Fixed-focus optical system and security lens
By designing the lens combination in the fixed-focus optical system, the problems of low pixel count and insufficient image clarity in existing security lenses have been solved, achieving imaging effects with large aperture, large target surface, infrared confocal focus, and high resolution.
Patent Information
- Application Number
- CN202422980299.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-11-04
- Estimated Expiration
- 2034-12-03
AI Technical Summary
Existing security lenses have low pixel count, small aperture, and low image clarity, making it impossible to achieve day and night co-focus and failing to meet consumers' high demands.
Design a fixed-focus optical system with a lens combination including a first lens with negative optical power and a fifth lens with positive optical power. By rationally allocating optical power and lens shape, the light path can be controlled to achieve infrared confocal imaging and high-resolution imaging.
It increases the field of view, achieves a large aperture and a large target surface, resulting in better imaging effects, wider applicability, day and night co-focus, brighter images, high resolution, and natural, distortion-free colors.
Smart Images
Figure CN223513385U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of optical technology, and in particular to a fixed-focus optical system and a security lens. Background Technology
[0002] With the improvement of living standards and the enhancement of people's safety awareness, consumers have put forward higher and higher requirements for security monitoring lenses, expecting products to have advantages such as ultra-wide field of view, high resolution, and suitability for both day and night scenarios.
[0003] Most lenses on the market suffer from low pixel count, small aperture, low image clarity, and inability to achieve day and night focus. Such lens designs are no longer able to meet the increasingly demanding needs of consumers. Utility Model Content
[0004] The main purpose of this invention is to propose a fixed-focus optical system and a security lens, which aims to improve resolution, achieve a large aperture and a large target surface, and improve imaging effect.
[0005] To achieve the above objectives, the present invention proposes a fixed-focus optical system, which has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus optical system is composed of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, an aperture stop, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a photosensitive chip arranged sequentially from the object side to the image side.
[0006] The first lens has a negative optical power, a convex object side, and a concave image side.
[0007] The second lens has a negative optical power, and both the object-side and image-side surfaces are concave.
[0008] The third lens has a positive optical power, a concave object side, and a convex image side.
[0009] The fourth lens has a negative optical power, a concave object side, and a convex image side.
[0010] The fifth lens has a positive optical power, a convex object side, and a convex image side;
[0011] The sixth lens has a positive optical power, a convex object-side surface, and a convex image-side surface;
[0012] The seventh lens has a positive optical power, a convex object side, and a convex image side;
[0013] The eighth lens has a positive optical power, a convex object side, and a convex image side;
[0014] The ninth lens has a positive optical power, a convex object side, and a convex image side.
[0015] In one embodiment, 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, the focal length of the ninth lens is f9, and the focal length of the tenth lens is f10. The focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens satisfy the following relationship:
[0016] 8mm<|f1|<14mm, 4mm<|f2|<7mm, 8mm<|f3|<15mm, 20mm<|f4|<30mm, 8mm<|f5|<14mm, 4mm<|f6|<8mm, 2mm<|f7|<5mm, 5mm<|f8|<9mm, 5mm<|f9|<10mm.
[0017] In one embodiment, 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, the refractive index of the eighth lens is n8, and the refractive index of the ninth lens is n9. The dispersion coefficient of the first lens is v1, the dispersion coefficient of the second lens is v2, the dispersion coefficient of the third lens is v3, the dispersion coefficient of the fourth lens is v4, the dispersion coefficient of the fifth lens is v5, the dispersion coefficient of the sixth lens is v6, the dispersion coefficient of the seventh lens is v7, the dispersion coefficient of the eighth lens is v8, and the dispersion coefficient of the ninth lens is v9. The first lens, the second lens, the third lens, the fourth lens... The refractive index and dispersion coefficient of the lenses, namely the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, and the tenth lens, satisfy the following relationships: 1.80≤n1≤2.05, 30.0≤v1≤45.0; 1.70≤n2≤1.95, 40.0≤v2≤55.0; 1.90≤n3≤2.05, 20.0≤v3≤35.0; 1.70≤n4≤1 .90, 40.0≤v4≤50.0; 1.60≤n5≤1.75, 40.0≤v5≤55.0; 1.50≤n6≤1.65, 55.0≤v6≤75.0; 1.70≤n7≤1.95, 25.0≤v7≤40.0; 1.60≤n8≤1.75, 40.0≤v8≤55.0; 1.60≤n9≤1.75, 45.0≤v9≤70.0.
[0018] In one embodiment, the diameter of the first lens is D1, where D1 < 25 mm.
[0019] In one embodiment, the image plane diameter of the photosensitive chip is IC, wherein IC ≤ 5.4 mm.
[0020] In one embodiment, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens are glass spherical lenses; and / or,
[0021] The sixth lens and the seventh lens are cemented together.
[0022] In one embodiment, the total optical length of the fixed-focus optical system is TTL, and the effective focal length of the fixed-focus optical system is EFL, wherein TTL / EFL≤18.
[0023] In one embodiment, the aperture value of the fixed-focus optical system is F, where F ≤ 2.0.
[0024] In one embodiment, the fixed-focus optical system includes a filter disposed along the optical axis between the ninth lens and the photosensitive chip; and / or,
[0025] The fixed-focus optical system also includes a protective glass, which is disposed along the optical axis between the ninth lens and the photosensitive chip, and is located close to the photosensitive chip.
[0026] This utility model also proposes a security lens, including a fixed-focus optical system. The fixed-focus optical system has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus optical system is composed of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, an aperture, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a photosensitive chip arranged sequentially from the object side to the image side.
[0027] The first lens has a negative optical power, a convex object side, and a concave image side.
[0028] The second lens has a negative optical power, and both the object-side and image-side surfaces are concave.
[0029] The third lens has a positive optical power, a concave object side, and a convex image side.
[0030] The fourth lens has a negative optical power, a concave object side, and a convex image side.
[0031] The fifth lens has a positive optical power, a convex object side, and a convex image side;
[0032] The sixth lens has a positive optical power, a convex object-side surface, and a convex image-side surface;
[0033] The seventh lens has a positive optical power, a convex object side, and a convex image side;
[0034] The eighth lens has a positive optical power, a convex object side, and a convex image side;
[0035] The ninth lens has a positive optical power, a convex object side, and a convex image side.
[0036] The technical solution of this utility model uses a first lens with negative optical power to facilitate the control and collection of light entering the entire optical system, effectively increasing the field of view. By using a fifth lens with positive optical power, the system's optical power is increased, changing the direction of light propagation and making it more conducive to the beam forming on the image plane. By comprehensively setting the optical power of each lens, the lens can effectively control the light path, introducing more light while improving structural aberration correction. Furthermore, by combining different lenses and rationally allocating optical power, infrared confocal imaging, high resolution, and a bright image can be achieved, resulting in better imaging effects. Attached Figure Description
[0037] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, 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 utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0038] Figure 1 A schematic diagram of an embodiment of the fixed-focus optical system provided by this utility model;
[0039] Figure 2 for Figure 1 A schematic diagram of the transverse chromatic aberration curve of an embodiment of a fixed-focus optical system;
[0040] Figure 3 for Figure 1 A schematic diagram of the light aberration curve of an embodiment of a fixed-focus optical system;
[0041] Figure 4 for Figure 1 A schematic diagram of field curvature distortion in an embodiment of a fixed-focus optical system;
[0042] Figure 5 for Figure 1 MTF plot of a fixed-focus optical system at 20°C;
[0043] Figure 6 for Figure 1 Visible defocus MTF plot at 20°C of an embodiment of a fixed-focus optical system;
[0044] Figure 7 for Figure 1 Infrared defocus MTF plot at 20°C of one embodiment of a fixed-focus optical system.
[0045] Explanation of icon numbers:
[0046] 100. Fixed-focus optical system; 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Seventh lens; 8. Eighth lens; 9. Ninth lens; 10. Aperture stop; 11. Photosensitive chip; 12. Filter; 13. Protective glass.
[0047] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0048] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present utility model.
[0049] It should be noted that if the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.
[0050] Furthermore, if the embodiments of this utility model involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.
[0051] This utility model proposes a fixed-focus optical system 100.
[0052] First, it's important to understand that optical power is equal to the difference between the image-side convergence and the object-side convergence of the light beam; it characterizes the ability of an optical system to deflect light rays. The larger the absolute value of the optical power, the stronger its ability to bend light; the smaller the absolute value, the weaker its ability to bend light. When the optical power is positive, the refraction of light rays is converging; when the optical power is negative, the refraction of light rays is diverging. Optical power can be used to characterize a single refractive surface of a lens, a single lens, or a system formed by multiple lenses.
[0053] Please see Figure 1 In one embodiment of this utility model, the fixed-focus optical system 100 has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus optical system 100 is composed of a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, an aperture stop 10, a sixth lens 6, a seventh lens 7, an eighth lens 8, a ninth lens 9, and a photosensitive chip 11 arranged sequentially from the object side to the image side. The first lens 1 has a negative optical power, a convex object side, and a concave image side; the second lens 2 has a negative optical power, a concave object side, and a concave image side. The third lens 3 has a positive optical power, a concave object side, and a convex image side; the fourth lens 4 has a negative optical power, a concave object side, and a convex image side; the fifth lens 5 has a positive optical power, a convex object side, and a convex image side; the sixth lens 6 has a positive optical power, a convex object side, and a convex image side; the seventh lens 7 has a positive optical power, a convex object side, and a convex image side; the eighth lens 8 has a positive optical power, a convex object side, and a convex image side; and the ninth lens 9 has a positive optical power, a convex object side, and a convex image side.
[0054] The first lens 1 has a negative optical power and a convex object side and a concave image side, which allows more light to be introduced, which is beneficial for the light collection of the optical system and can effectively increase the field of view. The aperture 10 is located between the fifth lens 5 and the sixth lens 6, which can adjust the size of the field of view, block off-axis light rays, avoid the impact of off-axis light rays on image quality, improve image quality, and enable the lens to have a large light transmission capacity. By comprehensively setting the optical power and shape matching relationship of each lens, infrared confocality can be achieved. In addition, it also ensures that the second lens 2 and the third lens 3 have positive optical power, controls the light path, and improves the resolution.
[0055] The technical solution of this utility model, by setting a first lens 1 with negative optical power, facilitates the control and collection of light entering the entire optical system, and can effectively increase the field of view; by setting a fifth lens 5 with positive optical power, it undertakes a large optical power of the system, changes the propagation direction of the light beam, and is more conducive to the image formation of the light beam on the image plane; by comprehensively setting the optical power of each lens, the lens can control the light trend well, introduce more light while improving the correction of structural aberrations, and by combining different lenses and rationally allocating the optical power, it can achieve infrared confocal, high resolution, and bright image, resulting in better imaging effect.
[0056] Please see Figure 1 In one embodiment of this utility model, it should be understood that focal length refers to the distance from the rear surface of a lens to the image plane in an optical system. Focal length determines the magnification and viewing angle of the image. Optical power is the reciprocal of focal length. The focal length of the first lens 1 is f1, the focal length of the second lens 2 is f2, the focal length of the third lens 3 is f3, the focal length of the fourth lens 4 is f4, the focal length of the fifth lens 5 is f5, the focal length of the sixth lens 6 is f6, the focal length of the seventh lens 7 is f7, the focal length of the eighth lens 8 is f8, the focal length of the ninth lens 9 is f9, and the focal length of the tenth lens is f10. The first lens 1, the second lens 2, the third lens 3, and the fourth lens... 4. The focal lengths of the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9 satisfy the following relationships: 8mm < |f1| < 14mm, 4mm < |f2| < 7mm, 8mm < |f3| < 15mm, 20mm < |f4| < 30mm, 8mm < |f5| < 14mm, 4mm < |f6| < 8mm, 2mm < |f7| < 5mm, 5mm < |f8| < 9mm, 5mm < |f9| < 10mm. Furthermore, by reasonably setting the focal length range, the fixed-focus optical system 100 possesses a wide angle of view, day and night confocality, and excellent image quality, resulting in a broader field of view, wider applicability, and more stable performance.
[0057] In one embodiment of this utility model, the refractive index of the first lens 1 is n1, the refractive index of the second lens 2 is n2, the refractive index of the third lens 3 is n3, the refractive index of the fourth lens 4 is n4, the refractive index of the fifth lens 5 is n5, the refractive index of the sixth lens 6 is n6, the refractive index of the seventh lens 7 is n7, the refractive index of the eighth lens 8 is n8, and the refractive index of the ninth lens 9 is n9. The dispersion coefficient of the first lens 1 is v1, the dispersion coefficient of the second lens 2 is v2, and the refractive index of the third lens 3 is n3. The dispersion coefficient of lens 3 is v3, the dispersion coefficient of the fourth lens 4 is v4, the dispersion coefficient of the fifth lens 5 is v5, the dispersion coefficient of the sixth lens 6 is v6, the dispersion coefficient of the seventh lens 7 is v7, the dispersion coefficient of the eighth lens 8 is v8, and the dispersion coefficient of the ninth lens 9 is v9. The first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, the ninth lens 9, and the tenth lens... The refractive index and dispersion coefficient satisfy the following relationships: 1.80≤n1≤2.05, 30.0≤v1≤45.0; 1.70≤n2≤1.95, 40.0≤v2≤55.0; 1.90≤n3≤2.05, 20.0≤v3≤35.0; 1.70≤n4≤1.90, 40.0≤v4≤50.0; 1.60≤n5≤1.75, 40.0≤v5≤55.0; 1.50≤n6≤1.65, 55.0≤v6≤75.0; 1.70≤n7≤1.95, 25.0≤v7≤40.0; 1.60≤n8≤1.75, 40.0≤v8≤55.0; 1.60≤n9≤1.75, 45.0≤v9≤70.0; By controlling the refractive index and dispersion coefficient of each lens, the refraction angle and path of light can be controlled more precisely, thereby ensuring that the light converges to the correct position. At the same time, the corresponding dispersion coefficient can effectively balance the refractive index differences of various wavelengths of light, reduce color difference, make the image edges clearer, the color transition natural, and form a clear, distortion-free image.
[0058] It is understandable that, in order to facilitate the installation of the fixed-focus optical system 100 and reduce the volume of the fixed-focus optical system 100, the aperture of the first lens 1 should not be too large. In one embodiment of the present invention, the diameter of the first lens 1 is D1, wherein D1 < 25mm. By limiting the diameter of the first lens 1, it is easier to install and the volume of the fixed-focus optical system 100 is reduced, making it suitable for more scenarios.
[0059] In one embodiment of this utility model, it is understood that when the image plane diameter is too large, the lenses cannot collect all the light, which will increase the physical size of the lens and thus affect the realization of the maximum aperture. Therefore, the image plane diameter of the photosensitive chip 11 is IC, wherein IC≤5.4mm, so that the fixed-focus optical system 100 can collect a complete image and improve the imaging effect.
[0060] Please see Figure 1 In one embodiment of this utility model, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9 are glass spherical lenses.
[0061] By using glass spherical lenses, which have a very high surface finish, light scattering and reflection are reduced, various optical aberrations are reduced, and chromatic aberration of the system is effectively suppressed, thus improving imaging effect. Glass has low sensitivity to temperature changes, and its shape and optical properties remain stable under temperature changes and are not easily deformed. Therefore, glass lenses can effectively resist the problem of lens deformation due to heat, maintain the high precision of the lens for a long time, and thus improve the stability of the fixed-focus optical system.
[0062] Furthermore, by employing an all-glass spherical structure, the manufacturing process is simplified by fully utilizing spherical lenses, and chromatic aberration is corrected by bonding lenses. Simultaneously, through the rational matching of lens materials, chromatic aberration is minimized, the angle is wide, the diagonal field of view can reach over 185°, and the imaging quality reaches up to 12M pixels, with a CRA ≤ 13°, indicating broad application prospects. It is understood that CRA usually refers to the Chief Ray Angle, which describes the angular characteristics of light propagating from the light source to various components of the optical system (such as lenses, mirrors, etc.) and finally reaching the detector or imaging plane. The smaller the CRA, the better the linearity of the fixed-focus optical system 100, the smaller the optical distortion, and the higher the imaging quality.
[0063] Furthermore, in one embodiment of this utility model, the sixth lens 6 and the seventh lens 7 are cemented together. By adding the seventh and eighth cemented doublet lenses, the chromatic aberration of the lens is better corrected, and the light height of the off-axis field of view is increased, so that the system has a larger target surface.
[0064] Specifically, in one embodiment of this utility model, the focal length of the fixed-focus optical system 100 is f = 1.98 mm, the aperture value is F = 2.0, the image plane diameter is 5.4 mm, and the diagonal field of view is 185°. The parameters of the fixed-focus optical system 100 are shown in Table 1 below.
[0065] Table 1
[0066]
[0067]
[0068] Figure 2 The figure shown is a schematic diagram of the vertical color difference curve provided in an embodiment of this utility model. Figure 3 This is a schematic diagram of the light aberration curve according to an embodiment of the present invention. Figure 4 This is a schematic diagram of field curvature distortion according to an embodiment of the present invention. Figure 5 This is an MTF chart of an embodiment of the present invention at 20°C. Figure 6 This is a visible defocused MTF image at 20°C according to an embodiment of the present invention. Figure 7 This is an infrared defocused MTF image at 20°C according to an embodiment of the present invention. Figure 2-7 It can be seen that the fixed-focus optical system 100 provided in this embodiment has good imaging capabilities.
[0069] In one embodiment of this utility model, the total optical length of the fixed-focus optical system 100, that is, the distance from the vertex of the object side surface of the first lens 11 to the photosensitive chip 11, is TTL, and the effective focal length of the fixed-focus optical system 100 is EFL, wherein TTL / EFL≤18; by limiting the total optical length, the volume of the fixed-focus lens can be further reduced, which is beneficial to the miniaturization of the fixed-focus lens.
[0070] In one embodiment of this utility model, the aperture value of the fixed-focus optical system 100 is F, wherein F≤2.0; when the aperture value F of the fixed-focus optical system 100 is within this range, the lens has the best resolution and contrast performance, and the lens has a large light transmission, high image brightness, and better imaging effect.
[0071] In one embodiment of the present invention, the fixed-focus optical system 100 includes a filter 12, which is disposed between the ninth lens 9 and the photosensitive chip 11 along the optical axis; and / or, the fixed-focus optical system 100 further includes a protective glass 13, which is disposed between the ninth lens 9 and the photosensitive chip 11 along the optical axis and is located close to the photosensitive chip 11.
[0072] The filter 12 can filter out stray light and prevent stray light from reaching the photosensitive chip 11 and interfering with normal visible light imaging, thereby improving the imaging quality. The protective glass 13 is set close to the photosensitive chip 11 and can provide effective protection for the photosensitive chip 11.
[0073] It is understood that the filter 12 and the protective glass 13 can be set separately, but in order to provide better imaging effect, the filter 12 and the protective glass 13 can also be set simultaneously. The light carrying the information of the photographed object can pass through the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the aperture 10, the sixth lens 6, the seventh lens 7, the eighth lens 8, the ninth lens 9, the filter 12 and the protective glass 13 in sequence and finally be imaged on the photosensitive chip 11.
[0074] This utility model also proposes a security lens, which includes a fixed-focus optical system 100. The specific structure of the fixed-focus optical system 100 is as described in the above embodiments. Since this security lens adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.
[0075] The above description is merely an exemplary embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural transformations made based on the technical concept of the present utility model and the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.
Claims
1. A fixed-focus optical system, characterized in that, The fixed-focus optical system has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus optical system is composed of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, an aperture stop, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a photosensitive chip arranged sequentially from the object side to the image side. The first lens has a negative optical power, a convex object side, and a concave image side. The second lens has a negative optical power, and both the object-side and image-side surfaces are concave. The third lens has a positive optical power, a concave object side, and a convex image side. The fourth lens has a negative optical power, a concave object side, and a convex image side. The fifth lens has a positive optical power, a convex object side, and a convex image side; The sixth lens has a positive optical power, a convex object-side surface, and a convex image-side surface; The seventh lens has a positive optical power, a convex object side, and a convex image side; The eighth lens has a positive optical power, a convex object side, and a convex image side; The ninth lens has a positive optical power, a convex object side, and a convex image side.
2. The fixed-focus optical system as described in claim 1, characterized in that, 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 ninth lens is f9. The focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens satisfy the following relationship: 8mm<|f1|<14mm, 4mm<|f2|<7mm, 8mm<|f3|<15mm, 20mm<|f4|<30mm, 8mm<|f5|<14mm, 4mm<|f6|<8mm, 2mm<|f7|<5mm, 5mm<|f8|<9mm, 5mm<|f9|<10mm.
3. The fixed-focus optical system as described in claim 1, characterized in that, 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, the refractive index of the eighth lens is n8, and the refractive index of the ninth lens is n9. The dispersion coefficient of the first lens is v1, the dispersion coefficient of the second lens is v2, the dispersion coefficient of the third lens is v3, the dispersion coefficient of the fourth lens is v4, the dispersion coefficient of the fifth lens is v5, the dispersion coefficient of the sixth lens is v6, the dispersion coefficient of the seventh lens is v7, the dispersion coefficient of the eighth lens is v8, and the dispersion coefficient of the ninth lens is v9. The first lens, the second lens, the third lens, the fourth lens... The refractive index and dispersion coefficient of the lenses, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, satisfy the following relationships: 1.80≤n1≤2.05, 30.0≤v1≤45.0; 1.70≤n2≤1.95, 40.0≤v2≤55.0; 1.90≤n3≤2.05, 20.0≤v3≤35.0; 1.70≤n4≤1.90 , 40.0≤v4≤50.0; 1.60≤n5≤1.75, 40.0≤v5≤55.0; 1.50≤n6≤1.65, 55.0≤v6≤75.0; 1.70≤n7≤1.95, 25.0≤v7≤40.0; 1.60≤n8≤1.75, 40.0≤v8≤55.0; 1.60≤n9≤1.75, 45.0≤v9≤70.
0.
4. The fixed-focus optical system as described in claim 1, characterized in that, The diameter of the first lens is D1, where D1 < 25 mm.
5. The fixed-focus optical system as described in claim 1, characterized in that, The image plane diameter of the photosensitive chip is IC, where IC ≤ 5.4 mm.
6. The fixed-focus optical system as described in claim 1, characterized in that, The first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens are glass spherical lenses; and / or, The sixth lens and the seventh lens are cemented together.
7. The fixed-focus optical system as described in claim 1, characterized in that, The total optical length of the fixed-focus optical system is TTL, and the effective focal length of the fixed-focus optical system is EFL, wherein TTL / EFL≤18.
8. The fixed-focus optical system as described in claim 1, characterized in that, The aperture value of the fixed-focus optical system is F, where F≤2.
0.
9. The fixed-focus optical system as described in claim 1, characterized in that, The fixed-focus optical system includes a filter disposed between the ninth lens and the photosensitive chip along the optical axis; and / or, The fixed-focus optical system also includes a protective glass, which is disposed along the optical axis between the ninth lens and the photosensitive chip, and is located close to the photosensitive chip.
10. A security camera lens, characterized in that, Includes the fixed-focus optical system as described in claims 1-9.