Fixed-focus lenses and surveillance equipment

Abstract

The present invention discloses a fixed-focus lens and monitoring equipment. The fixed-focus lens includes a first convexo-concave lens with a negative optical power, a second biconcave lens with a negative optical power, a third convexo-concave lens with a negative optical power, a fourth biconvex lens with a positive optical power, a fifth biconvex lens with a positive optical power, a sixth biconcave lens with a negative optical power, and a seventh biconvex lens with a positive optical power. By rationally setting the optical powers and shapes of the seven lenses, the fixed-focus lens can well control the direction of light, while introducing more light and making the structure more compact. The total length of the fixed-focus lens is controlled within 22.5 mm, and the aperture value F satisfies 0.8≤F≤1.1, supporting a 1 / 2.5-inch image plane. The fixed-focus lens can also produce clear images in low light. By rationally setting the focal length ratio, the lens does not defocus under environmental conditions of -40°C to +85°C, the operating performance is more stable, and the field of view angle can reach 140°±5%, thereby providing a large aperture, large angle, small high and low temperature fixed-focus lens.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a fixed-focus lens and monitoring equipment. Background Art

[0002] The current closed-circuit surveillance industry is moving towards miniaturization, multifunctionality, and strong environmental adaptability. However, existing technologies suffer from the following major drawbacks: Due to the complexities of different regional environments, they cannot adapt to large temperature fluctuations, easily causing defocus and affecting the quality of images. Furthermore, when surveillance cameras operate for extended periods, their circuits generate heat, which can affect lens focus under high temperatures. At night or in low-light areas, existing cameras are prone to color loss, blurred details, and insufficient brightness under infrared fill light, resulting in poor image quality. They also suffer from narrow shooting angles and fields of view, resulting in inadequate data collection. Summary of the Invention

[0003] The main purpose of the present invention is to provide a fixed-focus lens and monitoring equipment, aiming to provide a fixed-focus lens with large aperture, large angle, small size and high and low temperature performance.

[0004] To achieve the above objectives, the present invention provides a fixed-focus lens, the fixed-focus lens having an object side and an image side arranged opposite to each other along an optical axis, the fixed-focus lens including a first convex-concave lens with negative optical power, a second biconcave lens with negative optical power, a third convex-concave lens with positive optical power, a fourth biconvex lens with positive optical power, a fifth biconvex lens with positive optical power, a sixth biconcave lens with negative optical power, and a seventh biconvex lens with positive optical power, arranged in sequence from the object side to the image side, wherein the concave surfaces of the first convex-concave lens, the second biconcave lens, the third convex-concave lens, the sixth biconcave lens, and the seventh biconvex lens are all aspherical lenses;

[0005] The total optical length TTL of the fixed-focus lens is ≤22.5 mm, the aperture number of the fixed-focus lens is F, and 0.8≤F≤1.1, and the field of view FOV=140°±5%.

[0006] Optionally, the fixed-focus lens further meets the following conditions:

[0007] -0.67≤φ1 / φ≤-0.25;

[0008] -0.60≤φ2 / φ≤0.4;

[0009] -0.35≤φ3 / φ≤0.3;

[0010] 0.3≤φ4 / φ≤0.6;

[0011] 0.3≤φ5 / φ≤0.7;

[0012] -0.8≤φ6 / φ≤-0.5;

[0013] 0.3≤φ7 / φ≤0.7;

[0014] Among them, the optical focal power of the fixed-focus lens is φ, the optical focal power of the first convex-concave lens is φ1, the optical focal power of the second biconcave lens is φ2, the optical focal power of the third convex-concave lens is φ3, the optical focal power of the fourth biconvex lens is φ4, the optical focal power of the fifth biconvex lens is φ5, the optical focal power of the sixth biconcave lens is φ6, and the optical focal power of the seventh biconvex lens is φ7.

[0015] Optionally, the fixed-focus lens further meets the following conditions:

[0016] 1.50≤n1≤1.60, 50.0≤v1≤65.0;

[0017] 1.50≤n2≤1.75, 20.0≤v2≤65.0;

[0018] 1.50≤n3≤1.70, 18.0≤v3≤25.0;

[0019] 1.49≤n4≤1.70, 60.0≤v4≤75.0;

[0020] 1.50≤n5≤1.60, 50.0≤v5≤75.0;

[0021] 1.60≤n6≤1.75, 15.0≤v6≤25.0;

[0022] 1.50≤n7≤1.60, 50.0≤v7≤60.0;

[0023] Among them, the refractive index of the first convex-concave lens is n1, and the dispersion coefficient is v1, the refractive index of the second biconcave lens is n2, and the dispersion coefficient is v2, the refractive index of the third convex-concave lens is n3, and the dispersion coefficient is v3, the refractive index of the fourth biconvex lens is n4, and the dispersion coefficient is v4, the refractive index of the fifth biconvex lens is n5, and the dispersion coefficient is v5, the refractive index of the sixth biconcave lens is n6, and the dispersion coefficient is v6, and the refractive index of the seventh biconvex lens is n7, and the dispersion coefficient is v7.

[0024] Optionally, the first convex-concave lens, the second biconcave lens, the third convex-concave lens, the fifth biconcave lens, the sixth biconcave lens and the seventh biconvex lens are all plastic lenses;

[0025] The fourth biconvex lens is a glass lens.

[0026] Optionally, the total focal length of the fixed-focus lens is f, the entrance pupil diameter of the fixed-focus lens is d, and 0.8≤f / d≤1.1.

[0027] Optionally, the back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL, wherein BFL / TTL≥0.1.

[0028] Optionally, the diameter of the first convex-concave lens is D1, and the total optical length of the fixed-focus lens is TTL, wherein D1 / TTL<0.7.

[0029] Optionally, an image plane diameter IC of the fixed-focus lens satisfies: IC≤7.3 mm.

[0030] Optionally, the fixed-focus lens further includes an aperture, a protective glass and a photosensitive chip from the object side to the image side, the aperture is arranged between the second biconcave lens and the third convex-concave lens, and the protective glass and the photosensitive chip are arranged on the side of the seventh biconvex lens close to the image side.

[0031] The present invention also provides a monitoring device, which includes the above-mentioned fixed-focus lens.

[0032] In the technical solution provided by the present invention, a first convex-concave lens with negative optical power, a second biconcave lens with negative optical power, a third convex-concave lens with positive optical power, a fourth biconvex lens with positive optical power, a fifth biconvex lens with positive optical power, a sixth biconcave lens with negative optical power, and a seventh biconvex lens with positive optical power are sequentially arranged from the object side to the image side. Due to the large aperture of the first convex-concave lens, more light information can be collected under the same focal length, so as to achieve the effect of clear imaging in weak light. The fourth biconvex lens bears the larger optical power of the system, changes the propagation direction of the light beam, and is more conducive to the imaging of the light beam on the image plane. Through the reasonable setting of the optical power and shape of the seven lenses, the fixed-focus lens can well control the light trend, introduce more light and make the structure more compact, so that the total length of the fixed-focus lens is controlled within 22.5 mm, and through the reasonable arrangement of aspheric lenses, various aberrations are corrected, the edge image quality is improved, and the imaging quality is high. The aperture value F satisfies 0.8≤F≤1.1, supports a 1 / 2.5-inch image plane, and the fixed-focus lens can produce clear images even in low light. By reasonably setting the focal length ratio, the lens does not defocus under environmental conditions of -40°C to +85°C, and the working performance is more stable. The field of view can reach 140°±5%, the field of view is wider, and the data information obtained is more sufficient, thereby providing a large aperture, large angle, small high and low temperature fixed-focus lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0034] Figure 1 A schematic structural diagram of the fixed-focus lens provided by the present invention;

[0035] Figure 2 for Figure 1 Schematic diagram of spherical aberration curve of fixed focus lens in;

[0036] Figure 3 for Figure 1 Schematic diagram of the light fan of the fixed focus lens in;

[0037] Figure 4 for Figure 1 Schematic diagram of field distortion / field curvature of a fixed-focus lens in .

[0038] Description of Figure Numbers:

[0039]

[0040] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), such directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0043] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] The current closed-circuit surveillance industry is moving towards miniaturization, multifunctionality, and strong environmental adaptability. However, existing technologies suffer from the following major drawbacks: Due to the complexities of different regional environments, they cannot adapt to large temperature fluctuations, easily causing defocus and affecting the quality of images. Furthermore, when surveillance cameras operate for extended periods, their circuits generate heat, which can affect lens focus under high temperatures. At night or in low-light areas, existing cameras are prone to color loss, blurred details, and insufficient brightness under infrared fill light, resulting in poor image quality. They also suffer from narrow shooting angles and fields of view, resulting in inadequate data collection.

[0045] In order to solve the above problems, the present invention provides a fixed-focus lens. Figures 1 to 4 This is a specific embodiment of the fixed-focus lens provided by the present invention.

[0046] See also Figure 1 The fixed-focus lens has an object side and an image side arranged opposite to each other along the optical axis, and includes a first convex-concave lens 1 with negative optical power, a second biconcave lens 2 with negative optical power, a third convex-concave lens 3 with positive optical power, a fourth biconvex lens 4 with positive optical power, a fifth biconvex lens 5 with positive optical power, a sixth biconcave lens 6 with negative optical power, and a seventh biconvex lens 7 with positive optical power, which are arranged in sequence from the object side to the image side. The concave surfaces of the first convex-concave lens, the second biconcave lens 2, the third convex-concave lens 3, and the sixth biconcave lens 6 are arranged towards the image side, and the first convex-concave lens, the second biconcave lens 2, the third convex-concave lens 3, the fifth biconvex lens 5, the sixth biconcave lens 6, and the seventh biconvex lens 7 are all aspherical lenses; the total optical length TTL of the fixed-focus lens is ≤22.5 mm, the aperture number of the fixed-focus lens is F, and 0.8≤F≤1.1, and the field of view FOV=140°±5%.

[0047] In the technical solution provided by the present invention, a first convex-concave lens 1 with negative optical power, a second biconcave lens 2 with negative optical power, a third convex-concave lens 3 with positive optical power, a fourth biconvex lens 4 with positive optical power, a fifth biconvex lens 5 with positive optical power, a sixth biconcave lens 6 with negative optical power, and a seventh biconvex lens 7 with positive optical power are sequentially arranged from the object side to the image side. Due to the large aperture of the first convex-concave lens, more light information can be collected under the same focal length, so as to achieve the effect of clear imaging in weak light. The fourth biconvex lens 4 bears the larger optical power of the system, changes the propagation direction of the light beam, and is more conducive to the imaging of the light beam on the image plane. Through the reasonable setting of the optical power and shape of the seven lenses, the fixed-focus lens can well control the light trend, introduce more light and make the structure more compact, so that the total length of the fixed-focus lens is controlled within 22.5 mm, and through the reasonable arrangement of aspheric lenses, various aberrations are corrected, the edge image quality is improved, and the imaging quality is high. The aperture value F satisfies 0.8≤F≤1.1, supports a 1 / 2.5-inch image plane, and the fixed-focus lens can produce clear images even in low light. By reasonably setting the focal length ratio, the lens does not defocus under environmental conditions of -40°C to +85°C, and the working performance is more stable. The field of view can reach 140°±5%, the field of view is wider, and the data information obtained is more sufficient, thereby providing a large aperture, large angle, small high and low temperature fixed-focus lens.

[0048] Specifically, in this embodiment, the fixed-focus lens also satisfies the following conditions: -0.67≤φ1 / φ≤-0.25; -0.60≤φ2 / φ≤0.4; -0.35≤φ3 / φ≤0.3; 0.3≤φ4 / φ≤0.6; 0.3≤φ5 / φ≤0.7; -0.8≤φ6 / φ≤-0.5; 0.3≤φ7 / φ≤0.7; wherein, the optical focal length of the fixed-focus lens is φ, the optical focal length of the first convex-concave lens 1 is φ1, the optical focal length of the second biconcave lens 2 is φ2, the optical focal length of the third convex-concave lens 3 is φ3, the optical focal length of the fourth biconvex lens 4 is φ4, the optical focal length of the fifth biconvex lens 5 is φ5, the optical focal length of the sixth biconcave lens 6 is φ6, and the optical focal length of the seventh biconvex lens 7 is φ7. Optical power, equal to the difference between the image-side and object-side beam convergence, characterizes the optical system's ability to deflect light. By properly setting the ratio limits for the optical power of the seven lenses, spherical aberration, coma, and astigmatism on each lens element compensate for each other, achieving clear imaging.

[0049] Specifically, in an optical lens, the dispersion of light can lead to undesirable chromatic aberration, thereby causing blur or blurring effects or "color fringing" around the observed object. In order to enable the fixed-focus lens to have better imaging quality, in this embodiment, the fixed-focus lens also meets the following conditions: 1.50≤n1≤1.60, 50.0≤v1≤65.0; 1.50≤n2≤1.75, 20.0≤v2≤65.0; 1.50≤n3≤1.70, 18.0≤v3≤25.0; 1.49≤n4≤1.70, 60.0≤v4≤75.0; 1.50≤n5≤1.60, 50.0≤v5≤75.0; 1.60 ≤n6≤1.75, 15.0≤v6≤25.0; 1.50≤n7≤1.60, 50.0≤v7≤60.0; wherein, the refractive index of the first convex-concave lens 1 is n1, and the dispersion coefficient is v1; the refractive index of the second biconcave lens 2 is n2, and the dispersion coefficient is v2; the refractive index of the third convex-concave lens 3 is n3, and the dispersion coefficient is v3; the refractive index of the fourth biconvex lens 4 is n4, and the dispersion coefficient is v4; the refractive index of the fifth biconvex lens 5 is n5, and the dispersion coefficient is v5; the refractive index of the sixth biconcave lens 6 is n6, and the dispersion coefficient is v6; the refractive index of the seventh biconvex lens 7 is n7, and the dispersion coefficient is v7. The dispersion coefficient is used to measure the degree of light dispersion in a transparent medium. The Abbe number is an index used to represent the dispersion ability of a transparent medium. The larger the dispersion coefficient (Abbe number), the less obvious the dispersion and the better the imaging quality of the lens. In this embodiment, the dispersion coefficient of each lens is controlled at a relatively high value, so that the dispersion of the fixed-focus lens is not obvious and the imaging quality of the lens is good.

[0050] Specifically, because resin lenses have strong impact resistance, are lightweight, and are low in cost, in this embodiment, the first convex-concave lens 1, the second biconcave lens 2, the third convex-concave lens 3, the fifth biconcave lens 5, the sixth biconcave lens 6, and the seventh biconvex lens 7 are all plastic lenses. The use of plastic aspheric lenses effectively controls costs, and aspheric lenses can effectively correct lens chromatic aberration, simultaneously correcting spherical aberration and sine aberration at high magnification positions while ensuring that purple fringing is controlled.

[0051] However, due to the chemical instability of plastic materials affected by ambient temperature, their refractive index is weaker than that of all-glass lenses, resulting in inferior image reproduction. To ensure the stability of the video lens under temperature fluctuations, in this embodiment, the fourth biconvex lens 4 is a glass lens. Because glass lenses are less susceptible to thermal expansion and contraction, which can cause focus shifts, they can effectively resist thermal deformation and maintain high lens precision over time. The fixed-focus lens is made of a glass-plastic hybrid material, which not only saves costs and provides strong impact resistance, but also ensures system stability and high and low temperature compatibility.

[0052] Specifically, in this embodiment, the total focal length of the fixed-focus lens is f, the entrance pupil diameter of the fixed-focus lens is d, and 0.8≤f / d≤1.1. When f and d satisfy the above relationship, the fixed-focus lens has an ultra-large aperture, enabling high luminous flux in low-light environments while still achieving excellent imaging quality, meeting imaging requirements in both bright and dark environments.

[0053] Specifically, in this embodiment, the back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL, where BFL / TTL ≥ 0.1. Thus, when the back focus BFL of the fixed-focus lens and the total optical length TTL of the fixed-focus lens satisfy the aforementioned relationship, sufficient installation space is ensured for the imaging sensor and the flat filter.

[0054] Specifically, in this embodiment, the diameter of the first convexo-concave lens is D1, and the total optical length of the fixed-focus lens is TTL, where D1 / TTL < 0.7. When D1 and TTL satisfy this relationship, the fixed-focus lens can be prevented from having an excessively large aperture, thus meeting the installation space requirements of the final product.

[0055] Specifically, in this embodiment, the image plane diameter IC of the fixed-focus lens satisfies: IC≤7.3 mm.

[0056] Furthermore, in this embodiment, the fixed-focus lens further includes an aperture 8, a protective glass 9, and a photosensitive chip 10 from the object side to the image side. The aperture 8 is arranged between the second biconcave lens 2 and the third convex-concave lens 3, and the protective glass 9 and the photosensitive chip 10 are arranged on the side of the seventh biconvex lens 7 close to the image side. Since the aperture 8 is used to adjust the light flux according to actual conditions, the imaging quality can be improved. The protective glass 9 can provide effective protection for the photosensitive chip 10IMAGE. The protective glass 9 can be set as a filter. The filter can effectively filter out stray light in non-working bands to reduce optical noise, reduce difficulties for the subsequent photoelectric module processing part, and thus improve imaging quality. It can be understood that the surface of the photosensitive chip 10 facing the object side is the imaging surface.

[0057] Specifically, the imaging surface can be understood as the surface of the photosensitive chip 10 facing the object side, that is, it can be the surface of a camera element such as a CCD or CMOS. It can be understood that the light carrying information of the object can pass through the first convex-concave lens 1, the second biconcave lens 2, the third convex-concave lens 3, the fourth biconvex lens 4, the fifth biconvex lens 5, the sixth biconcave lens 6 and the seventh biconvex lens 7 in sequence and finally form an image on the imaging surface.

[0058] Specifically, in this embodiment, the parameters of the fixed-focus lens are as follows:

[0059] The fixed-focus lens of this embodiment has a focal length of f=3.3 mm, an aperture value of F=1.09, an image plane diameter of 6.9 mm, and a diagonal field of view of 140°.

[0060] Specifically, in this embodiment, the refractive index, curvature radius, and thickness interval of the lens material are shown in Table 1 below:

[0061] Table 1

[0062]

[0063] Specifically, in this embodiment, the first convex-concave lens 1, the second biconcave lens 2, the third convex-concave lens 3, the fifth biconcave lens 5, the sixth biconcave lens 6 and the seventh biconvex lens 7 are all aspherical lenses. The characteristics of aspherical lenses are: the curvature changes continuously from the center of the lens to the periphery of the lens. Unlike spherical lenses with a constant curvature from the center of the lens to the periphery of the lens, aspherical lenses have better curvature radius characteristics and have the advantages of improving distortion aberration and improving astigmatism aberration. After using aspherical lenses, the aberrations that occur during imaging can be eliminated as much as possible, thereby improving the imaging quality of the lens. The use of glass lenses can reduce the impact of temperature on the optical performance of the lens.

[0064] Furthermore, in this embodiment, the aspheric surface shape of the aspheric lens satisfies the following conditions:

[0065]

[0066] Among them, z represents the axial sagittal height of the aspheric surface in the Z direction; y represents the height of the aspheric surface; c represents the curvature of the fitted sphere, which is the inverse of the curvature radius; k represents the cone coefficient; A, B, C, D, E, and F represent the high-order aspheric coefficients respectively. The above parameters can be used to set the shape and size of the aspheric surface on the object side and image side of the lens.

[0067] Table 2 Conic coefficient and aspheric coefficient corresponding to aspheric lenses:

[0068]

[0069] Figure 2 This is a schematic diagram of a spherical aberration curve of an embodiment of a fixed-focus lens provided by the present invention. Figure 3 This is a schematic diagram of a light fan of an embodiment of a fixed-focus lens provided by the present invention. Figure 4 A schematic diagram of field distortion / field curvature of a fixed-focus lens according to an embodiment of the present invention.

[0070] As can be seen from the above figures, the spherical aberration, field curvature and distortion of the fixed-focus lens in this embodiment can all be well corrected.

[0071] In summary, the aperture value F of the fixed-focus lens satisfies 0.8≤F≤1.1, supports a 1 / 2.5-inch image plane, does not defocus under environmental conditions of -40°C to +85°C, and has a field of view of up to 140°±5%.

[0072] The present invention also provides a monitoring device, which includes the fixed-focus lens described in the above technical solution. The specific structure of the fixed-focus lens refers to the above embodiment. Since the fixed-focus lens of this fixed-focus lens adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0073] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A fixed-focus lens, characterized in that: The fixed-focus lens has an object side and an image side that are arranged opposite to each other along the optical axis. The fixed-focus lens includes a first convex-concave lens with negative optical power, a second biconcave lens with negative optical power, a third convex-concave lens with positive optical power, a fourth biconvex lens with positive optical power, a fifth biconvex lens with positive optical power, a sixth biconcave lens with negative optical power, and a seventh biconvex lens with positive optical power, which are arranged in sequence from the object side to the image side. The concave surfaces of the first convex-concave lens, the second biconcave lens, the third convex-concave lens, and the sixth biconcave lens are arranged toward the image side, and the first convex-concave lens, the second biconcave lens, the third convex-concave lens, the fifth biconvex lens, the sixth biconcave lens, and the seventh biconvex lens are all aspherical lenses. The total optical length TTL of the fixed-focus lens is ≤ 22.5 mm, the aperture number of the fixed-focus lens is F, and 0.8 ≤ F ≤ 1.1, and the field of view FOV = 140° ± 5%; The fixed-focus lens also meets the following conditions: 1.50≤n1≤1.60, 50.0≤v1≤65.0; 1.50≤n2≤1.75, 20.0≤v2≤65.0; 1.50≤n3≤1.70, 18.0≤v3≤25.0; 1.49≤n4≤1.70, 60.0≤v4≤75.0; 1.50≤n5≤1.60, 50.0≤v5≤75.0; 1.60≤n6≤1.75, 15.0≤v6≤25.0; 1.50≤n7≤1.60, 50.0≤v7≤60.0; Among them, the refractive index of the first convex-concave lens is n1, and the dispersion coefficient is v1, the refractive index of the second biconcave lens is n2, and the dispersion coefficient is v2, the refractive index of the third convex-concave lens is n3, and the dispersion coefficient is v3, the refractive index of the fourth biconvex lens is n4, and the dispersion coefficient is v4, the refractive index of the fifth biconvex lens is n5, and the dispersion coefficient is v5, the refractive index of the sixth biconcave lens is n6, and the dispersion coefficient is v6, and the refractive index of the seventh biconvex lens is n7, and the dispersion coefficient is v7.

2. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens also meets the following conditions: -0.67≤φ1 / φ≤-0.25; -0.60≤φ2 / φ≤0.4; -0.35≤φ3 / φ≤0.3; 0.3≤φ4 / φ≤0.6; 0.3≤φ5 / φ≤0.7; -0.8≤φ6 / φ≤-0.5; 0.3≤φ7 / φ≤0.7; Among them, the optical focal power of the fixed-focus lens is φ, the optical focal power of the first convex-concave lens is φ1, the optical focal power of the second biconcave lens is φ2, the optical focal power of the third convex-concave lens is φ3, the optical focal power of the fourth biconvex lens is φ4, the optical focal power of the fifth biconvex lens is φ5, the optical focal power of the sixth biconcave lens is φ6, and the optical focal power of the seventh biconvex lens is φ7.

3. The fixed-focus lens according to claim 1, wherein: The first convex-concave lens, the second biconcave lens, the third convex-concave lens, the fifth biconcave lens, the sixth biconcave lens, and the seventh biconvex lens are all plastic lenses; The fourth biconvex lens is a glass lens.

4. The fixed-focus lens according to claim 1, wherein: The total focal length of the fixed-focus lens is f, the entrance pupil diameter of the fixed-focus lens is d, and 0.8≤f / d≤1.

1.

5. The fixed-focus lens according to claim 1, wherein: The back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL, wherein BFL / TTL≥0.

1.

6. The fixed-focus lens according to claim 1, wherein: The diameter of the first convex-concave lens is D1, and the total optical length of the fixed-focus lens is TTL, wherein D1 / TTL<0.

7.

7. The fixed-focus lens according to claim 1, wherein: The image plane diameter IC of the fixed-focus lens satisfies: IC≤7.3 mm.

8. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens further includes an aperture, a protective glass and a photosensitive chip from the object side to the image side, wherein the aperture is arranged between the second biconcave lens and the third convex-concave lens, and the protective glass and the photosensitive chip are arranged on the side of the seventh biconvex lens close to the image side.

9. A monitoring device, characterized in that: The fixed-focus lens according to any one of claims 1 to 8.

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