Prime lens

Abstract

The utility model discloses a prime lens, which relates to the technical field of optical lenses, is provided with an object side and an image side which are oppositely arranged along the direction of an optical axis, and comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are sequentially arranged along the optical axis from the object side to the image side, 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 negative, the focal power of the fourth lens is positive, the focal power of the fifth lens is positive, and the focal power of the eighth lens is positive. Wherein the fifth lens, the sixth lens and the seventh lens are bonded into a whole to form a glued lens group, or the sixth lens and the seventh lens are bonded into a whole to form a glued lens group; the cemented lens group is arranged in the prime lens to correct the chromatic aberration of the lens, so that the infrared confocal effect is better realized, the compact athermalization is realized through the matching of the focal powers of the lenses, and the virtual focus is avoided within the temperature difference range of-30 DEG C to 85 DEG C.

Description

Technical Field

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

[0002] With the continuous progress and development of science and technology, in recent years, optical imaging lenses have also developed rapidly, and people's requirements for optical imaging lenses have become higher and higher. Among them, day-night confocal has become a basic characteristic that most lenses need to possess. However, the existing day-night confocal lenses generally have the following defects: the infrared center defocus amount is relatively large, and the night vision imaging effect is poor; the defocus amount is relatively large under high and low temperature conditions, and the imaging quality drops significantly.

[0003] Therefore, how to achieve infrared confocal and not defocus in an environment with a relatively high temperature difference is an urgent problem to be solved by those skilled in the art. Summary of the Utility Model

[0004] The main purpose of the utility model is to propose a fixed-focus lens, aiming to achieve infrared confocal and not defocus within a temperature difference range of -30°C to 85°C.

[0005] To achieve the above purpose, the fixed-focus lens proposed by the utility model has an object side and an image side that are oppositely arranged along the optical axis. The fixed-focus lens includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens that are sequentially arranged along the optical axis from the object side to the image side. The optical power of the first lens is negative, the optical power of the second lens is negative, the optical power of the third lens is negative, the optical power of the fourth lens is positive, the optical power of the fifth lens is positive, and the optical power of the eighth lens is positive; wherein, the fifth lens, the sixth lens, and the seventh lens are bonded together to form a cemented lens group, or, the sixth lens and the seventh lens are bonded together to form a cemented lens group.

[0006] In one embodiment, the object side of the first lens is convex, and the image side is concave. The focal length of the first lens is f1, and f1 satisfies: -15 mm < f1 < -8 mm; the object side of the second lens is convex, and the image side is concave. The focal length of the second lens is f2, and f2 satisfies: -12 mm < f2 < -6 mm; the object side of the third lens is concave, and the image side is convex. The focal length of the third lens is f3, and f3 satisfies: -18 mm < f3 < -12 mm; the object side of the fourth lens is convex, and the image side is concave. The focal length of the fourth lens is f4, and f4 satisfies: 5 mm < f4 < 10 mm; the object side of the fifth lens is convex, and the image side is convex. The focal length of the fifth lens is f5, and f5 satisfies: 3 mm < f5 < 10 mm; the object side of the sixth lens is concave, and the image side is concave. The focal length of the sixth lens is f6, and f6 satisfies: -5 mm < f6 < -1 mm; the object side of the seventh lens is convex, and the image side is convex. The focal length of the seventh lens is f7, and f7 satisfies: 4 mm < f7 < 10 mm; the object side of the eighth lens is convex, and the image side is convex. The focal length of the eighth lens is f8, and f8 satisfies: 8 mm < f8 < 15 mm; wherein, the fifth lens, the sixth lens and the seventh lens form a cemented lens group.

[0007] In one embodiment, the refractive index n1 and the dispersion coefficient v1 of the first lens satisfy: 1.50 ≤ n1 ≤ 1.70; 55.0 ≤ v1 ≤ 75.0; the refractive index n2 and the dispersion coefficient v2 of the second lens satisfy: 1.50 ≤ n2 ≤ 1.60; 50.0 ≤ v2 ≤ 70.0; the refractive index n3 and the dispersion coefficient v3 of the third lens satisfy: 1.60 ≤ n3 ≤ 1.70; 18.0 ≤ v3 ≤ 26.0; the refractive index n4 and the dispersion coefficient v4 of the fourth lens satisfy: 1.60 ≤ n4 ≤ 1.9; 20.0 ≤ v4 ≤ 35.0; the refractive index n5 and the dispersion coefficient v5 of the fifth lens satisfy: 1.50 ≤ n5 ≤ 1.70; 60.0 ≤ v5 ≤ 90.0; the refractive index n6 and the dispersion coefficient v6 of the sixth lens satisfy: 1.70 ≤ n6 ≤ 1.95; 25.0 ≤ v6 ≤ 35.0; the refractive index n7 and the dispersion coefficient v7 of the seventh lens satisfy: 1.50 ≤ n7 ≤ 1.70; 60.0 ≤ v7 ≤ 90.0; the refractive index n8 and the dispersion coefficient v8 of the eighth lens satisfy: 1.50 ≤ n8 ≤ 1.60; 50.0 ≤ v8 ≤ 70.0.

[0008] In one embodiment, the object side of the first lens is convex and the image side is concave. The focal length of the first lens is f1, and f1 satisfies: -20 mm < f1 < -10 mm; the object side of the second lens is convex and the image side is concave. The focal length of the second lens is f2, and f2 satisfies: -15 mm < f2 < -6 mm; the object side of the third lens is concave and the image side is convex. The focal length of the third lens is f3, and f3 satisfies: -25 mm < f3 < -10 mm; the object side of the fourth lens is convex and the image side is convex. The focal length of the fourth lens is f4, and f4 satisfies: 5 mm < f4 < 10 mm; the object side of the fifth lens is concave and the image side is convex. The focal length of the fifth lens is f5, and f5 satisfies: 8 mm < f5 < 15 mm; the object side of the sixth lens is convex and the image side is convex. The focal length of the sixth lens is f6, and f6 satisfies: 4 mm < f6 < 50 mm; the object side of the seventh lens is concave and the image side is concave. The focal length of the seventh lens is f7, and f7 satisfies: -10 mm < f7 < -3 mm; the object side of the eighth lens is convex and the image side is convex. The focal length of the eighth lens is f8, and f8 satisfies: 5 mm < f8 < 15 mm; wherein, the sixth lens and the seventh lens form a cemented lens group.

[0009] In one embodiment, the refractive index n1 and the dispersion coefficient v1 of the first lens satisfy: 1.60 ≤ n1 ≤ 1.80; 50.0 ≤ v1 ≤ 75.0; the refractive index n2 and the dispersion coefficient v2 of the second lens satisfy: 1.50 ≤ n2 ≤ 1.60; 50.0 ≤ v2 ≤ 70.0; the refractive index n3 and the dispersion coefficient v3 of the third lens satisfy: 1.60 ≤ n3 ≤ 1.70; 18.0 ≤ v3 ≤ 26.0; the refractive index n4 and the dispersion coefficient v4 of the fourth lens satisfy: 1.75 ≤ n4 ≤ 2.00; 16.0 ≤ v4 ≤ 35.0; the refractive index n5 and the dispersion coefficient v5 of the fifth lens satisfy: 1.50 ≤ n5 ≤ 1.70; 55.0 ≤ v5 ≤ 90.0; the refractive index n6 and the dispersion coefficient v6 of the sixth lens satisfy: 1.45 ≤ n6 ≤ 1.70; 50.0 ≤ v6 ≤ 90.0; the refractive index n7 and the dispersion coefficient v7 of the seventh lens satisfy: 1.60 ≤ n7 ≤ 1.95; 18.0 ≤ v7 ≤ 35.0; the refractive index n8 and the dispersion coefficient v8 of the eighth lens satisfy: 1.50 ≤ n8 ≤ 1.60; 50.0 ≤ v8 ≤ 70.0.

[0010] In one embodiment, a diaphragm is disposed between the fourth lens and the fifth lens. The diameter d of the diaphragm satisfies: 1.8 ≤ EFL / d ≤ 2.2; wherein, EFL is the effective focal length of the fixed-focus lens.

[0011] In one embodiment, at least one of the fourth lens and the fifth lens is a glass aspherical lens.

[0012] In one embodiment, an image sensor chip is disposed on the image plane side of the eighth lens and is opposite to the eighth lens. The image sensor chip has an imaging plane close to the eighth lens. The distance between the vertex on the object plane side of the first lens and the imaging plane is TTL, and the effective focal length of the fixed-focus lens is EFL. TTL and EFL satisfy: TTL / EFL ≤ 7.6.

[0013] In one embodiment, the diameter IC of the imaging plane satisfies: IC ≤ 9.0 mm.

[0014] In one embodiment, the diameter D1 of the first lens satisfies: D1 < 15 mm.

[0015] The technical solution of the present utility model corrects the chromatic aberration of the lens by providing a cemented lens group in the fixed-focus lens, thereby realizing infrared confocal, and realizes compact athermalization through the cooperation of the optical powers of each lens, and does not defocus within the temperature difference range of -30°C to 85°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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 the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present utility model. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0017] Figure 1 FIG. 1 is a schematic structural diagram of the first embodiment of the fixed-focus lens provided by the present utility model;

[0018] Figure 2 For Figure 1 the schematic diagram of the vertical chromatic aberration curve;

[0019] Figure 3 For Figure 1 the schematic diagram of the ray aberration curve;

[0020] Figure 4 For Figure 1 the schematic diagram of the field curvature and distortion;

[0021] Figure 5 For Figure 1 the MTF graph at 20°C;

[0022] Figure 6 For Figure 1 the 20°C visible Through focus MTF graph;

[0023] Figure 7 For Figure 1 the 20°C infrared Through focus MTF graph;

[0024] Figure 8 is Figure 1 the -30°C visible Through focus MTF graph;

[0025] Figure 9 is Figure 1 the 85°C visible Through focus MTF graph;

[0026] Figure 10 is the structural schematic diagram of the second embodiment of the fixed-focus lens provided by the present utility model;

[0027] Figure 11 is Figure 10 the schematic diagram of the lateral chromatic aberration curve;

[0028] Figure 12 is Figure 10 the schematic diagram of the ray aberration curve;

[0029] Figure 13 is Figure 10 the schematic diagram of the field curvature and distortion;

[0030] Figure 14 is Figure 10 the MTF graph at 20°C;

[0031] Figure 15 is Figure 10 the 20°C visible Through focus MTF graph;

[0032] Figure 16 is Figure 10 the 20°C infrared Through focus MTF graph;

[0033] Figure 17 is Figure 10 the -30°C visible Through focus MTF graph;

[0034] Figure 18 is Figure 10 the 85°C visible Through focus MTF graph.

[0035] Explanation of the reference numerals in the drawings:

[0036] 100, fixed-focus lens; L1, first lens; L2, second lens; L3, third lens; L4, fourth lens; STO, aperture stop; L5, fifth lens; L6, sixth lens; L7, seventh lens; L8, eighth lens; L9, filter; L10, protective glass; L11, photosensitive chip;

[0037] S1, the object side of the first lens; S2, the image side of the first lens; S3, the object side of the second lens; S4, the image side of the second lens; S5, the object side of the third lens; S6, the image side of the third lens; S7, the object side of the fourth lens; S8, the image side of the fourth lens; S10, the object side of the fifth lens; S11, the image side of the fifth lens; S12, the object side of the sixth lens; S13, the image side of the sixth lens; S14, the object side of the seventh lens; S15, the image side of the seventh lens; S16, the object side of the eighth lens; S17, the image side of the eighth lens; S18, the object side of the filter; S19, the image side of the filter; S20, the object side of the protective glass; S21, the image side of the protective glass; S22, the imaging surface.

[0038] The realization, functional features and advantages of the purpose of the present utility model will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific embodiments

[0039] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with 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. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0040] 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 position relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0041] In addition, if there are descriptions such as "first" and "second" involved in the embodiments of the present utility model, the descriptions of "first" and "second" 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 various 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 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 protection scope required by the present utility model.

[0042] With the continuous progress and development of science and technology, in recent years, optical imaging lenses have also developed rapidly, and people's requirements for optical imaging lenses have become increasingly high. Among them, day-night confocal has become a basic characteristic that most lenses need to possess. The existing day-night confocal lenses generally have the following defects: the incident angle of light with a large target surface and a large field of view is large, resulting in poor imaging quality at the edge; the infrared center defocus amount is relatively large, and the night vision imaging effect is poor; the defocus amount is relatively large under high and low temperature conditions, and the imaging quality drops significantly.

[0043] In view of this, the present utility model proposes a fixed-focus lens, with a clarity reaching the 4K pixel level, capable of infrared confocal at the same time and not defocusing within the temperature difference range of -30°C to 85°C, a wide-angle lens with stable operation and wide applicability. Please refer to Figures 1 to 18 , the attached drawings show the specific embodiments of the fixed-focus lens.

[0044] Among them, Figures 1 to 9 is the first embodiment of the fixed-focus lens provided by the present utility model, Figures 10 to 18 is the second embodiment of the fixed-focus lens provided by the present utility model.

[0045] Embodiment 1

[0046] In the first embodiment of the present utility model, please refer to Figure 1 , the fixed-focus lens 100 has an object side and an image side that are oppositely arranged along the optical axis direction. The fixed-focus lens 100 includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 that are sequentially arranged along the optical axis from the object side to the image side. The optical power of the first lens L1 is negative, the optical power of the second lens L2 is negative, the optical power of the third lens L3 is negative, the optical power of the fourth lens L4 is positive, the optical power of the fifth lens L5 is positive, and the optical power of the eighth lens L8 is positive; among them, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are bonded together to form a cemented lens group.

[0047] The technical solution of the present utility model corrects chromatic aberration by adopting a cemented lens group in the fixed-focus lens 100, thereby realizing infrared confocal, and realizes athermalization through the cooperation of each lens, and does not defocus within the temperature difference range of -30°C to 85°C.

[0048] In the first embodiment of the present utility model, the object side of the first lens L1 is convex, and the image side is concave. The focal length of the first lens L1 is f1, and f1 satisfies: -15 mm < f1 < -8 mm; the object side of the second lens L2 is convex, and the image side is concave. The focal length of the second lens L2 is f2, and f2 satisfies: -12 mm < f2 < -6 mm; the object side of the third lens L3 is concave, and the image side is convex. The focal length of the third lens L3 is f3, and f3 satisfies: -18 mm < f3 < -12 mm; the object side of the fourth lens L4 is convex, and the image side is concave. The focal length of the fourth lens L4 is f4, and f4 satisfies: 5 mm < f4 < 10 mm; the object side of the fifth lens L5 is convex, and the image side is convex. The focal length of the fifth lens L5 is f5, and f5 satisfies: 3 mm < f5 < 10 mm; the object side of the sixth lens L6 is concave, and the image side is concave. The focal length of the sixth lens L6 is f6, and f6 satisfies: -5 mm < f6 < -1 mm; the object side of the seventh lens L7 is convex, and the image side is convex. The focal length of the seventh lens L7 is f7, and f7 satisfies: 4 mm < f7 < 10 mm; the object side of the eighth lens L8 is convex, and the image side is convex. The focal length of the eighth lens L8 is f8, and f8 satisfies: 8 mm < f8 < 15 mm; wherein, the fifth lens L5, the sixth lens L6 and the seventh lens L7 form a cemented lens group. With such a setting, through the first lens L1 with negative optical power, it is beneficial to collect light rays, and can effectively increase the field of view range; by setting the fourth lens L4 with positive optical power, it undertakes a large optical power of the system, changes the propagation direction of the light beam, and is more conducive to the imaging of the light beam. By comprehensively setting the optical power and the matching relationship of the shapes of each lens, athermalization can be achieved. By setting a doublet lens group, chromatic aberration can be minimized or eliminated to improve the image quality and reduce the reflection loss of light energy, thereby improving the imaging clarity. Through the setting of the optical power of each lens, a wide-angle 4K lens group is formed, with a wider field of view, and can well control the light ray trend. While introducing more light rays, the structure is made more compact, and the total length of the fixed-focus lens 100 can be controlled within 25 mm.

[0049] In the first embodiment of the present utility model, the refractive index n1 and the dispersion coefficient v1 of the first lens L1 satisfy: 1.50 ≤ n1 ≤ 1.70; 55.0 ≤ v1 ≤ 75.0; the refractive index n2 and the dispersion coefficient v2 of the second lens L2 satisfy: 1.50 ≤ n2 ≤ 1.60; 50.0 ≤ v2 ≤ 70.0; the refractive index n3 and the dispersion coefficient v3 of the third lens L3 satisfy: 1.60 ≤ n3 ≤ 1.70; 18.0 ≤ v3 ≤ 26.0; the refractive index n4 and the dispersion coefficient v4 of the fourth lens L4 satisfy: 1.60 ≤ n4 ≤ 1.9; 20.0 ≤ v4 ≤ 35.0; the refractive index n5 and the dispersion coefficient v5 of the fifth lens L5 satisfy: 1.50 ≤ n5 ≤ 1.70; 60.0 ≤ v5 ≤ 90.0; the refractive index n6 and the dispersion coefficient v6 of the sixth lens L6 satisfy: 1.70 ≤ n6 ≤ 1.95; 25.0 ≤ v6 ≤ 35.0; the refractive index n7 and the dispersion coefficient v7 of the seventh lens L7 satisfy: 1.50 ≤ n7 ≤ 1.70; 60.0 ≤ v7 ≤ 90.0; the refractive index n8 and the dispersion coefficient v8 of the eighth lens L8 satisfy: 1.50 ≤ n8 ≤ 1.60; 50.0 ≤ v8 ≤ 70.0. By optimizing the combination of the refractive indices and dispersion coefficients of each lens, it has the effect of achromatism to achieve infrared confocal, and is also beneficial to the athermalization of the fixed-focus lens 100.

[0050] In the first embodiment of the present utility model, a stop STO is provided between the fourth lens L4 and the fifth lens L5. The diameter d of the stop STO satisfies: 1.8 ≤ EFL / d ≤ 2.2; where EFL is the effective focal length of the fixed-focus lens 100. With such a setting, it has a higher light transmittance, allowing more light to enter. The fixed-focus lens 100 can also clearly image in low light, making the field of view of the fixed-focus lens 100 wider while obtaining more sufficient data information.

[0051] In the first embodiment of the present utility model, the fourth lens L4 is a glass aspherical lens. The lens pair near the stop STO is more sensitive to temperature changes. Therefore, the lens close to the stop STO is set as a glass aspherical lens. The lens made of glass material has a smaller thermal expansion coefficient, making the imaging less affected by temperature changes. At the same time, the glass aspherical lens can more directly affect the light with a large incident angle and can more effectively correct the aberration generated therefrom.

[0052] In the first embodiment of the present utility model, the eighth lens L8 is a plastic aspherical lens. The eighth lens L8 is not very sensitive to temperature changes. Using a plastic aspherical lens can better correct the field curvature and improve the performance.

[0053] Further, the first lens L1 is a glass spherical lens, the second lens L2 is a plastic aspherical lens, and the third lens L3 is a plastic aspherical lens. By setting the first lens L1 as a glass spherical lens, it has strong anti-corrosion and scratch-resistant capabilities and can achieve a smaller head size, reducing the volume of the fixed-focus lens 100.

[0054] Further, the fifth lens L5, the sixth lens L6, and the seventh lens L7 in the cemented lens group are all spherical lenses, and are made by cementing at least two different types of optical glass with an optical adhesive, such as crown glass, flint glass, crown glass, or other special materials. In this embodiment, by reasonably arranging the aspherical lenses, various aberrations are corrected, improving the edge image quality and achieving high imaging quality.

[0055] In the first embodiment of the present utility model, a photosensitive chip L11 opposite to the eighth lens L8 is provided on the image plane side of the eighth lens L8. The photosensitive chip L11 has an imaging plane close to the eighth lens L8. The distance between the vertex of the object plane side of the first lens L1 and the imaging plane is TTL, and TTL and EFL satisfy: TTL / EFL ≤ 7.6. With this setting, the total length TTL of the fixed-focus lens 100 is shortened, making the lens group lighter and more portable.

[0056] Further, a protective glass L10 and a filter L9 are provided between the eighth lens L8 and the photosensitive chip L11. The protective glass L10 can provide effective protection for the photosensitive chip L11, and the filter L9 can filter out stray light, further improving the imaging quality.

[0057] In the first embodiment of the present utility model, the diameter IC of the imaging plane satisfies: IC ≤ 9.0 mm. With this setting, the smaller diameter of the imaging plane makes the lens group design more compact, helping to reduce the volume and weight of the lens group.

[0058] In the first embodiment of the present utility model, the diameter D1 of the first lens L1 satisfies: D1 < 15 mm. This can prevent the aperture of the lens group from being too large and meet the installation space requirements of the final product.

[0059] Further, in this embodiment, the aspherical surface shape of the aspherical lens satisfies the following conditions:

[0060]

[0061] Among them, Z represents the distance of the curved surface from the vertex of the curved surface in the optical axis direction, c is the curvature of the vertex of the curved surface; y is the distance from the optical axis to the curved surface; k is the conic coefficient (when the k coefficient is less than -1, the surface curve is a hyperbola, when the k coefficient is equal to -1, it is a parabola, when the k coefficient is between -1 and 0, it is an ellipse, when the k coefficient is equal to 0, it is a circle, and when the k coefficient is greater than 0, it is an oblate circle). A, B, C, D, E, F, G respectively represent the aspheric coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, and sixteenth order. Through the above parameters, the shape and size of the aspheric surfaces on the object side and image side of the lens can be set.

[0062] Specifically, in this embodiment, the parameters of the fixed-focus lens are as follows:

[0063] The focal length EFL = 3.32 mm, the aperture value F = 2.0, the image plane diameter is 9.0 mm, and the diagonal field of view angle is 165°.

[0064] Specifically, in the first embodiment, the refractive index, radius of curvature, thickness interval, and other parameters of each lens are as shown in the following table:

[0065] Table 1 Parameters of each lens in Embodiment 1

[0066]

[0067]

[0068] Among them, inf indicates that the radius of curvature of the spherical surface is infinite, indicating that the lens is a flat glass, and S11 / S12 indicates that the image side of the fifth lens is glued to the object side of the sixth lens.

[0069] In an embodiment of the present utility model, the even-order coefficients of each aspheric surface are as shown in Table 2 below:

[0070] Table 2 Conic coefficients and aspheric coefficients corresponding to the aspheric lenses in Embodiment 1

[0071]

[0072]

[0073] In this embodiment, the lateral chromatic aberration, ray aberration, field curvature, and distortion of the fixed-focus lens are respectively as Figure 2 、 Figure 3 、 Figure 4 shown, and the MTF diagram at 20 °C, the 20 °C visible Through focus MTF diagram, the 20 °C infrared Through focus MTF diagram, the -30 °C visible Through focus MTF diagram, and the 85 °C visible Through focus MTF diagram are respectively as Figures 5 to 9 shown.

[0074] Figure 2 Schematic diagram of the lateral chromatic aberration curve for Example 1. From Figure 2 it can be seen that the lateral offset at the focal position does not exceed ±4 μm, and Example 1 can effectively correct chromatic aberration and reduce the occurrence of color fringes.

[0075] Figure 3 Schematic diagram of the ray aberration curve for Example 1, where the abscissa is the normalized pupil coordinate and the ordinate is the ray aberration value, with the unit scale being 4 μm. From Figure 3 it can be seen that for rays with wavelengths of 436 nm, 486 nm, 546 nm, 588 nm, and 656 nm incident within the designed pupil range, the ray aberration of Example 1 does not exceed ±20 μm. Example 1 can well correct aberration in the ray environment with wavelengths from 436 nm to 656 nm and improve the image quality.

[0076] Figure 4 Schematic diagram of the field curvature and distortion for Example 1. From Figure 4 it can be seen that the field curvature values of Example 1 are all within the range of ±0.03 mm, and both the field curvature and astigmatism are well corrected; the distortion is within 8%, and the distortion is well corrected.

[0077] Figure 5 MTF diagram at 20 °C for Example 1. When the spatial frequency of Example 1 is 0 - 80 lp / mm, its MTF is greater than 0.5. Example 1 can well maintain the contrast of details and has very excellent imaging performance.

[0078] Figures 6 to 9 They are respectively the 20 °C visible Through focus MTF, 20 °C infrared Through focus MTF diagram, -30 °C visible Through focus MTF diagram, and 85 °C visible Through focus MTF diagram. Example 1 has a high concentration and a low defocus amount within the temperature range of -30 °C to 85 °C and does not defocus within a large temperature difference range.

[0079] In summary, compared with the prior art, this embodiment adopts a glass - plastic hybrid structure, makes full use of the aspherical surface to reduce the volume of the optical system, and bonds the lenses to correct chromatic aberration; at the same time, by reasonably matching the lens materials, it can work stably at high and low temperatures, has a large angle, a horizontal field of view of more than 130°, high imaging quality, a large target surface, and the image surface height can reach and CRA ≤ 12° can match multiple SENSORS, with broad application prospects.

[0080] Example 2

[0081] In the second embodiment of the present utility model, please refer to Figure 10 , the fixed-focus lens 100 has an object side and an image side oppositely arranged along the optical axis direction. The fixed-focus lens 100 includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 arranged in sequence from the object side to the image side along the optical axis. The optical power of the first lens L1 is negative, the optical power of the second lens L2 is negative, the optical power of the third lens L3 is negative, the optical power of the fourth lens L4 is positive, the optical power of the fifth lens L5 is positive, and the optical power of the eighth lens L8 is positive; wherein, the sixth lens L6 and the seventh lens L7 form a cemented lens group.

[0082] The technical solution of the present utility model corrects chromatic aberration by adopting a cemented lens group in the fixed-focus lens 100, thereby realizing infrared confocal, and realizes athermalization through the cooperation of each lens, and does not defocus within the temperature difference range of -30°C to 85°C.

[0083] In the second embodiment of the present utility model, please refer to Figure 10, the object side of the first lens L1 is convex and the image side is concave. The focal length of the first lens L1 is f1, and f1 satisfies: -20mm < f1 < -10mm; the object side of the second lens L2 is convex and the image side is concave. The focal length of the second lens L2 is f2, and f2 satisfies: -15mm < f2 < -6mm; the object side of the third lens L3 is concave and the image side is convex. The focal length of the third lens L3 is f3, and f3 satisfies: -25mm < f3 < -10mm; the object side of the fourth lens L4 is convex and the image side is convex. The focal length of the fourth lens L4 is f4, and f4 satisfies: 5mm < f4 < 10mm; the object side of the fifth lens L5 is concave and the image side is convex. The focal length of the fifth lens L5 is f5, and f5 satisfies: 8mm < f5 < 15mm; the object side of the sixth lens L6 is convex and the image side is convex. The focal length of the sixth lens L6 is f6, and f6 satisfies: 4mm < f6 < 50mm; the object side of the seventh lens L7 is concave and the image side is concave. The focal length of the seventh lens L7 is f7, and f7 satisfies: -10mm < f7 < -3mm; the object side of the eighth lens L8 is convex and the image side is convex. The focal length of the eighth lens L8 is f8, and f8 satisfies: 5mm < f8 < 15mm; among them, the sixth lens L6 and the seventh lens L7 form a cemented lens group. With such a setting, through the first lens L1 with negative optical power, it is beneficial to collect light rays and can effectively increase the field of view; by setting the fourth lens L4 with positive optical power, it undertakes a large optical power of the system, changes the propagation direction of the light beam, and is more conducive to the imaging of the light beam. By comprehensively setting the optical power and the matching relationship of the shapes of each lens, athermalization can be achieved. A double cemented lens group is set to minimize or eliminate chromatic aberration to the greatest extent, improve the image quality, reduce the reflection loss of light energy, thereby improving the imaging clarity. Through the setting of the optical power of each lens, a wide-angle 4K lens group is formed, with a wider field of view, and can well control the light ray trend. While introducing more light rays, the structure is made more compact, and the total length of the fixed-focus lens 100 can be controlled within 25mm.

[0084] In the second embodiment of the present utility model, the refractive index n1 and the dispersion coefficient v1 of the first lens L1 satisfy: 1.60 ≤ n1 ≤ 1.80; 50.0 ≤ v1 ≤ 75.0; the refractive index n2 and the dispersion coefficient v2 of the second lens L2 satisfy: 1.50 ≤ n2 ≤ 1.60; 50.0 ≤ v2 ≤ 70.0; the refractive index n3 and the dispersion coefficient v3 of the third lens L3 satisfy: 1.60 ≤ n3 ≤ 1.70; 18.0 ≤ v3 ≤ 26.0; the refractive index n4 and the dispersion coefficient v4 of the fourth lens L4 satisfy: 1.75 ≤ n4 ≤ 2.00; 16.0 ≤ v4 ≤ 35.0; the refractive index n5 and the dispersion coefficient v5 of the fifth lens L5 satisfy: 1.50 ≤ n5 ≤ 1.70; 55.0 ≤ v5 ≤ 90.0; the refractive index n6 and the dispersion coefficient v6 of the sixth lens L6 satisfy: 1.45 ≤ n6 ≤ 1.70; 50.0 ≤ v6 ≤ 90.0; the refractive index n7 and the dispersion coefficient v7 of the seventh lens L7 satisfy: 1.60 ≤ n7 ≤ 1.95; 18.0 ≤ v7 ≤ 35.0; the refractive index n8 and the dispersion coefficient v8 of the eighth lens L8 satisfy: 1.50 ≤ n8 ≤ 1.60; 50.0 ≤ v8 ≤ 70.0. By optimizing the combination of the refractive index and the dispersion coefficient of each lens, it has the effect of achromatism to achieve infrared confocal, and it is also beneficial to the athermalization of the fixed-focus lens 100.

[0085] In the second embodiment of the present utility model, a stop STO is provided between the fourth lens L4 and the fifth lens L5, and the diameter d of the stop STO satisfies: 1.8 ≤ EFL / d ≤ 2.2; where EFL is the effective focal length of the fixed-focus lens 100. With such a setting, it has a higher light transmittance, allowing more light to enter. The fixed-focus lens 100 can also clearly image in low light, making the field of view of the fixed-focus lens 100 wider while obtaining more sufficient data information.

[0086] In the second embodiment of the present utility model, the fifth lens L5 is a glass aspherical lens. The lens pair near the stop STO is more sensitive to temperature changes. Therefore, the lens close to the stop STO is set as a glass aspherical lens. The lens made of glass has a smaller thermal expansion coefficient, making the imaging less affected by temperature changes. At the same time, the glass aspherical lens can more directly affect the light with a large incident angle and can more effectively correct the aberration generated therefrom.

[0087] In the second embodiment of the present utility model, the eighth lens L8 is a plastic aspherical lens. The eighth lens L8 is not very sensitive to temperature changes. Using a plastic aspherical lens can better correct the field curvature and improve the performance.

[0088] Further, the first lens L1 is a glass spherical lens, the second lens L2 is a plastic aspherical lens, the third lens L3 is a plastic aspherical lens, and the fourth lens L4 is a glass spherical lens. By setting the first lens L1 as a glass spherical lens, it has strong anti-corrosion and scratch-resistant capabilities and can obtain a smaller head size, reducing the volume of the fixed-focus lens 100.

[0089] Further, the sixth lens L6 and the seventh lens L7 in the cemented lens group are both spherical lenses, and are cemented by using two different optical glasses through an optical adhesive, such as crown glass and flint glass. In this embodiment, by reasonably arranging the aspherical lenses, various aberrations are corrected, improving the edge image quality and having high imaging quality.

[0090] In the second embodiment of the present utility model, an image sensor chip L11 opposite to the eighth lens L8 is provided on the image plane side of the eighth lens L8. The image sensor chip L11 has an imaging plane close to the eighth lens L8. The distance between the vertex on the object plane side of the first lens L1 and the imaging plane is TTL, and TTL and EFL satisfy: TTL / EFL ≤ 7.7. With such a setting, the total length TTL of the fixed-focus lens 100 is shortened, making the lens group lighter and more portable.

[0091] Further, a protective glass L10 and a filter L9 are provided between the eighth lens L8 and the image sensor chip L11. The protective glass L10 can provide effective protection for the image sensor chip L11, and the filter L9 can filter out stray light, further improving the imaging quality.

[0092] In the second embodiment of the present utility model, the diameter IC of the imaging plane satisfies: IC ≤ 9.0 mm. With such a setting, the smaller diameter of the imaging plane makes the lens group design more compact, helping to reduce the volume and weight of the lens group.

[0093] In the second embodiment of the present utility model, the diameter D1 of the first lens L1 satisfies: D1 < 15 mm. It can avoid the lens group having too large an aperture and meet the installation space requirements of the final product.

[0094] Further, in this embodiment, the aspherical surface shape of the aspherical lens satisfies the following conditions:

[0095]

[0096] Among them, Z represents the distance of the surface from the vertex of the surface in the optical axis direction, c is the curvature of the vertex of the surface; y is the distance from the optical axis to the surface; k is the conic coefficient (when the k coefficient is less than -1, the surface shape curve is a hyperbola, when the k coefficient is equal to -1, it is a parabola, when the k coefficient is between -1 and 0, it is an ellipse, when the k coefficient is equal to 0, it is a circle, and when the k coefficient is greater than 0, it is an oblate shape). A, B, C, D, E, F, and G respectively represent the aspheric coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, and sixteenth order. Through the above parameters, the shape and size of the aspheric surfaces on the object side and image side of the lens can be set.

[0097] Specifically, in this embodiment, the parameters of the fixed-focus lens are as follows:

[0098] The focal length EFL = 3.32 mm, the aperture value F = 2.0, the image plane diameter = 9.0 mm, and the diagonal field of view angle = 165°.

[0099] Specifically, in the second embodiment, the parameters such as the refractive index, curvature radius, and thickness interval of the lens material are shown in Table 3 below:

[0100] Table 3 Parameters of each lens in the second embodiment

[0101]

[0102] In an embodiment of the present invention, the even-order coefficients of each aspheric surface are shown in Table 4 below:

[0103] Table 4 Conic coefficients and aspheric coefficients corresponding to the aspheric lenses in the second embodiment

[0104]

[0105]

[0106] In this embodiment, the lateral chromatic aberration, ray aberration, field curvature, and distortion of the fixed-focus lens are respectively as Figure 11 、 Figure 12 、 Figure 13 shown, and the MTF diagrams at 20 °C, the 20 °C visible Through focus MTF diagrams, the 20 °C infrared Through focus MTF diagrams, the -30 °C visible Through focus MTF diagrams, and the 85 °C visible Through focus MTF diagrams are respectively as Figures 15 - 18 shown.

[0107] Figure 11 is a schematic diagram of the lateral chromatic aberration curve of the second embodiment. It can be seen from Figure 10 that the lateral offset at the focus position does not exceed ±4 μm, and the second embodiment can effectively correct chromatic aberration and reduce the appearance of colored edges.

[0108] Figure 12 Schematic diagram of the ray aberration curve for the second embodiment. Here, the abscissa is the normalized pupil coordinate, the ordinate is the ray aberration value, and the unit scale is 4 μm. From Figure 11 it can be seen that for rays with wavelengths of 436 nm, 486 nm, 546 nm, 588 nm, and 656 nm incident within the -designed pupil range, the spherical aberration of the second embodiment does not exceed ±20 μm. The second embodiment can well correct the aberration and improve the image quality in the ray environment with wavelengths from 436 nm to 656 nm.

[0109] Figure 13 Schematic diagram of the field curvature and distortion for the second embodiment. From Figure 12 it can be seen that the field curvature values of the second embodiment are all within the range of ±0.05 mm, and both the field curvature and astigmatism are well corrected; the distortion is within 9%, and the distortion is well corrected.

[0110] Figure 14 MTF graph of the second embodiment at 20°C. When the spatial frequency of the second embodiment is 0 - 80 lp / mm, its MTF is greater than 0.5, which can well maintain the contrast of details and has very excellent imaging performance.

[0111] Figures 15 to 18 They are respectively the 20°C visible Through focus MTF graph, the 20°C infrared Through focus MTF graph, the -30°C visible Through focus MTF graph, and the 85°C visible Through focus MTF graph. The second embodiment has a high concentration and a low defocus amount within the temperature range of -30°C to 85°C and does not defocus within a large temperature difference range.

[0112] In summary, compared with the prior art, this embodiment adopts a glass - plastic hybrid structure, makes full use of the aspherical surface to reduce the volume of the optical system, and uses bonded lenses to correct chromatic aberration; at the same time, by reasonably matching the lens materials, it can work stably at high and low temperatures, has a large angle, a horizontal field of view of more than 130°, high imaging quality, a large target surface, and the image surface height can reach and CRA ≤ 12° can match multiple SENSORS, with broad application prospects.

[0113] The above is only an exemplary embodiment of the present utility model, and thus 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 lens, characterized in that: The fixed-focus lens has an object side and an image side which are arranged opposite to each other along the optical axis direction, and comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are arranged in sequence from the object side to the image side along the optical axis, the first lens has a negative optical focal power, the second lens has a negative optical focal power, the third lens has a negative optical focal power, the fourth lens has a positive optical focal power, the fifth lens has a positive optical focal power, and the eighth lens has a positive optical focal power; The fifth lens, the sixth lens and the seventh lens are bonded together to form a bonded lens group, or the sixth lens and the seventh lens are bonded together to form a bonded lens group.

2. The fixed-focus lens according to claim 1, wherein: The object side of the first lens is convex, the image side is concave, the focal length of the first lens is f1, and f1 satisfies: -15mm <f1<-8mm; The object side of the second lens is convex, the image side is concave, the focal length of the second lens is f2, and f2 satisfies: -12mm <f2<-6mm; The object side of the third lens is concave, the image side is convex, the focal length of the third lens is f3, and f3 satisfies: -18mm <f3<-12mm; The object side of the fourth lens is convex, the image side is concave, the focal length of the fourth lens is f4, and f4 satisfies: 5mm <f4<10mm; The object side of the fifth lens is convex, the image side is convex, the focal length of the fifth lens is f5, and f5 satisfies: 3mm <f5<10mm; The object side of the sixth lens is concave, the image side is concave, the focal length of the sixth lens is f6, and f6 satisfies: -5mm <f6<-1mm; The object side of the seventh lens is convex, the image side is convex, the focal length of the seventh lens is f7, and f7 satisfies: 4mm <f7<10mm; The object side of the eighth lens is convex, the image side is convex, the focal length of the eighth lens is f8, and f8 satisfies: 8mm <f8<15mm; Wherein, the fifth lens, the sixth lens and the seventh lens form a cemented lens group.

3. The fixed-focus lens according to claim 2, wherein: The refractive index n1 and the dispersion coefficient v1 of the first lens satisfy: 1.50≤n1≤1.70; 55.0≤v1≤75.0; The refractive index n2 and the dispersion coefficient v2 of the second lens satisfy: 1.50≤n2≤1.60; 50.0≤v2≤70.0; The refractive index n3 and the dispersion coefficient v3 of the third lens satisfy: 1.60≤n3≤1.70; 18.0≤v3≤26.0; The refractive index n4 and the dispersion coefficient v4 of the fourth lens satisfy: 1.60≤n4≤1.9; 20.0≤v4≤35.0; The refractive index n5 and the dispersion coefficient v5 of the fifth lens satisfy: 1.50≤n5≤1.70; 60.0≤v5≤90.0; The refractive index n6 and the dispersion coefficient v6 of the sixth lens satisfy: 1.70≤n6≤1.95; 25.0≤v6≤35.0; The refractive index n7 and the dispersion coefficient v7 of the seventh lens satisfy: 1.50≤n7≤1.70; 60.0≤v7≤90.0; The refractive index n8 and the dispersion coefficient v8 of the eighth lens satisfy: 1.50≤n8≤1.60; 50.0≤v8≤70.

0.

4. The fixed-focus lens according to claim 1, wherein: The object side of the first lens is convex, the image side is concave, the focal length of the first lens is f1, and f1 satisfies: -20mm <f1<-10mm; The object side of the second lens is convex, the image side is concave, the focal length of the second lens is f2, and f2 satisfies: -15mm <f2<-6mm; The object side of the third lens is concave, the image side is convex, the focal length of the third lens is f3, and f3 satisfies: -25mm <f3<-10mm; The object side of the fourth lens is convex, the image side is convex, the focal length of the fourth lens is f4, and f4 satisfies: 5mm <f4<10mm; The object side of the fifth lens is concave, the image side is convex, the focal length of the fifth lens is f5, and f5 satisfies: 8mm <f5<15mm; The object side of the sixth lens is convex, the image side is convex, the focal length of the sixth lens is f6, and f6 satisfies: 4mm <f6<50mm; The object side of the seventh lens is concave, the image side is concave, the focal length of the seventh lens is f7, and f7 satisfies: -10mm <f7<-3mm; The object side of the eighth lens is convex, the image side is convex, the focal length of the eighth lens is f8, and f8 satisfies: 5mm <f8<15mm; Wherein, the sixth lens and the seventh lens form a cemented lens group.

5. The fixed-focus lens according to claim 4, wherein: The refractive index n1 and the dispersion coefficient v1 of the first lens satisfy: 1.60≤n1≤1.80; 50.0≤v1≤75.0; The refractive index n2 and the dispersion coefficient v2 of the second lens satisfy: 1.50≤n2≤1.60; 50.0≤v2≤70.0; The refractive index n3 and the dispersion coefficient v3 of the third lens satisfy: 1.60≤n3≤1.70; 18.0≤v3≤26.0; The refractive index n4 and the dispersion coefficient v4 of the fourth lens satisfy: 1.75≤n4≤2.00; 16.0≤v4≤35.0; The refractive index n5 and the dispersion coefficient v5 of the fifth lens satisfy: 1.50≤n5≤1.70; 55.0≤v5≤90.0; The refractive index n6 and the dispersion coefficient v6 of the sixth lens satisfy: 1.45≤n6≤1.70; 50.0≤v6≤90.0; The refractive index n7 and the dispersion coefficient v7 of the seventh lens satisfy: 1.60≤n7≤1.95; 18.0≤v7≤35.0; The refractive index n8 and the dispersion coefficient v8 of the eighth lens satisfy: 1.50≤n8≤1.60; 50.0≤v8≤70.

0.

6. The fixed-focus lens according to any one of claims 1 to 5, characterized in that: An aperture is disposed between the fourth lens and the fifth lens, and a diameter d of the aperture satisfies: 1.8≤EFL / d≤2.2; Wherein, EFL is the effective focal length of the fixed-focus lens.

7. The fixed-focus lens according to claim 6, wherein: At least one of the fourth lens and the fifth lens is a glass aspherical lens.

8. The fixed-focus lens according to claim 1, wherein: A photosensitive chip opposite to the eighth lens is arranged on the image plane side of the eighth lens, the photosensitive chip has an imaging surface close to the eighth lens, the distance between the object plane side vertex of the first lens and the imaging surface is TTL, the effective focal length of the fixed-focus lens is EFL, and TTL and EFL satisfy: TTL / EFL≤7.

7.

9. The fixed-focus lens according to claim 8, wherein: The diameter IC of the imaging surface satisfies: IC≤9.0 mm.

10. The fixed-focus lens according to claim 1, wherein: The diameter D1 of the first lens satisfies: D1<15 mm.

Images