Tilted imaging airborne long-wave infrared equal-ground-resolution continuous zooming system
By introducing a reflection subsystem and a zoom subsystem into the tilt imaging system, the problem of uneven imaging resolution at different object distances was solved, achieving uniform imaging resolution and information acquisition at different object distances, thus enhancing airborne stealth and target recognition capabilities.
Patent Information
- Application Number
- CN202511396687.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-28
- Publication Date
- 2025-11-18
AI Technical Summary
Existing tilt imaging systems exhibit higher imaging resolution at lower object distances than at higher object distances when imaging at different object distances, resulting in uneven image resolution and incomplete information acquisition.
The system employs a reflection subsystem and a zoom subsystem. The reflection subsystem includes a primary mirror, a secondary mirror, and a third mirror. The primary and secondary mirrors have standard reflective surfaces, while the third mirror has a freeform surface. The zoom subsystem includes a front fixed group, a zoom group, and a compensation group, enabling continuous zoom from 50 to 100 mm. The zoom interval is provided by moving the lens, ensuring uniform imaging resolution at different object distances.
It achieves uniformity of imaging resolution at different object distances, improves the integrity of information acquisition, enhances airborne stealth and target recognition capabilities, and is suitable for environments such as border reconnaissance.
Smart Images
Figure CN120972353A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical imaging technology, and more specifically to a tilt imaging airborne long-wave infrared and other ground resolution continuous zoom system. Background Technology
[0002] Infrared systems offer significant advantages over traditional optics. For example, they can search, identify, and track targets in adverse weather conditions. Their main applications include military and security, industrial inspection, medical diagnostics, autonomous driving, and heat leak detection. The core advantage of long-wave infrared is its ability to passively receive the heat radiated by the object itself, enabling imaging without an external light source. Therefore, it maintains high reliability even in complete darkness, smoke, or low-light environments. Furthermore, its strong atmospheric penetration (less affected by haze) makes it suitable for long-distance monitoring. Conventional imaging systems, such as cameras, photograph the target directly. However, in specialized fields, such as observing the ground with obstacles from high altitudes, cameras positioned directly above the area cannot observe it. This necessitates a special imaging system: an oblique imaging system.
[0003] Current tilt imaging systems produce images with higher resolution at lower object distances than at higher object distances, resulting in uneven image resolution and incomplete information acquisition. Summary of the Invention
[0004] In view of this, the present invention provides an airborne long-wave infrared and other ground resolution continuous zoom system for tilt imaging, which solves the problem of uneven image resolution and incomplete information acquisition caused by different object distances.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] A tilting imaging airborne long-wave infrared ground resolution continuous zoom system includes: a reflection subsystem and a zoom subsystem;
[0007] The reflection subsystem includes a primary mirror, a secondary mirror, and a third mirror. The primary mirror is positioned on the incident light path of the object-side ray, the secondary mirror is located on the reflected light path of the primary mirror, and the third mirror is located on the reflected light path of the secondary mirror. The reflecting surfaces of the primary mirror and the secondary mirror are standard surfaces, while the reflecting surface of the third mirror is a freeform surface.
[0008] The zoom subsystem is positioned on the reflected light path of the third mirror and is used for imaging at different object distances.
[0009] Furthermore, the reflective subsystem is an off-axis three-mirror system, with its aperture stop located on the third mirror and an off-axis field of view angle of 13°; the object-image relationship of the reflective subsystem is expressed as follows:
[0010]
[0011] Where ω is the field of view angle, 10°≤ω≤16°, as the field of view angle increases, the distance between the observation point and the point to be observed becomes closer and closer; FFL(ω) is the focal length of the field of view; GR(ω) is the ground resolution corresponding to the field of view angle ω; a is the size of a single pixel unit; and H is the altitude of the tilting imaging lens.
[0012] Furthermore, after adding a small increment Δω to the field of view angle ω, the image height on the image plane changes by Δh, and the focal length FFL(ω) is:
[0013]
[0014] Furthermore, the optical powers of the primary mirror, the secondary mirror, and the third mirror are positive, negative, and positive, respectively; the radii of curvature at the vertices of the three mirrors approximately satisfy the Pittswan condition. R1, R2, and R3 are the radii of the primary mirror, secondary mirror, and tertiary mirror, respectively.
[0015] Furthermore, the zoom subsystem achieves continuous zoom of 50-100mm, including a front fixed group, a zoom group, a compensation group, and a rear fixed group; the front fixed group includes a first lens L1, the zoom group includes a second lens L2 and a third lens L3, the compensation group includes a fourth lens L4, and the rear fixed group includes a fifth lens L5 and a sixth lens L6.
[0016] Furthermore, the first lens L1, the third lens L3, the fourth lens L4, and the sixth lens L6 are made of germanium, while the second lens L2 and the fifth lens L5 are made of zinc selenide.
[0017] Furthermore, for any lens, the light incident surface is taken as the object side surface, and the light exit surface is taken as the image side surface.
[0018] The center thickness of the first lens L1 is -21.088 mm, the object side radius of curvature is -101.916 mm, and the image side radius of curvature is -141.603 mm.
[0019] The second lens L2 has a center thickness of -16.607 mm, an object side radius of curvature of -101.160 mm, and an image side radius of curvature of -87.153 mm.
[0020] The third lens L3 has a center thickness of -22.689 mm, an object-side radius of curvature of 313.360 mm, and an image-side radius of curvature of 174.908 mm.
[0021] The fourth lens L4 has a center thickness of -22.619 mm, an object-side radius of curvature of -120.434 mm, and an image-side radius of curvature of -134.541 mm.
[0022] The fifth lens L5 has a center thickness of -13.786 mm, an object-side radius of curvature of 39.689 mm, and an image-side radius of curvature of 53.480 mm.
[0023] The sixth lens L6 has a center thickness of -22.816 mm, an object-side radius of curvature of -48.277 mm, and an image-side radius of curvature of -59.436 mm.
[0024] Furthermore, the object-side and image-side surfaces of the first lens L1, the image-side surface of the second lens L2, the object-side and image-side surfaces of the fifth lens L5, and the object-side and image-side surfaces of the sixth lens L6 are all aspherical. The expression for an aspherical surface is:
[0025]
[0026] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R, where R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; and A, B, C, D, and E are higher-order aspherical coefficients.
[0027] Furthermore, in the zoom subsystem, three zoom intervals are provided by moving the first lens L1, the third lens L3, and the fourth lens L4; the air thickness variation range of the image side of the first lens L1 is -85.197mm to -61.041mm; the air thickness variation range of the image side of the second lens L2 is -13.188mm to -9.311mm; and the air thickness variation range of the image side of the fourth lens L4 is -41.695mm to -69.728mm.
[0028] Furthermore, the zoom system has a total length of 482.8 mm, a rectangular field of view of 5.5°×4.4°~10.86°×8.78°, and is compatible with detectors with a resolution of 640×512 and a pixel size of 15μm.
[0029] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:
[0030] The zoom subsystem of this invention, compared to a fixed-focus system, can image at different object distances. Furthermore, the equal ground resolution system achieved by freeform surfaces allows for tilted shooting, improving airborne stealth and making it highly valuable in environments such as border reconnaissance. It also facilitates target recognition and 3D reconstruction technology. Simultaneously, the zoom system's advantage over a fixed-focus system is that it can produce clear images at various altitudes on the UAV. The reflection subsystem also solves the problem of uneven image resolution and incomplete information acquisition caused by varying object distances. Attached Figure Description
[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0032] Figure 1 This is a schematic diagram of the structure of the tilt imaging airborne long-wave infrared and other ground resolution continuous zoom system provided by the present invention.
[0033] Figure 2 This is a schematic diagram showing the positional relationship between the tilting imaging lens and the area to be observed.
[0034] Figure 3 A diagram showing the relationship between the focal length and the field of view of an optical system used as a tilting imaging lens, provided in an embodiment of the present invention.
[0035] Figure 4 This is a resolution comparison diagram between the image generated by the system of the present invention (i.e., the optimized system) and the image generated by the conventional optical system (i.e., the unoptimized system).
[0036] Figure 5 The transfer function diagram of the short focal length optical system provided in the embodiment of the present invention.
[0037] Figure 6 A dot diagram of the short focal length optical system provided in an embodiment of the present invention.
[0038] Figure 7 The transfer function diagram of the optical system at the focal end of the lens provided in the embodiment of the present invention.
[0039] Figure 8 A dot diagram of the focal length optical system in a lens provided in an embodiment of the present invention.
[0040] Figure 9 The transfer function diagram of the telephoto end optical system of the lens provided in the embodiment of the present invention.
[0041] Figure 10 A dot diagram of the telephoto end optical system of the lens provided in an embodiment of the present invention. Detailed Implementation
[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0043] like Figure 1 As shown, this embodiment of the invention discloses an airborne long-wave infrared ground resolution continuous zoom system for oblique imaging, comprising: a reflection subsystem and a zoom subsystem;
[0044] The reflection subsystem includes a primary mirror M1, a secondary mirror M2, and a third mirror M3. The primary mirror M1 is positioned on the incident light path of the object-side ray, the secondary mirror M2 is located on the reflected light path of the primary mirror M1, and the third mirror M3 is located on the reflected light path of the secondary mirror M2. The order in which the light passes through the mirrors from incident to exit is as follows: first reflected by the primary mirror M1, then incident on the secondary mirror M2, then exiting through the secondary mirror M2, and finally incident on the third mirror M3. The reflecting surfaces of the primary mirror M1 and the secondary mirror M2 are standard surfaces, while the reflecting surface of the third mirror M3 is a freeform surface. Through the unique light-adjusting function of the freeform surface of the third mirror M3, the system can achieve equal ground resolution imaging.
[0045] The zoom subsystem is located in the reflected light path of the third mirror and is used for imaging at different object distances.
[0046] The zoom subsystem enables continuous zoom from 50-100mm and includes a front fixed group, a zoom group, a compensation group, and a rear fixed group. The front fixed group includes a first lens L1, the zoom group includes a second lens L2 and a third lens L3, the compensation group includes a fourth lens L4, and the rear fixed group includes a fifth lens L5 and a sixth lens L6. Its optical path transmission is as follows: Figure 3 As shown.
[0047] In one specific embodiment, the reflector subsystem is an off-axis three-mirror system. The system avoids obstruction by being off-axis. The system's optical path is the main ray that propagates along the line connecting the vertices of each element. The secondary mirror is located on the focal plane of the third mirror, and the aperture stop is located on the third mirror. The off-axis angle of the field of view is 13°. For ease of assembly, none of the three mirrors are tilted.
[0048] The optical powers of the primary, secondary, and third reflecting mirrors are positive, negative, and positive (i.e., concave, convex, and concave), respectively; the radii of curvature at the vertices of the three reflecting mirrors approximately satisfy the Pittswan condition. R1, R2, and R3 are the radii of the primary mirror, secondary mirror, and third mirror, respectively. The radii and surface shapes of the primary mirror M1, secondary mirror M2, and third mirror M3 were optimized using optical design software, and the specific structural parameters obtained are shown in Table 1.
[0049] Table 1. Parameters and coefficients of the three mirrors in the off-axis three-mirror system.
[0050] parameter M1 M2 M3 Radius (mm) -505.1 -120.5 -69.9 Interval (mm) -90.798 90.798 -112.16 Half-diameter (mm) 63.74 11.005 14.16 Inclination (°) 0 0 0 Eccentricity (mm) -97.83 64.62 -17.66 Conic coefficient -2.676 2.492 -1.325
[0051] Note: The interval along the X-axis is +X from left to right and -X from right to left. The radius is the radius of curvature. Positive and negative lenses exist, so the radius can be positive or negative.
[0052] The distance between the primary reflector M1 and the secondary reflector M2 along the z-axis is between 90 mm and 91 mm; the distance between the secondary reflector M2 and the third reflector M3 along the z-axis is between 90 mm and 91 mm.
[0053] In another embodiment, the three reflecting mirrors M3 use an xy polynomial freeform surface. Generally, xy polynomial freeform surfaces are easier to obtain better image quality than aspherical surfaces. The reflecting surface of the third reflecting mirror M3 is an xy polynomial surface with a highest order of 5, retaining only the even-degree terms of x. The equation of this xy polynomial surface is:
[0054]
[0055] Where z is the surface elevation, c is the surface curvature, k is the quadratic surface coefficient, and A i It is the coefficient of the i-th term in the polynomial. Since the system is symmetric about the yoz plane, the freeform surface can retain only the even-degree terms with respect to x. At the same time, higher-degree terms increase the manufacturing difficulty, while too low a degree increases the design difficulty of the system.
[0056] For the curvature c, quadratic surface coefficient k, and values of each coefficient in the xy polynomial of the third reflecting mirror M3, please refer to Table 2. It is understood that the values of curvature c, quadratic surface coefficient k, and each coefficient are not limited to those in Table 2, and those skilled in the art can adjust them according to actual needs.
[0057] Table 2: Parameters and coefficients of the third mirror in an off-axis three-mirror system
[0058] polynomial Third reflector coefficient <![CDATA[y1]]> -0.297 x2 3.54 x 10 -3 ]] [ y2 ] 3.141 x 10 -3 ]] <![CDATA[x2y1]]> <![CDATA[-9.598×10 -6 ]]> <![CDATA[y3]]> <![CDATA[-1.081×10 -5 ]]> <![CDATA[x4]]> <![CDATA[-1.734×10 -7 ]]> <![CDATA[x2y2]]> <![CDATA[-3.9×10 -7 ]]> <![CDATA[y4]]> <![CDATA[-2.227×10 -7 ]]> <![CDATA[x4y1]]> <![CDATA[-5.055×10 -10 ]]> <![CDATA[x2y3]]> <![CDATA[-1.215×10 -9 ]]> <![CDATA[y5]]> <![CDATA[-7.49×10 -10 ]]>
[0059] The materials of the primary reflector M1, secondary reflector M2, and third reflector M3 are not limited, as long as they have high reflectivity. The primary reflector M1, secondary reflector M2, and third reflector M3 can be made of metals such as aluminum. To further increase the reflectivity of the primary reflector M1, secondary reflector M2, and third reflector M3, a high-reflectivity film can be deposited on their respective reflective surfaces. This high-reflectivity film can be a gold film. In this embodiment, the primary reflector M1, secondary reflector M2, and third reflector M3 all use aluminum as the substrate, and a single layer of gold film is deposited on their reflective surfaces.
[0060] Figure 2 The relationship between ground resolution and instantaneous field of view is shown, where H is the altitude of the lens and ∠POQ is the instantaneous field of view angle corresponding to the evaluated ω field of view. Figure 2 The instantaneous field of view angle is magnified; the actual instantaneous field of view angle is very small. PQ is the ground resolution corresponding to the ω-field of view to be evaluated. Draw a perpendicular line from point P to OQ, with PS perpendicular to OQ.
[0061] Figure 2 In this system, ∠COP is the observation angle of the ω-field of view. The system's field of view is greater than or equal to 10° and less than or equal to 16°. A 10° field of view is used to observe distant targets, and a 16° field of view is used to observe nearby targets. As the field of view increases, the distance between the observation point and the target point decreases. That is, the observation angle corresponding to a 10° field of view is 16°, and the observation angle corresponding to a 16° field of view is 10°. Therefore, the observation angle ∠COP = -26° + ω. For ease of calculation, an approximate relationship between ground resolution and field of view focal length is given here. Since ∠POQ is very small, ∠COP ≈ ∠COQ, and ∠CPO ≈ ∠CQO. Therefore, ∠OPS ≈ ∠COP. Hence:
[0062] PS=PQ×cos(∠OPS)≈PQ×cos(∠COP)
[0063] Since the instantaneous field of view is very small, and PQ is also very small, OP and OS are approximately equal. Therefore:
[0064]
[0065] The relationship between the instantaneous field of view angle ∠POQ and the focal length of the field of view is:
[0066]
[0067] Where 'a' is the size of a single pixel unit. Representing PQ as GR(ω), the relationship between the field of view focal length and ground resolution can be obtained by combining the above formulas, expressed as:
[0068]
[0069] Where ω is the field of view angle, 10°≤ω≤16°, as the field of view angle increases, the distance between the observation point and the point to be observed becomes closer and closer; FFL(ω) is the focal length of the field of view; GR(ω) is the ground resolution corresponding to the field of view angle ω; a is the size of a single pixel unit; and H is the altitude of the tilting imaging lens.
[0070] After obtaining the above formula, given the ground resolution value, the size of a single pixel unit, and the altitude of the tilting imaging lens, the desired field-of-view focal length distribution can be obtained, i.e., FFL(ω) in the formula. This allows for the calculation of the desired field-of-view focal length distribution pattern when the field of view angle is between 10° and 16°, as shown below. Figure 3 As shown.
[0071] The field of view focal length (FFL(ω)) reflects the change in image height (Δh) on the image plane after a small increment Δω is added to the ω-field of view. The field of view focal length (FFL(ω)) is:
[0072]
[0073] Based on the above formula, given the distribution of field focal lengths (FFL) (ω) corresponding to each field of view, the expected image height value of each field of view can be calculated according to this distribution. This expected image height value represents the new object-image relationship.
[0074] For different fields of view, light rays will converge to different image points. The formula for calculating the ideal image point is as follows:
[0075]
[0076] Among them, T ideal,x T ideal,y T ideal,z Let X, Y, and Z represent the ideal image points of the X, Y, and Z axes, respectively, and let α0 represent the tilt angle about the X-axis, ω... x ω represents the angle value in the X direction. x,central Represents the center image point of the X-axis, ω y ω represents the angle value in the Y direction. y,central The center image point on the Y-axis is represented by x0, y0, and z0, which represent the actual image heights in the X, Y, and Z directions, respectively.
[0077] In one embodiment, the first lens L1, the third lens L3, the fourth lens L4, and the sixth lens L6 are made of germanium, and the second lens L2 and the fifth lens L5 are made of zinc selenide.
[0078] For any lens, the light incident surface is taken as the object side surface, and the light exit surface is taken as the image side surface.
[0079] In optical systems, the sign is defined as positive if the light travels from left to right, and negative if it travels from right to left. Since the light path in a refracting zoom lens group is from right to left, opposite to the traditional light path, the sign of the thickness also changes. This can be understood as the light passing through a lens traveling from right to left from the incident surface to the exit surface; therefore, the thickness of the air and the lens center is negative.
[0080] The center thickness of the first lens L1 is -21.088 mm, the radius of curvature of the object side is -101.916 mm, and the radius of curvature of the image side is -141.603 mm.
[0081] The center thickness of the second lens L2 is -16.607mm, the object side radius of curvature is -101.160mm, and the image side radius of curvature is -87.153mm.
[0082] The center thickness of the third lens L3 is -22.689 mm, the object side radius of curvature is 313.360 mm, and the image side radius of curvature is 174.908 mm.
[0083] The center thickness of the fourth lens L4 is -22.619mm, the object side radius of curvature is -120.434mm, and the image side radius of curvature is -134.541mm.
[0084] The center thickness of the fifth lens L5 is -13.786mm, the object side radius of curvature is 39.689mm, and the image side radius of curvature is 53.480mm.
[0085] The center thickness of the sixth lens L6 is -22.816mm, the object side radius of curvature is -48.277mm, and the image side radius of curvature is -59.436mm.
[0086] The object-side surface (L1S1) and image-side surface (L1S2) of the first lens L1, the image-side surface (L2S2) of the second lens L2, the object-side surface (L5S1) and image-side surface (L5S2) of the fifth lens L5, and the object-side surface (L6S1) and image-side surface (L6S2) of the sixth lens L6 are all aspherical. The expression for an aspherical surface is:
[0087]
[0088] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R, where R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; and A, B, C, D, and E are higher-order aspherical coefficients. The usage of the aspherical surface in this example is shown in Table 3.
[0089] Table 3 Aspherical Coefficients
[0090] surface Conic coefficient 4th order 6th order 8th order <![CDATA[L1S1]]> -10.195 5.60E-10 -2.39E-07 -3.41E-13 L1S2 -34.046 7.65E-10 3.18E-07 5.91E-13 <![CDATA[L2S2]]> 0.152 2.61E-12 -5.21E-08 -7.65E-15 <![CDATA[L5S1]]> -0.59 1.03E-09 -1.22E-06 -6.87E-13 <![CDATA[L5S2]]> -0.55 3.43E-10 -3.22E-07 -1.79E-13 <![CDATA[L6S1]]> 0.077 1.31E-10 3.39E-07 -5.16E-14 L6S2 -0.086 -1.11E-09 6.02E-07 -3.53E-13
[0091] The zoom subsystem employs a variable aperture zoom method, providing three zoom intervals by moving the first lens L1, the third lens L3, and the fourth lens L4. The air thickness variation range of the image side (L1S2) of the first lens L1 is -85.197mm to -61.041mm; the air thickness variation range of the image side (L2S2) of the second lens L2 is -13.188mm to -9.311mm; and the air thickness variation range of the image side (L4S2) of the fourth lens L4 is -41.695mm to -69.728mm.
[0092] The specific zoom interval in this example is shown in Table 4, which contains lens zoom interval parameters.
[0093] Table 4 Lens zoom interval parameters
[0094] surface Short focal length Middle coke end telephoto end Zoom interval 1 -85.197 -68.488 -61.041 Zoom interval 2 -13.188 -12.539 -9.311 Zoom interval 3 -41.695 -59.053 -69.728
[0095] The total length of the system of this invention is 482.8 mm, and the rectangular field of view ranges from 5.5°×4.4° to 10.86°×8.78° (rectangular field of view, i.e., X-direction field of view × Y-direction field of view), adapting to detectors with a resolution of 640×512 and a pixel size of 15μm×15μm. The parameters of the long-wave infrared zoom lens group in this embodiment, from the first lens L1 to the sixth lens L6, are shown in Table 5.
[0096] Table 5 Zoom Lens Group Data
[0097]
[0098]
[0099] In the table, I1 is IMAGE 1, which is the first image plane (i.e., the image formed by the reflection system); I2 is IMAGE 2, the final image plane (i.e., the image formed by the reflection system as the object of the refracting lens). INFINITY means that the radius of curvature is infinite and the image plane and object plane are flat.
[0100] like Figure 4 The diagram shows a comparison between the resolution of the optical system (new system) used as a tilting imaging equal-ground resolution lens according to an embodiment of the present invention and the resolution of the conventional optical system (initial system). Between 10° and 16° of field of view, the image formed by the optical system used as a tilting imaging camera lens according to the embodiment of the present invention shows a clear trend towards flattening resolution at points A and B; while the image formed by the conventional optical system exhibits greater resolution variation, affecting the image quality.
[0101] Figure 5, Figure 7 , Figure 9 The graphs show the modulation transfer function (MTF) curves at the short focal length, medium focal length, and long focal length of the optical system in this embodiment at the image plane. It can be seen that the MTF curves of each field of view approximate the diffraction-limited curve of the system, indicating that the imaging quality is close to the diffraction limit.
[0102] Figure 6 , Figure 8 , Figure 10 This is a point map of each field of view of the optical system in this embodiment on the image plane, which is smaller than the radius of the Airy disk, and the system imaging quality is close to the diffraction limit.
[0103] The operating band of the system of the present invention is the long-wave infrared band, but it is not limited to this embodiment. Those skilled in the art can adjust it according to actual needs.
[0104] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.
[0105] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A tilting imaging airborne long-wave infrared continuous zoom system with ground resolution, characterized in that, include: Reflection subsystem and zoom subsystem; The reflection subsystem includes a primary mirror, a secondary mirror, and a third mirror. The primary mirror is positioned on the incident light path of the object-side ray, the secondary mirror is located on the reflected light path of the primary mirror, and the third mirror is located on the reflected light path of the secondary mirror. The reflecting surfaces of the primary mirror and the secondary mirror are standard surfaces, while the reflecting surface of the third mirror is a freeform surface. The zoom subsystem is positioned on the reflected light path of the third mirror and is used for imaging at different object distances.
2. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 1, characterized in that, The reflection subsystem is an off-axis three-mirror system, with its aperture stop located on the third mirror and an off-axis field of view angle of 13°; the object-image relationship of the reflection subsystem is expressed as follows: Where ω is the field of view angle, 10°≤ω≤16°, as the field of view angle increases, the distance between the observation point and the point to be observed becomes closer and closer; FFL(ω) is the focal length of the field of view; GR(ω) is the ground resolution corresponding to the field of view angle ω; a is the size of a single pixel unit; and H is the altitude of the tilting imaging lens.
3. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 1, characterized in that, After adding a small increment Δω to the field of view angle ω, the image height on the image plane changes by Δh, and the focal length FFL(ω) is:
4. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 1, characterized in that, The optical powers of the primary mirror, the secondary mirror, and the third mirror are positive, negative, and positive, respectively; the radii of curvature at the vertices of the three mirrors approximately satisfy the Pittswan condition. R1, R2, and R3 are the radii of the primary mirror, secondary mirror, and tertiary mirror, respectively.
5. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 1, characterized in that, The zoom subsystem enables continuous zoom from 50 to 100 mm and includes a front fixed group, a zoom group, a compensation group, and a rear fixed group. The front fixed group includes a first lens L1, the zoom group includes a second lens L2 and a third lens L3, the compensation group includes a fourth lens L4, and the rear fixed group includes a fifth lens L5 and a sixth lens L6.
6. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 5, characterized in that, The first lens L1, the third lens L3, the fourth lens L4, and the sixth lens L6 are made of germanium, while the second lens L2 and the fifth lens L5 are made of zinc selenide.
7. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 5, characterized in that, For any lens, the light incident surface is taken as the object side surface, and the light exit surface is taken as the image side surface. The center thickness of the first lens L1 is -21.088 mm, the object side radius of curvature is -101.916 mm, and the image side radius of curvature is -141.603 mm. The second lens L2 has a center thickness of -16.607 mm, an object side radius of curvature of -101.160 mm, and an image side radius of curvature of -87.153 mm. The third lens L3 has a center thickness of -22.689 mm, an object-side radius of curvature of 313.360 mm, and an image-side radius of curvature of 174.908 mm. The fourth lens L4 has a center thickness of -22.619 mm, an object-side radius of curvature of -120.434 mm, and an image-side radius of curvature of -134.541 mm. The fifth lens L5 has a center thickness of -13.786 mm, an object-side radius of curvature of 39.689 mm, and an image-side radius of curvature of 53.480 mm. The sixth lens L6 has a center thickness of -22.816 mm, an object-side radius of curvature of -48.277 mm, and an image-side radius of curvature of -59.436 mm.
8. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 7, characterized in that, The object-side and image-side surfaces of the first lens L1, the image-side surface of the second lens L2, the object-side and image-side surfaces of the fifth lens L5, and the object-side and image-side surfaces of the sixth lens L6 are all aspherical. The expression for an aspherical surface is: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R, where R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; and A, B, C, D, and E are higher-order aspherical coefficients.
9. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 1, characterized in that, In the zoom subsystem, three zoom intervals are provided by moving the first lens L1, the third lens L3, and the fourth lens L4; the air thickness on the image side of the first lens L1 varies from -85.197mm to -61.041mm; the air thickness on the image side of the second lens L2 varies from -13.188mm to -9.311mm; and the air thickness on the image side of the fourth lens L4 varies from -41.695mm to -69.728mm.
10. The tilting imaging airborne long-wave infrared and other ground resolution continuous zoom system according to claim 1, characterized in that, The zoom system has a total length of 482.8 mm and a rectangular field of view of 5.5°×4.4°~10.86°×8.78°. It is compatible with detectors with a resolution of 640×512 and a pixel size of 15μm.