A fixed focus lens

Abstract

The present invention discloses a fixed-focus lens, comprising 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 arranged in sequence from an object plane to an image plane along an optical axis; the first lens, the third lens and the seventh lens are all negative optical power lenses, and the second lens, the fourth lens, the fifth lens, the sixth lens and the eighth lens are all positive optical power lenses. The fixed-focus lens provided by the present invention has low cost and small size, and meets the requirements of low cost, easy processing, miniaturization, ultra-large light flux and high-definition imaging performance of day and night confocality.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of optical devices, and in particular to a fixed-focus lens. Background Art

[0002] With the increasing popularity of security monitoring facilities, the market has higher and higher requirements for the security monitoring lenses used. At present, large aperture lenses are often difficult to control in terms of total optical length and cost, and the performance of achieving day and night parfocality has increased in cost. In addition, it is often difficult to interchange with common micro security lenses due to the long total length. At the same time, the market has an increasingly strong demand for miniaturized and low-cost lenses. Therefore, it is necessary to develop a miniaturized, low-cost optical lens with ultra-large aperture day and night parfocality. Summary of the invention

[0003] The present invention provides a fixed-focus lens to reduce the lens cost and size, thereby meeting the requirements of low cost, easy processing, miniaturization, ultra-large light flux, and high-definition imaging performance of day and night confocality.

[0004] An embodiment of the present invention provides a fixed-focus lens, comprising 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 arranged in sequence from an object plane to an image plane along an optical axis;

[0005] The first lens, the third lens and the seventh lens are all negative power lenses, and the second lens, the fourth lens, the fifth lens, the sixth lens and the eighth lens are all positive power lenses.

[0006] Optionally, the first lens, the second lens, the third lens, the sixth lens, the seventh lens and the eighth lens are all aspherical lenses; and the fourth lens and the fifth lens are all spherical lenses.

[0007] Optionally, the first lens, the second lens, the sixth lens, the seventh lens and the eighth lens are all plastic aspherical lenses;

[0008] The third lens is a glass aspherical lens;

[0009] The fourth lens and the fifth lens are both glass spherical lenses.

[0010] Optionally, the fixed-focus lens further includes a diaphragm;

[0011] The aperture stop is disposed in an optical path between the third lens and the fourth lens.

[0012] Optionally, the fourth lens and the fifth lens are cemented lenses.

[0013] Optionally, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, the focal length of the eighth lens is f8, and the focal length of the fixed-focus lens is f;

[0014] Among them, 2<|f1 / f|<4;

[0015] 2<|f2 / f|<40;

[0016] |f3 / f|>2;

[0017] 5<|f4 / f|<4;

[0018] 5<|f5 / f|<25;

[0019] 1<|(f4+f5) / f|<4;

[0020] 0.5<|f6 / f|<2;

[0021] 0.5<|f7 / f|<2;

[0022] 1.5<|f8 / f|<11.

[0023] Optionally, a refractive index of the first lens is n1, a refractive index of the second lens is n2, a refractive index of the third lens is n3, a refractive index of the fourth lens is n4, a refractive index of the fifth lens is n5, a refractive index of the sixth lens is n6, a refractive index of the seventh lens is n7, and a refractive index of the eighth lens is n8;

[0024] The Abbe rate of the first lens is v1, the Abbe rate of the second lens is v2, the Abbe rate of the third lens is v3, the Abbe rate of the fourth lens is v4, the Abbe rate of the fifth lens is v5, the Abbe rate of the sixth lens is v6, the Abbe rate of the seventh lens is v7, and the Abbe rate of the eighth lens is v8;

[0025] Of which, 1.40 <n1<1.60,50<v1<70;

[0026] 1.40 <n2<1.60,50<v2<70;

[0027] 1.40 <n3<1.80,20<v3<85;

[0028] 1.40 <n4<1.60,50<v4<85;

[0029] 1.40 <n5<1.80,20<v5<80;

[0030] 1.40 <n6<1.60,50<v6<70;

[0031] 1.55 <n7<1.70,15<v7<40;

[0032] 1.40 <n8<1.60,50<v8<70。

[0033] Optionally, the surface of the lens close to the image plane is the object side, and the surface of the lens close to the image plane is the image side.

[0034] The object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface;

[0035] The object side surface of the second lens is a concave surface, and the image side surface of the second lens is a convex surface;

[0036] The object side surface of the third lens is a concave surface, and the image side surface of the third lens is a convex surface;

[0037] The object side surface of the fourth lens is a convex surface, and the image side surface of the fourth lens is a convex surface;

[0038] The object side surface of the fifth lens is a concave surface, and the image side surface of the first lens is a convex surface;

[0039] The object side surface of the sixth lens is a concave surface, and the image side surface of the sixth lens is a convex surface;

[0040] The object side surface of the seventh lens is a concave surface, and the image side surface of the seventh lens is a concave surface;

[0041] The object-side surface of the eighth lens is a convex surface, and the image-side surface of the eighth lens is a convex surface.

[0042] Optionally, the aperture number of the fixed-focus lens is F, the focal length of the fixed-focus lens is f, and the total length of the fixed-focus lens is TTL, wherein: F≤1.2, TTL / f<6.

[0043] Optionally, the maximum aperture of the first lens is D1, the total length of the fixed-focus lens is TTL, wherein D1 / TTL<0.55;

[0044] The surface of the lens close to the image plane is the image side surface, and the distance from the optical axis center of the image side surface of the eighth lens to the image plane is BFL, wherein BFL / TTL>0.15.

[0045] The fixed-focus lens provided in the embodiment of the present invention adopts a combination of 8 lenses, including 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, which are arranged in sequence from the object plane to the image plane along the optical axis, and the optical power combination mode is negative, positive, negative, positive, positive, positive, negative, positive. By reasonably setting the number of lenses in the fixed-focus lens and the combination relationship of the optical power of each lens, the size of the lens is reduced under the premise of low cost, and the requirements of low cost, easy processing, miniaturization, ultra-large light flux and high-definition imaging performance of day and night confocality are met. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic structural diagram of a fixed-focus lens provided by an embodiment of the present invention;

[0047] Figure 2 A light fan diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0048] Figure 3 An axial chromatic aberration diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0049] Figure 4 A field curvature distortion diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0050] Figure 5 A schematic structural diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0051] Figure 6 A light fan diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0052] Figure 7 An axial chromatic aberration diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0053] Figure 8 This is a field curvature distortion diagram of a fixed-focus lens provided in Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0055] Figure 1 Schematic diagram of the structure of a fixed-focus lens provided by an embodiment of the present invention. Figure 1As shown, the fixed-focus lens provided by the embodiment of the present invention includes a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, a seventh lens 170 and an eighth lens 180 which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110, the third lens 130 and the seventh lens 170 are all negative power lenses, and the second lens 120, the fourth lens 140, the fifth lens 150, the sixth lens 160 and the eighth lens 180 are all positive power lenses.

[0056] Exemplarily, the focal length is equal to the difference between the convergence degree of the image beam and the convergence degree of the image beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal length, the stronger the ability to bend light, and the smaller the absolute value of the focal length, the weaker the ability to bend light. When the focal length is a positive number, the refraction of light is convergent; when the focal length is a negative number, the refraction of light is divergent. The focal length can be used to characterize a refractive surface of a lens (i.e., a surface of a lens), can be used to characterize a lens, and can also be used to characterize a system formed by multiple lenses (i.e., a lens group).

[0057] Specifically, each lens can be fixed to a lens barrel ( Figure 1 (not shown in the figure), the first lens 110 is set as a negative power lens, which is used to control the incident angle of light of the optical system and correct the field curvature; the second lens 120 is a positive power lens, and the third lens 130 is a negative power lens. The second lens 120 and the third lens 130 are used to correct off-axis aberrations; the fourth lens 140 is a positive power lens, the fifth lens 150 is a positive power lens, and the third lens 130 has a negative power, which plays a key role in correcting the aberrations of the rear positive focal power fourth lens 140 and the positive focal power fifth lens, and can be in an environment of -40 to 80°C without defocusing at high and low temperatures; the sixth lens 160 and the eighth lens are both positive power lenses, and the seventh lens 170 is a negative power lens. The sixth lens 160, the seventh lens 170, and the eighth lens 180 are used to correct off-axis aberrations, including field curvature, coma, astigmatism and other aberrations.

[0058] The fixed-focus lens provided in the embodiment of the present invention adopts a combination of 8 lenses, including 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, which are arranged in sequence from the object plane to the image plane along the optical axis, and the optical power combination mode is negative, positive, negative, positive, positive, positive, negative, positive. By reasonably setting the number of lenses in the fixed-focus lens and the relative relationship of the optical power of each lens, the size of the lens is reduced under the premise of low cost, and the requirements of low cost, easy processing, miniaturization, ultra-large light flux and high-definition imaging performance of day and night confocality are met.

[0059] Optionally, the fixed-focus lens further includes an aperture (not shown in the figure); the aperture is arranged in the light path between the third lens 130 and the fourth lens 140 .

[0060] Specifically, by arranging the aperture in the light path between the third lens 130 and the fourth lens 140, the propagation direction of the light beam can be adjusted, and the incident angle of the light beam can be adjusted, which is beneficial to improving the imaging quality.

[0061] Optional, continue to refer to Figure 1 The first lens 110, the second lens 120, the third lens 130, the sixth lens 160, the seventh lens 170 and the eighth lens 180 are all aspherical lenses; the fourth lens 140 and the fifth lens 150 are all spherical lenses.

[0062] Among them, the use of aspherical lenses can play a role in correcting all high-order aberrations, and the first lens 110, the second lens 120, the third lens 130, the sixth lens 160, the seventh lens 170 and the eighth lens 180 are all aspherical lenses. The fourth lens 140 and the fifth lens 150 are spherical lenses, which are the main components of the entire lens for converging axial light.

[0063] Optional, continue to refer to Figure 1 The first lens 110, the second lens 120, the sixth lens 160, the seventh lens 170 and the eighth lens 180 are all plastic aspherical lenses; the third lens is a glass aspherical lens; the fourth lens and the fifth lens are all glass spherical lenses.

[0064] Among them, considering that the cost of plastic lenses is much lower than that of glass lenses, the first lens 110, the second lens 120, the sixth lens 160, the seventh lens 170 and the eighth lens 180 are all plastic aspherical lenses. This setting not only meets the requirements of high lens pixels but also low costs. Further, considering that glass materials are more stable than plastic materials in high and low temperature environments, the third lens 130 is set to be a glass aspherical lens, and the fourth lens 140 and the fifth lens 150 are both glass spherical lenses. Among them, placing the third lens 130 near the aperture can effectively correct the off-axis image quality and axial chromatic aberration while ensuring that the focus does not shift at high and low temperatures, and ensure confocality during the day and night.

[0065] Optionally, the fourth lens 140 and the fifth lens 150 are cemented lenses. The fourth lens 140 and the fifth lens 150 are set as cemented lenses to focus the front light beam. The negative focal length of the front third lens 130 corrects the positive focal length aberration of the rear cemented lens, which plays a key role in preventing the focus from shifting at high and low temperatures, and can effectively correct the off-axis image quality and axial chromatic aberration, ensuring the use characteristics of day and night confocality.

[0066] The fixed-focus lens provided in the embodiment of the present invention has the advantages of high image quality and low cost by arranging a combination of 5 plastic aspherical lenses, 1 glass aspherical lens and 2 glass spherical lenses. And because the two types of materials have a mutual compensation effect, the fixed-focus lens can still ensure that the resolution meets the imaging requirements in an environment of -40 to 80°C and can still be used normally.

[0067] It should be noted that the material of the above plastic aspheric lens can be various plastics known to those skilled in the art, and the material of the glass spherical lens can be various types of glass known to those skilled in the art, which will not be elaborated or limited in the embodiments of the present invention.

[0068] As a feasible implementation method, continue to refer to Figure 1 The surface of the lens close to the image plane is the object side surface, the surface of the lens close to the image plane is the image side surface, the object side surface of the first lens 110 is convex, and the image side surface of the first lens 120 is concave; the object side surface of the second lens 120 is concave, and the image side surface of the second lens 120 is convex; the object side surface of the third lens 130 is concave, and the image side surface of the third lens 130 is convex; the object side surface of the fourth lens 140 is convex, and the image side surface of the fourth lens 140 is convex; the object side surface of the fifth lens 150 is concave, and the image side surface of the fifth lens 150 is convex; the object side surface of the sixth lens 160 is concave, and the image side surface of the sixth lens 160 is convex; the object side surface of the seventh lens 170 is concave, and the image side surface of the seventh lens 170 is concave; the object side surface of the eighth lens 180 is convex, and the image side surface of the eighth lens 180 is convex.

[0069] Exemplarily, by setting the shape characteristics of the object side and image side of the first lens 110 to the eighth lens 180, a first lens 110 having a convex-concave negative power aspheric lens, a second lens 120 having a concave-convex positive power aspheric lens, a third lens 130 having a concave-convex negative power aspheric lens, a fourth lens 140 having a double-convex positive power spherical lens, a fifth lens 150 having a concave-convex positive power spherical lens, a sixth lens 160 having a concave-convex positive power aspheric lens, a seventh lens 170 having a double-concave negative power aspheric lens, and an eighth lens 180 having a double-convex positive power aspheric lens can be obtained to obtain a specific combination of optical system structures. Among them, the first lens adopts this shape to effectively reduce the total optical length and reduce the size of the lens.

[0070] Furthermore, by reasonably setting the curvature radius, center thickness, focal length, refractive index, Abbe number, etc. of the lens, it can be miniaturized to meet the performance of ultra-large light throughput and day and night confocality, and is suitable for monitoring needs under low illumination conditions. At the same time, it can ensure clear color imaging under low illumination conditions, and can also achieve clear imaging under extremely low illumination conditions through infrared fill light.

[0071] As a feasible implementation, Table 1 shows the optical physical parameters of the curvature radius and thickness of each lens in the fixed focus lens provided in an embodiment of the present invention. The curvature radius and thickness of the first lens to the eighth lens are set to meet the following conditions:

[0072] Table 1 Optical and physical parameters of fixed-focus lenses

[0073] Surface number Radius of curvature thickness 1 R1＝2.0～5.0 T1＝0.8～4.0 2 R2＝1.0～5.0 T2＝0.05～3.0 3 R3＝-2.0～-10.0 T3＝0.8～4.0 4 R4＝-10.0～-3.0 T4＝0.05～3.0 5 R5＝-10.0～-1.0 T5＝0.8～4.0 6 R6＝-7.0～-2.0 T6＝0.05～3.0 7 R7＝5.0～10.0 T7＝0.8～4.0 8 R8＝-5.0～-4.0 T8＝0.05～3.0 9 R9＝-30.0～-10.0 T9＝0.8～4.0 10 R10＝-25.0～-5.0 T10＝0.05～3.0 11 R11＝-5.0～-1.0 T11＝0.8～4.0 12 R12＝-7.0～-1.0 T12＝0.05～3.0 13 R13＝-∞～-2.0 T13＝0.8～4.0 14 R14＝-100～-1.0 T14＝0.05～3.0 15 R15＝-10.0～-3.0

[0074] In Table 1, "R" is the radius of curvature, "T" is the thickness, and "-" represents the negative direction. Among them, R1, R3, R5, R7, R10, R12, and R14 represent the radius of curvature of the center of the surface of the first lens 110 to the seventh lens 170 close to the image plane in sequence; R2, R4, R6, R9, R11, R13, and R15 represent the radius of curvature of the center of the surface of the first lens 110 to the eighth lens 180 close to the image plane in sequence; R8 is the radius of curvature of the cemented surface, T1, T3, T5, T7, T8, T10, T12, and T14 represent the center thickness of the first lens 110 to the eighth lens 180 in sequence; T2, T4, T6, T9, T11, and T13 represent the air interval of the first lens 110 to the eighth lens 180 in sequence.

[0075] Specifically, the units of the radius of curvature, the center thickness and the air interval are all in millimeters (mm). By setting the radius of curvature of the first lens 110 to the seventh lens 180, it is helpful to shorten the total length of the optical path and ensure that the overall volume of the lens is small. By setting the center thickness of the first lens 110 to the eighth lens 180 and the air interval of the first lens 110 to the eighth lens 180, the total length of the optical path is short through the optical system composed of the above lenses, thereby ensuring that the overall volume of the lens is small, and the overall volume of the optical system is controlled from a structural perspective.

[0076] Optionally, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, the focal length of the eighth lens is f8, and the focal length of the fixed-focus lens is f;

[0077] Among them, 2<|f1 / f|<4; 2<|f2 / f|<40; |f3 / f|>2;

[0078] 5<|f4 / f|<4; 5<|f5 / f|<25; 1<|(f4+f5) / f|<4;

[0079] 0.5<|f6 / f|<2; 0.5<|f7 / f|<2; 1.5<|f8 / f|<11.

[0080] Specifically, the seventh lens is set as the element with the largest negative optical power in the entire lens, and the ratio of its focal length to the focal length f of the fixed-focus lens satisfies: 0.5 < |f7 / f| < 2, which has the function of correcting magnification chromatic aberration and axial chromatic aberration to ensure the balance of high and low temperatures. By reasonably setting the ratio relationship between the focal lengths of each lens and the fixed-focus lens, the spherical aberration and field curvature of the entire optical system are reduced simultaneously, ensuring the image quality of the on-axis and off-axis fields of view, and ensuring the super-large light transmission and day-night confocal performance of the optical system.

[0081] Optionally, the refractive index of the first lens is n1, the refractive index of the second lens is n2, the refractive index of the third lens is n3, the refractive index of the fourth lens is n4, the refractive index of the fifth lens is n5, the refractive index of the sixth lens is n6, the refractive index of the seventh lens is n7, and the refractive index of the eighth lens is n8; the Abbe number of the first lens is v1, the Abbe number of the second lens is v2, the Abbe number of the third lens is v3, the Abbe number of the fourth lens is v4, the Abbe number of the fifth lens is v5, the Abbe number of the sixth lens is v6, the Abbe number of the seventh lens is v7, and the Abbe number of the eighth lens is v8;

[0082] Among them, 1.40 < n1 < 1.60, 50 < v1 < 70; 1.40 < n2 < 1.60, 50 < v2 < 70;

[0083] 1.40 < n3 < 1.80, 20 < v3 < 85; 1.40 < n4 < 1.60, 50 < v4 < 85;

[0084] 1.40 < n5 < 1.80, 20 < v5 < 80; 1.40 < n6 < 1.60, 50 < v6 < 70;

[0085] 1.55 < n7 < 1.70, 15 < v7 < 40; 1.40 < n8 < 1.60, 50 < v8 < 70.

[0086] Among them, the refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium, mainly used to describe the refractive ability of the material to light, and the refractive indices of different materials are different. The Abbe number is an index used to represent the dispersion ability of a transparent medium. The more serious the dispersion of the medium, the smaller the Abbe number; conversely, the lighter the dispersion of the medium, the larger the Abbe number.

[0087] Specifically, the first lens and the second lens can be set to satisfy: 2 < |f1 / f| < 4, 2 < |f2 / f| < 40; 1.40 < n1 < 1.60, 50 < v1 < 70; 1.40 < n2 < 1.60, 50 < v2 < 70. By setting within this parameter range, the first lens and the second lens have the function of correcting the spherical aberration, field curvature, astigmatism, and coma of the lens.

[0088] The third lens is set to satisfy: 2 < |f3 / f|, 1.40 < n3 < 1.80, 20 < v3 < 85. By setting within this parameter range, it can effectively promote the balance of aberrations, play a role in converging light rays to reduce the light height, and correct spherical aberration, chromatic aberration of magnification, and axial chromatic aberration at the same time.

[0089] The fourth lens and the fifth lens are set to satisfy: 1.5 < |f4 / f| < 4, 5 < |f5 / f| < 25, 1 < |(F4 + F5) / F| < 4. Further, the fourth lens and the fifth lens can be set to be cemented. The cemented lens formed is the main component for converging the on-axis light rays in the entire lens. The ratio of its focal length to that of the entire lens will greatly affect whether there is defocus at high and low temperatures. When the settings meet this range, defocus can be better avoided, enabling the optical system to be used in the environment of -40 to 80 °C to ensure that the resolution meets the imaging requirements and meet the performance of a large aperture and day-night confocal.

[0090] The sixth lens and the eighth lens are set to satisfy: 0.5 < |f6 / f| < 2, 1.5 < |f8 / f| < 11, 1.40 < n6 < 1.60, 50 < v6 < 70; 1.55 < n7 < 1.70, 15 < v7 < 40; 1.40 < n8 < 1.60, 50 < v8 < 70. By setting within this parameter range, the sixth lens and the eighth lens can play a better role in correcting aberrations such as field curvature, astigmatism, spherical aberration, and coma.

[0091] In this way, by setting the refractive index and Abbe number of each lens in the fixed-focus lens in combination, the balance of the incident angle sizes of the front and rear lens groups is ensured, so as to reduce the sensitivity of the lens and facilitate the realization of a higher pixel resolution.

[0092] Optionally, the maximum light-gathering aperture of the first lens is D1, and the total length of the fixed-focus lens is TTL, where D1 / TTL < 0.55; the surface of the lens closer to the image plane is the image side surface, and the distance from the optical axis center of the image side surface of the eighth lens to the image plane is BFL, where BFL / TTL > 0.15.

[0093] Further, to ensure that the lens will not interfere with the base and the housing during installation, the maximum light-gathering aperture of the first lens is set to D1 and the total length of the fixed-focus lens is set to TTL, satisfying the parameter D1 / TTL < 0.55; at the same time, the surface of the lens closer to the image plane is defined as the image side surface and the distance from the optical axis center of the image side surface of the eighth lens to the image plane is defined as BFL, satisfying BFL / TTL > 0.15, which can ensure that the entire fixed-focus lens has a compact structure, high integration, is easy to install and use, meets the miniaturization requirements, and is suitable for the monitoring requirements under low illumination conditions.

[0094] As a feasible implementation manner, the aperture number of the fixed-focus lens provided in the embodiment of the present invention is F, the focal length of the fixed-focus lens is f, and the total length of the fixed-focus lens is TTL, wherein: F≤1.2, TTL / f<6.

[0095] The fixed-focus lens provided in the embodiment of the present invention adopts a method of mixing glass spherical mirrors and plastic aspherical surfaces, and ensures the performance of the optical system while ensuring low cost and easy processing of the lens by reasonably allocating the optical power, surface shape, Abbe number, center thickness, etc. of each lens. Under the premise of ensuring that the lens has an aperture F number ≤ 1.2, the ratio of the total length TTL of the optical system to the focal length f of the optical system satisfies: TTL / f<6. This design meets the performance of ultra-large light throughput and day and night confocality, is miniaturized, and is suitable for monitoring needs under low illumination conditions. At the same time, it can not only ensure clear color imaging under low illumination conditions, but also achieve clear imaging under extremely low illumination conditions through infrared fill light.

[0096] Specific embodiments of the fixed-focus lens applicable to the above-mentioned embodiments are further described below with reference to the accompanying drawings.

[0097] Embodiment 1

[0098] Continue to refer to Figure 1 The fixed-focus lens provided by the embodiment of the present invention includes a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, a seventh lens 170 and an eighth lens 180 which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110, the third lens 130 and the seventh lens 170 are all negative power lenses, and the second lens 120, the fourth lens 140, the fifth lens 150, the sixth lens 160 and the eighth lens 180 are all positive power lenses.

[0099] Table 2 shows the surface type, curvature radius, thickness and optical physical parameters of the material of each lens in the fixed-focus lens provided in Example 1.

[0100] Table 2 Optical and physical parameters of fixed-focus lenses

[0101] Surface number Surface type Radius of curvature thickness Materials (n.d.) S1 Aspheric 3.6 1.8 1.54 / 55.7 S2 Aspheric 2.1 2.6 S3 Aspheric -7.0 1.6 1.54 / 55.7 S4 Aspheric -6.5 0.1 S5 Aspheric -4.4 2.5 1.61 / 58.0 S6 Aspheric -4.0 0.04 Aperture S7 Spherical 6.4 3.0 1.44 / 95.1 S8 Spherical -5.3 0.7 1.49 / 70.4 S9 Spherical -28.9 0.08 S10 Aspheric -9.6 1.6 1.54 / 55.7 S11 Aspheric -2.5 0.2 S12 Non-planar -3.3 0.7 1.63 / 23.2 S13 Aspheric -10.2 0.1 S14 Aspheric -6.8 1.5 1.54 / 55.7 S15 Spherical -5.4 3.0 S16 Spherical unlimited 0.7 1.52 / 64.2 S17 Spherical unlimited 1.7

[0102] In Table 2, the surface numbers are numbered according to the order of the surfaces of each lens. For example, the surfaces numbered S1 and S2 are the object side surface and the image side surface of the first lens 110, respectively; the surfaces numbered S3 and S4 are the object side surface and the image side surface of the second lens 120, respectively; and so on. The radius of curvature represents the curvature of the lens surface. A positive value represents that the surface is curved toward the image side, and a negative value represents that the surface is curved toward the object side. The thickness represents the central axial distance from the current surface to the next surface. The units of the radius of curvature and the thickness are both millimeters (mm).

[0103] Based on the above implementation, optionally, the first lens 110, the second lens 120, the sixth lens 160, the seventh lens 170 and the eighth lens 180 are all plastic aspheric lenses; the third lens is a glass aspheric lens; and the fourth lens and the fifth lens are both glass spherical lenses.

[0104] The fixed-focus lens provided in the first embodiment of the present invention further includes an aperture (not shown in the figure); the aperture is arranged in the optical path between the third lens 130 and the fourth lens 140. By adding the aperture, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. The aperture can be located in the optical path between the third lens 130 and the fourth lens 140, but the embodiment of the present invention does not limit the specific position of the aperture.

[0105] The aspherical surface shape equation Z of the first lens 110, the second lens 120, the sixth lens 160, the seventh lens 170 and the eighth lens 180 satisfies:

[0106]

[0107] Wherein, Z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of y along the optical axis; c = 1 / R, R represents the paraxial curvature radius of the mirror surface; K is the cone coefficient; A, B, C, D, E, and F are high-order aspheric coefficients, where the units of Z, R, and y are all mm.

[0108] Exemplarily, Table 3 describes in detail the aspheric coefficients of each lens in the first embodiment in a feasible implementation manner.

[0109] Table 3 Aspheric coefficients in fixed focus lenses

[0110]

[0111] Among them, -1.49E-03 means that the coefficient A of the face number 1 is -1.49*10 -3 , and so on.

[0112] The fixed-focus lens of the first embodiment achieves the following technical indicators:

[0113] Focal length: f=6.0mm;

[0114] Relative aperture F = 1.2;

[0115] Field of view: 2w ≥ 70°;

[0116] Applicable spectral range: 436~656nm;

[0117] Resolution: Compatible with 5-megapixel high-resolution CCD or CMOS cameras.

[0118] further, Figure 2 This is a light fan diagram of a fixed-focus lens provided in Embodiment 1 of the present invention; Figure 2 As shown, the imaging range of different wavelengths of light (0.436μm, 0.486μm, 0.588μm, 0.656μm and 0.850μm) at different field angles of the fixed-focus lens is all within 50μm and the curves are very concentrated, ensuring that the aberrations in different field areas are small, which means that the fixed-focus lens can better correct the aberrations of the optical system.

[0119] Figure 3 An axial chromatic aberration diagram of a fixed-focus lens provided by an embodiment of the present invention, Figure 4 A field curvature distortion diagram of a fixed-focus lens provided in Embodiment 1 of the present invention, combined with Figure 3 and Figure 4 As shown, the fixed-focus lens provided by the embodiment of the present invention has small vertical axis chromatic aberration and small field curvature, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; the image quality is high, meeting the requirements of ultra-large light throughput and day and night confocal performance.

[0120] In summary, the fixed-focus lens provided in the first embodiment of the present invention adopts a combination of 8 lenses that are a mixture of glass spherical lenses and plastic aspherical lenses. By reasonably setting the number of lenses in the fixed-focus lens, the optical focal length of each lens, and the relative relationship between the focal lengths of each lens, under the premise of low cost, the entire lens combination ensures that the refractive index and the optical focal length of the optical system are approximately proportionally distributed, and even when used in an environment of -40 to 80°C, the resolution can still meet the imaging requirements, thereby achieving low cost, easy processing, miniaturization, ultra-large light throughput, and high-definition imaging performance requirements of day and night confocality.

[0121] Embodiment 2

[0122] Figure 5 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present invention, such as Figure 5 As shown, the fixed-focus lens provided by the embodiment of the present invention includes a first lens 210, a second lens 220, a third lens 230, a fourth lens 240, a fifth lens 250, a sixth lens 260, a seventh lens 270 and an eighth lens 280 which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens 210, the third lens 230 and the seventh lens 270 are all negative power lenses, and the second lens 220, the fourth lens 240, the fifth lens 250, the sixth lens 260 and the eighth lens 280 are all positive power lenses.

[0123] Table 4 shows optical physical parameters such as surface type, curvature radius, thickness and material of each lens in the fixed-focus lens provided in Example 2.

[0124] Table 4 Optical and physical parameters of fixed-focus lenses

[0125] Surface number Surface type Radius of curvature thickness Materials (n.d.) S1 Aspheric 3.0 1.3 1.54 / 55.7 S2 Aspheric 2.0 2.5 S3 Aspheric -5.9 1.8 1.54 / 55.7 S4 Aspheric -4.1 0.4 S5 Aspheric -2.9 2.2 1.61 / 58.0 S6 Aspheric -3.6 0.05 Aperture S7 Spherical 6.5 2.9 1.44 / 95.1 S8 Spherical -6.5 0.8 1.49 / 70.4 S9 Spherical -47.1 0.07 S10 Aspheric -14.5 1.8 1.54 / 55.7 S11 Aspheric -2.8 0.2 S12 Non-planar -3.7 0.8 1.63 / 23.2 S13 Aspheric -24.1 0.08 S14 Aspheric -13.2 1.6 1.54 / 55.7 S15 Aspheric -6.5 3.0 S16 Spherical unlimited 0.7 1.52 / 64.2 S17 Spherical unlimited 1.7

[0126] In Table 4, the surface numbers are numbered according to the order of the surfaces of each lens. For example, the surfaces numbered S1 and S2 are the object side surface and the image side surface of the first lens 210, respectively; the surfaces numbered S3 and S4 are the object side surface and the image side surface of the second lens 220, respectively; and so on. The radius of curvature represents the curvature of the lens surface. A positive value represents that the surface is curved toward the image side, and a negative value represents that the surface is curved toward the object side. The thickness represents the central axial distance from the current surface to the next surface. The units of the radius of curvature and the thickness are both millimeters (mm).

[0127] Based on the above implementation, optionally, the first lens 210, the second lens 220, the sixth lens 260, the seventh lens 270 and the eighth lens 280 are all plastic aspherical lenses; the third lens 230 is a glass aspherical lens; and the fourth lens 240 and the fifth lens 250 are both glass spherical lenses.

[0128] Continue to refer to Figure 5 The fixed focus lens provided in the first embodiment of the present invention further includes an aperture (not shown in the figure); the aperture is arranged in the optical path between the third lens 230 and the fourth lens 240. By adding the aperture, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. The aperture can be located in the optical path between the third lens 230 and the fourth lens 240, but the embodiment of the present invention does not limit the specific position of the aperture.

[0129] The aspherical surface shape equation Z of the first lens 210, the second lens 220, the sixth lens 260, the seventh lens 270 and the eighth lens 280 satisfies:

[0130]

[0131] Wherein, Z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of y along the optical axis; c = 1 / R, R represents the paraxial curvature radius of the mirror surface; K is the cone coefficient; A, B, C, D, E, and F are high-order aspheric coefficients, where the units of Z, R, and y are all mm.

[0132] Exemplarily, Table 5 describes in detail the aspheric coefficients of each lens in the second embodiment in a feasible implementation manner.

[0133] Table 5 Aspheric coefficients in fixed focus lenses

[0134]

[0135] Among them, -1.69E-03 means that the coefficient A of the face number 1 is -1.69*10 -3 , and so on.

[0136] The fixed-focus lens of the second embodiment achieves the following technical indicators:

[0137] Focal length: f=6.2mm;

[0138] Aperture number F = 1.2;

[0139] Field of view: 2w ≥ 70°;

[0140] Applicable spectral range: 436~656nm;

[0141] Resolution: Compatible with 5-megapixel high-resolution CCD or CMOS cameras.

[0142] further, Figure 6 A light fan diagram of a fixed-focus lens provided in the second embodiment of the present invention, such as Figure 6 As shown, the imaging range of different wavelengths of light (0.436μm, 0.486μm, 0.588μm, 0.656μm and 0.850μm) at different field angles of the fixed-focus lens is all within 50μm and the curves are very concentrated, ensuring that the aberrations in different field areas are small, which means that the fixed-focus lens can better correct the aberrations of the optical system.

[0143] Figure 7 This is an axial chromatic aberration diagram of a fixed-focus lens provided in Embodiment 2 of the present invention, Figure 8 A field curvature distortion diagram of a fixed-focus lens provided in Embodiment 2 of the present invention, combined with Figure 7 and Figure 8 As shown, the fixed-focus lens provided by the embodiment of the present invention has small vertical axis chromatic aberration and small field curvature, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; the image quality is high, meeting the requirements of ultra-large light throughput and day and night confocal performance.

[0144] In summary, the fixed-focus lens provided in the second embodiment of the present invention adopts a combination of 8 lenses that are a mixture of glass spherical lenses and plastic aspherical lenses. By reasonably setting the number of lenses in the fixed-focus lens, the optical focal length of each lens, and the relative relationship between the focal lengths of each lens, under the premise of low cost, the entire lens combination ensures that the refractive index and optical focal length of the optical system are approximately proportionally distributed, and even when used in an environment of -40 to 80°C, the resolution can still meet the imaging requirements, thereby achieving low cost, easy processing, miniaturization, ultra-large light throughput, and high-definition imaging performance requirements of day and night confocality.

[0145] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that: It includes 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 which are arranged in sequence from the object plane to the image plane along the optical axis; The first lens, the third lens and the seventh lens are all negative power lenses, and the second lens, the fourth lens, the fifth lens, the sixth lens and the eighth lens are all positive power lenses; The aperture number of the fixed-focus lens is F, the focal length of the fixed-focus lens is f, and the total length of the fixed-focus lens is TTL, wherein: F≤1.2, TTL / f<6; Each of the lenses is fixed in a lens barrel.

2. The fixed-focus lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, the sixth lens, the seventh lens and the eighth lens are all aspherical lenses; and the fourth lens and the fifth lens are all spherical lenses.

3. The fixed-focus lens according to claim 2, characterized in that: The first lens, the second lens, the sixth lens, the seventh lens and the eighth lens are all plastic aspherical lenses; The third lens is a glass aspherical lens; The fourth lens and the fifth lens are both glass spherical lenses.

4. The fixed-focus lens according to claim 1, characterized in that: The fixed-focus lens further includes an aperture; The aperture stop is disposed in an optical path between the third lens and the fourth lens.

5. The fixed-focus lens according to claim 1, wherein: The fourth lens and the fifth lens are a cemented lens.

6. The fixed-focus lens according to claim 1, wherein: The focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, the focal length of the eighth lens is f8, and the focal length of the fixed-focus lens is f; Among them, 2<|f1 / f|<4; 2<|f2 / f|<40; |f3 / f|>2; 5<|f4 / f|<4; 5<|f5 / f|<25; 1<|(f4+f5) / f|<4; 0.5<|f6 / f|<2; 0.5<|f7 / f|<2; 1.5<|f8 / f|<11.

7. The fixed-focus lens according to claim 1, wherein: The refractive index of the first lens is n1, the refractive index of the second lens is n2, the refractive index of the third lens is n3, the refractive index of the fourth lens is n4, the refractive index of the fifth lens is n5, the refractive index of the sixth lens is n6, the refractive index of the seventh lens is n7, and the refractive index of the eighth lens is n8; The Abbe rate of the first lens is v1, the Abbe rate of the second lens is v2, the Abbe rate of the third lens is v3, the Abbe rate of the fourth lens is v4, the Abbe rate of the fifth lens is v5, the Abbe rate of the sixth lens is v6, the Abbe rate of the seventh lens is v7, and the Abbe rate of the eighth lens is v8; Of which, 1.40 <n1<1.60,50<v1<70; 1.40 <n2<1.60,50<v2<70; 1.40 <n3<1.80,20<v3<85; 1.40 <n4<1.60,50<v4<85; 1.40 <n5<1.80,20<v5<80; 1.40 <n6<1.60,50<v6<70; 1.55 <n7<1.70,15<v7<40; 1.40 <n8<1.60,50<v8<70。 8. The fixed-focus lens according to claim 1, wherein: The surface of the lens close to the object plane is the object side surface, and the surface of the lens close to the image plane is the image side surface; The object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; The object side surface of the second lens is a concave surface, and the image side surface of the second lens is a convex surface; The object side surface of the third lens is a concave surface, and the image side surface of the third lens is a convex surface; The object side surface of the fourth lens is a convex surface, and the image side surface of the fourth lens is a convex surface; The object side surface of the fifth lens is a concave surface, and the image side surface of the first lens is a convex surface; The object side surface of the sixth lens is a concave surface, and the image side surface of the sixth lens is a convex surface; The object side surface of the seventh lens is a concave surface, and the image side surface of the seventh lens is a concave surface; The object-side surface of the eighth lens is a convex surface, and the image-side surface of the eighth lens is a convex surface.

9. The fixed-focus lens according to claim 1, wherein: The maximum aperture of the first lens is D1, and the total length of the fixed-focus lens is TTL, wherein D1 / TTL<0.55; The surface of the lens close to the image plane is the image side surface, and the distance from the optical axis center of the image side surface of the eighth lens to the image plane is BFL, wherein BFL / TTL>0.15.

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