fixed focus lens

Abstract

The present application relates to a kind of fixed focus lens, in the direction of optical axis from object side to image side, it includes successively: the first lens (L1) of negative power, the second lens (L2) of positive power, the third lens (L3) of positive power, diaphragm (STO), the fourth lens (L4) of positive power, the fifth lens (L5) of negative power, the sixth lens (L6) of positive power, the seventh lens (L7) of positive power and the eighth lens (L8) of negative power, the shape of object side of the fifth lens (L5) is concave, the sixth lens (L6) is convex convex lens, the eighth lens (L8) is near-axis area concave convex lens.This fixed focus lens has the characteristics of large target surface, super large aperture, large light quantity, low cost, miniaturization and high imaging performance, and the image is clear in the temperature range of-40 ℃~+80 ℃.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and more particularly to a fixed-focus lens. Background Technology

[0002] With the rapid development of security and public safety work, the demand for fixed-focus surveillance lenses is also gradually increasing. To achieve higher light transmission at night, ultra-large aperture lenses better meet market needs, making their research and development essential. However, most lenses on the market prioritize daytime image quality, with nighttime image quality significantly decreasing at practical aperture settings. Therefore, to address the shortcomings of existing technologies, a large-aperture security lens with a large focal length, low cost, and no blurring within a temperature range of -40℃ to 80℃ is needed. Summary of the Invention

[0003] The purpose of this invention is to provide a fixed-focus lens with a large target area, low cost, and non-defocusing within a temperature range of -40℃ to 80℃, and an ultra-large aperture.

[0004] To achieve the above-mentioned objective, the present invention provides a fixed-focus lens, which, along the optical axis from the object side to the image side, sequentially includes: a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power, an aperture stop, a fourth lens with positive optical power, a fifth lens with negative optical power, a sixth lens with positive optical power, a seventh lens with positive optical power, and an eighth lens with negative optical power.

[0005] According to one aspect of the invention, along the optical axis from the object side to the image side,

[0006] The first lens is a paraxial convex-concave lens;

[0007] The second lens is a concave-convex lens;

[0008] The paraxial region of the object-side surface of the third lens is convex.

[0009] The image-side surface of the fourth lens is convex.

[0010] The object-side surface of the fifth lens is concave.

[0011] The sixth lens is a convex-convex lens;

[0012] The seventh lens is a convex-convex lens;

[0013] The eighth lens is a paraxial concave-convex lens.

[0014] According to one aspect of the present invention, the first lens, the second lens, the third lens, the seventh lens, and the eighth lens are aspherical lenses;

[0015] The fourth lens, the fifth lens, and the sixth lens are spherical lenses.

[0016] According to one aspect of the present invention, the first lens, the second lens, the third lens, the seventh lens, and the eighth lens are plastic lenses;

[0017] The fourth lens, the fifth lens, and the sixth lens are glass lenses.

[0018] According to one aspect of the invention, the fourth lens and the fifth lens are cemented together to form a cemented lens assembly.

[0019] According to one aspect of the invention, the focal length F45 of the cemented lens group and the effective focal length F of the fixed-focus lens satisfy: -4.0≤F45 / F≤16.5.

[0020] According to one aspect of the invention, the focal length F45 of the cemented lens group and the rear group focal length FB of the fixed-focus lens satisfy: -2.2≤F45 / FB≤10.5.

[0021] According to one aspect of the invention, the total optical length (TTL) of the fixed-focus lens and the back focal length (BFL) of the fixed-focus lens satisfy: 5.8 ≤ TTL / BFL ≤ 8.0.

[0022] According to one aspect of the invention, the effective focal length F of the fixed-focus lens and the back focal length BFL of the fixed-focus lens satisfy: 1.0 ≤ F / BFL ≤ 1.5.

[0023] According to one aspect of the invention, the effective focal length F of the fixed-focus lens and the maximum image height IH of the fixed-focus lens satisfy: 0.4≤F / IH≤0.8.

[0024] According to one aspect of the invention, the focal length F1 of the first lens and the effective focal length F of the fixed-focus lens satisfy: -2.2≤F1 / F≤-1.6.

[0025] According to one aspect of the invention, the center distance D12 between the first lens and the second lens on the optical axis and the total optical length TTL of the fixed-focus lens satisfy: 0.1≤D12 / TTL≤0.3.

[0026] According to one aspect of the invention, the refractive index Nd3 and Abbe number Vd3 of the third lens satisfy the following conditions: 1.6≤Nd3≤1.7; 20≤Vd3≤30.

[0027] According to one aspect of the invention, the refractive index Nd4 and Abbe number Vd4 of the fourth lens satisfy the following conditions: 1.70≤Nd4≤1.8; 50≤Vd4≤60.

[0028] The refractive index Nd5 and Abbe number Vd5 of the fifth lens satisfy the following conditions: 1.70≤Nd5≤1.9; 20≤Vd5≤30.

[0029] According to one aspect of the invention, the refractive index Nd6 and Abbe number Vd6 of the sixth lens satisfy the following conditions: 1.40≤Nd6≤1.5; 90≤Vd6≤95.

[0030] According to one aspect of the invention, the focal length F6 of the sixth lens and the effective focal length F of the fixed-focus lens satisfy: 2.6≤F6 / F≤4.5.

[0031] According to one aspect of the invention, the edge thickness ET8 and the center thickness CT8 of the eighth lens satisfy: 1.6≤ET8 / CT8≤2.6.

[0032] According to one aspect of the invention, the focal length F8 of the eighth lens and the effective focal length F of the fixed-focus lens satisfy: -5.6≤F8 / F≤-2.6.

[0033] According to one aspect of the invention, the fixed-focus lens further includes a filter.

[0034] The effective optical aperture SDF of the filter and the effective half-aperture SD1 of the first lens satisfy the condition: 0.6≤SDF / SD1≤0.9.

[0035] According to one aspect of the invention, the optically effective diameter SDS of the aperture and the optically effective half-aperture SD1 of the first lens satisfy: 0.5≤SDS / SD1≤0.9.

[0036] According to the present invention, by employing eight lenses arranged in the aforementioned manner and optimizing their configuration, including their optical power, different shapes, specific materials, focal length relationships, and various lens parameters, this fixed-focus lens can achieve high-quality imaging performance, providing clear imaging within a temperature range of -40℃ to +80℃. It also features a large sensor size, ultra-large aperture, high light throughput, low cost, and miniaturization, making it suitable for 1 / 1.8" large sensor chips. Furthermore, through a two-stop variable aperture design, this fixed-focus lens supports two stops of F1.0 / F1.6 in visible light, achieving day and night confocal focusing at the F1.6 stop. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0038] Figure 1 This schematic diagram illustrates the structure of a fixed-focus lens according to Embodiment 1 of the present invention.

[0039] Figure 2 This schematic diagram illustrates the light fan of a fixed-focus lens according to Embodiment 1 of the present invention.

[0040] Figure 3 This schematic diagram illustrates the structure of the fixed-focus lens according to Embodiment 2 of the present invention.

[0041] Figure 4 This schematic diagram illustrates the light fan of the fixed-focus lens according to Embodiment 2 of the present invention.

[0042] Figure 5 This schematic diagram illustrates the structure of a fixed-focus lens according to Embodiment 3 of the present invention.

[0043] Figure 6 This schematic diagram illustrates the light fan of the fixed-focus lens according to Embodiment 3 of the present invention.

[0044] Figure 7 This schematic diagram illustrates the structure of a fixed-focus lens according to Embodiment 4 of the present invention.

[0045] Figure 8 This diagram illustrates the light spectrum of the fixed-focus lens according to Embodiment 4 of the present invention. Specific Implementation

[0046] The description of the embodiments in this specification should be taken in conjunction with the accompanying drawings, which should form part of the complete specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and may be indicated in a simplified or convenient manner. Furthermore, parts of the various structures in the drawings will be described separately; it is worth noting that elements not shown in the figures or not described in words are in a form known to those skilled in the art.

[0047] The description of the embodiments herein, including any references to directions and orientations, is for ease of description only and should not be construed as limiting the scope of the invention. The following description of preferred embodiments involves combinations of features, which may exist independently or in combination; the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.

[0048] like Figure 1As shown, this embodiment of the invention provides a fixed-focus lens, which, along the optical axis from the object side to the image side, sequentially includes: a first lens L1, a second lens L2, a third lens L3, an aperture stop STO, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. Among these, the first lens L1, the fifth lens L5, and the eighth lens L8 are all negative power lenses, while the second lens L2, the third lens L3, the fourth lens L4, the sixth lens L6, and the seventh lens L7 are all positive power lenses.

[0049] Along the optical axis from the object side to the image side, the first lens L1 is a paraxial convex-concave lens, the second lens L2 is a concave-convex lens, the paraxial shape of the object side of the third lens L3 is convex, the shape of the image side of the fourth lens L4 is convex, the shape of the object side of the fifth lens L5 is concave, the sixth lens L6 and the seventh lens L7 are both convex-convex lenses, and the eighth lens L8 is a paraxial concave-convex lens.

[0050] According to the above technical solution, by employing eight lenses arranged in the aforementioned manner and optimizing the optical power and object-side and image-side shapes of each lens, this fixed-focus lens can achieve high-quality imaging performance, providing clear imaging within a temperature range of -40℃ to +80℃, enabling a large target area and ultra-large aperture, suitable for 1 / 1.8" large target area chips. Furthermore, through the design of a two-stop variable aperture (STO), this fixed-focus lens supports two stops of F1.0 / F1.6 in visible light. At the F1.6 stop, the lens can achieve day and night confocal focusing functionality.

[0051] In this embodiment of the invention, the first lens L1, the second lens L2, the third lens L3, the seventh lens L7, and the eighth lens L8 are all aspherical lenses, while the fourth lens L4, the fifth lens L5, and the sixth lens L6 are all spherical lenses. By employing the above-mentioned aspherical lenses and their combinations, the aberrations of the fixed-focus lens optical system can be efficiently adjusted, thereby improving lens performance.

[0052] In this embodiment of the invention, the first lens L1, the second lens L2, the third lens L3, the seventh lens L7, and the eighth lens L8 are all plastic lenses, while the fourth lens L4, the fifth lens L5, and the sixth lens L6 are all glass lenses. Through this optimized hybrid arrangement of glass and plastic materials in the lenses, instability correction and temperature drift compensation for high and low temperature imaging can be achieved, thereby reducing lens costs and realizing low-cost lens design.

[0053] In this embodiment of the invention, the fourth lens L4 and the fifth lens L5 are cemented together to form a cemented lens group. This cemented lens group can correct off-axis aberrations such as field curvature, coma, and astigmatism, further improving the lens's imaging performance. Preferably, the focal length F45 of this cemented lens group and the effective focal length F of the fixed-focus lens satisfy: -4.0 ≤ F45 / F ≤ 16.5. Preferably, in this cemented lens group, the refractive index Nd4 and Abbe number Vd4 of the fourth lens L4 satisfy the following conditions: 1.70 ≤ Nd4 ≤ 1.8; 50 ≤ Vd4 ≤ 60. The refractive index Nd5 and Abbe number Vd5 of the fifth lens L5 satisfy the following conditions: 1.70 ≤ Nd5 ≤ 1.9; 20 ≤ Vd5 ≤ 30. Thus, by rationally combining and setting the cemented lenses, and designing the refractive index and dispersion coefficient of the fourth lens L4 and the fifth lens L5, aberrations in the lens optical system can be effectively reduced.

[0054] Preferably, the focal length F45 of the cemented lens group and the rear focal length FB of the fixed-focus lens satisfy: -2.2 ≤ F45 / FB ≤ 10.5. Here, the rear focal length FB refers to the combined focal length from the object side to the image side, from the fourth lens L4 to the eighth lens L8. By designing the focal length ratio of the above-mentioned cemented lens group and the rear focal length of the lens, it is beneficial to balance the aberrations when incident light enters the optical system.

[0055] In this embodiment of the invention, the total optical length (TTL), effective focal length (F), and back focal length (BFL) of the fixed-focus lens satisfy the following conditions: 5.8 ≤ TTL / BFL ≤ 8.0; 1.0 ≤ F / BFL ≤ 1.5. By rationally and optimally designing the parameters of the total optical length, focal length, and back focal length of the lens, miniaturization can be achieved, meeting the performance requirements of small size. It should be noted that in this embodiment of the invention, the back focal length (BFL) of the fixed-focus lens refers to the distance from the image-side surface of the last lens, i.e., the eighth lens L8, to the image plane IMA.

[0056] In this embodiment of the invention, the effective focal length F and the maximum image height IH of the fixed-focus lens satisfy the condition: 0.4≤F / IH≤0.8, which is beneficial to improving the resolving power of the fixed-focus lens and reducing lens sensitivity.

[0057] In this embodiment of the invention, the focal length F1 of the first lens L1 and the effective focal length F of the fixed-focus lens satisfy: -2.2≤F1 / F≤-1.6, which allows light to enter the rear optical structure of the lens correctly and smoothly, increasing the amount of light transmitted and improving the resolution performance.

[0058] In this embodiment of the invention, the center distance D12 between the first lens L1 and the second lens L2 on the optical axis and the total optical length TTL of the fixed-focus lens satisfy: 0.1≤D12 / TTL≤0.3, which can effectively control the deflection angle of light emitted from the image side of the first lens L1, thereby effectively controlling the lens principal angle CRA.

[0059] In this embodiment of the invention, the refractive index Nd3 and Abbe number Vd3 of the third lens L3 satisfy the following conditions: 1.6≤Nd3≤1.7; 20≤Vd3≤30. By setting the refractive index and dispersion coefficient of the plastic lens in this way, both costs can be reduced and the resolution quality of the lens under high and low temperature conditions can be improved.

[0060] In this embodiment of the invention, the refractive index Nd6 and Abbe number Vd6 of the sixth lens L6 satisfy the following conditions: 1.40≤Nd6≤1.5; 90≤Vd6≤95. The focal length F6 of the sixth lens L6 and the effective focal length F of the fixed-focus lens satisfy: 2.6≤F6 / F≤4.5. By satisfying the above two conditions, it is beneficial to balance the confocal state of the lens in visible light and infrared light.

[0061] In this embodiment of the invention, the edge thickness ET8 and the center thickness CT8 of the eighth lens L8 satisfy the following condition: 1.6 ≤ ET8 / CT8 ≤ 2.6. By reasonably setting the thickness parameters of the eighth lens L8, the production difficulty of the plastic lens can be reduced. The focal length F8 of the eighth lens L8 and the effective focal length F of the fixed-focus lens satisfy the following condition: -5.6 ≤ F8 / F ≤ -2.6, which is beneficial for the smooth entry of light into the image plane IMA, and for concentrating the defocus curve, thus helping to improve the resolving performance of the lens.

[0062] In this embodiment of the invention, the fixed-focus lens further includes a filter ( Figures 1 to 4 In the diagram, the filter is denoted as a surface S13. The effective optical aperture SDF of the filter and the effective half-aperture SD1 of the first lens L1 satisfy: 0.6≤SDF / SD1≤0.9, which can filter out light and further improve the resolution performance while ensuring the maximum light transmission.

[0063] In this embodiment of the invention, the optical effective diameter SDS of the aperture stop STO and the optical effective half-aperture SD1 of the first lens L1 satisfy: 0.5≤SDS / SD1≤0.9, which makes the aperture diameter large enough. By changing the aperture size, the ultra-large aperture function of the lens in infrared mode can be realized.

[0064] In summary, by adopting the above technical solutions, a fixed-focus lens with a large target area, ultra-large aperture, low cost, miniaturization, and high imaging performance is obtained. It produces clear images within a temperature range of -40℃ to +80℃ and is suitable for 1 / 1.8" large target area chips. Furthermore, the lens supports two stops of F1.0 and F1.6 in visible light, achieving day and night confocal focusing at the F1.6 stop.

[0065] The fixed-focus lens of the present invention will be specifically described below with reference to four embodiments, accompanying drawings, and tables. In the following embodiments, the aperture stop STO is referred to as one side, the cemented surface of the cemented lens group is referred to as one side, the filter is referred to as one side, the parallel plate CG is referred to as two sides, and the image plane IMA is referred to as one side.

[0066] The parameters for each embodiment that meets the above conditions are shown in Table 1 below:

[0067]

[0068]

[0069] Table 1

[0070] In an embodiment of the present invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0071]

[0072] In the above formula, z is the axial distance from the vertex to the surface at a position perpendicular to the optical axis at a height h; c represents the curvature at the vertex of the aspherical surface; k is the conic coefficient; A4, A6, A8, A 10 A 12 A 14 A 16 ...represent aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth orders, respectively.

[0073] Example 1

[0074] See Figure 1 The parameters of the fixed-focus lens in this embodiment are as follows:

[0075] Fno: 1.09; Total optical length TTL: 30.30mm. The third lens L3 is a paraxial convex-concave lens, the fourth lens L4 is a concave-convex lens, and the fifth lens L5 is a concave-concave lens.

[0076] The relevant parameters of each lens in the fixed-focus lens of this embodiment include: surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 2 below.

[0077]

[0078]

[0079] Table 2

[0080] The aspherical coefficients of each aspherical lens in the fixed-focus lens of this embodiment include: the quadratic surface constant K, the fourth-order aspherical coefficient A4, the sixth-order aspherical coefficient A6, the eighth-order aspherical coefficient A8, and the tenth-order aspherical coefficient A10. 10 12th order aspherical coefficient A 12 Fourteenth-order aspherical coefficient A 14 and the sixteenth-order aspherical coefficient A 16 As shown in Table 3 below.

[0081]

[0082]

[0083] Table 3

[0084] Combination Figure 1 , Figure 2 As shown in Tables 1 to 3 above, the fixed-focus lens of this embodiment features a large target area, ultra-large aperture, low cost, miniaturization, and high imaging performance. It produces clear images within a temperature range of -40℃ to +80℃ and is suitable for 1 / 1.8" large target area chips. Furthermore, the lens supports two focal lengths (F1.0 and F1.6) in visible light, achieving day and night confocal focusing at F1.6.

[0085] Example 2

[0086] See Figure 3 The parameters of the fixed-focus lens in this embodiment are as follows:

[0087] Fno: 1.10; Total optical length TTL: 30.30mm. The third lens L3 is a paraxial convex-concave lens, the fourth lens L4 is a concave-convex lens, and the fifth lens L5 is a concave-concave lens.

[0088] The relevant parameters of each lens in the fixed-focus lens of this embodiment include: surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 4 below.

[0089]

[0090]

[0091] Table 4

[0092] The aspherical coefficients of each aspherical lens in the fixed-focus lens of this embodiment include: the quadratic surface constant K, the fourth-order aspherical coefficient A4, the sixth-order aspherical coefficient A6, the eighth-order aspherical coefficient A8, and the tenth-order aspherical coefficient A10. 10 12th order aspherical coefficient A 12 Fourteenth-order aspherical coefficient A 14 and the sixteenth-order aspherical coefficient A 16 As shown in Table 5 below.

[0093]

[0094]

[0095] Table 5

[0096] Combination Figure 3 , Figure 4 As shown in Tables 1, 4, and 5 above, the fixed-focus lens of this embodiment features a large target area, ultra-large aperture, low cost, miniaturization, and high imaging performance. It produces clear images within a temperature range of -40℃ to +80℃ and is suitable for 1 / 1.8" large target area chips. Furthermore, the lens supports two focal lengths (F1.0 and F1.6) in visible light, achieving day and night confocal focusing at F1.6.

[0097] Example 3

[0098] See Figure 5 The parameters of the fixed-focus lens in this embodiment are as follows:

[0099] Fno: 1.07; Total optical length TTL: 28.51mm. The third lens L3 is a paraxial convex-concave lens, the fourth lens L4 is a concave-convex lens, and the fifth lens L5 is a concave-concave lens.

[0100] The relevant parameters of each lens in the fixed-focus lens of this embodiment include: surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 6 below.

[0101]

[0102]

[0103] Table 6

[0104] The aspherical coefficients of each aspherical lens in the fixed-focus lens of this embodiment include: the quadratic surface constant K, the fourth-order aspherical coefficient A4, the sixth-order aspherical coefficient A6, the eighth-order aspherical coefficient A8, and the tenth-order aspherical coefficient A10. 10 12th order aspherical coefficient A 12 Fourteenth-order aspherical coefficient A 14 and the sixteenth-order aspherical coefficient A16 As shown in Table 7 below.

[0105]

[0106] Table 7

[0107] Combination Figure 5 , Figure 6 As shown in Tables 1, 6, and 7 above, the fixed-focus lens of this embodiment features a large target area, ultra-large aperture, low cost, miniaturization, and high imaging performance. It produces clear images within a temperature range of -40℃ to +80℃ and is suitable for 1 / 1.8" large target area chips. Furthermore, the lens supports two focal lengths (F1.0 and F1.6) in visible light, achieving day and night confocal focusing at F1.6.

[0108] Example 4

[0109] See Figure 7 The parameters of the fixed-focus lens in this embodiment are as follows:

[0110] Fno: 1.07; Total optical length TTL: 30.30mm. The third lens L3 is a paraxial convex-concave lens, the fourth lens L4 is a convex-convex lens, and the fifth lens L5 is a concave-convex lens.

[0111] The relevant parameters of each lens in the fixed-focus lens of this embodiment include: surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, as shown in Table 8 below.

[0112]

[0113]

[0114] Table 8

[0115] The aspherical coefficients of each aspherical lens in the fixed-focus lens of this embodiment include: the quadratic surface constant K, the fourth-order aspherical coefficient A4, the sixth-order aspherical coefficient A6, the eighth-order aspherical coefficient A8, and the tenth-order aspherical coefficient A10. 10 12th order aspherical coefficient A 12 Fourteenth-order aspherical coefficient A 14 and the sixteenth-order aspherical coefficient A 16 As shown in Table 9 below.

[0116]

[0117] Table 9

[0118] Combination Figure 7 , Figure 8As shown in Tables 1, 8, and 9 above, the fixed-focus lens of this embodiment features a large target area, ultra-large aperture, low cost, miniaturization, and high imaging performance. It produces clear images within a temperature range of -40℃ to +80℃ and is suitable for 1 / 1.8" large target area chips. Furthermore, the lens supports two focal lengths (F1.0 and F1.6) in visible light, achieving day and night confocal focusing at F1.6.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fixed-focus lens, characterized in that, Along the optical axis from the object side to the image side, the lenses sequentially include: a first lens with negative optical power (L1), a second lens with positive optical power (L2), a third lens with positive optical power (L3), an aperture stop (STO), a fourth lens with positive optical power (L4), a fifth lens with negative optical power (L5), a sixth lens with positive optical power (L6), a seventh lens with positive optical power (L7), and an eighth lens with negative optical power (L8), for a total of eight lenses with optical power. The object-side surface of the fifth lens (L5) is concave, the sixth lens (L6) is a convex-convex lens, and the eighth lens (L8) is a paraxial concave-convex lens. The refractive index Nd4 and Abbe number Vd4 of the fourth lens (L4) satisfy the following conditions: 1.70≤Nd4≤1.8; 50≤Vd4≤60. The refractive index Nd5 and Abbe number Vd5 of the fifth lens (L5) satisfy the following conditions: 1.70≤Nd5≤1.9; 20≤Vd5≤30. The refractive index Nd6 and Abbe number Vd6 of the sixth lens (L6) satisfy the following conditions: 1.40≤Nd6≤1.5; 90≤Vd6≤95.

2. The fixed-focus lens according to claim 1, characterized in that, Along the optical axis from the object side to the image side, The first lens (L1) is a paraxial convex-concave lens; The second lens (L2) is a concave-convex lens; The paraxial region of the object side of the third lens (L3) is convex. The image-side surface of the fourth lens (L4) is convex. The seventh lens (L7) is a convex-convex 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 seventh lens (L7), and the eighth lens (L8) are aspherical lenses; The fourth lens (L4), the fifth lens (L5), and the sixth lens (L6) are spherical lenses.

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

5. The fixed-focus lens according to claim 1, characterized in that, The fourth lens (L4) and the fifth lens (L5) are cemented together to form a cemented lens assembly.

6. The fixed-focus lens according to claim 5, characterized in that, The focal length F45 of the cemented lens group and the effective focal length F of the fixed-focus lens satisfy: -4.0≤F45 / F≤16.

5.

7. The fixed-focus lens according to claim 5, characterized in that, The focal length F45 of the cemented lens group and the rear focal length FB of the fixed-focus lens satisfy: -2.2≤F45 / FB≤10.5; Wherein, the rear group focal length FB refers to the combined focal length of the fourth lens (L4) to the eighth lens (L8) from the object side to the image side.

8. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The total optical length (TTL) and the back focal length (BFL) of the fixed-focus lens satisfy the following condition: 5.8 ≤ TTL / BFL ≤ 8.

0.

9. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The effective focal length F and the back focal length BFL of the fixed-focus lens satisfy the following condition: 1.0 ≤ F / BFL ≤ 1.

5.

10. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The effective focal length F and the maximum image height IH of the fixed-focus lens satisfy the condition: 0.4≤F / IH≤0.

8.

11. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The focal length F1 of the first lens (L1) and the effective focal length F of the fixed-focus lens satisfy: -2.2≤F1 / F≤-1.

6.

12. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The center distance D12 between the first lens (L1) and the second lens (L2) on the optical axis and the total optical length TTL of the fixed-focus lens satisfy: 0.1≤D12 / TTL≤0.

3.

13. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The refractive index Nd3 and Abbe number Vd3 of the third lens (L3) satisfy the following conditions: 1.6≤Nd3≤1.7; 20≤Vd3≤30.

14. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The focal length F6 of the sixth lens (L6) and the effective focal length F of the fixed-focus lens satisfy: 2.6≤F6 / F≤4.

5.

15. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The edge thickness ET8 and the center thickness CT8 of the eighth lens (L8) satisfy: 1.6≤ET8 / CT8≤2.

6.

16. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The focal length F8 of the eighth lens (L8) and the effective focal length F of the fixed-focus lens satisfy: -5.6≤F8 / F≤-2.

6.

17. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The fixed-focus lens also includes a filter. The effective optical aperture SDF of the filter and the effective half-aperture SD1 of the first lens (L1) satisfy: 0.6≤SDF / SD1≤0.

9.

18. The fixed-focus lens according to any one of claims 1 to 7, characterized in that, The optically effective diameter SDS of the aperture stop (STO) and the optically effective half-aperture SD1 of the first lens (L1) satisfy: 0.5≤SDS / SD1≤0.9.

Images