A small and light long-wave infrared continuous zoom optical system

Abstract

The present application relates to a kind of small light weight long-wave infrared continuous zoom optical system, by the coaxial arrangement of first meniscus positive lens, double-concave negative lens, biconvex positive lens, first meniscus negative lens, second meniscus positive lens, second meniscus negative lens in order from object side to image side, double-concave negative lens is variable magnification lens, biconvex positive lens is compensation lens. Through the reasonable distribution of the refractive power of each lens and the optimized setting of aspheric surface position, while realizing the continuous zooming in the range of 22mm~88mm, the imaging quality is high, there is no jamming phenomenon in the zooming process, and it does not contain diffraction surface, so as to avoid the problem of optical system transmittance decline caused by diffraction efficiency loss, thereby improving the system throughput and sensitivity;The system is adapted to the long-wave infrared detector with resolution of 1024x768 and pixel pitch of 12 μm, and the length is short, the weight is light, the total length of the system is 135mm, and the total weight of the 6 lenses is 300g, which is beneficial to realize miniaturization and light weight.

Description

Technical Field

[0001] This invention relates to the field of infrared imaging optical systems, and more specifically to a small, lightweight long-wave infrared continuous zoom optical system. Background Technology

[0002] Optoelectronic systems used for target search and identification require infrared thermal imaging systems to achieve both wide-field-of-view target search and narrow-field-of-view identification of distant targets. Therefore, single-field-of-view infrared optical systems cannot meet this requirement. The optical system of an infrared thermal imager needs to be designed as a zoom optical system to achieve this function. Continuous zoom infrared optical systems offer wide coverage with a wide field of view at short focal lengths and high resolution with a narrow field of view at long focal lengths. The wide field of view can be used for searching a large area of ​​targets, while the narrow field of view can be used for target identification; the target image remains clear throughout the zoom process, allowing for any field of view transition within the zoom range, without losing track of the target during continuous zooming, and can select an appropriate working field of view based on scene and target characteristics, greatly improving human-machine interface efficiency.

[0003] Currently, with the development of infrared technology, the array size of uncooled infrared detectors is constantly increasing, and domestically produced cores with a resolution of 1024×768 and a diameter of 12μm are beginning to be widely used. Due to the high resolution of the detectors, uncooled infrared continuous zoom lenses currently incorporate diffraction surfaces for aberration correction to achieve miniaturization. However, diffraction surfaces reduce light transmission efficiency, and their manufacturing cost is also high. Therefore, developing a small, lightweight, long-wave infrared continuous zoom optical system without diffraction surfaces is of great significance. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a small, lightweight, long-wave infrared continuous zoom optical system without a diffraction surface.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A small, lightweight long-wave infrared continuous zoom optical system is disclosed. The optical system comprises a first meniscus positive lens, a biconcave negative lens, a biconvex positive lens, a first meniscus negative lens, a second meniscus positive lens, and a second meniscus negative lens arranged coaxially from the object side to the image side. The first meniscus positive lens, the second meniscus positive lens, and the second meniscus negative lens are all bent towards the image side, and the first meniscus negative lens is bent towards the object side. The biconcave negative lens is a zoom lens, and the biconvex positive lens is a compensation lens.

[0007] Furthermore, the center-to-center distance between the first meniscus positive lens and the first biconcave negative lens is 13.4–30.9 mm, the center-to-center distance between the biconcave negative lens and the biconvex positive lens is 4.0–44.8 mm, and the center-to-center distance between the biconvex positive lens and the first meniscus negative lens is 14.4–38.7 mm.

[0008] Furthermore, during the transition from a large field of view to a small field of view, the travel of the biconcave negative lens is 17.5 mm, and the travel of the biconvex positive lens is 24.3 mm.

[0009] Furthermore, the system employs axial movement of the first meniscus negative lens to achieve image plane defocus compensation within the temperature range of -40℃ to +60℃, as well as system defocus compensation caused by changes in the distance of the observed scene.

[0010] Furthermore, the first meniscus positive lens, the biconcave negative lens, and the biconvex positive lens are all made of single-crystal germanium (Ge), the first meniscus negative lens is made of ZnSe, and the second meniscus positive lens and the second meniscus negative lens are both made of chalcogenide glass IRG206.

[0011] Furthermore, the optical system satisfies the following conditions: 0.7≤f1 / f≤0.9, -0.3≤f2 / f≤-0.2, 0.3≤f3 / f≤0.5, -3.3≤f4 / f≤-3.1, 0.2≤f5 / f≤0.4, -1.8≤f6 / f≤-1.6;

[0012] Where: f is the focal length of the optical system in its telephoto state; f1 is the effective focal length of the first meniscus positive lens; f2 is the effective focal length of the biconcave negative lens; f3 is the effective focal length of the biconvex positive lens; f4 is the effective focal length of the first meniscus negative lens; f5 is the effective focal length of the second meniscus positive lens; and f6 is the effective focal length of the second meniscus negative lens.

[0013] Furthermore, the surfaces of the biconcave negative lens facing the image side, the biconvex positive lens facing the object side, the first meniscus negative lens facing the object side, and the second meniscus positive lens facing the object side are all aspherical.

[0014] Furthermore, the technical parameters achieved by the optical system are as follows: operating wavelength: 8μm~12μm; F # : 1.2; Focal length: 22mm~88mm; Field of view: 31.2°×23.6°~7.99°×5.99°; Adapted to 1024×768, 12μm long-wave infrared detector, where F # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0015] Beneficial effects:

[0016] 1. The optical system of the present invention does not contain a diffraction surface, which can avoid the problem of decreased optical system transmittance due to diffraction efficiency loss, thereby improving the system's transmittance efficiency and sensitivity.

[0017] 2. Through the reasonable allocation of the optical power of each lens and the optimized setting of the aspherical surface position, the distance from the front surface of the first meniscus positive lens to the imaging plane, i.e. the total optical length of the system, is 135mm, and the total weight of the 6 lenses is 300g.

[0018] 3. The optical system is short and the lenses are lightweight, which is conducive to the miniaturization and weight reduction of the system. While achieving continuous zoom in the range of 22mm to 88mm, the optical system has a high transfer function value at the characteristic frequency, which can increase the signal-to-noise ratio of the system and thus effectively improve the temperature resolution of the infrared thermal imaging system.

[0019] 4. The optical system of this invention has a smooth and continuous motion curve without inflection points during the zoom process, thereby ensuring clear imaging throughout the zoom process without any jamming. Attached Figure Description

[0020] Figure 1 This is the optical path diagram of the optical system in the short focal length (22mm) state.

[0021] Figure 2 This is the optical path diagram of the optical system at a focal length of 50mm.

[0022] Figure 3 This is the optical path diagram of the optical system at a focal length of 88mm.

[0023] Figure 4 Transfer function graph of the optical system at a short focal length of 22mm;

[0024] Figure 5 Transfer function diagram of the optical system at a focal length of 50mm;

[0025] Figure 6 Transfer function graph of the optical system at a telephoto focal length of 88mm;

[0026] Figure 7 Dot plot of the optical system at a short focal length of 22mm;

[0027] Figure 8 Dot diagram of the optical system at a focal length of 50mm;

[0028] Figure 9 Dot plot of the optical system at a telephoto focal length of 88mm;

[0029] Figure 10 Optical system zoom curve diagram;

[0030] Reference numerals in the attached figures: 1 is the first meniscus positive lens, 2 is the biconcave negative lens, 3 is the biconvex positive lens, 4 is the first meniscus negative lens, 5 is the second meniscus positive lens, 6 is the second meniscus negative lens, and 7 is the image plane. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," and "right," etc., indicating orientation or positional relationships, are merely for the purpose of describing the present invention and do not indicate or imply that the device or element referred to must have a specific orientation. The terms "first," "second," and "third" are used for descriptive purposes only, referring to the order in which lenses of this type appear, and should not be construed as indicating or implying relative importance.

[0032] like Figures 1-3 As shown, a small, lightweight long-wave infrared continuous zoom optical system without diffraction surfaces consists of a first meniscus positive lens 1, a biconcave negative lens 2, a biconvex positive lens 3, a first meniscus negative lens 4, a second meniscus positive lens 5, and a second meniscus negative lens 6 arranged sequentially from the object side to the image side.

[0033] As is common knowledge, the direction closer to object space is called the object side, and the direction closer to 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.

[0034] Furthermore, the first meniscus positive lens 1, the biconcave negative lens 2, the biconvex positive lens 3, the first meniscus negative lens 4, the second meniscus positive lens 5, and the second meniscus negative lens 6 are arranged coaxially from the object side to the image side.

[0035] Furthermore, the first meniscus positive lens 1, the second meniscus positive lens 5, and the second meniscus negative lens 6 are all bent towards the image side, while the first meniscus negative lens is bent towards the object side.

[0036] The biconcave negative lens 2 is a zoom lens. The system focal length is changed by moving the biconcave negative lens 2 along the axis. When the system changes from long focal length to short focal length, the zoom lens moves towards the object side. The biconvex positive lens 3 is a compensation lens. The system defocus compensation caused by the movement of the zoom lens is achieved by moving the biconvex positive lens 3 along the axis. When the system changes from long focal length to short focal length, the compensation lens moves away from the object side (towards the image side).

[0037] The center-to-center distance between the first meniscus positive lens 1 and the first biconcave negative lens 2 is 13.4–30.9 mm, the center-to-center distance between the biconcave negative lens 2 and the biconvex positive lens 3 is 4.0–44.8 mm, and the center-to-center distance between the biconvex positive lens 3 and the first meniscus negative lens 4 is 14.4–38.7 mm. During the transition from a large field of view to a small field of view, the travel distance of the biconcave negative lens 2 is 17.5 mm, and the travel distance of the biconvex positive lens 3 is 24.3 mm.

[0038] The small, lightweight long-wave infrared continuous zoom optical system uses an axially moving first meniscus negative lens 4 to achieve image plane defocus compensation within a temperature range of -40℃ to +60℃, as well as system defocus compensation caused by changes in the distance of the observed object, thereby ensuring clear imaging of objects at different distances.

[0039] Preferably, the first meniscus positive lens 1, the biconcave negative lens 2, and the biconvex positive lens 3 are all made of single-crystal germanium (Ge), the first meniscus negative lens 4 is made of ZnSe, and the second meniscus positive lens 5 and the second meniscus negative lens 6 are both made of chalcogenide glass IRG206.

[0040] The first meniscus positive lens 1 satisfies the following condition: 0.7≤f1 / f≤0.9, where f is the focal length of the optical system in its telephoto state and f1 is the effective focal length of the first meniscus positive lens 1;

[0041] The biconcave negative lens 2 satisfies the following condition: -0.3≤f2 / f≤-0.2, where f is the focal length of the optical system in its telephoto state and f2 is the effective focal length of the biconcave negative lens 2;

[0042] The biconvex positive lens 3 satisfies the following condition: 0.3≤f3 / f≤0.5, where f is the focal length of the optical system in its telephoto state and f3 is the effective focal length of the biconvex positive lens 3;

[0043] The first meniscus negative lens 4 satisfies the following condition: -3.3≤f4 / f≤-3.1, where f is the focal length of the optical system in telephoto mode and f4 is the effective focal length of the first meniscus negative lens 4;

[0044] The second meniscus positive lens 5 satisfies the following condition: 0.2≤f5 / f≤0.4, where f is the focal length of the optical system in its telephoto state and f5 is the effective focal length of the second meniscus positive lens 5;

[0045] The second meniscus negative lens 6 satisfies the following condition: -1.8≤f6 / f≤-1.6, where f is the focal length of the optical system in telephoto mode and f6 is the effective focal length of the second meniscus negative lens 6;

[0046] Table 1 shows the technical specifications of the present invention, where F # The formula for calculating the F-number of an optical system is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0047] Table 1 Technical Specifications of the Invention

[0048]

[0049] Table 2 lists detailed data for embodiments of the optical system according to the present invention with focal lengths ranging from 22mm to 88mm, including the surface shape, radius of curvature, thickness, and material of each lens. The units for the radius of curvature and thickness of the lens are mm. The radius of curvature of spherical and aspherical surfaces refers to the radius of curvature at the intersection of the lens surface and the optical axis. In Table 2, the "Surface Number" is counted along the direction of light propagation. For example, the incident surface of the first meniscus positive lens 1 is number S1, and the exit surface is number S2, and so on for other surfaces. The "Radius" in Table 2 represents the radius of curvature of the surface. Its sign is determined by taking the intersection of the surface and the principal optical axis as the starting point and the center of the surface as the ending point. If the direction of the line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the surface is planar, its radius of curvature is infinite. The "Thickness" in Table 2 gives the distance between two adjacent surfaces on the optical axis. Its sign is determined by taking the vertex of the current surface as the starting point and the vertex of the next surface as the ending point. If the direction of the connecting line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the material between the two surfaces is infrared material, then the thickness represents the lens thickness; if there is no material between the two surfaces, it represents the air gap between the two lenses.

[0050] Table 2 Detailed data of the optical system embodiments of the present invention

[0051]

[0052] The small, lightweight long-wave infrared continuous zoom optical system of the present invention has the following surfaces along the object-to-image direction: the first meniscus positive lens 1, the biconcave negative lens 2, the biconvex positive lens 3, the first meniscus negative lens 4, the second meniscus positive lens 5, and the second meniscus negative lens 6 are respectively labeled as S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, and S12; the surface S4 of the biconcave negative lens 3 facing the image direction, the surface S5 of the biconvex positive lens 4 facing the object direction, the surface S7 of the first meniscus negative lens 4 facing the object direction, and the surface S9 of the second meniscus positive lens 5 facing the object direction are all aspherical surfaces.

[0053] Furthermore, the surface equations of the above-mentioned aspherical surfaces are:

[0054]

[0055] Where z is the distance vector from the vertex of the aspherical surface at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspherical coefficient, B is the sixth-order aspherical coefficient, and C is the eighth-order aspherical coefficient.

[0056] Table 3 lists the aspherical coefficients of the image-side surface S4 of the biconcave negative lens 3, the object-side surface S5 of the biconvex positive lens 4, the object-side surface S7 of the first meniscus negative lens 4, and the object-side surface S9 of the second meniscus positive lens 5 according to the present invention. The table uses scientific notation; for example, -8.531073e-007 represents -8.531073 × 10⁻⁶. -7 .

[0057] Table 3 Aspheric coefficients in this invention

[0058]

[0059] After simulation using optical design software, such as Figure 4 , Figure 5 , Figure 6 As shown, the transfer function of the optical system of the present invention is greater than 0.25 in short focal length, medium focal length, and long focal length states; as Figure 7 , Figure 8 , Figure 9 The image shows a dot plot of the optical system in short-focal, medium-focal, and long-focal-length states. The diameter of the blur spot in this system is comparable to the pixel size of the detector. Figure 10 The figure shows the zoom curve of this continuous zoom optical system. The horizontal axis represents the focal length of the continuous zoom optical system, and the vertical axis represents the axial distance between the zoom group and the compensation group relative to the front fixed group. As can be seen from the figure, the zoom curve of this system is smooth and continuous, without any abrupt changes, which can effectively avoid the system from jamming during zooming.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A small, lightweight long-wave infrared continuous zoom optical system, characterized in that, The optical system consists of a first meniscus positive lens, a biconcave negative lens, a biconvex positive lens, a first meniscus negative lens, a second meniscus positive lens, and a second meniscus negative lens arranged coaxially from the object side to the image side. The first meniscus positive lens, the second meniscus positive lens, and the second meniscus negative lens are all bent towards the image side, and the first meniscus negative lens is bent towards the object side. The biconcave negative lens is a zoom lens, and the biconvex positive lens is a compensation lens.

2. The compact and lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, The center-to-center distance between the first meniscus positive lens and the first biconcave negative lens is 13.4–30.9 mm, the center-to-center distance between the biconcave negative lens and the biconvex positive lens is 4.0–44.8 mm, and the center-to-center distance between the biconvex positive lens and the first meniscus negative lens is 14.4–38.7 mm.

3. The small, lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, During the transition from a large field of view to a small field of view, the travel of the biconcave negative lens is 17.5 mm, and the travel of the biconvex positive lens is 24.3 mm.

4. The small, lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, The system employs axial movement of the first meniscus negative lens to achieve image plane defocus compensation within a temperature range of -40℃ to +60℃, as well as system defocus compensation caused by changes in the distance of the observed object.

5. A small, lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, The first meniscus positive lens, the biconcave negative lens, and the biconvex positive lens are all made of single-crystal germanium (Ge), the first meniscus negative lens is made of ZnSe, and the second meniscus positive lens and the second meniscus negative lens are both made of chalcogenide glass IRG206.

6. The compact and lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, The optical system satisfies the following condition: 0.7 ≤ f 1 / f ≤0.9, -0.3≤ f 2 / f ≤-0.2, 0.3≤ f 3 / f ≤0.5, -3.3≤ f 4 / f ≤-3.1, 0.2≤ f 5 / f ≤0.4, -1.8≤ f 6 / f ≤-1.6; in: f The focal length of the optical system in its telephoto state. f 1 represents the effective focal length of the first meniscus positive lens; f 2 represents the effective focal length of the biconcave negative lens; f 3 represents the effective focal length of the biconvex positive lens; f 4 represents the effective focal length of the first meniscus negative lens; f 5 represents the effective focal length of the second meniscus positive lens; f 6 represents the effective focal length of the second meniscus negative lens.

7. A small, lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, The surfaces of the biconcave negative lens facing the image side, the biconvex positive lens facing the object side, the first meniscus negative lens facing the object side, and the second meniscus positive lens facing the object side are all aspherical.

8. A small, lightweight long-wave infrared continuous zoom optical system according to claim 1, characterized in that, The technical parameters achieved by the optical system are: operating wavelength: 8μm~12μm; F # : 1.2; Focal length: 22mm~88mm; Field of view: 31.2°x23.6°~7.99°x5.99°; Adapted to 1024x768, 12μm long-wave infrared detector, wherein, F # The calculation formula is f / D , f The focal length of the optical system. D The diameter is the entrance pupil.

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