Large-view-field and large-aperture lens system for color low-illumination imaging

Abstract

The invention discloses a large-view-field large-aperture lens system for color low-illumination imaging. A meniscus first lens, a meniscus second lens, a biconvex spherical third lens, a diaphragm, a biconvex spherical fourth lens, a biconvex spherical fifth lens, a biconcave spherical sixth lens and an aspheric seventh lens are sequentially arranged from an object plane to an image plane; according to the scheme, optical parameters of all the lenses are reasonably set and used in cooperation, aberration can be corrected, meanwhile, positive focal power is matched, the structure is simple, the light path is reasonable, the problems that an existing large-view-field lens is small in aperture and insufficient in definition are solved, and the color low-illumination imaging function can be achieved by matching an image sensor with the large pixel size.

Description

Technical Field

[0001] The invention belongs to the field of optics, and in particular relates to a large-field-of-view and large-aperture lens system for color low-illumination imaging. Background Art

[0002] With the rapid development of aerospace technology, pilots have put forward higher requirements for the performance and functions of airborne cameras. In order to monitor the external environment data under low illumination in real time, so that pilots can make correct judgments and ensure flight safety, new airborne cameras need to be equipped with optical systems with large field of view and large aperture.

[0003] In order to meet the needs of low-light imaging, airborne cameras often use image sensors with larger pixel sizes and are equipped with optical lenses with large apertures to ensure that the image sensors can collect sufficient light signals under low illumination. Large-field-of-view lenses with large apertures have strong low-light light-gathering capabilities, but they are difficult to design, especially optical lenses that match large-target image sensors. They require a combination of more spherical lenses and aspherical lenses to correct aberrations, which is not conducive to the lightweight and miniaturization of lenses. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide a large-field-of-view and large-aperture lens system for color low-light imaging, which adopts a combination of spherical and aspherical lenses to simplify the optical path design.

[0005] The specific technical solution for achieving the purpose of the present invention is:

[0006] A large-viewing-field and large-aperture lens system for color low-light imaging, comprising a first curved moon lens, a second curved moon lens, a third biconvex spherical lens, an aperture, a fourth biconvex spherical lens, a fifth biconvex spherical lens, a sixth biconcave spherical lens, and a seventh aspherical lens;

[0007] The first meniscus moon lens, the second meniscus moon lens, the third biconvex spherical lens, the aperture, the fourth biconvex spherical lens, the fifth biconvex spherical lens, the sixth biconcave spherical lens and the seventh aspherical lens are arranged in sequence from the object plane to the image plane;

[0008] Wherein, the first lens of the curved moon surface has negative optical power, with its convex surface facing the object surface and its concave surface facing the image surface;

[0009] The second lens of the meniscus moon has negative optical power, with its concave surface facing the object surface and its convex surface facing the image surface;

[0010] The biconvex spherical third lens has positive optical power; the biconvex spherical fourth lens has positive optical power; the biconvex spherical fifth lens has positive optical power; the biconcave spherical sixth lens has negative optical power;

[0011] The aspherical seventh lens has positive refractive power, a convex surface of which faces the object plane, and a concave surface of which faces the image plane.

[0012] Further, the center thickness of the first meniscus moon lens is LT1, the air interval between the first meniscus moon lens and the second meniscus moon lens is AT12, the center thickness of the second meniscus moon lens is LT2, the air interval between the second meniscus moon lens and the third biconvex spherical lens is AT23, the center thickness of the third biconvex spherical lens is LT3, the air interval between the third biconvex spherical lens and the fourth biconvex spherical lens is AT34, the center thickness of the fourth biconvex spherical lens is LT4, the air interval between the fourth biconvex spherical lens and the fifth biconvex spherical lens is AT45, the center thickness of the fifth biconvex spherical lens is LT5, the center thickness of the sixth biconcave spherical lens is LT6, and the air interval between the sixth biconcave spherical lens and the aspherical seventh lens is AT67;

[0013] The relationship between the center thickness of each lens and the air space between lenses satisfies:

[0014] 0.65<(LT1+LT2) / AT12<0.75;

[0015] 8.45<(LT2+LT3) / AT23<8.60;

[0016] 2.15<(LT3+LT4) / AT34<2.35;

[0017] 6.65<(LT4+LT5+LT6) / AT45<6.85;

[0018] 3.10<(LT5+LT6+LT7) / AT67<3.20;

[0019] Used to control the overall optical length of the lens system.

[0020] Further, the total focal length of the lens system is f, the focal length of the first meniscus lens is f1, the focal length of the second meniscus lens is f2, the focal length of the third biconvex spherical lens is f3, the focal length of the fourth biconvex spherical lens is f4, the focal length of the fifth biconvex spherical lens is f5, the focal length of the sixth biconcave spherical lens is f6, and the focal length of the aspherical seventh lens is f7. The focal lengths of the lenses are set to satisfy the following formula for correcting phase aberration:

[0021] 1.5<f1 / f<1.7;

[0022] 5.5<f2 / f<5.7;

[0023] 3.2<f3 / f<3.4;

[0024] 3.7<f4 / f<3.9;

[0025] 2.2<f5 / f<2.4;

[0026] 1.8<f6 / f<2.0;

[0027] 4.0<f7 / f<4.2.

[0028] Further, the refractive index of the first meniscus moon lens is n1, the refractive index of the second meniscus moon lens is n2, the refractive index of the third biconvex spherical lens is n3, the refractive index of the fourth biconvex spherical lens is n4, the refractive index of the fifth biconvex spherical lens is n5, the refractive index of the sixth biconcave spherical lens is n6, and the refractive index of the seventh aspherical lens is n7, wherein:

[0029] 1.80<n1<1.90;

[0030] 1.70<n2<1.80;

[0031] 1.80<n3<1.95;

[0032] 1.40<n4<1.50;

[0033] 1.45<n5<1.55;

[0034] 1.70<n6<1.80;

[0035] 1.50<n7<1.60.

[0036] Further, the Abbe number of the first meniscus moon lens is Vd1, the Abbe number of the second meniscus moon lens is Vd2, the Abbe number of the third biconvex spherical lens is Vd3, the Abbe number of the fourth biconvex spherical lens is Vd4, the Abbe number of the fifth biconvex spherical lens is Vd5, the Abbe number of the sixth biconcave spherical lens is Vd6, and the Abbe number of the seventh aspherical lens is Vd7. The Abbe number of each lens satisfies the following formula to achieve system chromatic aberration correction:

[0037] 39<Vd1<41;

[0038] 48<Vd2<50;

[0039] 39<Vd3<41;

[0040] 93<Vd4<95;

[0041] 80<Vd5<82;

[0042] 21<Vd6<23;

[0043] 62<Vd7<64.

[0044] Furthermore, a filter is arranged between the aspherical seventh lens and the image plane to filter out near-infrared light.

[0045] Furthermore, the biconvex spherical fifth lens and the biconcave spherical sixth lens are fixed by gluing to form a cemented lens.

[0046] Furthermore, the aspheric surface shape of the aspheric seventh lens satisfies the following formula:

[0047]

[0048] Among them, c is the curvature corresponding to the radius of the aspherical seventh lens, y is the radial coordinate of the aspherical seventh lens, the unit of the radial coordinate is the same as the unit of the lens length, k is the coefficient of the conic quadratic curve, Z is the vector height of the aspherical seventh lens, and a2 to a8 respectively represent the coefficients corresponding to each radial coordinate.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The solution of the present invention corrects aberrations by matching 6 glass spherical lenses and 1 glass aspherical lens, and at the same time, the positive optical power is matched, the structure is simple, and the optical path is reasonable. It solves the problems of small aperture and insufficient clarity of existing large-field-of-view lenses, and can achieve color low-light imaging function by matching an image sensor with a large pixel size.

[0051] The present invention is further described below in conjunction with specific implementation modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of the optical path structure of a large-field-of-view and large-aperture lens system for color low-light imaging in an embodiment of the present invention.

[0053] Figure 2 It is the function value of MTF of the large-field-of-view and large-aperture lens system for color low-illumination imaging under visible light in the embodiment of the present invention.

[0054] Figure 3 This is a point arrangement diagram of the large-field-of-view and large-aperture lens system for color low-illumination imaging in the present invention under visible light.

[0055] Figure 4 This is a field curvature distortion diagram of the large-field-of-view and large-aperture lens system for color low-illumination imaging in the present invention under visible light.

[0056] Figure 5 This is a relative illumination diagram of the large-field-of-view and large-aperture lens system for color low-light imaging in the present invention. DETAILED DESCRIPTION

[0057] In order to clearly describe the technical solution and the effects achieved by the present invention, the technical solution of the present invention is clearly explained below in combination with the accompanying drawings and specific embodiments of the present invention, so that technical personnel in the field can implement the invention without performing creative work. The structure shown in the accompanying drawings is not the entire actual structure but only a part of the actual structure. It should be noted that all other embodiments made by ordinary technical personnel in the field on the basis of the embodiments of the present invention without performing creative work should fall within the protection scope of the present invention.

[0058] The following examples are only for better explanation of the present invention, but the content of the present invention is not limited to the application in the examples. Therefore, those skilled in the art can make non-essential modifications to the implementation scheme based on the above invention content and apply it to other embodiments, which is still within the protection scope of the present invention. In addition, the experimental methods without specific conditions in the following examples should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the expressions in the text are not specially explained, they are only used for distinction and have no other meanings.

[0059] Example

[0060] Combination Figure 1 , a large-field-of-view and large-aperture lens system for color low-light imaging, comprising a first curved moon lens 1, a second curved moon lens 2, a biconvex spherical third lens 3, an aperture, a biconvex spherical fourth lens 4, a biconvex spherical fifth lens 5, a biconcave spherical sixth lens 6 and an aspherical seventh lens 7;

[0061] The first meniscus lens 1, the second meniscus lens 2, the biconvex spherical third lens 3, the aperture, the biconvex spherical fourth lens 4, the biconvex spherical fifth lens 5, the biconcave spherical sixth lens 6 and the aspherical seventh lens 7 are arranged in sequence from the object plane to the image plane;

[0062] Wherein, the first curved moon lens 1 has negative optical power, with its convex surface facing the object surface and its concave surface facing the image surface;

[0063] The second lens 2 of the curved moon surface has negative optical power, with its concave surface facing the object surface and its convex surface facing the image surface;

[0064] The biconvex spherical third lens 3 has positive focal power; the biconvex spherical fourth lens 4 has positive focal power; the biconvex spherical fifth lens 5 has positive focal power; the biconcave spherical sixth lens 6 has negative focal power;

[0065] The aspherical seventh lens 7 has positive refractive power, with a convex surface facing the object plane and a concave surface facing the image plane.

[0066] The optical specifications of the entire large-field-of-view and large-aperture lens system in this embodiment are as follows:

[0067] (1) Working band: 400nm~700nm;

[0068] (2) Aperture value Fno: Fno ≤ 1.5;

[0069] (3) Field of view 2ω: 0°≤2ω≤140°;

[0070] (4) Total length TTL and image plane height h: 2.5<TTL / h<3.2;

[0071] (5) Lens aperture D: D ≤ 29.7 mm;

[0072] (6) Matching sensor pixel size: 12μm.

[0073] More specifically, the center thickness of the first meniscus moon lens 1 is LT1, the air interval between the first meniscus moon lens 1 and the second meniscus moon lens 2 is AT12, the center thickness of the second meniscus moon lens 2 is LT2, the air interval between the second meniscus moon lens 2 and the biconvex spherical third lens 3 is AT23, the center thickness of the biconvex spherical third lens 3 is LT3, the air interval between the biconvex spherical third lens 3 and the biconvex spherical fourth lens 4 is AT34, the center thickness of the biconvex spherical fourth lens 4 is LT4, the air interval between the biconvex spherical fourth lens 4 and the biconvex spherical fifth lens 5 is AT45, the center thickness of the biconvex spherical fifth lens 5 is LT5, the center thickness of the biconcave spherical sixth lens 6 is LT6, and the air interval between the biconcave spherical sixth lens 6 and the aspherical seventh lens 7 is AT67;

[0074] The relationship between the center thickness of each lens and the air space between lenses satisfies:

[0075] 0.65<(LT1+LT2) / AT12<0.75;

[0076] 8.45<(LT2+LT3) / AT23<8.60;

[0077] 2.15<(LT3+LT4) / AT34<2.35;

[0078] 6.65<(LT4+LT5+LT6) / AT45<6.85;

[0079] 3.10<(LT5+LT6+LT7) / AT67<3.20;

[0080] Used to control the overall optical length of the lens system.

[0081] In this embodiment, the air gap between the first meniscus lens 1 and the second meniscus lens 2 is 11.56 mm, the air gap between the second meniscus lens 2 and the biconvex spherical third lens 3 is 1.99 mm, the air gap between the biconvex spherical third lens 3 and the aperture is 6.22 mm, the air gap between the aperture and the biconvex spherical fourth lens 4 is 1.20 mm, the air gap between the biconvex spherical fourth lens 4, the biconvex spherical fifth lens 5 and the biconcave spherical sixth lens 6, the air gap between the cemented lens formed by the biconvex spherical fifth lens 5 and the biconcave spherical sixth lens 6 and the aspherical seventh lens 7 is 5.00 mm, the distance between the aspherical seventh lens 7 and the imaging surface is 11.40 mm, and the relationship between the center thickness and the air gap satisfies the above formula. Within this range, the total optical length can be effectively controlled.

[0082] The total focal length of the lens system is f, the focal length of the first meniscus lens 1 is f1, the focal length of the second meniscus lens 2 is f2, the focal length of the biconvex spherical third lens 3 is f3, the focal length of the biconvex spherical fourth lens 4 is f4, the focal length of the biconvex spherical fifth lens 5 is f5, the focal length of the biconcave spherical sixth lens 6 is f6, and the focal length of the aspherical seventh lens 7 is f7. The focal lengths of the various lenses are set to satisfy the following formula. Within this range, the focal lengths of the various lenses can be reasonably controlled, so that the single lens and double cemented lens in the system can achieve the purpose of effectively correcting aberrations:

[0083] 1.5<f1 / f<1.7;

[0084] 5.5<f2 / f<5.7;

[0085] 3.2<f3 / f<3.4;

[0086] 3.7<f4 / f<3.9;

[0087] 2.2<f5 / f<2.4;

[0088] 1.8<f6 / f<2.0;

[0089] 4.0<f7 / f<4.2.

[0090] The refractive index of the first meniscus lens 1 is n1, the refractive index of the second meniscus lens 2 is n2, the refractive index of the biconvex spherical third lens 3 is n3, the refractive index of the biconvex spherical fourth lens 4 is n4, the refractive index of the biconvex spherical fifth lens 5 is n5, the refractive index of the biconcave spherical sixth lens 6 is n6, and the refractive index of the aspherical seventh lens 7 is n7, wherein:

[0091] 1.80<n1<1.90;

[0092] 1.70<n2<1.80;

[0093] 1.80<n3<1.95;

[0094] 1.40<n4<1.50;

[0095] 1.45<n5<1.55;

[0096] 1.70<n6<1.80;

[0097] 1.50<n7<1.60.

[0098] The Abbe number of the first meniscus lens 1 is Vd1, the Abbe number of the second meniscus lens 2 is Vd2, the Abbe number of the biconvex spherical third lens 3 is Vd3, the Abbe number of the biconvex spherical fourth lens 4 is Vd4, the Abbe number of the biconvex spherical fifth lens 5 is Vd5, the Abbe number of the biconcave spherical sixth lens 6 is Vd6, and the Abbe number of the aspherical seventh lens 7 is Vd7. The Abbe number of each lens satisfies the following formula to achieve system chromatic aberration correction:

[0099] 39<Vd1<41;

[0100] 48<Vd2<50;

[0101] 39<Vd3<41;

[0102] 93<Vd4<95;

[0103] 80<Vd5<82;

[0104] 21<Vd6<23;

[0105] 62<Vd7<64.

[0106] A filter is arranged between the aspherical seventh lens 7 and the image plane to filter out near-infrared light.

[0107] Furthermore, the biconvex spherical fifth lens 5 and the biconcave spherical sixth lens 6 are fixed by gluing to form a glued lens.

[0108] The aspheric surface shape of the aspheric seventh lens 7 satisfies the following formula:

[0109]

[0110] Wherein, c is the curvature corresponding to the radius of the aspherical seventh lens 7, y is the radial coordinate of the aspherical seventh lens 7, the unit of the radial coordinate is the same as the unit of the lens length, k is the conic quadratic coefficient, Z is the vector height of the aspherical seventh lens 7, and a2 to a8 represent the coefficients corresponding to each radial coordinate respectively;

[0111] When k < -1, the surface curve of the lens is a hyperbola;

[0112] When k = -1, the surface curve of the lens is a parabola;

[0113] When -1<k<0, the surface curve of the lens is an ellipse;

[0114] When k = 0, the surface curve of the lens is circular;

[0115] When k>0, the surface curve of the lens is an oblate circle;

[0116] The parameters of each lens in this embodiment are shown in Table 1:

[0117] Table 1 Lens parameters

[0118]

[0119] The aspheric coefficient table is shown in Table 2:

[0120] Table 2 Aspheric coefficient table

[0121]

[0122]

[0123] By adopting the above technical solutions, Figure 2 to Figure 5 The function value of MTF, point diagram, field curvature distortion diagram and relative illumination diagram of the optical system under visible light are given respectively. Due to the use of glass aspherical lenses, the optical system has good resolution at a frequency of 41.6lp / mm. The RMS radius of the edge point diagram of the optical system is controlled at about 12μm, ensuring a good imaging granularity. The field curvature of the optical system is controlled within 0.2mm, and the distortion is controlled within -59%, which comprehensively balances the aberration and distortion indicators of the large field of view lens. The relative illumination of the edge field of view of the optical system is greater than 60%, ensuring the brightness uniformity of the imaging surface.

[0124] This solution provides a large-field-of-view, large-aperture lens for low-light imaging. It corrects aberrations by matching 6 glass spherical lenses and 1 glass aspherical lens. At the same time, it has positive optical power matching, simple structure, reasonable optical path, and an ultra-large aperture of 1.4. By matching an image sensor with a large pixel size of 12μm, it can achieve color low-light imaging function.

[0125] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A large-field-of-view and large-aperture lens system for color low-light imaging, characterized in that: It includes a first lens with a curved moon surface, a second lens with a curved moon surface, a third lens with a biconvex spherical surface, an aperture, a fourth lens with a biconvex spherical surface, a fifth lens with a biconvex spherical surface, a sixth lens with a biconcave spherical surface, and a seventh lens with an aspherical surface; The first meniscus moon lens, the second meniscus moon lens, the third biconvex spherical lens, the aperture, the fourth biconvex spherical lens, the fifth biconvex spherical lens, the sixth biconcave spherical lens and the seventh aspherical lens are arranged in sequence from the object plane to the image plane; Wherein, the first lens of the curved moon surface has negative optical power, with its convex surface facing the object surface and its concave surface facing the image surface; The second lens of the meniscus moon has negative optical power, with its concave surface facing the object surface and its convex surface facing the image surface; The biconvex spherical third lens has positive optical power; the biconvex spherical fourth lens has positive optical power; the biconvex spherical fifth lens has positive optical power; the biconcave spherical sixth lens has negative optical power; The aspherical seventh lens has positive refractive power, a convex surface of which faces the object plane, and a concave surface of which faces the image plane.

2. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: The center thickness of the first meniscus moon lens is LT1, the air interval between the first meniscus moon lens and the second meniscus moon lens is AT12, the center thickness of the second meniscus moon lens is LT2, the air interval between the second meniscus moon lens and the third biconvex spherical lens is AT23, the center thickness of the third biconvex spherical lens is LT3, the air interval between the third biconvex spherical lens and the fourth biconvex spherical lens is AT34, the center thickness of the fourth biconvex spherical lens is LT4, the air interval between the fourth biconvex spherical lens and the fifth biconvex spherical lens is AT45, the center thickness of the fifth biconvex spherical lens is LT5, the center thickness of the sixth biconcave spherical lens is LT6, and the air interval between the sixth biconcave spherical lens and the aspherical seventh lens is AT67; The relationship between the center thickness of each lens and the air space between lenses satisfies: 0.65<(LT1+LT2) / AT12<0.75; 8.45<(LT2+LT3) / AT23<8.60; 2.15<(LT3+LT4) / AT34<2.35; 6.65<(LT4+LT5+LT6) / AT45<6.85; 3.10<(LT5+LT6+LT7) / AT67<3.20; Used to control the overall optical length of the lens system.

3. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: The total focal length of the lens system is f, the focal length of the first meniscus lens is f1, the focal length of the second meniscus lens is f2, the focal length of the third biconvex spherical lens is f3, the focal length of the fourth biconvex spherical lens is f4, the focal length of the fifth biconvex spherical lens is f5, the focal length of the sixth biconcave spherical lens is f6, and the focal length of the seventh aspherical lens is f7. The focal lengths of the lenses are set to satisfy the following formula for correcting phase aberration: 1.5<f1 / f<1.7; 5.5<f2 / f<5.7; 3.2<f3 / f<3.4; 3.7<f4 / f<3.9; 2.2<f5 / f<2.4; 1.8<f6 / f<2.0; 4.0<f7 / f<4.

2.

4. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: The refractive index of the first meniscus moon lens is n1, the refractive index of the second meniscus moon lens is n2, the refractive index of the third biconvex spherical lens is n3, the refractive index of the fourth biconvex spherical lens is n4, the refractive index of the fifth biconvex spherical lens is n5, the refractive index of the sixth biconcave spherical lens is n6, and the refractive index of the seventh aspherical lens is n7, wherein: 1.80＜n1＜1.90； 1.70＜n2＜1.80； 1.80＜n3＜1.95； 1.40＜n4＜1.50； 1.45＜n5＜1.55； 1.70＜n6＜1.80； 1.50＜n7＜1.60。 5. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: The Abbe number of the first meniscus lens is Vd1, the Abbe number of the second meniscus lens is Vd2, the Abbe number of the third biconvex spherical lens is Vd3, the Abbe number of the fourth biconvex spherical lens is Vd4, the Abbe number of the fifth biconvex spherical lens is Vd5, the Abbe number of the sixth biconcave spherical lens is Vd6, and the Abbe number of the seventh aspherical lens is Vd7. The Abbe number of each lens satisfies the following formula to achieve system chromatic aberration correction: 39<Vd1<41; 48<Vd2<50; 39<Vd3<41; 93<Vd4<95; 80<Vd5<82; 21<Vd6<23; 62<Vd7<64.

6. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: A filter is arranged between the aspherical seventh lens and the image plane to filter out near-infrared light.

7. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: The biconvex spherical fifth lens and the biconcave spherical sixth lens are fixed by gluing to form a glued lens.

8. The large-field-of-view and large-aperture lens system for color low-light imaging according to claim 1, characterized in that: The aspheric surface shape of the aspheric seventh lens satisfies the following formula: Among them, c is the curvature corresponding to the radius of the aspherical seventh lens, y is the radial coordinate of the aspherical seventh lens, the unit of the radial coordinate is the same as the unit of the lens length, k is the coefficient of the conic quadratic curve, Z is the vector height of the aspherical seventh lens, and a2 to a8 respectively represent the coefficients corresponding to each radial coordinate.

Images