Fixed focal length lens

Abstract

A fixed-focus lens of the present invention includes, in order from the object side to the image side of the optical axis: a first lens with negative focal power, a second lens with negative focal power, a third lens with positive focal power, a fourth lens with positive focal power, a fifth lens with positive or negative focal power, a sixth lens with positive focal power, a seventh lens with negative focal power, and an eighth lens with positive focal power, wherein the second lens is a paraxial convex-concave lens, the third lens is a paraxial convex-concave lens, and the fifth lens is a paraxial convex-concave lens; the aperture is located between the third lens and the fourth lens or on the object side of the fourth lens; the distance T1 between the object side of the sixth lens and the image side of the eighth lens and the back focal length BFL satisfy the following relationship: 1.30≤T1 / BFL≤1.35. The fixed-focus lens of the present invention has the characteristics of miniaturization, high performance, and low cost, and the lens has clear imaging in the temperature range of ‑40°C to +80°C, the relative illumination is above 40%, and has the characteristic of a relatively long back focal length, which is conducive to the assembly of the fixed-focus lens.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging, and in particular to a fixed-focus lens. Background Art

[0002] With the popularization of work in the fields of security and public safety, the demand for fixed-focus surveillance lenses is increasing. Among them, super-large aperture lenses have higher light throughput and are more in line with market demand in terms of performance, so the research and development of super-large aperture lenses is very necessary. However, high light throughput often means that more lenses are needed to correct aberrations and chromatic aberrations, and the complex lens structure makes it difficult to control the material cost and processing cost of the lens, which is not conducive to the popularization of the lens. While ensuring the performance of the lens, the lower the cost of the lens and the more reasonable the structure, the more mass production can be achieved to meet the growing security needs. Therefore, how to reduce costs while ensuring lens performance is a technical problem that super-large aperture surveillance lenses need to solve. Summary of the invention

[0003] The object of the present invention is to solve the above problems and provide a low-cost, small-volume, ultra-large-aperture fixed-focus lens that is not out of focus in the temperature range of -40°C to 80°C.

[0004] To achieve the above object, the present invention provides a fixed-focus lens, which includes, in order from the object side to the image side of the optical axis: a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with positive optical power, a fifth lens with positive or negative optical power, a sixth lens with positive optical power, a seventh lens with negative optical power, and an eighth lens with positive optical power, wherein the second lens and the third lens are paraxial convex-concave lenses, and the fifth lens is a paraxial convex-convex lens;

[0005] The aperture stop is disposed between the third lens and the fourth lens or on the object side surface of the fourth lens;

[0006] A distance T1 from the object side surface of the sixth lens to the image side surface of the eighth lens and a back focal length BFL of the fixed focus lens satisfy the following relationship: 1.30≤T1 / BFL≤1.35.

[0007] According to one aspect of the present invention, the first lens is a paraxial convex-concave lens, the fourth lens, the sixth lens and the eighth lens are paraxial convex-convex lenses, and the seventh lens is a paraxial concave-concave lens.

[0008] According to one aspect of the present invention, the first lens, the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are aspherical lenses;

[0009] The fourth lens is a spherical lens.

[0010] According to one aspect of the present invention, the first lens, the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are plastic lenses;

[0011] The fourth lens is a glass lens.

[0012] According to one aspect of the present invention, the total optical length TTL of the fixed-focus lens and the back focal length BFL of the fixed-focus lens satisfy the following relationship:

[0013] 4.8≤TTL / BFL≤5.2.

[0014] According to one aspect of the present invention, the total optical length TTL of the fixed-focus lens and the effective focal length F of the fixed-focus lens satisfy the following relationship:

[0015] 5.6≤TTL / F≤6.9.

[0016] According to one aspect of the present invention, the curvature radius R11 of the object-side surface of the first lens and the effective focal length F of the fixed-focus lens satisfy the following relationship:

[0017] 0≤F / R11≤0.2.

[0018] According to one aspect of the present invention, a distance D34 between the image side surface of the third lens and the object side surface of the fourth lens and a distance T2 between the object side surface and the image side surface of the fourth lens satisfy the following relationship:

[0019] 0≤D34 / T2≤0.05.

[0020] According to one aspect of the present invention, a distance D0 between the aperture stop and the object side surface of the fourth lens element satisfies the following relationship:

[0021] D0≤0.

[0022] According to one aspect of the present invention, the sag SAG41 of the object-side surface of the fourth lens element satisfies the following relationship:

[0023] 0.45≤SAG41≤0.6.

[0024] According to one aspect of the present invention, the sag height SAG51 of the object side surface of the fifth lens and the optical effective semi-aperture D1 of the fifth lens satisfy the following relationship:

[0025] -0.5≤SAG51 / D1≤-0.3.

[0026] According to one aspect of the present invention, the curvature radius R81 of the object-side surface of the eighth lens, the curvature radius R82 of the image-side surface of the eighth lens, and the effective focal length F8 of the object-side surface of the eighth lens satisfy the following relationship:

[0027] -0.35≤0.5(R81+R82) / F8≤-0.1.

[0028] According to one aspect of the present invention, the combined focal length F678 of the sixth lens, the seventh lens and the eighth lens and the effective focal length F of the fixed focus lens satisfy the following relationship:

[0029] 2.1≤F678 / F≤2.7.

[0030] According to one scheme of the present invention, the fixed-focus lens of the present invention can achieve high resolution performance of the lens by reasonably allocating the optical focal length of each lens and optimizing the shape of each lens, so that the relative illumination is above 40%. On the basis of achieving miniaturization, it has the characteristic of a relatively long back focal length, which is beneficial to the assembly of the fixed-focus lens and facilitates production.

[0031] According to one solution of the present invention, by optimizing the configuration of each aperture position and the sagittal height of the object side of the fourth lens, the fixed-focus lens of the present invention can achieve a large aperture, the aperture FNO number can reach 1.06, and the position of the aperture in the front group can increase the amount of light entering, so that the relative illumination reaches more than 40%, meeting the imaging requirements of light and dark environments.

[0032] According to one solution of the present invention, the use of aspheric lenses can efficiently adjust system aberrations, and plastic materials can achieve low cost of lenses. At the same time, clear imaging without blurring can be achieved in the temperature range of -40°C to 80°C, overcoming the difficulty of focus drift caused by plastic aspheric lenses in high and low temperature environments due to their large expansion coefficient.

[0033] According to one solution of the present invention, by reasonably configuring the diopter and focal length of each lens, the fixed-focus lens of the present invention can effectively avoid the aberration generated when light is incident, reduce the molding sensitivity of the lens, facilitate the production of the first lens, and ensure the production quality.

[0034] According to one solution of the present invention, the second lens is set as a convex-concave lens, which is conducive to converging light and allowing the light diverged by the first lens to smoothly enter the rear; the second lens is located at the inflection point, which is conducive to improving the resolution, and the appropriate ratio between the curvature and the focal length can reduce the coma and field curvature when the light enters the system.

[0035] According to one solution of the present invention, by reasonably configuring the effective semi-aperture of the sagittal height of the object side of the fifth lens, the ratio of the focal lengths of the sixth lens, the seventh lens and the eighth lens to the effective focal length of the fixed-focus lens, it is beneficial to ensure a smooth mirror surface, reduce molding sensitivity, and improve resolution.

[0036] According to one solution of the present invention, by reasonably configuring the curvature radii and focal length of the object side and image side of the last lens, the eighth lens, it is helpful to reduce the residual aberration after the light passes through the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the structure of the fixed-focus lens of Example 1 of the present invention;

[0038] Figure 2 Schematic diagram of the light fan of the fixed-focus lens of Example 1 of the present invention;

[0039] Figure 3 Schematic diagram of the structure of a fixed-focus lens according to Embodiment 2 of the present invention;

[0040] Figure 4 Schematic diagram of the light fan of the fixed-focus lens of Example 2 of the present invention;

[0041] Figure 5 Schematic diagram of the structure of a fixed-focus lens according to Embodiment 3 of the present invention;

[0042] Figure 6 Schematic diagram of the light fan of the fixed-focus lens of Example 3 of the present invention;

[0043] Figure 7 Schematic diagram of the structure of a fixed-focus lens according to Embodiment 4 of the present invention;

[0044] Figure 8 Schematic diagram of the light fan of the fixed-focus lens of Example 4 of the present invention. DETAILED DESCRIPTION

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0046] When describing the embodiments of the present invention, the orientation or positional relationship expressed by the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or positional relationship shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0047] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not therefore limited to the following embodiments.

[0048] Figure 1 Schematically shows the structure of a fixed-focus lens according to an embodiment of the present invention. Figure 1 As shown, the fixed-focus lens of the present invention includes, in order from the object side to the image side of the optical axis: a first lens L1 with negative optical power, a second lens L2 with negative optical power, a third lens L3 with positive optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with positive or negative optical power, a sixth lens L6 with positive optical power, a seventh lens L7 with negative optical power, and an eighth lens L8 with positive optical power, the second lens L2 is a paraxial convex-concave lens, the third lens L3 is a paraxial convex-concave lens, and the fifth lens L5 is a paraxial convex-convex lens;

[0049] The aperture STO is disposed between the third lens L3 and the fourth lens L4 or on the object-side surface of the fourth lens L4;

[0050] A distance T1 between the object-side surface of the sixth lens L6 and the image-side surface of the eighth lens L8 and a back focal length BFL satisfy the following relationship: 1.30≤T1 / BFL≤1.35.

[0051] By reasonably allocating the focal length of each lens and optimizing the shape of each lens, high resolution performance of the lens can be achieved, so that the relative illumination is above 40%. On the basis of miniaturization, it has the characteristic of a relatively long back focal length, which is conducive to the assembly of fixed-focus lenses and facilitates production.

[0052] In the present invention, along the direction from the object side to the image side, the first lens L1 is a paraxial convex-concave lens, the fourth lens L4 is a convex-convex lens, the sixth lens L6 is a paraxial convex-convex lens, the seventh lens L7 is a paraxial convex-concave lens, and the eighth lens L8 is a paraxial convex-convex lens.

[0053] In the present invention, a cover glass CG is further included, and the cover glass CG is located on the image side of the eighth lens L8.

[0054] In the present invention, along the direction from the object side to the image side, the first lens L1, the second lens L2, the third lens L3, the fifth lens L5, the sixth lens L6, the seventh lens L7 and the eighth lens L8 are aspherical lenses;

[0055] The fourth lens L4 is a spherical lens.

[0056] Among them, the aspherical surface satisfies the following formula:

[0057]

[0058] Where z is the axial distance from the surface to the vertex at a height h perpendicular to the optical axis along the optical axis; c represents the curvature at the vertex of the aspheric surface; k is the cone coefficient; A 4 , A 6 , A 8 , A 10 , A 12 , A 14 , A 16 ...are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth, sixteenth, etc. respectively.

[0059] In the present invention, the first lens L1, the second lens L2, the third lens L3, the fifth lens L5, the sixth lens L6, the seventh lens L7 and the eighth lens L8 are plastic lenses;

[0060] The fourth lens L4 is a glass lens.

[0061] By using aspherical lenses, the system aberration can be adjusted efficiently, and plastic materials can achieve low cost of the lens. At the same time, the lens can achieve clear imaging in the temperature range of -40℃ to +80℃.

[0062] In addition, the total optical length TTL of the fixed-focus lens of the present invention and the back focal length BFL of the fixed-focus lens satisfy the following relationship: 4.8≤TTL / BFL≤5.2. When this relationship is satisfied, the total optical length TTL of the fixed-focus lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.6≤TTL / F≤6.9, which effectively reduces the volume of the fixed-focus lens and is conducive to miniaturization of the fixed-focus lens.

[0063] The curvature radius R11 of the object side surface of the first lens L1 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 0≤F / R11≤0.2, which can avoid aberrations caused by incident light and reduce the molding sensitivity of the lens, which is beneficial to the production of the first lens L1 and ensures the quality of the first lens L1, thereby improving the imaging quality of the fixed-focus lens.

[0064] The curvature radius R21 of the object side surface of the second lens L2, the curvature radius R22 of the object image side surface of the second lens L2 and the focal length F2 of the second lens L2 satisfy the following relationship: -0.45≤0.5(R21+R22) / F2≤-0.1. By setting the second lens L2 as a convex-concave lens, when the above relationship is satisfied, it is more conducive to converging light, so that the light diverged by the first lens L1 can smoothly enter the rear; the second lens L2 has an inflection point, which is conducive to improving the resolution. When the curvature and the focal length satisfy the above relationship, the coma and field curvature when the light enters the system can be more effectively reduced.

[0065] The distance D34 between the image side surface of the third lens L3 and the object side surface of the fourth lens L4 and the distance T2 between the object side surface of the fourth lens L4 and the image plane satisfy the following relationship: 0≤D34 / T2≤0.05, which is conducive to ensuring the stability of the front group and reducing the sensitivity of the assembly process.

[0066] The front group is represented by a lens group from the object side to the image side of the fifth lens L5 along the optical axis, including the first lens L1, the second lens L2, the third lens L3, the fourth lens L4 and the fifth lens L5.

[0067] The distance D0 between the aperture STO and the object side of the fourth lens L4 satisfies the following relationship: D0≤0; the sag height SAG41 of the object side of the fourth lens L4 satisfies the following relationship: 0.45≤SAG41≤0.6. When the above relationship is met, the fixed focus lens can achieve a large aperture FNO1.06, and the aperture is set at the front group position to increase the amount of light entering, so that the relative illumination reaches more than 40%.

[0068] The sagittal height SAG51 of the object side surface of the fifth lens L5 and the optical effective semi-aperture D1 of the fifth lens L5 satisfy the following relationship: -0.5≤SAG51 / D1≤-0.3, which is conducive to ensuring a smooth mirror surface and reducing molding sensitivity.

[0069] The curvature radius R81 of the object side surface of the eighth lens L8, the curvature radius R82 of the image side surface of the eighth lens L8, and the focal length F8 of the object side surface of the eighth lens L8 satisfy the following relationship: -0.35≤0.5(R81+R82) / F8≤-0.1, which is beneficial to reducing the residual aberration after the light passes through the optical system.

[0070] The focal length F678 of the sixth lens L6, the seventh lens L7 and the eighth lens L8 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 2.1≤F678 / F≤2.7, which is conducive to smooth transition of light, reduced tolerance sensitivity and improved resolution.

[0071] Based on the above settings, the fixed-focus lens of the present invention can achieve a total lens length less than or equal to 22.4 mm and a lens back focal length greater than or equal to 4.3 mm, making the fixed-focus lens more compact. While meeting high performance requirements, an aspheric lens made of plastic is used to reduce production costs.

[0072] In addition, by optimizing the configuration of the diopter of each lens and selecting reasonable materials, the FNO number of the fixed-focus lens of the present invention can reach 1.06, realizing the characteristics of a large aperture, and the amount of light entering is sufficient while ensuring the imaging quality, meeting the imaging requirements of bright and dark environments.

[0073] At the same time, the present invention can achieve non-defocusing in the temperature range of -40°C to 80°C, overcoming the difficulty that the plastic aspheric lens is prone to focus drift in high and low temperature environments due to its large expansion coefficient.

[0074] Four groups of specific embodiments are given below to specifically illustrate the fixed-focus lens according to the above-mentioned configuration of the present invention. Because the fixed-focus lens according to the present invention has eight lenses, plus the aperture STO protection glass CG and the image plane IMA, when the aperture STO is set on the object side of the fourth lens L4, there are a total of 19 surfaces; when the aperture STO is set between the third lens L3 and the fourth lens L4, there are a total of 20 surfaces. For the convenience of description, the surfaces other than the image plane are numbered as S1, S2 to S19.

[0075] Four sets of example data are shown in Table 1 below:

[0076]

[0077]

[0078] Table 1

[0079] Embodiment 1:

[0080] Figure 1 Schematic diagram of the structure of the fixed-focus lens of Example 1 of the present invention;

[0081] Figure 2 Schematic diagram of the light fan of the fixed-focus lens of Example 1 of the present invention.

[0082] In Example 1, the aperture FNO=1.07, and the total length of the lens is 22.27 mm; the fifth lens L5 has positive focal power, and the stop STO is disposed between the third lens L3 and the fourth lens L4.

[0083] Table 2 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0084] Surface number Surface type Curvature radius R Thickness d Refractive index Nd Abbe number Vd S1 Aspheric 19.71 0.80 1.54 55.7 S2 Aspheric 2.99 2.87 S3 Aspheric 6.29 1.29 1.54 55.7 S4 Aspheric 2.78 0.32 S5 Aspheric 9.86 2.39 1.64 23.5 S6 Aspheric 27.55 0.56 STO Spherical Infinity -0.44 S8 Spherical 9.64 1.73 1.70 55.5 S9 Spherical -9.64 0.71 S10 Aspheric -3.46 1.50 1.54 55.7 S11 Aspheric -3.80 0.18 S12 Aspheric 4.54 2.18 1.54 55.7 S13 Aspheric -24.37 0.04 S14 Aspheric -15.94 0.80 1.64 23.5 S15 Aspheric 4.51 0.33 S16 Aspheric 4.74 2.51 1.54 55.7 S17 Aspheric -8.75 3.50 S18 Spherical Infinity 0.80 1.52 64.2 S19 Spherical Infinity 0.20 IMA Spherical Infinity 0.00

[0085] Table 2

[0086] In this embodiment, the aspheric surface data are shown in Table 3 below, where K is the quadratic constant of the surface, A 4 , A 6 , A 8 , A 10 , A 12 , A 14 , A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively:

[0087]

[0088] Table 3

[0089] See also Figure 1 to Figure 2 , combined with Table 1 to Table 3, in this embodiment, the aperture of the fixed-focus lens can reach 1.07, which can be suitable for low-light environments, and the relative illumination reaches more than 40%. At the same time, the lens can achieve clear imaging in the temperature range of -40℃ to +80℃, and the back focal length BFL is 4.5mm, which has the characteristics of miniaturization, low cost and high performance.

[0090] Embodiment 2:

[0091] Figure 3 Schematic diagram of the structure of a fixed-focus lens according to Embodiment 2 of the present invention;

[0092] Figure 4 Schematic diagram of the light fan of the fixed-focus lens of Example 2 of the present invention.

[0093] In Example 2, the aperture FNO=1.06, and the total length of the lens is 22.19 mm; the fifth lens L5 has positive focal power, and the stop STO is disposed between the third lens L3 and the fourth lens L4.

[0094] Table 4 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0095]

[0096]

[0097] Table 4

[0098] In this embodiment, the aspheric surface data are shown in Table 5 below, where K is the quadratic surface constant of the surface, and A4, A6, A8, A10, A12, A14, and A16 are aspheric surface coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth order, respectively:

[0099]

[0100] Table 5

[0101] See also Figure 3 to Figure 4 , combined with Table 1, Table 4 and Table 5, in this embodiment, the aperture of the fixed-focus lens can reach 1.06, which can be suitable for low-light environments, and the relative illumination reaches more than 40%. At the same time, the lens can achieve clear imaging in the temperature range of -40℃ to +80℃, and the back focal length BFL is 4.3mm, which has the characteristics of miniaturization, low cost and high performance.

[0102] Embodiment 3:

[0103] Figure 3 Schematic diagram of the structure of a fixed-focus lens according to Embodiment 3 of the present invention;

[0104] Figure 4 Schematic diagram of the light fan of the fixed-focus lens of Example 3 of the present invention.

[0105] In Example 3, the aperture FNO=1.06, and the total length of the lens is 22.10 mm; the fifth lens L5 has a negative focal power, and the stop STO is disposed on the object side surface of the fourth lens L4.

[0106] Table 6 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0107] Surface number Surface type Curvature radius R Thickness d Refractive index Nd Abbe number Vd S1 Aspheric 97.714 1.09 1.54 55.7 S2 Aspheric 3.441 1.69 S3 Aspheric 4.379 1.03 1.54 55.7 S4 Aspheric 2.807 0.34 S5 Aspheric 10.751 1.90 1.64 23.5 S6 Aspheric 19.708 0.11 S7 Spherical 9.004 2.50 1.70 55.5 S8 Spherical -9.004 1.01 S9 Aspheric -2.748 1.90 1.54 55.7 S10 Aspheric -3.489 0.04 S11 Aspheric 4.191 2.31 1.54 55.7 S12 Aspheric -231.864 0.10 S13 Aspheric -20.205 0.81 1.64 23.5 S14 Aspheric 4.448 0.17 S15 Aspheric 5.008 2.55 1.54 55.7 S16 Aspheric -7.926 3.55 S17 Spherical Infinity 0.8 1.52 64.2 S18 Spherical Infinity 0.2 IMA Spherical Infinity 0

[0108] Table 6

[0109] In this embodiment, the aspheric surface data are shown in Table 7 below, where K is the quadratic constant of the surface, A 4 , A 6 , A 8 , A 10 , A 12 , A 14 , A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively:

[0110]

[0111]

[0112] Table 7

[0113] See also Figures 5 and 6, combined with Table 1, Table 7 and Table 8, in this embodiment, the aperture of the fixed-focus lens can reach 1.06, which can be suitable for low-light environments, and the relative illumination reaches more than 40%. At the same time, the lens can achieve clear imaging in the temperature range of -40℃ to +80℃, and the back focal length BFL is 4.55mm, which has the characteristics of miniaturization, low cost and high performance.

[0114] Embodiment 4:

[0115] Figure 7 Schematic diagram of the structure of a fixed-focus lens according to Embodiment 4 of the present invention;

[0116] Figure 8 Schematic diagram of the light fan of the fixed-focus lens of Example 4 of the present invention.

[0117] In Example 4, the aperture FNO=1.06, and the total length of the lens is 22.40 mm; the fifth lens L5 has positive focal power, and the stop STO is disposed between the third lens L3 and the fourth lens L4.

[0118] Table 8 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0119] Surface number Surface type Curvature radius R Thickness d Refractive index Nd Abbe number Vd S1 Aspheric 39.983 1.04 1.54 55.7 S2 Aspheric 3.042 2.68 S3 Aspheric 6.111 1.15 1.54 55.7 S4 Aspheric 2.956 0.35 S5 Aspheric 10.097 2.46 1.64 23.5 S6 Aspheric 26.054 0.52 STO Spherical Infinity -0.45 S8 Spherical 9.416 1.66 1.70 55.5 S9 Spherical -9.416 0.98 S10 Aspheric -3.433 1.79 1.54 55.7 S11 Aspheric -3.787 0.07 S12 Aspheric 4.543 2.14 1.54 55.7 S13 Aspheric -23.539 0.11 S14 Aspheric -14.813 0.79 1.64 23.5 S15 Aspheric 4.53 0.2 S16 Aspheric 5.595 2.53 1.54 55.7 S17 Aspheric -6.866 3.37 S18 Spherical Infinity 0.80 1.52 64.2 S19 Spherical Infinity 0.20 IMA Spherical Infinity 0.00

[0120] Table 8

[0121] In this embodiment, the aspheric surface data are shown in Table 9 below, where K is the quadratic constant of the surface, A 4 , A 6 , A 8 , A 10 , A 12 , A 14 , A 16 They are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders respectively:

[0122]

[0123] Table 9

[0124] See also Figures 7 and 8 , combined with Table 1, Table 8 and Table 9, in this embodiment, the aperture of the fixed-focus lens can reach 1.06, which can be suitable for low-light environments, and the relative illumination reaches more than 40%. At the same time, the lens can achieve clear imaging in the temperature range of -40℃ to +80℃, and the back focal length BFL is 4.37mm, which has the characteristics of miniaturization, low cost and high performance.

[0125] The fixed-focus lens of the present invention can achieve high resolution performance of the lens by reasonably allocating the focal length of each lens and optimizing the shape of each lens, so that the relative illumination is above 40%. On the basis of achieving miniaturization, the fixed-focus lens has the characteristic of relatively long back focal length, which is beneficial to the assembly of the fixed-focus lens, convenient for production, and can achieve a large aperture, the aperture FNO number can reach 1.06, and the aperture can increase the amount of light entering at the position of the front group, so that the relative illumination reaches above 40%, meeting the imaging requirements of bright and dark environments; the use of aspherical lenses can efficiently adjust the system aberration, the plastic material can achieve low cost of the lens, and at the same time, can achieve clear imaging without out-of-focus in the temperature range of -40°C to 80°C, overcome the difficulty of plastic aspherical lenses that are easy to cause focus drift in high and low temperature environments due to their large expansion coefficient, effectively avoid aberrations generated when light is incident, reduce the molding sensitivity of the lens, and is beneficial to the production of the first lens, ensuring the production quality; at the same time, it can also reduce coma and field curvature when light is incident on the system, ensure the smoothness of the mirror surface, reduce the molding sensitivity, and improve the resolution.

[0126] The above is only one embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fixed-focus lens, comprising, in order from the object side to the image side along the optical axis: A first lens (L1) with negative optical power, a second lens (L2) with negative optical power, a third lens (L3) with positive optical power, a fourth lens (L4) with positive optical power, a fifth lens (L5) with positive or negative optical power, a sixth lens (L6) with positive optical power, a seventh lens (L7) with negative optical power, and an eighth lens (L8) with positive optical power, wherein the second lens (L2) and the third lens (L3) are paraxial convex-concave lenses, and the fifth lens (L5) is a paraxial convex-concave lens; The aperture stop (STO) is arranged between the third lens (L3) and the fourth lens (L4) or on the object side surface of the fourth lens (L4); A distance T1 from the object side surface of the sixth lens (L6) to the image side surface of the eighth lens (L8) and a back focal length BFL of the fixed-focus lens satisfy the following relationship: 1.30≤T1 / BFL≤1.

35.

2. The fixed-focus lens according to claim 1, characterized in that: The first lens (L1) is a paraxial convex-concave lens, the fourth lens (L4), the sixth lens (L6) and the eighth lens (L8) are paraxial convex-convex lenses, and the seventh lens (L7) is a paraxial concave-concave lens.

3. The fixed-focus lens according to claim 1, characterized in that: The first lens (L1), the second lens (L2), the third lens (L3), the fifth lens (L5), the sixth lens (L6), the seventh lens (L7) and the eighth lens (L8) are aspherical lenses; The fourth lens (L4) is a spherical lens.

4. The fixed-focus lens according to claim 1, wherein: The first lens (L1), the second lens (L2), the third lens (L3), the fifth lens (L5), the sixth lens (L6), the seventh lens (L7) and the eighth lens (L8) are plastic lenses; The fourth lens (L4) is a glass lens.

5. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The total optical length TTL of the fixed-focus lens and the back focal length BFL of the fixed-focus lens satisfy the following relationship: 4.8≤TTL / BFL≤5.

2.

6. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The total optical length TTL of the fixed-focus lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.6≤TTL / F≤6.

9.

7. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The curvature radius R11 of the object side surface of the first lens (L1) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 0≤F / R11≤0.

2.

8. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The distance D34 between the image side surface of the third lens (L3) and the object side surface of the fourth lens (L4) and the distance T2 between the object side surface and the image side surface of the fourth lens (L4) satisfy the following relationship: 0≤D34 / T2≤0.

05.

9. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The distance D0 between the aperture stop (STO) and the object side surface of the fourth lens (L4) satisfies the following relationship: D0≤0。 10. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The sag SAG41 of the object side surface of the fourth lens (L4) satisfies the following relationship: 0.45≤SAG41≤0.

6.

11. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The sagittal height SAG51 of the object side surface of the fifth lens (L5) and the optical effective semi-aperture D1 of the fifth lens (L5) satisfy the following relationship: -0.5≤SAG51 / D1≤-0.

3.

12. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The curvature radius R81 of the object side surface of the eighth lens (L8), the curvature radius R82 of the image side surface of the eighth lens (L8), and the effective focal length F8 of the eighth lens (L8) satisfy the following relationship: -0.35≤0.5(R81+R82) / F8≤-0.

1.

13. The fixed-focus lens according to any one of claims 1 to 4, characterized in that: The combined focal length F678 of the sixth lens (L6), the seventh lens (L7) and the eighth lens (L8) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 2.1≤F678 / F≤2.7.

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