A starlight-level optical lens and imaging method thereof

Abstract

The present invention relates to a starlight-level optical lens and an imaging method thereof, comprising a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged from front to back along the incident optical path of light, the first lens and the second lens are both meniscus negative lenses, the third lens is a double convex positive lens, the first lens, the second lens and the third lens constitute a front lens group with negative optical power; the fourth lens is a double convex positive lens, the fifth lens is a double concave negative lens, the sixth lens is a double convex positive lens, and the fourth lens, the fifth lens and the sixth lens constitute a rear lens group with positive optical power. The present invention is reasonably designed, has an ultra-large aperture, and a large overall light flux; has high imaging quality and a large target surface, and can reach a four-million-pixel camera level; has a day and night confocal function, and the optimal resolution imaging position remains unchanged in a white light environment and an infrared environment; has a temperature compensation function, and maintains clear imaging in a temperature range of ‑40°C to 85°C.

Description

Technical field:

[0001] The invention belongs to the field of optical systems, and in particular relates to a starlight-level optical lens and an imaging method thereof. Background technology:

[0002] Starlight optical lens cameras are hot products in the surveillance industry that have been launched in recent years with the development of semiconductor technology. In terms of camera function classification, starlight cameras belong to low-light cameras, which are cameras that can still capture clear images under low light illumination conditions. At present, the security industry usually divides front-end cameras into four levels: ordinary cameras, generally with illumination values ​​greater than 0.1lux; cameras with illumination values ​​ranging from 0.1lux to 0.01lux are generally called low-light cameras; cameras with illumination values ​​ranging from 0.01lux to 0.001lux are called moonlight cameras; when the minimum illumination value reaches or even falls below 0.001lux, it reaches the "starlight level".

[0003] Although traditional infrared fill light technology can obtain clear imaging under low illumination, it will lose color and can only form black and white images. In addition, through infrared fill light, highly reflective objects such as license plates are easily overexposed, resulting in unrecognizable objects. Therefore, the demand for clear color imaging under low illumination is increasing. In a starlight environment without any auxiliary light source, starlight-level optical lenses can display clear color images, which is different from ordinary cameras that can only display black and white images. Therefore, in many fields with relatively high requirements for day and night monitoring, such as safe cities, military, border defense, banks, hospitals, highways, etc., starlight-level optical lenses have very good application prospects.

[0004] In view of the existing application scope, the present invention aims to provide a starlight-level optical lens to meet higher road monitoring requirements. Summary of the invention:

[0005] The purpose of the present invention is to provide a starlight-level optical lens and an imaging method thereof in view of the above shortcomings, which has a reasonable structural design and high-definition imaging quality.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a starlight-level optical lens, comprising a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens and a sixth lens which are arranged in sequence from front to back along the incident light path of the light, wherein the first lens and the second lens are both meniscus negative lenses, the third lens is a biconvex positive lens, the first lens, the second lens and the third lens constitute a front lens group with negative optical power; the fourth lens is a biconvex positive lens, the fifth lens is a biconcave negative lens, the sixth lens is a biconvex positive lens, and the fourth lens, the fifth lens and the sixth lens constitute a rear lens group with positive optical power.

[0007] Furthermore, the air gap between the front lens group and the rear lens group is 1.5 mm.

[0008] Furthermore, the air gap between the first lens and the second lens is 2.2 mm, the air gap between the second lens and the third lens is 0.1 mm, the air gap between the third lens and the aperture is 1.1 mm, the air gap between the aperture and the fourth lens is 0.5 mm, the air gap between the fourth lens and the fifth lens is 0.1 mm, and the air gap between the fifth lens and the sixth lens is 0.1 mm.

[0009] Furthermore, the concave surface of the first lens faces the aperture, and the concave surface of the second lens faces away from the aperture.

[0010] Furthermore, the focal length of the optical system composed of the front lens group and the rear lens group is f, the focal lengths of the first lens, the second lens, and the third lens are f1, f2, and f3 respectively, and the focal lengths of the front lens group satisfy the following ratio of f1, f2, f3 and f: -2<f1 / f<-1, -3.5<f2 / f<-2.5, 3<f3 / f<4.

[0011] Furthermore, the focal lengths of the fourth lens, the fifth lens, and the sixth lens are f4, f5, and f6 respectively, and the focal lengths of the rear lens group satisfy the following ratio of f4, f5, f6 and f:

[0012] 1<f4 / f<2, -1<f5 / f<-2, 1.5<f6 / f<2.5.

[0013] Furthermore, the first lens satisfies the relationship: N d ≥1.5, V d ≥50; the second lens satisfies the relationship: N d ≥1.5, V d ≥50; the third lens satisfies the relationship: N d ≥1.6, V d ≤35; the fourth lens satisfies the relationship: N d ≥1.5, V d ≥50; the fifth lens satisfies the relationship: N d ≥1.6, V d ≤35; the sixth lens satisfies the relationship: N d ≤1.5, V d ≥65; where N d is the refractive index, V d is the Abbe constant.

[0014] Furthermore, the first lens, the second lens, the third lens, the fourth lens and the fifth lens are all aspherical lenses made of plastic; the sixth lens is a spherical lens made of glass.

[0015] Another technical solution adopted by the present invention is: an imaging method of a starlight-level optical lens. During imaging, the light path sequentially enters a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens to perform imaging.

[0016] Compared with the prior art, the present invention has the following effects:

[0017] (1) The 1G5P design structure not only has better imaging quality than the all-glass design, but also has a smaller size and mass; the overall system reliability is high, and the assembly sensitivity is reduced, which increases the yield and reduces the cost, which is conducive to large-scale production;

[0018] (2) By rationally designing the aspheric lens surface and rationally allocating the focal length of each lens, not only can the high-level aberration and chromatic aberration of the entire optical system be effectively corrected, but also the incident angle of light on each mirror surface is small. The image quality is high and the target surface is large, which can reach the level of 4 million pixel camera;

[0019] (3) It has a day and night confocal function, which can ensure that the optimal imaging surface position remains unchanged in white light environment and infrared environment; the lens has a long back focus, which is convenient for adding IR-CUT filters, improving the day and night confocal imaging quality;

[0020] (4) It has a temperature compensation function, which ensures that the high-definition image quality of the lens remains unchanged within the temperature range of -40℃ to +85℃. Description of the drawings:

[0021] Figure 1 is a schematic diagram of the optical structure of an embodiment of the present invention;

[0022] Figure 2 is a visible light MTF curve diagram of an embodiment of the present invention;

[0023] Figure 3 850nm band MTF curve diagram of an embodiment of the present invention;

[0024] Figure 4 Defocus curve diagram of an embodiment of the present invention at a low temperature of -40°C;

[0025] Figure 5 Defocus curve diagram of an embodiment of the present invention at a high temperature of +85°C.

[0026] In the figure:

[0027] A1-first lens; A2-second lens; A1-third lens; B1-fourth lens; B2-fifth lens; B3-sixth lens; C-aperture; D-filter. Specific implementation method:

[0028] In order to more clearly illustrate the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and a person of ordinary skill in the art can obtain other drawings based on these drawings without creative work.

[0029] like Figure 1 As shown, a starlight-level optical lens of the present invention comprises a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged from front to back along the incident light path of the light, wherein the first lens and the second lens are both meniscus negative lenses, the third lens is a biconvex positive lens, the first lens, the second lens and the third lens constitute a front lens group with negative optical power; the fourth lens is a biconvex positive lens, the fifth lens is a biconcave negative lens, the sixth lens is a biconvex positive lens, and the fourth lens, the fifth lens and the sixth lens constitute a rear lens group with positive optical power.

[0030] In this embodiment, the air gap between the front lens group and the rear lens group is 1.5 mm; the air gap between the first lens and the second lens is 2.2 mm, the air gap between the second lens and the third lens is 0.1 mm, the air gap between the third lens and the aperture is 1.1 mm, the air gap between the aperture and the fourth lens is 0.5 mm, the air gap between the fourth lens and the fifth lens is 0.1 mm, and the air gap between the fifth lens and the sixth lens is 0.1 mm.

[0031] In this embodiment, the concave surface of the first lens faces the aperture, and the concave surface of the second lens faces away from the aperture.

[0032] In this embodiment, a filter D is disposed on the rear side of the sixth lens.

[0033] In this embodiment, the focal length of the optical system composed of the front lens group and the rear lens group is f, and the focal lengths of the first lens, the second lens, and the third lens are f1, f2, and f3 respectively. The focal lengths of the front lens group satisfy that f1, f2, f3 and f satisfy the following ratio: -2<f1 / f<-1, -3.5<f2 / f<-2.5, 3<f3 / f<4.

[0034] In this embodiment, the focal lengths of the fourth lens, the fifth lens, and the sixth lens are f4, f5, and f6 respectively, and the focal lengths of the rear lens group satisfy the following ratio of f4, f5, and f6 to f:

[0035] 1<f4 / f<2, -1<f5 / f<-2, 1.5<f6 / f<2.5.

[0036] By reasonably distributing the focal power of the optical system formed by the present invention according to the above ratio, each lens is in a certain ratio relative to the focal length of the system, so that the aberration of the optical system formed by the present invention in the wavelength range of 420 to 850 nm can be reasonably corrected and balanced.

[0037] In this embodiment, the first lens satisfies the relationship: N d ≥1.5, V d ≥50; the second lens satisfies the relationship: N d ≥1.5, V d ≥50; the third lens satisfies the relationship: N d ≥1.6, V d ≤35; the fourth lens satisfies the relationship: N d ≥1.5, V d ≥50; the fifth lens satisfies the relationship: N d ≥1.6, V d ≤35; the sixth lens satisfies the relationship: N d ≤1.5, V d ≥65; where N d is the refractive index, V d is the Abbe constant.

[0038] In this embodiment, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all aspherical lenses made of plastic; the sixth lens is a spherical lens made of glass.

[0039] In this embodiment, the curvature radius R, thickness d, and refractive index N of each lens of the optical lens are d and the Abbe number V d As shown in Table 1.

[0040]

[0041] Table 1, specific lens parameters

[0042] This embodiment uses six lenses as an example, and through the reasonable allocation of the focal length, surface shape, center thickness of each lens, and the on-axis spacing between lenses, etc., the lens has small distortion and high illumination; at the same time, various aberrations are corrected to improve the resolution and imaging quality of the lens. The surface shape Z of each aspherical surface is defined by the following formula:

[0043]

[0044] Wherein, Z is the height of the aspheric surface from the vertex of the aspheric surface when the aspheric surface is at a height of h along the optical axis; c is the paraxial curvature of the aspheric surface, c=1 / R (i.e., the paraxial curvature c is the reciprocal of the curvature radius R in Table 1 above); k is the cone constant; A, B, C, D, and E are all high-order coefficients. Table 2 shows the cone constant k and high-order coefficients A, B, C, D, and E that can be used for the surfaces of each aspheric lens in this embodiment.

[0045]

[0046] Table 2, parameters of various aspherical lenses

[0047] In this embodiment, the technical indicators achieved by this optical system are as follows:

[0048] (1) Focal length: EFFL = 3.6 mm; (2) Aperture F = 1.6; (3) Field of view: 2w ≥ 120°; (4) Optical distortion: <-41%; (5) Imaging circle diameter greater than φ8; (6) Working band: 420-650 nm & 850 nm; (7) Total optical length TTL ≤ 22.5 mm, optical back focus BFL ≥ 7.3 mm; (8) This lens is suitable for 4-megapixel CCD or CMOS cameras.

[0049] In this embodiment, a typical front negative and rear positive structure is adopted, and the negative optical power of the front lens corrects the positive optical power aberration of the rear lens. Five aspherical lenses correct all high-order aberrations and spherical aberrations, and through reasonable refractive index and optical power ratio distribution, the light incident angle of the lens of the front lens and the lens of the rear lens is limited. A smaller light incident angle can effectively reduce the image curvature of the optical system.

[0050] In this embodiment, in the front lens group, the first lens A1 has a large refractive index and focal length, ensuring that the system can collect light within a large field of view; the second lens A2 adopts an aspherical lens, and by selecting a suitable surface shape, the astigmatism of the optical system is effectively corrected. In the rear lens group, the fifth lens B2 with a medium refractive index and ultra-high dispersion complements the sixth lens B3 with a medium refractive index and ultra-low dispersion, effectively correcting the chromatic aberration and astigmatism of the imaging system. At the same time, the sixth lens B3 has a negative refractive index temperature coefficient, providing the function of compensating the high and low temperature characteristics of the system.

[0051] Through the optical system composed of the above lenses, the total length of the optical path is short, the size of the lens is small, and the back focus is large. The wavelength cut-off filter can be added to enhance the day and night confocal function; at the same time, the system aperture is large, which meets the application scenarios of starlight lenses; among them, the first lens A1, the second lens A2, the third lens A3, the fourth lens B1, and the fifth lens B2 are plastic aspheric lenses with good image quality, low cost, high overall reliability of the lens group, and excellent cost performance.

[0052] Depend on Figure 2 It can be seen that the optical system has good MTF performance in the visible light band. At a spatial frequency of 120pl / mm, its MTF value is greater than 0.6, and at a spatial frequency of 60pl / mm, its MTF value is greater than 0.8, which can meet the resolution requirements of 4 million high-definition. Figure 3 It can be seen that the optical system also exhibits good resolution in the 850nm band. At a spatial frequency of 120pl / mm, its MTF value is greater than 0.35, and at a spatial frequency of 60pl / mm, its MTF value is greater than 0.7. Therefore, the optical system has good day and night confocal characteristics.

[0053] Figure 3 and Figure 4 The MTF defocus curves of the optical system at -40℃ and +85℃ are shown in the figure. It can be seen from the figure that the defocus of the central field of view of the optical system is -4μm at -40℃, and the defocus of the central field of view is 2μm at 85℃. It has very good high and low temperature characteristics, and the image quality performance fully meets the use requirements of automotive lenses in high and low temperature environments.

[0054] Another technical solution adopted by the present invention is: an imaging method of a starlight-level optical lens. During imaging, the light path sequentially enters a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens to perform imaging.

[0055] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A starlight-level optical lens, characterized in that: The lens comprises a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged from front to back along the incident light path of the light, wherein the first lens and the second lens are both meniscus negative lenses, the third lens is a biconvex positive lens, and the first lens, the second lens and the third lens constitute a front lens group with negative optical power; the fourth lens is a biconvex positive lens, the fifth lens is a biconcave negative lens, the sixth lens is a biconvex positive lens, and the fourth lens, the fifth lens and the sixth lens constitute a rear lens group with positive optical power; The air gap between the front lens group and the rear lens group is 1.5 mm; The air gap between the first lens and the second lens is 2.2 mm, the air gap between the second lens and the third lens is 0.1 mm, the air gap between the third lens and the aperture is 1.1 mm, the air gap between the aperture and the fourth lens is 0.5 mm, the air gap between the fourth lens and the fifth lens is 0.1 mm, and the air gap between the fifth lens and the sixth lens is 0.1 mm; The focal length of the optical system composed of the front lens group and the rear lens group is f, the focal lengths of the first lens, the second lens, and the third lens are f1, f2, and f3 respectively, and the focal lengths of the front lens group satisfy the following ratios of f1, f2, and f3 to f: -2<f1 / f<-1, -3.5<f2 / f<-2.5, 3<f3 / f<4; The focal lengths of the fourth lens, the fifth lens, and the sixth lens are f4, f5, and f6 respectively, and the focal lengths of the rear lens group satisfy the following ratios of f4, f5, and f: 1<f4 / f<2, -1<f5 / f<-2, 1.5<f6 / f<2.5; The first lens satisfies the relationship: N d ≥1.5, V d ≥50; the second lens satisfies the relationship: N d ≥1.5, V d ≥50; the third lens satisfies the relationship: N d ≥1.6, V d ≤35; the fourth lens satisfies the relationship: N d ≥1.5, V d ≥50; the fifth lens satisfies the relationship: N d ≥1.6, V d ≤35; the sixth lens satisfies the relationship: N d ≤1.5, V d ≥65; where N d is the refractive index, V d is the Abbe constant; The first lens, the second lens, the third lens, the fourth lens and the fifth lens are all aspherical lenses made of plastic; the sixth lens is a spherical lens made of glass.

2. A starlight-level optical lens according to claim 1, characterized in that: The concave surface of the first lens faces the aperture, and the concave surface of the second lens faces away from the aperture.

3. An imaging method of a starlight-level optical lens, characterized in that: The invention comprises adopting the starlight optical lens as claimed in any one of claims 1 to 2. When imaging, the light path sequentially enters the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens to perform imaging.

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