Fixed focus optical system

Abstract

The invention discloses a fixed-focus optical system, and relates to the technical field of optical learning systems, the fixed-focus optical system is provided with an object side and an image side which are correspondingly arranged along the optical axis direction, and the fixed-focus optical system comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an image surface which are sequentially arranged from the object side to the image side, the first lens, the third lens, the fourth lens, the fifth lens and the sixth lens are spherical lenses, and the second lens and the seventh lens are aspheric lenses. Thus, low cost and light weight of the fixed-focus optical system can be realized by comprehensively setting the matching relation of the focal lengths of the seven lenses, and the imaging quality of the fixed-focus optical system is ensured by reasonably arranging the seven lenses, so that the fixed-focus optical system has a large target surface and high light transmission, and the optical system is suitable for large-scale popularization and application. The total length of the lens of the fixed-focus optical system is limited within 30mm, and the fixed-focus optical system has good high and low temperature stability.

Description

Technical Field

[0001] The present invention relates to the technical field of optical systems, and particularly relates to a fixed-focus optical system. Background Art

[0002] With the development of network technology, the network transmission of high-pixel images has been further improved. As a result, video conferencing and webcasting have become more and more popular. The lenses used for video conferencing and webcasting are usually high-pixel wide-angle lenses. A wide-angle lens is a photographic lens with a focal length shorter than that of a standard lens, a field angle larger than that of a standard lens, a focal length longer than that of a fish-eye lens, and a field angle smaller than that of a fish-eye lens. Currently, the wide-angle lenses used for video conferencing and webcasting generally have many lenses, large volume, low and uneven MTF resolution, large distortion, or poor light transmittance and poor high and low temperature stability due to the use of more plastic lenses to improve performance. Summary of the Invention

[0003] The main object of the present invention is to propose a fixed-focus optical system, aiming to improve the problems of existing wide-angle lenses with many lenses, large volume, low and uneven MTF resolution, large distortion, and poor light transmittance and poor high and low temperature stability due to the use of more plastic lenses to improve performance.

[0004] To achieve the above object, the fixed-focus optical system proposed by the present invention has an object side and an image side arranged corresponding to each other along the optical axis direction. The fixed-focus optical system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an image plane arranged in sequence from the object side to the image side. The first lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are arranged as spherical lenses, and the second lens and the seventh lens are arranged as aspherical lenses. The fixed-focus optical system satisfies the following conditions: -18mm < f1 < -10mm; and -140mm < f2 < -90mm; and 6mm < f3 < 15mm; and 4mm < f4 < 8mm; and -8mm < f5 < -3mm; and 8mm < f6 < 15mm; and 80mm < f7 < 120mm; 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.

[0005] In one embodiment, the optical power of the first lens is negative, the object side surface of the first lens is convex, and the image side surface is concave; The optical power of the second lens is negative, the object side surface of the second lens is concave, and the image side surface is convex; The third lens has a positive optical power, and both the object side and the image side of the third lens are convex. The fourth lens has a positive optical power, and both the object side and the image side of the fourth lens are convex. The fifth lens has a negative optical power, and the object-side surface of the fifth lens is concave, while the image-side surface is the object surface. The sixth lens has a positive optical power, and its object-side surface is convex while its image-side surface is concave. The seventh lens has a positive optical power, and its object-side surface is concave while its image-side surface is convex.

[0006] In one embodiment, the refractive index of the first lens is n1, where 1.50 ≤ n1 ≤ 1.70; The refractive index of the second lens is n2, where 1.50 ≤ n2 ≤ 1.60; The refractive index of the third lens is n3, where 1.70 ≤ n3 ≤ 1.90; The refractive index of the fourth lens is n4, where 1.50 ≤ n4 ≤ 1.65; The refractive index of the fifth lens is n5, where 1.60 ≤ n5 ≤ 1.75; The refractive index of the sixth lens is n6, where 1.40 ≤ n6 ≤ 1.60; The refractive index of the seventh lens is n7, where 1.50 ≤ n7 ≤ 1.60.

[0007] In one embodiment, the dispersion coefficient of the first lens is v1, where 40.0 ≤ v1 ≤ 70.0; The dispersion coefficient of the second lens is v2, 50.0≤v2≤60.0; The dispersion coefficient of the third lens is v3, 45.0≤v3≤65.0; The dispersion coefficient of the fourth lens is v4, 55.0≤v4≤75.0; The dispersion coefficient of the fifth lens is v5, 30.0≤v5≤45.0; The dispersion coefficient of the sixth lens is v6, where 60.0 ≤ v6 ≤ 95.0; The dispersion coefficient of the seventh lens is v7, where 50.0 ≤ v7 ≤ 60.0.

[0008] In one embodiment, the fourth lens, the fifth lens, and the sixth lens are cemented together.

[0009] In one embodiment, the aperture value of the fixed-focus optical system is F, where 2.0 ≤ F ≤ 2.4.

[0010] In one embodiment, the diameter of the first lens is D1, where D1 < 13 mm.

[0011] In one embodiment, the diameter of the image plane is IC, where C ≤ 10.6 mm.

[0012] In one embodiment, the distance between the object-side vertex of the first lens of the fixed-focus optical system and the image plane is TTL, the effective focal length of the fixed-focus optical system is EFL, and TTL / EFL≤4.

[0013] In one embodiment, the fixed-focus optical system further includes an aperture stop disposed between the third lens and the fourth lens; and / or, The fixed-focus optical system further includes a filter disposed between the eighth lens and the image plane; and / or, The fixed-focus optical system also includes a photosensitive chip, which is disposed on the image-side of the seventh lens, and the end face of the photosensitive chip facing the object side forms the image plane.

[0014] In the technical solution of the present invention, the fixed-focus optical system is composed of seven lenses. Among them, by setting the focal length of the first lens to be negative and limiting the focal length of the first lens to -18 mm < f1 < -10 mm, it is beneficial for the fixed-focus optical system to collect light, thereby effectively increasing the field of view range of the fixed-focus optical system, and correcting astigmatism and field curvature. At the same time, by setting the focal length of the third lens to be positive and limiting the focal length of the third lens to 6 mm < f3 < 15 mm, the third lens can carry a relatively large optical power of the fixed-focus optical system, so as to change the propagation direction of the light beam, and further be more conducive to the imaging of the light beam on the image plane. At the same time, the first lens, the third lens, the fourth lens, the fifth lens and the sixth lens are set as spherical lenses. By using spherical lenses, the cost of the fixed-focus optical system can be reduced on the premise of ensuring the imaging quality and reliability of the fixed-focus optical system, thereby reducing the assembly sensitivity and improving the yield rate of the finished product. And the second lens and the seventh lens are set as aspherical lenses. The material cost of plastic aspherical lenses is lower, and the manufacturing cost of the entire fixed-focus optical system can be effectively reduced on the premise of ensuring the imaging quality. At the same time, the plastic material has certain flexibility and is less likely to be damaged than the glass lens when subjected to slight external force impact, improving the durability of the fixed-focus optical system. Thus, by comprehensively setting the cooperation relationship of the focal lengths of the seven lenses, the low cost and light weight of the fixed-focus optical system can be achieved, and by reasonably arranging the seven lenses to ensure the imaging quality of the fixed-focus optical system, the fixed-focus optical system has a large target surface and high light transmittance, limits the total length of the lens of the fixed-focus optical system within 30 mm, and has good high and low temperature stability. Brief Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0016] Figure 1 It is a schematic structural diagram of an embodiment of the fixed-focus optical system provided by the present invention; Figure 2 It is a schematic diagram of spherical aberration, field curvature and distortion curves of the fixed-focus optical system provided by the present invention; Figure 3 It is a 20°C MTF schematic diagram of the fixed-focus optical system provided by the present invention; Figure 4This is a schematic diagram of the -40℃ MTF of the fixed-focus optical system provided by the present invention; Figure 5 This is a schematic diagram of the 80℃ MTF of the fixed-focus optical system provided by the present invention.

[0017] Explanation of icon numbers: 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 stop; 9. Filter; 10. Photosensitive chip.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text implies three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] This invention proposes a fixed-focus optical system, which aims to improve the problems of existing wide-angle lenses, such as large lens size, low MTF resolution, unevenness, large distortion, and poor light transmission and high and low temperature stability caused by the use of more plastic lenses to improve performance.

[0023] Please refer to Figure 1 In an embodiment of the present invention, the fixed-focus optical system 100 has an object side and an image side arranged corresponding to each other along the optical axis direction. The fixed-focus optical system 100 includes a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an image plane arranged in sequence from the object side to the image side. The first lens 1, the third lens 3, the fourth lens 4, the fifth lens 5 and the sixth lens 6 are set as spherical lenses, and the second lens 2 and the seventh lens 7 are set as aspherical lenses. The fixed-focus optical system 100 satisfies the following conditions: -18 mm < f1 < -10 mm; and -140 mm < f2 < -90 mm; and 6 mm < f3 < 15 mm; and 4 mm < f4 < 8 mm; and -8 mm < f5 < -3 mm; and 8 mm < f6 < 15 mm; and 80 mm < f7 < 120 mm, where 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.

[0024] In the technical solution of the present invention, the fixed-focus optical system 100 is composed of seven lenses. Among them, by setting the focal length of the first lens 1 to be negative and restricting the focal length of the first lens 1 to -18 mm < f1 < -10 mm, this is beneficial for the fixed-focus optical system 100 to collect light, so as to effectively increase the field of view range of the fixed-focus optical system 100, and correct astigmatism and field curvature. At the same time, by setting the focal length of the third lens 3 to be positive and restricting the focal length of the third lens 3 to 6 mm < f3 < 15 mm, the third lens 3 can carry a relatively large optical power of the fixed-focus optical system 100, so as to change the propagation direction of the light beam, and thus it is more beneficial for the light beam to form an image on the image plane. At the same time, the first lens 1, the third lens 3, the fourth lens 4, the fifth lens 5 and the sixth lens 6 are set as spherical lenses. By using spherical lenses, the cost of the fixed-focus optical system 100 can be reduced on the premise of ensuring the imaging quality and reliability of the fixed-focus optical system 100, thereby reducing the assembly sensitivity and improving the yield rate of the finished product. And the second lens 2 and the seventh lens 7 are set as aspherical lenses. The material cost of the plastic aspherical lens is lower, and it can effectively reduce the manufacturing cost of the entire fixed-focus optical system 100 on the premise of ensuring the imaging quality. At the same time, the plastic material has certain flexibility and is less likely to be damaged than the glass lens when subjected to a slight external force impact, improving the durability of the fixed-focus optical system 100. Thus, by comprehensively setting the matching relationship of the focal lengths of the seven lenses, the low cost and light weight of the fixed-focus optical system 100 can be achieved. And through the reasonable arrangement of the seven lenses, the imaging quality of the fixed-focus optical system 100 is ensured, so that the fixed-focus optical system 100 has a large target surface and high light transmittance, limits the total length of the lens of the fixed-focus optical system 100 within 30 mm, and has good high and low temperature stability.

[0025] First of all, the present invention does not limit the specific surface shapes 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 and the seventh lens 7. In the present invention, the selection of the surface shapes of the object side and the image side 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 and the seventh lens 7 can correspond to their respective focal length ranges.

[0026] For example, in one embodiment of the present invention, the first lens 1 has a negative optical power, the object-side surface of the first lens 1 is convex, and the image-side surface is concave; the second lens 2 has a negative optical power, the object-side surface of the second lens 2 is concave, and the image-side surface is convex; the third lens 3 has a positive optical power, the object-side surface of the third lens 3 is convex, and the image-side surface is convex; the fourth lens 4 has a positive optical power, the object-side surface of the fourth lens 4 is convex, and the image-side surface is convex; the fifth lens 5 has a negative optical power, the object-side surface of the fifth lens 5 is concave, and the image-side surface is the object surface; the sixth lens 6 has a positive optical power, the object-side surface of the sixth lens 6 is convex, and the image-side surface is concave; the seventh lens 7 has a positive optical power, the object-side surface of the seventh lens 7 is concave, and the image-side surface is convex. Thus, by configuring the surface shapes 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, and the seventh lens 7, a good cooperative relationship is formed among the seven lenses, thereby ensuring the imaging quality of the fixed-focus optical system 100.

[0027] Of course, the present invention does not limit the specific values ​​of the focal lengths 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, and the seventh lens 7. In the present invention, the focal lengths 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, and the seventh lens 7 can be selected according to the actual situation, as long as the specific values ​​of the focal lengths of each lens are within the corresponding value range.

[0028] For example, in one embodiment of the present invention, the focal length of the first lens 1 can be set to -13.095mm, the focal length of the second lens 2 can be set to -104.184mm, the focal length of the third lens 3 can be set to 10.278mm, the focal length of the fourth lens 4 can be set to 5.983mm, the focal length of the fifth lens 5 can be set to -3.244mm, the focal length of the sixth lens 6 can be set to 9.091mm, and the focal length of the seventh lens 7 can be set to 96.382mm. With this setting, the focal lengths of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, and the sixth lens 6 are all within their respective ranges, thereby ensuring that the fixed-focus optical system 100 has good imaging quality.

[0029] Furthermore, in this invention, the second lens 2 and the seventh lens 7 can be configured as glass lenses. This configuration allows the glass material to have high thermal stability and a low coefficient of thermal expansion, enabling the glass lens to effectively resist thermal deformation and reduce the impact of temperature on the fixed-focus optical system 100. When the temperature changes, the shape and size of the aspherical glass lens change very little, effectively resisting the problem of thermal deformation of the fixed-focus optical system 100. This ensures that the fixed-focus optical system 100 maintains stable optical performance under different temperature environments, reduces aberrations caused by temperature changes, and ensures consistent image quality.

[0030] Furthermore, in this invention, the refractive index of the first lens 1 is n1, 1.50≤n1≤1.70; the refractive index of the second lens 2 is n2, 1.50≤n2≤1.60; the refractive index of the third lens 3 is n3, 1.70≤n3≤1.90; the refractive index of the fourth lens 4 is n4, 1.50≤n4≤1.65; the refractive index of the fifth lens 5 is n5, 1.60≤n5≤1.75; the refractive index of the sixth lens 6 is n6, 1.40≤n6≤1.60; and the refractive index of the seventh lens 7 is n7, 1.50≤n7≤1.60.

[0031] Of course, the present invention does not limit the refractive index 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, and the seventh lens 7. In actual settings, the refractive indices of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens, and the seventh lens 7 can all be selected according to the actual situation, as long as the specific values ​​of the refractive indices of each lens are within the corresponding value range.

[0032] For example, in one embodiment of the present invention, the refractive index of the first lens 1 can be set to 1.57, the refractive index of the second lens 2 can be set to 1.54, the refractive index of the third lens 3 can be set to 1.77, the refractive index of the fourth lens 4 can be set to 1.57, the refractive index of the fifth lens 5 can be set to 1.65, the refractive index of the sixth lens 6 can be set to 1.44, and the refractive index of the seventh lens 7 can be set to 1.54. It is understood that in this embodiment, the specific values ​​of the refractive indices 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, and the seventh lens 7 are all within their respective numerical ranges to ensure stable imaging of the fixed-focus optical system 100.

[0033] Similarly, in this invention, the dispersion coefficient of the first lens 1 is v1, 40.0≤v1≤70.0; the dispersion coefficient of the second lens 2 is v2, 50.0≤v2≤60.0; the dispersion coefficient of the third lens 3 is v3, 45.0≤v3≤65.0; the dispersion coefficient of the fourth lens 4 is v4, 55.0≤v4≤75.0; the dispersion coefficient of the fifth lens 5 is v5, 30.0≤v5≤45.0; the dispersion coefficient of the sixth lens 6 is v6, 60.0≤v6≤95.0; and the dispersion coefficient of the seventh lens 7 is v7, 50.0≤v7≤60.0.

[0034] This invention does not limit the specific values ​​of the dispersion coefficients of the seven lenses. In this invention, the dispersion coefficients 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, and the seventh lens 7 can also be selected according to the actual situation, as long as the specific values ​​of the dispersion coefficients of each lens are within the corresponding value range.

[0035] In a specific embodiment of the present invention, the dispersion coefficient of the first lens 1 can be set to 49.5, the dispersion coefficient of the second lens 2 can be set to 55.6, the dispersion coefficient of the third lens 3 can be set to 49.6, the dispersion coefficient of the fourth lens 4 can be set to 71.3, the dispersion coefficient of the fifth lens 5 can be set to 39.5, the dispersion coefficient of the sixth lens 6 can be set to 94.5, and the dispersion coefficient of the seventh lens 7 can be set to 55.6. It is also understood that in this embodiment, the specific values ​​of the dispersion coefficients 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, and the seventh lens 7 are all within their respective numerical ranges, thereby ensuring stable imaging of the fixed-focus optical system 100.

[0036] Furthermore, to further correct the chromatic aberration of the fixed-focus optical system 100 and improve its imaging quality, in a further embodiment of the present invention, the fourth lens 4, the fifth lens 5, and the sixth lens 6 are cemented together. This arrangement, through the cemented connection of the fourth lens 4, the fifth lens 5, and the sixth lens 6, allows for better correction of the chromatic aberration of the fixed-focus optical system 100. Simultaneously, the cemented connection reduces light loss, increases image sharpness, and protects the scale surface, thereby further optimizing the manufacturing process to meet design requirements. Therefore, the rational use of cemented components improves the image quality of the optical system.

[0037] Furthermore, the present invention does not limit the aperture value of the fixed-focus optical system 100. In one embodiment of the present invention, the aperture value of the fixed-focus optical system 100 is F, where 2.0 ≤ F ≤ 2.4. This setting enables the fixed-focus optical system 100 to have a large light transmission and high image brightness, enabling clear imaging even in low light conditions, and also allows the fixed-focus optical system 100 to support an image plane of 1 / 1.56 inch.

[0038] To enable adjustment of the aperture value of the fixed-focus optical system 100, in an embodiment of the present invention, the fixed-focus optical system 100 further includes an aperture stop 8, which is disposed between the third lens 3 and the fourth lens 4. Thus, the fixed-focus optical system 100 can adjust the light throughput according to actual conditions, thereby improving image quality.

[0039] In a further embodiment of the present invention, the diameter of the first lens 1 is D1, where D1 < 13 mm. This configuration, by limiting the diameter of the first lens 1, limits the aperture of the fixed-focus optical system 100, thereby preventing the aperture of the fixed-focus optical system 100 from becoming too large and thus meeting the installation space requirements of the final product.

[0040] It should also be noted that, in this invention, the volume of the fixed-focus optical system 100 can be further controlled. In one embodiment of this invention, the diameter of the image plane is IC, where C≤10.6mm.

[0041] Furthermore, in another embodiment of the present invention, the distance between the object-side vertex of the first lens 1 of the fixed-focus optical system 100 and the image plane is TTL, the effective focal length of the fixed-focus optical system 100 is EFL, and TTL / EFL≤4.

[0042] To further improve the imaging quality of the fixed-focus optical system 100, in one embodiment of the present invention, the fixed-focus optical system 100 further includes a filter 9, which is disposed between the seventh lens 7 and the image plane. The filter 9 can effectively filter out stray light in non-working wavelength bands to reduce optical noise and further improve imaging quality.

[0043] In addition, the fixed-focus optical system 100 also includes a photosensitive chip 10, which is disposed on the image side of the seventh lens 7, and the image plane is formed by the end face of the photosensitive chip 10 facing the object side.

[0044] In a specific embodiment of the present invention, the fixed-focus optical system 100 has a focal length f=7.57mm, an aperture value F=2.4, an image plane diameter IC=10.6mm, and a focusing field of view of 76°.

[0045] In this embodiment, the surface type, radius of curvature, thickness, material refractive index, Abbe number, and semi-diameter of the multiple lenses are shown in Table 1 below: Table 1

[0046] In this application, since both the second lens 2 and the seventh lens 7 are aspherical lenses, the aspherical surface shape of the aspherical lens satisfies the following conditions:

[0047] Where z represents the axial sagitta in the Z direction of the aspherical surface; y represents the height of the aspherical surface; c represents the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k represents the conic coefficient; and the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms represent higher-order aspherical coefficients, respectively.

[0048] One design value for the aspheric coefficient in this embodiment is shown in Table 2 below: Table 2

[0049] It should be noted that Table 2 is a design value of the aspherical coefficient of the lens in the fixed-focus optical system 100 described in this embodiment. The specific value of the aspherical coefficient design can be adjusted according to the needs of the product, and the present invention does not limit it.

[0050] Please see Figure 2 , Figure 2 This is a schematic diagram of the spherical aberration, field curvature, and distortion curves of the fixed-focus optical system 100 in this embodiment.

[0051] Please see Figure 3 , Figure 3 This is a schematic diagram of the 20°C MTF of the fixed-focus optical system 100 in this embodiment.

[0052] Please see Figure 4 , Figure 4 This is a schematic diagram of the -40℃ MTF of the fixed-focus optical system 100 in this embodiment.

[0053] Please see Figure 5 , Figure 5 This is a schematic diagram of the 80°C MTF of the fixed-focus optical system 100 in this embodiment.

[0054] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any 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 applications in other related technical fields, are included within 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 arranged corresponding to each other along the optical axis direction. The fixed-focus optical system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an image plane arranged in sequence from the object side to the image side. The first lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are configured as spherical lenses, and the second lens and the seventh lens are configured as aspherical lenses. The fixed-focus optical system satisfies the following conditions: -18 mm < f1 < -10 mm; and -140 mm < f2 < -90 mm; and 6 mm < f3 < 15 mm; and 4 mm < f4 < 8 mm; and -8 mm < f5 < -3 mm; and 8 mm < f6 < 15 mm; and 80 mm < f7 < 120 mm; 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.

2. The fixed-focus optical system as described in claim 1, characterized in that, The optical power of the first lens is negative. The object side surface of the first lens is convex, and the image side surface is concave; The optical power of the second lens is negative. The object side surface of the second lens is concave, and the image side surface is convex; The optical power of the third lens is positive. The object side surface of the third lens is convex, and the image side surface is convex; The optical power of the fourth lens is positive. The object side surface of the fourth lens is convex, and the image side surface is convex; The optical power of the fifth lens is negative. The object side surface of the fifth lens is concave, and the image side surface is the object side surface; The optical power of the sixth lens is positive. The object side surface of the sixth lens is convex, and the image side surface is concave; The optical power of the seventh lens is positive. The object side surface of the seventh lens is concave, and the image side surface is convex.

3. The fixed-focus optical system as described in claim 1, characterized in that, The refractive index of the first lens is n1, 1.50 ≤ n1 ≤ 1.70; The refractive index of the second lens is n2, 1.50 ≤ n2 ≤ 1.60; The refractive index of the third lens is n3, 1.70 ≤ n3 ≤ 1.90; The refractive index of the fourth lens is n4, 1.50 ≤ n4 ≤ 1.65; The refractive index of the fifth lens is n5, 1.60 ≤ n5 ≤ 1.75; The refractive index of the sixth lens is n6, 1.40 ≤ n6 ≤ 1.60; The refractive index of the seventh lens is n7, 1.50 ≤ n7 ≤ 1.

60.

4. The fixed-focus optical system as described in claim 1, characterized in that, The dispersion coefficient of the first lens is v1, 40.0 ≤ v1 ≤ 70.0; The dispersion coefficient of the second lens is v2, 50.0 ≤ v2 ≤ 60.0; The dispersion coefficient of the third lens is v3, 45.0 ≤ v3 ≤ 65.0; The dispersion coefficient of the fourth lens is v4, 55.0 ≤ v4 ≤ 75.0; The dispersion coefficient of the fifth lens is v5, 30.0 ≤ v5 ≤ 45.0; The dispersion coefficient of the sixth lens is v6, 60.0 ≤ v6 ≤ 95.0; The dispersion coefficient of the seventh lens is v7, 50.0 ≤ v7 ≤ 60.

0.

5. The fixed-focus optical system as described in claim 1, characterized in that, The fourth lens, the fifth lens, and the sixth lens are bonded together.

6. The fixed-focus optical system as described in claim 1, characterized in that, The aperture value of the fixed-focus optical system is F, where 2.0 ≤ F ≤ 2.

4.

7. The fixed-focus optical system as described in claim 1, characterized in that, The diameter of the first lens is D1, where D1 < 13 mm.

8. The fixed-focus optical system as described in claim 1, characterized in that, The diameter of the image plane is IC, where C≤10.6mm.

9. The fixed-focus optical system as described in claim 1, characterized in that, The distance between the object-side vertex of the first lens of the fixed-focus optical system and the image plane is TTL, the effective focal length of the fixed-focus optical system is EFL, and TTL / EFL≤4.

10. The fixed-focus optical system as claimed in claim 1, characterized in that, The fixed-focus optical system further includes an aperture stop, which is disposed between the third lens and the fourth lens; and / or, The fixed-focus optical system further includes a filter disposed between the eighth lens and the image plane; and / or, The fixed-focus optical system also includes a photosensitive chip, which is disposed on the image-side of the seventh lens, and the end face of the photosensitive chip facing the object side forms the image plane.

Images