Dual view infrared lens and optical system

Abstract

This application discloses an imaging system, including a dual-field-of-view infrared lens and a detector capable of receiving images from the infrared lens. The infrared lens comprises a first lens, a second lens, a third lens, and a fourth lens arranged sequentially along the optical axis from the object side to the image side. The second lens is movable along the optical axis. The air gap between the third and fourth lenses is 13 mm. When the focal length of the infrared lens is 25 mm, the air gap between the first and second lenses is 14.21 mm, and the air gap between the second and third lenses is 11.21 mm. When the focal length of the infrared lens is 50 mm, the air gap between the first and second lenses is 21.42 mm, and the air gap between the second and third lenses is 4 mm. The focal length of the infrared lens can switch between 25 mm and 50 mm, with a zoom ratio of 2x, achieving clear dual-field-of-view imaging, and operating in the 8-12 μm wavelength range.

Description

Technical Field

[0001] This application belongs to the field of infrared optical equipment technology, specifically relating to a dual-field infrared lens and optical system. Background Technology

[0002] With the development of science and technology, infrared imaging technology has been widely used in national defense, industry, medicine and other fields. Infrared detection has a certain ability to penetrate smoke, fog, haze and snow, as well as the ability to identify camouflage. It is not blinded by strong light or flashes, and can achieve long-distance, all-weather observation. It is especially suitable for target detection at night and under adverse weather conditions.

[0003] In optical system design, while continuous zoom systems can achieve clear imaging of the target continuously during zooming, their complex structure and difficult manufacturing and assembly lead to decreased system transmittance and image quality, affecting imaging performance. Furthermore, when used for measurement, line-of-sight movement increases measurement errors. Dual-field-of-view optical systems, on the other hand, have a simple structure and combine the wide coverage of a short focal length field of view with the high resolution of a long focal length field of view. Working together, they can achieve both large-field-of-sight target search and small-field-of-sight target tracking and measurement. Therefore, there is an urgent need to design a dual-field-of-sight optical lens that can simultaneously meet the requirements of short-focal-length large-field-of-sight search and long-focal-length high-resolution imaging and high-precision measurement. Summary of the Invention

[0004] Therefore, it is necessary to provide a dual-field infrared lens and optical system capable of performing large field-of-view search and small field-of-view tracking and measurement.

[0005] The technical solution proposed in this application is as follows: A dual-field infrared lens is available, capable of switching between a 25mm focal length and a 50mm focal length. The infrared lens comprises a first lens, a second lens, a third lens, and a fourth lens arranged sequentially along the optical axis from the object side to the image side. The first lens is a meniscus lens with its convex surface facing the object side, the second lens is a biconcave lens, the third lens is a biconvex lens, and the fourth lens is a biconvex lens. The second lens is movable along the optical axis. The air gap between the third lens and the fourth lens is 13mm; and when the focal length of the infrared lens is 25mm, the air gap between the first lens and the second lens is 14.21mm, and the air gap between the second lens and the third lens is 11.21mm; when the focal length of the infrared lens is 50mm, the air gap between the first lens and the second lens is 21.42mm, and the air gap between the second lens and the third lens is 4mm.

[0006] Furthermore, the first lens has a center thickness of 4.9 mm, an object-side radius of curvature of 41.44 mm, and an image-side radius of curvature of 55.65 mm; the second lens has a center thickness of 1.8 mm, an object-side radius of curvature of -58.06 mm, and an image-side radius of curvature of 66.42 mm; the third lens has a center thickness of 4.4 mm, an object-side radius of curvature of 88.47 mm, and an image-side radius of curvature of -135 mm; and the fourth lens has a center thickness of 2.8 mm, an object-side radius of curvature of 183.49 mm, and an image-side radius of curvature of -247.42 mm.

[0007] Furthermore, all lenses are made of germanium.

[0008] Furthermore, the relative aperture of the infrared lens is 0.89-1.1, and the operating wavelength is 8-12μm.

[0009] Furthermore, the image-side surface of the first lens, the object-side surface of the second lens, the two side surfaces of the third lens, and the object-side surface of the fourth lens are all aspherical surfaces, and satisfy the aspherical surface formula: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0010] Furthermore, the object-side surface of the third lens is a binary surface, which includes an aspherical surface and a diffraction surface.

[0011] An optical system includes the dual-field-of-view infrared lens and a detector that receives images from the infrared lens.

[0012] Furthermore, the detector has a resolution of 640*512 and a pixel size of 12μm.

[0013] Furthermore, the detector includes a protective window and an image plane arranged sequentially, the air gap between the fourth lens and the protective window is 15 mm, and the air gap between the protective window and the image plane is 1.38 mm.

[0014] In summary, the infrared lens provided in this application has a focal length that can switch between 25mm and 50mm, a zoom ratio of 2x, and achieves clear imaging in both fields of view, with an operating wavelength of 8-12μm. The corresponding detector resolution is 640*512, and the pixel size is 12μm. It uses only one focusing group, achieves switching between large and small fields of view, ensures the stability of dual-field-of-view imaging quality, and has a simple structure. Attached Figure Description

[0015] The accompanying drawings are provided to further understand this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof.

[0016] Figure 1 This is a schematic diagram of the optical path structure of an optical system provided in an embodiment of this application; Figure 2 A dot plot of the dual-field infrared lens provided in this application at a focal length of 25mm at room temperature; Figure 3 MTF diagram of the dual-field infrared lens provided in this application at a focal length of 25mm at room temperature; Figure 4 A dot plot of the dual-field infrared lens provided in this application at a focal length of 50mm at room temperature; Figure 5 The MTF diagram of the dual-field infrared lens provided in this application at a focal length of 50mm at room temperature.

[0017] Label Explanation: 11. First lens; 12. Second lens; 13. Third lens; 14. Fourth lens; 21. Protective window; 22. Image plane. Detailed Implementation

[0018] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0020] This application provides an optical system including a dual-field-of-view infrared lens and a detector capable of receiving the image captured by the infrared lens. The infrared lens is switchable between a 25mm focal length and a 50mm focal length, and its relative aperture is 0.89-1.1, with an operating wavelength of 8-12μm. The detector has a resolution of 640*512 and a pixel size of 12μm. Specifically, when the infrared lens has a focal length of 25mm, its relative aperture is 0.89; when the infrared lens has a focal length of 50mm, its relative aperture is 1.1.

[0021] like Figure 1 As shown, in one embodiment, the infrared lens is composed of a first lens 11, a second lens 12, a third lens 13, and a fourth lens 14 arranged sequentially from the object side to the image side along the optical axis; the first lens 11 is a meniscus lens with its convex surface facing the object side, the second lens 12 is a biconcave lens, the third lens 13 is a biconvex lens, and the fourth lens 14 is a biconvex lens; the second lens 12 can move along the optical axis to achieve switching between a large field of view and a small field of view.

[0022] Furthermore, the air gap between the third lens 13 and the fourth lens 14 is 13mm; and when the focal length of the infrared lens is 25mm, the air gap between the first lens 11 and the second lens 12 is 14.21mm, and the air gap between the second lens 12 and the third lens 13 is 11.21mm; when the focal length of the infrared lens is 50mm, the air gap between the first lens 11 and the second lens 12 is 21.42mm, and the air gap between the second lens 12 and the third lens 13 is 4mm.

[0023] In one embodiment, the detector includes a protective window 21 and an image plane 22 arranged sequentially. The air gap between the fourth lens 14 and the protective window 21 is 15 mm, and the air gap between the protective window 21 and the image plane 22 is 1.38 mm. Light passes sequentially through the first lens 11, the second lens 12, the third lens 13, and the fourth lens 14, and then through the protective window 21 to form an image on the image plane 22.

[0024] In one embodiment, the first lens 11 has a center thickness of 4.9 mm, an object-side radius of curvature of 41.44 mm, and an image-side radius of curvature of 55.65 mm; the second lens 12 has a center thickness of 1.8 mm, an object-side radius of curvature of -58.06 mm, and an image-side radius of curvature of 66.42 mm; the third lens 13 has a center thickness of 4.4 mm, an object-side radius of curvature of 88.47 mm, and an image-side radius of curvature of -135 mm; and the fourth lens 14 has a center thickness of 2.8 mm, an object-side radius of curvature of 183.49 mm, and an image-side radius of curvature of -247.42 mm.

[0025] It should be noted that, understandably, in Figure 1 In the embodiment shown, light is transmitted from left to right. Taking the first lens 11 as an example, the left side S1 surface of the first lens 11 is the object side surface, and the right side S2 surface is the image side surface. The same applies to other lenses, which will not be described in detail here.

[0026] In one embodiment, the first lens 11, the second lens 12, the third lens 13, and the fourth lens 14 are all made of germanium. Specific parameters of the lenses can be found in Table 1.

[0027] Table 1 Parameters of each lens In one embodiment, the image-side surface of the first lens 11, the object-side surface of the second lens 12, the two side surfaces of the third lens 13, and the object-side surface of the fourth lens 14 are all aspherical surfaces and satisfy the aspherical formula: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients. Furthermore, the above aspherical data are shown in Table 2.

[0028] Table 2 Aspherical Data In one embodiment, the object-side surface of the third lens 13 is a binary surface, and the binary surface includes an aspherical surface and a diffractive surface. Furthermore, the object-side surface of the third lens 13 satisfies the Zemax expression equation for a binary surface: M(B1ρ) 2 +B2ρ 4 Where M is the diffraction order (1), B1 and B2 are the phase coefficients of the binary surface, and ρ is the normalized radius. The binary surface data are shown in Table 3. Table 3 Binary Surface Data Please see Figures 2 to 5 , Figure 2 and Figure 3 The image shows the dot plot and MTF plot of the infrared lens at a focal length of 25mm at room temperature (20℃). Figure 4 and Figure 5 The figures show the dot plot and MTF (Mean Transformation Factor) of the infrared lens at a focal length of 50mm at room temperature. As can be seen from the figures, the MTF of this infrared lens is close to the diffraction limit, the root mean square diameter of the diffuse spot is smaller than the Airy disk diameter, and the image quality is good.

[0029] In summary, the infrared lens provided in this application has a focal length that can switch between 25mm and 50mm, a zoom ratio of 2x, and achieves clear imaging in both fields of view, with an operating wavelength of 8-12μm. The corresponding detector resolution is 640*512, and the pixel size is 12μm. It uses only one focusing group, achieves switching between large and small fields of view, ensures the stability of dual-field-of-view imaging quality, and has a simple structure.

[0030] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dual-field-of-view infrared lens, characterized in that, The infrared lens is capable of switching between a 25mm focal length and a 50mm focal length. It consists of a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the object side to the image side along the optical axis. The first lens is a meniscus lens with its convex surface facing the object side, the second lens is a biconcave lens, the third lens is a biconvex lens, and the fourth lens is a biconvex lens. The second lens is movable along the optical axis. The air gap between the third lens and the fourth lens is 13mm; and when the focal length of the infrared lens is 25mm, the air gap between the first lens and the second lens is 14.21mm, and the air gap between the second lens and the third lens is 11.21mm; when the focal length of the infrared lens is 50mm, the air gap between the first lens and the second lens is 21.42mm, and the air gap between the second lens and the third lens is 4mm.

2. The dual-field infrared lens according to claim 1, characterized in that, The first lens has a center thickness of 4.9 mm, an object-side radius of curvature of 41.44 mm, and an image-side radius of curvature of 55.65 mm; the second lens has a center thickness of 1.8 mm, an object-side radius of curvature of -58.06 mm, and an image-side radius of curvature of 66.42 mm; the third lens has a center thickness of 4.4 mm, an object-side radius of curvature of 88.47 mm, and an image-side radius of curvature of -135 mm; and the fourth lens has a center thickness of 2.8 mm, an object-side radius of curvature of 183.49 mm, and an image-side radius of curvature of -247.42 mm.

3. The dual-field infrared lens according to claim 1, characterized in that, All lenses are made of germanium.

4. The dual-field infrared lens according to claim 1, characterized in that, The infrared lens has a relative aperture of 0.89-1.1 and an operating wavelength of 8-12 μm.

5. The dual-field infrared lens according to claim 1, characterized in that, The image-side surface of the first lens, the object-side surface of the second lens, the two side surfaces of the third lens, and the object-side surface of the fourth lens are all aspherical surfaces and satisfy the aspherical formula: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

6. The dual-field infrared lens according to claim 5, characterized in that, The object-side surface of the third lens is a binary surface, which includes an aspherical surface and a diffraction surface.

7. An optical system, characterized in that, It includes the dual-field infrared lens as described in any one of claims 1-6 and the detector that receives the image from the infrared lens.

8. The optical system according to claim 7, characterized in that, The detector has a resolution of 640*512 and a pixel size of 12μm.

9. The optical system according to claim 7, characterized in that, The detector includes a protective window and an image plane arranged sequentially. The air gap between the fourth lens and the protective window is 15 mm, and the air gap between the protective window and the image plane is 1.38 mm.

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