Optical imaging systems and machine vision systems

Abstract

This application relates to the field of machine vision technology and proposes an optical imaging system, including: a first lens group with negative optical power; an aperture stop; the aperture stop being disposed on one side of the first lens group; a second lens group with positive optical power; and a third lens group with positive optical power. The first lens group, aperture stop, second lens group, and third lens group are arranged sequentially from the object side to the image side along the optical axis. The second lens group can move between the aperture stop and the third lens group along the incident direction of the light. This application also proposes a machine vision system, including an optical imaging system. The optical imaging system provided by this application has the characteristics of high resolution, low distortion, uniform image quality, wide working object distance range, good color reproduction, and high contrast, and is highly practical.

Description

Technical Field

[0001] This application belongs to the field of machine vision technology, and in particular relates to an optical imaging system and a machine vision system. Background Technology

[0002] Machine vision is a rapidly developing branch of artificial intelligence. Simply put, machine vision uses machines to replace human eyes for measurement and judgment. Therefore, machine vision imaging systems have very high requirements for pixels, image uniformity, distortion, brightness, and color reproduction.

[0003] With the booming development of machine vision in recent years, the demand for optical imaging systems, which are the "eyes" of machine vision systems, is also constantly increasing. However, the short focal length wide-angle lenses currently on the market have poor image quality under low distortion conditions, and the images are not delicate enough, have poor uniformity, low dynamic range, and poor color and contrast, which cannot meet the needs of high-end users. Summary of the Invention

[0004] To address the aforementioned issues, this application provides an optical imaging system and a machine vision system, which at least solves the problem of poor image quality of short-focal-length wide-angle lenses under low distortion conditions in the prior art.

[0005] This application provides an optical imaging system comprising a first lens group, an aperture stop, a second lens group, and a third lens group:

[0006] The optical power of the first lens group is negative;

[0007] The aperture is located on one side of the first lens group;

[0008] The optical power of the third lens group is positive;

[0009] The first lens group, the aperture stop, the second lens group, and the third lens group are arranged sequentially from the object side to the image side along the optical axis. The second lens group can move between the aperture stop and the third lens group along the incident direction of the light.

[0010] In one embodiment, the first lens group includes at least a first positive lens and a second positive lens. The first positive lens is disposed on the side of the first lens group away from the aperture stop, and the side of the first positive lens facing the object side protrudes towards the object side. The second positive lens is disposed on the side of the first lens group close to the aperture stop.

[0011] The first lens group further includes at least a first negative lens, a second negative lens, and a third negative lens, which are arranged sequentially between the first positive lens and the second positive lens along the incident direction of the light; the side of the first negative lens facing the object side protrudes towards the object side.

[0012] In one embodiment, the refractive index of the second positive lens is greater than or equal to 1.85 and less than or equal to 1.96; the Abbe number of the second positive lens is greater than or equal to 15.0 and less than or equal to 35.0.

[0013] In one embodiment, the second lens group includes at least one third positive lens and a cemented lens.

[0014] In one embodiment, the third lens group includes at least a fourth positive lens for converging incident light rays.

[0015] In one embodiment, the second lens group includes a cemented lens.

[0016] In one embodiment, the third lens group includes at least a third positive lens and a fourth positive lens.

[0017] In one embodiment, the focal length of the cemented lens is greater than or equal to 39 mm and less than or equal to 68 mm.

[0018] In one embodiment, the refractive index of the third positive lens or the fourth positive lens is greater than or equal to 1.45 and less than or equal to 1.63;

[0019] The Abbe number of the third positive lens or the fourth positive lens is greater than or equal to 60.0 and less than or equal to 91.0;

[0020] The relative refractive index temperature coefficient of the third or fourth positive lens is greater than or equal to -5.0 × 10⁻⁶. -6 / ℃ and less than or equal to -3.5×10 -6 / ℃.

[0021] In one embodiment, the focal length f1 of the first lens group satisfies:

[0022] -0.130≤f / f1≤-0.100;

[0023] Where f is the focal length of the optical imaging system.

[0024] In one embodiment, the optical imaging system satisfies:

[0025] 0.150 ≤ H / L ≤ 0.175;

[0026] Where H is the holoimage height of the optical imaging system, and L is the total optical length of the optical imaging system.

[0027] This application also provides a machine vision system, including the aforementioned optical imaging system.

[0028] This application addresses the problem of poor image quality in prior art short-focal-length wide-angle lenses under low distortion conditions by improving the design. It utilizes a first lens group to reduce the optical sensitivity of the optical imaging system to improve distortion; a second lens group to reduce the tolerance sensitivity of the optical imaging system to improve image quality; and a third lens group to focus light rays to further reduce the tolerance sensitivity of the optical imaging system and further improve image quality.

[0029] This application has a simple structure and uses a first lens group, a second lens group, and a third lens group arranged at intervals along the optical axis for focusing. This enables the optical imaging system provided by this application to have the characteristics of high resolution, low distortion, uniform image quality, wide working object distance range, good color reproduction, and high contrast, making it highly practical. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the lens arrangement of an optical imaging system provided in an embodiment of this application.

[0032] Figure 2 for Figure 1 The diagram shows the modulation transfer function of the optical imaging system.

[0033] Figure 3 for Figure 1 The distortion diagram of the optical imaging system shown.

[0034] Figure 4 This is a schematic diagram of the lens arrangement of an optical imaging system provided in another embodiment of this application.

[0035] Figure 5 for Figure 4 The diagram shows the modulation transfer function of the optical imaging system.

[0036] Figure 6 for Figure 4 The distortion diagram of the optical imaging system shown.

[0037] Figure 7This is a schematic diagram of the lens arrangement of an optical imaging system provided in another embodiment of this application.

[0038] Figure 8 for Figure 7 The diagram shows the modulation transfer function of the optical imaging system.

[0039] Figure 9 for Figure 7 The distortion diagram of the optical imaging system shown.

[0040] The markings in the diagram mean:

[0041] 100. Optical imaging system;

[0042] 10. First lens group; 11. First positive lens; 12. Second positive lens; 13. First negative lens; 14. Second negative lens; 15. Third negative lens;

[0043] 20. Aperture;

[0044] 30. Second lens group; 31. Third positive lens; 32. Cemented lens;

[0045] 40. Third lens group; 41. Fourth positive lens. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0047] In the description of this application, it should be understood that the terms "length", "width", "upper", "lower", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0049] Machine vision imaging systems have very high requirements for pixels, image uniformity, distortion, brightness, and color reproduction. However, the short-focal-length wide-angle lenses currently on the market have poor image quality under low distortion conditions. Their images are not delicate enough, have poor uniformity, low dynamic range, and poor color and contrast, which cannot meet the needs of high-end users.

[0050] Therefore, this application provides an optical imaging system and a machine vision system, which utilizes a first lens group, a second lens group and a third lens group arranged sequentially and at intervals along the incident direction of light for focusing, so that the optical imaging system has the characteristics of high resolution, low distortion, uniform image quality, wide working object distance range, good color reproduction and high contrast.

[0051] To illustrate the technical solutions described in this application, the following description is provided in conjunction with specific accompanying drawings and embodiments.

[0052] refer to Figures 1 to 3 The optical imaging system 100 provided in the first aspect of this application consists of a first lens group 10, an aperture 20, a second lens group 30 and a third lens group 40, which are arranged sequentially along the direction of light incidence.

[0053] The first lens group 10 is used to reduce the sensitivity of the optical imaging system 100 and reduce distortion. At the same time, it is used to diverge light rays incident at large angles to change the direction of the light rays, so that the light rays can be scattered towards the aperture 20 at a small angle away from the optical axis. Specifically, the first lens group 10 can be a combination of positive and negative lenses to achieve the effect of changing the direction of the light rays. For example, two positive lenses are combined with two negative lenses, two positive lenses are combined with three negative lenses, or other lens combinations can be used.

[0054] The aperture 20 is used to constrain light rays and limit the beam range, thereby limiting the image size, so that the light rays passing through the first lens group 10 can all enter the second lens group 30 after passing through the aperture 20.

[0055] The second lens group 30 is used to reduce the tolerance sensitivity of the optical imaging system 100 and can reduce aberrations, so as to improve the color reproduction, contrast and imaging effect of the image; the second lens group 30 can be a cylindrical lens, a cemented lens or other lenses or lens groups that can reduce tolerance sensitivity.

[0056] The second lens group 30 moves between the aperture stop 20 and the third lens group 40 along the direction of light incidence to achieve focusing at different object distances.

[0057] The third lens group 40 is used to focus light rays. Light rays from the second lens group 30 to the third lens group 40 are focused by the third lens group 40 and then emitted to reduce tolerance sensitivity and ensure imaging effect. The third lens group 40 can be a positive lens or other lens or lens group that can focus light rays.

[0058] The two sides of the optical imaging system 100 are the object side and the image side, respectively. Light enters the optical imaging system 100 from the object side. Specifically, the light passes through the first lens group 10, the aperture 20, the second lens group 30 and the third lens group 40 in sequence and exits to the image side.

[0059] The optical path in this embodiment is as follows: light rays enter the first lens group 10 from the object side, are focused by the first lens group 10, and exit. The light rays exiting from the first lens group 10 are closer to the optical axis and have a smaller angle with the optical axis. The light rays exiting from the first lens group 10 penetrate the aperture 20 and enter the second lens group 30, and exit after passing through the second lens group 30. The light rays exiting from the second lens group 30 diverge relative to the optical axis. The light rays exiting from the second lens group enter the third lens group 40, are focused by the third lens group 40, and exit to the image side.

[0060] The beneficial effects of this application embodiment are as follows: The first lens group 10 is provided to reduce the optical sensitivity of the optical imaging system 100 and improve distortion; the second lens group 30 is provided to reduce the tolerance sensitivity of the optical imaging system 100 and improve image quality; the third lens group 40 is provided to focus light rays, further reducing the tolerance sensitivity of the optical imaging system 100 and further improving image quality.

[0061] In this embodiment, the focal length of the first lens group 10 satisfies the following formula:

[0062] -0.130≤f / f1≤-0.100;

[0063] Where f is the focal length of the optical imaging system 100, and f1 is the focal length of the first lens group 10.

[0064] The focal length of the first lens group 10 and the focal length of the optical imaging system 100 are set such that light passes through the aperture 20 at a small angle with the optical axis, reducing optical sensitivity and ensuring stability. The focal length of the second lens group 30 and the focal length of the optical imaging system 100 are set such that the focusing efficiency of the second lens group 30 is better guaranteed, and the second lens group 30 has a smaller focusing stroke, reducing the moving distance of the second lens group 30 and realizing the miniaturization of the optical imaging system 100.

[0065] In this embodiment, the optical imaging system 100 satisfies the following formula:

[0066] 0.150≤H / L≤0.175;

[0067] Where H is the holographic height of the optical imaging system 100 and L is the total optical length of the optical imaging system 100. This setting can meet the requirements of the optical imaging system 100 for overall miniaturization.

[0068] refer to Figure 1 In one embodiment, the first lens group 10 includes at least two positive lenses and at least three negative lenses.

[0069] The two positive lenses are referred to as the first positive lens 11 and the second positive lens 12, respectively. The first positive lens 11 is located on the side of the first lens group 10 away from the aperture 20, that is, the first positive lens 11 is located on the side of the first lens group 10 closer to the object side. The second positive lens 12 is located on the side of the second lens group 30 closer to the aperture 20. Optionally, the first positive lens 11 is a meniscus concave-convex lens, and the first positive lens 11 protrudes towards the object side. This arrangement can effectively reduce distortion and reduce optical sensitivity.

[0070] The three negative lenses are referred to as the first negative lens 13, the second negative lens 14, and the third negative lens 15, respectively. The first negative lens 13, the second negative lens 14, and the third negative lens 15 are all disposed between the first positive lens 11 and the second positive lens 12, and the first negative lens 13, the second negative lens 14, and the third negative lens 15 are arranged sequentially along the incident direction of light. Optionally, the first negative lens 13 is a meniscus concave-convex lens, and the first negative lens 13 protrudes towards the object side. This arrangement can cause light rays that enter the first negative lens 13 at a large angle to scatter out in a direction away from the optical axis, thereby changing the direction of light.

[0071] In this embodiment, the refractive index of the second positive lens 12 is greater than or equal to 1.85 and less than or equal to 1.96, and the Abbe number of the second positive lens 12 is greater than or equal to 15.0 and less than or equal to 35.0. That is, the second positive lens 12 satisfies the following formula:

[0072] 1.85≤nd G1_Lx ≤1.96;

[0073] 15.0≤vd G1_Lx ≤35.0;

[0074] Among them, nd G1_Lx Let vd be the refractive index of the second positive lens 12. G1_Lx This is the Abbe number of the second positive lens 12.

[0075] This configuration allows the second positive lens 12 to converge light, causing light rays emitted from the first lens group 10 to pass through the aperture 20 at a small angle, thereby reducing optical sensitivity and improving image quality.

[0076] refer to Figure 1In one embodiment, the second lens group 30 includes at least one positive lens and one cemented lens 32.

[0077] The positive lens in the second group is called the third positive lens 31, which is used to converge the light transmitted through the aperture 20.

[0078] The cemented lens 32 is formed by cementing a biconvex positive lens and a concave-convex negative lens. The cemented lens 32 has a long focal length, a large magnification and good image quality. The cemented lens 32 can reduce tolerance sensitivity and improve the imaging effect.

[0079] In this embodiment, the third positive lens 31 and the cemented lens 32 are arranged sequentially along the direction of light incidence, with the biconvex positive lens in the cemented lens 32 being close to the third positive lens 31.

[0080] In this embodiment, the focal length of the cemented lens 32 is greater than or equal to 39mm and less than or equal to 68mm, that is, the focal length of the cemented lens 32 satisfies the following formula:

[0081] 39.00≤f 2j ≤68.00;

[0082] Among them, f 2j This is the focal length of the cemented lens 32.

[0083] This setting effectively ensures the focal length of the second lens group 30, thereby guaranteeing focusing efficiency, focusing stability, and imaging quality.

[0084] refer to Figure 1 In one embodiment, the third lens group 40 includes at least one positive lens and is referred to as the fourth positive lens 41. The fourth positive lens 41 is used to converge the incident light rays. Optionally, the fourth positive lens 41 is a biconvex positive lens.

[0085] In this embodiment, the refractive index of the third positive lens 31 or the fourth positive lens 41 is greater than or equal to 1.45 and less than or equal to 1.63; the Abbe number of the third positive lens 31 or the fourth positive lens 41 is greater than or equal to 60.0 and less than or equal to 91.0; and the relative refractive index temperature coefficient of the third positive lens 31 or the fourth positive lens 41 is greater than or equal to -5.0 × 10⁻⁶. -6 / ℃ and less than or equal to -3.5×10 -6 / ℃, that is, the refractive index, Abbe number, and relative refractive index temperature coefficient of the third positive lens 31 or the fourth positive lens 41 respectively satisfy the following formula:

[0086] 1.45≤ndG 2 / 3_Lx ≤1.63

[0087] 60.0≤vdG 2 / 3_Lx ≤91.0

[0088] -5.0×10 -6 / ℃≤dn / dtG 2 / 3_Lx ≤-3.5×10 -6 / ℃

[0089] Among them, ndG 2 / 3_Lx vdG represents the refractive index of the third positive lens 31 or the fourth positive lens 41. 2 / 3_Lx The Abbe number of the third positive lens 31 or the fourth positive lens 41, dn / dtG 2 / 3_Lx The relative refractive index temperature coefficient of the third positive lens 31 or the fourth positive lens 41.

[0090] The setting of the refractive index and Abbe number of the third positive lens 31 or the fourth positive lens 41 can effectively reduce chromatic aberration and improve imaging quality; the setting of the relative refractive index temperature coefficient of the third positive lens 31 or the fourth positive lens 41 is beneficial to the temperature correction of the anechoic optical imaging system 100, and can effectively balance the image plane drift of the optical imaging system 100 under high and low temperature conditions.

[0091] In one embodiment, specific parameters of each lens in a first aspect embodiment of this application are provided.

[0092] First positive lens 11: The radius of curvature facing the object side is 23.548 mm, and the thickness is 4.04 mm; the radius of curvature facing the image side is 78.695 mm, and the distance between it and the adjacent lens is 0.12 mm; the refractive index is 1.64, and the Abbe number is 60.2.

[0093] The first negative lens 13 has a surface radius of 18.758 mm facing the object side and a thickness of 1.66 mm; a surface radius of 7.860 mm facing the image side and a distance of 2.80 mm from the adjacent lens; a refractive index of 1.64 and an Abbe number of 60.2.

[0094] The second negative lens 14 has a surface radius of 21.540 mm on the object side and a thickness of 1.00 mm; a surface radius of 7.969 mm on the image side and a distance of 1.95 mm from the adjacent lens; a refractive index of 1.90 and an Abbe number of 31.3.

[0095] The third negative lens 15 has a surface radius of 44.456 mm on the object side and a thickness of 2.23 mm; a surface radius of 8.253 mm on the image side and a distance of 4.77 mm from the adjacent lens; a refractive index of 1.52 and an Abbe number of 64.2.

[0096] The second positive lens 12 has a surface radius of 17.998 mm on the object side and a thickness of 4.58 mm; a surface radius of -53.483 mm on the image side and a distance of 5.67 mm from the adjacent lens; a refractive index of 1.90 and an Abbe number of 31.3.

[0097] Aperture 20: Thickness is 0.48~1.13mm.

[0098] The third positive lens 31 has a surface radius of -68.500 mm on the object side and a thickness of 3.41 mm; a surface radius of -15.734 mm on the image side and a distance of 0.12 mm from the adjacent lens; a refractive index of 1.83 and an Abbe number of 42.7.

[0099] Cemented lens 32: The radius of curvature facing the object side is 37.540 mm, the thickness is 3.36 mm, the refractive index is 1.68, and the Abbe number is 55.5; the radius of curvature of the cemented surfaces is -7.372 mm, and the thickness is 2.06 mm; the radius of curvature facing the image side is -24.652 mm, and the distance between the surface and the adjacent lens is 2.71 to 2.91 mm; the refractive index is 1.92, and the Abbe number is 20.9.

[0100] Fourth positive lens 41: The radius of curvature on the object side is 24.578 mm, and the thickness is 1.43 mm; the radius of curvature on the image side is -295.605 mm, and the distance between it and the adjacent lens is 9.57 mm; the refractive index is 1.50, the Abbe number is 81.6, and the relative refractive index temperature coefficient is -4.8 × 10⁻⁶. -6 / ℃.

[0101] The optical imaging system 100 has a total length L of 51.92 mm, a focal length f of 6.33 mm, and an effective focal length to incident aperture ratio of 2.8.

[0102] refer to Figure 2 , Figure 2 The diagram shows the MTF (modulation transfer function) of the optical imaging system 100 provided in the first aspect embodiment of this application. The horizontal axis represents the spatial frequency per millimeter, and the vertical axis represents the optical modulation transfer function. The curves in the diagram are the modulation transfer functions of the optical imaging system 100 in the sagittal and meridional directions. The closer each value on each line is to 1, the better the performance. The closer each line is to the other, the more stable the performance.

[0103] refer to Figure 3 , Figure 3 The image shows a distortion diagram of the optical imaging system 100 provided in the first aspect embodiment of this application, with the horizontal axis representing the distortion percentage and the vertical axis representing the height of the light rays on the image plane after being scaled by the optical imaging system 100.

[0104] refer to Figures 4 to 6The optical imaging system 100 provided in the second aspect embodiment of this application includes a first lens group 10, an aperture 20, a second lens group 30 and a third lens group 40, which are arranged sequentially along the direction of light incidence.

[0105] In this embodiment, the first lens group 10 includes three positive lenses and three negative lenses.

[0106] Two of the three positive lenses are referred to as the first positive lens 11 and the second positive lens 12, respectively. The first positive lens 11 is located on the side of the first lens group 10 away from the aperture stop 20, that is, the first positive lens 11 is located on the side of the first lens group 10 closer to the object side. The second positive lens 12 is located on the side of the second lens group 30 closer to the aperture stop 20. Optionally, the first positive lens 11 is a meniscus concave-convex lens, and the first positive lens 11 protrudes towards the object side. This arrangement can effectively reduce distortion and reduce optical sensitivity.

[0107] The three negative lenses are referred to as the first negative lens 13, the second negative lens 14, and the third negative lens 15, respectively. The first negative lens 13, the second negative lens 14, and the third negative lens 15 are all disposed between the first positive lens 11 and the second positive lens 12, and the first negative lens 13, the second negative lens 14, and the third negative lens 15 are arranged sequentially along the incident direction of light. Optionally, the first negative lens 13 is a meniscus concave-convex lens, and the first negative lens 13 protrudes towards the object side. This arrangement can cause light rays that enter the first negative lens 13 at a large angle to scatter out in a direction away from the optical axis, thereby changing the direction of light.

[0108] The remaining positive lens among the three is an additional positive lens, located between the third negative lens 15 and the second positive lens 12.

[0109] In this embodiment, the second lens group 30 includes a third positive lens 31 and a cemented lens 32.

[0110] In this embodiment, the third lens group 40 includes a fourth positive lens 41.

[0111] In one embodiment, specific parameters of each lens in a second aspect embodiment of this application are provided.

[0112] First positive lens 11: The radius of curvature facing the object side is 20.800 mm, and the thickness is 5.76 mm; the radius of curvature facing the image side is 40.500 mm, and the distance between it and the adjacent lens is 0.15 mm; the refractive index is 1.73, and the Abbe number is 54.7.

[0113] The first negative lens 13 has a surface radius of 15.698 mm facing the object side and a thickness of 1.06 mm; a surface radius of 7.689 mm facing the image side and a distance of 3.84 mm from the adjacent lens; a refractive index of 1.85 and an Abbe number of 23.8.

[0114] The second negative lens 14 has a surface radius of 40.598 mm on the object side and a thickness of 1.65 mm; a surface radius of 9.652 mm on the image side and a distance of 2.10 mm from the adjacent lens; a refractive index of 1.83 and an Abbe number of 42.7.

[0115] The third negative lens 15 has a surface radius of -95.637 mm on the object side and a thickness of 1.76 mm; a surface radius of 14.635 mm on the image side and a distance of 2.08 mm from the adjacent lens; a refractive index of 1.70 and an Abbe number of 30.1.

[0116] The added positive lens has a surface radius of -45.651 mm on the object side and a thickness of 5.68 mm; a surface radius of -20.865 mm on the image side and a distance of 0.24 mm from the adjacent lens; a refractive index of 1.85 and an Abbe number of 23.8.

[0117] The second positive lens 12 has a surface radius of 15.967 mm facing the object side and a thickness of 4.68 mm; a surface radius of 89.639 mm facing the image side and a distance of 7.74 mm from the adjacent lens; a refractive index of 1.90 and an Abbe number of 31.3.

[0118] Aperture 20: Thickness is 1.33~1.67mm.

[0119] The third positive lens 31 has a surface radius of 48.635 mm on the object side and a thickness of 1.18 mm; a surface radius of -26.648 mm on the image side and a distance of 1.89 mm from the adjacent lens; a refractive index of 1.69 and an Abbe number of 54.5.

[0120] Cemented lens 32: The radius of curvature facing the object side is 35.986 mm, the thickness is 2.45 mm, the refractive index is 1.60, the Abbe number is 65.5, and the relative refractive index temperature coefficient of the lens closest to the third positive lens 31 is -3.7 × 10⁻⁶. -6 / ℃; the radius of the mutually bonded curved surfaces is -7.846mm, and the thickness is 0.82mm; the radius of the curved surface facing the image side is -18.647mm, and the distance between it and the adjacent lens is 1.60~1.94mm; the refractive index is 1.92, and the Abbe number is 20.9.

[0121] The fourth positive lens 41 has a surface radius of 48.958 mm on the object side and a thickness of 2.44 mm; a surface radius of -45.687 mm on the image side and a distance of 7.23 mm from the adjacent lens; a refractive index of 1.73 and an Abbe number of 54.7.

[0122] The optical imaging system 100 has a total length L of 57.68 mm, a focal length f of 5.53 mm, and an effective focal length to incident aperture ratio of 2.8.

[0123] refer to Figure 5 , Figure 5 The diagram shows the MTF (modulation transfer function) of the optical imaging system 100 provided in the second aspect embodiment of this application. The horizontal axis represents the spatial frequency per millimeter, and the vertical axis represents the optical modulation transfer function. The curves in the diagram are the modulation transfer functions of the optical imaging system 100 in the sagittal and meridional directions. The closer each value on each line is to 1, the better the performance. The closer each line is to the other, the more stable the performance.

[0124] refer to Figure 6 , Figure 6 The image shows a distortion diagram of an optical imaging system 100 provided in a second aspect embodiment of this application. The horizontal axis represents the distortion percentage, and the vertical axis represents the height of the light rays on the image plane after being scaled by the optical imaging system 100.

[0125] refer to Figures 7 to 9 The optical imaging system 100 provided in the third aspect embodiment of this application includes a first lens group 10, an aperture 20, a second lens group 30 and a third lens group 40, which are arranged sequentially along the direction of light incidence.

[0126] In this embodiment, the first lens group 10 includes three positive lenses and three negative lenses.

[0127] Two of the three positive lenses are referred to as the first positive lens 11 and the second positive lens 12, respectively. The first positive lens 11 is located on the side of the first lens group 10 away from the aperture stop 20, that is, the first positive lens 11 is located on the side of the first lens group 10 closer to the object side. The second positive lens 12 is located on the side of the second lens group 30 closer to the aperture stop 20. Optionally, the first positive lens 11 is a meniscus concave-convex lens, and the first positive lens 11 protrudes towards the object side. This arrangement can effectively reduce distortion and reduce optical sensitivity.

[0128] The three negative lenses are referred to as the first negative lens 13, the second negative lens 14, and the third negative lens 15, respectively. The first negative lens 13, the second negative lens 14, and the third negative lens 15 are all disposed between the first positive lens 11 and the second positive lens 12, and the first negative lens 13, the second negative lens 14, and the third negative lens 15 are arranged sequentially along the incident direction of light. Optionally, the first negative lens 13 is a meniscus concave-convex lens, and the first negative lens 13 protrudes towards the object side. This arrangement can cause light rays that enter the first negative lens 13 at a large angle to scatter out in a direction away from the optical axis, thereby changing the direction of light.

[0129] The remaining positive lens among the three is an additional positive lens, located between the third negative lens 15 and the second positive lens 12.

[0130] In this embodiment, the second lens group 30 includes only the cemented lens 32.

[0131] In this embodiment, the third lens group 40 includes a fourth positive lens 41 and a third positive lens 31. The fourth positive lens 41 and the third positive lens 31 are arranged sequentially along the incident direction of light, that is, the fourth positive lens 41 is close to the second lens group 30, and the third positive lens 31 is far away from the second lens group 30; the fourth positive lens 41 is formed by cementing two lenses together.

[0132] In one embodiment, specific parameters of each lens in a third aspect of this application are provided.

[0133] First positive lens 11: The radius of curvature facing the object side is 20.298 mm, and the thickness is 4.64 mm; the radius of curvature facing the image side is 54.339 mm, and the distance between it and the adjacent lens is 0.12 mm; the refractive index is 1.68, and the Abbe number is 55.5.

[0134] The first negative lens 13 has a surface radius of 11.885 mm facing the object side and a thickness of 1.09 mm; a surface radius of 7.174 mm facing the image side and a distance of 2.98 mm from the adjacent lens; a refractive index of 1.91 and an Abbe number of 35.3.

[0135] The second negative lens 14 has a surface radius of 13.854 mm on the object side and a thickness of 0.78 mm; a surface radius of 7.112 mm on the image side and a distance of 3.00 mm from the adjacent lens; a refractive index of 1.88 and an Abbe number of 39.2.

[0136] The third negative lens 15 has a surface radius of -25.000 mm on the object side and a thickness of 1.68 mm; a surface radius of 14.240 mm on the image side and a distance of 1.10 mm from the adjacent lens; a refractive index of 1.83 and an Abbe number of 42.7.

[0137] The added positive lens has a surface radius of -336.681 mm on the object side and a thickness of 3.82 mm; a surface radius of -40.125 mm on the image side and a distance of 7.06 mm from the adjacent lens; a refractive index of 1.90 and an Abbe number of 31.3.

[0138] The second positive lens 12 has a surface radius of 35.261 mm on the object side and a thickness of 3.68 mm; a surface radius of -60.232 mm on the image side and a distance of 3.18 mm from the adjacent lens; a refractive index of 1.95 and an Abbe number of 17.9.

[0139] Aperture 20: Thickness is 1.48~3.48mm.

[0140] Cemented lens 32: The radius of curvature facing the object side is -53.802 mm, the thickness is 2.01 mm, the refractive index is 1.50, the Abbe number is 81.6, and the relative refractive index temperature coefficient of the lens closest to the third positive lens 31 is -4.8 × 10⁻⁶. -6 / ℃; the radius of the mutually bonded curved surfaces is -8.253, and the thickness is 1.37mm; the radius of the curved surface facing the image side is -12.873mm, and the distance between it and the adjacent lens is 1.14~3.14mm; the refractive index is 1.90, and the Abbe number is 31.3.

[0141] Fourth positive lens 41: The radius of curvature facing the object side is 34.829 mm, the thickness is 0.74 mm, the refractive index is 1.95, and the Abbe number is 17.9; the radius of curvature of the cemented surfaces is 9.406 mm, and the thickness is 2.15 mm; the radius of curvature facing the image side is -45.608 mm, and the distance between the surface and the adjacent lens is 0.12 mm; the refractive index is 1.64, and the Abbe number is 60.2.

[0142] The third positive lens 31 has a surface radius of 10.785 mm facing the object side and a thickness of 1.90 mm; a surface radius of 30.000 mm facing the image side and a distance of 13.59 mm from the adjacent lens; a refractive index of 1.79 and an Abbe number of 47.5.

[0143] The optical imaging system 100 has a total length L of 59.64 mm, a focal length f of 4.83 mm, and an effective focal length to incident aperture ratio of 2.4.

[0144] refer to Figure 8 , Figure 8The diagram shows the MTF (modulation transfer function) of the optical imaging system 100 provided in the third aspect embodiment of this application. The horizontal axis represents the spatial frequency per millimeter, and the vertical axis represents the optical modulation transfer function. The curves in the diagram are the modulation transfer functions of the optical imaging system 100 in the sagittal and meridional directions. The closer each value on each line is to 1, the better the performance. The closer each line is to the other, the more stable the performance.

[0145] refer to Figure 9 , Figure 9 The image shows a distortion diagram of an optical imaging system 100 provided in a third aspect embodiment of this application. The horizontal axis represents the distortion percentage, and the vertical axis represents the height of the light rays on the image plane after being scaled by the optical imaging system 100.

[0146] The fourth aspect of this application provides a machine vision system including the first aspect embodiment, the second aspect embodiment, or the third aspect embodiment.

[0147] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. An optical imaging system, characterized in that, It consists of a first lens group, an aperture stop, a second lens group, and a third lens group; The optical power of the first lens group is negative; The aperture is located on one side of the first lens group; The optical power of the second lens group is positive; The optical power of the third lens group is positive; The first lens group, the aperture, the second lens group, and the third lens group are arranged sequentially from the object side to the image side along the optical axis, and the second lens group can move between the aperture and the third lens group along the optical axis. The first lens group includes at least a first positive lens and a second positive lens. The first positive lens is disposed on the side of the first lens group away from the aperture stop, and the side of the first positive lens facing the object side protrudes towards the object side. The second positive lens is disposed on the side of the first lens group closer to the aperture stop. The first lens group further includes at least a first negative lens, a second negative lens, and a third negative lens, which are sequentially disposed between the first positive lens and the second positive lens along the incident direction of the light; the side of the first negative lens facing the object side protrudes towards the object side; The focal length f1 of the first lens group satisfies: -0.130≤f / f1≤-0.100; Where f is the focal length of the optical imaging system; The optical imaging system satisfies: 0.150≤H / L≤0.175; Where H is the holoimage height of the optical imaging system, and L is the total optical length of the optical imaging system.

2. The optical imaging system according to claim 1, characterized in that, The refractive index of the second positive lens is greater than or equal to 1.85 and less than or equal to 1.96; the Abbe number of the second positive lens is greater than or equal to 15.0 and less than or equal to 35.

0.

3. The optical imaging system according to claim 1, characterized in that, The second lens group includes at least one third positive lens and a cemented lens.

4. The optical imaging system according to claim 3, characterized in that, The third lens group includes at least a fourth positive lens, which is used to converge the incident light rays.

5. The optical imaging system according to claim 1, characterized in that, The second lens group includes cemented lenses.

6. The optical imaging system according to claim 5, characterized in that, The third lens group includes at least a third positive lens and a fourth positive lens.

7. The optical imaging system according to any one of claims 3-6, characterized in that, The focal length of the cemented lens is greater than or equal to 39 mm and less than or equal to 68 mm.

8. The optical imaging system according to claim 4 or 6, characterized in that, The refractive index of the third positive lens or the fourth positive lens is greater than or equal to 1.45 and less than or equal to 1.63; The Abbe number of the third positive lens or the fourth positive lens is greater than or equal to 60.0 and less than or equal to 91.0; The relative refractive index temperature coefficient of the third or fourth positive lens is greater than or equal to -5.0 × 10⁻⁶. -6 / ℃ and less than or equal to -3.5×10 -6 / ℃.

9. A machine vision system, characterized in that, Includes the optical imaging system as described in any one of claims 1-8.

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