Infrared lens and thermal imager

Abstract

This application discloses an infrared lens and a thermal imager. The infrared lens includes a first lens, a second lens, a third lens, and a fourth lens arranged sequentially along the optical axis A from the object side to the image side. The first lens is a positive meniscus lens, with a first surface being a convex surface facing the object side and a second surface being a concave surface facing the image side. The second lens is a biconvex lens, having two convex surfaces facing both the object and image sides. The third lens is a negative meniscus lens, having a concave surface facing the object side and a convex surface facing the image side. The fourth lens is also a biconvex lens, similarly including two convex surfaces. The overall focal length of the infrared lens is f, and the focal lengths of each lens are f1, f2, f3, and f4, respectively, satisfying the following focal length relationships: -2 < f1 / f < -1, 2 < f2 / f < 3, -11 < f3 / f < -10, 2 < f4 / f < 3. Through the above structure and focal length matching, this infrared lens can achieve excellent imaging performance and good optical correction, making it suitable for high-performance infrared imaging systems.

Description

Technical Field

[0001] This application relates to the field of optical devices, specifically to infrared lenses and thermal imagers. Background Technology

[0002] Infrared imaging technology is an imaging method that achieves image observation by detecting the infrared radiation emitted by the target itself. This technology features passive operation, no need for external lighting, and non-contact measurement. It has good environmental adaptability and can operate stably under harsh conditions such as darkness, rain, snow, and electromagnetic interference. It is widely used in fields such as night surveillance, industrial inspection, and reconnaissance.

[0003] With the increasing demand for infrared imaging applications, higher requirements are being placed on the performance of imaging systems, especially in applications such as wide-area monitoring and rapid response. Infrared lenses need to have a wider field of view to achieve real-time observation of large-scale scenes. However, early infrared lenses generally suffered from narrow field of view and limited coverage. When observing at close ranges of 1 to 5 meters, mechanical rotating platforms or multi-lens stitching systems were often required, resulting in complex system structures, increased costs, and decreased reliability.

[0004] Furthermore, to achieve good image quality and temperature adaptability, traditional infrared optical systems often require complex thermal compensation structures, resulting in large lens size, heavy weight, and high manufacturing costs. Especially in close-range (e.g., 1-meter object distance) wide-angle imaging applications, how to balance miniaturization, lightweight design, and low cost while ensuring imaging performance has become a key issue in infrared lens design.

[0005] Therefore, it is necessary to design an ultra-wide field-of-view infrared lens optimized for close-range (e.g., 1-meter object distance) imaging, which, while ensuring image clarity, also features low cost, lightweight design, and passive heat-free operation, in order to meet the demand for efficient and stable close-range wide-angle imaging in complex environments. Summary of the Invention

[0006] To overcome or mitigate at least one of the shortcomings of the prior art, one objective of this application is to provide an infrared lens that solves the problem of narrow field of view, making it difficult to cover large-scale scenes. Another objective of this application is to provide a thermal imager.

[0007] To achieve the above-mentioned objectives, the present application may adopt the following technical solutions.

[0008] This application provides an infrared lens, comprising the following components arranged sequentially along optical axis A from the object side to the image side:

[0009] The first lens is a positive meniscus lens, comprising a first surface and a second surface, wherein the first surface is convex and faces the object side, and the second surface is concave and faces the image side;

[0010] The second lens is a biconvex lens, including a third surface and a fourth surface, wherein the third surface is convex and faces the object side, and the fourth surface is convex and faces the image side;

[0011] The third lens is a negative meniscus lens, comprising a fifth surface and a sixth surface. The fifth surface is concave and faces the object side, and the sixth surface is convex and faces the image side.

[0012] The fourth lens is a biconvex lens, comprising a seventh surface and an eighth surface, wherein the seventh surface is convex and faces the object side, and the eighth surface is convex and faces the image side;

[0013] Wherein: the overall focal length of the infrared lens is f;

[0014] The focal length of the first lens is f1, which satisfies: -2 < f1 / f < -1;

[0015] The focal length of the second lens is f2, which satisfies: 2 < f2 / f < 3;

[0016] The focal length of the third lens is f3, which satisfies: -11 < f3 / f < -10;

[0017] The focal length of the fourth lens is f4, which satisfies: 2 < f4 / f < 3.

[0018] In at least one embodiment, the overall focal length is 1.9 mm.

[0019] In at least one embodiment, at least one of the first surface, the second surface, the third surface, the fourth surface, the fifth surface, the sixth surface, the seventh surface, and the eighth surface is an aspherical surface.

[0020] In at least one embodiment, the profile of the aspherical surface on the optical axis satisfies:

[0021]

[0022] Where z is the sag of a point on the aspherical surface along the optical axis, r is the shortest distance between the point and the optical axis, c is the radius of curvature at the vertex of the aspherical surface, k is the conic coefficient of the aspherical surface, and α i Let i be the aspherical coefficient of the aspherical surface, i be the index of the polynomial term in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface.

[0023] in:

[0024] The first surface satisfies: 185mm ≤ c ≤ 190mm;

[0025] The second face satisfies: 0mm≤c≤5mm, k=0, α2=1.10e-3, α3=1.3e-4, α4=-2.70e-5, α5=4.90e-6, α6=1.9e-9;

[0026] The third surface satisfies: 15mm≤c≤20mm, k=0, α2=-1.0e-4, α3=-5.3e-6, α4=9.0e-7, α5=2.0e-8, α6=2.0e-8;

[0027] The fourth surface satisfies: -20mm≤c≤-15mm, k=0, α2=-1.0e-4, α3=-5.3e-6, α4=9.0e-7, α5=2.0e-8, α6=2.0e-8;

[0028] The fifth surface satisfies: -10mm≤c≤-5mm;

[0029] The sixth surface satisfies: -10mm≤c≤-5mm;

[0030] The seventh face satisfies: 15mm≤c≤20mm, k=-24, α2=-7.67e-4, α3=-5.23e-5, α4=8.1e-7, α5=-1.43e-8, α6=2.0e-8;

[0031] The eighth face satisfies: -10mm≤c≤-5mm, k=5.4, α2=-2.0e-4, α3=1.1e-5, α4=-1.3e-7, α5=-1.43e-8, α6=2.0e-8.

[0032] In at least one embodiment, the eighth surface is a diffraction surface.

[0033] The diffraction surface satisfies

[0034]

[0035] Where Φ is the phase of the diffraction surface, M is the diffraction order of the diffraction surface, and A i Let be the coefficients of each term in the diffraction surface, ρ be the normalized radial aperture coordinates of the diffraction surface, i be the index of the polynomial term in the diffraction surface, and N be the total number of polynomial terms in the diffraction surface.

[0036] The eighth face satisfies M=100, A1=-23128.619, A2=9733206.4, A3=-1.1787688e+10, A4=8.2302806e+12, A5=-2.1632627e+15.

[0037] In at least one embodiment, the first lens and the third lens are made of chalcogenide glass of IRG202, and the second lens and / or the fourth lens are made of chalcogenide glass of IRG206.

[0038] In at least one embodiment, the optical parameters of the infrared lens satisfy the following conditions:

[0039] The overall focal length is 1.9mm;

[0040] The aperture is 1.0;

[0041] The field of view is greater than or equal to 172°;

[0042] The total optical length is less than or equal to 19 mm;

[0043] The optical back intercept is greater than or equal to 3.68 mm;

[0044] The operating wavelength range is 8μm to 14μm.

[0045] In at least one embodiment, in the optical axis direction,

[0046] The center thickness of the first lens is 1.0m;

[0047] The center thickness of the second lens is 2.0 mm;

[0048] The center thickness of the third lens is 1.0 mm;

[0049] The center thickness of the fourth lens is 4.0 mm; and

[0050] The air gap between the first lens and the second lens is 4 mm;

[0051] The air gap between the second lens and the third lens is 2.1 mm;

[0052] The air gap between the third lens and the fourth lens is 0.75 mm.

[0053] In at least one embodiment, the infrared lens further includes a flat glass plate located on the image side of the fourth lens; and the air gap between the flat glass plate and the fourth lens on the optical axis is 2.6 mm.

[0054] This application also provides a thermal imager, which includes a photosensitive element and the aforementioned infrared lens.

[0055] By adopting the above technical solution, this application provides an infrared lens and a thermal imager. Through the rational configuration of the first to fourth lenses, this infrared lens can effectively achieve close-range wide-angle imaging while ensuring a large field of view. Furthermore, by optimizing the focal length configuration of each lens, the infrared lens exhibits excellent image quality, thermal stability, and image plane flatness. Simultaneously, the optical structure design of the lens simplifies traditional thermal compensation requirements, reduces weight and cost, improves system reliability, and is suitable for efficient and stable operation in complex environments. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the structure of an infrared lens according to an embodiment of this application;

[0057] Figure 2 This is a graph showing the optical modulation transfer function of an infrared lens according to an embodiment of this application at 20°C.

[0058] Figure 3 This is a graph showing the optical modulation transfer function of an infrared lens according to an embodiment of this application at -40°C.

[0059] Figure 4 This is a graph showing the optical modulation transfer function of an infrared lens according to an embodiment of this application at 60°C.

[0060] Figure 5 A field curvature diagram of an infrared lens according to an embodiment of this application;

[0061] Figure 6 A distortion diagram of an infrared lens according to an embodiment of this application;

[0062] Figure 7 This is a relative illumination diagram of an infrared lens according to an embodiment of this application.

[0063] Explanation of reference numerals in the attached figures

[0064] 11 First lens; 12 Second lens; 13 Third lens; 14 Fourth lens; 15 Flat glass;

[0065] 20 image sensors;

[0066] S1 First side; S2 Second side; S3 Third side; S4 Fourth side; S5 Fifth side; S6 Sixth side; S7 Seventh side; S8 Eighth side;

[0067] A-axis Detailed Implementation

[0068] Exemplary embodiments of this application are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are for teaching those skilled in the art how to implement this application only, and are not intended to exhaust all possible methods of this application, nor to limit the scope of this application.

[0069] In this application, some numerical values ​​are expressed in scientific notation. For example, 1.40e-7 represents 1.40 × 10⁻⁷. -7 Unless otherwise specified, "from one value to another" should be understood to include the values ​​at both endpoints themselves.

[0070] In this application, Figure 1 The dashed line in the diagram represents the optical axis A of the infrared lens, where the left side of optical axis A is the object side and the right side is the image side.

[0071] In the following formulas involving ratios, the units of all parameters remain consistent. For example, if the numerator is in millimeters (mm), then the denominator is also in millimeters (mm) to ensure the physical consistency of the ratio.

[0072] Furthermore, the positive and negative directions of the radius of curvature of an optical surface are defined as follows: if the optical surface (including the object side or the image side) is convex towards the object side, its radius of curvature is positive; if the optical surface is convex towards the image side, which is equivalent to being concave towards the object side, its radius of curvature is negative.

[0073] It should be noted that the shape of the lens and the degree of concavity and convexity of the two sides of the image shown in the accompanying drawings are only schematic representations intended to aid understanding and do not constitute any limitation on the specific implementation of this application.

[0074] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0075] like Figure 1 As shown, an embodiment of this application provides an infrared lens, which may include a plurality of optical elements arranged sequentially along the optical axis A from the object side to the image side, including: a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, and a flat glass 15.

[0076] The first lens 11 can be a positive meniscus lens, which can include a first surface S1 and a second surface S2. The first surface S1 can be a convex surface facing the object side, and the second surface S2 can be a concave surface facing the image side.

[0077] The second lens 12 can be a biconvex lens, which can include a third surface S3 and a fourth surface S4. The third surface S3 can be a convex surface facing the object side, and the fourth surface S4 can be a convex surface facing the image side.

[0078] The third lens 13 can be a negative meniscus lens, which can include a fifth surface S5 and a sixth surface S6. The fifth surface S5 can be concave and face the object side, and the sixth surface S6 can be convex and face the image side.

[0079] The fourth lens 14 can be a biconvex lens, which can include a seventh surface S7 and an eighth surface S8. The seventh surface S7 can be convex and face the object side, and the eighth surface S8 can be convex and face the image side.

[0080] The flat glass 15 can be located on the image side of the fourth lens 14 for sealing, protection or other optical functions.

[0081] In this embodiment, the overall focal length of the infrared lens is denoted as f, the focal length of the first lens 11 is denoted as f1, the focal length of the second lens 12 is denoted as f2, the focal length of the third lens 13 is denoted as f3, and the focal length of the fourth lens 14 is denoted as f4, satisfying the following relationship:

[0082] The focal length of the first lens 11 is denoted as f1, which satisfies -2 < f1 / f < -1;

[0083] Let the focal length of the second lens 12 be f2, which satisfies 2 < f2 / f < 3;

[0084] The focal length of the third lens 13 is denoted as f3, which satisfies -11 < f3 / f < -10;

[0085] The focal length of the fourth lens 14 is denoted as f4, which satisfies 2 < f4 / f < 3.

[0086] In some preferred embodiments, the overall focal length f of the infrared lens can be 1.9 mm.

[0087] Furthermore, the relative positional relationship of the above optical elements can be understood as follows: the first lens 11 is located on the object side of the second lens 12, the third lens 13 is located on the image side of the second lens 12, the fourth lens 14 is located on the image side of the third lens 13, and the flat glass 15 is located on the image side of the fourth lens 14.

[0088] Furthermore, in this embodiment, the center thickness (i.e., the thickness along the optical axis A) of each lens element is as follows:

[0089] The center thickness of the first lens 11 can be 1.0 mm;

[0090] The center thickness of the second lens 12 can be 2mm;

[0091] The center thickness of the third lens 13 can be 1 mm;

[0092] The center thickness of the fourth lens 14 can be 4mm.

[0093] Furthermore, the air gap between the lens elements along the optical axis A can be set as follows:

[0094] The air gap between the first lens 11 and the second lens 12 can be 4mm;

[0095] The air gap between the second lens 12 and the third lens 13 can be 2.1 mm.

[0096] The air gap between the third lens 13 and the fourth lens 14 can be 0.75 mm;

[0097] The air gap between the fourth lens 14 and the flat glass 14 can be 2.6 mm.

[0098] Preferably, the first lens 11, the second lens 12, the third lens 13, and the fourth lens 14 may include aspherical optical surfaces. Specifically, at least one of the optical surfaces S1 to S8 is aspherical. In a preferred embodiment, all eight optical surfaces S1 to S8 may be aspherical.

[0099] Aspherical shapes can satisfy the following general relationship:

[0100]

[0101] Where z is the sag of a point on the aspherical surface along the optical axis A, r is the shortest distance between the point and the optical axis A, c is the radius of curvature at the vertex of the aspherical surface, k is the conic coefficient of the aspherical surface, and α i denoted as the aspherical coefficients, i is the index of the polynomial term in the aspherical surface, and N is the total number of polynomial terms in the aspherical surface.

[0102] For example, in this embodiment, the parameter ranges corresponding to each optical surface from S1 to S8 can be set as follows:

[0103] The first surface S1 satisfies: 185mm≤c≤190mm;

[0104] The second surface S2 satisfies: 0mm≤c≤5mm, k=0, α2=1.10e-3, α3=1.3e-4, α4=-2.70e-5, α5=4.90e-6, α6=1.9e-9;

[0105] The third surface S3 satisfies: 15mm≤c≤20mm, k=0, α2=-1.0e-4, α3=-5.3e-6, α4=9.0e-7, α5=2.0e-8, α6=2.0e-8;

[0106] The fourth face S4 satisfies: -20mm≤c≤-15mm, k=0, α2=-1.0e-4, α3=-5.3e-6, α4=9.0e-7, α5=2.0e-8, α6=2.0e-8;

[0107] The fifth surface S5 satisfies: -10mm ≤ c ≤ -5mm;

[0108] The sixth surface S6 satisfies: -10mm ≤ c ≤ -5mm;

[0109] The seventh face S7 satisfies: 15mm≤c≤20mm, k=-24, α2=-7.67e-4, α3=-5.23e-5, α4=8.1e-7, α5=-1.43e-8, α6=2.0e-8;

[0110] The eighth face S8 satisfies: -10mm≤c≤-5mm, k=5.4, α2=-2.0e-4, α3=1.1e-5, α4=-1.3e-7, α5=-1.43e-8, α6=2.0e-8;

[0111] Furthermore, the fourth lens 14 may include a diffraction surface to optimize chromatic aberration of the lens. For example, the eighth surface S8 of the fourth lens 14 may be designed as a diffraction surface, and its phase function satisfies the following relationship:

[0112]

[0113] Where Φ is the phase function of the diffraction plane, M is the diffraction order of the diffraction plane, and A i ρ represents the coefficients of each term in the diffraction plane, ρ represents the normalized radial aperture coordinates, i represents the index of the polynomial term in the diffraction plane, and N represents the total number of polynomial terms in the diffraction plane.

[0114] For example, in some preferred embodiments, the parameters of the eighth surface S8 can be set as follows:

[0115] M=100, A1=-23128.619, A2=9733206.4, A3=-1.1787688e+10,

[0116] A4=8.2302806e+12, A5=-2.1632627e+15.

[0117] In this embodiment, the first lens 11 and the third lens 13 may be made of chalcogenide glass of IRG202, and the second lens 12 and the fourth lens 14 may be made of chalcogenide glass of IRG206.

[0118] Furthermore, in this embodiment, the total optical length of the infrared lens can be less than or equal to 19 mm, and the optical back focal length can be greater than or equal to 3.68 mm, making it suitable for integrated installation in compact infrared imaging modules. The aperture coefficient (F-number) of the infrared lens can be 1.0, providing high light throughput and high-sensitivity imaging capabilities, while the field of view is greater than or equal to 172°, enabling near-panoramic infrared observation.

[0119] Figures 2 to 4 The diagram shows the optical modulation transfer function (MTF) curves of the infrared lens provided in this embodiment at different temperatures. The MTF curve represents the change in the lens's ability to reproduce the details of the subject onto the image plane as a function of spatial frequency. The horizontal axis represents spatial frequency in lines pairs per millimeter (lp / mm), and the vertical axis represents the coefficients of the optical transfer function (OTF).

[0120] Reference Figure 2 It shows the MTF curves of the infrared lens at 20°C for different image plane heights (0.384mm, 0.768mm, 1.152mm, 1.536mm, 1.92mm) at operating wavelengths from 8μm to 12μm, with 42 line pairs of spatial frequencies in the meridional and sagittal directions. Figure 2 As can be seen, the MTF values ​​in the meridional and sagittal directions at the central field of view (image height of 0 mm) are both higher than 0.40, and the MTF values ​​in the other fields of view are also higher than 0.33.

[0121] It is understandable that the modulation transfer function is an important indicator for measuring the imaging quality of a lens. The higher the value, the stronger the image contrast and detail reproduction capability, thus reflecting that the infrared lens has good imaging performance and field uniformity.

[0122] Therefore, from Figure 2 It can be seen that the infrared lens maintains a high MTF performance at room temperature (20℃), indicating that it has good imaging quality.

[0123] See Figure 3 It shows the MTF curves of the infrared lens at 42 line pairs spatial frequencies in the meridional and sagittal directions at different image plane heights (0.384mm, 0.768mm, 1.152mm, 1.536mm, 1.92mm) at operating wavelengths from 8μm to 12μm, at -40℃. Figure 3It can be seen that the MTF values ​​in both the meridional and sagittal directions at the central field of view (image plane height of 0 mm) are greater than 0.40, and the MTF values ​​in the other fields of view are also higher than 0.27. Overall, the infrared lens maintains a high MTF performance even in a low-temperature environment (-40℃), indicating that it has good low-temperature imaging quality.

[0124] See Figure 4 It shows the MTF curves of the infrared lens at 60°C for different image plane heights (0.384mm, 0.768mm, 1.152mm, 1.536mm, 1.92mm) at operating wavelengths from 8μm to 12μm, with 42 line pairs of spatial frequencies in the meridional and sagittal directions. From Figure 4 It can be seen that the MTF values ​​in both the meridional and sagittal directions at the central field of view (image plane height of 0mm) are higher than 0.40, and the MTF values ​​in the other fields of view are also higher than 0.30. Overall, this indicates that the lens still has good imaging performance and temperature stability in high-temperature (60℃) environments.

[0125] See Figure 5 This diagram shows the field curvature of an infrared lens at different operating wavelengths (8μm, 10μm, 12μm), evaluating the difference in image quality between the center and edges of the lens's imaging plane. The horizontal axis represents the field curvature value at a point on the image plane, in mm, and the vertical axis represents the field of view. Figure 5 As can be seen, regardless of the wavelength, the field curvature values ​​in the meridional and sagittal directions are controlled within the range of -0.05mm to 0.05mm, indicating that the infrared lens has good image plane flatness and can ensure clear and consistent imaging.

[0126] See Figure 6 The figure shows the distortion characteristics of the infrared lens. The horizontal axis represents the percentage of distortion, and the vertical axis represents the field of view. As can be seen from the figure, the maximum distortion of this infrared lens is 93%, which effectively expands the field of view and meets the requirements of large field-of-view applications.

[0127] See Figure 7 The figure shows the relative illuminance distribution of the infrared lens, where relative illuminance is the ratio of brightness at the center to that at the edge. The horizontal axis represents the image plane height in mm, and the vertical axis represents the normalized illuminance. It can be seen that the relative illuminance at the center of the lens is 1, indicating no energy loss in the central region of the optical system; the relative illuminance at the edge is also greater than 0.87, indicating that the overall illuminance distribution of the lens is uniform and it possesses good illumination balance performance.

[0128] comprehensive Figures 3 to 7 The analysis results show that the infrared lens provided in this embodiment performs excellently in terms of imaging quality, thermal stability, image plane flatness, field of view coverage and illumination uniformity, and can meet the application requirements of high-performance infrared imaging systems in complex environments.

[0129] The infrared lens provided in this application embodiment is optimized for close-range (e.g., 1-meter object distance). Through the aforementioned optical structure configuration, it achieves an ultra-wide field of view while ensuring image clarity. This infrared lens does not rely on a focusing mechanism, effectively meeting the optical system's requirements for optical power, achromatic aberration, and thermal aberration reduction, ensuring efficient and stable close-range wide-angle imaging in complex environments. This design achieves passive, thermal-free optics, meaning the lens can maintain stable performance at different temperatures without the need for an additional focusing mechanism. This design is not only simple in structure but also improves reliability, while possessing good process adaptability, making it suitable for large-scale integration and industrial applications.

[0130] An embodiment of this application also provides a thermal imager, which may include the infrared lens described above and a photosensitive element 20 disposed on the optical axis A.

[0131] Preferably, see Figure 1 The photosensitive element 20 can be an uncooled long-wave infrared detector, which is positioned on the optical axis A and located on the image side of the flat glass 15. Specifically, the resolution of the photosensitive element 20 can reach 256×192, the pixel pitch can be 12μm, and the operating wavelength range of the infrared lens can cover 8μm to 14μm.

[0132] It should be noted that the infrared lens provided in this application embodiment is not only applicable to thermal imagers, but can also be widely used in electronic imaging devices such as smartphones, tablets, and surveillance cameras, which will not be listed here.

[0133] It should be understood that the above-described embodiments, examples, or examples are merely exemplary and are not intended to limit this application. Those skilled in the art can make various modifications and changes to the above-described embodiments, examples, or examples under the teachings of this application without departing from the scope of this application.

Claims

1. An infrared lens, characterized in that, Including those arranged sequentially along the optical axis (A) from the object side to the image side: The first lens (11) is a positive meniscus lens, including a first surface (S1) and a second surface (S2). The first surface (S1) is convex and faces the object side, and the second surface (S2) is concave and faces the image side. The second lens (12) is a biconvex lens, including a third surface (S3) and a fourth surface (S4), wherein the third surface (S3) is convex and faces the object side, and the fourth surface (S4) is convex and faces the image side; The third lens (13) is a negative meniscus lens, including a fifth surface (S5) and a sixth surface (S6), wherein the fifth surface (S5) is concave and faces the object side, and the sixth surface (S6) is convex and faces the image side; The fourth lens (14) is a biconvex lens, including a seventh surface (S7) and an eighth surface (S8), wherein the seventh surface (S7) is convex and faces the object side, and the eighth surface (S8) is convex and faces the image side; Wherein: the overall focal length of the infrared lens is f; The focal length of the first lens (11) is f1, which satisfies: -2 < f1 / f < -1; The focal length of the second lens (12) is f2, which satisfies: 2 < f2 / f < 3; The focal length of the third lens (13) is f3, which satisfies: -11 < f3 / f < -10; The focal length of the fourth lens (14) is f4, which satisfies: 2 < f4 / f < 3; At least one of the first surface (S1), the second surface (S2), the third surface (S3), the fourth surface (S4), the fifth surface (S5), the sixth surface (S6), the seventh surface (S7), and the eighth surface (S8) is an aspherical surface; The profile of the aspherical surface on the optical axis (A) satisfies: wherein z is the sag of a point on the aspheric surface in the axial direction of the optical axis (A), r is the shortest distance of the point to the optical axis (A), c is the radius of curvature at the vertex of the aspheric surface, k is the conic coefficient of the aspheric surface, a i is the aspheric surface coefficient of the aspheric surface, i is the serial number of the polynomial term in the aspheric surface, and N is the total number of polynomials in the aspheric surface. in: The first surface (S1) satisfies: 185 mm ≤ c ≤ 190 mm; The second surface (S2) satisfies: 0 mm ≤ c ≤ 5 mm, k = 0, α2 = 1.10e-3, α3 = 1.3e-4, α4 = -2.70e-5, α5 = 4.90e-6, α6 = 1.9e-9; The third surface (S3) satisfies: 15 mm ≤ c ≤ 20 mm, k = 0, α2 = -1.0e-4, α3 = -5.3e-6, α4 = 9.0e-7, α5 = 2.0e-8, α6 = 2.0e-8; The fourth surface (S4) satisfies: -20 mm ≤ c ≤ -15 mm, k=0, α2=-1.0e-4, α3=-5.3e-6, α4=9.0e-7, α5=2.0e-8, α6=2.0e-8; The fifth surface (S5) satisfies: -10 mm ≤ c ≤ -5 mm; The sixth surface (S6) satisfies: -10 mm ≤ c ≤ -5 mm; The seventh surface (S7) satisfies: 15 mm ≤ c ≤ 20 mm, k = -24, α2 = -7.67e-4, α3 = -5.23e-5, α4 = 8.1e-7, α5 = -1.43e-8, α6 = 2.0e-8; The eighth surface (S8) satisfies: -10 mm ≤ c ≤ -5 mm, k = 5.4, α2 = -2.0e-4, α3 = 1.1e-5, α4 = -1.3e-7, α5 = -1.43e-8, α6 = 2.0e-8.

2. The infrared lens according to claim 1, characterized in that, The overall focal length is 1.9 mm.

3. The infrared lens according to claim 1 or 2, characterized in that, The eighth surface (S8) is a diffraction surface. The diffraction surface satisfies Where Φ is the phase of the diffraction surface, M is the diffraction order of the diffraction surface, and A i Let be the coefficients of each term in the diffraction surface, ρ be the normalized radial aperture coordinates of the diffraction surface, i be the index of the polynomial term in the diffraction surface, and N be the total number of polynomial terms in the diffraction surface. The eighth face (S8) satisfies M=100, A1= -23128.619, A2= 9733206.4, A3= -1.1787688e+10, A4=8.2302806e+12, A5= -2.1632627e+15.

4. The infrared lens according to claim 1 or 2, characterized in that, The first lens (11) and the third lens (13) are made of chalcogenide glass of IRG202, and the second lens (12) and / or the fourth lens (14) are made of chalcogenide glass of IRG206.

5. The infrared lens according to claim 1 or 2, characterized in that, The optical parameters of the infrared lens meet the following conditions: The overall focal length is 1.9 mm; The aperture is 1.0; The field of view is greater than or equal to 172°; The total optical length is less than or equal to 19 mm; The optical back intercept is greater than or equal to 3.68 mm; The operating wavelength range is 8 μm to 14 μm.

6. The infrared lens according to claim 1, characterized in that, In the direction of the optical axis (A), The center thickness of the first lens (11) is 1.0 m; The center thickness of the second lens (12) is 2.0 mm; The center thickness of the third lens (13) is 1.0 mm; The center thickness of the fourth lens (14) is 4.0 mm; and The air gap between the first lens (11) and the second lens (12) is 4 mm; The air gap between the second lens (12) and the third lens (13) is 2.1 mm; The air gap between the third lens (13) and the fourth lens (14) is 0.75 mm.

7. The infrared lens according to claim 1 or 2, characterized in that, The infrared lens also includes a flat glass plate (15) located on the image side of the fourth lens (14); and On the optical axis (A), the air gap between the flat glass (15) and the fourth lens (14) is 2.6 mm.

8. A thermal imager, characterized in that, It includes a photosensitive element (20) and an infrared lens according to any one of claims 1 to 7.

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