Fixed focus optical system

Abstract

The invention discloses a fixed focus optical system, and relates to the technical field of optical systems, and the fixed focus optical system is provided with an object side and an image side which are oppositely arranged in the optical axis direction. 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 plane which are sequentially arranged from the object side to the image side. Through the arrangement, the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are reasonably controlled through material combination and surface type distribution of the plurality of lenses of the fixed-focus optical system, and the focal lengths are enabled to be-8mlt; f1lt; 5 mm; the thickness is-30 mmlt; f2lt; f2lt; -20 mm;-20 mm; the thickness is 4 mmlt; f3lt; f3t; 7 mm; the thickness is 3 mmlt; f4lt; f4t; 6 mm; the thickness is-9 mmlt; f5lt; f5t; -4 mm; the thickness is 10 mmlt; f61t; f61t; 25 mm; the thickness is-25 mmlt; f7lt; f7lt; therefore, the fixed-focus optical system has good performances such as very small chromatic aberration and the like on the premise that the fixed-focus optical system has a large visual angle, high pixel and athermalization.

Description

Technical Field

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

[0002] With the development of mobile Internet, photos and videos tend to be shared on the Internet to record every bit of life, which has given rise to action cameras. Accordingly, the demand for the corresponding optical lenses is also increasing. Since action cameras are mostly used in extreme environmental temperatures, extremely high requirements are imposed on the lenses they are paired with, which need to simultaneously meet a large field of view angle, high-definition imaging effects, small volume for easy carrying, and the ability to adapt to large temperature differences without defocusing. Summary of the Invention

[0003] The main object of the present invention is to propose a fixed-focus optical system, aiming to improve the problem that the existing optical systems cannot simultaneously meet a large field of view angle, high definition, and the inability to adapt to large temperature differences without defocusing.

[0004] To achieve the above object, the fixed-focus optical system proposed by the present invention has an object side and an image side disposed opposite to each other in 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 sequentially arranged from the object side to the image side. 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. The fixed-focus optical system satisfies the following conditions:

[0005] -8mm < f1 < -5mm; and -30mm < f2 < -20mm; and 4mm < f3 < 7mm; and 3mm < f4 < 6mm; and -9mm < f5 < -4mm; and 10mm < f6 < 25mm; and -25mm < f7 < -12mm;

[0006] Among them, the first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are plastic aspherical lenses.

[0007] In one embodiment, the refractive index of the first lens is n1, 1.50 ≤ n1 ≤ 1.75;

[0008] The refractive index of the second lens is n2, 1.60 ≤ n2 ≤ 1.70;

[0009] The refractive index of the third lens is n3, 1.75 ≤ n3 ≤ 1.95;

[0010] The refractive index of the fourth lens is n4, 1.50≤n4≤1.60;

[0011] The refractive index of the fifth lens is n5, 1.60≤n5≤1.70;

[0012] The refractive index of the sixth lens is n6, 1.50≤n6≤1.60;

[0013] The refractive index of the seventh lens is n7, 1.50≤n7≤1.68.

[0014] In one embodiment, the dispersion coefficient of the first lens is v1, 50.0≤v1≤70.0;

[0015] The dispersion coefficient of the second lens is v2, 18.0≤v2≤26.0;

[0016] The dispersion coefficient of the third lens is v3, 30.0≤v3≤50.0;

[0017] The dispersion coefficient of the fourth lens is v4, 50.0≤v4≤70.0;

[0018] The dispersion coefficient of the fifth lens is v5, 18.0≤v5≤26.0;

[0019] The dispersion coefficient of the sixth lens is v6, 50.0≤v6≤70.0;

[0020] The dispersion coefficient of the seventh lens is v7, 50.0≤v7≤70.0.

[0021] 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;

[0022] 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;

[0023] The third lens has a positive optical power, an object side surface of the third lens is a convex surface, and an image side surface is a concave surface;

[0024] The fourth lens has a positive refractive power, and the object side surface and image side surface of the fourth lens are convex;

[0025] 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 convex;

[0026] 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 flat;

[0027] The optical power of the seventh lens is negative;

[0028] Wherein, the fourth lens is glued to the fifth lens.

[0029] In one embodiment, the distance between the vertex of the object-side surface of the first lens and the image plane is TTL, and the effective focal length of the fixed-focus optical system is EFL, wherein TTL≤13.5 mm; and TTL / EFL≤3.42.

[0030] In one embodiment, the aperture value of the fixed-focus optical lens is F, where F≤2.8.

[0031] In one embodiment, the diameter of the first lens is D, wherein D1<10 mm.

[0032] In one embodiment, the height of the image plane is φ, and φ≤10.3 mm.

[0033] In one embodiment, the fixed-focus optical system further includes an aperture stop, and the aperture stop is disposed between the third lens and the fourth lens.

[0034] In one embodiment, the fixed-focus optical system further includes:

[0035] a photosensitive chip, arranged at intervals on the image side of the seventh lens, wherein one end surface of the photosensitive chip facing the object side is the image surface; and

[0036] The filter is arranged between the seventh lens and the photosensitive chip.

[0037] In the technical solution of the present invention, the first lens and the third lens are glass spherical lenses. Glass lenses can well resist the problem of lens thermal deformation, reduce the influence of temperature on the optical performance of the lens, maintain the high precision of the lens for a long time, and the spherical lenses are easy to process, which can ensure low processing costs, have low assembly sensitivity, and improve the yield of finished products. Aspherical lenses have better curvature radius characteristics and have the advantages of improving distortion aberration, astigmatism and aberration. After using aspherical lenses, the aberration that appears during imaging can be eliminated as much as possible, the edge image quality can be improved, and thus the imaging quality of the lens can be improved. At the same time, using plastic aspherical lenses can further reduce the manufacturing cost of the fixed-focus optical system. With such a setting, by combining the materials and surface types of multiple lenses of the fixed-focus optical system and reasonably controlling the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens, so that -8mm < f1 < -5mm; and -30mm < f2 < -20mm; and 4mm < f3 < 7mm; and 3mm < f4 < 6mm; and -9mm < f5 < -4mm; and 10mm < f6 < 25mm; and -25mm < f7 < -12mm, so that the fixed-focus optical system can have good performance such as very small chromatic aberration on the premise of having a large viewing angle, high pixels and athermalization. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 use in 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 be obtained based on the structures shown in these drawings.

[0039] Figure 1 It is a schematic structural diagram of an embodiment of a fixed-focus optical system provided by the present invention;

[0040] Figure 2 is Figure 1 a schematic diagram of the spherical aberration curve of the fixed-focus optical system in

[0041] Figure 3 is Figure 1 a schematic diagram of the vertical chromatic aberration curve of the fixed-focus optical system in

[0042] Figure 4 is Figure 1 a schematic diagram of the ray aberration curve of the fixed-focus optical system in

[0043] Figure 5 is Figure 1 a schematic diagram of the field curvature and distortion of the fixed-focus optical system in

[0044] Figure 6 for Figure 1 Schematic diagram of 20℃ MTF of medium fixed focus optical system;

[0045] Figure 7 for Figure 1 Schematic diagram of -40℃ MTF of medium fixed focus optical system;

[0046] Figure 8 for Figure 1 Schematic diagram of 90°C MTF of a medium fixed-focus optical system.

[0047] Description of Figure Numbers:

[0048] 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.

[0049] 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

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0051] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0052] In addition, if the descriptions such as "first" and "second" are involved in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and should not be construed 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 scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0053] The present invention provides a fixed-focus optical system, aiming to solve the problems that the existing optical systems cannot simultaneously meet a large field of view, high definition, and cannot adapt to large temperature differences without defocusing.

[0054] 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 oppositely arranged in 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 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. The fixed-focus optical system 100 satisfies the following conditions: -8 mm < f1 < -5 mm; and -30 mm < f2 < -20 mm; and 4 mm < f3 < 7 mm; and 3 mm < f4 < 6 mm; and -9 mm < f5 < -4 mm; and 10 mm < f6 < 25 mm; and -25 mm < f7 < -12 mm; the first lens 1 and the third lens 3 are glass spherical lenses, and the second lens 2, the fourth lens 4, the fifth lens 5, the sixth lens 6, and the seventh lens 7 are plastic aspherical lenses.

[0055] In the technical solution of the present invention, the first lens 1 and the third lens 3 are glass spherical lenses. Glass lenses can well resist the problem of lens thermal deformation, reduce the influence of temperature on the optical performance of the lens, maintain high precision of the lens for a long time, and the spherical lenses are easy to process, which can ensure low processing costs, have low assembly sensitivity, and improve the yield of finished products. Aspherical lenses have better curvature radius characteristics and have the advantages of improving distortion aberration, astigmatism, and aberration. After using aspherical lenses, it is possible to eliminate the aberration that appears during imaging as much as possible, improve the edge image quality, and thus improve the imaging quality of the lens. At the same time, using plastic aspherical lenses can further reduce the manufacturing cost of the fixed-focus optical system 100. With such a setting, by combining the materials and surface types of multiple lenses of the fixed-focus optical system 100 and reasonably controlling 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, such that -8 mm < f1 < -5 mm; and -30 mm < f2 < -20 mm; and 4 mm < f3 < 7 mm; and 3 mm < f4 < 6 mm; and -9 mm < f5 < -4 mm; and 10 mm < f6 < 25 mm; and -25 mm < f7 < -12 mm, so that the fixed-focus optical system 100 can have good performance such as very small chromatic aberration on the premise of having a large viewing angle, high pixels, and athermalization.

[0056] It can be understood that in the embodiment of the present invention, by setting the first lens 1 as a glass spherical lens, the influence of the high temperature on the object side of the fixed-focus optical system 100 on the imaging of the first lens 1 can be reduced, thereby ensuring clear imaging of the fixed-focus optical system 100.

[0057] It should be noted that the present invention does not limit the specific values of the focal length f1 of the first lens 1, the focal length f2 of the second lens 2, the focal length f3 of the third lens 3, the focal length f4 of the fourth lens 4, the focal length f5 of the fifth lens 5, the focal length f6 of the sixth lens 6, and the focal length f7 of the seventh lens 7. The focal length f1 of the first lens 1, the focal length f2 of the second lens 2, the focal length f3 of the third lens 3, the focal length f4 of the fourth lens 4, the focal length f5 of the fifth lens 5, the focal length f6 of the sixth lens 6, and the focal length f7 of the seventh lens 7 can be set to any value within the corresponding range, and the present invention does not limit this. In actual setting, it can be selected according to requirements.

[0058] In addition, in one embodiment of the present invention, the refractive index of the first lens 1 is n1, 1.50≤n1≤1.75; the refractive index of the second lens 2 is n2, 1.60≤n2≤1.70; the refractive index of the third lens 3 is n3, 1.75≤n3≤1.95; the refractive index of the fourth lens 4 is n4, 1.50≤n4≤1.60; the refractive index of the fifth lens 5 is n5, 1.60≤n5≤1.70; the refractive index of the sixth lens 6 is n6, 1.50≤n6≤1.60; and the refractive index of the seventh lens 7 is n7, 1.50≤n7≤1.68.

[0059] It can be understood that the present invention also does not limit the values ​​of the refractive index n1 of the first lens 1, the refractive index n2 of the second lens 2, the refractive index n3 of the third lens 3, the refractive index n4 of the fourth lens 4, the refractive index n5 of the fifth lens 5, the refractive index n6 of the sixth lens 6 and the refractive index n7 of the seventh lens 7.

[0060] In the embodiment of the present invention, the refractive index n1 of the first lens 1, the refractive index n2 of the second lens 2, the refractive index n3 of the third lens 3, the refractive index n4 of the fourth lens 4, the refractive index n5 of the fifth lens 5, the refractive index n6 of the sixth lens 6 and the refractive index n7 of the seventh lens 7 can be set to any value within the corresponding range, and the present invention is not limited to this. In actual setting, it can be selected according to needs.

[0061] In a further embodiment of the present invention, the dispersion coefficient of the first lens 1 is v1, 50.0≤v1≤70.0; the dispersion coefficient of the second lens 2 is v2, 18.0≤v2≤26.0; the dispersion coefficient of the third lens 3 is v3, 30.0≤v3≤50.0; the dispersion coefficient of the fourth lens 4 is v4, 50.0≤v4≤70.0; the dispersion coefficient of the fifth lens 5 is v5, 18.0≤v5≤26.0; the dispersion coefficient of the sixth lens 6 is v6, 50.0≤v6≤70.0; and the dispersion coefficient of the seventh lens 7 is v7, 50.0≤v7≤70.0.

[0062] Similarly, the present invention does not limit the values ​​of the dispersion coefficient v1 of the first lens 1, the dispersion coefficient v2 of the second lens 2, the dispersion coefficient v3 of the third lens 3, the dispersion coefficient v4 of the fourth lens 4, the dispersion coefficient v5 of the fifth lens 5, the dispersion coefficient v6 of the sixth lens 6 and the dispersion coefficient v7 of the seventh lens 7.

[0063] In actual settings, the dispersion coefficient v1 of the first lens 1, the dispersion coefficient v2 of the second lens 2, the dispersion coefficient v3 of the third lens 3, the dispersion coefficient v4 of the fourth lens 4, the dispersion coefficient v5 of the fifth lens 5, the dispersion coefficient v6 of the sixth lens 6 and the dispersion coefficient v7 of the seventh lens 7 can be set to any value within the corresponding range, which can be selected according to needs, and the present invention is not limited to this.

[0064] In a further embodiment of the present invention, the focal power of the first lens 1 is negative, the object side surface of the first lens 1 is convex, and the image side surface is concave; the focal power of the second lens 2 is negative, the object side surface of the second lens 2 is concave, and the image side surface is convex; the focal power of the third lens 3 is positive, the object side surface of the third lens 3 is convex, and the image side surface is concave; the focal power of the fourth lens 4 is positive, the object side surface of the fourth lens 4 is convex, and the image side surface is convex; the focal power of the fifth lens 5 is negative, the object side surface of the fifth lens 5 is concave, and the image side surface is convex; the focal power of the sixth lens 6 is positive, the object side surface of the sixth lens 6 is convex, and the image side surface is flat; the focal power of the seventh lens 7 is negative. In this way, through the coordination relationship of the focal power and shape of the seven lenses, compactness and lightness can be achieved, and the light trend can be well controlled, and the structure of the fixed-focus optical system 100 is made more compact while introducing more light.

[0065] In this embodiment, by setting the first lens 1 as a lens with negative optical power, it is possible to facilitate the collection of light by the fixed-focus optical system 100, thereby effectively increasing the field of view of the fixed-focus optical system 100.

[0066] At the same time, the third lens 3 is set to a lens with positive optical power, so that the third lens 3 bears a larger optical power of the fixed-focus optical system 100, so as to better correct the chromatic aberration of the fixed-focus optical system 100 and compress the volume of the fixed-focus optical system 100.

[0067] It should also be noted that, in this embodiment, the fourth lens 4 is glued to the fifth lens 5. Such an arrangement can further reduce light energy loss, increase imaging clarity, and protect the scale surface, thereby optimizing the processing flow to meet design requirements. By rationally using glued parts, optical components can improve the image quality of the fixed-focus optical system 100.

[0068] In another embodiment of the present invention, the distance between the vertex of the object side surface of the first lens 1 and the image plane is TTL, and the effective focal length of the fixed-focus optical system 100 is EFL, wherein TTL≤13.5mm; and TTL / EFL≤3.42. In this way, the total lens length of the fixed-focus optical system 100 is controlled within 13.5mm to ensure the compactness of the structure and small volume performance of the fixed-focus optical system 100.

[0069] In another embodiment of the present invention, the diameter of the first lens 1 is D, wherein D1<10 mm. This arrangement can prevent the aperture of the fixed-focus optical system 100 from being too large, and meet the installation space requirements of the final product.

[0070] In addition, in one embodiment of the present invention, the aperture value of the fixed-focus optical lens is F, wherein F≤2.8. This configuration enables the fixed-focus optical system 100 to have a large light flux, thereby enabling the fixed-focus optical system 100 to have excellent picture brightness, thereby further improving the imaging quality of the fixed-focus optical system 100.

[0071] It can be understood that the present invention does not limit the specific value of the aperture value F of the fixed-focus optical system 100. In the embodiment of the present invention, the aperture value F of the fixed-focus optical system 100 can be set to any value within a range. The present invention does not limit this. In actual setting, it can be selected according to needs.

[0072] It should also be noted that, in another embodiment of the present invention, the height of the image plane is φ, φ≤10.3mm. With such a setting, in conjunction with the large aperture value of the fixed-focus optical lens, the fixed-focus optical system 100 can also form a clear image in weak light, and through the combination of different lenses and the reasonable allocation of optical power, it has good performances such as a large viewing angle, high pixels, and very good heat elimination, with a wider field of view and more complete data information.

[0073] In order to enable the fixed-focus optical system 100 to adjust the light flux according to actual conditions, in one embodiment of the present invention, the fixed-focus optical system 100 further includes an aperture 8, and the aperture 8 is disposed between the third lens 3 and the fourth lens 4. The aperture 8 limits the aperture of the light beam on the optical axis, intercepts part of the light, thereby reducing the light spot and improving the image contrast, thereby improving the imaging quality of the fixed-focus optical system 100.

[0074] At the same time, since the aperture 8 is arranged on the side of the cemented lens formed by the fourth lens 4 and the fifth lens 5 facing the object side, the chromatic aberration of the fixed-focus optical system 100 can be better corrected and the volume of the fixed-focus optical system 100 can be compressed.

[0075] It is also necessary to further explain that the fixed-focus optical system 100 further includes a photosensitive chip 9 and a filter 10, wherein the photosensitive chip 9 is arranged at intervals on the image side of the seventh lens 7, an end surface of the photosensitive chip 9 facing the object side is the image surface, and the filter 10 is arranged between the seventh lens 7 and the photosensitive chip 9. The setting of the filter 10 can filter out stray light while protecting the photosensitive chip 9, thereby further improving the imaging quality.

[0076] In a specific embodiment of the present invention, the object-side surface of the first lens 1 is S1, and the image-side surface is S2; the object-side surface of the second lens 2 is S3, and the image-side surface is S4; the object-side surface of the third lens 3 is S5, and the image-side surface is S6; the object-side surface of the fourth lens 4 is S8, and the image-side surface is S9; the object-side surface of the fifth lens 5 is S9, and the image-side surface is S10; the object-side surface of the sixth lens 6 is S11, and the image-side surface is S12; the object-side surface of the seventh lens 7 is S13, and the image-side surface is S14.

[0077] In this embodiment, the fixed-focus optical system 100 has a focal length f=3.89 mm, an aperture value F=2.8, an image plane diameter of 10.3 mm, and a diagonal field angle of 155°.

[0078] It should be noted that, in this embodiment, the basic parameter table of the lens surface type, curvature radius, thickness, refractive index, dispersion coefficient and semi-diameter of the fixed-focus optical system 100 is shown in Table 1:

[0079] Table 1

[0080] Surface number Surface type (mm) Curvature radius (mm) Thickness(mm) Refractive Index Dispersion coefficient Semi-diameter(mm) 1 Spherical 24.540 0.400 1.59 68.3 4.325 2 Spherical 3.073 2.263 2.689 3 Aspheric -6.726 0.882 1.66 20.4 2.583 4 Aspheric -12.526 0.075 2.433 5 Spherical 3.997 1.829 1.91 35.3 3.000 6 Spherical 21.687 0.692 2.400 STO Spherical inf -0.023 0.960 8 Aspheric 5.719 1.122 1.54 55.6 1.032 9 Aspheric -2.857 0.651 1.66 20.4 1.329 10 Aspheric -17.773 0.792 1.737 11 Aspheric 5.851 1.026 1.54 55.6 2.468 12 Aspheric 16.746 0.577 2.871 13 Aspheric 4.623 1.191 1.54 55.6 2.994 14 Aspheric 2.857 1.203 4.185 15 Spherical inf 0.500 1.52 64.2 4.912 16 Spherical inf 0.100 5.092 17 Spherical inf - - - -

[0081] It can be understood that, in this embodiment, the first lens 1 and the third lens 3 are glass spherical lenses. With such an arrangement, the use of spherical lenses reduces costs while ensuring image quality and reliability, has low assembly sensitivity, and improves the yield of finished products.

[0082] Correspondingly, in this embodiment, the second lens 2, the fourth lens 4, the fifth lens 5, the sixth lens 6 and the seventh lens 7 are plastic aspherical lenses. The characteristics of aspherical lenses are: the curvature changes continuously from the center of the lens to the periphery of the lens. Different from a spherical lens with a constant curvature from the center of the lens to the periphery of the lens, the aspherical lens has a better curvature radius characteristic, and has the advantages of improving distortion aberration and improving astigmatism aberration. After adopting the aspherical lens, the aberration occurring during imaging can be eliminated as much as possible, thereby improving the imaging quality of the lens.

[0083] It should be noted that, in this embodiment, the object side surface of the sixth lens 6 is a convex surface, and the image side surface is a plane surface. However, since the sixth lens 6 is an aspheric lens, according to the definition of an aspheric lens, in this embodiment, the curvature radius of the second lens 22 can be a positive value. The same is true for the seventh lens 7.

[0084] Further, in this embodiment, the aspheric surface shape of the aspheric lens satisfies the following conditions:

[0085]

[0086] Among them, z represents the axial vector height of the aspheric surface in the Z direction; y represents the height of the aspheric surface; c represents the curvature of the fitted sphere, which is the inverse of the radius of curvature; k represents the cone coefficient; the 4th-order term, 6th-order term, 8th-order term, 10th-order term, 12th-order term, 14th-order term, and 16th-order term represent the higher-order aspheric coefficients, respectively.

[0087] In this embodiment, the high-order coefficients of each aspherical mirror surface can be seen from the following Table 2:

[0088] Table 2

[0089] Surface number K 4th-order term 6th order term 8th order term 10th order term 12th order term 14th order term 16th order term 3 -0.644 -1.28E-03 3.82E-04 -1.76E-05 -3.44E-06 1.02E-07 5.18E-08 -4.08E-09 4 0.806 -3.83E-04 4.68E-04 -5.93E-05 1.80E-06 4.58E-07 -1.14E-07 8.29E-09 8 -0.531 -5.02E-03 7.37E-03 -1.64E-02 1.52E-02 -5.06E-03 -1.94E-04 0.00E+00 9 -0.745 -1.72E-02 4.91E-03 5.80E-04 -2.86E-03 2.01E-04 2.31E-04 0.00E+00 10 21.821 -6.75E-03 3.10E-03 -1.15E-03 1.99E-04 -2.29E-05 2.08E-07 0.00E+00 11 1.489 -3.83E-03 -8.36E-04 -1.04E-04 3.68E-05 -4.93E-06 1.43E-07 -3.28E-09 12 30.447 4.35E-03 -1.33E-03 8.65E-06 2.15E-06 -2.20E-07 -3.71E-08 2.60E-09 13 -1.297 -2.44E-02 2.33E-03 -1.51E-04 -3.10E-06 5.64E-08 3.91E-08 -2.43E-09 14 -4.294 -1.17E-02 1.13E-03 -6.92E-05 6.59E-07 8.32E-08 -6.59E-10 -8.48E-11

[0090] With this setting, by reasonably allocating the lens power, adjusting the glass shape and material combination, effectively eliminating chromatic aberration and secondary spectrum, the spherical aberration, coma, astigmatism, etc. on each lens compensate and cancel each other out, so as to achieve a clear imaging effect and realize the optimal correction of high-order aberrations and chromatic aberrations.

[0091] In addition, in this embodiment, the spherical aberration curve of the fixed-focus optical system 100 is as follows: Figure 2 As shown; the vertical axis chromatic aberration curve of the fixed-focus optical system 100 is as shown Figure 3 As shown; the light aberration curve of the fixed-focus optical system 100 is as shown Figure 4 As shown; the field curvature distortion of the fixed-focus optical system 100 is as shown Figure 5 shown.

[0092] It should be noted that Table 2 is a design value of the aspheric coefficient of the lens in the fixed-focus optical system 100 described in this embodiment. The specific numerical value of the aspheric coefficient design value can be adjusted according to product requirements, and the present invention does not limit this.

[0093] The 20°C MTF curve of the fixed-focus optical system 100 in this embodiment is as follows: Figure 6 As shown; the -40°C MTF curve of the fixed-focus optical system 100 is as shown Figure 7 As shown; the 90°C MTF curve of the fixed-focus optical system 100 is as shown Figure 8As shown, in this embodiment, it is determined that the fixed-focus optical system 100 can adapt to large temperature differences without being out of focus.

[0094] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A fixed-focus optical system, characterized in that: The fixed-focus optical system has an object side and an image side that are oppositely arranged in 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 that are arranged in sequence from the object side to the image side. 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. The fixed-focus optical system satisfies the following conditions: -8 mm < f1 < -5 mm; and -30 mm < f2 < -20 mm; and 4 mm < f3 < 7 mm; and 3 mm < f4 < 6 mm; and -9 mm < f5 < -4 mm; and 10 mm < f6 < 25 mm; and -25 mm < f7 < -12 mm; Among them, the first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are plastic aspherical lenses.

2. The fixed-focus optical system according to claim 1, wherein: The refractive index of the first lens is n1, 1.50 ≤ n1 ≤ 1.75; The refractive index of the second lens is n2, 1.60 ≤ n2 ≤ 1.70; The refractive index of the third lens is n3, 1.75 ≤ n3 ≤ 1.95; The refractive index of the fourth lens is n4, 1.50 ≤ n4 ≤ 1.60; The refractive index of the fifth lens is n5, 1.60 ≤ n5 ≤ 1.70; The refractive index of the sixth lens is n6, 1.50 ≤ n6 ≤ 1.60; The refractive index of the seventh lens is n7, 1.50 ≤ n7 ≤ 1.

68.

3. The fixed-focus optical system according to claim 1, wherein: The Abbe number of the first lens is v1, 50.0 ≤ v1 ≤ 70.0; The Abbe number of the second lens is v2, 18.0 ≤ v2 ≤ 26.0; The Abbe number of the third lens is v3, 30.0 ≤ v3 ≤ 50.0; The Abbe number of the fourth lens is v4, 50.0 ≤ v4 ≤ 70.0; The Abbe number of the fifth lens is v5, 18.0 ≤ v5 ≤ 26.0; The Abbe number of the sixth lens is v6, 50.0 ≤ v6 ≤ 70.0; The Abbe number of the seventh lens is v7, 50.0 ≤ v7 ≤ 70.

0.

4. The fixed-focus optical system according to claim 1, wherein: 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 concave; 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 convex; 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 flat; The optical power of the seventh lens is negative; Among them, the fourth lens and the fifth lens are adhesively connected.

5. The fixed-focus optical system according to claim 1, wherein: The distance between the vertex of the object side surface of the first lens and the image plane is TTL, and the effective focal length of the fixed-focus optical system is EFL, wherein TTL≤13.5 mm; and TTL / EFL≤3.

42.

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

8.

7. The fixed-focus optical system according to claim 1, wherein: The diameter of the first lens is D, wherein D1<10 mm.

8. The fixed-focus optical system according to claim 1, wherein: The height of the image plane is φ, φ≤10.3 mm.

9. The fixed-focus optical system according to claim 1, wherein: The fixed-focus optical system further includes a stop, and the stop is disposed between the third lens and the fourth lens.

10. The fixed-focus optical system according to claim 1, wherein: The fixed-focus optical system further comprises: A photosensitive chip is arranged at intervals on the image side of the seventh lens, and one end surface of the photosensitive chip facing the object side is the image surface; and The filter is arranged between the seventh lens and the photosensitive chip.

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