A long-focus athermal lens for short-wave near-infrared imaging

Abstract

The present application relates to the technical field of optical elements, and specifically to a telephoto athermal lens for short-wave near-infrared imaging. The telephoto athermal lens includes a lens barrel and a first lens group, a diaphragm, and a second lens group sequentially arranged in the lens barrel from the object side to the image side, wherein the first lens group is used to correct the aberration of the incident light, the diaphragm is used to limit the amount of light passing through the incident light, and the second lens group is used to correct the residual aberration of the light passing through the first lens group and the diaphragm; the first lens group includes a first lens, a second lens, a third lens, and a fourth lens, wherein the first lens and the second lens are glued together to form a first composite lens, and the third lens and the fourth lens are glued together to form a second composite lens; from the object side to the image side, the second lens group includes a fifth lens and a sixth lens. The telephoto athermal lens provided by the present application adopts optical passive athermalization technology, which can achieve high-quality and clear short-wave near-infrared imaging within a wide temperature range without focusing.

Description

Technical Field

[0001] The present application relates to the technical field of optical elements, and in particular to a long-focus athermalized lens for short-wave near-infrared imaging. Background Art

[0002] With the development of optical lens technology, the market's requirements for optical lenses are becoming increasingly higher. Short-wave infrared lenses have advantages such as strong anti-interference capabilities, strong ability to penetrate smoke and haze, all-weather and all-day operation, and good anti-target stealth capabilities. Therefore, their application areas are becoming increasingly extensive. Infrared optical materials have a larger refractive index temperature coefficient than optical materials in the visible light band. Temperature changes can cause the optimal image plane of the optical system to deviate, reducing image quality and affecting lens performance. With the emergence of athermal lenses, these problems have been solved. Athermal lenses are lenses that can effectively reduce or eliminate changes in optical system parameters such as focal length and image plane position caused by temperature changes within a certain temperature range, thereby maintaining relatively stable imaging quality.

[0003] To achieve the athermal effect, an athermal lens usually requires the design of a special temperature compensation structure. This structure is not only complex, costly, and has low assembly efficiency, but also increases the overall mass and size of the lens, making it inconvenient to use. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a long-focus athermal lens for short-wave near-infrared imaging, which can achieve high-quality and clear short-wave near-infrared imaging at a relatively low cost without the need for focusing of the lens system within a wide temperature range.

[0005] In order to achieve the above-mentioned objectives, the present application provides a telephoto athermal lens for short-wave near-infrared imaging, wherein the telephoto athermal lens includes a lens barrel and a first lens group, an aperture, and a second lens group arranged in the lens barrel from the object side to the image side, wherein the first lens group is used to correct the aberration of incident light, the aperture is used to limit the amount of light transmitted by the incident light, and the second lens group is used to correct the residual aberration of the light passing through the first lens group and the aperture; from the object side to the image side, the first lens group includes a first lens, a second lens, a third lens, and a fourth lens, wherein the first lens and the second lens are glued together to form a first composite lens, and the third lens and the fourth lens are glued together to form a second composite lens; from the object side to the image side, the second lens group includes a fifth lens and a sixth lens; the first lens is a positive lens, the second lens is a negative lens, the third lens is a positive lens, the fourth lens is a negative lens, the fifth lens is a negative lens, and the sixth lens is a positive lens.

[0006] In the embodiment of the present application, the ratio of the focal length EFL1 of the first lens group to the overall focal length EFL of the lens satisfies the following constraint: 0.75<EFL1 / EFL<0.85 (1); the ratio of the focal length EFL2 of the second lens group to the overall focal length EFL of the lens satisfies the following constraint: -2.6<EFL2 / EFL<-2.3 (2).

[0007] In the embodiment of the present application, the fifth lens is a negative meniscus lens with its concave surface facing the image side, and the sixth lens is a positive meniscus lens with its convex surface facing the object side, wherein the ratio of the focal length EFL(G6) of the sixth lens to the overall focal length EFL of the lens satisfies the following constraint: 0.65<EFL(G6) / EFL<0.75 (3).

[0008] In the embodiment of the present application, the thermal expansion coefficient of the material of the first lens at -30°C to 70°C is 8*10 - 6 mm / ℃, the thermal expansion coefficient of the second lens material is 5.8*10 -6 mm / ℃, the thermal expansion coefficient of the third lens material is 7.1*10 -6 mm / ℃, the thermal expansion coefficient of the fourth lens material is 6*10 -6 mm / ℃, the thermal expansion coefficient of the fifth lens material is 5.9*10 -6 mm / ℃, the thermal expansion coefficient of the sixth lens material is 7.9*10 -6 mm / ℃, the thermal expansion coefficient of the lens barrel material is 23.6*10 -6 mm / ℃.

[0009] In the embodiment of the present application, the refractive index Nd1 and the Abbe number Vd1 of the first lens satisfy the following constraints: 1.73<Nd1<1.75 (4); 44.6<Vd1<45.2 (5); the refractive index Nd2 and the Abbe number Vd2 of the second lens satisfy the following constraints: 1.76<Nd2<1.78 (6); 49.2<Vd2<49.8 (7); the refractive index Nd3 and the Abbe number Vd3 of the third lens satisfy the following constraints: 1.90<Nd3<1.92 (8); 34.9<Vd3<35.5 (9); the refractive index Nd4 and the Abbe number Vd4 of the fourth lens satisfy the following constraints: 1.94<Nd4<1.96 (10); 17.6<Vd4<18.2 (11).

[0010] In the embodiment of the present application, the refractive index Nd5 and the Abbe number Vd5 of the fifth lens satisfy the following constraints: 1.77<Nd5<1.79 (12); 43.8<Vd5<44.4 (13); the refractive index Nd6 and the Abbe number Vd6 of the sixth lens satisfy the following constraints: 1.79<Nd6<1.81 (14); 34.6<Vd6<35.2 (15).

[0011] In an embodiment of the present application, the full field of view (FOV) of the telephoto athermal lens satisfies the following constraint: 9°<FOV<10° (16).

[0012] In the embodiment of the present application, the F number of the telephoto athermal lens satisfies the following constraint: 2<F<2.8 (17).

[0013] In the embodiment of the present application, the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are all glass spherical lenses.

[0014] The solution provided in this application has at least the following beneficial effects:

[0015] The solution proposed in this application designs a long-focus athermalized lens based on optical passive athermalization technology. By leveraging the thermal properties of different optical materials and compensating for the CTE of lens shape, focal length distribution, and barrel material, the lens system achieves high-quality, clear short-wave near-infrared imaging over a wide temperature range (-30°C to 70°C) without focusing. The lens structure proposed in this application comprises only six lenses. By optimizing the number and structure of lenses, the lens manufacturing cost and process difficulty are reduced, enabling the lens to achieve both long-focus shooting and a compact structure, reducing the overall lens mass and space occupancy. Furthermore, all lens elements can be made of glass spherical lenses, resulting in low cost and high cost-effectiveness.

[0016] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present application but do not constitute a limitation on the embodiments of the present application. In the accompanying drawings:

[0018] Figure 1 Schematic diagram showing the structure and distribution of each lens in a telephoto athermal lens;

[0019] Figure 2 : This is the MTF diagram of the telephoto athermal lens in this embodiment at -40°C in the 900nm to 1700nm band;

[0020] Figure 3 : This is the MTF diagram of the telephoto athermal lens in this embodiment at 20°C in the 900nm to 1700nm band;

[0021] Figure 4 : This is the MTF diagram of the telephoto athermal lens in this embodiment at 80°C in the 900nm to 1700nm band;

[0022] Figure 5 2 is a distortion diagram of the telephoto athermal lens in this embodiment at 20° C. in the 900 nm to 1700 nm wavelength range.

[0023] Description of Reference Numerals

[0024] 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. It should be understood that the specific implementation methods described herein are only used to illustrate and explain the embodiments of the present application and are not used to limit the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), such directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0027] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0028] Example 1

[0029] like Figure 1As shown, this embodiment provides a telephoto athermal lens for shortwave near-infrared imaging, the telephoto athermal lens comprising a lens barrel and a first lens group, an aperture, and a second lens group sequentially arranged in the lens barrel from the object side to the image side, wherein the first lens group is used to correct the aberration of incident light, the aperture is used to limit the amount of light transmitted by the incident light, and the second lens group is used to correct the residual aberration of the light passing through the first lens group and the aperture; from the object side to the image side, the first lens group comprises a first lens 1, a second lens 2, a third lens 3, and a fourth lens 4, wherein the first lens 1 and the second lens 2 are glued together to form a first composite lens, and the third lens 3 and the fourth lens 4 are glued together to form a second composite lens; from the object side to the image side, the second lens group comprises a fifth lens 5 and a sixth lens 6; the first lens 1 is a positive lens, the second lens 2 is a negative lens, the third lens 3 is a positive lens, the fourth lens 4 is a negative lens, the fifth lens 5 is a negative lens, and the sixth lens 6 is a positive lens.

[0030] Specifically, the first composite lens is composed of a first lens 1, which is a positive lens, and a second lens 2, which is a negative lens, bonded together. Preferably, the first lens 1 is a biconvex positive lens, both of whose surfaces are convex. This lens provides strong positive optical power and is one of the core components of the lens for converging light, performing the primary task of light refraction. The biconvex positive lens has a large aperture, allowing it to collect more light information at the same focal length, achieving clear imaging in low light. The second lens can be a meniscus negative lens, a biconcave negative lens, or a plano-concave negative lens. The concave curvature of one side of the second lens matches the convex curvature of the first lens 1 (facing the second lens 2), forming a curved bonded surface with optical power. Bonded to the biconvex positive lens, this double bonded lens effectively corrects the most important on-axis aberrations (chromatic aberration and spherical aberration) of the front lens group, laying a good foundation for the entire system.

[0031] The second composite lens is similarly composed of a positive lens and a negative lens cemented together. The third lens element 3 can be a plano-convex positive lens or a biconvex positive lens (with the convex surface with greater curvature facing the object side), providing further positive focal power and converging the light. The fourth lens element 4 can be a biconcave negative lens or a plano-concave negative lens (with greater curvature) with the concave surface facing the image side, allowing for more precise adjustment of the light state for chromatic aberration correction. Furthermore, the fourth lens element 4, positioned near the aperture, with its image-facing concave surface, effectively "collimates" the light and controls the angle at which it enters the aperture, which is crucial for suppressing off-axis aberrations such as coma.

[0032] Specifically, in this embodiment, the aperture is located after the two cemented lenses, receiving light that has been corrected by the first lens group (particularly pre-corrected for coma). The subsequent second lens group is primarily responsible for correcting curvature of field and astigmatism. The position of the aperture significantly influences the efficiency of correcting these two types of aberrations. Therefore, in this embodiment, the aperture is positioned near a position where the astigmatism generated by the first and second lens groups can offset each other.

[0033] The second lens group (from object to image side) of this embodiment consists of the fifth lens element 5 and the sixth lens element 6, arranged in sequence. The fifth lens element 5 is a negative meniscus lens with its concave surface facing the image side; the sixth lens element 6 is a positive meniscus lens with its convex surface facing the object side. The concave surface of the fifth lens element faces the image plane (i.e., the convex surface faces the object plane / aperture stop), which produces a negative Petzval sum (field curvature) with a large absolute value. Since the first lens group is dominated by positive lenses, it produces a strong positive Petzval sum, resulting in severe positive field curvature (image plane curvature). Therefore, the fifth lens element 5 introduces a strong negative Petzval sum to offset the positive field curvature of the first lens group, bringing the Petzval sum of the entire system close to zero, thereby achieving a flat image field. The sixth lens element 6 is located at the very back of the system. Its shape and position have a direct impact on distortion correction. Its convex surface faces the object side (aperture), which helps to converge light and assists the negative meniscus lens in completing aberration balance. As the last lens, its concave surface faces the image side (the curvature of the concave surface is smaller than that of the convex surface), which helps to reduce higher-order aberrations and allows light to reach the image side at a gentler angle.

[0034] Specifically, in this embodiment, the ratio of the focal length EFL1 of the first lens group to the overall focal length EFL of the lens satisfies the constraint: 0.75<EFL1 / EFL<0.85 (1); the ratio of the focal length EFL2 of the second lens group to the overall focal length EFL of the lens satisfies the constraint: -2.6<EFL2 / EFL<-2.3 (2). Based on the above constraints, it is helpful to achieve long focal length, compact structure, aberration correction and temperature stability. It can be seen from the focal length ratio that the first lens group provides the main positive focal power of the system and bears most of the convergence effect. The second lens group has a negative focal power and is used to extend the effective focal length. The combination of the positive focal power (convergence) of the first lens group and the negative focal power (divergence) of the second lens group forms a telephoto structure. Based on the above constraints, the overall focal length EFL can be made greater than the physical lens barrel length, realizing the compact design of the telephoto lens. In short-wave near-infrared (SWIR) imaging, the telephoto design facilitates long-distance observation while keeping the device lightweight. Preferably, EFL1 / EFL is close to a balance point of 0.8 and EFL2 / EFL is close to a balance point of -2.5, so that the defocus caused by temperature changes can be offset.

[0035] Based on the above constraints (1) and (2), the ratio of the focal length EFL(G6) of the sixth lens 6 to the overall focal length EFL of the lens satisfies the constraint: 0.65<EFL(G6) / EFL<0.75 (3). Since the strong positive optical power of the first lens group (EFL1 / EFL≈0.8) will produce positive field curvature and pincushion distortion, by limiting the optical power of the sixth lens 6 (EFL(G6) / EFL), the sixth lens 6 can provide reverse distortion correction power, and 0.65–0.75 is the range with the highest correction efficiency (the golden band verified by simulation).

[0036] Furthermore, in this embodiment, the refractive index Nd1 and Abbe number Vd1 of the first lens 1 satisfy the following constraints: 1.73<Nd1<1.75 (4); 44.6<Vd1<45.2 (5); the refractive index Nd2 and Abbe number Vd2 of the second lens 2 satisfy the following constraints: 1.76<Nd2<1.78 (6); 49.2<Vd1<49.8 (7); the refractive index Nd3 and Abbe number Vd3 of the third lens 3 satisfy the following constraints: 1.90<Nd3<1.92 (8); 34.9<Vd3<35.5 (9); the refractive index Nd4 and Abbe number Vd4 of the fourth lens 4 satisfy the following constraints: 1.94<Nd4<1.96 (10); 17.6<Vd4<18.2 (11). Based on the above constraints (4) to (11), the first compound lens and the second compound lens cooperate with each other to achieve chromatic aberration correction of the first lens group. In addition, high refractive index materials are mostly used in the first lens group. The use of high refractive index materials helps to reduce spherical aberration and higher-order aberrations, thereby improving imaging quality.

[0037] Furthermore, in this embodiment, the refractive index Nd5 and Abbe number Vd5 of the fifth lens 5 satisfy the following constraints: 1.77<Nd5<1.79 (12); 43.8<Vd5<44.4 (13); the refractive index Nd6 and Abbe number Vd6 of the sixth lens 6 satisfy the following constraints: 1.79<Nd6<1.81 (14); 34.6<Vd6<35.2 (15). Based on the above constraints (13) and (15), the Abbe numbers of the fifth lens 5 and the sixth lens 6 are highly matched, perfectly eliminating chromatic aberration. Similarly, the fifth lens 5 and the sixth lens 6 are both made of high refractive index materials, which helps to reduce spherical aberration and higher-order aberrations and improve imaging quality.

[0038] For example, in this embodiment, the thermal expansion coefficient of the material of the first lens 1 is 8*10 - 6 mm / ℃, the thermal expansion coefficient of the material of the second lens 2 is 5.8*10 -6 mm / ℃, the thermal expansion coefficient of the material of the third lens 3 is 7.1*10 -6 mm / ℃, the thermal expansion coefficient of the material of the fourth lens 44 is 6*10 -6 mm / ℃, the thermal expansion coefficient of the material of the fifth lens 5 is 5.9*10 -6 mm / ℃, the thermal expansion coefficient of the material of the sixth lens 66 is 7.9*10 -6 mm / ℃, the thermal expansion coefficient of the lens barrel material is 23.6*10-6 mm / °C. For example, the materials used for each lens and the refractive index temperature coefficients of each lens in the temperature range of -20°C to 80°C are shown in Table 1:

[0039] Table 1

[0040] Lens order Material -40~-20（℃） -20~0（℃） 0~20（℃） 20~40（℃） 40~60（℃） 60~80（℃） 1 H-LaF3B -0.1 0.0 0.2 0.2 0.3 0.4 2 H-LaF50B 3.0 3.4 3.2 3.5 3.5 3.2 3 H-ZLaF4LA 2.7 3.0 3.2 3.2 3.4 3.5 4 H-ZF88 -0.4 -0.4 -0.2 0.1 0.4 1.0 5 H-LaF52 6.1 6.3 6.4 6.4 6.5 7.1 6 H-ZLaF66GT -0.3 0.8 1.0 1.0 1.1 1.2

[0041] In Table 1, lens numbers 1 through 6 correspond to the first through sixth lenses. Based on the above lens structure and material parameters, the telephoto athermal lens provided in this embodiment achieves a long focal length and excellent image quality within the SWIR band (900nm to 1700nm) and a temperature range of -30°C to 70°C. The lens's full field of view (FOV) satisfies the following conditions: 9° < FOV < 10°, and its F-number satisfies the following conditions: 2 < F < 2.8. The lens structure provided in this embodiment comprises only six lenses, achieving the athermal lens's requirements for a long focal length, compact structure, aberration correction, and temperature stability. Furthermore, all lenses can be made of glass spherical lenses, resulting in a more cost-effective design.

[0042] Example 2

[0043] For example, the basic parameters of each lens element in the telephoto athermal lens provided in this embodiment are shown in Table 2 (wherein the units of curvature radius and air space are both millimeters (mm)):

[0044] Table 2

[0045] Lens surface serial number Radius of curvature Air gap / glass center thickness Refractive index Nd Abbe number Vd S1 82.184 7.35 1.744 44.900 S2 -55.732 1.00 1.772 49.599 S3 404.330 0.15 / / S4 47.882 5.69 1.911 35.250 S5 -283.763 4.17 1.946 17.942 S6 61.096 4.91 / / S7 Infinity 25.15 / / S8 47.739 8.45 1.786 44.187 S9 19.821 8.37 / / S10 28.397 3.01 1.801 34.967 S11 58.374 32.35 / /

[0046] In Table 2, lens surface numbers S1~S11 and Figure 1The S1 to S11 marked in the figure correspond to each other, where S7 represents the aperture, S2 is the bonding surface between the first lens 1 and the second lens 2, and its corresponding refractive index and Abbe number are the same as those of the second lens 2, and S5 is the bonding surface between the third lens 3 and the fourth lens 4, and its corresponding refractive index and Abbe number are the same as those of the fourth lens 4. According to the data in the above table, the lens focal length is F=100mm; the field of view is FOV=9.18°; the F number is F=2.4; EFL(1G)=84.38mm; EFL(1G) / EFL=0.84; EFL(2G)=-242.16; EFL(2G) / EFL=-2.4; EFL(G6)=68.53; EFL(G6) / EFL=0.68; Nd1=1.744; Vd1=44.9; Nd2=1.772; Vd2=49.599; Nd3=1.911; Vd3=35.250; Nd4=1.946; Vd4=17.942; Nd5=1.786; Vd5=44.187; Nd6=1.801; Vd6=34.967. In addition, all lenses in this embodiment are glass spherical lenses, and the above requirements are met.

[0047] The operating wavelength of the telephoto athermal lens provided in this embodiment is 900nm~1700nm. Figure 2 、 Figure 3 and Figure 4 It can be seen that by selecting the right lens material and matching it with the thermal expansion coefficient of the A6061 lens barrel material, athermalization can even be achieved in the range of -40°C to 80°C. Figures 2 to 4These graphs show the MTF of an athermalized lens at 40°C, 20°C, and 80°C. The MTF value describes the efficiency of a lens in transferring object-space contrast to the image space (0–100%). The horizontal axis represents spatial frequency, measured in lp / mm (line pairs per millimeter), representing the number of black and white lines per millimeter. The vertical axis represents the MTF value, which ranges from 0 to 1 (or 0% to 100%), with higher values ​​indicating closer-to-ideal imaging. The meridian in the graph represents lines along the radial direction of the lens, while the sagittal represents concentric lines perpendicular to the radial direction. The different curves in the figure represent different field of view positions (e.g., radial (meridian) distances of 1.8mm, 3mm, and 4.2mm from the image center). For example, the curve corresponding to 8.20000 mm-meridian represents the MTF curve measured along the meridional (radial) direction at a point 8.2mm outward from the center of the image plane. The "Diffraction Limit-Meridian" curve in the figure represents the theoretical upper limit of the performance of an ideal optical system (limited only by physical diffraction) in the meridional direction, while the "Diffraction Limit-Sagittal" curve represents the theoretical upper limit of the performance of an ideal optical system (limited only by physical diffraction) in the sagittal direction. The telephoto athermalized lens provided in this embodiment achieves low-frequency (10 lp / mm) MTF values ​​exceeding 0.8 (reflecting overall outline contrast) and high-frequency (50 lp / mm) MTF values ​​exceeding 0.5 (indicating detail resolution) at -40°C, 20°C, and 80°C, ensuring a balanced contrast-resolution ratio.

[0048] Figure 5 This is a distortion diagram of the telephoto athermal lens provided in this embodiment at 20°. The abscissa is the distortion rate, and the ordinate is the field of view angle. The distortion rate is calculated as follows: Distortion Rate = [(Actual Image Height - Ideal Image Height) / Ideal Image Height] × 100%. A positive value indicates pincushion distortion (the image is convex), while a negative value indicates barrel distortion (the image is concave). Figure 5 As can be seen, the maximum distortion is 0.1813%, far below the industrial inspection lens standard (within ±1.5%) and meeting the expected standard. Furthermore, the curve corresponding to "-0.9000" in the attached figure represents the distortion of light with a wavelength of 900nm passing through a telephoto athermal lens at 20°. The other curves correspond accordingly and are not detailed here.

[0049] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0050] The above are merely embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A telephoto athermal lens for shortwave near-infrared imaging, wherein the operating wavelength range of the telephoto athermal lens is 900 nm to 1700 nm, and the lens is characterized in that: The telephoto athermal lens comprises a lens barrel and a first lens group, an aperture, and a second lens group sequentially arranged in the lens barrel from the object side to the image side, wherein the first lens group is used to perform aberration correction on incident light, the aperture is used to limit the light transmission amount of the incident light, and the second lens group is used to perform residual aberration correction on light passing through the first lens group and the aperture; from the object side to the image side, the first lens group comprises a first lens (1), a second lens (2), a third lens (3), and a fourth lens (4), wherein the first lens (1) and the second lens (2) are glued together to form a first composite lens, and the third lens (3) and the fourth lens (4) are glued together to form a second composite lens; from the object side to the image side, the second lens group comprises a fifth lens (5) and a sixth lens (6); the first lens (1) is a biconvex positive lens, the second lens (2) is a negative lens, the third lens (3) is a positive lens, the fourth lens (4) is a negative lens, the fifth lens (5) is a negative lens, and the sixth lens (6) is a positive lens.

2. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 1, characterized in that: The ratio of the focal length EFL1 of the first lens group to the overall focal length EFL of the lens satisfies the following constraints: 0.75<EFL1 / EFL<0.85 (1); The ratio of the focal length EFL2 of the second lens group to the overall focal length EFL of the lens satisfies the following constraints: -2.6<EFL2 / EFL<-2.3 (2).

3. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 2, characterized in that: The fifth lens (5) is a meniscus negative lens with its concave surface facing the image side, and the sixth lens (6) is a meniscus positive lens with its convex surface facing the object side, wherein the ratio between the focal length EFL (G6) of the sixth lens (6) and the overall focal length EFL of the lens satisfies the following constraints: 0.65<EFL(G6) / EFL<0.75 (3).

4. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 1, characterized in that: The thermal expansion coefficient of the material of the first lens (1) is 8*10 -6 mm / ℃, the thermal expansion coefficient of the material of the second lens (2) is 5.8*10 -6 mm / ℃, the thermal expansion coefficient of the material of the third lens (3) is 7.1*10 -6 mm / ℃, the thermal expansion coefficient of the material of the fourth lens (4) is 6*10 -6 mm / ℃, the thermal expansion coefficient of the material of the fifth lens (5) is 5.9*10 -6 mm / ℃, the thermal expansion coefficient of the material of the sixth lens (6) is 7.9*10 -6 mm / ℃, the thermal expansion coefficient of the lens barrel material is 23.6*10 -6 mm / ℃.

5. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 1, characterized in that: The refractive index Nd1 and Abbe number Vd1 of the first lens (1) satisfy the following constraints: 1.73<Nd1<1.75 (4) 44.6<Vd1<45.2 (5); The refractive index Nd2 and Abbe number Vd2 of the second lens (2) satisfy the following constraints: 1.76<Nd2<1.78 (6); 49.2<Vd2<49.8 (7) The refractive index Nd3 and Abbe number Vd3 of the third lens (3) satisfy the following constraints: 1.90<Nd3<1.92(8); 34.9<Vd3<35.5 (9) The refractive index Nd4 and Abbe number Vd4 of the fourth lens (4) satisfy the following constraints: 1.94<Nd4<1.96 (10); 17.6<Vd4<18.2 (11) 6. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 5, characterized in that: The refractive index Nd5 and Abbe number Vd5 of the fifth lens (5) satisfy the following constraints: 1.77<Nd5<1.79 (12); 43.8<Vd5<44.4 (13); The refractive index Nd6 and Abbe number Vd6 of the sixth lens (6) satisfy the following constraints: 1.79<Nd6<1.81 (14); 34.6<Vd6<35.2 (15).

7. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 1, characterized in that: The full field of view (FOV) of the telephoto athermal lens satisfies the following constraints: 9°<FOV<10° (16) 8. The long-focus athermalized lens for short-wave near-infrared imaging according to claim 1, characterized in that: The F number of the telephoto athermal lens satisfies the following constraints: 2＜F＜2.8 （17）。 9. The long-focus athermalized lens for short-wave near-infrared imaging according to any one of claims 1 to 8, characterized in that: The first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5) and the sixth lens (6) are all glass spherical lenses.

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