Optical system

Abstract

The invention relates to an optical system, which comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens in sequence from an object side to an image side along an optical axis, the convex surface of the first lens faces the object side; the convex surface of the second lens faces the object side, and the second lens has negative focal power; the concave surface of the third lens faces the object side, and the third lens has positive focal power; the convex surface of the fourth lens faces the object side, and the fourth lens has negative focal power; the convex surface of the fifth lens faces the object side, and the fifth lens has positive focal power; the concave surface of the sixth lens faces the object side, and the sixth lens has negative focal power; the convex surface of the seventh lens faces the object side, and the seventh lens has positive focal power; wherein the sixth lens and the seventh lens can move at the same time or only the seventh lens moves to realize re-scanning. The large-field-of-view infrared fisheye lens meets the requirements of the large-field-of-view infrared fisheye lens for full-field-of-view relative aperture consistency and good relative illumination uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal infrared large field-of-view staring imaging, and in particular to an optical system. Background Art

[0002] Since the last century, with the development needs of infrared monitoring applications, the thermal infrared large field-of-view staring imaging technology has emerged. Compared with other infrared staring imaging technologies such as small field-of-view rotation, scanning, and multi-sensor mosaicking, it has the advantages of small volume, good real-time performance, and large single-machine space coverage rate, and is widely used in fields such as astronomical observation, large field-of-view early warning, laser detection, and stereo vision.

[0003] The fish-eye lens is a widely used lens in the large field-of-view staring imaging technology. It is an optical system evolved from a retrofocus type structure, and the full field-of-view angle can reach 180° or even larger. Its structure usually uses a meniscus negative lens as the front group of the optical system to compress the incident light beam of the ultra-large object space field-of-view, and then the light beam is converged onto the image plane by the rear group of the optical system.

[0004] The basic problem of this kind of lens lies in the huge offset of the aperture relative to the light rays at a large field-of-view angle, that is, for the light rays of a large field-of-view, the aperture of the system is completely tilted. First, this will cause the entrance pupil of the lens to be compressed, thus limiting the incident light flux of the light rays of the large field-of-view. As the incident angle of the image plane increases, the relative illuminance of the edge field-of-view will also become worse. In addition, this structure no longer follows the design idea of paraxial approximation, and the focusing positions of the light beam in the meridional plane and the sagittal plane are inconsistent, and the wavefront seriously deviates from the spherical surface.

[0005] To solve the problems of the relative aperture of the system being compressed in the large field-of-view and the relative illuminance of the edge field-of-view being reduced, the structure of this patent adopts an image-space telecentric optical path to optimize the relative illuminance problem. Rescanning means that the system uses a piezoelectric ceramic to scan a pixel distance on the image plane to improve the resolution of infrared target detection. However, the telecentric structure will increase the overall design difficulty of the system, and the sensitivity of the fish-eye lens to tolerances (especially the eccentricity of components) is enhanced, making it difficult to implement the function of the lateral micro-moving component for rescanning.

[0006] Most of the infrared fish-eye lenses reported in the existing literature do not adopt a telecentric structure. Existing patents such as Chinese Invention Patent (CN106547074A), Chinese Invention Patent (CN117741927A), etc. also do not adopt a telecentric structure. The minimum value of its relative illuminance is 0.82, and due to the large number of aspherical surfaces, the lens has high requirements for tolerances and it is difficult to achieve the function of rescanning.

[0007] In addition, a Chinese utility model patent (CN218675475U) proposes an approximate telecentric structure design, but it uses a binary diffractive surface, and the field of view is 100°, leaving room for further optimization. The National Institute for Astrophysics in Italy designed an 180° fisheye lens for detecting the comet's tail, with an F-number of 3 for the system, and its F-θ distortion is less than 0.5%. Although this system adopts a telecentric structure, its F-number is small and it is easy to implement. Zhang Jiyan et al. from Xiamen University of Technology proposed a design method for a long-wave infrared fisheye staring optical system. It has a large number of aspherical surfaces, a large angle of light refraction by the optical lens, and very strict tolerances, which will bring great difficulties to the processing and alignment of the lens and is also difficult to achieve the function of rescan to improve the resolution.

[0008] Therefore, there is an urgent need to propose a telecentric fisheye lens design with a compact structure and insensitive tolerances to meet the requirements of good consistency of the relative aperture of the system's full field of view and strong uniformity of the relative illuminance of the system. Summary of the Invention

[0009] In view of the deficiencies of the prior art, the present invention discloses an optical system.

[0010] The technical solution adopted by the present invention is as follows:

[0011] An optical system includes, in order from the object side to the image side along the optical axis: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens;

[0012] The convex surface of the first lens faces the object side;

[0013] The convex surface of the second lens faces the object side, and the second lens has a negative optical power;

[0014] The concave surface of the third lens faces the object side, and the third lens has a positive optical power;

[0015] The convex surface of the fourth lens faces the object side, and the fourth lens has a negative optical power;

[0016] The convex surface of the fifth lens faces the object side, and the fifth lens has a positive optical power;

[0017] The concave surface of the sixth lens faces the object side, and the sixth lens has a negative optical power;

[0018] The convex surface of the seventh lens faces the object side, and the seventh lens has a positive optical power;

[0019] Wherein, the sixth lens and the seventh lens can move simultaneously or only the seventh lens moves to achieve rescan.

[0020] In one embodiment of the present invention, the first lens is a hemispherical meniscus lens.

[0021] In one embodiment of the present invention, the fourth lens is an aspherical lens; the aspherical surface of the fourth lens satisfies the following even-order aspherical equation:

[0022]

[0023] where: Z lens4 is the sagitta of the aspherical surface of the fourth lens along the optical axis of the optical system at a position with a height of r, which is the distance from the vertex of the aspherical surface of the fourth lens; c is the curvature of the aspherical surface of the fourth lens; k is the conic coefficient; C is the high-order aspherical coefficient.

[0024] In one embodiment of the present invention, the seventh lens is an aspherical lens; the aspherical surface of the seventh lens satisfies the following even-order aspherical equation:

[0025]

[0026] where: Z lens7 is the sagitta of the aspherical surface of the seventh lens 8 along the optical axis of the optical system at a position with a height of r, which is the distance from the vertex of the aspherical surface of the seventh lens 8; c is the curvature of the aspherical surface of the seventh lens 8; k is the conic coefficient; B is the high-order aspherical coefficient.

[0027] In one embodiment of the present invention, the first lens satisfies: -0.6 ≤ φ1 / φ ≤ -0.4;

[0028] The second lens satisfies: -0.6 ≤ φ2 / φ ≤ -0.4;

[0029] The third lens satisfies: 0.02 ≤ φ3 / φ ≤ 0.03;

[0030] The fourth lens satisfies: -0.3 ≤ φ4 / φ ≤ -0.1;

[0031] The fifth lens satisfies: 1.1 ≤ φ5 / φ ≤ 1.3;

[0032] The sixth lens satisfies: -0.2 ≤ φ6 / φ ≤ -0.19;

[0033] The seventh lens satisfies: 1 ≤ φ7 / φ ≤ 1.1;

[0034] where: φ is the optical power of the optical system; φ1 is the optical power of the first lens; φ2 is the optical power of the second lens; φ3 is the optical power of the third lens; φ4 is the optical power of the fourth lens; φ5 is the optical power of the fifth lens; φ6 is the optical power of the sixth lens; φ7 is the optical power of the seventh lens.

[0035] In one embodiment of the present invention, the second lens, the third lens, the fifth lens, and the sixth lens are all spherical lenses.

[0036] In one embodiment of the present invention, it further includes a diaphragm disposed at the front surface of the fifth lens.

[0037] In one embodiment of the present invention, the operating wavelength of the optical system is 8μm - 12.5μm.

[0038] In one embodiment of the present invention, the second lens, the fourth lens, and the fifth lens are all made of single crystal germanium.

[0039] In one embodiment of the present invention, the third lens and the sixth lens are both made of zinc selenide.

[0040] The above technical solution of the present invention has the following advantages compared with the prior art:

[0041] The optical system described in the present invention meets the requirements of a large field of view infrared fish-eye lens for consistent relative aperture of the entire field of view and good relative illuminance uniformity, and is applicable to infrared staring technology application scenarios such as large field of view early warning, laser detection, and stereo vision.

[0042] The optical system described in the present invention has a high relative illuminance and a small number of aspherical surfaces, which is beneficial to reducing the tolerance sensitivity of the system, reducing the alignment difficulty, and can realize a large aperture image space telecentric optical structure with an image plane rescan function, including two aspherical germanium mirrors, three spherical germanium mirrors, and two spherical zinc selenide lenses, specifically a meniscus lens and two lens groups with "negative-positive-negative" and "positive-negative-positive" structures.

[0043] The optical system described in the present invention is beneficial to realizing the rescan function of the element micro-displacement and improving the system resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to make the content of the present invention easier to be clearly understood, the following further describes the present invention in detail according to the specific embodiments of the present invention and in conjunction with the accompanying drawings.

[0045] Figure 1 is a schematic diagram of the optical system in the present invention.

[0046] Figure 2 is a relative illuminance curve graph of each field of view of the optical system in the present invention.

[0047] Figure 3 is a transfer function curve graph of the optical system in the present invention at 0°C, 20°C, and 40°C.

[0048] Figure 4 is a spot diagram of the optical system in the present invention at 0°C, 20°C, and 40°C.

[0049] Figure 5 It is the transfer function curve of the system when the lateral micro-displacement of the sixth lens and the seventh lens in the optical system of the present invention is 15.8 μm.

[0050] Figure 6 It is the transfer function curve of the system when the lateral micro-displacement of the seventh lens in the optical system of the present invention is 11.8 μm.

[0051] Figure 7 It is the full field of view F-θ distortion curve of the optical system of the present invention.

[0052] Explanation of the reference numerals in the drawings of the specification: 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Diaphragm; 6. Fifth lens; 7. Sixth lens; 8. Seventh lens; 9. Detector window; 10. Image plane. Detailed implementation manners

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0054] Regarding the foregoing and other technical contents, features and effects of the present invention, they will be clearly presented in the following detailed description of the embodiments with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as: up, down, left, right, front or rear, etc., are only with reference to the directions in the accompanying drawings. Therefore, the directional terms used are for illustration and not for limiting the present invention. In addition, in all embodiments, the same reference numerals represent the same elements.

[0055] Referring to Figure 1 As shown, an optical system includes, in order from the object side to the image side along the optical axis 10: a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 6, a sixth lens 7, and a seventh lens 8;

[0056] The convex surface of the first lens 1 faces the object side;

[0057] The convex surface of the second lens 2 faces the object side, and the second lens 2 has a negative optical power;

[0058] The concave surface of the third lens 3 faces the object side, and the third lens 3 has a positive optical power;

[0059] The convex surface of the fourth lens 4 faces the object side, and the fourth lens 4 has a negative optical power;

[0060] The convex surface of the fifth lens 6 faces the object side, and the fifth lens 6 has a positive optical power;

[0061] The concave surface of the sixth lens 7 faces the object side, and the sixth lens 7 has a negative optical power;

[0062] The convex surface of the seventh lens 8 faces the object side, and the seventh lens 8 has a positive optical power;

[0063] Among them, the sixth lens 7 and the seventh lens 8 can move simultaneously or only the seventh lens 8 moves to achieve rescan.

[0064] This embodiment provides an optical system. Except for the first hemispherical meniscus lens, the optical system is composed of two lens groups of "negative, positive, negative" and "positive, negative, positive". The full field of view of the optical system is 180°, the F number is 1, the working wavelength is 8μm - 12.5μm, the detector pixel size is 12μm×12μm, and the detector scale is 1280×1024. This optical system meets the requirements of a large field of view infrared fisheye lens for consistent relative aperture of the full field of view and good relative illuminance uniformity, is insensitive to tolerances, and can achieve the rescan function, and is applicable to infrared staring technology application scenarios such as large field of view early warning, laser detection, and stereoscopic vision.

[0065] In this embodiment, the optical power of the first lens 1 is -0.6 to -0.4 times the optical power of the entire optical system. The optical power of the second lens 2 is -0.6 to -0.4 times the optical power of the entire optical system. The optical power of the third lens 3 is 0.02 to 0.03 times the optical power of the entire optical system. The optical power of the fourth lens 4 is -0.3 to -0.1 times the optical power of the entire optical system. The optical power of the fifth lens 6 is 1.1 to 1.3 times the optical power of the entire optical system. The optical power of the sixth lens 7 is -0.3 to -0.1 times the optical power of the entire optical system. The optical power of the seventh lens 8 is 0.9 to 1.1 times the optical power of the entire optical system.

[0066] Specifically, the S11 surface of the first lens 1 is a convex surface, and the S12 surface is an approximately hemispherical concave surface. The optical power of the first lens 1 is -0.45 times the optical power of the entire optical system.

[0067] The S21 surface of the second lens 2 is a concave surface, and the S22 surface is a convex surface. The optical power of the second lens 2 is -0.5 times the optical power of the entire optical system.

[0068] The S31 surface of the third lens 3 is a convex surface, and the S32 surface is a concave surface. The optical power of the third lens 3 is 0.03 times the optical power of the entire optical system.

[0069] The S41 surface of the fourth lens 4 is a convex surface, and the S42 surface is a concave surface. The optical power of the fourth lens 4 is -0.2 times the optical power of the entire optical system.

[0070] The S61 surface of the fifth lens 6 is a convex surface, and the S62 surface is also a convex surface. The diaphragm 5 is placed at the front surface of the fifth lens 6. The diaphragm 5 limits the light beam passing through the fifth lens 6 by its aperture size, allowing only a specific part of the light to enter the optical system. By adjusting the aperture of the diaphragm 5, the amount of light passing through the fifth lens 6 can be controlled, thereby adjusting the brightness of the imaging system. The optical power of the fifth lens 6 is 1.2 times that of the entire optical system. It can be understood that the fifth lens 6 near the diaphragm 5 is a biconvex positive lens, and the diaphragm 5 is placed between two lens groups of "negative-positive-negative" and "positive-negative-positive".

[0071] The S71 surface of the sixth lens 7 is a concave surface, and the S72 surface is also a concave surface. The optical power of the sixth lens 7 is -0.2 times that of the entire optical system.

[0072] The S81 surface of the seventh lens 8 is a convex surface, and S82 is a concave surface. The optical power of the seventh lens 8 is 1 times that of the entire optical system.

[0073] Furthermore, in the example of the present invention, the S42 surface of the fourth lens 4 and the S81 surface of the seventh lens 8 are even aspherical surfaces.

[0074] Furthermore, the above aspherical surface satisfies the following formula:

[0075]

[0076] In the formula: Z is the sagitta of the distance from the vertex of the aspherical surface when the aspherical surface is at a position with a height of r along the optical axis Z of the optical system;

[0077] c is the curvature of the aspherical surface;

[0078] k is the conic coefficient;

[0079] B and C are the coefficients of the high-order aspherical surface.

[0080] The aspherical coefficients of the two surfaces of S42 and S81 are given in Table 1 below.

[0081] Table 1

[0082] Surface k B C S42 3.12 <![CDATA[-1.23×10 -10 > S81 -3.79 <![CDATA[-1.4×10 -8 >

[0083] The optical element parameters of the above optical system can be seen in Table 2 below:

[0084] Table 2

[0085]

[0086]

[0087] As can be seen from Table 2 above, the above-mentioned second lens 2, fourth lens 4, and fifth lens 6 are all made of single-crystalline germanium, and the above-mentioned third lens 3 and sixth lens 7 are both made of zinc selenide.

[0088] In this embodiment, a detector window 9 is provided in front of the image side 10 to convert the optical signal into an electrical signal or other forms of signals for further processing and analysis.

[0089] Reference Figure 2 , the relative illumination of the entire field of view of this optical system is better than 0.91, which is better than the existing fisheye lenses.

[0090] Figure 3 The a in Figure 3 is the transfer function curve of the optical system at 0 °C, Figure 3 the b in Figure 4 is the transfer function curve of the optical system at 20 °C, Figure 4 the c in Figure 4 is the transfer function curve of the optical system at 40 °C. Reference Figure 3 and Figure 4 , this optical system can maintain good thermal stability at a temperature of 0 °C - 40 °C.

[0091] Reference Figure 5 , the F-θ distortion of this optical system is less than 10% in the entire field of view, meeting the usage requirements.

[0092] Reference Figure 6 , by jointly moving the sixth lens 7 and the seventh lens 8 laterally by 15.8 μm, the optical system realizes the function of rescaning one pixel at the image plane.

[0093] Reference Figure 7 , by moving the seventh lens 8 alone laterally by 11.8 μm, the optical system realizes the function of rescaning one pixel at the image plane.

[0094] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. An optical system, characterized in that, Including, in sequence from the object side to the image side (10) along the optical axis: a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), a fifth lens (6), a sixth lens (7), and a seventh lens (8); The convex surface of the first lens (1) faces the object side; The convex surface of the second lens (2) faces the object side, and the second lens (2) has a negative optical power; The concave surface of the third lens (3) faces the object side, and the third lens (3) has a positive optical power; The convex surface of the fourth lens (4) faces the object side, and the fourth lens (4) has a negative optical power; The convex surface of the fifth lens (6) faces the object side, and the fifth lens (6) has a positive optical power; The concave surface of the sixth lens (7) faces the object side, and the sixth lens (7) has a negative optical power; The convex surface of the seventh lens (8) faces the object side, and the seventh lens (8) has a positive optical power; Wherein, the sixth lens (7) and the seventh lens (8) can move simultaneously or only the seventh lens (8) moves to achieve rescan.

2. The optical system according to claim 1, characterized in that, The first lens (1) is a hemispherical meniscus lens.

3. The optical system according to claim 1, wherein, The fourth lens (4) is an aspherical lens; the aspherical surface of the fourth lens (4) satisfies the following even-order aspherical equation: Where: Z lens4 is the sagitta, which is the distance from the vertex of the aspherical surface of the fourth lens (4) to the aspherical surface of the fourth lens (4) when the height is r along the optical axis of the optical system; c is the aspherical curvature of the fourth lens (4); k is the conic constant; C is the high-order aspherical coefficient.

4. The optical system according to claim 1, characterized in that, The seventh lens (8) is an aspherical lens; the aspherical surface of the seventh lens (8) satisfies the following even-order aspherical equation: Where: Z lens7 is the sagitta, which is the distance from the vertex of the aspherical surface of the seventh lens (8) to the position at height r along the optical axis of the optical system; c is the aspherical curvature of the seventh lens (8); k is the conic coefficient; B is the high-order aspherical coefficient.

5. The optical system according to claim 1, wherein The first lens (1) satisfies: -0.6 ≤ φ1 / φ ≤ -0.4; The second lens (2) satisfies: -0.6 ≤ φ2 / φ ≤ -0.4; The third lens (3) satisfies: 0.02 ≤ φ3 / φ ≤ 0.03; The fourth lens (4) satisfies: -0.3 ≤ φ4 / φ ≤ -0.1; The fifth lens (6) satisfies: 1.1 ≤ φ5 / φ ≤ 1.3; The sixth lens (7) satisfies: -0.2 ≤ φ6 / φ ≤ -0.19; The seventh lens (8) satisfies: 1 ≤ φ7 / φ ≤ 1.1; Where: φ is the optical power of the optical system; φ1 is the optical power of the first lens (1); φ2 is the optical power of the second lens (2); φ3 is the optical power of the third lens (3); φ4 is the optical power of the fourth lens (4); φ5 is the optical power of the fifth lens (6); φ6 is the optical power of the sixth lens (7); φ7 is the optical power of the seventh lens (8).

6. The optical system according to claim 1, characterized in that, The second lens (2), the third lens (3), the fifth lens (6), and the sixth lens (7) are all spherical lenses.

7. The optical system according to claim 1, characterized in that It further includes a diaphragm (5) disposed on the front surface of the fifth lens (6).

8. The optical system according to claim 1, characterized in that, The working wavelength of the optical system is 8 μm - 12.5 μm.

9. The optical system according to claim 1, characterized in that, The second lens (2), the fourth lens (4), and the fifth lens (6) are all made of single crystal germanium.

10. The optical system according to claim 1, characterized in that, The third lens (3) and the sixth lens (7) are all made of zinc selenide.

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