical system 10 according to Example 9. In Table 19, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0104]

[0105] Table 20 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 9. The aspherical data shown in Table 20 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0106]

[0107] In the optical system 10 according to Example 9, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 16.

[0108] Fig. 18A is a graph showing the spherical aberration of the optical system 10 of Fig. 17. Fig. 18B is a graph showing the astigmatism of the optical system 10 of Fig. 17. Fig. 18C is a graph showing the distortion of the optical system 10 of Fig. 17. As shown in Figs. 18A, 18B, and 18C, according to Example 9, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0109] Example 10 Fig. 19 is a lens configuration diagram of an optical system 10 according to Example 10 of the present disclosure. Fig. 19 shows an optical cross section of the lens configuration of the optical system 10 according to Example 10. As shown in Fig. 19, in the optical system 10 of Example 10, the powers and shapes of the first lens 18, the second lens 19, the third lens 20, the fourth lens 21, the fifth lens 22, the sixth lens 24, and the seventh lens 25 are as described above.

[0110] Table 21 shows basic lens data including specifications of the optical system 10 according to Example 10. In Table 21, for the aspherical surfaces S10 and S11 indicated with "*", the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0111]

[0112] Table 22 shows aspherical data including aspherical coefficients of the optical system 10 according to Example 10. The aspherical data shown in Table 22 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0113]

[0114] In the optical system 10 according to Example 10, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 16.

[0115] Fig. 20A is a graph showing the spherical aberration of the optical system 10 of Fig. 19. Fig. 20B is a graph showing the astigmatism of the optical system 10 of Fig. 19. Fig. 20C is a graph showing the distortion of the optical system 10 of Fig. 19. As shown in Figs. 20A, 10B, and 20C, according to Example 10, spherical aberration, astigmatism, distortion, etc. are well corrected, and an optical system 10 with excellent imaging performance can be obtained.

[0116] Comparative Example 1 Fig. 21 is a lens configuration diagram of an optical system 10' according to Comparative Example 1 of the present disclosure. Fig. 21 shows the lens configuration of the optical system 10' according to Comparative Example 1 in an optical cross section. As shown in Fig. 21 , in the optical system 10' of Comparative Example 1, the powers and shapes of the first lens 18', second lens 19', third lens 20', fourth lens 21', fifth lens 22', sixth lens 24', and seventh lens 25' are as described above.

[0117] Table 23 shows basic lens data including specifications of the optical system 10′ according to Comparative Example 1. In Table 23, for the aspherical surfaces S10 and S11 indicated with an asterisk (*), the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0118]

[0119] Table 24 shows aspherical data including aspherical coefficients of the optical system 10′ according to Comparative Example 1. The aspherical data shown in Table 24 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0120]

[0121] In the optical system 10' according to Comparative Example 1, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 16.

[0122] Fig. 22A is a graph showing the spherical aberration of the optical system 10' of Fig. 21. Fig. 22B is a graph showing the astigmatism of the optical system 10' of Fig. 21. Fig. 22C is a graph showing the distortion of the optical system 10' of Fig. 21.

[0123] Comparative Example 2 Fig. 23 is a lens configuration diagram of an optical system 10' according to Comparative Example 2 of the present disclosure. Fig. 23 shows the lens configuration of the optical system 10' according to Comparative Example 1 in an optical cross section. As shown in Fig. 23, in the optical system 10' of Comparative Example 2, the powers and shapes of the first lens 18', second lens 19', third lens 20', fourth lens 21', fifth lens 22', sixth lens 24', and seventh lens 25' are as described above.

[0124] Table 25 shows basic lens data including specifications of the optical system 10′ according to Comparative Example 2. In Table 25, for the aspherical surfaces S10 and S11 indicated with an asterisk (*), the value of the radius of curvature Ri indicates the paraxial radius of curvature.

[0125]

[0126] Table 26 shows aspherical data including aspherical coefficients of the optical system 10′ according to Comparative Example 2. The aspherical data shown in Table 26 is data for each of the surfaces S10 and S11 of the fifth lens 22.

[0127]

[0128] In the optical system 10' according to Comparative Example 2, f5 / f, (ν4+ν5) / f46, f34 / f, and R21 / f2 were as shown in Table 16.

[0129] Fig. 24A is a graph showing the spherical aberration of the optical system 10' of Fig. 23. Fig. 24B is a graph showing the astigmatism of the optical system 10' of Fig. 23. Fig. 24C is a graph showing the distortion of the optical system 10' of Fig. 23.

[0130] In one embodiment, (1) an optical system includes: a front group consisting of a first lens having negative power, a second lens located closer to the image than the first lens and having negative power, a third lens located closer to the image than the second lens and having positive power, and a fourth lens located closer to the image than the third lens and having positive power; a stop located closer to the image than the front group; and a rear group consisting of a fifth lens having aspherical surfaces on both sides and having positive power, and a cemented lens formed by cementing together a sixth lens located closer to the image than the fifth lens and having positive power with a seventh lens located closer to the image than the sixth lens and having negative power, wherein when the focal length of the fifth lens is f5 and the focal length of the optical system is f, conditional expression (1) is satisfied.

[0131] (2) The optical system of (1) above satisfies conditional expression (5) when the Abbe number of the fourth lens is v4, the Abbe number of the fifth lens is v5, and the composite focal length of the fourth lens, the fifth lens, and the sixth lens is f46.

[0132] (3) In the optical system of (1) or (2) above, when the composite focal length of the third lens and the fourth lens is f34, the conditional expression (3) is satisfied.

[0133] (4) In any one of the optical systems (1) to (3) above, conditional expression (2) is satisfied when the radius of curvature of the object-side surface of the second lens is R21 and the focal length of the second lens is f2.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 10, 10' Optical system 11, 11' Imaging device 12, 12' Imaging element 13, 13' Front group 14, 14' Aperture 15, 15' Rear group 16, 16' Infrared cut filter 17, 17' Cover glass 18, 18' First lens 19, 19' Second lens 20, 20' Third lens 21, 21' Fourth lens 22, 22' Fifth lens 23, 23' Cemented lens 24, 24' Sixth lens 25, 25' Seventh lens is Image plane ox Optical axis

Claims

1. An optical system comprising a front group consisting of a first lens having negative power, a second lens located closer to the image than the first lens and having negative power, a third lens located closer to the image than the second lens and having positive power, and a fourth lens located closer to the image than the third lens and having positive power, an aperture located closer to the image than the front group, a fifth lens having aspherical surfaces on both sides and having positive power, and a rear group consisting of a cemented lens formed by cementing together a sixth lens located closer to the image than the fifth lens and having positive power with a seventh lens located closer to the image than the sixth lens and having negative power, wherein the optical system satisfies the following condition (1): 1.68≦f5 / f≦8.76 (1) 2. The optical system according to claim 1, wherein the Abbe number of the fourth lens is v4, the Abbe number of the fifth lens is v5, and the composite focal length of the fourth lens, the fifth lens, and the sixth lens is f46, satisfies the following conditional expression (2): 9.21≦(v4+v5) / f46≦15.22 (2) 3. The optical system according to claim 1 or 2, wherein, when the composite focal length of the third lens and the fourth lens is f34, the optical system satisfies the following conditional expression (3): 1.22≦f34 / f≦2.42 (3) 4. An optical system according to any one of claims 1 to 3, wherein the radius of curvature of the object-side surface of the second lens is R21 and the focal length of the second lens is f2, and satisfies the following conditional expression (4): -1.04≦R21 / f2≦-0.31 (4)

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