Small low-cost CCTV wide-angle prime lens and imaging method thereof

Abstract

The invention relates to a small-sized low-cost CCTV wide-angle prime lens and an imaging method thereof, the small-sized low-cost CCTV wide-angle prime lens comprises an optical system, and the optical system is composed of a first lens, a second lens, a diaphragm, a third lens and a fourth lens which are sequentially arranged from left to right along a light incident light path; the first lens is a meniscus concave negative lens, the second lens is a biconvex positive lens, the third lens is a biconvex positive lens, and the fourth lens is a biconcave negative lens. The optical lens is simple in structure and reasonable in design, the optical structure that one glass lens is matched with three plastic lenses is adopted, the advantage of aberration correction of the aspherical lens is fully played, high-definition imaging is met, meanwhile, the optical lens has the smaller outer diameter of the lens and the shorter optical total length, miniaturization of the lens is guaranteed, and higher optical performance stability is achieved; and meanwhile, the cost is reduced while the system adapts to the environment, and the system has the advantages of relatively high imaging definition, large clear aperture, relatively low tolerance sensitivity, relatively good high and low temperature stability and the like, and can monitor a target more comprehensively.

Description

Technical Field

[0001] This invention relates to a small, low-cost CCTV wide-angle fixed-focus lens and its imaging method. Background Technology

[0002] Over the past few decades, the development of surveillance cameras has been rapid and ever-changing. In terms of imaging range, surveillance cameras have evolved from small-angle, narrow-range lenses to wide-angle lenses with a wide field of view and even ultra-wide-angle fisheye lenses that can achieve panoramic monitoring. In terms of pixels and image quality, surveillance cameras have progressed from standard definition with hundreds of thousands of pixels to high-definition and ultra-high-definition with millions or even tens of millions of pixels. However, this has also led to an increase in production costs and complexity. Summary of the Invention

[0003] The present invention improves upon the above-mentioned problems. Specifically, the technical problem to be solved by the present invention is to provide a small, low-cost CCTV wide-angle fixed-focus lens and its imaging method, while taking into account the optical characteristics of low cost, wide spectrum, large relative aperture, miniaturization, high image quality, and day and night confocal monitoring.

[0004] The present invention is configured as follows: it includes an optical system consisting of a first lens, a second lens, an aperture stop, a third lens, and a fourth lens arranged sequentially from left to right along the incident light path; the first lens is a meniscus negative lens, the second lens is a biconvex positive lens, the third lens is a biconvex positive lens, and the fourth lens is a biconcave negative lens.

[0005] Furthermore, the object-side surface of the first lens is convex, and the image-side surface is concave; the object-side surface of the second lens is convex, and the image-side surface is convex; the object-side surface of the third lens is convex, and the image-side surface is convex; the object-side surface of the fourth lens is concave, and the image-side surface is concave.

[0006] Furthermore, the focal length of the optical imaging system is f, and the focal lengths of the first lens, second lens, third lens, and fourth lens are f1, f2, f3, and f4, respectively, where f1, f2, f3, and f4 satisfy the following ratio with f: -2.0 <f1 / f<-1.0,2.0<f2 / f<3.0,1.0<f3 / f<2.0,-2.0<f4 / f<-1.0。

[0007] Furthermore, the first lens satisfies the relationship: 1.5 ≤ N d ≤1.8, V d ≥50.0; The second lens satisfies the relationship: 1.4≤N d ≤1.7, V d ≥50.0; The third lens satisfies the relationship: 1.5≤N d ≤1.8, Vd ≥50.0; The fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; where N d V is the refractive index. d Let be Abbe's constant.

[0008] Furthermore, the air gap between the first lens and the aperture stop is 6.5~7.0mm; the air gap between the aperture stop and the second lens is 2.0~2.5mm; the air gap between the second lens and the third lens is 1.0~1.5mm; and the air gap between the third lens and the fourth lens is 0.1~0.5mm.

[0009] Furthermore, the first, third, and fourth lenses are all aspherical lenses, and the equation for the aspherical curve is expressed as follows: ; Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; k is the conic constant; and α1, α2, α3, α4, α5, α6, α7, and α8 are all higher-order coefficients.

[0010] Furthermore, the total optical length (TTL) of the optical system and the focal length (f) of the optical system satisfy the following condition: TTL / f ≤ 6.0.

[0011] Furthermore, the F-number of the optical system is ≤1.6.

[0012] Furthermore, the image height H of the optical system and the focal length f of the optical system satisfy the following condition: H / f≤1.0.

[0013] Furthermore, an equivalent glass plate and an imaging surface are provided behind the fourth lens. Furthermore, in the imaging method of a small, low-cost CCTV wide-angle fixed-focus lens, light passes sequentially through a first lens, a second lens, an aperture stop, a third lens, and a fourth lens before forming an image.

[0014] Compared with existing technologies, this invention has the following advantages: 1. The lens has an imaging angle greater than 110 degrees, and simultaneously possesses advantages such as high imaging clarity, large aperture, low tolerance sensitivity, and good high and low temperature stability, enabling more comprehensive target monitoring; 2. Through reasonable matching of various optical lenses, the system structure is compact and reasonable, easy to assemble, with low tolerance sensitivity, making it more suitable for large-scale high-yield production; 3. Using one glass lens with three plastic lenses results in a lighter system weight compared to an all-glass system, and stronger optical performance stability compared to an all-plastic system, while reducing costs while adapting to different environments; 4. It can effectively compensate for focal plane displacement at high and low temperatures, possessing adaptability to complex environments; 5. It corrects chromatic aberration along each axis, transverse chromatic aberration, and higher-order chromatic aberrations, ensuring high imaging quality even at large angles; 6. It uses domestically produced plastic materials, reducing material costs; 7. The glass lens adopts a simple lens design, further reducing production costs. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the optical structure of an embodiment of the present invention; Figure 2 This is an axial chromatic aberration diagram of the entire working band of this invention embodiment; Figure 3 This is a transverse chromatic aberration diagram of the entire working band of this invention; Figure 4 This is a field curvature distortion diagram of the entire working band of this invention embodiment; In the diagram: STO - aperture stop; L1 - first lens; L2 - second lens; L3 - third lens; L4 - fourth lens; L5 - equivalent glass plate; IMA - imaging plane. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0017] Example: Figures 1-4 As shown, the present invention provides a small, low-cost CCTV wide-angle fixed-focus lens, including an optical system. The optical system consists of a first lens, a second lens, an aperture stop, a third lens, and a fourth lens arranged sequentially from left to right along the incident light path. The first lens is a meniscus negative lens, the second lens is a biconvex positive lens, the third lens is a biconvex positive lens, and the fourth lens is a biconcave negative lens.

[0018] During imaging: Light passes sequentially through the first lens, the second lens, the aperture stop, the third lens, and the fourth lens to form an image. The first lens is an aspherical lens with negative optical power, which adjusts large-angle light while reducing optical system distortion. Through a reasonable lens combination, the optical system achieves low cost, small size, a 110° ultra-wide angle, large aperture, day / night confocal focus, and low temperature drift design. It also effectively corrects on-axis and off-axis aberrations, resulting in good image quality.

[0019] This lens design employs an optical structure consisting of a single glass lens and three plastic lenses. It fully leverages the aberration correction advantages of aspherical lenses, achieving high-definition imaging while maintaining a smaller lens outer diameter and shorter overall optical length, ensuring lens miniaturization. The hybrid glass-plastic system is lighter than an all-glass system and offers stronger optical performance stability compared to an all-plastic system. It also reduces costs while adapting to different environments. This lens has an imaging angle greater than 110 degrees and boasts advantages such as high image clarity, a large aperture, low tolerance sensitivity, and good high and low temperature stability, enabling more comprehensive target monitoring.

[0020] In this embodiment of the invention, without considering the curvature caused by the aspherical coefficient, the object side of the first lens is convex and the image side is concave; the object side of the second lens is convex and the image side is convex; the object side of the third lens is convex and the image side is convex; and the object side of the fourth lens is concave and the image side is concave.

[0021] In this embodiment of the invention, the focal length of the optical imaging system is f, and the focal lengths of the first lens, second lens, third lens, and fourth lens are f1, f2, f3, and f4, respectively, wherein f1, f2, f3, and f4 satisfy the following ratio with f: -2.0 <f1 / f<-1.0,2.0<f2 / f<3.0,1.0<f3 / f<2.0,-2.0<f4 / f<-1.0。

[0022] In this embodiment of the invention, the first lens satisfies the relationship: 1.5 ≤ N d ≤1.8, V d ≥50.0; The second lens satisfies the relationship: 1.4≤N d ≤1.7, V d ≥50.0; The third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; The fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; where N d V is the refractive index. d Let be Abbe's constant.

[0023] In this embodiment of the invention, the air gap between the first lens and the aperture stop is 6.5~7.0mm; the air gap between the aperture stop and the second lens is 2.0~2.5mm; the air gap between the second lens and the third lens is 1.0~1.5mm; and the air gap between the third lens and the fourth lens is 0.1~0.5mm.

[0024] In this embodiment of the invention, the first, third, and fourth lenses are all aspherical lenses, and the equation of the aspherical curve is expressed as follows: ; Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; k is the conic constant; and α1, α2, α3, α4, α5, α6, α7, and α8 are all higher-order coefficients.

[0025] The first, second, third, and fourth lenses are made of glass or plastic, with the third lens being a glass spherical lens and the first, second, and fourth lenses being plastic aspherical lenses.

[0026] In this embodiment of the invention, the total optical length (TTL) of the optical system and the focal length (f) of the optical system satisfy the following condition: TTL / f ≤ 6.0.

[0027] In this embodiment of the invention, the F-number of the optical system is ≤1.6.

[0028] In this embodiment of the invention, the image height H of the optical system and the focal length f of the optical system satisfy the following condition: H / f≤1.0.

[0029] In this embodiment of the invention, an equivalent glass plate and an imaging surface are provided behind the fourth lens. In this embodiment of the invention, the technical specifications achieved by the optical system are as follows: (1) Focal length: 3.5≤EFFL≤4.5mm; (2) Aperture F≤1.6; (3) Field of view: 2w ≥ 110°; (4) Operating bands: visible light and short-wave infrared bands.

[0030] To achieve the above design parameters, the specific design parameters of the optical system in this embodiment of the invention are shown in Table 1 below: Table 1 The aspherical coefficients of each aspherical lens in the optical system of this embodiment are shown in Table 2 below: Table 2 This embodiment achieves lens miniaturization by rationally allocating the optical power, surface shape, center thickness of each lens, and on-axis distance between each lens, while meeting the lens's 110° ultra-wide-angle imaging performance requirements and reducing the overall length of the lens and the radial dimensions of each lens element.

[0031] Unless otherwise stated, if any of the technical solutions disclosed in this invention specify a numerical range, then the disclosed numerical range is a preferred numerical range. Anyone skilled in the art should understand that the preferred numerical range is merely one among many feasible numerical values ​​that has a more obvious or representative technical effect. Because there are many numerical values, it is impossible to list them all. Therefore, this invention discloses only some numerical values ​​to illustrate the technical solutions of this invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

[0032] Furthermore, if the present invention discloses or relates to mutually fixedly connected components or structural parts, then unless otherwise stated, a fixed connection can be understood as: a detachable fixed connection (e.g., using bolts or screws), or a non-detachable fixed connection (e.g., riveting, welding). Of course, mutually fixed connections can also be replaced by an integral structure (e.g., manufactured using a casting process) (except where it is obviously impossible to use an integral molding process).

[0033] If the terms "first" or "second" are used in this document to specify components, those skilled in the art should know that the use of "first" or "second" is merely for the purpose of distinguishing components in description, and unless otherwise stated, the above terms have no special meaning.

[0034] In addition, unless otherwise stated, the terms used in any of the technical solutions disclosed in this invention to indicate positional relationships or shapes include states or shapes that are similar to, close to, or approximate with those states or shapes.

[0035] Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured by a one-piece molding process.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A small, low-cost CCTV wide-angle fixed-focus lens, characterized in that, The system includes an optical system consisting of a first lens, a second lens, an aperture stop, a third lens, and a fourth lens arranged sequentially from left to right along the incident light path; the first lens is a meniscus negative lens, the second lens is a biconvex positive lens, the third lens is a biconvex positive lens, and the fourth lens is a biconcave negative lens.

2. The small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The first lens has a convex object-side surface and a concave image-side surface; the second lens has a convex object-side surface and a convex image-side surface; the third lens has a convex object-side surface and a convex image-side surface; and the fourth lens has a concave object-side surface and a concave image-side surface.

3. The small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The focal length of the optical imaging system is f, and the focal lengths of the first lens, the second lens, the third lens, and the fourth lens are f1, f2, f3, and f4, respectively. The following ratios are satisfied between f1, f2, f3, f4 and f: -2.0 < f1 / f < -1.0, 2.0 < f2 / f < 3.0, 1.0 < f3 / f < 2.0, and -2.0 < f4 / f < -1.

0.

4. The small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The first lens satisfies the relationship: 1.5 ≤ N d ≤1.8, V d ≥50.0; The second lens satisfies the relationship: 1.4≤N d ≤1.7, V d ≥50.0; The third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; The fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; where N d V is the refractive index. d Let be Abbe's constant.

5. A small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The air gap between the first lens and the aperture stop is 6.5~7.0mm; the air gap between the aperture stop and the second lens is 2.0~2.5mm; the air gap between the second lens and the third lens is 1.0~1.5mm; and the air gap between the third lens and the fourth lens is 0.1~0.5mm.

6. A small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The first, third, and fourth lenses are all aspherical lenses, and the equation for the aspherical curve is: Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; k is the conic constant; α1, α2, α3, α4, α5, α6, α7, and α8 are all higher-order coefficients.

7. A small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The total optical length (TTL) of an optical system and the focal length (f) of the optical system satisfy the following condition: TTL / f ≤ 6.

0.

8. A small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The F-number of the optical system is ≤1.

6.

9. A small, low-cost CCTV wide-angle fixed-focus lens according to claim 1, characterized in that, The image height H of the optical system and the focal length f of the optical system satisfy the following condition: H / f≤1.

0.

10. An imaging method using a small, low-cost CCTV wide-angle fixed-focus lens as described in any one of claims 1-9, characterized in that, The light rays pass through the first lens, the second lens, the aperture, the third lens, and the fourth lens in sequence to form an image.

Images