Compact linear medium-wave infrared continuous zooming optical system

Abstract

The invention relates to a compact linear medium-wave infrared continuous zooming optical system, and belongs to the technical field of infrared continuous zooming optical lenses. The problems that in the prior art, a refrigeration type infrared continuous zooming optical system is long in length and large in caliber, and meanwhile, the refrigeration type infrared continuous zooming optical system cannot be compatible with the F number 4.0 and the F number 5.5 are solved. The system comprises a front fixing group, a zooming group, a compensation group and a focusing group which are coaxially arranged in sequence from an object side to an image side, the front fixed group sequentially comprises a first lens with positive focal power and a second lens with negative focal power from an object side to an image side; the zoom group comprises a third lens with negative focal power; the compensation group sequentially comprises a fourth lens with positive focal power and a fifth lens with negative focal power from the object side to the image side; the focusing group sequentially comprises sixth to eighth lenses from the object space to the image space, and the sixth to eighth lenses sequentially have negative focal power, positive focal power and positive focal power. And an optical system compatible with F numbers of 4.0 and 5.5 is realized.

Description

Technical Field

[0001] This invention relates to the field of infrared continuous zoom optical lens technology, and in particular to a compact linear mid-wave infrared continuous zoom optical system. Background Technology

[0002] Infrared imaging systems are passive infrared detector systems with advantages such as anti-interference, good concealment, and high accuracy at night. They are widely used in military fields such as shipborne, reconnaissance, and guidance.

[0003] Continuous zoom lenses can detect targets in a wide field of view and then switch to a narrower field of view for target tracking. During the focal length and field of view transitions, the tracked target remains within the zoom lens's field of view, which is beneficial for searching and tracking high-speed moving targets and solves the problem of target loss with fixed-focus lenses, dual-field-of-view lenses, and triple-field-of-view lenses. A continuous zoom system must satisfy two conditions: continuously variable focal length and stable image plane position.

[0004] Cooled detectors are used in the military field due to their advantages such as high sensitivity, low noise, and good background uniformity. From a design perspective, cooled infrared continuous zoom optical systems require good handling of cold reflections across the entire focal length range, which significantly increases the difficulty of optical design. Enhanced cold reflections can cause image non-uniformity, severely affecting target detection and identification. Current mid-wave cooled infrared optical systems are relatively long, as seen in patents "CN 108169880 A A Compact Continuous Zoom Infrared Optical System" and "CN 111061050 A Mid-Wave Cooled Infrared Zoom Lens with Added Teleconverter Group". Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a compact linear mid-wave infrared continuous zoom optical system to solve the problems of existing cooled infrared continuous zoom optical systems having long lengths, large apertures, and inability to be compatible with F-numbers of 4.0 and 5.5.

[0006] This invention provides a compact linear mid-wave infrared continuous zoom optical system, which includes a front fixed group, a zoom group, a compensation group, and a focusing group arranged coaxially from the object side to the image side.

[0007] The front fixing group, from the object side to the image side, includes a first lens with positive optical power and a second lens with negative optical power in sequence.

[0008] The zoom group includes a third lens with negative optical power;

[0009] The compensation group, from the object side to the image side, includes a fourth lens with positive optical power and a fifth lens with negative optical power.

[0010] The focusing group includes the sixth to eighth lenses from the object side to the image side, and the sixth to eighth lenses have negative optical power, positive optical power, and positive optical power respectively.

[0011] The F-number of this system is either 4.0 or 5.5.

[0012] Furthermore, the first and second lenses are both meniscus lenses with their convex surfaces facing the object; the third lens is a biconcave lens; the fourth lens is a biconvex lens; the fifth lens is a meniscus lens with its concave surface facing the object; the sixth lens is a meniscus lens with its convex surface facing the object; the seventh lens is a biconvex lens; and the eighth lens is a biconvex lens.

[0013] Furthermore, the first, fourth, and eighth lenses are made of silicon; the second, third, and fifth lenses are made of germanium; the sixth lens is made of zinc arsenide; and the seventh lens is made of zinc sulfide.

[0014] Furthermore, the radii of curvature of the first to eighth lenses successively satisfy the following condition:

[0015] 70mm<R1<80mm, 120mm<R1′<130mm,

[0016] 90mm<R2<100mm, 60mm<R2′<70mm,

[0017] -100mm<R3<-80mm, 30mm<R3′<50mm,

[0018] 50mm<R4<70mm,-70mm<R4′<-50mm,

[0019] -80mm<R5<-70mm,-150mm<R5′<-130mm,

[0020] 5mm<R6<10mm, 5mm<R6′<10mm,

[0021] 0mm<R7<100mm,-20mm<R7′<-10mm,

[0022] 70mm<R8<80mm,-70mm<R8′<-50mm,

[0023] Wherein, R1-R8 are the radii of curvature of the first lens to the eighth lens on the object side, and R1′-R8′ are the radii of curvature of the first lens to the eighth lens on the image side.

[0024] Furthermore, under normal temperature and small field of view conditions, the air gap between the first and second lenses is 2.4 mm, the air gap between the second and third lenses is 40 mm, the air gap between the third and fourth lenses is 3 mm, the air gap between the fourth and fifth lenses is 9 mm, the air gap between the fifth and sixth lenses is 12 mm, the air gap between the sixth and seventh lenses is 10.5 mm, the air gap between the seventh and eighth lenses is 3 mm, and the air gap between the eighth lens and the detector window glass is 6.5 mm.

[0025] Under normal temperature and large field of view conditions, the air gap between the second and third lenses is 14.7 mm, the air gap between the third and fourth lenses is 42.5 mm, the air gap between the fourth and fifth lenses is 1.6 mm, and the air gap between the fifth and sixth lenses is 5.2 mm; the air gaps between the remaining lenses are the same as those under the small field of view conditions.

[0026] Furthermore, the center thickness of the first lens is 9mm, the center thickness of the second lens is 4mm, the center thickness of the third lens is 2mm, the center thickness of the fourth lens is 3mm, the center thickness of the fifth lens is 2mm, the center thickness of the sixth lens is 6mm, the center thickness of the seventh lens is 3mm, and the center thickness of the eighth lens is 2.2mm.

[0027] Furthermore, the zoom group exhibits a linear motion trajectory with a stroke of 25.3 mm; the compensation group exhibits a non-linear motion trajectory with a stroke of 15.6 mm and a cam rotation angle of 150°.

[0028] Furthermore, the second and third lenses are aspherical lenses on the image-side, and the fourth, sixth, and eighth lenses are aspherical lenses on the object-side; the first, fifth, and seventh lenses are spherical lenses.

[0029] Furthermore, the system's focal length ranges from 15mm to 300mm.

[0030] Furthermore, the system has a zoom ratio of 20x, a length of 112mm, and a light transmission aperture of 85mm.

[0031] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0032] 1. The optical system of this invention employs a silicon positive lens as the first lens and a germanium negative lens as the second lens in the front fixed group, effectively correcting the chromatic aberration introduced by the front fixed group. The center thickness of the first lens is 9mm, and the center thickness of the second lens is 4mm. While ensuring manufacturing processes, the center thickness of both lenses has been minimized. The air gap between the silicon and germanium lenses is 2.4mm, effectively shortening the overall optical length. Further reduction in the overall optical length would degrade the optical image quality; this is mitigated by using aspherical lenses. The image-side of the second lens in the front fixed group is aspherical, effectively contributing to reducing the optical system length. Furthermore, the entire system adopts a compact, linear layout for secondary imaging, resolving the issue of a significant increase in the aperture of the first lens caused by the rear placement of the cooled detector's cold stop. This reduces the radial space, achieving a light-transmitting aperture of 85mm and a length of 112mm.

[0033] 2. In this invention, the zoom group, the fourth lens of the compensation group, and the fifth lens are three-element zoom. Compared with the conventional two-element zoom method, three-element zoom adds more variables to the zoom data. In this invention, the added variable is the air gap between the fifth lens of the compensation group and the sixth lens of the focusing group. The addition of this variable shortens the zoom travel, that is, shortens the total optical length.

[0034] 3. The focusing group of this invention consists of lenses six through eight. This focusing group compensates for the defocusing caused by high and low temperatures, providing focusing functionality for close-range imaging. Specifically, in a small field of view, at an extreme high temperature of 60°C, the focusing group moves 0.8mm towards the object side; at a low temperature of -40°C, it moves 0.88mm towards the image side. In a large field of view, at a high temperature of 60°C, the focusing group moves 0.3mm towards the object side; at a low temperature of -40°C, it moves 0.36mm towards the image side. To shorten the overall optical length, the seventh lens of the second imaging optical system of this invention uses zinc sulfide material and the eighth lens uses silicon material. Only two lenses are needed to correct inherent aberrations, achieving good image quality. Furthermore, the air gap between the seventh and eighth lenses is only 3mm, effectively contributing to the reduction of the overall optical length. This invention eliminates the rear fixing group. Compared to adding a rear fixing group after the zoom assembly, eliminating the rear fixing group simplifies the structural design and reduces unnecessary components. Including the sixth lens as part of the focusing group further reduces the focusing amount at high and low temperatures.

[0035] 4. This invention does not use a reflector, reducing the possibility of stray light and effectively correcting cold reflections. The system has a small difference in the cold reflection coefficient, reducing the probability of cold reflections in different scenarios, improving background uniformity, increasing the probability of target recognition, and greatly assisting in target tracking.

[0036] 5. The present invention is a continuous zoom lens with a zoom ratio of 20x. The large field of view can be used to search and find targets over a wide area, while the small field of view can be used to track and identify targets in a small area. It can realize the detection of all fields of view and will not lose the target due to the change of field of view during zooming.

[0037] 6. This invention employs a mechanical compensation method for optical design, resulting in high optomechanical reliability, excellent optical axis stability, and mature manufacturing processes. The mechanical compensation zoom system changes the combined focal length of the system through the relative movement of the zoom group and the compensation group, while maintaining the final image plane position, enabling the system to obtain a continuously clear image during zooming. It utilizes a negative zoom group and positive compensation group zoom configuration, allowing the optical system to achieve continuous focal length changes while maintaining image plane stability. The zoom cam curve is smooth without inflection points, resulting in good image quality across the entire focal length range. The mechanical compensation method uses a cam mechanism. The zoom motor drives the cam to rotate via gears. The cam moves the outer frame pins of the zoom group and the compensation group within the cam guide groove, thereby causing the zoom group lens and the compensation group lens to move accordingly along the optical axis, completing the continuous zooming of the optical system. The zoom group travel is 25.3 mm, the compensation group travel is 15.6 mm, and the cam rotation angle is 150°. It can achieve 20x zoom and image compensation within a limited space. The applicable F-numbers for the zoom optical system are 4.0 or 5.5.

[0038] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0039] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0040] Figure 1 This is a schematic diagram of a compact linear mid-wave infrared continuous zoom optical system with a small field of view.

[0041] Figure 2 A schematic diagram of a large field-of-view optical path for a compact linear mid-wave infrared continuous zoom optical system;

[0042] Figure 3 The small field-of-view optical path transfer function diagram of a compact linear mid-wave infrared continuous zoom optical system;

[0043] Figure 4 The large field-of-view optical path transfer function diagram of a compact linear mid-wave infrared continuous zoom optical system;

[0044] Figure 5 It is the cold reflection coefficient of a compact linear mid-wave infrared continuous zoom optical system.

[0045] Figure label:

[0046] 1-First lens;

[0047] 2-Second lens;

[0048] 3-Third lens;

[0049] 4-Fourth lens;

[0050] 5 - The fifth lens;

[0051] 6-Sixth lens;

[0052] 7-Seventh Lens;

[0053] 8 - The eighth lens;

[0054] 9-Front fixed group;

[0055] 10-Focusing Group;

[0056] 11-Detector optical components. Detailed Implementation

[0057] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0058] A specific embodiment of the present invention discloses a compact linear mid-wave infrared continuous zoom optical system, the system comprising a front fixed group 9, a zoom group, a compensation group, and a focusing group 10 arranged coaxially from the object side to the image side;

[0059] The front fixed assembly 9, from the object side to the image side, includes a first lens 1 with positive optical power and a second lens 2 with negative optical power.

[0060] The zoom group includes a third lens 3 with negative optical power;

[0061] The compensation group, from the object side to the image side, includes a fourth lens 4 with positive optical power and a fifth lens 5 with negative optical power.

[0062] The focusing group 10 includes the sixth to eighth lenses 8 from the object side to the image side, and the sixth lens 6 to the eighth lens 8 have negative optical power, positive optical power and positive optical power respectively.

[0063] The F-number of this system is either 4.0 or 5.5.

[0064] Specifically, this invention does not use a reflector, reducing the possibility of stray light, and cold reflection is well corrected. Figure 5 The cold reflection coefficient of the optical system is listed. The small difference in the cold reflection coefficient reduces the probability of cold reflection in different scenarios, improves background uniformity, and increases the probability of target recognition.

[0065] The first and second lenses are both meniscus lenses with their convex surfaces facing the object; the third lens 3 is a biconcave lens; the fourth lens 4 is a biconvex lens; the fifth lens 5 is a meniscus lens with its concave surface facing the object; the sixth lens 6 is a meniscus lens with its convex surface facing the object; the seventh lens 7 is a biconvex lens; and the eighth lens 8 is a biconvex lens.

[0066] Specifically, the first lens 1 is a meniscus lens with its convex surface facing the object side, possessing positive optical power. It is made of silicon material, which has a high refractive index and low dispersion, thus facilitating aberration correction. The second lens 2 is also a meniscus lens with its convex surface facing the object side, possessing negative optical power. It is made of germanium material, whose refractive index and dispersion coefficient are higher than those of silicon, thus facilitating the elimination of chromatic aberration and balancing on-axis aberrations.

[0067] The first lens 1, the fourth lens 4, and the eighth lens 8 are made of silicon; the second lens 2, the third lens 3, and the fifth lens 5 are made of germanium; the sixth lens 6 is made of zinc selenide, and the seventh lens 7 is made of zinc sulfide.

[0068] The radii of curvature of the first lens 1 to the eighth lens 8 successively satisfy the following conditions:

[0069] 70mm<R1<80mm, 120mm<R1′<130mm,

[0070] 90mm<R2<100mm, 60mm<R2′<70mm,

[0071] -100mm<R3<-80mm, 30mm<R3′<50mm,

[0072] 50mm<R4<70mm,-70mm<R4′<-50mm,

[0073] -80mm<R5<-70mm,-150mm<R5′<-130mm,

[0074] 5mm<R6<10mm, 5mm<R6′<10mm,

[0075] 0mm<R7<100mm,-20mm<R7′<-10mm,

[0076] 70mm<R8<80mm,-70mm<R8′<-50mm,

[0077] Wherein, R1-R8 are the radii of curvature of the first lens 1 to the eighth lens 8 on the object side, and R1′-R8′ are the radii of curvature of the first lens 1 to the eighth lens 8 on the image side.

[0078] Under normal temperature and small field of view conditions, the air gap between the first lens 1 and the second lens 2 is 2.4 mm, the air gap between the second lens 2 and the third lens 3 is 40 mm, the air gap between the third lens 3 and the fourth lens 4 is 3 mm, the air gap between the fourth lens 4 and the fifth lens 5 is 9 mm, the air gap between the fifth lens 5 and the sixth lens 6 is 12 mm, the air gap between the sixth lens 6 and the seventh lens 7 is 10.5 mm, the air gap between the seventh lens 7 and the eighth lens 8 is 3 mm, and the air gap between the eighth lens 8 and the detector window glass is 6.5 mm.

[0079] Under normal temperature and large field of view conditions, the air gap between the second lens 2 and the third lens 3 is 14.7 mm, the air gap between the third lens 3 and the fourth lens 4 is 42.5 mm, the air gap between the fourth lens 4 and the fifth lens 5 is 1.6 mm, and the air gap between the fifth lens 5 and the sixth lens 6 is 5.2 mm; the air gaps between the remaining lenses are the same as those under the small field of view conditions.

[0080] The center thickness of the first lens 1 is 9mm, the center thickness of the second lens 2 is 4mm, the center thickness of the third lens 3 is 2mm, the center thickness of the fourth lens 4 is 3mm, the center thickness of the fifth lens 5 is 2mm, the center thickness of the sixth lens 6 is 6mm, the center thickness of the seventh lens 7 is 3mm, and the center thickness of the eighth lens 8 is 2.2mm.

[0081] Table 1 shows the parameters of each lens in the optical system of a specific embodiment of the present invention.

[0082] Table 1 Parameters of each lens in the optical system

[0083]

[0084]

[0085] The focusing assembly compensates for the defocusing caused by high and low temperatures, providing focusing functionality for close-range imaging. Therefore, the focusing assembly will move as a whole under high and low temperature conditions. In a small field of view, at the extreme high temperature of 60℃, the three lenses of the focusing assembly move synchronously 0.8mm towards the object side; in the extreme low temperature of -40℃, the three lenses move synchronously 0.88mm towards the image side. In a large field of view, at the extreme high temperature of 60℃, the focusing assembly moves 0.3mm towards the object side; in the extreme low temperature of -40℃, the focusing assembly moves 0.36mm towards the image side. Therefore, the air gaps between the fifth and sixth lenses, and between the eighth lens and the detector window glass, will change as shown in Table 1. Surfaces numbered S1, S3, S5, S7, S9, S11, S13, S15, S17, S19, and S21 are objects-oriented surfaces; surfaces numbered S2, S4, S6, S8, S10, S12, S14, S16, S18, S20, and S22 are images-oriented surfaces.

[0086] like Figure 1 The optical components of the detector 11 include a detector window glass, a detector filter, and a detector aperture.

[0087] The zoom group exhibits a linear motion trajectory with a stroke of 25.3 mm; the compensation group exhibits a non-linear motion trajectory with a stroke of 15.6 mm and a cam rotation angle of 150°.

[0088] Specifically, the zoom group is a biconcave lens with negative optical power, made of germanium material, and exhibits a linear motion trajectory in the optical path, enabling continuous change of the system's focal length.

[0089] The fourth lens 4 in the compensation group is a biconvex lens with negative optical power. It is made of silicon and exhibits a non-linear motion trajectory with a non-linear step size. It is used to compensate for the image plane position shift caused by the zoom group during zooming, maintain image plane stability, and correct aberrations generated by the zoom group at different positions.

[0090] The fifth lens 5 of the compensation group is a meniscus lens with its concave surface facing the object surface. It has negative optical power and is made of germanium. It has the same function as the fourth lens 4 of the compensation group. The fifth lens 5 of the compensation group is a monolithic lens and exhibits a nonlinear motion trajectory.

[0091] Specifically, the optical design is based on a mechanical compensation method. This mechanical compensation method uses a cam mechanism. The zoom motor and the focus motor drive the cam to rotate via gears. The zoom motor drives the cam to rotate, and the cam moves the outer frame pins of the zoom group and the compensation group within the cam guide groove, thereby causing the zoom group lens and the compensation group lens to move accordingly along the optical axis, completing the continuous zoom of the optical system. The focus motor drives the cam to rotate via gears, and the cam moves the outer frame pin of the focus group 10 within the cam guide groove, thereby causing the focus group 10 lens to move accordingly along the optical axis. The focus group 10 is used to correct residual aberrations and compensate for high and low temperatures.

[0092] It adopts a zoom form with negative group zoom and positive group compensation. The optical system can achieve continuous focal length change and maintain image plane stability. The zoom cam curve is smooth without inflection points, and the image quality is good across the entire focal length.

[0093] like Figure 1 The diagram shows a small field-of-view optical path of the optical system; as shown Figure 2 The diagram shows the optical path of the large field of view optical system.

[0094] like Figure 3 The diagram shows the optical path transfer function for a small field of view; as shown... Figure 4 The diagram shows the optical path transfer function for a large field of view.

[0095] The second lens 2 and the third lens 3 are aspherical lenses on the image side, the fourth lens 4, the sixth lens 6, and the eighth lens 8 are aspherical lenses on the object side, and the first lens 1, the fifth lens 5, and the seventh lens 7 are spherical lenses.

[0096] Specifically, the formula for aspherical surfaces is as follows:

[0097]

[0098] Where Z is the position along the optical axis; r is the radial height; c is the radius of curvature; k is the conic coefficient; and A, B, C, and D are aspheric coefficients. Table 2 shows the aspheric coefficient table.

[0099] Table 2 Aspherical Coefficients

[0100] Surface serial number k A B C D S4 0 3.956189e-08 6.3736659e-012 3.0011645e-015 S6 0 -1.2494076e-05 3.221488e-08 -2.1554281e-010 8.26624e-013 S7 0 -8.965402e-06 -3.69837e-09 8.956148e-011 -2.632984e-013 S11 0 -3.58364e-05 6.731023e-07 -2.128553e-08 S15 0 -2.67526e-05 4.1311693e-08 -5.995998e-010

[0101] Wherein, S4 is the image-side surface of the second lens 2, S6 is the image-side surface of the third lens 3, S7 is the object-side surface of the fourth lens 4, S11 is the object-side surface of the sixth lens 6, and S15 is the object-side surface of the eighth lens 8.

[0102] The system's focal length ranges from 15mm to 300mm.

[0103] The system has a zoom ratio of 20x, a length of 112mm, and a light transmission aperture of 85mm.

[0104] Specifically, the length of 112mm represents the distance between the most convex point of the first lens 1 facing the object side and the most convex point of the eighth lens 8 of the focusing group facing the image side. The detector is a cooled mid-wave 640×512 detector with a pixel size of 15μm and an operating wavelength of 3μm-5μm.

[0105] The focal lengths of the large and small fields of view are 15mm and 300mm respectively, and the zoom ratio of the large and small fields of view is 20x.

[0106] Compared with existing technologies, the optical system provided in this embodiment uses a silicon positive lens (first lens 1) and a germanium negative lens (second lens 2) in the front fixing group 9, which effectively corrects the chromatic aberration caused by the front fixing group 9. The center thickness of the first lens 1 is 9mm, and the center thickness of the second lens 2 is 4mm. While ensuring the manufacturing process, the center thickness of the two lenses has been made as thin as possible. The air gap between silicon and germanium is 2.4mm, which effectively shortens the total optical length. If the total optical length is further reduced, the optical imaging quality will deteriorate. The application of aspherical lenses improves this phenomenon. The image-side of the second lens 2 in the front fixing group 9 is aspherical, which effectively helps to reduce the length of the optical system. In addition, the entire system adopts a compact linear layout secondary imaging optical system, which solves the problem of the increased aperture of the first lens 1 caused by the rear placement of the cooled detector's cold aperture, reduces the radial space, and can achieve a light-transmitting aperture of 85mm and a length of 112mm. The zoom group, compensation group (fourth lens 4, fifth lens 5) provided in this embodiment constitute a three-element zoom. Compared to the conventional two-element zoom method, three-element zoom adds more variables to the zoom data. In this embodiment, the added variable is the air gap between the compensation group (fifth lens 5) and the focusing group (sixth lens 6). This increase in variable shortens the zoom travel, i.e., shortens the total optical length. The focusing group 10 provided in this embodiment consists of the sixth lens 6 to the eighth lens 8. The focusing group 10 compensates for the defocusing caused by high and low temperatures, providing focusing functionality for close-range imaging. Specifically, in the small field of view, under extreme conditions of 60°C, the focusing group moves 0.8mm towards the object side; at -40°C, it moves 0.88mm towards the image side. In the large field of view, at 60°C, it moves 0.3mm towards the object side; at -40°C, it moves 0.36mm towards the image side. To shorten the overall optical length, in this embodiment, the seventh lens 7 of the second imaging optical system is made of zinc sulfide and the eighth lens 8 is made of silicon. Only two lenses are needed to correct inherent aberrations, achieving good image quality. Furthermore, the air gap between the seventh lens 7 and the eighth lens 8 is only 3mm, effectively contributing to the reduction of the overall optical length. This invention eliminates the rear fixing group. Compared to adding a rear fixing group after the zoom assembly, eliminating the rear fixing group simplifies the structural design and reduces unnecessary components. This invention incorporates the sixth lens 6 as part of the focusing group 10, resulting in smaller focusing requirements at high and low temperatures. This invention does not use a reflector, reducing the possibility of stray light, and cold reflections are well corrected. Figure 5The cold reflection coefficient of this optical system is listed. The small difference in this coefficient reduces the probability of cold reflections in different scenes, improves background uniformity, increases target recognition probability, and greatly assists in target tracking. The optical system provided in this embodiment features a 20x continuous zoom lens. Its large field of view allows for wide-range target search and discovery, while its small field of view enables small-range target tracking and identification. It can achieve reconnaissance across all fields of view without losing targets due to changes in the field of view during zooming. This embodiment uses a mechanical compensation method for optical design, resulting in high optomechanical reliability, good optical axis stability, and mature technology. The mechanical compensation zoom system changes the combined focal length of the system through the relative movement of the zoom group and the compensation group, while maintaining the final image plane position, allowing the system to obtain a continuously clear image during zooming. Employing a negative zoom group and positive compensation zoom method, the optical system can achieve continuous focal length changes while maintaining image plane stability. The zoom cam curve is smooth without inflection points, resulting in good image quality across the entire focal length. The mechanical compensation method employs a cam mechanism. The zoom motor drives the cam to rotate via gears. The cam, in turn, moves the outer frame pins of the zoom and compensation groups within their guide grooves, thereby causing the zoom and compensation lenses to move along the optical axis, completing continuous zooming of the optical system. The zoom group has a travel of 25.3 mm, the compensation group has a travel of 15.6 mm, and the cam rotation angle is 150°. It can achieve 20x zoom and image compensation within a limited space. The applicable F-numbers for the zoom optical system are 4.0 or 5.5.

[0107] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0108] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A compact linear mid-wave infrared continuous zoom optical system, characterized in that, The system includes a front fixed group, a zoom group, a compensation group, and a focusing group, which are arranged coaxially from the object side to the image side. The front fixing group, from the object side to the image side, includes a first lens with positive optical power and a second lens with negative optical power in sequence. The zoom group includes a third lens with negative optical power; The compensation group, from the object side to the image side, includes a fourth lens with positive optical power and a fifth lens with negative optical power. The focusing group includes the sixth to eighth lenses from the object side to the image side, and the sixth to eighth lenses have negative optical power, positive optical power, and positive optical power respectively. The F-number of this system is either 4.0 or 5.

5.

2. The infrared continuous zoom optical system according to claim 1, characterized in that, The first and second lenses are both meniscus lenses with their convex surfaces facing the object; the third lens is a biconcave lens; the fourth lens is a biconvex lens; the fifth lens is a meniscus lens with its concave surface facing the object; the sixth lens is a meniscus lens with its convex surface facing the object; the seventh lens is a biconvex lens; and the eighth lens is a biconvex lens.

3. The infrared continuous zoom optical system according to claim 2, characterized in that, The first, fourth, and eighth lenses are made of silicon; the second, third, and fifth lenses are made of germanium; the sixth lens is made of zinc arsenide; and the seventh lens is made of zinc sulfide.

4. The infrared continuous zoom optical system according to claim 2, characterized in that, The radii of curvature of the first to eighth lenses successively satisfy the following conditions: 70mm<R1<80mm, 120mm<R1′<130mm, 90mm<R2<100mm, 60mm<R2′<70mm, -100mm<R3<-80mm, 30mm<R3′<50mm, 50mm<R4<70mm,-70mm<R4′<-50mm, -80mm<R5<-70mm,-150mm<R5′<-130mm, 5mm<R6<10mm, 5mm<R6′<10mm, 0mm<R7<100mm,-20mm<R7′<-10mm, 70mm<R8<80mm,-70mm<R8′<-50mm, Wherein, R1-R8 are the radii of curvature of the first lens to the eighth lens on the object side, and R1′-R8′ are the radii of curvature of the first lens to the eighth lens on the image side.

5. The infrared continuous zoom optical system according to claim 4, characterized in that, Under normal temperature and small field of view conditions, the air gap between the first and second lenses is 2.4 mm, the air gap between the second and third lenses is 40 mm, the air gap between the third and fourth lenses is 3 mm, the air gap between the fourth and fifth lenses is 9 mm, the air gap between the fifth and sixth lenses is 12 mm, the air gap between the sixth and seventh lenses is 10.5 mm, the air gap between the seventh and eighth lenses is 3 mm, and the air gap between the eighth lens and the detector window glass is 6.5 mm. Under normal temperature and large field of view conditions, the air gap between the second and third lenses is 14.7 mm, the air gap between the third and fourth lenses is 42.5 mm, the air gap between the fourth and fifth lenses is 1.6 mm, and the air gap between the fifth and sixth lenses is 5.2 mm; the air gaps between the remaining lenses are the same as those under the small field of view conditions.

6. The infrared continuous zoom optical system according to claim 5, characterized in that, The center thickness of the first lens is 9mm, the center thickness of the second lens is 4mm, the center thickness of the third lens is 2mm, the center thickness of the fourth lens is 3mm, the center thickness of the fifth lens is 2mm, the center thickness of the sixth lens is 6mm, the center thickness of the seventh lens is 3mm, and the center thickness of the eighth lens is 2.2mm.

7. The infrared continuous zoom optical system according to claim 1, characterized in that, The zoom group exhibits a linear motion trajectory with a stroke of 25.3 mm; the compensation group exhibits a non-linear motion trajectory with a stroke of 15.6 mm and a cam rotation angle of 150°.

8. The infrared continuous zoom optical system according to claim 1, characterized in that, The second and third lenses are aspherical lenses on the image-side, and the fourth, sixth, and eighth lenses are aspherical lenses on the object-side; the first, fifth, and seventh lenses are spherical lenses.

9. The infrared continuous zoom optical system according to claim 1, characterized in that, The system's focal length ranges from 15mm to 300mm.

10. The infrared continuous zoom optical system according to claim 1, characterized in that, The system has a zoom ratio of 20x, a length of 112mm, and a light transmission aperture of 85mm.

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