A fixed-focus lens

Abstract

An embodiment of the present invention discloses 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, and an eighth lens, arranged sequentially along the optical axis from the object side to the image side. The first, second, and seventh lenses have negative optical power, the fourth, sixth, and eighth lenses have positive optical power, and the third and fifth lenses have positive or negative optical power. The second, third, fifth, sixth, seventh, and eighth lenses are plastic aspheric lenses, the first lens is a plastic lens or a glass lens, and the fourth lens is a glass spherical lens or a glass aspheric lens. The embodiment of the present invention utilizes eight lenses to achieve an ultra-large aperture of F1.0 at a low cost, providing a low-cost, large-area, ultra-large-aperture, and ultra-high-definition fixed-focus lens.

Description

Technical Field

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

[0002] With the increasing popularity of security monitoring facilities, monitoring equipment has higher and higher requirements for monitoring environment and images, and monitoring equipment needs to provide monitoring images with higher pixels and greater light transmittance.

[0003] Infrared fill light is commonly used in security surveillance to achieve imaging at night and in low-light conditions. However, infrared fill light has a limited imaging range and severe color distortion. To achieve better nighttime imaging, the demand for low-light cameras is increasing. Currently, the most common high-quality, large-aperture lenses on the market are F1.4, with few lenses reaching F1.2, and even fewer reaching F1.0. Furthermore, existing lenses are typically paired with a 1 / 2.7′ sensor, resulting in a smaller sensor surface. The lenses often use glass spherical or aspherical lenses, which are difficult to manufacture and have high production costs. Summary of the Invention

[0004] The present invention provides a fixed-focus lens, which can realize an ultra-large aperture while ensuring a large target surface and ultra-high-definition imaging quality of the fixed-focus lens and reducing costs.

[0005] In a first aspect, an embodiment of 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, and an eighth lens, arranged in sequence along an optical axis from the object side to the image side; the first lens, the second lens, and the seventh lens have negative optical power, the fourth lens, the sixth lens, and the eighth lens have positive optical power, and the third lens and the fifth lens have positive or negative optical power;

[0006] The second lens, the third lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are plastic aspheric lenses, the first lens is a plastic lens or a glass lens, and the fourth lens is a glass spherical lens or a glass aspheric lens.

[0007] Optionally, the focal length f1 of the first lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.1<|f1 / f|<8;

[0008] The focal length f2 of the second lens and the focal length f of the fixed-focus lens satisfy the relationship: |f2 / f|>1.5;

[0009] The focal length f3 of the third lens and the focal length f of the fixed-focus lens satisfy the relationship: |f3 / f|>2.5;

[0010] The focal length f4 of the fourth lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.1<|f4 / f|<9;

[0011] The focal length f5 of the fifth lens and the focal length f of the fixed-focus lens satisfy the relationship: |f5 / f|>2.4;

[0012] The focal length f6 of the sixth lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.1<|f6 / f|<10;

[0013] The focal length f7 of the seventh lens and the focal length f of the fixed-focus lens satisfy the relationship: 1<|f7 / f|<5;

[0014] The focal length f8 of the eighth lens and the focal length f of the fixed-focus lens satisfy the relationship: 1<|f8 / f|<5.

[0015] Optionally, the first lens to the seventh lens meet the following conditions:

[0016] 1.50 <n1<1.78,43<v1<75;

[0017] 1.50 <n2<1.60,50<v2<60;

[0018] 1.55 <n3<1.70,20<v3<38;

[0019] 1.58 <n4<1.94,35<v4<60;

[0020] 1.50 <n5<1.70,20<v5<60;

[0021] 1.50 <n6<1.60,50<v6<60;

[0022] 1.55 <n7<1.70,20<v7<38;

[0023] 1.50 <n8<1.60,50<v8<60;

[0024] Among them, n1-n8 are the refractive indices of the first lens to the eighth lens respectively, and v1-v8 are the Abbe numbers of the first lens to the eighth lens respectively.

[0025] Optionally, the fixed-focus lens further includes a stop, and the stop is located between the third lens and the fourth lens, or between the fourth lens and the fifth lens, or between the fifth lens and the sixth lens.

[0026] Optionally, the second lens and the third lens are cemented together to form a cemented lens group, and the sixth lens and the seventh lens are cemented together to form a cemented lens group.

[0027] Optionally, the first lens is a convex-concave lens, the third lens is a convex-concave lens, the fourth lens is a biconvex lens, the fifth lens is a concave-convex lens, the sixth lens is a biconvex lens, and the eighth lens is a biconvex lens.

[0028] Optionally, the optical back focus BFL of the fixed-focus lens and the total optical length TTL of the fixed-focus lens satisfy the relationship: 4.5 <TTL / BFL<9。

[0029] The fixed-focus lens provided by an embodiment of the present invention is configured by sequentially arranging a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens along the optical axis from the object side to the image side; wherein the first lens, the second lens, and the seventh lens have negative optical power, the fourth lens, the sixth lens, and the eighth lens have positive optical power, and the third lens and the fifth lens have positive or negative optical power; the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are plastic aspherical lenses, the first lens is a plastic lens or a glass lens, and the fourth lens is a glass spherical lens or a glass aspherical lens. The optical power of each lens can be coordinated to achieve a fixed-focus lens with an ultra-large aperture and a large target surface. At the same time, the mutual compensation between the plastic lens and the glass lens can correct aberrations and ensure imaging resolution. The fixed-focus lens provided by an embodiment of the present invention can ensure the balance of the incident angles of the front and rear lens groups, reduce the sensitivity of the lens, and improve the feasibility of production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 1 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0031] Figure 2 yes Figure 1 Axial aberration curve diagram of the fixed focus lens shown;

[0032] Figure 3 yes Figure 1 Ray fan diagram of the fixed focus lens shown;

[0033] Figure 4 yes Figure 1 Spot diagram of the fixed focal length lens shown;

[0034] Figure 5 1 is a structural diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0035] Figure 6 yes Figure 5 Axial aberration curve diagram of the fixed focus lens shown;

[0036] Figure 7 yes Figure 5 Ray fan diagram of the fixed focus lens shown;

[0037] Figure 8 yes Figure 5 Spot diagram of the fixed focal length lens shown;

[0038] Figure 9 1 is a schematic structural diagram of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0039] Figure 10 yes Figure 9 Axial aberration curve diagram of the fixed focus lens shown;

[0040] Figure 11 yes Figure 9 Ray fan diagram of the fixed focus lens shown;

[0041] Figure 12 yes Figure 9 Spot diagram of the fixed focal length lens shown;

[0042] Figure 13 1 is a schematic structural diagram of a fixed-focus lens provided in a fourth embodiment of the present invention;

[0043] Figure 14 yes Figure 13 Axial aberration curve diagram of the fixed focus lens shown;

[0044] Figure 15 yes Figure 13 Ray fan diagram of the fixed focus lens shown;

[0045] Figure 16 yes Figure 13 Spot diagram for the fixed focal length lens shown. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0047] Figure 1 is a structural diagram of a fixed-focus lens provided by an embodiment of the present invention, with reference to Figure 1The fixed-focus lens comprises a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17 and an eighth lens 18, which are arranged in sequence from the object side to the image side along the optical axis; the first lens 11, the second lens 12 and the seventh lens 17 have negative optical power, the fourth lens 14, the sixth lens 16 and the eighth lens 18 have positive optical power, and the third lens 13 and the fifth lens 15 have positive or negative optical power;

[0048] The second lens 12 , the third lens 13 , the fifth lens 15 , the sixth lens 16 , the seventh lens 17 and the eighth lens 18 are plastic aspherical lenses, the first lens 11 is a plastic lens or a glass lens, and the fourth lens 14 is a glass spherical lens or a glass aspherical lens.

[0049] Among them, it can be understood that the focal length of a lens is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam, which characterizes the ability of an optical system to deflect light. The larger the absolute value of the focal length, the stronger the ability to bend light, and the smaller the absolute value of the focal length, the weaker the ability to bend light. When the focal length is a positive number, the refraction of light is convergent; when the focal length is a negative number, the refraction of light is divergent. In the case of Figure 1 In the fixed-focus lens shown, the first lens 11, the second lens 12, and the seventh lens 17 have negative optical powers, while the fourth lens 14, the sixth lens 16, and the eighth lens 18 have positive optical powers. The third lens 13 and the fifth lens 15 are configured with either positive or negative optical powers. Each lens can converge or diverge light. By coordinating the optical powers of the lenses, a fixed-focus lens with an ultra-large aperture and a large image area can be achieved. For example, the first lens 11 can be a convex-concave lens, the third lens 13 can be a convex-concave lens, the fourth lens 14 can be a biconvex lens, the fifth lens 15 can be a concave-convex lens, the sixth lens 16 can be a biconvex lens, and the eighth lens 18 can be a biconvex lens. Specifically, the negative optical powers of the first and second lenses 11 and 12 can coordinately control the incident angle of the optical system, ensuring a wide field of view. Furthermore, by coordinating the optical powers of the other lenses, aberrations of this fixed-focus lens with an ultra-large aperture and a large image area can be corrected, ensuring high resolution. Setting the second lens 12, the third lens 13, the fifth lens 15, the sixth lens 16, the seventh lens 17 and the eighth lens 18 as plastic lenses can reduce the number of glass lenses and reduce costs. Setting these lenses as aspherical lenses can correct field curvature and also correct higher-order aberrations.

[0050] Based on the above, the first lens 11 can be a plastic lens or a glass lens, and the fourth lens 14 can be a glass spherical lens or a glass aspherical lens, respectively. The glass material properties are utilized to reduce the sensitivity of imaging to temperature, ensuring clear imaging in high and low temperature environments. In this embodiment of the present invention, 6 to 7 plastic lenses and 1 to 2 glass lenses are configured to compensate for each other, correcting aberrations and optimizing imaging quality. Furthermore, compared to glass lenses, plastic lenses are easier and less expensive to prepare, facilitating the preparation of aspheric lenses. Correcting aberrations with aspheric lenses also helps reduce manufacturing costs and facilitates mass production.

[0051] The fixed-focus lens provided by an embodiment of the present invention is configured by sequentially arranging a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens along the optical axis from the object side to the image side; wherein the first lens, the second lens, and the seventh lens have negative optical power, the fourth lens, the sixth lens, and the eighth lens have positive optical power, and the third lens and the fifth lens have positive or negative optical power; the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are plastic aspherical lenses, the first lens is a plastic lens or a glass lens, and the fourth lens is a glass spherical lens or a glass aspherical lens. The optical power of each lens can be coordinated to achieve a fixed-focus lens with an ultra-large aperture and a large target surface. At the same time, the mutual compensation between the plastic lens and the glass lens can correct aberrations and ensure imaging resolution. The fixed-focus lens provided by an embodiment of the present invention can ensure the balance of the incident angles of the front and rear lens groups, reduce the sensitivity of the lens, and improve the feasibility of production.

[0052] Based on the above embodiments, Figure 1 The focal length f2 of the second lens 12 and the focal length f of the fixed-focus lens can be set to satisfy the relationship: |f2 / f|>1.5; the focal length f3 of the third lens and the focal length f of the fixed-focus lens can be set to satisfy the relationship: |f3 / f|>2.5; the focal length f5 of the fifth lens and the focal length f of the fixed-focus lens can be set to satisfy the relationship: |f5 / f|>2.4.

[0053] Among them, by reasonably setting the proportional relationship between the focal lengths of the second lens 12, the third lens 13 and the fifth lens 15 and the focal length f of the fixed-focus lens, it is possible to converge the light and reduce the off-axis height of the light. At the same time, it is possible to correct high-order spherical aberration, balance various aberrations, ensure the imaging quality of light in each band, and achieve an ultra-large aperture and a large target surface.

[0054] To further optimize image quality, while meeting the above parameter requirements, the focal length parameters of the other lenses need to be adjusted accordingly. Therefore, the focal length f1 of the first lens can be set to satisfy the relationship: 1.1 < |f1 / f| < 8; the focal length f4 of the fourth lens can satisfy the relationship: 1.1 < |f4 / f| < 9; the focal length f6 of the sixth lens can satisfy the relationship: 1.1 < |f6 / f| < 10; the focal length f7 of the seventh lens can satisfy the relationship: |1 < |f7 / f| < 5; and the focal length f8 of the eighth lens can satisfy the relationship: 1 < |f8 / f| < 5.

[0055] It should be noted that the imaging quality of an optical lens is not only related to the focal length coordination and surface shape of each lens, but also to the material of each lens. In the above-mentioned fixed-focus lens, a combination of plastic lenses and glass lenses is used. On the one hand, the difficulty and cost of preparing plastic lenses are relatively low, which is conducive to reducing manufacturing costs and mass production. On the other hand, the use of aspheric lenses can meet the requirements of each lens for optical focal length while also performing appropriate aberration correction. Therefore, on this basis, in order to enable each lens to more reasonably correct aberrations and chromatic aberrations, balance the aberrations of the entire lens, and optimize the imaging quality, the first to eighth lenses can be set to meet the following conditions:

[0056] 1.50 <n1<1.78,43<v1<75;

[0057] 1.50 <n2<1.60,50<v2<60;

[0058] 1.55 <n3<1.70,20<v3<38;

[0059] 1.58 <n4<1.94,35<v4<60;

[0060] 1.50 <n5<1.70,20<v5<60;

[0061] 1.50 <n6<1.60,50<v6<60;

[0062] 1.55 <n7<1.70,20<v7<38;

[0063] 1.50 <n8<1.60,50<v8<60;

[0064] Among them, n1-n8 are the refractive indices of the first to eighth lenses respectively, and v1-v8 are the Abbe numbers of the first to eighth lenses respectively.

[0065] In addition, the fixed-focus lens of the embodiment of the present invention further includes an aperture, which can be set between the third lens 13 and the fourth lens 14 , or between the fourth lens 14 and the fifth lens 15 , or between the fifth lens 15 and the sixth lens 16 .

[0066] Among them, the aperture in the optical system is used to limit the beam size, determining the amount of light passing through the lens and entering the photosensitive element, that is, it is used to control the light transmission amount of the lens, and also directly determines the size of the aperture of the fixed-focus lens. In the fixed-focus lens provided by the embodiment of the present invention, the aperture can be set between two lenses at the middle position, and the light transmission amount is controlled by using the waist position of the entire optical system. On the basis of effectively limiting the aperture size of the optical system, the amount of light passing through the aperture can be ensured to ensure the imaging brightness; in addition, the aperture can block off-axis light, effectively reducing off-axis aberration and ensuring the imaging clarity.

[0067] In a preferred embodiment, the second lens 12 and the third lens 13 can be optionally glued together to form a glued lens group, and the sixth lens 16 and the seventh lens 17 can be glued together to form a glued lens group. Among them, the glued lens group can reduce the distance between lenses, can appropriately correct chromatic aberration, and can also improve field curvature and coma, thereby further optimizing the imaging quality.

[0068] Optionally, when designing the fixed-focus lens, the relevant parameters of each lens can be adjusted according to the requirements of the actual lens size, so as to meet the size requirements during actual assembly. On the basis of the fixed-focus lens provided in the above embodiment, it is optionally set that the optical back focal length BFL of the fixed-focus lens and the optical total length TTL of the fixed-focus lens satisfy the relational expression: 4.5 < TTL / BFL < 9. The optical back focal length BFL refers to the distance from the eighth lens 18 to the image plane, and the optical total length is the distance from the first lens 11 to the image plane. By setting the ratio of the optical back focal length BFL to the optical total length of the fixed-focus lens to satisfy the numerical range of 4.5 - 9, the overall ratio and overall size of the fixed-focus lens can be limited, ensuring that the fixed-focus lens meets the size requirements during actual assembly.

[0069] The above fixed-focus lens will be described and exemplified below with four specific embodiments. In Embodiment 1, as Figure 1 shown, the fixed-focus lens includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17, and an eighth lens 18 arranged in sequence along the optical axis from the object side to the image side; the first lens 11, the second lens 12, and the seventh lens 17 have negative optical powers, and the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16, and the eighth lens 18 have positive optical powers;

[0070] The second lens 12, the third lens 13, the fifth lens 15, the sixth lens 16, the seventh lens 17, and the eighth lens 18 are plastic aspherical lenses, the first lens 11 is a glass spherical lens, and the fourth lens 14 is a glass aspherical lens.

[0071] In this embodiment, the design values ​​of the first lens 11 to the eighth lens 18 are shown in Table 1 below.

[0072] Table 1 shows a design value of the fixed-focus lens (f=4mm; aperture F1.08):

[0073]

[0074]

[0075] The surface numbers in Table 1 are numbered according to the order of the surfaces of the various lenses, where "S1" represents the front surface of the first lens, "S2" represents the back surface of the first lens, and so on. The radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface is curved toward the image plane, and a negative value indicating that the surface is curved toward the object plane. The thickness represents the central axial distance from the current surface to the next surface, and the refractive index represents the ability of the material between the current surface and the next surface to deflect light. A blank space represents the current position as air with a refractive index of 1. It should be noted that STO represents the aperture, which is set between the third and fourth lenses, specifically on the front surface S7 of the fourth lens.

[0076] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following expression method:

[0077]

[0078] Among them, z is the axial sagittal height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the curvature radius; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0079] The aspheric surface parameters in this embodiment are shown in Table 2:

[0080] Table 2 shows a design value of the aspheric coefficient in the fixed focus lens.

[0081]

[0082] The optical system of this embodiment meets the following technical indicators: focal length: f = 4mm; aperture: F = 1.08; TTL / BFL = 6.229; field of view: 2w ≥ 138° (image side 2η ≥ Φ9.2mm); distortion: <-56.7%; resolution: compatible with 8-megapixel high-resolution CCD or CMOS cameras.

[0083] Figure 2 yes Figure 1 Axial aberration curve diagram of the fixed focus lens shown; Figure 3 yes Figure 1 Ray fan diagram of the fixed focus lens shown; Figure 4 yes Figure 1 Spot diagram of the fixed focal length lens shown; refer to Figure 2 , the axial chromatic aberration of light of different wavelengths (0.436μm, 0.486μm, 0.588μm, and 0.656μm) in this fixed-focus lens is no more than 0.03mm. Therefore, it can be seen that the other fixed-focus lens provided by the embodiment of the present invention can also effectively correct chromatic aberration, ensuring that there is little difference in the imaging chromatic aberration of violet light and visible light. At the same time, it can be seen from the light fan diagram and the point diagram that the imaging range of different wavelengths under different field of view angles is within ±20μm, ensuring that the aberration difference in different field of view areas is small, which also shows that the fixed-focus lens effectively corrects the aberration of the optical system and has better imaging quality.

[0084] Figure 5 This is a structural diagram of a fixed-focus lens provided by Example 2 of the present invention, with reference to Figure 5 The fixed-focus lens comprises a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17 and an eighth lens 18, which are arranged in sequence from the object side to the image side along the optical axis; the first lens 11, the second lens 12, the third lens 13, the fifth lens 15 and the seventh lens 17 have negative optical power, and the fourth lens 14, the sixth lens 16 and the eighth lens 18 have positive optical power;

[0085] The second lens 12 , the third lens 13 , the fifth lens 15 , the sixth lens 16 , the seventh lens 17 and the eighth lens 18 are plastic aspherical lenses, and the first lens 11 and the fourth lens 14 are glass spherical lenses.

[0086] In this embodiment, the design values ​​of the first lens 11 to the eighth lens 18 are shown in Table 3 below.

[0087] Table 3 shows a design value of the fixed-focus lens (f=4.14mm; aperture F1.1):

[0088]

[0089]

[0090] As shown in Table 3, the rear surface of the second lens 12 and the front surface of the third lens 13 are cemented together to form an aspheric surface S4, and the rear surface of the sixth lens 16 and the front surface of the seventh lens 17 are cemented together to form an aspheric surface S11. A stop STO is provided between the fifth lens 15 and the sixth lens 16, specifically on the front surface S10 of the sixth lens.

[0091] The aspheric surface parameters in this embodiment are shown in Table 4:

[0092] Table 4 shows a design value of the aspheric coefficient in the fixed focus lens.

[0093] Surface number K A B C D E F S3 -20.5079 2.19E-04 7.84E-06 -4.75E-06 3.19E-07 -9.28E-09 2.03E-11 S4 -1.2013 2.10E-04 -8.48E-05 1.33E-05 -1.11E-06 4.49E-08 -1.06E-09 S5 7.5891 6.54E-04 -5.60E-05 1.52E-06 -1.35E-07 1.68E-09 4.19E-12 S8 -5.1634 6.59E-04 8.39E-07 -1.71E-06 -1.53E-08 3.74E-09 -2.58E-10 S9 -2.8768 1.75E-03 -1.05E-04 4.86E-06 -9.43E-08 -4.12E-09 1.27E-10 S10 -4.7883 1.13E-03 -3.24E-05 1.46E-06 1.07E-08 -2.95E-09 7.15E-11 S11 6.6536 -1.11E-03 3.16E-05 2.42E-06 -2.84E-07 1.95E-08 -4.80E-10 S12 -10.6139 8.46E-04 2.73E-05 -2.03E-06 -7.43E-08 1.19E-08 -2.61E-10 S13 -12.6956 1.40E-03 2.18E-05 -3.30E-06 4.96E-08 3.53E-09 -1.08E-10 S14 -2.2981 5.18E-04 2.82E-05 -1.93E-06 1.58E-07 -7.69E-09 1.10E-10

[0094] The optical system of this embodiment meets the following technical indicators: focal length: f = 4.14mm; aperture: F = 1.1; TTL / BFL = 5.328; field of view: 2w ≥ 136° (image side 2η ≥ Φ9.2mm); distortion: <-57%; resolution: compatible with 8-megapixel high-resolution CCD or CMOS cameras.

[0095] Figure 6 yes Figure 5 Axial aberration curve diagram of the fixed focus lens shown; Figure 7 yes Figure 5 Ray fan diagram of the fixed focus lens shown; Figure 8 yes Figure 5 Spot diagram of the fixed focal length lens shown; refer to Figure 6 , the axial chromatic aberration of light of different wavelengths (0.436μm, 0.486μm, 0.588μm and 0.656μm) in this fixed-focus lens is no more than 0.03mm. Therefore, it can be seen that the other fixed-focus lens provided by the embodiment of the present invention can also effectively correct chromatic aberration, ensuring that there is a small difference in the imaging chromatic aberration of violet light and visible light. At the same time, it can be seen from the light fan diagram and the point diagram that the imaging range of different wavelengths under different field of view angles is within ±10μm, ensuring that the aberration difference in different field of view areas is small, which also shows that the fixed-focus lens effectively corrects the aberration of the optical system and has better imaging quality.

[0096] Figure 9 This is a structural diagram of a fixed-focus lens provided by Example 3 of the present invention, with reference to Figure 9 The fixed-focus lens comprises a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17 and an eighth lens 18, which are arranged in sequence from the object side to the image side along the optical axis; the first lens 11, the second lens 12, the fifth lens 15 and the seventh lens 17 have negative optical power, and the third lens 13, the fourth lens 14, the sixth lens 16 and the eighth lens 18 have positive optical power;

[0097] The second lens 12 , the third lens 13 , the fifth lens 15 , the sixth lens 16 , the seventh lens 17 and the eighth lens 18 are plastic aspherical lenses, and the first lens 11 and the fourth lens 14 are glass spherical lenses.

[0098] In this embodiment, the design values ​​of the first lens 11 to the eighth lens 18 are shown in Table 5 below.

[0099] Table 5 shows a design value of the fixed-focus lens (f=4.07mm; aperture F1.08):

[0100]

[0101]

[0102] As shown in Table 5, the aperture STO is disposed between the fourth lens 14 and the fifth lens 15 , and specifically can be disposed on the rear surface S8 of the fourth lens.

[0103] The aspheric surface parameters in this embodiment are shown in Table 6:

[0104] Table 6 shows a design value of the aspheric coefficient in the fixed focus lens

[0105] Surface number K A B C D E F S3 -19.9997 -2.92E-03 2.07E-04 -7.25E-06 -2.14E-07 2.48E-08 -5.81E-10 S4 -8.4024 7.84E-04 -5.59E-05 3.27E-06 -3.20E-07 2.15E-08 -2.43E-10 S5 -1.1198 1.39E-03 -9.03E-05 1.38E-06 1.84E-08 1.23E-09 9.11E-11 S6 16.7070 1.50E-03 -3.84E-05 -3.83E-07 -2.64E-08 -2.41E-10 4.09E-11 S9 -7.9686 7.07E-04 -4.97E-05 1.47E-06 3.27E-08 -8.09E-10 -6.82E-11 S10 -0.8754 1.22E-03 -6.31E-05 3.08E-06 -3.02E-08 -1.72E-11 -1.67E-11 S11 -5.4068 7.22E-04 -7.00E-05 2.05E-06 6.79E-08 -5.16E-09 4.84E-11 S12 -11.9603 -2.06E-03 4.65E-05 2.39E-07 -3.10E-08 -6.72E-10 2.19E-11 S13 -7.0416 1.07E-03 -7.59E-05 2.03E-06 -1.73E-09 -1.18E-09 4.23E-11 S14 20.0680 2.46E-03 -2.20E-05 -5.00E-06 2.65E-07 -2.60E-09 -5.98E-11 S15 -12.2727 -4.04E-04 6.12E-05 -5.98E-07 -7.70E-09 1.06E-10 7.77E-12 S16 -5.7221 -8.92E-04 3.89E-05 -6.72E-07 6.92E-08 -3.13E-09 6.55E-11

[0106] The optical system of this embodiment meets the following technical specifications: focal length: f = 4.07 mm; aperture: F = 1.08; TTL / BFL = 5.66; field of view: 2w ≥ 138° (image side 2η ≥ Φ9.2 mm); distortion: <-56.7%; resolution: compatible with 8-megapixel high-resolution CCD or CMOS cameras;

[0107] Figure 10 yes Figure 9 Axial aberration curve diagram of the fixed focus lens shown; Figure 11 yes Figure 9 Ray fan diagram of the fixed focus lens shown; Figure 12 yes Figure 9 Spot diagram of the fixed focal length lens shown; refer to Figure 10 , the axial chromatic aberration of light of different wavelengths (0.436μm, 0.486μm, 0.588μm, and 0.656μm) in this fixed-focus lens is no more than 0.03mm. Therefore, it can be seen that the other fixed-focus lens provided by the embodiment of the present invention can also effectively correct chromatic aberration, ensuring that there is little difference in the imaging chromatic aberration of violet light and visible light. At the same time, it can be seen from the light fan diagram and the point diagram that the imaging range of different wavelengths under different field of view angles is within ±20μm, ensuring that the aberration difference in different field of view areas is small, which also shows that the fixed-focus lens effectively corrects the aberration of the optical system and has better imaging quality.

[0108] Figure 13 This is a structural diagram of a fixed-focus lens provided by Example 4 of the present invention, with reference to Figure 13The fixed-focus lens comprises a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16, a seventh lens 17 and an eighth lens 18, which are arranged in sequence from the object side to the image side along the optical axis; the first lens 11, the second lens 12 and the seventh lens 17 have negative optical power, and the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16 and the eighth lens 18 have positive optical power;

[0109] The first lens 11 , the second lens 12 , the third lens 13 , the fifth lens 15 , the sixth lens 16 , the seventh lens 17 and the eighth lens 18 are plastic aspherical lenses, and the fourth lens 14 is a glass spherical lens.

[0110] In this embodiment, the design values ​​of the first lens 11 to the eighth lens 18 are shown in Table 7 below.

[0111] Table 7 shows a design value of the fixed-focus lens (f=4.32mm; aperture F1.08):

[0112]

[0113]

[0114] As shown in Table 7, the stop STO is disposed between the fourth lens 14 and the fifth lens 15 , and specifically, can be disposed on the rear surface S8 of the fourth lens.

[0115] The aspheric surface parameters in this embodiment are shown in Table 8:

[0116] Table 8 shows a design value of the aspheric coefficient in the fixed-focus lens.

[0117]

[0118]

[0119] The optical system of this embodiment meets the following technical indicators: focal length: f = 4.32mm; aperture: F = 1.08; TTL / BFL = 5.53; field of view: 2w ≥ 139° (image side 2η ≥ Φ9.2mm); distortion: <-60.1%; resolution: compatible with 8-megapixel high-resolution CCD or CMOS cameras.

[0120] Figure 14 yes Figure 13 Axial aberration curve diagram of the fixed focus lens shown; Figure 15 yes Figure 13 Ray fan diagram of the fixed focus lens shown; Figure 16 yes Figure 13 Spot diagram of the fixed focal length lens shown; refer to Figure 14, the axial chromatic aberration of light of different wavelengths (0.436μm, 0.486μm, 0.588μm and 0.656μm) in this fixed-focus lens is no more than 0.03mm. Therefore, it can be seen that the other fixed-focus lens provided by the embodiment of the present invention can also effectively correct chromatic aberration, ensuring that there is a small difference in the imaging chromatic aberration of violet light and visible light. At the same time, it can be seen from the light fan diagram and the point diagram that the imaging range of different wavelengths under different field of view angles is within ±10μm, ensuring that the aberration difference in different field of view areas is small, which also shows that the fixed-focus lens effectively corrects the aberration of the optical system and has better imaging quality.

[0121] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations, and substitutions are possible for those skilled in the art without departing from the scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the scope of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that: The optical system comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, which are arranged in sequence along the optical axis from the object side to the image side; the first lens, the second lens, and the seventh lens have negative optical power, the fourth lens, the sixth lens, and the eighth lens have positive optical power, the third lens has positive optical power, and the fifth lens has positive or negative optical power; The second lens, the third lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are plastic aspheric lenses, the first lens is a plastic lens or a glass lens, and the fourth lens is a glass spherical lens or a glass aspheric lens; The fixed-focus lens further includes an aperture stop, and the aperture stop is located between the third lens and the fourth lens, or between the fourth lens and the fifth lens, or between the fifth lens and the sixth lens; The first lens is a convex-concave lens, the third lens is a convex-concave lens, the fourth lens is a biconvex lens, the fifth lens is a concave-convex lens, the sixth lens is a biconvex lens, and the eighth lens is a biconvex lens; The optical back focus BFL of the fixed-focus lens and the total optical length TTL of the fixed-focus lens satisfy the relationship: 4.5 <TTL / BFL<9。 2. The fixed-focus lens according to claim 1, wherein: The focal length f1 of the first lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.1<|f1 / f|<1.955; The focal length f2 of the second lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.5<|f2 / f|<2.907; The focal length f3 of the third lens and the focal length f of the fixed-focus lens satisfy the relationship: 2.5<|f3 / f|<8.445; The focal length f4 of the fourth lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.1<|f4 / f|<2.307; The focal length f5 of the fifth lens and the focal length f of the fixed-focus lens satisfy the relationship: |f5 / f|>2.4; The focal length f6 of the sixth lens and the focal length f of the fixed-focus lens satisfy the relationship: 1.1<|f6 / f|<2.544; The focal length f7 of the seventh lens and the focal length f of the fixed-focus lens satisfy the relationship: 1<|f7 / f|<1.995; The focal length f8 of the eighth lens and the focal length f of the fixed-focus lens satisfy the relationship: 1<|f8 / f|<1.

745.

3. The fixed-focus lens according to claim 2, wherein: The first lens to the eighth lens meet the following conditions: 1.50 <n1<1.78,43<v1<75; 1.50 <n2<1.60,50<v2<60; 1.55 <n3<1.70,20<v3<38; 1.58 <n4<1.94,35<v4<60; 1.50 <n5<1.70,20<v5<60; 1.50 <n6<1.60,50<v6<60; 1.55 <n7<1.70,20<v7<38; 1.50 <n8<1.60,50<v8<60; Among them, n1-n8 are the refractive indices of the first lens to the eighth lens respectively, and v1-v8 are the Abbe numbers of the first lens to the eighth lens respectively.

4. The fixed-focus lens according to claim 1, wherein: The second lens and the third lens are cemented together to form a cemented lens group, and the sixth lens and the seventh lens are cemented together to form a cemented lens group.

Images