Fixed focus optical system

Abstract

The utility model 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 utility model relates to the technical field of optics, in particular to a fixed-focus optical system. Background Art

[0002] With the advancement of 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 can have advantages such as ultra-large field of view, high pixels, and stable performance under high and low temperatures. The existing lenses on the market generally have defects such as low pixels, small aperture, low image clarity, and inability to work stably at high and low temperatures. This type of lens design can no longer meet the gradually increasing usage needs of consumers. Utility Model Content

[0003] The main purpose of the utility model 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 proposes a fixed-focus optical system, wherein the fixed-focus optical system has an object side and an image side disposed opposite to each other along the optical axis, 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, which are arranged in sequence from the object side to the image side.

[0005] 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. 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 refractive index and Abbe number 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, where D1<25 mm.

[0018] In one embodiment, the image plane diameter of the photosensitive chip is IC, where 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 embodiment, 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 focal power and a second lens with positive focal power, which can effectively increase the field of view; by setting a fifth lens and a sixth lens with positive focal power, a larger focal power 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 set between the fourth lens and the fifth lens, which can adjust the size of the field of view, block far-axis light, avoid the influence of far-axis light on the imaging quality, improve the image quality, and make the lens have a large light throughput; by comprehensively setting the focal power of each lens, the lens can well control the trend of light, make the structure more compact while introducing more light, and by combining different lenses and reasonably allocating the focal power, the lens has high resolution, wide viewing angle, no heat, and better imaging effect.

[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 providing 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 providing 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 well control the trend of light, while introducing more light and making the structure more compact; and by combining different lenses and reasonably distributing the optical focal length, high resolution, wide viewing angle, no thermalization and better imaging effect are achieved. 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 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.

[0028] Figure 1 This is a structural schematic diagram of an embodiment of a fixed-focus optical system provided by the present utility model;

[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 light aberration curves 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 Visible through-focus MTF diagram at 20°C of an embodiment of a medium fixed-focus optical system;

[0034] Figure 7 for Figure 1 Visible through-focus MTF diagram at -30°C for 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 embodiments described 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 making creative efforts shall fall 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 indications 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 for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning 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.

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

[0043] First, it's important to understand that focal power is equal to the difference between the image-side and object-side beam convergences, and it characterizes an optical system's ability to deflect light. The larger the absolute value of the focal power, the greater the light-bending ability; the smaller the absolute value, the weaker the light-bending ability. When the focal power is a positive number, the light is refracted in a convergent manner; when the focal power is a negative number, the light is refracted in a divergent manner. Focal power can be applied to characterize a specific refractive surface of a lens, a single lens, or a system composed of 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. 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, which are arranged in sequence from the object side to the image side.

[0045] Among them, the first lens 1 has a negative optical power, a convex object-side surface, and a concave image-side surface; the second lens 2 has a negative optical power, a convex object-side surface, and a concave image-side surface; the third lens 3 has a negative optical power, a concave object-side surface, and a concave image-side surface; the fourth lens 4 has a positive optical power, a concave object-side surface, and a convex image-side surface; the fifth lens 5 has a positive optical power, a convex object-side surface, and a concave image-side surface; the sixth lens 6 has a positive optical power, a convex object-side surface, and a convex image-side surface; the seventh lens 7 has a positive optical power, a concave object-side surface, and a convex image-side surface; the eighth lens 8 has a positive optical power, a convex object-side surface, and a convex image-side surface; and the ninth lens 9 has a negative optical 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, facilitate light collection in the optical system, and 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 far-axis light, prevent far-axis light from affecting the imaging quality, improve image quality, and enable the lens to 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 for each other, thereby maintaining the focus and image quality of the system unchanged when the temperature changes, and achieving athermalization. Moreover, 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 focal power and a second lens 2 with positive focal power, which can effectively increase the field of view; by setting a fifth lens 5 and a sixth lens 6 with positive focal power, a larger focal power 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, 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 focal power 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 focal power, the resolution is high, the viewing angle is large, the thermalization is eliminated, 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 an optical system. The focal length determines the magnification and viewing angle of the image. The optical 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 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 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, and 8mm<|f9|<15mm. By combining different lenses and rationally allocating their optical focal lengths, the optical system has a small size while improving the resolution of the fixed-focus optical system 100. In addition, by rationally setting the focal length ratio, the fixed-focus optical system 100 does not experience defocus within a temperature range of -10°C to 50°C, and its operating 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 emissivity 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, the volume of the fixed-focus optical system 100 is reduced, and it is adaptable 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 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 and astigmatism. 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] Where 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 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 f of the fixed-focus optical system is 2.21 mm, the aperture value F is 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's aspherical surface to correct distortion and minimize aberrations that occur during imaging, 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 required 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 system chromatic aberration, thereby improving imaging effects. Glass is less sensitive 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.

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

[0061] Furthermore, in an embodiment of the present invention, the sixth lens and the seventh lens are cemented together to better correct the chromatic aberration of the lens, while increasing 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 The figure shows a schematic diagram of a vertical axis chromatic aberration curve provided by an embodiment of the present invention. Figure 3 This is a schematic diagram of a light aberration curve according to an embodiment of the present invention. Figure 4 This 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 the visible through-focus MTF diagram at 20°C of an embodiment of the present invention. Figure 7 This is the visible through-focus MTF diagram of an embodiment of the present invention at -30°C. Figure 8 This is the visible defocus MTF diagram at 70°C of 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 stray light from reaching the photosensitive chip and interfering with normal visible light imaging, thereby improving 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 merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention specification and drawings under the technical 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 optical system, characterized in that: The fixed-focus optical system has an object side and an image side that are opposite to each other along the optical axis, 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, which are arranged in sequence from the object side to the image side; 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 chromatic aberration coefficient of the first lens is v1, the chromatic aberration coefficient of the second lens is v2, the chromatic aberration coefficient of the third lens is v3, the chromatic aberration coefficient of the fourth lens is v4, the chromatic aberration coefficient of the fifth lens is v5, the chromatic aberration coefficient of the sixth lens is v6, the chromatic aberration coefficient of the seventh lens is v7, the chromatic aberration coefficient of the eighth lens is v8, and the chromatic aberration coefficient of the ninth lens is v9. The refractive index and Abbe number 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 is less than 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, where F≤2.

0.

10. The fixed-focus optical system according to claim 1, wherein: 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, 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.

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