Fixed-focus lens

Abstract

The present invention relates to a fixed-focus lens, which 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), an eighth lens (L8), and a ninth lens (L9) arranged in sequence from the object side to the image side along the optical axis. The optical powers of the first lens (L1), the second lens (L2), and the sixth lens (L6) are negative, and the optical powers of the third lens (L3), the fourth lens (L4), the fifth lens (L5), the seventh lens (L7), the eighth lens (L8), and the ninth lens (L9) are positive. The fixed-focus lens of the present invention has the characteristics of low cost, miniaturization, an ultra-large aperture of F1.0, high resolution, large image height, no defocusing within the temperature range of -40°C to 80°C, no need for infrared, and can be used day and night.

Description

Technical Field

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

[0002] In the digital age, work in the fields of security and public safety is in full swing, so the demand for monitoring facilities is also increasing. Fixed-focus lenses are widely used in various fields due to their advantages such as high-definition imaging, wide monitoring field of view, and clear imaging under low-light conditions. In the existing technology, high-quality night imaging lenses mostly use a large aperture of F1.4 with infrared fill light technology to achieve the imaging purpose. However, due to the small infrared imaging range and the inability to restore color information, the emergence of low-light cameras has become imperative. Therefore, how to ensure clear imaging of the lens at night or in an environment with insufficient lighting conditions is a technical problem that needs to be solved urgently in the security field. Summary of the invention

[0003] The object of the present invention is to provide a fixed-focus lens.

[0004] To achieve the above-mentioned object of the invention, the present invention provides a fixed-focus lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens arranged in sequence from the object side to the image side along the optical axis, wherein the optical power of the first lens, the second lens and the sixth lens is negative, and the optical power of the third lens, the fourth lens, the fifth lens, the seventh lens, the eighth lens and the ninth lens is positive.

[0005] According to one aspect of the present invention, the first lens and the ninth lens are convex-concave lenses, the second lens and the eighth lens are concave-convex lenses, the third lens, the fourth lens, the fifth lens and the seventh lens are convex-convex lenses, and the sixth lens is a concave-concave lens.

[0006] According to one aspect of the present invention, the first lens, the second lens, the fourth lens, the eighth lens and the ninth lens are aspherical lenses, and the third lens, the fifth lens, the sixth lens and the seventh lens are spherical lenses.

[0007] According to one aspect of the present invention, the first lens, the second lens, the fourth lens, the eighth lens and the ninth lens are made of plastic, and the third lens, the fifth lens, the sixth lens and the seventh lens are made of glass.

[0008] According to one aspect of the present invention, the fifth lens, the sixth lens and the seventh lens are cemented together to form a cemented lens group.

[0009] According to one aspect of the present invention, it further includes a diaphragm located between the second lens and the third lens.

[0010] According to one aspect of the present invention, the optical total length TTL and the focal length F of the fixed-focus lens satisfy the following relationship: 5.9 ≤ TTL / F ≤ 6.7.

[0011] According to one aspect of the present invention, the optical back focal length BFL and the focal length F of the fixed-focus lens satisfy the following relationship: 0.8 ≤ BFL / F ≤ 1.

[0012] According to one aspect of the present invention, the focal length F3 of the third lens and the focal length F1 of the first lens satisfy the following relationship: -1.3 ≤ F3 / F1 ≤ -1.1.

[0013] According to one aspect of the present invention, the combined focal length F567 of the fifth lens, the sixth lens and the seventh lens and the focal length F of the fixed-focus lens satisfy the following relationship: 6.5 ≤ F567 / F ≤ 8.2.

[0014] According to one aspect of the present invention, the focal length F8 of the eighth lens and the focal length F of the fixed-focus lens satisfy the following relationship: 7.2 ≤ F8 / F ≤ 14.2.

[0015] According to one aspect of the present invention, the focal length F9 of the ninth lens and the focal length F of the fixed-focus lens satisfy the following relationship: 10.4 ≤ F9 / F ≤ 21.6.

[0016] According to one aspect of the present invention, the combined focal length F89 of the eighth lens and the ninth lens and the focal length F of the fixed-focus lens satisfy the following relationship: 5.1 ≤ F89 / F ≤ 6.5.

[0017] According to one aspect of the present invention, the central thickness db1 of the cemented lens group composed of the fifth lens, the sixth lens and the seventh lens and the central thickness d6 of the sixth lens satisfy the following relationship: 9.2 ≤ db1 / d6 ≤ 14.8.

[0018] According to one aspect of the present invention, the central length d23 from the image side of the second lens to the object side of the third lens, the central length d34 from the image side of the third lens to the object side of the fourth lens and the central thickness d3 of the third lens satisfy the following relationship: 1.6 ≤ (d23 + d34) / d3 ≤ 2.

[0019] According to the concept of the present invention, there is provided a low-cost, miniaturized, F1.0 ultra-large aperture, high resolution, large image height, non-defocusing within the temperature range of -40°C to 80°C, without the need for infrared, and capable of dual use day and night glass-plastic hybrid security fixed-focus lens.

[0020] According to an embodiment of the present invention, by reasonably setting the optical power and shape of each lens of the fixed-focus lens, a large aperture can be achieved, and the lens assembly sensitivity can be made lower and defocusing can be avoided within the temperature range of -40°C to 80°C.

[0021] According to an embodiment of the present invention, by reasonably using the cemented lens group, the fixed-focus lens can have a high resolution of 5 million pixels, and defocusing can be avoided within the temperature range of -40°C to 80°C.

[0022] According to an embodiment of the present invention, by reasonably matching the plastic and glass materials of each lens of the fixed-focus lens, an optical structure of 4G5P is formed for the fixed-focus lens, so that the high and low temperature performance of the lens can be balanced, and the lens has the characteristics of low cost and light weight.

[0023] According to an embodiment of the present invention, by reasonably setting the relationship among the focal length, the overall optical length, and the back focal length of the fixed-focus lens, miniaturization of the lens can be achieved.

[0024] According to an embodiment of the present invention, by reasonably setting the relationship between the focal lengths of the third lens and the first lens, the light path of the entire optical system can be controlled, and the aberration caused by the large-angle light entering through the aperture can be reduced.

[0025] According to an embodiment of the present invention, by reasonably setting the relationship between the focal lengths of the three-cemented lens group and the fixed-focus lens and the relationship between the center thickness of the three-cemented lens group and the center thickness of the sixth lens, the chromatic aberration and aberration caused by the light entering through the aperture and the fourth lens can be corrected.

[0026] According to an embodiment of the present invention, by reasonably setting the relationship between the focal lengths of the eighth lens, the ninth lens, and their combined focal length and the focal length of the fixed-focus lens, the distortion can be effectively controlled, which is beneficial to the realization of a large target surface.

[0027] According to an embodiment of the present invention, by reasonably setting the relationship among the center lengths of the second lens and the third lens, the center lengths of the third lens and the fourth lens, and the center thickness of the third lens, it is beneficial to reduce the sensitivity of the three lenses, namely the second lens, the third lens, and the fourth lens, to the MTF of the lens. At the same time, the lens structure can be made compact, which is beneficial to the realization of miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A structural diagram schematically showing a fixed-focus lens according to the first embodiment of the present invention;

[0029] Figure 2 A structural diagram schematically showing a fixed-focus lens according to the second embodiment of the present invention;

[0030] Figure 3Structural diagram of a fixed-focus lens schematically showing the third embodiment of the present invention;

[0031] Figure 4 Structural diagram of a fixed-focus lens schematically showing the fourth embodiment of the present invention;

[0032] Figure 5 Structural diagram of a fixed-focus lens schematically showing the fifth embodiment of the present invention. Detailed implementation manners

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings required for use in the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings can be obtained based on these drawings without creative efforts.

[0034] When describing the embodiments of the present invention, the orientation or positional relationship expressed by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" is based on the orientation or positional relationship shown in the relevant accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0035] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners. The implementation manners cannot be elaborated one by one here, but the implementation manners of the present invention are not limited to the following implementation manners.

[0036] See Figure 1 , the fixed-focus lens of the present invention includes a first lens L1, a second lens L2, a diaphragm S, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, an eighth lens L8, and a ninth lens L9 arranged in sequence from the object side to the image side along the optical axis. Of course, it also includes a parallel flat plate A.

[0037] In the present invention, the optical powers of the first lens L1, the second lens L2, and the sixth lens L6 are negative, and the optical powers of the third lens L3, the fourth lens L4, the fifth lens L5, the seventh lens L7, the eighth lens L8, and the ninth lens L9 are positive. The first lens L1 and the ninth lens L9 are convex-concave lenses, the second lens L2 and the eighth lens L8 are concave-convex lenses, the third lens L3, the fourth lens L4, the fifth lens L5, and the seventh lens L7 are convex-convex lenses, and the sixth lens L6 is a concave-concave lens. In this way, the optical architecture formed by the above combination of optical powers and shapes of each lens can achieve a large aperture, low sensitivity in lens assembly, and no defocusing in the temperature range of -40°C to 80°C.

[0038] In the present invention, the first lens L1, the second lens L2, the fourth lens L4, the eighth lens L8, and the ninth lens L9 are aspherical lenses, and the third lens L3, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are spherical lenses. Among them, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are glued together to form a glued lens group. In this way, by reasonably setting the glued lens group, the lens can have a high resolution of 5 million pixels and can be free of defocusing in the temperature range of -40°C to 80°C.

[0039] In the present invention, the materials of the first lens L1, the second lens L2, the fourth lens L4, the eighth lens L8, and the ninth lens L9 are plastics, and the materials of the third lens L3, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are glasses. In this way, the lens forms an optical architecture of 4G5P, thereby balancing the high and low temperature performance of the lens and achieving a low-cost and lightweight design.

[0040] In the present invention, the total optical length TTL of the fixed-focus lens (i.e., the distance from the center of the object side of the first lens L1 to the center of the image plane) and the focal length F satisfy the following relationship: 5.9 ≤ TTL / F ≤ 6.7. The back focal length BFL of the fixed-focus lens (i.e., the distance from the center of the image side of the last lens of the lens to the center of the imaging plane) and the focal length F satisfy the following relationship: 0.8 ≤ BFL / F ≤ 1. Satisfying the above relationships can achieve the miniaturization of the fixed-focus lens.

[0041] In the present invention, the focal length F3 of the third lens L3 and the focal length F1 of the first lens L1 satisfy the following relationship: -1.3 ≤ F3 / F1 ≤ -1.1. In this way, the light path of the entire optical system can be controlled, and the aberration caused by the large-angle light entering through the diaphragm S can be reduced.

[0042] In the present invention, the combined focal length F567 of the fifth lens L5, the sixth lens L6, and the seventh lens L7 and the focal length F of the fixed-focus lens satisfy the following relationship: 6.5 ≤ F567 / F ≤ 8.2. The central thickness db1 of the cemented lens group composed of the fifth lens L5, the sixth lens L6, and the seventh lens L7 and the central thickness d6 of the sixth lens L6 satisfy the following relationship: 9.2 ≤ db1 / d6 ≤ 14.8. By setting the parameters of the cemented lens group in this way, chromatic aberration and spherical aberration caused by the light rays entering through the diaphragm S and the fourth lens L4 can be corrected.

[0043] In the present invention, the focal length F8 of the eighth lens L8 and the focal length F of the fixed-focus lens satisfy the following relationship: 7.2 ≤ F8 / F ≤ 14.2. The focal length F9 of the ninth lens L9 and the focal length F of the fixed-focus lens satisfy the following relationship: 10.4 ≤ F9 / F ≤ 21.6. The combined focal length F89 of the eighth lens L8 and the ninth lens L9 and the focal length F of the fixed-focus lens satisfy the following relationship: 5.1 ≤ F89 / F ≤ 6.5. In this way, distortion can be effectively controlled, which is beneficial to achieving a large target surface.

[0044] In the present invention, the central length d23 from the image side of the second lens L2 to the object side of the third lens L3, the central length d34 from the image side of the third lens L3 to the object side of the fourth lens L4, and the central thickness d3 of the third lens L3 satisfy the following relationship: 1.6 ≤ (d23 + d34) / d3 ≤ 2. In this way, it is beneficial to reduce the sensitivity of the three lenses, namely the second lens L2, the third lens L3, and the fourth lens L4, to the MTF of the fixed-focus lens, and at the same time make the lens structure compact, which is beneficial to achieving miniaturization.

[0045] In summary, the fixed-focus lens of the present invention has the characteristics of an ultra-large aperture of 1.0, low-light imaging, no defocusing within the temperature range of -40°C to 80°C, and day-night confocal. In addition, this lens also has the advantages of low cost, miniaturization, light weight, and low sensitivity to assembly tolerances, and also has a high resolution of 5 million pixels. By reasonably setting the cemented lens group, it is beneficial to chromatic aberration and spherical aberration correction. Moreover, the fixed-focus lens of the present invention can also achieve a large target surface.

[0046] The following describes the fixed-focus lens of the present invention in detail with five sets of embodiments. In the following embodiments, 1, 2,..., N are used to represent the surfaces of each optical element. Among them, the cemented surface of the cemented lens group is denoted as surface one.

[0047] In the present invention, the aspherical lens satisfies the following formula:

[0048]

[0049] In the formula, z is the axial distance from the vertex of the curved surface at the position perpendicular to the optical axis with a height h along the optical axis; c represents the curvature at the vertex of the aspherical surface; k is the conic coefficient; A 4 、A6 , A 8 , A 10 , A 12 , A 14 , A 16 … respectively represent the aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, sixteenth order…

[0050] The shapes, optical powers, surface shapes, materials, and positions of the stop S of the lenses in the fixed-focus lenses of the embodiments of the present invention are shown in Table 1 below:

[0051]

[0052] Table 1

[0053] The parameters of the embodiments specifically meeting the above conditional expressions are shown in Table 2 and Table 3 below:

[0054]

[0055]

[0056] Table 2

[0057]

[0058] Table 3

[0059] The first embodiment

[0060] See Figure 1 , the relevant parameters of the lenses of the fixed-focus lens of this embodiment include the R value, thickness, refractive index Nd, Abbe number Vd, and K value, as shown in Table 4 below:

[0061]

[0062]

[0063] Table 4

[0064] The aspherical parameters are shown in Table 5 below:

[0065] Surf A4 A6 A8 A10 A12 1 -5.162E-04 1.045E-05 -1.072E-07 6.391E-10 -1.127E-12 2 -9.554E-04 2.740E-05 -6.081E-07 1.186E-08 -1.050E-10 3 2.070E-04 -2.713E-06 8.687E-08 -1.553E-09 1.080E-11 4 3.028E-04 4.583E-08 2.417E-08 -7.509E-11 -3.005E-12 8 3.556E-05 1.515E-07 -3.330E-10 3.424E-11 -2.304E-13 9 6.522E-05 2.382E-08 1.123E-09 3.180E-11 -2.971E-13 14 2.200E-04 -3.083E-06 -4.545E-10 8.803E-11 -1.208E-12 15 1.185E-04 -3.271E-06 7.082E-09 1.219E-10 -9.647E-13 16 -2.804E-04 -2.160E-06 4.121E-09 9.737E-10 -6.084E-12 17 -3.326E-04 -2.667E-06 1.199E-07 -1.362E-09 9.082E-12

[0066] Table 5

[0067] The second embodiment

[0068] See Figure 2 , the relevant parameters of the lenses of the fixed-focus lens of this embodiment include the R value, thickness, refractive index Nd, Abbe number Vd, and K value, as shown in Table 6 below:

[0069]

[0070]

[0071] Table 6

[0072] The aspherical parameters are shown in Table 7 below:

[0073] Surf A4 A6 A8 A10 A12 1 -5.489E-04 1.041E-05 -1.067E-07 6.361E-10 -1.543E-12 2 -9.725E-04 2.759E-05 -6.161E-07 1.208E-08 -1.199E-10 3 2.039E-04 -3.078E-06 8.707E-08 -1.145E-09 2.364E-12 4 2.978E-04 -2.288E-08 2.777E-08 -6.942E-11 -2.850E-12 8 3.662E-05 1.377E-07 -4.176E-10 3.238E-11 -2.524E-13 9 6.566E-05 3.674E-08 1.015E-09 3.024E-11 -3.272E-13 14 2.164E-04 -3.051E-06 -1.480E-10 8.141E-11 -1.274E-12 15 1.172E-04 -3.288E-06 6.941E-09 1.225E-10 -1.010E-12 16 -2.929E-04 -2.047E-06 4.978E-09 9.614E-10 -5.962E-12 17 -3.362E-04 -2.942E-06 1.212E-07 -1.341E-09 8.979E-12

[0074] Table 7

[0075] The third implementation mode

[0076] See Figure 3 , the relevant parameters of each lens of the fixed-focus lens in this implementation mode include the R value, thickness, refractive index Nd, Abbe number Vd, and K value, as shown in Table 8 below:

[0077]

[0078]

[0079] Table 8

[0080] The aspherical parameters are shown in Table 9 below:

[0081] Surf A4 A6 A8 A10 A12 1 -5.113E-04 1.014E-05 -1.077E-07 6.494E-10 -1.577E-12 2 -9.658E-04 2.802E-05 -5.767E-07 1.071E-08 -1.029E-10 3 2.238E-04 -2.565E-06 8.793E-08 -1.665E-09 1.044E-11 4 2.970E-04 7.642E-08 1.531E-08 5.738E-11 -3.028E-12 8 3.261E-05 1.562E-07 -2.659E-10 2.573E-11 -3.823E-13 9 6.878E-05 9.337E-09 7.516E-10 2.971E-11 -5.061E-13 14 2.217E-04 -2.998E-06 -3.009E-10 7.627E-11 -1.215E-12 15 1.145E-04 -3.328E-06 6.822E-09 1.259E-10 -9.926E-13 16 -2.961E-04 -2.229E-06 4.286E-09 9.837E-10 -5.979E-12 17 -3.403E-04 -2.676E-06 1.210E-07 -1.378E-09 8.948E-12

[0082] Table 9

[0083] The fourth implementation mode

[0084] See Figure 4 , the relevant parameters of each lens of the fixed-focus lens in this implementation mode include the R value, thickness, refractive index Nd, Abbe number Vd, and K value, as shown in Table 10 below:

[0085] Surface number R value Thickness Refractive index Nd Abbe number Vd K value 1 13.071 1.984 1.54 56 -8.876 2 5.206 4.668 -1.129 3 -7.273 3.248 1.61 25.6 -0.988 4 -14.470 3.991 -0.840 5(S) Infinity 0.000 6 31.536 4.600 1.85 23.8 7 -33.777 4.521 8 117.156 2.713 1.54 56 106.266 9 -21.832 0.450 -5.556 10 45.822 4.630 1.62 63.4 11 -12.373 0.806 1.8 23.8 12 18.271 5.042 1.59 68.6 13 -18.296 1.748 14 -25.442 3.713 1.64 23.4 -78.367 15 -17.431 0.100 -7.706 16 9.865 3.096 1.54 55.7 -6.369 17 9.974 6.984 -7.447 18 Infinity 0.800 1.52 64.2 19 Infinity 0.200 Image plane (I) Infinity -

[0086] Table 10

[0087] The aspherical parameters are shown in Table 11 below:

[0088] Surf A4 A6 A8 A10 A12 1 -5.145E-04 1.011E-05 -1.058E-07 6.511E-10 -1.496E-12 2 -9.596E-04 2.752E-05 -5.821E-07 1.065E-08 -9.398E-11 3 2.193E-04 -3.247E-06 1.037E-07 -1.865E-09 1.337E-11 4 2.961E-04 -1.074E-07 1.908E-08 1.053E-10 -3.827E-12 8 3.311E-05 1.660E-07 -3.463E-10 2.456E-11 -4.077E-13 9 7.125E-05 -9.052E-10 6.385E-10 2.849E-11 -5.183E-13 14 2.253E-04 -2.950E-06 -1.732E-10 7.010E-11 -1.156E-12 15 1.189E-04 -3.287E-06 7.174E-09 1.185E-10 -9.361E-13 16 -2.983E-04 -2.209E-06 7.134E-09 9.782E-10 -6.189E-12 17 -3.347E-04 -2.610E-06 1.192E-07 -1.328E-09 8.662E-12

[0089] Table 11 The fifth implementation mode

[0090] See Figure 5 , the relevant parameters of each lens of the fixed-focus lens in this implementation mode include the R value, thickness, refractive index Nd, Abbe number Vd, and K value, as shown in Table 12 below:

[0091] Surface number R value Thickness Refractive index Nd Abbe number Vd K value 1 11.531 1.765 1.54 56 -8.474 2 5.009 4.645 -1.215 3 -7.110 3.249 1.61 25.6 -0.986 4 -14.099 4.051 -0.841 5(S) Infinity 0.000 6 31.301 4.610 1.85 23.8 7 -33.964 4.144 8 117.353 2.694 1.54 56 108.924 9 -21.846 0.257 -6.210 10 45.860 5.162 1.62 63.4 11 -12.319 0.800 1.8 23.8 12 17.168 5.236 1.59 68.6 13 -17.934 1.355 14 -26.547 3.836 1.64 23.4 -87.446 15 -17.748 0.100 -8.136 16 9.866 3.063 1.54 55.7 -6.385 17 9.846 6.995 -7.361 18 Infinity 0.800 1.52 64.2 19 Infinity 0.200 Image plane (I) Infinity -

[0092] Table 12

[0093] The aspherical parameters are shown in Table 13 below:

[0094]

[0095]

[0096] Table 13

[0097] 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 changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fixed-focus lens, comprising 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), an eighth lens (L8), and a ninth lens (L9) arranged in sequence from the object side to the image side along the optical axis. There are a total of nine lenses with optical power. Characterized in that, The optical powers of the first lens (L1), the second lens (L2), and the sixth lens (L6) are negative, and the optical powers of the third lens (L3), the fourth lens (L4), the fifth lens (L5), the seventh lens (L7), the eighth lens (L8), and the ninth lens (L9) are positive; The combined focal length F567 of the fifth lens (L5), the sixth lens (L6), and the seventh lens (L7) and the focal length F of the fixed-focus lens satisfy the following relationship: 6.5 ≤ F567 / F ≤ 8.

2.

2. The fixed-focus lens according to claim 1, Characterized in that, The first lens (L1) and the ninth lens (L9) are convex-concave lenses, the second lens (L2) and the eighth lens (L8) are concave-convex lenses, the third lens (L3), the fourth lens (L4), the fifth lens (L5), and the seventh lens (L7) are convex-convex lenses, and the sixth lens (L6) is a concave-concave lens.

3. The fixed-focus lens according to claim 1, Characterized in that, The first lens (L1), the second lens (L2), the fourth lens (L4), the eighth lens (L8), and the ninth lens (L9) are aspherical lenses, and the third lens (L3), the fifth lens (L5), the sixth lens (L6), and the seventh lens (L7) are spherical lenses.

4. The fixed-focus lens according to claim 3, Characterized in that, The materials of the first lens (L1), the second lens (L2), the fourth lens (L4), the eighth lens (L8), and the ninth lens (L9) are plastics, and the materials of the third lens (L3), the fifth lens (L5), the sixth lens (L6), and the seventh lens (L7) are glass.

5. The fixed-focus lens according to claim 1, Characterized in that, The fifth lens (L5), the sixth lens (L6), and the seventh lens (L7) are glued together to form a glued lens group.

6. The fixed-focus lens according to claim 1, Characterized in that, It further includes a diaphragm (S) located between the second lens (L2) and the third lens (L3).

7. The fixed-focus lens according to any one of claims 1-6, Characterized in that, The optical total length TTL of the fixed-focus lens and the focal length F satisfy the following relationship: 5.9 ≤ TTL / F ≤ 6.

7.

8. The fixed-focus lens according to any one of claims 1-6, Characterized in that, The optical back focal length BFL of the fixed-focus lens and the focal length F satisfy the following relationship: 0.8 ≤ BFL / F ≤ 1.

9. The fixed-focus lens according to any one of claims 1-6, characterized in that, the focal length F3 of the third lens (L3) and the focal length F1 of the first lens (L1) satisfy the following relationship: -1.3 ≤ F3 / F1 ≤ -1.

1.

10. The fixed-focus lens according to any one of claims 1-6, characterized in that, the focal length F8 of the eighth lens (L8) and the focal length F of the fixed-focus lens satisfy the following relationship: 7.2 ≤ F8 / F ≤ 14.

2.

11. The fixed-focus lens according to any one of claims 1-6, characterized in that, the focal length F9 of the ninth lens (L9) and the focal length F of the fixed-focus lens satisfy the following relationship: 10.4 ≤ F9 / F ≤ 21.

6.

12. The fixed-focus lens according to any one of claims 1-6, characterized in that, the combined focal length F89 of the eighth lens (L8) and the ninth lens (L9) and the focal length F of the fixed-focus lens satisfy the following relationship: 5.1 ≤ F89 / F ≤ 6.

5.

13. The fixed-focus lens according to claim 5, characterized in that, the central thickness db1 of the cemented lens group composed of the fifth lens (L5), the sixth lens (L6) and the seventh lens (L7) and the central thickness d6 of the sixth lens (L6) satisfy the following relationship: 9.2 ≤ db1 / d6 ≤ 14.

8.

14. The fixed-focus lens according to any one of claims 1-6, characterized in that, the central length d23 from the image side of the second lens (L2) to the object side of the third lens (L3), the central length d34 from the image side of the third lens (L3) to the object side of the fourth lens (L4), and the central thickness d3 of the third lens (L3) satisfy the following relationship: 1.6 ≤ (d23 + d34) / d3 ≤ 2.

Images