Fixed-focus lens

Abstract

The present invention relates to a fixed-focus lens, which comprises a first lens (L1) with negative optical power, a second lens (L2) with positive optical power, a stop (STO), a third lens (L3) with positive or negative optical power, a fourth lens (L4) with positive optical power, a fifth lens (L5) with negative optical power, a sixth lens (L6) with positive optical power, a seventh lens (L7) with positive optical power, and an eighth lens (L8) with negative optical power, which are arranged in sequence along the optical axis from the object side to the image side. The fixed-focus lens of the present invention has the characteristics of low cost, miniaturization, super large aperture, high resolution, and dual use for day and night, and does not defocus within the temperature range of -40°C to 80°C.

Description

Technical Field

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

[0002] With the increasing emphasis on the work in the field of public security in society, the demand and requirements for monitoring facilities are also continuously improving. Fixed-focus lenses are widely used in various security facilities due to their advantages such as high-definition imaging and clear imaging under low illuminance conditions. Existing security lenses usually adopt dual-band confocal technology to achieve daytime and nighttime shooting. However, this method is only a primary technology for nighttime shooting, and day-night full color is the future development goal. In the existing technology, increasing the lens aperture is the main means to achieve day-night full color. However, since it is difficult to control the overall optical length of a large-aperture lens (FNO < 1.2) and its volume is also large, this method does not conform to the development concept of small volume and high image quality for security lenses. Summary of the Invention

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

[0004] To achieve the above-mentioned invention purpose, the present invention provides a fixed-focus lens, which includes a first lens with a negative optical power, a second lens with a positive optical power, a diaphragm, a third lens with a positive or negative optical power, a fourth lens with a positive optical power, a fifth lens with a negative optical power, a sixth lens with a positive optical power, a seventh lens with a positive optical power, and an eighth lens with a negative optical power, which are arranged in sequence from the object side to the image side along the optical axis.

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

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

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

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

[0009] According to one aspect of the present invention, the total optical length TTL of the fixed-focus lens and the effective focal length F satisfy the following relationship: 3.4 ≤ TTL / F ≤ 3.7.

[0010] According to one aspect of the present invention, the back focal length BFL of the fixed-focus lens and the total optical length TTL satisfy the following relationship: 0.68 ≤ BFL / TTL ≤ 0.75.

[0011] According to one aspect of the present invention, the effective focal length F1 of the first lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: -3 ≤ F1 / F ≤ -2.8.

[0012] According to one aspect of the present invention, the effective focal length F2 of the second lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 8.75 ≤ F2 / F ≤ 10.25.

[0013] According to one aspect of the present invention, the effective focal length F3 of the third lens and the effective focal length F2 of the second lens satisfy the following relationship: -69 ≤ F3 / F2 ≤ 75.

[0014] According to one aspect of the present invention, the effective focal length F4 of the fourth lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 2.387 ≤ F4 / F ≤ 2.642.

[0015] According to one aspect of the present invention, the effective focal length F5 of the fifth lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: -1.41 ≤ F5 / F ≤ -1.32.

[0016] According to one aspect of the present invention, the effective focal length F6 of the sixth lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 0.85 ≤ F6 / F ≤ 0.91.

[0017] According to one aspect of the present invention, the combined focal length F56 of the fifth lens and the sixth lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 1.89 ≤ F56 / F ≤ 2.21.

[0018] According to one aspect of the present invention, the combined focal length F78 of the seventh lens and the eighth lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.2 ≤ F78 / F ≤ 15.5.

[0019] According to one aspect of the present invention, the air interval length d78 between the seventh lens and the eighth lens and the sum of the thicknesses of the seventh lens and the eighth lens (d7 + d8) satisfy the following relationship: 0.029 ≤ d78 / (d7 + d8) ≤ 0.035.

[0020] According to the concept of the present invention, a day-night dual-purpose security fixed-focus lens with low cost, miniaturization, super large aperture (F1.0), high resolution, and low-light imaging is provided.

[0021] According to one solution of the present invention, by reasonably setting the optical power and concavity / convexity of each lens in the fixed-focus lens, the performance of the fixed-focus lens can be high, the volume can be small, the aperture can be large, and it can be used day and night. Moreover, it can also achieve non-defocusing and clear imaging within the temperature range of -40°C to 80°C.

[0022] According to one solution of the present invention, by reasonably setting the surface shape and material of each lens in the fixed-focus lens, the cost of the fixed-focus lens can be low and the image quality can be high.

[0023] According to one solution of the present invention, by reasonably setting the relationship between the overall optical length and the effective focal length of the fixed-focus lens and the relationship between the optical back focal length and the overall optical length of the fixed-focus lens, it is beneficial for the fixed-focus lens to achieve the purpose of miniaturization.

[0024] According to one solution of the present invention, by reasonably setting the relationship between the effective focal length of the first lens and the effective focal length of the fixed-focus lens and the relationship between the effective focal length of the second lens and the effective focal length of the fixed-focus lens, the incident light can be effectively controlled, thereby reducing the system aberration and being beneficial to improving the image quality.

[0025] According to one solution of the present invention, by reasonably setting the relationship between the effective focal length of the third lens and the effective focal length of the second lens, the aberration caused by the aperture stop can be effectively reduced.

[0026] According to one solution of the present invention, by reasonably setting the relationship between the effective focal length of the fourth lens and the effective focal length of the fixed-focus lens, it is beneficial to balance the high and low temperature performance of the fixed-focus lens.

[0027] According to one solution of the present invention, by reasonably setting the cemented lens group and its related parameters, the chromatic aberration can be effectively calibrated.

[0028] According to one solution of the present invention, by reasonably setting the relationship between the combined focal length of the seventh lens and the eighth lens and the effective focal length of the fixed-focus lens and the relationship between the air interval length between the seventh lens and the eighth lens and the sum of the thicknesses of the seventh lens and the eighth lens, the distortion can be effectively controlled and the optical imaging performance can be improved. Description of the Drawings

[0029] Figure 1Structural diagram schematically showing a fixed-focus lens according to the first embodiment of the present invention;

[0030] Figure 2 MTF graph schematically showing a fixed-focus lens according to the first embodiment of the present invention;

[0031] Figure 3 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm according to the first embodiment of the present invention;

[0032] Figure 4 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm at a high temperature of 80 °C according to the first embodiment of the present invention;

[0033] Figure 5 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm at a low temperature of -40 °C according to the first embodiment of the present invention;

[0034] Figure 6 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm at an infrared wavelength of 850 nm according to the first embodiment of the present invention;

[0035] Figure 7 Structural diagram schematically showing a fixed-focus lens according to the second embodiment of the present invention;

[0036] Figure 8 MTF graph schematically showing a fixed-focus lens according to the second embodiment of the present invention;

[0037] Figure 9 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm according to the second embodiment of the present invention;

[0038] Figure 10 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm at a high temperature of 80 °C according to the second embodiment of the present invention;

[0039] Figure 11 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm at a low temperature of -40 °C according to the second embodiment of the present invention;

[0040] Figure 12 Through-Focus-MTF graph of a fixed-focus lens with a frequency of 125 lp / mm at an infrared wavelength of 850 nm according to the second embodiment of the present invention;

[0041] Figure 13 Structural diagram schematically showing a fixed-focus lens according to the third embodiment of the present invention;

[0042] Figure 14 MTF diagram schematically showing a fixed-focus lens according to the third embodiment of the present invention;

[0043] Figure 15 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the third embodiment of the present invention with a frequency of 125 lp / mm;

[0044] Figure 16 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the third embodiment of the present invention at a high temperature of 80 °C with a frequency of 125 lp / mm;

[0045] Figure 17 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the third embodiment of the present invention at a low temperature of -40 °C with a frequency of 125 lp / mm;

[0046] Figure 18 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the third embodiment of the present invention at an infrared wavelength of 850 nm with a frequency of 125 lp / mm;

[0047] Figure 19 Structural diagram schematically showing a fixed-focus lens according to the fourth embodiment of the present invention;

[0048] Figure 20 MTF diagram schematically showing a fixed-focus lens according to the fourth embodiment of the present invention;

[0049] Figure 21 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the fourth embodiment of the present invention with a frequency of 125 lp / mm;

[0050] Figure 22 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the fourth embodiment of the present invention at a high temperature of 80 °C with a frequency of 125 lp / mm;

[0051] Figure 23 Through-Focus-MTF diagram schematically showing a fixed-focus lens according to the fourth embodiment of the present invention at a low temperature of -40 °C with a frequency of 125 lp / mm;

[0052] Figure 24Schematic diagram showing the Through-Focus-MTF graph of the fixed-focus lens of the fourth embodiment of the present invention at an infrared wavelength of 850 nm and a frequency of 125 lp / mm. Detailed implementation mode

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0054] 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 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.

[0055] The present invention will be described in detail below with reference to the drawings and specific implementation modes. The implementation modes cannot be elaborated one by one here, but the implementation modes of the present invention are not limited to the following implementation modes.

[0056] See Figure 1 , the fixed-focus lens of the present invention includes a first lens L1 with negative optical power, a second lens L2 with positive optical power, a diaphragm STO, a third lens L3 with positive or negative optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with negative optical power, a sixth lens L6 with positive optical power, a seventh lens L7 with positive optical power, and an eighth lens L8 with negative optical power, which are arranged in sequence from the object side to the image side along the optical axis.

[0057] In the present invention, the first lens L1 is a convex-concave lens, the second lens L2 is a concave-convex lens, the third lens L3 is a convex-concave lens, the fourth lens L4 is a convex-convex lens, the fifth lens L5 is a convex-concave lens, the sixth lens L6 is a convex-convex lens, the seventh lens L7 is a concave-convex lens, and the eighth lens L8 is a convex-concave lens in the paraxial region.

[0058] Satisfying the above settings can make the fixed-focus lens of the present invention have the characteristics of high performance, miniaturization, a super large aperture of F1.0, and dual use for day and night. Moreover, it can also achieve clear imaging within the temperature range of -40°C to 80°C.

[0059] In the present invention, the first lens L1 is an aspherical lens, the second lens L2 is an aspherical lens, the third lens L3 is an aspherical lens, the fourth lens L4 is a spherical lens, the fifth lens L5 is a spherical lens, the sixth lens L6 is a spherical lens, the seventh lens L7 is an aspherical lens, and the eighth lens L8 is an aspherical lens. The first lens L1 is a plastic lens, the second lens L2 is a plastic lens, the third lens L3 is a plastic lens, the fourth lens L4 is a glass lens, the fifth lens L5 is a glass lens, the sixth lens L6 is a glass lens, the seventh lens L7 is a plastic lens, and the eighth lens L8 is a plastic lens. In this way, the cost of the fixed-focus lens can be relatively low, and the image quality can be relatively high.

[0060] In the present invention, the optical total length TTL of the fixed-focus lens and the effective focal length F satisfy the following relationship: 3.4 ≤ TTL / F ≤ 3.7. The optical back focal length (i.e., the distance from the image side of the last lens to the image plane IMAGE) BFL of the fixed-focus lens and the optical total length TTL satisfy the following relationship: 0.68 ≤ BFL / TTL ≤ 0.75. In this way, it is beneficial to achieve the purpose of miniaturization of the fixed-focus lens.

[0061] In the present invention, the effective focal length F1 of the first lens L1 and the effective focal length F of the fixed-focus lens satisfy the following relationship: -3 ≤ F1 / F ≤ -2.8. The effective focal length F2 of the second lens L2 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 8.75 ≤ F2 / F ≤ 10.25. In this way, the incident light can be effectively controlled, thereby reducing the system aberration, which is beneficial to improving the image quality.

[0062] In the present invention, the effective focal length F3 of the third lens L3 and the effective focal length F2 of the second lens L2 satisfy the following relationship: -69 ≤ F3 / F2 ≤ 75. Satisfying this relationship can effectively reduce the aberration caused by the aperture STO.

[0063] In the present invention, the effective focal length F4 of the fourth lens L4 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 2.387 ≤ F4 / F ≤ 2.642. In this way, it is beneficial to balance the high and low temperature performance of the fixed-focus lens.

[0064] In the present invention, the fifth lens L5 and the sixth lens L6 are glued together to form a glued lens group with positive optical power. The effective focal length F5 of the fifth lens L5 and the effective focal length F of the fixed-focus lens satisfy the following relationship: -1.41 ≤ F5 / F ≤ -1.32. The effective focal length F6 of the sixth lens L6 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 0.85 ≤ F6 / F ≤ 0.91. The combined focal length F56 of the fifth lens L5 and the sixth lens L6 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 1.89 ≤ F56 / F ≤ 2.21. In this way, by reasonably setting the glued lens group, the chromatic aberration can be effectively calibrated.

[0065] In the present invention, the combined focal length F78 of the seventh lens L7 and the eighth lens L8 and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.2 ≤ F78 / F ≤ 15.5. The air interval length d78 between the seventh lens L7 and the eighth lens L8 and the sum of the thicknesses (d7 + d8) of the seventh lens L7 and the eighth lens L8 satisfy the following relationship: 0.029 ≤ d78 / (d7 + d8) ≤ 0.035. Thus, distortion can be effectively controlled and the optical imaging performance can be improved.

[0066] In summary, the overall optical length of the fixed-focus lens of the present invention ≤ 22.5 mm (with the flat protective glass CG), thereby enabling a small volume. The fixed-focus lens adopts a lens combination of plastic and glass, and uses an aspherical surface type, thereby reducing costs while improving image quality. The fixed-focus lens of the present invention has high performance, has a high resolution of 5 million pixels, and the Fno of the lens ≤ 1.07, having an ultra-large aperture, enabling low-light imaging. In addition, the fixed-focus lens also has good performance in the infrared band, can be used for both day and night, and can achieve clear imaging in the temperature range of -40°C to 80°C to adapt to high and low temperature environmental conditions.

[0067] The following uses four specific embodiments to elaborate in detail on the fixed-focus lens of the present invention. In the following embodiments, S1, S2,..., SN represent the surfaces of each optical element. Among them, the aperture stop STO can also be denoted as STO, and the image plane IMAGE can also be denoted as IMA.

[0068] Among them, the plastic aspherical lens satisfies the following formula:

[0069]

[0070] In the formula, z is the axial distance from the vertex of the curved surface to the position at a height h perpendicular to the optical axis along the optical axis direction; 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 the aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, sixteenth order, ··· respectively.

[0071] The parameters of each embodiment specifically meeting the above conditional formulas are shown in Table 1 below:

[0072]

[0073]

[0074] Table 1

[0075] The first embodiment

[0076] SeeFigures 1 to 6 In this embodiment, the parameters of the fixed-focus lens are as follows: F#: 1.07; total lens length: 21.99; field of view angle: 66.7°. Among them, the third lens L3 has a negative optical power.

[0077] The relevant parameters of each lens of the fixed-focus lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, are shown in Table 2 below:

[0078] Surface number Surface type R value Thickness Refractive index Abbe number S1 Aspherical surface 4.17 1.38 1.54 55.71 S2 Aspherical surface 2.58 2.79 S3 Aspherical surface -2.82 2.14 1.54 55.71 S4 Aspherical surface -3.29 0.03 S5 (STO) Spherical surface Infinity 0.03 S6 Aspherical surface 4.96 1.69 1.66 20.38 S7 Aspherical surface 4.25 0.13 S8 Spherical surface 7.12 2.55 1.44 95.1 S9 Spherical surface -123.11 0.29 S10 Spherical surface 13.64 0.96 1.70 30.05 S11 Spherical surface 3.93 3.39 1.57 71.31 S12 Spherical surface -9.01 0.08 S13 Aspherical surface -7.51 0.99 1.54 55.98 S14 Aspherical surface -3.57 0.06 S15 Aspherical surface 6.19 1.00 1.64 23.53 S16 Aspherical surface 3.62 3.48 S17 Spherical surface Infinity 0.8 1.52 64.21 S18 Spherical surface Infinity 0.2 S19 (IMA) Spherical surface Infinity - - -

[0079] Table 2

[0080] The aspheric coefficients of each aspheric lens in this embodiment are shown in Table 3 below:

[0081]

[0082] Table 3

[0083] Among them, K is the conic constant of the surface, and A4, A6, A8, A 10 , A 12 are the aspheric coefficients of the fourth, sixth, eighth, tenth, and twelfth orders, respectively.

[0084] The second embodiment

[0085] Refer to Figures 7 to 12 In this embodiment, the parameters of the fixed-focus lens are as follows: F#: 1.07; total lens length: 22.34; field of view angle: 65.5°. Among them, the third lens L3 has a positive optical power.

[0086] The relevant parameters of each lens of the fixed-focus lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number, are shown in Table 4 below:

[0087]

[0088]

[0089] Table 4

[0090] The aspheric coefficients of each aspheric lens in this embodiment are shown in Table 5 below:

[0091]

[0092] Table 5

[0093] Among them, K is the conic constant of the surface, and A4, A6, A8, A 10 , A 12 are the aspheric coefficients of the fourth, sixth, eighth, tenth, and twelfth orders, respectively.

[0094] The third implementation mode

[0095] Refer to Figures 13 to 18 , in this implementation mode, the parameters of the fixed-focus lens are as follows: F#: 1.06; total lens length: 22.46; field of view angle: 65.9°. Among them, the third lens L3 has a negative optical power.

[0096] The relevant parameters of each lens of the fixed-focus lens in this implementation mode, including surface type, radius of curvature, thickness, refractive index of the material, Abbe number, are shown in Table 6 below:

[0097] Surface number Surface type R value Thickness Refractive index Abbe number S1 Aspherical surface 4.11 1.21 1.54 55.71 S2 Aspherical surface 2.58 2.71 S3 Aspherical surface -2.82 2.21 1.54 55.71 S4 Aspherical surface -3.29 0.06 S5 (STO) Spherical surface Infinity 0.05 S6 Aspherical surface 4.90 1.55 1.66 20.38 S7 Aspherical surface 4.27 0.55 S8 Spherical surface 7.14 2.94 1.44 95.1 S9 Spherical surface -99.76 0.07 S10 Spherical surface 13.22 0.67 1.70 30.05 S11 Spherical surface 4.00 3.95 1.57 71.31 S12 Spherical surface -8.60 0.08 S13 Aspherical surface -7.04 0.93 1.54 55.98 S14 Aspherical surface -3.64 0.06 S15 Aspherical surface 6.39 0.98 1.64 23.53 S16 Aspherical surface 3.54 3.44 S17 Spherical surface Infinity 0.8 1.52 64.21 S18 Spherical surface Infinity 0.2 S19 (IMA) Spherical surface Infinity - - -

[0098] Table 6

[0099] The aspheric coefficients of each aspheric lens in this implementation mode are shown in Table 7 below:

[0100]

[0101]

[0102] Table 7

[0103] Among them, K is the conic constant of the surface, and A4, A6, A8, A 10 、A 12 are the aspheric coefficients of the fourth, sixth, eighth, tenth, and twelfth orders respectively.

[0104] The fourth implementation mode

[0105] Refer to Figures 19 to 24 , in this implementation mode, the parameters of the fixed-focus lens are as follows: F#: 1.069; total lens length: 22.46; field of view angle: 65.7°. Among them, the third lens L3 has a positive optical power.

[0106] The relevant parameters of each lens of the fixed-focus lens in this implementation mode, including surface type, radius of curvature, thickness, refractive index of the material, Abbe number, are shown in Table 8 below:

[0107] Surface number Surface type R value Thickness Refractive index Abbe number S1 Aspherical surface 4.09 1.17 1.54 55.71 S2 Aspherical surface 2.59 2.78 S3 Aspherical surface -2.82 2.2 1.54 55.71 S4 Aspherical surface -3.29 0.04 S5 (STO) Spherical surface Infinity 0.05 S6 Aspherical surface 4.92 1.61 1.66 20.38 S7 Aspherical surface 4.29 0.64 S8 Spherical surface 7.13 2.77 1.44 95.1 S9 Spherical surface -92.84 0.05 S10 Spherical surface 13.15 0.68 1.70 30.05 S11 Spherical surface 4.01 4.04 1.57 71.31 S12 Spherical surface -8.58 0.08 S13 Aspherical surface -7.00 0.87 1.54 55.98 S14 Aspherical surface -3.65 0.06 S15 Aspherical surface 6.42 0.97 1.64 23.53 S16 Aspherical surface 3.53 3.45 S17 Spherical surface Infinity 0.8 1.52 64.21 S18 Spherical surface Infinity 0.2 S19 (IMA) Spherical surface Infinity - - -

[0108] Table 8

[0109] The aspheric coefficients of each aspheric lens in this implementation mode are shown in Table 9 below:

[0110]

[0111] Table 9

[0112] Among them, K is the conic constant of the surface, and A4, A6, A8, A 10, A 12 They are aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, and twelfth order respectively.

[0113] The above is only one embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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, characterized in that, It includes eight lenses with focal power, namely, a first lens (L1) with negative focal power, a second lens (L2) with positive focal power, a stop (STO), a third lens (L3) with positive or negative focal power, a fourth lens (L4) with positive focal power, a fifth lens (L5) with negative focal power, a sixth lens (L6) with positive focal power, a seventh lens (L7) with positive focal power, and an eighth lens (L8) with negative focal power, which are arranged in sequence from the object side to the image side along the optical axis. The combined focal length F56 of the fifth lens (L5) and the sixth lens (L6) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 1.89 ≤ F56 / F ≤ 2.

21.

2. The fixed-focus lens according to claim 1, wherein, The first lens (L1) is a convex-concave lens, the second lens (L2) is a concave-convex lens, the third lens (L3) is a convex-concave lens, the fourth lens (L4) is a double-convex lens, the fifth lens (L5) is a convex-concave lens, the sixth lens (L6) is a double-convex lens, the seventh lens (L7) is a concave-convex lens, and the eighth lens (L8) is a convex-concave lens in the paraxial region.

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

4. The fixed-focus lens according to claim 3, characterized in that, The first lens (L1) is a plastic lens, the second lens (L2) is a plastic lens, the third lens (L3) is a plastic lens, the fourth lens (L4) is a glass lens, the fifth lens (L5) is a glass lens, the sixth lens (L6) is a glass lens, the seventh lens (L7) is a plastic lens, and the eighth lens (L8) is a plastic lens.

5. The fixed-focus lens according to claim 1, wherein The fifth lens (L5) and the sixth lens (L6) are cemented together to form a cemented lens group with positive focal power.

6. The fixed-focus lens according to any one of claims 1-5, characterized in that, The optical total length TTL of the fixed-focus lens and the effective focal length F satisfy the following relationship: 3.4 ≤ TTL / F ≤ 3.

7.

7. The fixed-focus lens according to any one of claims 1-5, characterized in that, The optical back focal length BFL of the fixed-focus lens and the optical total length TTL satisfy the following relationship: 0.68 ≤ BFL / TTL ≤ 0.

75.

8. The fixed-focus lens according to any one of claims 1-5, characterized in that, The effective focal length F1 of the first lens (L1) and the effective focal length F of the fixed-focus lens satisfy the following relationship: -3 ≤ F1 / F ≤ -2.

8.

9. The fixed-focus lens according to any one of claims 1-5, characterized in that, The effective focal length F2 of the second lens (L2) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 8.75 ≤ F2 / F ≤ 10.

25.

10. The fixed-focus lens according to any one of claims 1-5, characterized in that, The effective focal length F3 of the third lens (L3) and the effective focal length F2 of the second lens (L2) satisfy the following relationship: -69 ≤ F3 / F2 ≤ 75.

11. The fixed-focus lens according to any one of claims 1-5, characterized in that, The effective focal length F4 of the fourth lens (L4) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 2.387 ≤ F4 / F ≤ 2.

642.

12. The fixed-focus lens according to claim 5, characterized in that, The effective focal length F5 of the fifth lens (L5) and the effective focal length F of the fixed-focus lens satisfy the following relationship: -1.41 ≤ F5 / F ≤ -1.

32.

13. The fixed-focus lens according to claim 5, characterized in that, The effective focal length F6 of the sixth lens (L6) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 0.85 ≤ F6 / F ≤ 0.

91.

14. The fixed-focus lens according to any one of claims 1-5, characterized in that, The combined focal length F78 of the seventh lens (L7) and the eighth lens (L8) and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.2 ≤ F78 / F ≤ 15.

5.

15. The fixed-focus lens according to any one of claims 1-5, characterized in that, The air interval length d78 between the seventh lens (L7) and the eighth lens (L8) and the sum of the thicknesses (d7 + d8) of the seventh lens (L7) and the eighth lens (L8) satisfy the following relationship: 0.029 ≤ d78 / (d7 + d8) ≤ 0.035.

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