Fixed-focus lens

Abstract

The present invention relates to a fixed-focus lens, which sequentially includes, along the optical axis from the object side to the image side: a first lens with a negative optical power, a second lens with a positive optical power, a diaphragm, a third lens with a positive optical power, a fourth lens with a negative optical power, a fifth lens with a positive optical power, and a protective flat glass. The effective focal length F of the fixed-focus lens and the effective focal length F1 of the first lens satisfy the following relationship: 1.2 ≤ |F1 / F| ≤ 1.5. For the fixed-focus lens of the present invention, by reasonably setting the concavity and convexity, material, and optical power distribution of each lens, it can better collect and transmit light, helps to obtain a larger field of view angle, effectively corrects visible light, infrared, and high and low temperature aberrations. Under the requirement of better light transmissibility, the miniaturization and low cost of the fixed-focus lens are realized. Under the requirement of high performance, it can achieve no defocus within the temperature range of -40°C to 70°C and day-night confocal, so as to be applicable to various environments.

Description

Technical Field

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

[0002] With the progress and development of science and technology, people's demand for security is changing with each passing day. The scale of video doorbells has developed rapidly and become increasingly popular. Currently, they have been widely used in various private and public places. The fixed-focus fish-eye lens is widely used in various fields due to its advantages such as a wide monitoring field of view and clear imaging.

[0003] Most doorbell systems are exposed to the outdoor environment. Therefore, it is necessary to ensure that the lens can obtain clear imaging in different temperature environments. At the same time, since the brightness of the images captured by the lens is insufficient at night or in environments with insufficient light conditions and clear imaging cannot be achieved, the doorbell lens usually uses infrared supplementary lighting to achieve the imaging purpose. Most fixed-focus lenses on the market, although the cost has been greatly reduced, it is difficult to simultaneously take into account excellent properties such as miniaturization, large field of view, no defocusing at high and low temperatures, and day-night confocal under low-cost conditions. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide a fixed-focus lens with low cost, miniaturization, large field of view, no defocusing in the temperature range of -40°C to 70°C, and day-night confocal.

[0005] To achieve the above purpose, the present invention provides a fixed-focus lens, which sequentially includes, along the optical axis from the object side to the image side: a first lens with a negative optical power, a second lens with a positive optical power, a diaphragm, a third lens with a positive optical power, a fourth lens with a negative optical power, a fifth lens with a positive optical power, and a protective flat glass. The effective focal length F of the fixed-focus lens and the effective focal length F1 of the first lens satisfy the following relationship:

[0006] 1.2 ≤ |F1 / F| ≤ 1.5.

[0007] According to one aspect of the present invention, the first lens and the fourth lens are aspherical lenses with a convex-concave shape in the paraxial region, the second lens is an aspherical lens with a concave-convex shape in the paraxial region, the third lens is a spherical lens with a concave-convex or double-convex shape, and the fifth lens is an aspherical lens with a double-convex shape in the paraxial region.

[0008] According to one aspect of the present invention, the first lens, the second lens, the fourth lens, and the fifth lens are plastic lenses, and the third lens is a glass lens.

[0009] According to one aspect of the present invention, the effective focal length F of the fixed-focus lens and the effective focal length F2 of the second lens satisfy the following relationship:

[0010] 3.1 ≤ |F2 / F| ≤ 3.8.

[0011] According to one aspect of the present invention, the refractive index value nd3 of the third lens and the Abbe value vd3 of the third lens satisfy the following relationship: 1.45 ≤ nd3 ≤ 1.65; 65 ≤ vd3 ≤ 85.

[0012] According to one aspect of the present invention, the effective focal length F of the fixed-focus lens and the effective focal length F3 of the third lens satisfy the following relationship:

[0013] 2.0 ≤ |F3 / F| ≤ 2.3.

[0014] According to one aspect of the present invention, the effective focal length F of the fixed-focus lens and the effective focal length F4 of the fourth lens satisfy the following relationship: 1.4 ≤ |F4 / F| ≤ 1.7.

[0015] According to one aspect of the present invention, the effective focal length F of the fixed-focus lens and the effective focal length F5 of the fifth lens satisfy the following relationship: 1.2 ≤ |F5 / F| ≤ 1.6.

[0016] According to one aspect of the present invention, the effective focal length F of the fixed-focus lens and the semi-image height H of the image plane of the fixed-focus lens satisfy the following relationship:

[0017] 0.6 ≤ F / H ≤ 0.8.

[0018] According to one aspect of the present invention, the effective diameter D1 of the object side surface of the first lens and the overall optical length TTL of the fixed-focus lens satisfy the following relationship: 0.4 ≤ D1 / TTL ≤ 0.6.

[0019] According to one aspect of the present invention, the overall optical length TTL of the fixed-focus lens and the effective focal length F of the fixed-focus lens satisfy the following relationship:

[0020] 5.2 ≤ TTL / F ≤ 5.5.

[0021] According to the solution of the present invention, the fixed-focus lens of the present invention uses a total of five lenses. By reasonably setting the concavity and convexity, material, and optical power distribution of each lens, it can better collect and transmit light, helping to obtain a larger field of view angle (the full field of view angle reaches 172° - 180°), effectively correct visible light, infrared, and high and low temperature aberrations. Under the requirement of better light transmission, the miniaturization of the fixed-focus lens (the overall optical length TTL including the protective flat glass ≤ 13 mm) and low cost are achieved. Under the requirement of high performance, it can achieve no defocus within the temperature range of -40°C to 70°C and day-night confocal, thus being applicable to various environments.

[0022] According to one aspect of the present invention, by reasonably configuring the refractive index and Abbe number, spherical aberration and chromatic aberration of the optical system can be effectively corrected, and at the same time, the back focal shift of the fixed-focus lens in the infrared state is compensated, ensuring the sharpness of the lens infrared imaging to achieve higher image quality.

[0023] According to one aspect of the present invention, by reasonably configuring the diopter and focal length of each lens, the distribution mode of positive and negative optical powers is beneficial to aberration correction, and at the same time, it ensures that the optical system is not defocused under high and low temperature conditions.

[0024] According to one aspect of the present invention, it is possible to achieve no defocus within the temperature range of -40°C to 70°C, overcoming the difficulty that plastic aspherical lenses are prone to focus drift in high and low temperature environments due to their large expansion coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of a fixed-focus lens according to Embodiment 1 of the present invention;

[0026] Figure 2 It is a schematic structural diagram of a fixed-focus lens according to Embodiment 2 of the present invention;

[0027] Figure 3 It is a schematic structural diagram of a fixed-focus lens according to Embodiment 3 of the present invention;

[0028] Figure 4 It is a schematic structural diagram of a fixed-focus lens according to Embodiment 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] When describing the embodiments of the present invention, the orientation or positional relationship expressed by the terms "longitudinal", "lateral", "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.

[0031] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments cannot be enumerated one by one here, but the embodiments of the present invention are not limited to the following embodiments accordingly.

[0032] Figure 1 It is a schematic structural diagram of a fixed-focus lens showing an embodiment according to the present invention. As Figure 1 shown, the fixed-focus lens of the present invention includes five lenses. Along the optical axis from the object side to the image side, they are in sequence: a first lens L1 with a negative optical power, a second lens L2 with a positive optical power, a stop STO, a third lens L3 with a positive optical power, a fourth lens L4 with a negative optical power, a fifth lens L5 with a positive optical power, and a protective flat glass CG. The first lens L1 and the fourth lens L4 are aspherical lenses with a convex-concave shape in the paraxial region. The second lens L2 is an aspherical lens with a concave-convex shape in the paraxial region. The third lens L3 is a spherical lens with a concave-convex or biconvex shape. The fifth lens L5 is an aspherical lens with a biconvex shape. The effective focal length F of the fixed-focus lens and the effective focal length F1 of the first lens L1 satisfy the following relationship: 1.2 ≤ |F1 / F| ≤ 1.5.

[0033] The fixed-focus lens uses a total of five lenses. By reasonably setting the concavity and convexity, materials, and optical power distribution of each lens, it can better collect and transmit light, helping to obtain a larger field of view (the full field of view reaches 172° - 180°), effectively correct visible light, infrared, and high and low temperature aberrations. While meeting the requirements of better light transmission, the miniaturization of the fixed-focus lens (the overall optical length TTL including the protective flat glass ≤ 13 mm) and low cost are achieved. While meeting the requirements of high performance, it can achieve no defocus within the temperature range of -40°C to 70°C and be day-night confocal, thus being applicable to various environments.

[0034] In the present invention, the first lens L1 is an aspherical lens with a convex-concave shape in the paraxial region; the second lens L2 is an aspherical lens with a concave-convex shape in the paraxial region; the third lens L3 is a spherical lens with a concave-convex or biconvex shape; the fourth lens L4 is an aspherical lens with a convex-concave shape in the paraxial region; the fifth lens L5 is an aspherical lens with a biconvex shape in the paraxial region.

[0035] Among them, the aspherical surface satisfies the following formula:

[0036]

[0037] In the formula, z is the axial distance from the vertex of the surface at a position perpendicular to the optical axis with a height of h along the optical axis; c represents the curvature at the vertex of the aspherical surface; k is the conic coefficient; A4, A6, A8, A10, A12, A14, A16... are the aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, sixteenth order... respectively.

[0038] By reasonably configuring spherical and aspherical lenses, various aberrations of the system are effectively corrected, thereby improving the resolution of the lens. At the same time, through the ingenious combination of plastic and glass lenses, the back focus shift of the lens under high and low temperature conditions is compensated. While reducing costs, the imaging under high and low temperatures is corrected, ensuring that the fixed-focus lens does not defocus within the temperature range of -40°C to 70°C, is confocal day and night, and improves the applicability of the lens.

[0039] In the present invention, the effective focal length F of the fixed-focus lens and the effective focal length F2 of the second lens L2 satisfy the following relationship: 3.1 ≤ |F2 / F| ≤ 3.8, which can better collect and transmit light, contributing to obtaining a larger field of view angle, and the full field of view angle reaches 172° to 180°.

[0040] In the present invention, the refractive index value nd3 of the third lens L3 and the Abbe value vd3 of the third lens L3 satisfy the following relationship: 1.45 ≤ nd3 ≤ 1.65; 65 ≤ vd3 ≤ 85.

[0041] By reasonably configuring the refractive index and Abbe number of each lens, the spherical aberration and chromatic aberration of the optical system are effectively corrected. At the same time, the back focus shift of the fixed-focus lens in the infrared state is compensated, ensuring the sharpness of the infrared imaging of the fixed-focus lens, thereby improving the imaging quality of the fixed-focus lens.

[0042] In the present invention, the effective focal length F of the fixed-focus lens and the effective focal length F3 of the third lens L3 satisfy the following relationship: 2.0 ≤ |F3 / F| ≤ 2.3; the effective focal length F of the fixed-focus lens and the effective focal length F4 of the fourth lens L4 satisfy the following relationship: 1.4 ≤ |F4 / F| ≤ 1.7, and the effective focal length F of the fixed-focus lens and the effective focal length F5 of the fifth lens L5 satisfy the following relationship: 1.2 ≤ |F5 / F| ≤ 1.6. The distribution method of positive and negative optical powers is conducive to aberration correction and at the same time ensures that the optical system does not defocus under high and low temperature conditions.

[0043] In the present invention, the effective focal length F of the fixed-focus lens and the aperture number Fno of the fixed-focus lens satisfy the following relationship: 1.0 ≤ F / Fno ≤ 1.3, and the effective focal length F of the fixed-focus lens and the semi-image height H of the image plane of the fixed-focus lens satisfy the following relationship: 0.6 ≤ F / H ≤ 0.8; the effective diameter D1 of the object side of the first lens L1 and the total optical length TTL of the fixed-focus lens satisfy the following relationship: 0.4 ≤ D1 / TTL ≤ 0.6, which is conducive to ensuring a smaller volume while achieving a larger field of view angle and higher image quality.

[0044] In the present invention, the total optical length TTL of the fixed-focus lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.2 ≤ TTL / F ≤ 5.5, and the total optical length TTL including the protective flat glass satisfies the relationship TTL ≤ 13 mm, making the fixed-focus lens have a smaller volume and being conducive to the miniaturization of the fixed-focus lens.

[0045] Four specific embodiments are given below according to the above settings of the present invention to specifically illustrate the fixed-focus lens according to the present invention. Since the fixed-focus lens according to the present invention has a total of five lenses, plus the aperture STO, the protective flat glass CG and the image plane, there are a total of 15 surfaces. For the convenience of description, the numbers of each surface except the image plane are numbered as S1, S2 to S15.

[0046] The parameters of each specific embodiment that specifically meet the above relational expressions are shown in Table 1 below:

[0047]

[0048]

[0049] Table 1

[0050] Embodiment 1:

[0051] Figure 1 It schematically shows the structural diagram of the fixed-focus lens according to Embodiment 1 of the present invention.

[0052] In Embodiment 1, the aperture FNO = 2.00, the total optical length TTL including the protective flat glass is 12.84 mm; the field of view angle is 172°, and the third lens L3 is a concave-convex plastic aspherical lens.

[0053] The following Table 2 lists the relevant parameters of each lens in this embodiment, including the surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0054] Surface Serial Number Surface Type R Value Thickness Refractive Index Abbe Number S1 Aspherical 16.536 0.517 1.54 55.7 S2 Aspherical 1.615 1.615 S3 Aspherical -6.472 1.773 1.64 23.5 S4 Aspherical -3.071 -0.219 S5(STO) Spherical Infinity 0.987 S6 Spherical -56.737 1.262 1.59 68.6 S7 Spherical -2.944 -0.093 S8 Spherical Infinity 0.1705 S9 Aspherical 5.842 0.460 1.66 20.4 S10 Aspherical 1.656 0.173 S11 Aspherical 3.246 1.976 1.54 55.7 S12 Aspherical -3.316 2.000 S13 Spherical Infinity 0.700 1.52 64.2 S14 Spherical Infinity 1.517 S15(IMA) Spherical Infinity - - -

[0055] Table 2

[0056] In this embodiment, the aspherical data is shown in Table 3 below, where K is the conic constant of the surface, and A4, A6, A8, A10, A12, A14 are the aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, and fourteenth order respectively:

[0057]

[0058]

[0059] Table 3

[0060] Embodiment 2:

[0061] Figure 2 It schematically shows the structural diagram of the fixed-focus lens according to Embodiment 2 of the present invention.

[0062] In Embodiment 2, the aperture FNO = 2.00, the total optical length TTL including the protective flat glass is 12.76 mm; the field of view angle is 172°, and the third lens L3 is a biconvex plastic aspherical lens.

[0063] The following Table 4 lists the relevant parameters of each lens in this embodiment, including the surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0064] Surface Serial Number Surface Type R Value Thickness Refractive Index Abbe Number S1 Aspherical 18.396 0.466 1.54 55.7 S2 Aspherical 1.560 1.672 S3 Aspherical -6.842 1.348 1.64 23.5 S4 Aspherical -3.325 -0.011 S5(STO) Spherical Infinity 0.905 S6 Spherical 410.863 1.497 1.59 68.6 S7 Spherical -2.945 -0.033 S8 Spherical Infinity 0.171 S9 Aspherical 5.690 0.497 1.66 20.4 S10 Aspherical 1.645 0.157 S11 Aspherical 2.814 1.919 1.54 55.7 S12 Aspherical -3.587 2.000 S13 Spherical Infinity 0.700 1.52 64.2 S14 Spherical Infinity 1.470 S15(IMA) Spherical Infinity - - -

[0065] Table 4

[0066] In this embodiment, the aspherical data is shown in the following Table 5, where K is the conic constant of the surface, and A4, A6, A8, A10, A12, A14 are the aspherical coefficients of the fourth, sixth, eighth, tenth, twelfth, and fourteenth orders respectively:

[0067]

[0068]

[0069] Table 5

[0070] Embodiment 3:

[0071] Figure 3 It schematically shows the fixed-focus lens structure diagram according to Embodiment 3 of the present invention.

[0072] In Embodiment 3, the aperture FNO = 2.0, the total optical length TTL including the protective flat glass is 13.00 mm; the field of view angle is 180°, and the third lens L3 is a biconvex plastic aspherical lens.

[0073] The following Table 6 lists the relevant parameters of each lens in this embodiment, including the surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0074] Surface Serial Number Surface Type R Value Thickness Refractive Index Abbe Number S1 Aspherical 41.716 0.419 1.54 55.7 S2 Aspherical 1.685 1.676 S3 Aspherical -8.414 1.605 1.64 23.5 S4 Aspherical -3.687 -0.012 S5(STO) Spherical Infinity 1.222 S6 Spherical 44.292 1.244 1.59 68.6 S7 Spherical -3.141 -0.122 S8 Spherical Infinity 0.171 S9 Aspherical 5.516 0.518 1.66 20.4 S10 Aspherical 1.757 0.192 S11 Aspherical 3.178 1.768 1.54 55.7 S12 Aspherical -4.112 2.000 S13 Spherical Infinity 0.700 1.52 64.2 S14 Spherical Infinity 1.627 S15(IMA) Spherical Infinity - - -

[0075] Table 6

[0076] In the embodiment, the aspherical data is shown in the following Table 7, where K is the conic constant of the surface, and A4, A6, A8, A10, A12, A14 are the aspherical coefficients of the fourth, sixth, eighth, tenth, twelfth, and fourteenth orders respectively:

[0077]

[0078]

[0079] Table 7

[0080] Embodiment 4:

[0081] Figure 4 It schematically shows the structural diagram of a fixed-focus lens according to Embodiment 4 of the present invention.

[0082] In Embodiment 4, the aperture FNO = 2.00, the overall optical length TTL including the protective flat glass is 12.84 mm; the field of view angle is 172°, and the third lens L3 is a biconvex plastic aspherical lens.

[0083] The following Table 8 lists the relevant parameters of each lens in this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, Abbe number:

[0084] Surface Serial Number Surface Type R Value Thickness Refractive Index Abbe Number S1 Aspherical 18.424 0.522 1.54 55.7 S2 Aspherical 1.469 1.581 S3 Aspherical -7.78 1.616 1.64 23.5 S4 Aspherical -3.407 -0.199 S5(STO) Spherical Infinity 0.894 S6 Spherical 23.808 1.309 1.59 68.6 S7 Spherical -2.736 0.213 S8 Aspherical 7.094 0.594 1.50 81.6 S9 Aspherical 1.7 0.158 S10 Aspherical 2.693 2.189 1.54 55.7 S11 Aspherical -3.416 2.000 S12 Spherical Infinity 0.700 1.52 64.2 S13 Spherical Infinity 1.265 S14(IMA) Spherical Infinity - - -

[0085] Table 8

[0086] In this embodiment, the aspherical data is shown in the following Table 9, where K is the conic constant of the surface, and A4, A6, A8, A10, A12, A14 are the aspherical coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, and fourteenth order respectively:

[0087]

[0088]

[0089] Table 9

[0090] According to the above embodiments of the present invention, the fixed-focus lens of the present invention uses a total of five lenses. By reasonably setting the concavity and convexity, material, and optical power distribution of each lens, it can better collect and transmit light, helping to obtain a larger field of view angle (the full field of view angle reaches 172° - 180°), effectively correct visible light, infrared, and high and low temperature aberrations. While meeting the requirement of better light transmission, it realizes the miniaturization of the fixed-focus lens (the overall optical length TTL including the protective flat glass ≤ 13 mm) and low cost. While meeting the high-performance requirements, it can achieve no defocus within the temperature range of -40°C to 70°C and day-night confocal, thus being applicable to various environments.

[0091] The above description is only one embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention 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, sequentially comprising, along the optical axis from the object side to the image side: A first lens (L1) with a negative focal power, a second lens (L2) with a positive focal power, a stop (STO), a third lens (L3) with a positive focal power, a fourth lens (L4) with a negative focal power, a fifth lens (L5) with a positive focal power, and a protective flat glass (CG). There are a total of five lenses with focal powers. It is characterized in that the effective focal length F of the fixed-focus lens and the effective focal length F1 of the first lens (L1) satisfy the following relationship: 1.2 ≤ |F1 / F| ≤ 1.5; The effective focal length F of the fixed-focus lens and the semi-image height H of the image plane of the fixed-focus lens satisfy the following relationship: 0.6 ≤ F / H ≤ 0.8; The field of view FOV of the fixed-focus lens satisfies the following relationship: 172° ≤ FOV ≤ 180°.

2. The fixed-focus lens according to claim 1, wherein The first lens (L1) and the fourth lens (L4) are aspherical lenses that are convex-concave in the paraxial region, the second lens (L2) is an aspherical lens that is concave-convex in the paraxial region, the third lens (L3) is a spherical lens that is concave-convex or biconvex, and the fifth lens (L5) is an aspherical lens that is biconvex in the paraxial region.

3. The fixed-focus lens according to claim 1, wherein The first lens (L1), the second lens (L2), the fourth lens (L4), and the fifth lens (L5) are plastic lenses, and the third lens (L3) is a glass lens.

4. The fixed-focus lens according to any one of claims 1 to 3, characterized in that, The effective focal length F of the fixed-focus lens and the effective focal length F2 of the second lens (L2) satisfy the following relationship: 3.1 ≤ |F2 / F| ≤ 3.

8.

5. The fixed-focus lens according to any one of claims 1 to 3, characterized in that The refractive index nd3 of the third lens (L3) satisfies the following relationship: 1.45 ≤ nd3 ≤ 1.65; The Abbe number vd3 of the third lens (L3) satisfies the following relationship: 65 ≤ vd3 ≤ 85.

6. The fixed-focus lens according to any one of claims 1 to 3, characterized in that, The effective focal length F of the fixed-focus lens and the effective focal length F3 of the third lens (L3) satisfy the following relationship: 2.0 ≤ |F3 / F| ≤ 2.

3.

7. The fixed-focus lens according to any one of claims 1 to 3, characterized in that, The effective focal length F of the fixed-focus lens and the effective focal length F4 of the fourth lens (L4) satisfy the following relationship: 1.4 ≤ |F4 / F| ≤ 1.

7.

8. The fixed-focus lens according to any one of claims 1 to 3, characterized in that, The effective focal length F of the fixed-focus lens and the effective focal length F5 of the fifth lens (L5) satisfy the following relationship: 1.2 ≤ |F5 / F| ≤ 1.

6.

9. The fixed-focus lens according to any one of claims 1 to 3, characterized in that, The effective diameter D1 of the object side of the first lens (L1) and the total optical length TTL of the fixed-focus lens satisfy the following relationship: 0.4 ≤ D1 / TTL ≤ 0.

6.

10. The fixed-focus lens according to any one of claims 1 to 3, characterized in that, The total optical length TTL of the fixed-focus lens and the effective focal length F of the fixed-focus lens satisfy the following relationship: 5.2 ≤ TTL / F ≤ 5.5.

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