Long-focus low-distortion imaging optical system and camera module applied by same

Abstract

The invention provides a long-focus low-distortion imaging optical system and a camera module applying the same, the long-focus low-distortion imaging optical system is composed of eight lenses, the first lens has focal power, the object side surface is a convex surface, the image side surface is a concave surface, the second lens has positive focal power, the object side surface is a convex surface, the image side surface is a concave surface, the third lens has negative focal power, the object side surface is a convex surface, and the image side surface is a concave surface. The fourth lens has negative focal power, the fifth lens has focal power, the sixth lens has positive focal power, the seventh lens has focal power, and the eighth lens has negative focal power. Eight glass lenses are selected, and the refractive power and the surface type of each lens are reasonably configured; therefore, the optical lens has the advantages of being compact in structure, light in weight, low in distortion and large in aperture, meanwhile, detail information of an object can be well captured, the detail capturing capacity of the optical lens for shooting the object is improved, the picture texture of the optical lens is improved, and the resolution ratio and the imaging definition of the optical lens are improved, so that the requirements of various aerial photography applications are met.

Description

Technical Field

[0001] The present application relates to the field of optical imaging, and in particular to a telephoto low-distortion imaging optical system and a camera module using the same. Background Art

[0002] With the rapid development of drone technology and the increasing popularity of aerial photography, performance requirements for aerial optical imaging systems are becoming increasingly demanding. Aerial lenses must not only meet lightweight and compact design requirements but also possess high resolution and low distortion to meet the unique demands of high-altitude photography. However, existing aerial lenses often suffer from image quality degradation and increased distortion during capture, making it difficult to stitch aerial images together and causing loss of detail.

[0003] In order to obtain better imaging quality, traditional solutions usually require increasing the number of lenses to correct aberrations, but this will increase the weight and volume of the lens, which conflicts with the strict requirements of drones for payload.

[0004] Furthermore, external factors such as temperature fluctuations and mechanical vibrations can significantly impact image quality. Especially when shooting with a telephoto lens, even a slight lens shift can cause noticeable image blur, severely impacting the quality of the aerial photography.

[0005] Therefore, how to achieve high resolution, low distortion and good environmental adaptability while ensuring the lightweight of the lens has become a key technical challenge in the research and development of aerial photography optical systems. Summary of the Invention

[0006] The present application aims to provide a long-focus, low-distortion imaging optical system with the characteristics of long focus, low distortion, low cost and large aperture. It has a compact structure and is easy to process and install. At the same time, the large aperture configuration can increase the amount of light entering the optical system and achieve higher imaging quality.

[0007] To achieve the purpose, the present invention adopts the following technical solutions: A telephoto low-distortion imaging optical system, which is composed of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens in sequence from the object plane to the image plane along the optical axis; The first lens has optical power, an object-side surface thereof is convex, and an image-side surface thereof is concave; The second lens has positive refractive power, an object-side surface thereof is convex, and an image-side surface thereof is concave; The third lens has negative optical power, its object side surface is convex, and its image side surface is concave; The fourth lens has negative optical power; The fifth lens has optical power; The sixth lens has positive optical power; The seventh lens has optical power; The eighth lens has negative optical power; The second lens and the third lens constitute a cemented lens, and the fourth lens and the fifth lens constitute a cemented lens.

[0008] The imaging optical system satisfies the following relationship: 1.2<|f3+f4| / |f3-f4|<3.4; -3.5 <f4 / |(f4+f5)|<0; 0<(f5+f6) / f6<2.1; Among them, f3 is the effective focal length of the third lens, f4 is the effective focal length of the fourth lens, f5 is the effective focal length of the fifth lens, and f6 is the effective focal length of the sixth lens.

[0009] The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 0.2<|f345 / f|<0.7; Wherein, f345 is the effective combined focal length of the third lens, the fourth lens, and the fifth lens, and f is the effective focal length of the imaging optical system.

[0010] The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 1.6 <f / R3<2.4; Wherein, R6 is the curvature radius of the image side surface of the third lens, f is the effective focal length of the imaging optical system, and R3 is the curvature radius of the object side surface of the second lens.

[0011] The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 1.3<(R1+R2) / R2<2.2; -2.0<(R5-R6) / R5<-0.9; 1.5 <f / R3<2.4; Among them, R1 is the curvature radius of the object side of the first lens, R2 is the curvature radius of the image side of the first lens, R5 is the curvature radius of the object side of the third lens, R6 is the curvature radius of the image side of the third lens, f is the effective focal length of the imaging optical system, and R3 is the curvature radius of the object side of the second lens.

[0012] The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 1.0<(CT6+CT7) / BFL<2.6; Wherein, BFL is the shortest distance from the image-side surface of the eighth lens to the imaging plane of the optical system along the optical axis (also known as the optical back focus), CT6 is the center thickness of the sixth lens on the optical axis, and CT7 is the center thickness of the seventh lens on the optical axis. The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 1.3 <TTL / f<1.7; Wherein, f is the effective focal length of the imaging optical system, and TTL is the on-axis distance from the object side of the first lens to the imaging surface.

[0013] The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 1.6 ≤ f / EPD ≤ 2.0; Where f is the effective focal length of the imaging optical system, and EPD is the entrance pupil diameter of the optical imaging lens.

[0014] The telephoto low-distortion imaging optical system as described above satisfies the following relationship: 8.4<(FNO*f*ImgH) / TTL<11.2; Wherein, FNO is the F number of the optical imaging lens, f is the effective focal length of the imaging optical system, ImgH is half the diagonal length of the effective pixel area on the imaging plane, and TTL is the on-axis distance from the object side of the first lens to the imaging plane.

[0015] In the telephoto low-distortion imaging optical system described above, the system aperture is disposed between the third lens element and the fourth lens element.

[0016] The telephoto low-distortion imaging optical system as described above has an F number of ≤2.0 and an overall length of ≤62.0 mm.

[0017] On the other hand, an embodiment of the present application further provides a camera module, which includes at least an optical lens, in which the above-mentioned telephoto low-distortion imaging optical system is installed.

[0018] Compared with the prior art, the present invention has the following advantages: The present invention provides a telephoto low-distortion imaging optical system and a camera module used therein. By selecting eight glass lenses and rationally configuring the refractive power and surface shape of each lens, the optical lens has the characteristics of a compact structure, lightweight, low distortion, and a large aperture. At the same time, it can better capture object detail information, improve the optical lens's ability to capture details of the photographed object, improve the image quality of the optical lens, and enhance the resolution and imaging clarity of the optical lens to meet the needs of various aerial photography applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments.

[0020] Figure 1 Schematic diagram of the structure of the optical system or camera module of Example 1 of the present application; Figure 2 axial chromatic aberration, astigmatism, and distortion curves of the optical system or camera module of Example 1 of the present application; Figure 3 2 is a schematic structural diagram of an optical system or camera module according to embodiment 2 of the present application; Figure 4 axial chromatic aberration, astigmatism, and distortion curves of the optical system or camera module of Example 2 of the present application; Figure 5 Schematic diagram of the structure of the optical system or camera module according to Example 3 of the present application; Figure 6 axial chromatic aberration, astigmatism, and distortion curves of the optical system or camera module of Example 3 of the present application; Figure 7 Schematic diagram of the structure of the optical system or camera module according to Example 4 of the present application; Figure 8 This is the axial chromatic aberration, astigmatism and distortion curve of the optical system or camera module of Example 4 of the present application. DETAILED DESCRIPTION The present application provides a telephoto, low-distortion imaging optical system, comprising a first lens E1, a second lens E2, a third lens E3, an aperture STO, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, and an infrared filter E9, arranged in sequence from the object side; the first lens has optical power, its object-side surface is convex, and its image-side surface is concave; the second lens has positive optical power, its object-side surface is convex, and its image-side surface is concave; the third lens has negative optical power, its object-side surface is convex, and its image-side surface is concave; the fourth lens has negative optical power; the fifth lens has optical power; the sixth lens has positive optical power; the seventh lens has optical power; and the eighth lens has negative optical power; the second and third lenses constitute a cemented lens; the fourth and fifth lenses constitute a cemented lens; the imaging optical system has an F number ≤ 2.0 and an overall length ≤ 62.0 mm.

[0021] The present invention provides a long-focus, low-distortion imaging optical system. By selecting eight glass lenses and rationally configuring the refractive power and surface shape of each lens, the optical lens has the characteristics of compact structure, lightweight, low distortion and large aperture. At the same time, it can also better capture object detail information, improve the optical lens's ability to capture details of the photographed object, improve the image quality of the optical lens, and enhance the resolution and imaging clarity of the optical lens to meet the needs of various aerial photography applications.

[0022] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 8.4<(FNO*f*ImgH) / TTL<11.2, wherein FNO is the F number of the optical imaging lens, f is the effective focal length of the optical imaging system, ImgH is half the diagonal length of the effective pixel area on the imaging plane, and TTL is the on-axis distance from the object side of the first lens to the imaging plane. By limiting the aperture, effective focal length, and the ratio of half the diagonal length of the effective pixel area on the imaging plane to the on-axis distance from the object side of the first lens to the imaging plane of the optical imaging system, it is possible to ensure that the aberration is within the correctable range and reduce the complexity of the design. When it is lower than the lower limit of the relationship, while ensuring a large aperture of the optical system, the total optical length of the optical system increases, resulting in a limitation of the actual luminous flux, affecting the relative illumination, and reducing the optical imaging quality in low-light environments; when it is higher than the upper limit of the relationship, it may cause the incident angle of the edge field light to be too large, increasing astigmatism or coma. As a preferred embodiment of this application, the imaging optical system satisfies the following relationship: 1.6 ≤ f / EPD ≤ 2.0, where f is the effective focal length of the optical imaging system and EPD is the entrance pupil diameter of the optical imaging lens. By limiting this relationship to a reasonable range, excessive performance degradation of the optical imaging system can be avoided while simultaneously meeting the low distortion requirements of the optical imaging lens.

[0023] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 1.2<|f3+f4| / |f3-f4|<3.4, wherein f3 is the effective focal length of the third lens, and f4 is the effective focal length of the fourth lens. By reasonably controlling the focal length ratio of the third lens and the fourth lens, the optical system can achieve a large field of view angle range while also obtaining a higher imaging resolution. If the upper limit of the relationship is exceeded, the refractive power of the third lens and the fourth lens is insufficient, and large-angle light rays are difficult to enter the optical system, which is not conducive to expanding the field of view angle range of the optical system; if the relationship is lower than the lower limit, the refractive power of the third lens and the fourth lens is too strong, which easily produces strong astigmatism and chromatic aberration, and is not conducive to high-resolution imaging characteristics.

[0024] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: -3.5 < f4 / |(f4 + f5)| < 0, where f4 is the effective focal length of the fourth lens and f5 is the effective focal length of the fifth lens. By reasonably allocating the proportion of the optical power of the fourth and fifth optical components near the image plane within a reasonable range, the remaining spherical aberration after balancing can balance the spherical aberration generated by the first three lenses, thereby finely adjusting and controlling the spherical aberration of the system and strengthening the precise control of the axial field aberration.

[0025] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 0 < (f5 + f6) / f6 < 2.1, where f5 is the effective focal length of the fifth lens and f6 is the effective focal length of the sixth lens. By reasonably controlling the range of the above formula, it is possible to contribute reasonable positive third-order spherical aberration and negative fifth-order spherical aberration, balance the negative third-order spherical aberration and positive fifth-order spherical aberration generated by the fifth lens and the sixth lens, make the system have smaller spherical aberration, and ensure good imaging quality of the axial field.

[0026] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 0.2 < |f345 / f| < 0.7, where f345 is the effective combined focal length of the third, fourth, and fifth lenses, and f is the effective focal length of the optical imaging system. By restricting the ratio of the combined focal length of the third, fourth, and fifth lenses to the effective focal length of the optical lens, the optical power distribution of the third, fourth, and fifth lenses can be made appropriate, allowing the fourth lens to produce diverse cooperation, thereby achieving the balance of the internal aberration of the optical lens, and further helping to adjust the field curvature and astigmatism of the imaging edge of the optical lens, and meeting the imaging quality of the optical lens for the surrounding environment.

[0027] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 1.3 < (R1 + R2) / R2 < 2.2, where R1 is the curvature radius of the object side surface of the first lens and R2 is the curvature radius of the image side surface of the first lens. By controlling the curvature radii of the object side surface and the image side surface of the first lens, it is possible to reasonably control the total deflection angle of the object side surface and the image side surface of the first lens at the edge field within a reasonable range, and effectively reduce the sensitivity of the system.

[0028] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: -2.0 < (R5 - R6) / R5 < -0.9, where R5 is the curvature radius of the object side surface of the third lens and R6 is the curvature radius of the image side surface of the third lens. By limiting the ratio range of the curvature radii of the object side surface and the image side surface of the third lens, the shape of the third lens can be effectively constrained, and then the aberration contribution rates of the object side and the image side surfaces of the third lens can be effectively controlled to effectively balance the aberration related to the aperture band of the system, and further effectively improve the imaging quality of the system.

[0029] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 1.5 < f / R3 < 2.4, where f is the effective focal length of the optical imaging system and R3 is the radius of curvature of the object side surface of the second lens. By limiting the range of the above relationship, it is beneficial to restrict the bending degree of the object side surface of the second lens, allowing more light to enter the optical system. At the same time, it is also beneficial to reasonably distribute the refractive power of the optical system and correct the off-axis aberration of the optical system. Exceeding the upper limit of the relationship results in too large a focal length of the optical system, which is not conducive to achieving miniaturization characteristics and further affects the thinness and lightness of the entire optical system. Below the lower limit of the relationship, the radius of curvature of the object side surface of the second lens is too small, and the image side surface of the second lens is too curved, thus increasing the risk of ghost images.

[0030] As a preferred embodiment of the present application, the imaging optical system satisfies the following relationship: 1.0 < (CT6 + CT7) / BFL < 2.6, where BFL is the shortest distance from the image side surface of the eighth lens to the imaging surface of the optical system in the optical axis direction (also known as the optical back focal length), CT6 is the central thickness of the sixth lens on the optical axis, and CT7 is the central thickness of the seventh lens on the optical axis. When the above conditional formula is satisfied, by controlling the above optical back focal length within a reasonable range, the matching degree between the captured image and the image sensor is effectively ensured, guaranteeing the matching of the optical system and the image sensor. At the same time, the thicknesses of the sixth lens and the seventh lens are controlled, reducing the thickness tolerance sensitivity of the optical system, which is beneficial to realizing the control of the assembly thickness tolerance of the entire optical system, thereby reducing production costs.

[0031] Example 1: The following refers to Figures 1 to 2 Describe the optical imaging lens according to Embodiment 1 of the present application. Figure 1 Fig. shows a schematic structural diagram of the optical imaging lens according to Embodiment 1 of the present application.

[0032] As Figure 1 shown, the optical imaging lens according to an exemplary embodiment of the present application sequentially includes, along the optical axis from the object side to the image side: a first lens E1, a second lens E2, a third lens E3, STO, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, an infrared filter E9, and an imaging surface S17.

[0033] The first lens E1 has positive optical power, with its object-side surface S1 being convex and its image-side surface S2 being concave. The second lens E2 has positive optical power, with its object-side surface S3 being convex and its image-side surface S4 being concave. The third lens E3 has negative optical power, with its object-side surface S4 being convex and its image-side surface S5 being concave. The fourth lens E4 has negative optical power, with its object-side surface S6 being concave and its image-side surface S7 being convex. The fifth lens E5 has positive optical power, with its object-side surface S7 being concave and its image-side surface S8 being convex. The sixth lens E6 has positive optical power, with its object-side surface S9 being convex and its image-side surface S10 being flat. The seventh lens E7 has negative optical power, with its object-side surface S11 being convex and its image-side surface S12 being concave. The eighth lens E8 has negative optical power, with its object-side surface S13 being convex and its image-side surface S14 being concave. The optical filter E9 has an object-side surface S15 and an image-side surface S16. Light from an object passes through the surfaces S1 to S16 in sequence and is finally imaged on the imaging surface S17 .

[0034] Table 1 shows the surface type, curvature radius, thickness, and material of each lens of the optical imaging lens of Example 1, wherein the units of curvature radius and thickness are both millimeters (mm).

[0035] Table 1

[0036] In Table 1, both the object-side surface and the image-side surface of the eighth lens element E8 are Q-type aspherical surfaces. The surface shape of each aspherical lens element can be defined by, but not limited to, the following aspherical surface formula:

[0037] Where Z is the distance from the corresponding point on the aspheric surface to the plane tangent to the vertex of the surface, r is the radial coordinate of the aspheric surface, c is the curvature of the aspheric vertex, K is the cone coefficient, Am is the aspheric coefficient, r is the radius of the aspheric surface, and c is the curvature of the aspheric vertex. max is the maximum radial radius coordinate, u=r / r max Table 2 shows the conic coefficients and high-order coefficients A4, A6, A8, A10, A12, A14, A16, A18, and A20 of various aspheric surfaces that can be used in the first embodiment.

[0038] Table 2

[0039] Example 2: The following reference Figures 3 and 4 The optical imaging lens according to Example 2 of the present application is described. Figure 3 A schematic structural diagram of an optical imaging lens according to Example 2 of the present application is shown.

[0040] like Figure 3As shown, the optical imaging lens according to an exemplary embodiment of the present application includes, in order from the object side to the image side along the optical axis: a first lens E1, a second lens E2, a third lens E3, an STO, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, an infrared filter E9, and an imaging surface S17.

[0041] The first lens E1 has negative optical power, with its object-side surface S1 being convex and its image-side surface S2 being concave. The second lens E2 has positive optical power, with its object-side surface S3 being convex and its image-side surface S4 being concave. The third lens E3 has negative optical power, with its object-side surface S4 being convex and its image-side surface S5 being concave. The fourth lens E4 has negative optical power, with its object-side surface S6 being concave and its image-side surface S7 being convex. The fifth lens E5 has positive optical power, with its object-side surface S7 being concave and its image-side surface S8 being convex. The sixth lens E6 has positive optical power, with its object-side surface S9 being convex and its image-side surface S10 being flat. The seventh lens E7 has negative optical power, with its object-side surface S11 being concave and its image-side surface S12 being convex. The eighth lens E8 has negative optical power, with its object-side surface S13 being concave and its image-side surface S14 being concave. The filter E9 has an object-side surface S15 and an image-side surface S16. Light from an object passes through the surfaces S1 to S16 in sequence and is finally imaged on the imaging surface S17 .

[0042] Table 3 shows the surface type, curvature radius, thickness, and material of each lens of the optical imaging lens system of Example 2, where the units of curvature radius and thickness are both millimeters (mm).

[0043] Table 3

[0044] In Table 3, both the object-side surface and the image-side surface of the eighth lens element E8 are Q-type aspherical surfaces. The surface shape of each aspherical lens element can be defined by, but not limited to, the following aspherical surface formula:

[0045] Where Z is the distance from the corresponding point on the aspheric surface to the plane tangent to the vertex of the surface, r is the radial coordinate of the aspheric surface, c is the curvature of the aspheric vertex, K is the cone coefficient, Am is the aspheric coefficient, r is the radius of the aspheric surface, and c is the curvature of the aspheric vertex. max is the maximum radial radius coordinate, u=r / r max Table 4 shows the conic coefficients and high-order coefficients A4, A6, A8, A10, A12, A14, A16, A18, and A20 of various aspheric surfaces that can be used in the second embodiment.

[0046] Table 4

[0047] Example 3: The following reference Figures 5 and 6 The optical imaging lens according to Example 3 of the present application is described. Figure 5 A schematic structural diagram of an optical imaging lens according to Example 3 of the present application is shown.

[0048] like Figure 5 As shown, the optical imaging lens according to an exemplary embodiment of the present application includes, in order from the object side to the image side along the optical axis: a first lens E1, a second lens E2, a third lens E3, an STO, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, an infrared filter E9, and an imaging surface S17.

[0049] The first lens E1 has positive optical power, with its object-side surface S1 being convex and its image-side surface S2 being concave. The second lens E2 has positive optical power, with its object-side surface S3 being convex and its image-side surface S4 being concave. The third lens E3 has negative optical power, with its object-side surface S4 being convex and its image-side surface S5 being concave. The fourth lens E4 has negative optical power, with its object-side surface S6 being concave and its image-side surface S7 being convex. The fifth lens E5 has negative optical power, with its object-side surface S7 being concave and its image-side surface S8 being concave. The sixth lens E6 has positive optical power, with its object-side surface S9 being convex and its image-side surface S10 being convex. The seventh lens E7 has positive optical power, with its object-side surface S11 being convex and its image-side surface S12 being concave. The eighth lens E8 has negative optical power, with its object-side surface S13 being concave and its image-side surface S14 being convex. The optical filter E9 has an object-side surface S15 and an image-side surface S16. Light from an object passes through the surfaces S1 to S16 in sequence and is finally imaged on the imaging surface S17 .

[0050] Table 5 shows the surface type, curvature radius, thickness, and material of each lens of the optical imaging lens system of Example 3, where the units of curvature radius and thickness are both millimeters (mm).

[0051] Table 5

[0052] Example 4: The following reference Figures 7 and 8 An optical imaging lens according to Example 4 of the present application is described. Figure 7 A schematic structural diagram of an optical imaging lens according to Example 4 of the present application is shown.

[0053] like Figure 7 As shown, the optical imaging lens according to an exemplary embodiment of the present application includes, in order from the object side to the image side along the optical axis: a first lens E1, a second lens E2, a third lens E3, an STO, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, an infrared filter E9, and an imaging surface S17.

[0054] The first lens E1 has positive focal power, with its object-side surface S1 being convex and its image-side surface S2 being concave. The second lens E2 has positive focal power, with its object-side surface S3 being convex and its image-side surface S4 being concave. The third lens E3 has negative focal power, with its object-side surface S4 being convex and its image-side surface S5 being concave. The fourth lens E4 has negative focal power, with its object-side surface S6 being concave and its image-side surface S7 being concave. The fifth lens E5 has negative focal power, with its object-side surface S7 being convex and its image-side surface S8 being convex. The sixth lens E6 has positive focal power, with its object-side surface S9 being convex and its image-side surface S10 being convex. The seventh lens E7 has positive focal power, with its object-side surface S11 being convex and its image-side surface S12 being concave. The eighth lens E8 has negative focal power, with its object-side surface S13 being concave and its image-side surface S14 being concave. The optical filter E9 has an object-side surface S15 and an image-side surface S16. Light from an object passes through the surfaces S1 to S16 in sequence and is finally imaged on the imaging surface S17 .

[0055] Table 7 shows the surface type, curvature radius, thickness, and material of each lens of the optical imaging lens system of Example 4, where the units of curvature radius and thickness are both millimeters (mm).

[0056] Table 6

[0057] In Table 7, both the object-side surface and the image-side surface of the eighth lens element E8 are Q-type aspherical surfaces. The surface shape of each aspherical lens element can be defined by, but not limited to, the following aspherical surface formula:

[0058] Where Z is the distance from the corresponding point on the aspheric surface to the plane tangent to the vertex of the surface, r is the radial coordinate of the aspheric surface, c is the curvature of the aspheric vertex, K is the cone coefficient, Am is the aspheric coefficient, r is the radius of the aspheric surface, and c is the curvature of the aspheric vertex. max is the maximum radial radius coordinate, u=r / r max Table 4 shows the conic coefficients and higher-order coefficients A4, A6, A8, A10, A12, A14, A16, A18, and A20 of the aspheric surfaces that can be used in the fourth embodiment.

[0059] Table 7

[0060] In Examples 1-4, the basic data are as follows: Table 8

[0061] In Examples 1-4, each conditional expression satisfies the conditions in the following table: Table 9

[0062] A camera module includes at least an optical lens, in which the above-mentioned long-focus, low-distortion imaging optical system is installed. The camera module configured in the present invention has the characteristics of long focus, low distortion, low cost and large aperture, compact structure, and is easy to process and install. At the same time, the large aperture configuration can increase the amount of light entering the optical system and higher imaging quality.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A telephoto, low-distortion imaging optical system, comprising, in order from the object plane to the image plane along the optical axis, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, characterized in that: The first lens has an optical power, an object-side surface thereof being convex, and an image-side surface thereof being concave; The second lens has positive refractive power, an object-side surface thereof is convex, and an image-side surface thereof is concave; The third lens has negative optical power, its object side surface is convex, and its image side surface is concave; The fourth lens has negative optical power; The fifth lens has optical power; The sixth lens has positive optical power; The seventh lens has optical power; The eighth lens has negative optical power; The second lens and the third lens constitute a cemented lens, and the fourth lens and the fifth lens constitute a cemented lens; The imaging optical system satisfies the following relationship: 1.2 < |f3+f4| / |f3-f4| < 3.4; -3.5 < f4 / |(f4+f5)| < 0; 0 < (f5+f6) / f6 < 2.1; Among them, f3 is the effective focal length of the third lens, f4 is the effective focal length of the fourth lens, f5 is the effective focal length of the fifth lens, and f6 is the effective focal length of the sixth lens.

2. The telephoto low-distortion imaging optical system according to claim 1, wherein: The imaging optical system satisfies the following relationship: 0.2 < |f345 / f| < 0.7; Wherein, f345 is the effective combined focal length of the third lens, the fourth lens, and the fifth lens, and f is the effective focal length of the imaging optical system.

3. The telephoto low-distortion imaging optical system according to claim 1, wherein: The imaging optical system satisfies the following relationship: 1.5 < f / R3 < 2.4; Wherein, R6 is the curvature radius of the image side surface of the third lens, f is the effective focal length of the imaging optical system, and R3 is the curvature radius of the object side surface of the second lens.

4. The telephoto low-distortion imaging optical system according to any one of claims 1 to 3, wherein: The imaging optical system satisfies the following relationship: 1.3 < (R1+R2) / R2 < 2.2; -2.0 < (R5-R6) / R5 < -0.9; 1.6 < f / R3 < 2.4; Among them, R1 is the curvature radius of the object side of the first lens, R2 is the curvature radius of the image side of the first lens, R5 is the curvature radius of the object side of the third lens, R6 is the curvature radius of the image side of the third lens, f is the effective focal length of the imaging optical system, and R3 is the curvature radius of the object side of the second lens.

5. The telephoto low-distortion imaging optical system according to any one of claims 1 to 3, characterized in that: The imaging optical system satisfies the following relationship: 1.0 < (CT6+CT7) / BFL < 2.6; Wherein, BFL is the shortest distance from the image-side surface of the eighth lens to the imaging plane of the optical system along the optical axis (also known as the optical back focus), CT6 is the center thickness of the sixth lens on the optical axis, and CT7 is the center thickness of the seventh lens on the optical axis.

6. The telephoto low-distortion imaging optical system according to any one of claims 1 to 3, characterized in that: The imaging optical system satisfies the following relationship: 1.3 < TTL / f < 1.7; Wherein, f is the effective focal length of the imaging optical system, and TTL is the on-axis distance from the object side of the first lens to the imaging surface.

7. The long-focus, low-distortion imaging optical system according to any one of claims 1 to 3, wherein: The imaging optical system satisfies the following relationship: 1.6 ≤ f / EPD ≤ 2.0; Where f is the effective focal length of the imaging optical system, and EPD is the entrance pupil diameter of the optical imaging lens.

8. The long-focus, low-distortion imaging optical system according to any one of claims 1 to 3, wherein: The imaging optical system satisfies the following relationship: 8.4< (FNO*f*ImgH) / TTL < 11.2; Wherein, FNO is the F number of the optical imaging lens, f is the effective focal length of the imaging optical system, ImgH is half the diagonal length of the effective pixel area on the imaging plane, and TTL is the on-axis distance from the object side of the first lens to the imaging plane.

9. The long-focus, low-distortion imaging optical system according to any one of claims 1 to 3, wherein: The system aperture is arranged between the third lens and the fourth lens; The imaging optical system has an F number of ≤2.0 and an overall length of ≤62.0 mm.

10. A camera module, comprising at least an optical lens, characterized in that: The optical lens is equipped with the telephoto low-distortion imaging optical system according to any one of claims 1 to 9.

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