Fixed focus optical system

Abstract

The invention discloses a fixed-focus optical system, which relates to the technical field of optics and is provided with an object side and an image side which are oppositely arranged along the direction of an optical axis. The fixed-focus optical system is composed of a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens and a photosensitive chip which are sequentially arranged from the object side to the image side. The fixed-focus optical system is high in resolution, large in visual angle, athermalized and better in imaging effect.

Description

Technical Field

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

[0002] With the improvement of science and technology, the actual application scenarios of fisheye lenses are showing a more diversified trend. They are widely used in VR / AR, medical treatment, and video conferencing. It is expected that the products will have the advantages of ultra-large field of view, high pixels, and stable performance under high and low temperatures. The existing lenses on the market generally have the defects of low pixels, small aperture, low imaging clarity, and inability to work stably under high and low temperatures. This type of lens design can no longer meet the gradually increasing usage needs of consumers. Summary of the invention

[0003] The main purpose of the present invention is to provide a fixed-focus optical system, which has high resolution, large aperture, large target surface and better imaging effect.

[0004] To achieve the above-mentioned object, the present invention provides a fixed-focus optical system, wherein the fixed-focus optical system has an object side and an image side that are arranged opposite to each other along the optical axis direction, and the fixed-focus optical system is composed of a first lens, a second lens, a third lens, a fourth lens, an aperture, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a photosensitive chip that are sequentially arranged from the object side to the image side;

[0005] Wherein, the first lens has a negative optical power, a convex object side surface, and a concave image side surface;

[0006] The second lens has a negative optical power, a convex object side surface, and a concave image side surface;

[0007] The third lens has a negative optical power, a concave object side surface, and a concave image side surface;

[0008] The fourth lens has positive optical power, a concave object side surface, and a convex image side surface;

[0009] The fifth lens has positive optical power, a convex object-side surface, and a concave image-side surface;

[0010] The sixth lens has positive optical power, a convex object-side surface, and a convex image-side surface;

[0011] The seventh lens has positive optical power, a concave object side surface and a convex image side surface;

[0012] The eighth lens has positive optical power, a convex object-side surface and a convex image-side surface;

[0013] The ninth lens has negative optical power, a concave object-side surface, and a convex image-side surface.

[0014] 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, and the focal length of the ninth lens is f9, and 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:

[0015] 8mm<|f1|<14mm, 15mm<|f2|<30mm, 6mm<|f3|<12mm, 10mm<|f4|<20mm, 150mm<|f5|<500mm, 4mm<|f6|<8mm, 6mm<|f7|<12mm, 5mm<|f8|<15mm, 8mm<|f9|<15mm.

[0016] 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 refractive index and the dispersion coefficient of the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens and the ninth lens satisfy the following relationship: 1.80≤n1≤2.15, 20.0≤v1≤40.0; 1.80≤n2≤2.05, 20.0≤v2≤40.0; 1.50≤n3≤1.70, 45.0≤v3≤65.0; 1.80≤n4≤2. 05, 25.0≤v4≤40.0; 1.50≤n5≤1.60, 45.0≤v5≤65.0; 1.40≤n6≤1.60, 55.0≤v6≤95.0; 1.70≤n7≤1.95, 20.0≤v7≤35.0; 1.50≤n8≤1.60, 45.0≤v8≤65.0; 1.50≤n9≤1.65, 18.0≤v9≤30.0.

[0017] In one embodiment, the diameter of the first lens is D1, wherein D1<25 mm.

[0018] In one embodiment, the image plane diameter of the photosensitive chip is IC, wherein IC≤7mm.

[0019] In one embodiment, the fifth lens, the eighth lens, and the ninth lens are plastic aspherical lenses, and the first lens, the second lens, the third lens, the fourth lens, the sixth lens, and the seventh lens are glass spherical lenses.

[0020] In one implementation, the sixth lens and the seventh lens are cemented together.

[0021] 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≤25.

[0022] In one embodiment, the aperture value of the fixed-focus optical system is F, where F≤2.4.

[0023] In one embodiment, the fixed-focus optical system includes a filter, and the filter is arranged between the ninth lens and the photosensitive chip along the optical axis; and / or,

[0024] The fixed-focus optical system also includes a protective glass, which is arranged between the ninth lens and the photosensitive chip along the optical axis and is arranged close to the photosensitive chip.

[0025] The technical solution of the present invention is beneficial to the control of temperature drift of the optical system and the control and collection of light entering the entire optical system by setting a first lens with negative optical focal length and a second lens with positive optical focal length, which can effectively increase the field of view; by setting a fifth lens and a sixth lens with positive optical focal length, a larger optical focal length of the system is assumed, the propagation direction of the light beam is changed, and it is more conducive to the imaging of the light beam on the image plane; the aperture is arranged between the fourth lens and the fifth lens, which can adjust the size of the field of view, block the far-axis light, avoid the far-axis light from affecting the imaging quality, improve the image quality, and make the lens have a large light throughput; by comprehensively setting the optical focal length of each lens, the lens can well control the light trend, introduce more light and make the structure more compact, and by combining different lenses and reasonably allocating the optical focal length, the resolution is high, the viewing angle is large, the thermalization is non-thermal, and the imaging effect is better.

[0026] The technical solution of the present invention is beneficial to the control of temperature drift of the optical system and the control and collection of light entering the entire optical system by setting a first lens with negative optical focal length and a second lens with positive optical focal length, which can effectively increase the field of view; by setting a fifth lens and a sixth lens with positive optical focal length, a larger optical focal length of the system is assumed, the propagation direction of the light beam is changed, and it is more conducive to the imaging of the light beam on the image plane; by comprehensively setting the optical focal length of each lens, the lens can control the trend of light well, while introducing more light, making the structure more compact, and by combining different lenses with each other and reasonably distributing the optical focal length, the lens has high resolution, a wide viewing angle, no thermalization, and better imaging effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0028] Figure 1 A schematic structural diagram of an embodiment of a fixed-focus optical system provided by the present invention;

[0029] Figure 2 for Figure 1 A schematic diagram of a vertical axis chromatic aberration curve of an embodiment of a medium fixed focus optical system;

[0030] Figure 3 for Figure 1 A schematic diagram of a light aberration curve of an embodiment of a medium fixed-focus optical system;

[0031] Figure 4 for Figure 1 A schematic diagram of field distortion of an embodiment of a medium fixed-focus optical system;

[0032] Figure 5 for Figure 1 MTF diagram of an embodiment of a medium fixed focus optical system at 20°C;

[0033] Figure 6 for Figure 1 A visible through-focus MTF diagram at 20°C of an embodiment of a medium fixed-focus optical system;

[0034] Figure 7 for Figure 1 A visible through-focus MTF diagram at -30°C of an embodiment of a medium fixed-focus optical system;

[0035] Figure 8 for Figure 1 Visible through-focus MTF diagram at 70°C of an embodiment of a medium fixed-focus optical system.

[0036] Description of Figure Numbers:

[0037] 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; 11. Photosensitive chip; 12. Filter; 13. Protective glass.

[0038] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0041] 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 used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. 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 contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0042] The present invention provides a fixed-focus optical system 100 .

[0043] First of all, it is important to understand that the focal power is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal power, the stronger the ability to bend light, and the smaller the absolute value of the focal power, the weaker the ability to bend light. When the focal power is a positive number, the refraction of light is convergent; when the focal power is a negative number, the refraction of light is divergent. The focal power can be used to characterize a certain refractive surface of a lens, a certain lens, or a system formed by multiple lenses.

[0044] See also Figure 1 In one embodiment of the present invention, the fixed-focus optical system 100 has an object side and an image side that are oppositely arranged along the optical axis direction, and 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, an aperture 10, a fifth lens 5, a sixth lens 6, a seventh lens 7, an eighth lens 8, a ninth lens 9 and a photosensitive chip 11 that are sequentially arranged from the object side to the image side;

[0045] Among them, the first lens 1 has a negative focal power, a convex object side surface, and a concave image side surface, the second lens 2 has a negative focal power, a convex object side surface, and a concave image side surface, the third lens 3 has a negative focal power, a concave object side surface, and a concave image side surface, the fourth lens 4 has a positive focal power, a concave object side surface, and a convex image side surface, the fifth lens 5 has a positive focal power, a convex object side surface, and a concave image side surface, the sixth lens 6 has a positive focal power, a convex object side surface, and a convex image side surface, the seventh lens 7 has a positive focal power, a concave object side surface, and a convex image side surface, the eighth lens 8 has a positive focal power, a convex object side surface, and a convex image side surface, and the ninth lens 9 has a negative focal power, a concave object side surface, and a convex image side surface.

[0046] The first lens 1 has a positive optical power, a convex object side surface, and a concave image side surface, which can introduce more light, is beneficial to the light collection of the optical system, and can effectively increase the field of view; the aperture 10 is arranged between the fourth lens 4 and the fifth lens 5, and can adjust the size of the field of view, block the far-axis light, avoid the far-axis light from affecting the imaging quality, improve the image quality, and make the lens have a large light throughput; through the positive and negative combination of the optical power of each lens, the thermal expansion coefficient (CTE) and the temperature coefficient of refractive index (dn / dT) of the fixed-focus optical system 100 can compensate each other, so as to keep the focus and image quality of the system unchanged when the temperature changes, and achieve athermalization; and through the combination of different lenses and the reasonable distribution of optical power, the light trend is controlled and the resolution is improved.

[0047] The technical solution of the present invention is beneficial to the control of temperature drift of the optical system and the control and collection of light entering the entire optical system by setting a first lens 1 with negative optical focal length and a second lens 2 with positive optical focal length, which can effectively increase the field of view; by setting a fifth lens 5 and a sixth lens 6 with positive optical focal length, a larger optical focal length of the system is assumed, the propagation direction of the light beam is changed, and it is more conducive to the imaging of the light beam on the image plane; the aperture 10 is arranged between the fourth lens 4 and the fifth lens 5, and the size of the field of view can be adjusted, the far-axis light can be blocked, and the far-axis light can be prevented from affecting the imaging quality, the image quality can be improved, and the lens can have a large light throughput; by comprehensively setting the optical focal length of each lens, the lens can well control the light trend, introduce more light and make the structure more compact, and by combining different lenses and reasonably allocating the optical focal length, the resolution is high, the viewing angle is large, the thermalization is non-thermal, and the imaging effect is better.

[0048] See also Figure 1 In one embodiment of the present invention, it should be understood that the focal length refers to the distance from the rear surface of the lens to the image plane in the optical system. The focal length determines the magnification and viewing angle of the image. The focal power is the reciprocal of the 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, and the focal length of the ninth lens 9 is f9. The first lens 1, The focal lengths of 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 satisfy the following relationship: 8mm<|f1|<14mm, 15mm<|f2|<30mm, 6mm<|f3|<12mm, 10mm<|f4|<20mm, 150mm<|f5|<500mm, 4mm<|f6|<8mm, 6mm<|f7|<12mm, 5mm<|f8|<15mm, 8mm<|f9|<15mm. By combining different lenses and reasonably allocating the focal length, the optical system has a small volume and improves the resolution of the fixed-focus optical system 100; in addition, by reasonably setting the focal length ratio, the fixed-focus optical system 100 is not out of focus within the temperature difference range of -10°C to 50°C, and the working performance is more stable.

[0049] In one embodiment of the present invention, 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, the dispersion coefficient of the third 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 refractive indexes of 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 The rate and dispersion coefficient satisfy the following relationship: 1.80≤n1≤2.15, 20.0≤v1≤40.0; 1.80≤n2≤2.05, 20.0≤v2≤40.0; 1.50≤n3≤1.70, 45.0≤v3≤65.0; 1.80≤n4≤2.05, 25.0≤v4≤40.0; 1.50≤n5≤1.60, 45.0≤v5≤65.0; 1.40≤n6≤1.60, 55.0≤v6≤95.0; 1.70≤n7≤1.95, 20.0≤v7≤35.0; 1.50≤n8≤1.60, 45.0≤v8≤65.0; 1.50≤n9≤1.65, 18.0≤v9≤30.0; By limiting the refractive index and dispersion coefficient of each lens, the refraction angle and path of the light can be more finely controlled to ensure that the light converges to the correct position. At the same time, the corresponding dispersion coefficient can effectively balance the refractive index differences of light of various wavelengths, reduce chromatic aberration, make the image edge clearer, and the color transition natural, forming a clear, distortion-free image.

[0050] It can be understood 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, where D1<25 mm. By limiting the diameter of the first lens 1, installation is facilitated and the volume of the fixed-focus optical system 100 is reduced to adapt to more scenarios.

[0051] In one embodiment of the present invention, it can be 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. For this reason, the image plane diameter of the photosensitive chip 11 is IC, where IC≤7mm, so that the fixed-focus optical system 100 can collect a complete image and improve the imaging effect.

[0052] See also Figure 1 In one embodiment of the present invention, the fifth lens 5, the eighth lens 8, and the ninth lens 9 are plastic aspherical lenses, and the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the sixth lens 6, and the seventh lens 7 are glass spherical lenses.

[0053] It can be understood that 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 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.

[0054] Specifically, in one embodiment of the present invention, the surface shape of the aspheric lens in the fixed-focus optical system 100 should satisfy the following equation:

[0055]

[0056] Among them, c is the curvature corresponding to the radius; y is the radial coordinate (its unit is the same as the lens length unit); k is the conic quadratic curve coefficient, and A, B, C, D, E, F, G... represent the fourth-order, sixth-order, eighth-order, tenth-order, twelfth-order, fourteenth-order, sixteenth-order... aspheric coefficients respectively.

[0057] Specifically, in one embodiment of the present invention, the focal length of the fixed-focus optical system is f=2.21 mm, the aperture value is F=2.0, the image plane diameter is 7 mm, and the diagonal field angle is 190°. The parameters of the fixed-focus optical system are shown in Table 1 below.

[0058] The following parameters can be used to accurately set the shape and size of the lens' aspheric surface to correct distortion and eliminate aberrations that occur during imaging as much as possible, thereby improving the imaging quality of the lens. They can also be used to correct pupil aberrations caused by large apertures, thereby improving the imaging quality of the system. At the same time, the number of spherical lenses set can be greatly reduced, reducing the system volume.

[0059] The first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the sixth lens 6, and the seventh lens 7 are glass spherical lenses with very high surface finish, thereby reducing light scattering and reflection, reducing various optical aberrations, and effectively suppressing the chromatic aberration of the system to improve the imaging effect. Glass is less sensitive to temperature changes, and its shape and optical properties remain stable under temperature changes and are not easily deformed. Therefore, the glass lens can well resist the problem of lens deformation due to heat and maintain the high precision of the lens for a long time, thereby improving the stability of the fixed-focus optical system.

[0060] By adopting a glass-plastic hybrid structure and making full use of aspheric distortion correction, the aberration that occurs during imaging is eliminated as much as possible, thereby improving image quality.

[0061] Furthermore, in one embodiment of the present invention, the sixth lens and the seventh lens are glued together to better correct the chromatic aberration of the lens, and at the same time can increase the light height of the off-axis field of view, so that the system has a larger target surface.

[0062] Table 1

[0063]

[0064]

[0065] In this embodiment, the aspheric coefficients of the aspheric lens in the optical lens 100 include: the quadratic surface coefficient k, the fourth-order aspheric coefficient A, the sixth-order aspheric coefficient B, the eighth-order aspheric coefficient C, the tenth-order aspheric coefficient D, the twelfth-order aspheric coefficient E, and the fourteenth-order aspheric coefficient F of the surface, as shown in Table 2 below.

[0066] Table 2

[0067]

[0068] Figure 2 FIG. 1 is a schematic diagram of a vertical axis chromatic aberration curve provided by an embodiment of the present invention. Figure 3 is a schematic diagram of a light aberration curve according to an embodiment of the present invention, Figure 4 is a schematic diagram of field distortion according to an embodiment of the present invention, Figure 5 This is the MTF diagram of an embodiment of the present invention at 20°C. Figure 6 This is a visible through-focus MTF diagram at 20°C of an embodiment of the present invention. Figure 7 This is a visible through-focus MTF diagram at -30°C of an embodiment of the present invention. Figure 8 This is a visible defocus MTF diagram at 70°C according to an embodiment of the present invention. Figure 2-8 It can be seen that the fixed-focus optical system provided by this embodiment has good imaging capability.

[0069] In one embodiment of the present invention, the total optical length of the fixed-focus optical system 100, that is, the distance from the object side vertex of the first lens 1 to the photosensitive chip 11 is TTL, and the effective focal length of the fixed-focus optical system 100 is EFL, wherein TTL / EFL≤25; by limiting the ratio of the total optical length to the effective focal length, the volume of the fixed-focus optical system 100 can be further reduced, which is conducive to the miniaturization of the fixed-focus lens.

[0070] In an embodiment of the present invention, the aperture value of the fixed-focus optical system 100 is F, wherein F≤2.4; when the aperture value F of the fixed-focus optical system 100 is within this range, clear imaging can be achieved even in weak light.

[0071] In one embodiment of the present invention, the fixed-focus optical system 100 includes a filter 12, which is arranged between the ninth lens 9 and the photosensitive chip 11 along the optical axis; and / or, the fixed-focus optical system also includes a protective glass 13, which is arranged between the ninth lens 9 and the photosensitive chip 11 along the optical axis and is arranged close to the photosensitive chip 11.

[0072] The filter 12 can filter out stray light to prevent the stray light from reaching the photosensitive chip and interfering with normal visible light imaging, thereby improving the imaging quality. The protective glass 13 is arranged close to the photosensitive chip to provide effective protection for the photosensitive chip 11.

[0073] It can be understood that the filter 12 and the protective glass 13 can be set separately, and in order to provide a better imaging effect, the filter 12 and the protective glass 13 can also be set at the same time, and the light carrying the information of the subject can pass through the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the aperture 10, the fifth lens 5, 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 form an image on the photosensitive chip 11.

[0074] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A fixed-focus optical system, characterized in that: The fixed-focus optical system has an object side and an image side that are arranged opposite to each other along the optical axis direction, and the fixed-focus optical system is composed of a first lens, a second lens, a third lens, a fourth lens, an aperture, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a photosensitive chip that are arranged in sequence from the object side to the image side; Wherein, the first lens has a negative optical power, a convex object side surface, and a concave image side surface; The second lens has a negative optical power, a convex object side surface, and a concave image side surface; The third lens has a negative optical power, a concave object side surface, and a concave image side surface; The fourth lens has positive optical power, a concave object side surface, and a convex image side surface; The fifth lens has positive optical power, a convex object-side surface, and a concave image-side surface; The sixth lens has positive optical power, a convex object-side surface, and a convex image-side surface; The seventh lens has positive optical power, a concave object side surface and a convex image side surface; The eighth lens has positive optical power, a convex object-side surface and a convex image-side surface; The ninth lens has negative optical power, a concave object-side surface, and a convex image-side surface.

2. The fixed-focus optical system 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 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, 15mm<|f2|<30mm, 6mm<|f3|<12mm, 10mm<|f4|<20mm, 150mm<|f5|<500mm, 4mm<|f6|<8mm, 6mm<|f7|<12mm, 5mm<|f8|<15mm, 8mm<|f9|<15mm.

3. The fixed-focus optical system 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, 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 the dispersion coefficient of the lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens satisfy the following relationship: 1.80≤n1≤2.15, 20.0≤v1≤40.0; 1.80≤n2≤2.05, 20.0≤v2≤40.0; 1.50≤n3≤1.70, 45.0≤v3≤65.0; 1.80≤n4≤2.05 , 25.0≤v4≤40.0; 1.50≤n5≤1.60, 45.0≤v5≤65.0; 1.40≤n6≤1.60, 55.0≤v6≤95.0; 1.70≤n7≤1.95, 20.0≤v7≤35.0; 1.50≤n8≤1.60, 45.0≤v8≤65.0; 1.50≤n9≤1.65, 18.0≤v9≤30.

0.

4. The fixed-focus optical system according to claim 1, wherein: The diameter of the first lens is D1, where D1<25 mm.

5. The fixed-focus optical system according to claim 1, wherein: The image plane diameter of the photosensitive chip is IC, where IC≤7mm.

6. The fixed-focus optical system according to claim 1, wherein: The fifth lens, the eighth lens, and the ninth lens are plastic aspherical lenses, and the first lens, the second lens, the third lens, the fourth lens, the sixth lens, and the seventh lens are glass spherical lenses.

7. The fixed-focus optical system according to claim 1, wherein: The sixth lens and the seventh lens are cemented together.

8. The fixed-focus optical system according to claim 1, wherein: 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≤25.

9. The fixed-focus optical system according to claim 1, wherein: The aperture value of the fixed-focus optical system is F, wherein F≤2.

0.

10. The fixed-focus optical system according to claim 1, wherein: The fixed-focus optical system comprises a filter, and the filter is arranged 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 arranged between the ninth lens and the photosensitive chip along the optical axis and is arranged close to the photosensitive chip.

Images