Lightweight, compact, large zoom ratio medium-wave infrared continuous zoom optical system

Abstract

The present invention relates to a lightweight, compact, large-zoom medium-wave infrared continuous zoom optical system, belonging to the field of optical imaging technology. The system comprises: a positive-power meniscus lens as a front fixed group, a negative-power biconcave lens as a zoom group, a positive-power biconvex lens as a compensation group, a negative-power biconcave lens as a second compensation group, a positive-power meniscus lens as a rear fixed group, a first plane reflector, a second plane reflector, and a positive-power biconvex lens and a negative-power meniscus lens as a relay group, arranged sequentially along the optical axis. The optical system of the present invention features a wide zoom range, a small size envelope, and a lightweight system. It has broad application prospects in security fields such as navigation, search, tracking, surveillance, and reconnaissance.

Description

Technical Field

[0001] The present invention belongs to the field of optical imaging technology and relates to a lightweight, large-magnification medium-wave infrared continuous zoom optical system. Specifically, it relates to a refrigerated medium-wave infrared continuous zoom optical system mainly used for large-scale search and reconnaissance, long-distance tracking and identification in handheld infrared thermal imagers, vehicle-mounted infrared thermal imagers, airborne infrared thermal imagers, etc. Background Art

[0002] Infrared thermal imagers, with their excellent environmental adaptability, all-weather operation, and susceptibility to interference, are widely used in security, industrial monitoring, and military surveillance. In recent years, with the improvement of infrared detection device performance, cooled detectors have rapidly developed towards smaller size, lighter weight, and lower power consumption. These medium-wave infrared detectors, integrated with small refrigerators or split linear refrigerators, are widely used in space-constrained infrared optoelectronic systems such as weapon thermal sights, portable handheld thermal imagers, small drones, unmanned vehicles, remote-controlled snipers and weapon stations, and missile seekers. The miniaturization of cooled detectors has driven the development of infrared continuous zoom optical systems towards higher magnification, smaller size envelope, and lighter weight to meet the needs of various lightweight optoelectronic equipment such as security, surveillance, reconnaissance, search, and tracking. Therefore, lightweight, high-zoom-ratio infrared continuous zoom optical systems are widely used.

[0003] Through research on relevant literature, it is found that domestic research results on cooled medium-wave infrared continuous zoom optical systems have been quite extensive. For example, Wang Haiyang's "Design of a Large Zoom Ratio Medium-wave Infrared Continuous Zoom Optical System" uses 10 lenses and two U-folded reflectors to adapt to a 640×512@15μm medium-wave cooled detector. It uses a two-element positive group compensation technique to achieve a 30x F#4 focal length of 23mm-701mm, with a system size of 345mm×176mm×224mm (Infrared and Laser Engineering, 2013, 42(2)). Chen Jinjin's "Design of a High-Definition, Large-Zoom Medium-Wave Infrared Continuous Zoom Optical System" uses eight lenses and two U-folded reflectors to adapt to a 640×512@15μm medium-wave cooled detector. It uses a two-element positive group compensation technique to achieve a 35x F#4 focal length of 15mm-550mm, with a system size of 390mm×137.5mm×110mm (Infrared and Laser Engineering, 2013, 42(10)). Yu Yang's "Development of a Large-Zoom, Large-Relative-Aperture Continuous Zoom Infrared Optical System" uses eight lenses to adapt to a 640×512@15μm medium-wave detector. It uses a three-group linkage technique to achieve a 30x F#2 focal length of 6mm-330mm, with a total optical system length of 460mm (Journal of Infrared and Millimeter Waves, 2019, 38(1)). Gu Xiansong's "Design of a Compact Medium-Wave Infrared Continuous Zoom Optical System with a Large Zoom Ratio" uses 10 lenses, adapted to a 640×512@15μm medium-wave detector, and employs a two-element positive group compensation technique to achieve a 30x F#4 focal length of 18mm-550mm with a total length of 350mm (Applied Optics 2019, 40(1)). Peng Qingqing's "A New Athermal Design Method for Infrared Continuous Zoom Systems" uses 6 lenses, adapted to a 640×512@15μm medium-wave detector, and employs a two-element positive group compensation technique to achieve a 12x F#4.0 focal length of 25mm-300mm with a system size of 200mm×140mm×110mm (Laser & Infrared 2017, 47(1)).

[0004] Chinese patent CN102213822A discloses a medium-wave infrared continuous zoom lens that uses two-element positive group compensation technology, employs seven lenses, and two plane mirrors. It can be used with a 640×512 medium-wavelength detector, achieving a 10x F#4.0 focal length of 50mm-500mm. Chinese patent CN102590990B discloses a three-group linkage medium-wave infrared continuous zoom optical structure that uses three lens groups with nonlinear movement to achieve continuous zoom. Using 10 lenses, it is suitable for a 640×512@15μm medium-wavelength detector and achieves a 30x F#4 focal length of 25mm-750mm.

[0005] The designs in the aforementioned literature and patents either use a large number of lenses or multiple binary diffraction surfaces, increasing system costs; or they result in a large system envelope, making it difficult to meet the demands of lightweight and compact use. The current trend toward lightweight, high-performance, and low-cost vehicle-mounted and airborne infrared thermal imagers places higher demands on the image quality, overall length, and system volume of infrared continuous zoom optical systems. Therefore, overcoming the shortcomings of existing technologies is a pressing issue in the field of optical imaging technology. Summary of the Invention

[0006] The purpose of the present invention is to address the shortcomings of the existing technology and provide a lightweight, large-magnification medium-wave infrared continuous zoom optical system. The lightweight, small-sized infrared continuous zoom optical system using three-group linkage technology can achieve the goals of reducing system volume, shortening total length, reducing weight, and reducing the number of lenses, so that it can be widely used in military alert and civilian security fields such as navigation, search, tracking, and reconnaissance.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] Lightweight, compact, large zoom ratio medium-wave infrared continuous zoom optical system, including:

[0009] Along the optical axis, a positive-power meniscus lens as a front fixed group, a negative-power biconcave lens as a zoom group, a positive-power biconvex lens as a compensation group, a negative-power biconcave lens as a second compensation group, a positive-power meniscus lens as a rear fixed group, a first plane reflecting mirror, a second plane reflecting mirror, a positive-power biconvex lens as a relay group, and a negative-power meniscus lens as a relay group are sequentially arranged.

[0010] The positive power meniscus lens in the front fixed group has its concave surface facing the image side;

[0011] The positive power meniscus lens as the rear fixed group has its concave side facing the image side;

[0012] The negative power meniscus lens as the relay group has its concave side facing the image side;

[0013] The normal line of the first plane reflector and the normal line of the second plane reflector form an angle of 45° relative to the optical axis, and the optical path is U-shaped and folded 180°.

[0014] Furthermore, preferably, the material of the positive power meniscus lens of the front fixed group is silicon single crystal;

[0015] The negative power biconcave lens used as the zoom group is made of germanium single crystal or chalcogenide glass material;

[0016] The material of the positive power biconvex lens used as the compensation group is silicon single crystal;

[0017] The negative power biconcave lens of the second compensation group is made of germanium single crystal, silicon single crystal or chalcogenide glass material;

[0018] The positive power meniscus lens used as the rear fixed group is made of silicon single crystal, chalcogenide glass material or zinc selenide;

[0019] The material of the positive power biconvex lens used as the relay group is silicon single crystal, chalcogenide glass material or zinc selenide;

[0020] The material of the negative power meniscus lens used as the relay group is chalcogenide glass material, zinc sulfide or zinc selenide.

[0021] Furthermore, preferably, the positive power meniscus lens serving as the front fixed group is an aspherical positive power meniscus lens;

[0022] The negative power biconcave lens used as the zoom group is an aspherical negative power biconcave lens;

[0023] The positive power biconvex lens as a compensation group is an aspherical positive power biconvex lens;

[0024] The negative optical power biconcave lens as the second compensation group is an aspherical negative optical power biconcave lens;

[0025] The positive power meniscus lens as the rear fixed group is a spherical positive power meniscus lens;

[0026] The positive power biconvex lens as the relay group is a positive power aspheric diffraction lens;

[0027] The negative optical power meniscus lens as the relay group is a spherical negative optical power meniscus lens.

[0028] Furthermore, preferably, the focal lengths of the positive power meniscus lens as the front fixed group, the negative power biconcave lens as the variable magnification group, the positive power biconvex lens as the compensation group, and the negative power biconcave lens as the second compensation group need to meet the following conditions:

[0029] 3.2<|fL / f1|<5.6;

[0030] 16.8<|fL / f2|<28.8;

[0031] 10.4<|fL / f3|<20.8;

[0032] 8.2<|fL / f4|<18.2;

[0033] Among them, fL is the focal length of the telephoto end of the optical system, f1 is the focal length of the positive focal power meniscus lens as the front fixed group, f2 is the focal length of the negative focal power biconcave lens as the zoom group, f3 is the focal length of the positive focal power biconvex lens as the compensation group, and f4 is the focal length of the negative focal power biconcave lens as the second compensation group.

[0034] Furthermore, preferably, the positive optical power biconvex lens as the compensation group and the negative optical power biconcave lens as the second compensation group move in the same direction along the optical axis during the zooming process to achieve a continuous zoom compensation function.

[0035] Furthermore, preferably, the negative optical power biconcave lens as the zoom group moves forward and backward along the optical axis to achieve visual distance focusing and high and low temperature athermalization.

[0036] The system of the present invention is arranged so that the infrared radiation light of the target scene passes through a positive focal length meniscus lens as a front fixed group, a negative focal length biconcave lens as a zoom group, a positive focal length biconvex lens as a compensation group, a negative focal length biconcave lens as a second compensation group, a positive focal length meniscus lens as a rear fixed group, a first plane reflector, a second plane reflector, a positive focal length biconvex lens as a relay group, and a negative focal length meniscus lens as a relay group, and converges to the window of a medium-wave cooled detector and forms an image on the focal plane of the medium-wave cooled detector.

[0037] The negative power biconcave lens as the zoom group, the positive power biconvex lens as the compensation group, and the negative power biconcave lens as the second compensation group can all be moved axially to achieve continuous zooming, that is, when the negative power biconcave lens as the zoom group moves from a position close to the positive power meniscus lens as the front fixed group toward the positive power meniscus lens as the rear fixed group, the positive power biconvex lens as the compensation group and the negative power biconcave lens as the second compensation group move nonlinearly for compensation from a position close to the positive power meniscus lens as the rear fixed group toward the positive power meniscus lens as the front fixed group according to the compensation curve. During the corresponding zooming process, the focal length of the system continuously increases from short focus to long focus; when the negative power biconcave lens as the zoom group approaches the positive power meniscus lens as the front fixed group, the system is in the short focus position, and when the negative power biconcave lens as the zoom group approaches the positive power biconvex lens as the compensation group, the system is in the long focus position.

[0038] The negative optical power biconcave lens of the present invention as a zoom group has a focusing function of moving back and forth along the optical axis, and can compensate for system defocus in high and low temperature environments through focusing.

[0039] This system uses three-group linked zoom technology to compress the total length of the 30x medium-wave infrared continuous zoom optical system and uses two plane mirrors to U-shaped deflect the light path to further compress the longitudinal length of the system to achieve system miniaturization.

[0040] In the present invention, the positive power meniscus lens as the front fixed group, the negative power biconcave lens as the zoom group, the positive power biconvex lens as the compensation group, the negative power biconcave lens as the second compensation group, the positive power meniscus lens as the rear fixed group, the positive power biconvex lens as the relay group, and the negative power meniscus lens as the relay group have an optical structural layout in which the focal powers are positive, negative, positive, negative, positive, positive, and negative, respectively.

[0041] The zoom range of the system of the present invention is 14.8mm-460mm, the applicable range of the system F number is 3.5-5.5, the system volume envelope is ≤208mm (length)×136mm (width)×120mm (height), and the total weight of the system is ≤236g.

[0042] The refrigerated medium-wave infrared focal plane detector adapted to the system of the present invention is applicable to specifications such as 384×288 / 25μm, 640×512 / 15μm, 640×512 / 17μm, and 1024×768 / 10μm. The applicable wavelength range is medium wave 3.7μm-4.8μm, medium wave 3.2μm-4.3μm, and medium wave 3.0μm-5.0μm.

[0043] The present invention achieves a 30x continuous zoom function for a seven-lens refrigerated medium-wave infrared optical system by adopting three-group linked zoom technology; constrains the aperture of the front fixed group and achieves 100% cold screen efficiency of the system by adopting secondary imaging technology; compresses the longitudinal length by two plane mirrors to achieve system miniaturization; and achieves clear imaging of the continuous zoom optical system under high and low temperature conditions through the athermal difference technology of active focus compensation.

[0044] Key points of the present invention:

[0045] The optical system of the present invention adopts three-group linked continuous zoom technology to reduce the number of lenses and compress the total length of the system. A total of seven lenses are used to achieve a 30x lightweight and compact refrigerated medium-wave infrared continuous zoom function.

[0046] The present invention adopts the compensation technology of two compensation groups moving in the same direction along the optical axis to realize the continuous zoom compensation function and simplify the cam design technology or servo control technology.

[0047] The optical system of the present invention can achieve clear imaging by actively focusing the negative-power biconcave lens of the zoom group under low-temperature environments of -45°C and high-temperature environments of +70°C.

[0048] The optical system of the present invention reduces the size of optical parts and achieves 100% cold screen efficiency by adopting optical double focusing imaging to constrain the diameter of the front fixed group of positive focal length meniscus lenses.

[0049] The optical system of the present invention adopts two plane reflectors to U-shape deflect the light path, compressing the longitudinal length and limiting the longitudinal length of the 30x light and small refrigerated medium-wave infrared continuous zoom optical system to within 208 mm.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The lightweight, high-zoom medium-wave infrared continuous zoom optical system of this invention achieves 30x continuous zoom with just seven lenses. By employing optical double-focusing to constrain the diameter of the fixed positive meniscus lens group, the optical component size is reduced, 100% cooling efficiency is achieved, and imaging quality is improved. Active focusing and heat removal by the zoom group ensures that the system maintains excellent imaging quality within a temperature range of -45°C to 70°C.

[0052] The system has a zoom range of 14.8mm to 460mm, a system envelope of ≤208mm (length) × 136mm (width) × 120mm (height), and a total system weight of ≤236g, achieving a lightweight and compact high-zoom optical system. The entire system boasts a small number of lenses, a short axial dimension, light weight, compact size, low cost, and high transmittance. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the zoom process of the system of the present invention.

[0054] Figure 2 This is a diagram of an optical system with a small field of view and a focal length of 460mm according to an embodiment of the present invention.

[0055] Figure 3 This is a diagram of an optical system with a small field of view and a focal length of 275mm in Example 1 of the present invention.

[0056] Figure 4 This is a diagram of an optical system with a field of view of 109 mm and a focal length in Example 1 of the present invention.

[0057] Figure 5 This is a diagram of an optical system with a large field of view and a focal length of 14.8 mm according to an embodiment of the present invention.

[0058] Figure 6 This is a modulation transfer function diagram of a small field of view 460mm focal length according to an embodiment of the present invention.

[0059] Figure 7 This is a modulation transfer function diagram of a focal length of 275mm with a small field of view in Example 1 of the present invention.

[0060] Figure 8 This is a modulation transfer function diagram for a focal length of 109 mm field of view in Example 1 of the present invention.

[0061] Figure 9This is a modulation transfer function diagram of a large field of view (14.8 mm focal length) according to an embodiment of the present invention.

[0062] Figure 10 This is a modulation transfer function diagram of a 460mm focal length with a small field of view at -45°C according to the second embodiment of the present invention.

[0063] Figure 11 This is a modulation transfer function diagram of a 460mm focal length with a small field of view at +70°C according to the second embodiment of the present invention.

[0064] Figure 12 This is a cam curve diagram of the zooming process of the first zoom group, the compensation group, and the second compensation group in an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The present invention is described in further detail below with reference to the embodiments.

[0066] Those skilled in the art will understand that the following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or in the product specifications were used. Materials or equipment used without manufacturer identification are commercially available conventional products.

[0067] Example 1

[0068] like Figures 2 to 5 As shown, a lightweight, large-zoom-ratio medium-wave infrared continuous zoom optical system is characterized by comprising:

[0069] Along the optical axis, a positive power meniscus lens 1 as a front fixed group, a negative power biconcave lens 2 as a zoom group, a positive power biconvex lens 3 as a compensation group, a negative power biconcave lens 4 as a second compensation group, a positive power meniscus lens 5 as a rear fixed group, a first plane reflecting mirror 6, a second plane reflecting mirror 7, a positive power biconvex lens 8-2 as a relay group, and a negative power meniscus lens 8-1 as a relay group are sequentially arranged.

[0070] The positive power meniscus lens 1 of the front fixed group has its concave surface facing the image side;

[0071] The positive power meniscus lens 5 as the rear fixed group has its concave side facing the image side;

[0072] The negative optical power meniscus lens 8-1 as a relay group has its concave surface facing the image side;

[0073] The normal line of the first plane reflector 6 and the normal line of the second plane reflector 7 form an angle of 45° relative to the optical axis, thus making a U-shaped 180° turn of the optical path.

[0074] Example 2

[0075] like Figures 2 to 5 As shown, a lightweight, large-zoom-ratio medium-wave infrared continuous zoom optical system is characterized by comprising:

[0076] Along the optical axis, a positive power meniscus lens 1 as a front fixed group, a negative power biconcave lens 2 as a zoom group, a positive power biconvex lens 3 as a compensation group, a negative power biconcave lens 4 as a second compensation group, a positive power meniscus lens 5 as a rear fixed group, a first plane reflecting mirror 6, a second plane reflecting mirror 7, a positive power biconvex lens 8-2 as a relay group, and a negative power meniscus lens 8-1 as a relay group are sequentially arranged.

[0077] The positive power meniscus lens 1 of the front fixed group has its concave surface facing the image side;

[0078] The positive power meniscus lens 5 as the rear fixed group has its concave side facing the image side;

[0079] The negative optical power meniscus lens 8-1 as a relay group has its concave surface facing the image side;

[0080] The normal line of the first plane reflector 6 and the normal line of the second plane reflector 7 form an angle of 45° relative to the optical axis, thus making a U-shaped 180° turn of the optical path.

[0081] The positive power meniscus lens 1 as the front fixed group is made of silicon single crystal;

[0082] The negative power biconcave lens 2 as the zoom group is made of germanium single crystal or chalcogenide glass material;

[0083] The material of the positive power biconvex lens 3 as the compensation group is silicon single crystal;

[0084] The negative optical power biconcave lens 4 of the second compensation group is made of germanium single crystal, silicon single crystal or chalcogenide glass material;

[0085] The positive power meniscus lens 5 as the rear fixed group is made of silicon single crystal, chalcogenide glass material or zinc selenide;

[0086] The positive power biconvex lens 8-2 as the relay group is made of silicon single crystal, chalcogenide glass material or zinc selenide;

[0087] The material of the negative power meniscus lens 8-1 as the relay group is chalcogenide glass material, zinc sulfide or zinc selenide.

[0088] The positive power meniscus lens 1 as the front fixed group is an aspherical positive power meniscus lens;

[0089] The negative optical power biconcave lens 2 as the zoom group is an aspherical negative optical power biconcave lens;

[0090] The positive power biconvex lens 3 as a compensation group is an aspherical positive power biconvex lens;

[0091] The negative optical power biconcave lens 4 as the second compensation group is an aspherical negative optical power biconcave lens;

[0092] The positive power meniscus lens 5 as the rear fixed group is a spherical positive power meniscus lens;

[0093] The positive power biconvex lens 8-2 as the relay group is a positive power aspheric diffraction lens;

[0094] The negative power meniscus lens 8 - 1 as a relay group is a spherical negative power meniscus lens.

[0095] The focal lengths of the positive power meniscus lens 1 as the front fixed group, the negative power biconcave lens 2 as the zoom group, the positive power biconvex lens 3 as the compensation group, and the negative power biconcave lens 4 as the second compensation group must meet the following conditions:

[0096] 3.2<|fL / f1|<5.6;

[0097] 16.8<|fL / f2|<28.8;

[0098] 10.4<|fL / f3|<20.8;

[0099] 8.2<|fL / f4|<18.2;

[0100] Among them, fL is the focal length of the telephoto end of the optical system, f1 is the focal length of the positive focal power meniscus lens 1 as the front fixed group, f2 is the focal length of the negative focal power biconcave lens 2 as the zoom group, f3 is the focal length of the positive focal power biconvex lens 3 as the compensation group, and f4 is the focal length of the negative focal power biconcave lens 4 as the second compensation group.

[0101] The positive optical power biconvex lens 3 as a compensation group and the negative optical power biconcave lens 4 as a second compensation group move in the same direction along the optical axis during zooming to achieve a continuous zoom compensation function.

[0102] The negative optical power biconcave lens 2 as a zoom group moves forward and backward along the optical axis to achieve visual distance focusing and high and low temperature athermalization.

[0103] Application Example 1

[0104] The present invention provides a lightweight, large-magnification medium-wave infrared continuous zoom optical system, such as Figure 2As shown, in the direction of the optical axis determined by the path of the medium-wave infrared light radiated by the scene target, the following are arranged in sequence from the object side to the image side: a positive focal length meniscus lens 1 as a front fixed group, a negative focal length biconcave lens 2 as a zoom group, a positive focal length biconvex lens 3 as a compensation group, a negative focal length biconcave lens 4 as a second compensation group, a positive focal length meniscus lens 5 as a rear fixed group, a first plane reflector 6, a second plane reflector 7, a positive focal length biconvex lens 8-2 as a relay group, a negative focal length meniscus lens 8-1 as a relay group, and a medium-wave cooled detector window 9, imaging at The focal plane 10 of the medium-wave cooled detector is configured so that the infrared radiation of the target scene passes through the positive focal length meniscus lens 1 as the front fixed group, the negative focal length biconcave lens 2 as the zoom group, the positive focal length biconvex lens 3 as the compensation group, the negative focal length biconcave lens 4 as the second compensation group, the positive focal length meniscus lens 5 as the rear fixed group, the first plane reflector 6, the second plane reflector 7, the positive focal length biconvex lens 8-2 as the relay group, and the negative focal length meniscus lens 8-1 as the relay group, and converges to the medium-wave cooled detector window 9, and forms an image on the focal plane 10 of the medium-wave cooled detector.

[0105] The specific parameters of the optical system are shown in Table 1.

[0106] In Table 1, the front surface and the back surface refer to the side of each optical element close to the scene along the optical axis, which is the front surface, and the side facing the focal plane of the cooling detector is the back surface; the radius of curvature refers to the radius of curvature of the front and back surfaces of each optical lens; the center thickness refers to the center thickness of each optical lens; the spacing refers to the distance between the center of the back surface of each optical lens and the center of the front surface of the adjacent optical lens along the optical axis; the material is the optical material used for the optical element; and the aspheric parameters are the coefficients of the even-order aspheric equation of the aspheric surface of the optical lens.

[0107] In Table 1, A is the fourth-power coefficient of the equation, B is the sixth-power coefficient of the equation, and C is the eighth-power coefficient of the equation. The even-order aspheric equation is defined as follows:

[0108]

[0109] Where z is the lens sagittal height along the optical axis of the aspheric surface; C0 is the vertex curvature of the optical lens surface; K is the quadratic constant; Y is the semi-aperture of the lens perpendicular to the optical axis; A, B, C, and D are coefficients (D = 0 in Table 1);

[0110] Table 1 Optical system parameters (unit: mm)

[0111]

[0112]

[0113] The diffraction coefficient is the coefficient of the diffraction surface equation of the aspherical diffraction surface of the optical lens;

[0114] The diffraction surface equation is: φ=H1Y 2 +H2Y 4 +H3Y 6

[0115] Wherein, φ is the phase of the diffraction surface; Y is the semi-aperture of the lens perpendicular to the optical axis; H1, H2, and H3 are the phase coefficients of the diffraction surface (H3=0 in Table 1).

[0116] The schematic diagram of the system zoom process is as follows Figure 1 As shown, when the system zooms from a large field of view short focus position to a small field of view long focus position, the negative power biconcave lens 2 as a zoom group moves from a position close to the positive power meniscus lens 1 as a front fixed group toward the positive power biconvex lens 3 as a compensation group, and the positive power biconvex lens 3 as a compensation group moves from a position close to the positive power meniscus lens 5 as a rear fixed group toward the negative power biconcave lens 2 as a zoom group for compensation, and the negative power biconcave lens 4 as the second compensation group moves simultaneously with the positive power biconvex lens 3 as the compensation group in the same direction, and during the corresponding zooming process, the focal length of the system continuously increases; when the negative power biconcave lens 2 as the zoom group is close to the positive power meniscus lens 1 as the front fixed group, the system is in the short focus position, and when the negative power biconcave lens 2 as the zoom group is close to the positive power biconvex lens 3 as the compensation group, the system is in the long focus position.

[0117] like Figure 5 As shown, when the negative power biconcave lens 2 as the zoom group is close to the positive power meniscus lens 1 as the front fixed group, a 14.8mm short focal length and large field of view optical path of the system is formed. The positive power meniscus lens 1 as the front fixed group is 17.8mm away from the negative power biconcave lens 2 as the zoom group. The negative power biconcave lens 2 as the zoom group is 72.2mm away from the positive power biconvex lens 3 as the compensation group. The positive power biconvex lens 3 as the compensation group is 4.2mm away from the negative power biconcave lens 4 as the second compensation group. The negative power biconcave lens 4 as the second compensation group is 4.5mm away from the positive power meniscus lens 5 as the rear fixed group.

[0118] When the negative power biconcave lens 2 as the zoom group moves toward the positive power biconvex lens 3 as the compensation group, and at the same time, the positive power biconvex lens 3 as the compensation group and the negative power biconcave lens 4 as the second compensation group move toward the negative power biconcave lens 2 as the zoom group, the position movement is as follows: Figure 4As shown, at this time, the system's 109mm focal length mid-field optical path is composed of the positive focal power meniscus lens 1 as the front fixed group and the negative focal power biconcave lens 2 as the zoom group at a distance of 63.9mm, the negative focal power biconcave lens 2 as the zoom group and the positive focal power biconvex lens 3 as the compensation group at a distance of 52.8mm, the positive focal power biconvex lens 3 as the compensation group and the negative focal power biconcave lens 4 as the second compensation group at a distance of 9.8mm, and the negative focal power biconcave lens 4 as the second compensation group and the positive focal power meniscus lens 5 as the rear fixed group at a distance of 28.6mm.

[0119] When the negative power biconcave lens 2 as the zoom group continues to move toward the positive power biconvex lens 3 as the compensation group, and at the same time, the positive power biconvex lens 3 as the compensation group and the negative power biconcave lens 4 as the second compensation group continue to move toward the negative power biconcave lens 2 as the zoom group, the position movement is as follows: Figure 3 As shown, at this time, the system's small and medium field of view optical path with a focal length of 275mm is formed. The positive power meniscus lens 1 as the front fixed group is spaced 68.5mm from the negative power biconcave lens 2 as the zoom group. The negative power biconcave lens 2 as the zoom group is spaced 19.2mm from the positive power biconvex lens 3 as the compensation group. The positive power biconvex lens 3 as the compensation group is spaced 21.0mm from the negative power biconcave lens 4 as the second compensation group. The negative power biconcave lens 4 as the second compensation group is spaced 46.4mm from the positive power meniscus lens 5 as the rear fixed group.

[0120] When the negative power biconcave lens 2 as the zoom group continues to move toward the positive power biconvex lens 3 as the compensation group, and at the same time, the positive power biconvex lens 3 as the compensation group and the negative power biconcave lens 4 as the second compensation group continue to move toward the negative power biconcave lens 2 as the zoom group, the position movement is as follows: Figure 2 As shown, at this time, the system's 460mm focal length small field of view optical path is formed, the positive focal power meniscus lens 1 as the front fixed group is 72.5mm away from the negative focal power biconcave lens 2 as the zoom group, the negative focal power biconcave lens 2 as the zoom group is 5.0mm away from the positive focal power biconvex lens 3 as the compensation group, the positive focal power biconvex lens 3 as the compensation group is 30.4mm away from the negative focal power biconcave lens 4 as the second compensation group, and the negative focal power biconcave lens 4 as the second compensation group is 47.2mm away from the positive focal power meniscus lens 5 as the rear fixed group.

[0121] The system is adapted to a 640×512 / 15μm, F-number 4 cooled medium-wave infrared focal plane detector 10 in a 14.8mm short focal length and large field of view. The optical modulation transfer function of the system is as follows: Figure 9 As shown, the optical modulation transfer function of the system when the system is in the middle field of view of 109mm focal length is as follows: Figure 8As shown, the optical modulation transfer function of the system when the system is in a small field of view with a focal length of 275mm is as follows: Figure 7 As shown, the optical modulation transfer function of the system when the system is in a small field of view with a focal length of 460mm is as follows: Figure 6 As shown, the imaging quality remains good throughout the entire zoom process, and the image is clear.

[0122] The motion cam curves of the negative focal power biconcave lens 2 as the zoom group, the positive focal power biconvex lens 3 as the compensation group, and the negative focal power biconcave lens 4 as the second compensation group during the zooming process are as follows: Figure 12 As shown, the maximum stroke of the negative optical focal length biconcave lens 2 as the zoom group is 54.7mm, the maximum stroke of the positive optical focal length biconvex lens 3 as the compensation group is 72.5mm, and the maximum stroke of the negative optical focal length biconcave lens 4 as the second compensation group is 42.7mm. The cam curve is smooth and easy to servo control.

[0123] Application Example 2

[0124] The present invention provides a lightweight, large-magnification medium-wave infrared continuous zoom optical system, such as Figure 2 As shown, in the optical axis direction determined by the path of the medium-wave infrared light radiated by the scene target, the following are arranged in sequence from the object side to the image side: a positive focal length meniscus lens 1 as a front fixed group, a negative focal length biconcave lens 2 as a zoom group, a positive focal length biconvex lens 3 as a compensation group, a negative focal length biconcave lens 4 as a second compensation group, a positive focal length meniscus lens 5 as a rear fixed group, a first plane reflector 6, a second plane reflector 7, a positive focal length biconvex lens 8-2 and a negative focal length meniscus lens 8-1 as a relay group, and a medium-wave cooled detector window 9, imaging at The focal plane 10 of the medium-wave cooled detector is configured so that the infrared radiation of the target scene passes through the positive focal length meniscus lens 1 as the front fixed group, the negative focal length biconcave lens 2 as the zoom group, the positive focal length biconvex lens 3 as the compensation group, the negative focal length biconcave lens 4 as the second compensation group, the positive focal length meniscus lens 5 as the rear fixed group, the first plane reflector 6, the second plane reflector 7, the positive focal length biconvex lens 8-2 and the negative focal length meniscus lens 8-1 as the relay group, and converges to the medium-wave cooled detector window 9, and forms an image on the focal plane 10 of the medium-wave cooled detector.

[0125] When the negative power biconcave lens 2 as the zoom group is close to the positive power biconvex lens 3 as the compensation group, and the positive power biconvex lens 3 as the compensation group and the negative power biconcave lens 4 as the second compensation group are close to the negative power biconcave lens 2 as the zoom group, the position situation is as follows: Figure 2As shown, at this time, the system's 460mm focal length small field of view optical path is formed, the positive focal power meniscus lens 1 as the front fixed group is 72.5mm away from the negative focal power biconcave lens 2 as the zoom group, the negative focal power biconcave lens 2 as the zoom group is 5.0mm away from the positive focal power biconvex lens 3 as the compensation group, the positive focal power biconvex lens 3 as the compensation group is 30.4mm away from the negative focal power biconcave lens 4 as the second compensation group, and the negative focal power biconcave lens 4 as the second compensation group is 47.2mm away from the positive focal power meniscus lens 5 as the rear fixed group.

[0126] When the system is at a low temperature of -45°C, the focus compensation is performed by moving the negative optical power biconcave lens 2 as the zoom group backward along the optical axis by 0.32 mm. The optical modulation transfer function of the system after focus compensation is as follows: Figure 10 As shown, the system imaging is clear.

[0127] When the system is at a high temperature of +70°C, the focus compensation is performed by moving the negative optical power biconcave lens 2 as the zoom group forward 0.28mm along the optical axis. The optical modulation transfer function of the system after focus compensation is as follows: Figure 11 As shown, the system imaging is clear.

[0128] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. Lightweight, large zoom ratio medium-wave infrared continuous zoom optical system, characterized by: include: Along the optical axis, a positive focal meniscus lens (1) as a front fixed group, a negative focal biconcave lens (2) as a zoom group, a positive focal biconvex lens (3) as a compensation group, a negative focal biconcave lens (4) as a second compensation group, a positive focal meniscus lens (5) as a rear fixed group, a first plane reflector (6), a second plane reflector (7), a positive focal biconvex lens (8-2) as a relay group, and a negative focal meniscus lens (8-1) as a relay group are sequentially arranged; The normal line of the first plane reflector (6) and the normal line of the second plane reflector (7) form an angle of 45° relative to the optical axis, thereby folding the optical path in a U-shape by 180°; The positive power meniscus lens (1) serving as the front fixed group is an aspherical positive power meniscus lens; The negative optical power biconcave lens (2) used as the zoom group is an aspherical negative optical power biconcave lens; The positive power biconvex lens (3) as a compensation group is an aspherical positive power biconvex lens; The negative optical power biconcave lens (4) serving as the second compensation group is an aspherical negative optical power biconcave lens; The positive power meniscus lens (5) serving as the rear fixed group is a spherical positive power meniscus lens; The positive power biconvex lens (8-2) as the relay group is a positive power aspheric diffraction lens; The negative optical power meniscus lens (8-1) used as the relay group is a spherical negative optical power meniscus lens; The focal lengths of the positive focal power meniscus lens (1) as the front fixed group, the negative focal power biconcave lens (2) as the variable magnification group, the positive focal power biconvex lens (3) as the compensation group, and the negative focal power biconcave lens (4) as the second compensation group must meet the following conditions: 3.2<|fL / f1|<5.6; 16.8<|fL / f2|<28.8; 10.4<|fL / f3|<20.8; 8.2<|fL / f4|<18.2; Wherein, fL is the focal length of the telephoto end of the optical system, f1 is the focal length of the positive focal power meniscus lens (1) as the front fixed group, f2 is the focal length of the negative focal power biconcave lens (2) as the variable magnification group, f3 is the focal length of the positive focal power biconvex lens (3) as the compensation group, and f4 is the focal length of the negative focal power biconcave lens (4) as the second compensation group.

2. The lightweight, large-magnification medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The positive focal length meniscus lens (1) as the front fixed group is made of silicon single crystal; The negative power biconcave lens (2) used as the zoom group is made of germanium single crystal or chalcogenide glass material; The material of the positive power biconvex lens (3) as the compensation group is silicon single crystal; The negative optical power biconcave lens (4) of the second compensation group is made of germanium single crystal, silicon single crystal or chalcogenide glass material; The positive power meniscus lens (5) as the rear fixed group is made of silicon single crystal, chalcogenide glass material or zinc selenide; The material of the positive power biconvex lens (8-2) used as the relay group is silicon single crystal, chalcogenide glass material or zinc selenide; The material of the negative focal length meniscus lens (8-1) used as the relay group is chalcogenide glass material, zinc sulfide or zinc selenide.

3. The lightweight, large-zoom-ratio, medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The positive optical power biconvex lens (3) as a compensation group and the negative optical power biconcave lens (4) as a second compensation group move in the same direction along the optical axis during zooming, thereby realizing a continuous zoom compensation function.

4. The lightweight, large-zoom-ratio, medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The negative optical power biconcave lens (2) as a zoom group moves forward and backward along the optical axis to achieve visual distance focusing and high and low temperature heat elimination.

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