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 diaphragm, a fourth lens, a fifth lens, a sixth lens, a seventh lens and a photosensitive chip which are sequentially arranged from the object side to the image side. Wherein the focal power of the first lens is negative, the focal power of the second lens is negative, the focal power of the third lens is positive, the focal power of the fourth lens is positive, the focal power of the fifth lens is negative, the focal power of the sixth lens is positive, and the focal power of the seventh lens is negative; the fixed-focus optical system has the advantages of large visual angle, high pixel, small chromatic aberration and better imaging effect.

Description

Technical Field

[0001] The utility model relates to the technical field of optics, and particularly relates to a fixed-focus optical system. Background Art

[0002] With the development of digital imaging technology, users have higher and higher requirements for photographic equipment. Especially in the fields of landscape photography, indoor shooting, architectural photography, etc., wide-angle lenses are popular because they can capture a wider field of view. Traditional wide-angle lenses are often large in size, heavy in weight, and expensive in price, which limits their popularity in the consumer market. There are also a small number of lenses that sacrifice some resolution in order to reduce costs. Summary of the Utility Model

[0003] The main purpose of the utility model is to propose a fixed-focus optical system, aiming to enable the optical system to have a large viewing angle, high pixels, and small chromatic aberration, and the imaging effect is better.

[0004] To achieve the above object, the fixed-focus optical system proposed by the utility model has an object side and an image side that are relatively arranged along the optical axis direction. The fixed-focus optical system is composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an image sensor chip arranged in sequence from the object side to the image side;

[0005] Among them, the optical power of the first lens is negative, the object side surface is convex, and the image side surface is concave;

[0006] The optical power of the second lens is negative, the object side surface is concave, and the image side surface is concave;

[0007] The optical power of the third lens is positive, the object side surface is convex, and the image side surface is convex;

[0008] The optical power of the fourth lens is positive, the object side surface is convex, and the image side surface is convex;

[0009] The optical power of the fifth lens is negative, the object side surface is concave, and the image side surface is concave;

[0010] The optical power of the sixth lens is positive, the object side surface is convex, and the image side surface is convex;

[0011] The optical power of the seventh lens is negative.

[0012] In an 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, and the focal length of the seventh lens is f7;

[0013] Among them, 6mm < |f1| < 15mm, 6mm < |f2| < 12mm, 4mm < |f3| < 8mm, 4mm < |f4| < 8mm, 4mm < |f5| < 12mm, 4mm < |f6| < 10mm, 6mm < |f7| < 12mm.

[0014] 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, and the fixed-focus optical system satisfies the following relationship:

[0015] 1.50 ≤ n1 ≤ 1.75, 1.50 ≤ n2 ≤ 1.60, 1.75 ≤ n3 ≤ 1.95, 1.75 ≤ n4 ≤ 1.95, 1.70 ≤ n5 ≤ 1.85, 1.50 ≤ n6 ≤ 1.60, 1.52 ≤ n7 ≤ 1.68.

[0016] In one embodiment, 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, and the fixed-focus optical system satisfies the following relationship:

[0017] 50.0 ≤ v1 ≤ 70.0, 50.0 ≤ v2 ≤ 70.0, 30.0 ≤ v3 ≤ 50.0, 30.0 ≤ v4 ≤ 50.0, 20.0 ≤ v5 ≤ 35.0, 50.0 ≤ v6 ≤ 70.0, 18.0 ≤ v7 ≤ 30.0.

[0018] In one embodiment, the diameter of the first lens is D1, where D1 < 15mm.

[0019] In one embodiment, the image plane diameter of the fixed-focus optical system is IC, where 6mm ≤ IC ≤ 8mm.

[0020] In one embodiment, the first lens is a glass spherical lens, the second lens is a plastic aspherical lens, the third lens is a glass spherical lens, the fourth lens is a glass spherical lens, the fifth lens is a glass spherical lens, the sixth lens is a plastic aspherical lens, and the seventh lens is a plastic aspherical lens;

[0021] Among them, the fourth lens and the fifth lens are cemented.

[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, where TTL / EFL ≤ 6.5.

[0023] In one embodiment, the aperture value of the fixed-focus optical system is F, where 2.0 ≤ F ≤ 2.4.

[0024] In one embodiment, the fixed-focus optical system further includes a protective glass and a filter. The protective glass is located between the seventh lens and the photosensitive chip, and the filter is located between the protective glass and the seventh lens.

[0025] The technical solution of the present utility model is beneficial to the collection of light rays of the fixed-focus optical system by setting the first lens with negative optical power, and can effectively increase the field of view range; by setting the third lens with positive optical power, which undertakes a relatively large optical power of the fixed-focus optical system and changes the propagation direction of the light beam, it is more beneficial for the light beam to form an image on the image plane. In addition, a diaphragm is provided between the third spherical glass lens and the fourth spherical lens to adjust the light flux according to actual conditions and improve the imaging quality; by comprehensively setting the optical power and the matching relationship of the shapes of each lens, the lens can well control the light ray trend, make the structure more compact while introducing more light rays, and can achieve miniaturization and light weight; through the mutual combination of different lenses and the reasonable distribution of optical power, it has good performance such as a large viewing angle, high pixels, and very good thermal aberration correction, with a broader field of view and more sufficient data information obtained. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0027] Figure 1 It is a schematic structural diagram of an embodiment of the fixed-focus optical system provided by the present utility model;

[0028] Figure 2 For Figure 1 It is a schematic diagram of the spherical aberration curve of an embodiment of the fixed-focus optical system in

[0029] Figure 3 For Figure 1 It is a schematic diagram of the lateral chromatic aberration curve of an embodiment of the fixed-focus optical system in

[0030] Figure 4 For Figure 1 It is a schematic diagram of the ray aberration curve of an embodiment of the fixed-focus optical system in

[0031] Figure 5 For Figure 1 Schematic diagram of field distortion of an embodiment of a fixed-focus optical system;

[0032] Figure 6 For Figure 1 MTF graph at 20 °C of an embodiment of a fixed-focus optical system.

[0033] Explanation of reference numerals in the drawings:

[0034] 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, aperture; 9, photosensitive chip; 10, filter; 11, protective glass.

[0035] The realization, functional features and advantages of the object of the present utility model will be further described with reference to the embodiments and the accompanying drawings. Specific embodiments

[0036] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0037] It should be noted that if there are directional indications (such as up, down, left, right, front, back,...) involved in the embodiments of the present utility model, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0038] In addition, if there are descriptions such as "first", "second", etc. involved in the embodiments of the present utility model, 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 quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution where A and B are satisfied simultaneously. In addition, the technical solutions between the embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present utility model.

[0039] Traditional wide-angle lenses tend to be bulky, heavy, and expensive, which limits their popularity in the consumer market. Also, to reduce costs, some lenses sacrifice partial resolution, affecting the usage effect.

[0040] To solve the above problems, the present utility model proposes a fixed-focus optical system 100.

[0041] First of all, it should be understood that the optical power is equal to the difference between the convergence of the image-side light beam and the convergence of the object-side light beam, which characterizes the ability of the optical system to deflect light rays. The larger the absolute value of the optical power, the stronger the bending ability of the light rays; the smaller the absolute value of the optical power, the weaker the bending ability of the light rays. When the optical power is positive, the refraction of the light rays is convergent; when the optical power is negative, the refraction of the light rays is divergent. The optical power can be used to characterize a certain refracting surface of a lens, can be used to characterize a certain lens, or can be used to characterize a system formed by multiple lenses together.

[0042] Please refer to Figure 1 , in an embodiment of the present utility model, the fixed-focus optical system 100 has an object side and an image side that are oppositely arranged along the optical axis direction. The fixed-focus optical system 100 is composed of a first lens 1, a second lens 2, a third lens 3, a diaphragm 8, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7, and a photosensitive chip 9 arranged in sequence from the object side to the image side. Among them, the first lens 1 has a negative optical power, the object side surface is convex, and the image side surface is concave; the second lens 2 has a negative optical power, the object side surface is concave, and the image side surface is concave; the third lens 3 has a positive optical power, the object side surface is convex, and the image side surface is convex; the fourth lens 4 has a positive optical power, the object side surface is convex, and the image side surface is convex; the fifth lens 5 has a negative optical power, the object side surface is concave, and the image side surface is concave; the sixth lens 6 has a positive optical power, the object side surface is convex, and the image side surface is convex; the seventh lens 7 has a negative optical power.

[0043] By setting the object side surface of the first lens 1 to be convex and the image side surface to be concave, the object side surface of the second lens 2 to be concave and the image side surface to be concave, the object side surface of the third lens 3 to be convex and the image side surface to be convex, the object side surface of the fourth lens 4 to be convex and the image side surface to be convex, the object side surface of the fifth lens 5 to be concave and the image side surface to be concave, and the object side surface of the sixth lens 6 to be convex and the image side surface to be convex, the first lens 1 has a negative optical power, the second lens 2 has a negative optical power, the third lens 3 has a positive optical power, the fourth lens 4 has a positive optical power, the fifth lens 5 has a negative optical power, and the sixth lens 6 has a positive optical power;

[0044] The technical solution of the present utility model is to set the first lens 1 with negative optical power, which is beneficial to the collection of light rays of the fixed-focus optical system 100, and can effectively increase the field of view range; set the third lens 3 with positive optical power, which undertakes a relatively large optical power of the fixed-focus optical system 100 and changes the propagation direction of the light beam, making it more conducive to the light beam imaging on the image plane. In addition, a diaphragm 8 is provided between the third spherical lens and the fourth spherical lens to adjust the light flux according to the actual situation and improve the imaging quality. The photosensitive chip 9 is used to capture light rays and convert them into electrical signals; by comprehensively setting the optical power and the matching relationship of the shapes of each lens, the fixed-focus optical system 100 can well control the light ray trend, introduce more light rays while making the structure more compact, realize miniaturization and light weight, and control the total length of the lens within 18 mm; through the mutual combination of different lenses and the reasonable distribution of optical power, it has good performances such as a large viewing angle, high pixels, and very good achromatism, with a wider field of view, can be equipped with a 1 / 2-inch chip to achieve a large viewing angle of 152°, and obtain more sufficient data information.

[0045] Please refer to Figure 2 , in an embodiment of the present utility model, 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 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, and the focal length of the seventh lens 7 is f7; among them, 6 mm < |f1| < 15 mm, 6 mm < |f2| < 12 mm, 4 mm < |f3| < 8 mm, 4 mm < |f4| < 8 mm, 4 mm < |f5| < 12 mm, 4 mm < |f6| < 10 mm, 6 mm < |f7| < 12 mm; by the mutual combination of different lenses and the reasonable distribution of the focal length range, while the optical system has a large viewing angle, the resolution of the fixed-focus optical system 100 is improved.

[0046] In an embodiment of the present 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, and the refractive index of the seventh lens 7 is n7. The fixed-focus optical system 100 satisfies the following relationships: 1.50 ≤ n1 ≤ 1.75, 1.50 ≤ n2 ≤ 1.60, 1.75 ≤ n3 ≤ 1.95, 1.75 ≤ n4 ≤ 1.95, 1.70 ≤ n5 ≤ 1.85, 1.50 ≤ n6 ≤ 1.60, 1.52 ≤ n7 ≤ 1.68. By restricting the refractive indices of the lenses of the fixed-focus optical system 100, the refraction angle and path of light can be controlled more precisely, thereby ensuring that the light converges to the correct position to form a clear and distortion-free image. This helps to improve the sharpness and color accuracy of the picture.

[0047] In an embodiment of the present utility model, 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, and the dispersion coefficient of the seventh lens 7 is v7. The fixed-focus optical system 100 satisfies the following relationships: 50.0 ≤ v1 ≤ 70.0, 50.0 ≤ v2 ≤ 70.0, 30.0 ≤ v3 ≤ 50.0, 30.0 ≤ v4 ≤ 50.0, 20.0 ≤ v5 ≤ 35.0, 50.0 ≤ v6 ≤ 70.0, 18.0 ≤ v7 ≤ 30.0; It can be understood that lights of different colors have different degrees of refraction when passing through the lens due to their different wavelengths, resulting in different focusing positions, forming chromatic aberration, and affecting the clarity of the image and the accuracy of colors. By restricting the dispersion coefficients of the lenses of the fixed-focus optical system 100, the refractive index differences of various wavelength lights can be effectively balanced, chromatic aberration can be reduced, the image edges can be made clearer, and the color transition can be natural.

[0048] 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 an embodiment of the present utility model, the diameter of the first lens 1 is D1, where D1 < 15 mm. By restricting the diameter of the first lens 1, it is convenient for installation and reduces the volume of the fixed-focus optical system 100, making it suitable for more scenarios.

[0049] In an embodiment of the present utility model, it can be understood that when the image plane diameter of the fixed-focus optical system 100 is too large, each lens cannot collect all the light, which will increase the physical size of the lens, thus affecting the realization of the maximum aperture. When the image plane diameter is smaller than the size of the camera sensor, vignetting or image circle phenomena may also occur. Therefore, the image plane cannot be too small, which will affect the imaging quality. For this reason, the image plane diameter of the fixed-focus optical system 100 is IC, where 6 mm ≤ IC ≤ 8 mm, so that the fixed-focus optical system 100 can project a complete image without vignetting and other phenomena, improving the imaging effect.

[0050] Please refer to Figure 1 , in an embodiment of the present utility model, the first lens 1 is a glass spherical lens, the second lens 2 is a plastic aspherical lens, the third lens 3 is a glass spherical lens, the fourth lens 4 is a glass spherical lens, the fifth lens 5 is a glass spherical lens, the sixth lens 6 is a plastic aspherical lens, and the seventh lens 7 is a plastic aspherical lens; wherein, the fourth lens 4 and the fifth lens 5 are cemented.

[0051] It can be understood that the characteristics of an aspherical lens are that the curvature changes continuously from the center to the periphery of the lens. Different from a spherical lens with a constant curvature from the center to the periphery of the lens, an aspherical lens has better curvature radius characteristics and has the advantages of improving distortion aberration and astigmatism aberration. After using an aspherical lens, it is possible to eliminate the aberration that appears during imaging as much as possible, thereby improving the imaging quality of the lens.

[0052] Specifically, in an embodiment of the present utility model, the surface shape of the aspherical lens in the projection optical system should satisfy the following equation:

[0053]

[0054] where c is the curvature corresponding to the radius; y is the radial coordinate (its unit is the same as the unit of the lens length); k is the conic quadratic coefficient, and A, B, C, D, E, F, G... respectively represent the aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, sixteenth order...

[0055] More specifically, in an embodiment of the present utility model, the even-order coefficients of each aspherical surface are shown in Table 1 below.

[0056] Table 1

[0057]

[0058]

[0059] Through the above parameters, the shape and size of the aspherical lens can be accurately set to correct distortion, eliminate the aberration that appears during imaging as much as possible, thereby improving the imaging quality of the lens, correcting the pupil aberration caused by a large aperture, thereby improving the imaging quality of the system, and at the same time greatly reducing the number of spherical lenses set, reducing the system volume.

[0060] Furthermore, due to the high price and difficult manufacturing of glass lenses, in an embodiment of the present invention, the second lens 2, the sixth lens 6, and the seventh lens 7 are plastic lenses. Plastic lenses can be easily processed into various complex shapes and sizes through processes such as injection molding and die casting, making it easier to achieve aspherical design, facilitating the improvement of optical performance and reducing aberration.

[0061] The first lens 1, the third lens 3, the fourth lens 4, and the fifth lens 5 are glass lenses, which have a very high surface finish, thereby reducing light scattering and reflection, reducing various optical aberrations while effectively suppressing the chromatic aberration of the system, improving the imaging effect. Glass is less sensitive to temperature changes, and its shape and optical performance remain stable under temperature changes and are not easily deformed. Therefore, glass lenses can well resist the problem of lens thermal deformation, maintain the high precision of the lens for a long time, and thus improve the stability of the fixed-focus optical system 100.

[0062] In addition, by gluing the fourth lens 4 and the fifth lens 5 after the aperture stop 8, the chromatic aberration of the lens is better corrected, and at the same time, the ray height of the off-axis field of view can be increased, enabling the system to have a larger target surface.

[0063] By adopting a hybrid glass-plastic structure, the total length and volume of the optical system are reduced by making full use of the aspherical surface, while having a large angle, small chromatic aberration, high imaging quality, and a large target surface.

[0064] Specifically, in an embodiment of the present invention, the focal length f of the fixed-focus optical system 100 is 2.90 mm, the aperture value F is 2.4, the image plane diameter is 8.0 mm, and the diagonal field of view angle is 152°. The parameters of the fixed-focus optical system are shown in Table 2 below.

[0065] Table 2

[0066]

[0067]

[0068] Figure 2 The figure shows a schematic diagram of the spherical aberration curve of an embodiment of the present invention. Figure 3 The figure shows a schematic diagram of the lateral chromatic aberration curve provided by another embodiment of the present invention. Figure 4 It is a schematic diagram of the ray aberration curve of another embodiment of the present invention. Figure 5Schematic diagram of field distortion for another embodiment of the present utility model Figure 6 MTF graph at 20°C for another embodiment of the present utility model. It can be seen from Figure 2-6 that the fixed-focus lens provided in this embodiment has good imaging ability.

[0069] In one embodiment of the present utility model, the overall optical length of the fixed-focus optical system 100, that is, the distance from the object side of the first lens 1 to the photosensitive chip 9 is TTL, and the effective focal length of the fixed-focus optical system 100 is EFL. Among them, TTL / EFL ≤ 6.5. By restricting the overall optical length of the fixed-focus optical system 100, the volume of the fixed-focus optical system 100 can be further reduced, which is beneficial to realizing the miniaturization of the fixed-focus optical system 100.

[0070] In one embodiment of the present utility model, the aperture value of the fixed-focus optical system 100 is F. Among them, 2.0 ≤ F ≤ 2.4. When the aperture value F of the fixed-focus optical system 100 is within this range, the resolution and contrast performance of the lens are optimal, and the lens has a large light transmission amount. The lens can also clearly image in low light, and the image plane diameter can reach 8 mm, and the imaging effect is better.

[0071] In one embodiment of the present utility model, the fixed-focus optical system 100 further includes a protective glass 11 and a filter 10. The protective glass 11 is located between the seventh lens 7 and the photosensitive chip 9, and the filter 10 is located between the protective glass 11 and the seventh lens 7. The protective glass 11 is disposed close to the photosensitive chip 9 and can provide effective protection for the photosensitive chip 9. The filter 10 can filter out stray light and prevent stray light from reaching the photosensitive chip 9 and interfering with the normal visible light imaging, thereby improving the imaging quality. It can be understood that the light carrying the information of the photographed object can sequentially pass through the first lens 1, the second lens 2, the third lens 3, the aperture 8, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the infrared filter 10, and the protective glass 11 and finally form an image on the photosensitive chip 9.

[0072] The above is only an exemplary embodiment of the present utility model, and does not limit the patent scope of the present utility model. Any equivalent structural transformation made under the technical concept of the present utility model by using the content of the specification and drawings of the present utility model, or directly / indirectly applied in other related technical fields, is included in 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 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, an aperture, a fourth lens, a fifth lens, a sixth lens, a seventh 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 concave object side surface, and a concave image side surface; The third lens has positive optical power, a convex object side surface and a convex image side surface; The fourth lens has positive optical power, a convex object-side surface, and a convex image-side surface; The fifth lens has a negative optical power, a concave 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 negative optical power.

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, and the focal length of the seventh lens is f7; Among them, 6mm<|f1|<15mm, 6mm<|f2|<12mm, 4mm<|f3|<8mm, 4mm<|f4|<8mm, 4mm<|f5|<12mm, 4mm<|f6|<10mm, 6mm<|f7|<12mm.

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, and the refractive index of the seventh lens is n7, and the fixed-focus optical system satisfies the following relationship: 1.50≤n1≤1.75, 1.50≤n2≤1.60, 1.75≤n3≤1.95, 1.75≤n4≤1.95, 1.70≤n5≤1.85, 1.50≤n6≤1.60, 1.52≤n7≤1.

68.

4. The fixed-focus optical system according to claim 1, wherein: 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, and the dispersion coefficient of the seventh lens is v7. The fixed-focus optical system satisfies the following relationship: 50.0≤v1≤70.0, 50.0≤v2≤70.0, 30.0≤v3≤50.0, 30.0≤v4≤50.0, 20.0≤v5≤35.0, 50.0≤v6≤70.0, 18.0≤v7≤30.

0.

5. The fixed-focus optical system according to claim 1, wherein: The diameter of the first lens is D1, where D1<15 mm.

6. The fixed-focus optical system according to claim 1, wherein: The image plane diameter of the fixed-focus optical system is IC, wherein 6mm≤IC≤8mm.

7. The fixed-focus optical system according to claim 1, wherein: The first lens is a glass spherical lens, the second lens is a plastic aspherical lens, the third lens is a glass spherical lens, the fourth lens is a glass spherical lens, the fifth lens is a glass spherical lens, the sixth lens is a plastic aspherical lens, and the seventh lens is a plastic aspherical lens; Wherein, the fourth lens and the fifth lens are glued 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≤6.

5.

9. The fixed-focus optical system according to claim 1, wherein: The aperture value of the fixed-focus optical system is F, wherein 2.0≤F≤2.

4.

10. The fixed-focus optical system according to claim 1, wherein: The fixed-focus optical system also includes a protective glass and a filter. The protective glass is located between the seventh lens and the photosensitive chip, and the filter is located between the protective glass and the seventh lens.

Images