Medium-wave infrared continuous zoom lens with long focal length and large target surface

Abstract

The long-focal-length large-target-surface medium-wave infrared continuous zoom lens comprises a first front fixed group lens, a second front fixed group lens, a third front fixed group lens, a zoom lens, a compensation lens, a rear fixed group lens, a first rear group lens, a second rear group lens and a third rear group lens which are sequentially arranged from an object space to an image space along an optical axis, the distances among the first, second and third rear group lenses are fixed; continuous zooming is achieved by moving the zoom lens and the compensation lens back and forth on the optical axis, and thermal difference elimination of imaging during zooming is achieved by moving the whole first, second and third rear group lenses back and forth on the optical axis. The zoom lens and the compensation lens move back and forth on the optical axis to realize continuous zooming, and the first rear group lens, the second rear group lens and the third rear group lens which are fixed in distance move back and forth on the optical axis to realize thermal difference elimination of imaging during zooming, so that the lens has good imaging quality in a temperature range of-40 DEG C to + 70 DEG C.

Description

Technical Field

[0001] This invention relates to the field of mid-wave infrared optical systems, and more particularly to a long focal length, large target surface mid-wave infrared continuous zoom lens. Background Technology

[0002] Mid-wave infrared (MWI) bands lie within the atmospheric window, possessing strong smoke penetration capabilities and high object thermal radiation contrast. Their continuous zoom optical systems are core equipment for long-range thermal imaging, target recognition, and tracking, widely used in national defense, industrial inspection, and maritime search and rescue. In scenarios such as border control, high-voltage power line inspection, and long-range target monitoring, the requirements of both "wide-area wide-angle search" and "long-range telephoto detail recognition" must be met: a 70mm short focal length enables wide field-of-view coverage and rapid target area locking; a 1000mm telephoto length accurately captures the thermal radiation characteristics of distant (5-15km) targets; and a fixed aperture of F4 ensures stable light transmission across the entire focal length, guaranteeing thermal imaging sensitivity. Therefore, a mid-wave infrared continuous zoom system with a large zoom ratio (14×), 70-1000mm focal length, and F4 becomes a core requirement for high-performance infrared imaging equipment.

[0003] However, existing technologies struggle to balance the performance and practicality of this parameter combination. Large zoom ratios and long focal lengths easily lead to bulky systems and excessive weight. Using folding optical paths to compress size introduces additional aberrations, and controlling the optical axis stability of long focal length zoom mechanisms is difficult. Furthermore, existing systems have limitations in detector adaptability; the 1000mm focal length amplifies the non-uniformity of cooled InSb detectors, requiring the optical system to meet high MTF requirements across the entire field of view. Current designs struggle to balance zoom ratio, image quality, size, and environmental adaptability. Summary of the Invention

[0004] To address the problem that existing technologies struggle to simultaneously achieve system performance, practicality, and environmental adaptability, this invention primarily provides a long focal length, large target area, mid-wave infrared continuous zoom lens, thereby achieving a balance between zoom ratio, image quality, size, and environmental adaptability.

[0005] Therefore, the technical solution adopted by the present invention is as follows: A long focal length, large target area, mid-wave infrared continuous zoom lens is provided, comprising a first front fixed group lens, a second front fixed group lens, a third front fixed group lens, a zoom lens, a compensation lens, a rear fixed group lens, a first rear group lens, a second rear group lens, and a third rear group lens arranged sequentially along the optical axis from the object side to the image side. The distance between the first rear lens group, the second rear lens group, and the third rear lens group is fixed. Continuous zoom is achieved by moving the zoom lens and the compensation lens back and forth on the optical axis, and thermal difference in imaging during zoom is eliminated by moving the first rear lens group, the second rear lens group, and the third rear lens group as a whole back and forth on the optical axis.

[0006] According to the above scheme, the first front fixed lens group is a positive meniscus silicon lens with a convex object-facing orientation, the second front fixed lens group is a positive meniscus germanium lens with a convex object-facing orientation, the third front fixed lens group is a positive meniscus silicon lens with a convex object-facing orientation, the zoom lens is a biconcave negative germanium lens, the compensation lens is a biconvex silicon lens, the rear fixed lens group is a negative meniscus germanium lens with a convex image-facing orientation, the first rear lens group is a positive meniscus silicon lens with a convex object-facing orientation, the second rear lens group is a biconcave negative germanium lens, and the third rear lens group is a positive meniscus silicon lens with a convex image-facing orientation.

[0007] According to the above scheme, the mid-wave infrared continuous zoom lens adopts a mechanical compensation zoom method, and the cam curve adopts a double nonlinear design.

[0008] According to the above scheme, the focal length range of the mid-wave infrared continuous zoom lens is 70mm to 1000mm, the zoom ratio is 14×, and the image-side F number is 4.

[0009] According to the above scheme, during continuous zooming, the zoom lens and the compensation lens undergo nonlinear motion on the optical axis to obtain a clear image across the entire focal length.

[0010] According to the above scheme, the second front fixed group lens convex in the object direction, the zoom lens concave in the image direction, the compensating lens convex in the image direction, the second rear group lens concave in the object direction, and the third rear group lens convex in the object direction all adopt aspherical design.

[0011] According to the above scheme, the substrate of the zoom lens in the concave image direction has a diffraction surface formed by processing a continuous relief structure.

[0012] A long focal length, large target surface, mid-wave infrared continuous zoom optical system is also provided, wherein the optical system adopts the long focal length, large target surface, mid-wave infrared continuous zoom lens described above.

[0013] A large-area mid-wave cooled detector is also provided, which is used for the output light of the long focal length large-area mid-wave infrared continuous zoom lens described above.

[0014] According to the above scheme, the detector has a resolution of 640×512 and a target surface of 25μm.

[0015] The beneficial effects of this invention are as follows: This invention achieves continuous zoom by moving the zoom lens and the compensation lens back and forth on the optical axis, and eliminates thermal difference in imaging during zoom by moving the first, second, and third rear lens groups, which are fixed at a distance, back and forth on the optical axis. This results in the lens having good imaging quality in a temperature range of -40℃ to +70℃, and having good environmental adaptability while having a large zoom ratio and long focal length.

[0016] Furthermore, by selecting materials for each lens and designing the aspherical and diffraction surfaces of the lens surfaces, this invention achieves a large target surface mid-wave infrared zoom lens with clear imaging, a large 14× zoom ratio, a long focal length of 70mm to 1000mm, and a smooth zooming process, which is beneficial for large field-of-view search and observation as well as small field-of-view tracking and identification.

[0017] Furthermore, the cam curve of the present invention adopts a double nonlinear design, which effectively reduces the pressure rise angle and makes the cam motion smoother and more stable. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a long focal length, large target surface, mid-wave infrared continuous zoom lens according to an embodiment of the present invention. Figure 2 This is a two-dimensional schematic diagram of the long focal length, large target surface, mid-wave infrared continuous zoom lens of the present invention in the short focal length state of 70mm. Figure 3 This is a two-dimensional schematic diagram of the long focal length, large target surface, mid-wave infrared continuous zoom lens of this invention in the 1000mm focal length state. Figure 4 The transfer function curve of the long focal length, large target area, mid-wave infrared continuous zoom lens of this invention at a short focal length of 20 lp / mm is shown in this embodiment. Figure 5 The transfer function curve of the long focal length, large target area, mid-wave infrared continuous zoom lens of this invention at a focal length of 20 lp / mm is shown in this embodiment. Figure 6 This is a dot plot of the long focal length, large target area, mid-wave infrared continuous zoom lens of this invention at short focal length. Figure 7 This is a dot plot of the long focal length, large target area, mid-wave infrared continuous zoom lens of this invention at the telephoto focal length. Figure 8 The distortion curve of the long focal length, large target area, mid-wave infrared continuous zoom lens in this embodiment of the invention at short focal length. Figure 9 The distortion curve of the long focal length, large target area, mid-wave infrared continuous zoom lens in this embodiment of the invention is shown at the long focal length. Figure 10This is the cam curve of the long focal length, large target surface, mid-wave infrared continuous zoom lens in an embodiment of the present invention.

[0019] In the diagram, 1-first front fixed lens group, 2-second front fixed lens group, 3-third front fixed lens group, 4-zoom lens, 5-compensation lens, 6-rear fixed lens group, 7-first rear lens group, 8-second rear lens group, 9-third rear lens group. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] To address the limitations of existing mid-wave infrared continuous zoom optical systems, such as the difficulty in achieving a wide focal length range and the need for optical path refraction to reduce size, this invention provides a long focal length, large target area mid-wave infrared continuous zoom lens, such as... Figure 1 As shown, it includes nine lenses, specifically including a first front fixed group lens 1, a second front fixed group lens 2, a third front fixed group lens 3, a zoom lens 4, a compensation lens 5, a rear fixed group lens 6, a first rear group lens 7, a second rear group lens 8, and a third rear group lens 9 arranged sequentially along the optical axis from the object side to the image side. The distance between the first rear lens group 7, the second rear lens group 8, and the third rear lens group 9 is fixed. Continuous zoom is achieved by moving the zoom lens 4 and the compensation lens 5 back and forth on the optical axis, and thermal difference in imaging during zoom is eliminated by moving the first rear lens group 7, the second rear lens group 8, and the third rear lens group 9 back and forth as a whole on the optical axis.

[0022] Specifically, in infrared optical systems, changes in the refractive index of materials and the radius of curvature of lenses under high and low temperatures can lead to image plane shifts and aberration changes, requiring focusing to maintain image quality. In this embodiment, the first rear lens group 7, the second rear lens group 8, and the third rear lens group 9 are designed to move back and forth along the optical axis as a whole. This overall focusing of the three rear lenses can better balance aberrations, effectively controlling spherical aberration, coma, astigmatism, and field curvature of the entire optical system. The advantage of overall focusing of the rear group is that it keeps the relative positions within the lens group unchanged, and it can better balance optical power and aberration correction; it has less impact on the optical power of the optical system, achieves defocus compensation, corrects higher-order aberrations, and maintains image plane stability, thereby maintaining the aberration correction state within the rear optical system. In addition, in the optical system of this embodiment, the focusing margin using a single rear lens is insufficient, and the focusing effect of a single lens is not as good as the focusing effect of the whole group. Therefore, the axial movement of the whole group is used for high and low temperature focusing, thereby improving the image quality of the lens.

[0023] Specifically, during continuous zooming, the zoom lens 4 and the compensation lens 5 move toward the object side and the image side, respectively, to achieve the transformation from a small field of view to a large field of view; both the zoom lens 4 and the compensation lens 5 undergo nonlinear motion to obtain a clear image across the entire focal length.

[0024] Specifically, the first front fixed lens group 1 is a positive meniscus silicon lens with a convex object-facing orientation, the second front fixed lens group 2 is a positive meniscus germanium lens with a convex object-facing orientation, the third front fixed lens group 3 is a positive meniscus silicon lens with a convex object-facing orientation, the zoom lens 4 is a biconcave negative germanium lens, the compensation lens 5 is a biconvex silicon lens, the rear fixed lens group 6 is a negative meniscus germanium lens with a convex image-facing orientation, the first rear lens group 7 is a positive meniscus silicon lens with a convex object-facing orientation, the second rear lens group 8 is a biconcave negative germanium lens, and the third rear lens group 9 is a positive meniscus silicon lens with a convex image-facing orientation.

[0025] The direction closer to the object space is called the object side, and the direction closer to the image space is called the image side. From the object side to the image side, the two sides of the lens are the incident surface and the exit surface, respectively.

[0026] Specifically, in this embodiment of the invention, the focal lengths of lenses 1 to 9 at a wavelength of 4.2 μm satisfy the following conditions: 2.8≤f1 / f≤3.0, -0.8≤f2 / f≤-0.5, 0.8≤f3 / f≤1.0, -0.5≤f4 / f≤-0.3, 0.4≤f5 / f≤0.5, -3.4≤f6 / f≤-3, 0.1≤f7 / f≤0.3, -0.2≤f8 / f≤0, 0≤f9 / f≤0.3; Where f is the focal length of the optical system at its short focal length.

[0027] Specifically, the second front fixed group lens (convex surface towards the object), the zoom lens (concave surface towards the image), the compensating lens (convex surface towards the image), the second rear group lens (concave surface towards the object), and the third rear group lens (convex surface towards the object) all adopt aspherical designs, and the aspherical equations are as follows:

[0028] Where z is the aspherical height along the optical axis, c is the curvature, c=1 / R, R represents the radius of curvature of the lens, r is the radial coordinate, k is the quadratic curve constant, A is the fourth-order aspherical coefficient, B is the sixth-order aspherical coefficient, C is the eighth-order aspherical coefficient, and D is the tenth-order aspherical coefficient.

[0029] Specifically, the substrate of the zoom lens in the concave image area has a diffraction surface formed by machining a continuous relief structure. The diffraction surface can be machined on the substrate in the concave image area of ​​the zoom lens using a diamond turning tool, satisfying the equation:

[0030] Where HOR is the diffraction order, C1 and C2 are the diffraction surface coefficients, λ0 is the design center wavelength, n is the lens refractive index, and n0 is the air refractive index.

[0031] like Figure 2 and Figure 3 As shown, the biconcave negative lens is a zoom lens, and the biconvex positive lens is a compensating lens. The zoom lens and compensating lens change the focal length of the lens by axial movement. This is combined with the cam curve. Figure 10 At a short focal length of 70mm, the distance between the zoom lens and the compensation lens is 89.74mm. The zoom lens moves 58.8mm towards the image side, and the compensation lens moves 28.32mm towards the object side, reaching a long focal length of 1000mm. As shown by the cam curve, the zoom lens undergoes non-linear motion with a travel distance of 58.8mm, and the compensation lens group also undergoes non-linear motion with a travel distance of 28.32mm. Throughout the entire travel, the zoom curve is smooth without any abrupt drops.

[0032] Specifically, infrared optical materials change significantly with temperature, making infrared optical systems sensitive to temperature. To compensate for image plane shift caused by temperature changes, the entire rear group of lenses—the first, second, and third rear lenses—is moved axially to ensure that the system can maintain high image quality within a temperature range of -40℃ to +70℃.

[0033] Specifically, the mid-wave infrared continuous zoom lens of this embodiment of the invention has a focal length range of 70mm to 1000mm, a zoom ratio of 14×, and an image-side F number of 4.

[0034] Specifically, the detailed data of each lens in this embodiment when the focal length of the optical system is 70mm to 1000mm are shown in Table 1: Table 1 Optical parameters of the lens

[0035] As shown in Table 2, the aspherical coefficients of the second front fixed lens group (convex to the object side S4), the zoom lens (concave to the image side S8), the compensating lens (convex to the image side S10), the second rear lens group (concave to the object side S15), and the third rear lens group (convex to the image side S17) in this embodiment are: Table 2 Aspherical coefficients

[0036] As shown in Table 3, these are the diffraction aspherical coefficients of the concave image-side S8 plane of the zoom lens in this embodiment: Table 3. Diffraction Aspheric Coefficients

[0037] After design and simulation, such as Figure 4 ,5 The system is matched with a detector pixel size of 25 μm, corresponding to a spatial cutoff frequency of 20 lp / mm. At the cutoff frequency, the system's transfer function is close to the diffraction limit on the axis and greater than 0.2 off-axis. (Point array) Figure 6 , 7 It can reflect the dispersion of light rays in the imaging system. The smaller the RMS of the dispersion spot, the better the image quality. The RMS of the entire system is within two pixels in all fields of view. For example... Figure 8 , 9 The maximum distortion for both long and short focal lengths is within 3%, which meets the design and usage requirements.

[0038] In addition, this embodiment of the invention also provides a long focal length, large target surface, mid-wave infrared continuous zoom optical system, wherein the optical system adopts the long focal length, large target surface, mid-wave infrared continuous zoom lens described above.

[0039] In addition, this embodiment of the invention also provides a large target surface mid-wave cooled detector, which is used for the emitted light of the long focal length large target surface mid-wave infrared continuous zoom lens mentioned above, and the resolution of the detector is 640×512, and the target surface is 25μm.

[0040] The embodiments of the present invention achieve continuous zoom by moving the zoom lens and the compensation lens back and forth on the optical axis, and by moving the first rear lens group, the second rear lens group, and the third rear lens group, which are at a fixed distance, back and forth on the optical axis to eliminate the thermal difference in imaging during zooming. This allows the lens to have good imaging quality in a temperature range of -40℃ to +70℃, and to have good environmental adaptability while having a large zoom ratio and long focal length.

[0041] Furthermore, by selecting materials for each lens and designing the aspherical and diffraction surfaces of the lens surfaces, this embodiment of the invention achieves a large-area mid-wave infrared zoom lens with clear imaging, large zoom ratio, long focal length, and smooth zooming process, which is beneficial for large field-of-view search and observation as well as small field-of-view tracking and identification.

[0042] Furthermore, the cam curve in this embodiment of the invention adopts a double nonlinear design, which effectively reduces the pressure rise angle and makes the cam motion smoother and more stable.

[0043] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0044] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0045] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A long focal length, large target area, mid-wave infrared continuous zoom lens, characterized in that, It includes a first front fixed group lens, a second front fixed group lens, a third front fixed group lens, a zoom lens, a compensation lens, a rear fixed group lens, a first rear group lens, a second rear group lens, and a third rear group lens arranged sequentially along the optical axis from the object side to the image side; The distance between the first rear lens group, the second rear lens group, and the third rear lens group is fixed. Continuous zoom is achieved by moving the zoom lens and the compensation lens back and forth on the optical axis, and thermal difference in imaging during zoom is eliminated by moving the first rear lens group, the second rear lens group, and the third rear lens group as a whole back and forth on the optical axis.

2. The long focal length, large target area, mid-wave infrared continuous zoom lens according to claim 1, characterized in that, The first front fixed lens group is a positive meniscus silicon lens with a convex object-facing orientation; the second front fixed lens group is a positive meniscus germanium lens with a convex object-facing orientation; the third front fixed lens group is a positive meniscus silicon lens with a convex object-facing orientation; the zoom lens is a biconcave negative germanium lens; the compensation lens is a biconvex silicon lens; the rear fixed lens group is a negative meniscus germanium lens with a convex image-facing orientation; the first rear lens group is a positive meniscus silicon lens with a convex object-facing orientation; the second rear lens group is a biconcave negative germanium lens; and the third rear lens group is a positive meniscus silicon lens with a convex image-facing orientation.

3. The long focal length, large target area, mid-wave infrared continuous zoom lens according to claim 1, characterized in that, The mid-wave infrared continuous zoom lens uses mechanical compensation zoom and the cam curve adopts a double nonlinear design.

4. The long focal length, large target area, mid-wave infrared continuous zoom lens according to claim 1, characterized in that, The mid-wave infrared continuous zoom lens has a focal length range of 70mm to 1000mm, a zoom ratio of 14×, and an image-side F-number of 4.

5. The long focal length, large target area, mid-wave infrared continuous zoom lens according to claim 1, characterized in that, During continuous zooming, the zoom lens and the compensation lens undergo nonlinear motion along the optical axis to obtain a clear image across the entire focal length.

6. The long focal length, large target area, mid-wave infrared continuous zoom lens according to claim 2, characterized in that, The second front fixed lens group (convex towards the object), the zoom lens (concave towards the image), the compensating lens (convex towards the image), the second rear lens group (concave towards the object), and the third rear lens group (convex towards the object) all specifically adopt aspherical designs.

7. The long focal length, large target area, mid-wave infrared continuous zoom lens according to claim 2, characterized in that, The zoom lens has a diffraction surface formed by processing a continuous relief structure on the concave image side of the substrate.

8. A long focal length, large target surface mid-wave infrared continuous zoom optical system, characterized in that, The optical system employs the long focal length, large target surface, mid-wave infrared continuous zoom lens as described in any one of claims 1-7.

9. A large-target-area mid-wave cooled detector, characterized in that, The detector is used to sense the emitted light from the long focal length, large target surface, mid-wave infrared continuous zoom lens as described in any one of claims 1-7.

10. The large-target mid-wave cooled detector according to claim 9, characterized in that, The detector has a resolution of 640×512 and a target surface of 25μm.

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