Far infrared lens

Abstract

The utility model discloses a far infrared lens. The far infrared lens comprises a first lens and a second lens which are sequentially arranged from an object side to an image side along an optical axis; the first lens is a glass aspheric lens with negative focal power, and the second lens is a glass aspheric lens with positive focal power; wherein 0.5 < = TH / f < = 0.67; tH is the sum of the center thickness of the first lens and the center thickness of the second lens, and f is the effective focal length of the far infrared lens. According to the technical scheme, the far infrared lens can meet the requirements of large aperture, small distortion and compact structure.

Description

Technical Field

[0001] This utility model relates to the field of optical device technology, and in particular to a far-infrared lens. Background Technology

[0002] Far-infrared lenses can image clearly at night or in harsh environments based on thermal radiation, and have high transmittance, enabling them to capture targets at greater distances. They are suitable for long-distance monitoring and observation, thus enabling far-infrared lenses to be widely used in many fields such as industrial manufacturing, security monitoring, outdoor night vision, fire fighting, and medical care.

[0003] However, in the existing technology, far-infrared lenses with large apertures generally suffer from problems such as high cost and large size, which limits the application of far-infrared lenses and is not conducive to their promotion. Utility Model Content

[0004] This invention provides a far-infrared lens that combines the characteristics of large aperture, low distortion, and compact structure.

[0005] This utility model provides a far-infrared lens, which includes a first lens and a second lens arranged sequentially from the object side to the image side along the optical axis.

[0006] The first lens is a glass aspherical lens with negative optical power, and the second lens is a glass aspherical lens with positive optical power.

[0007] Wherein, 0.5≤TH / f≤0.67; TH is the sum of the center thickness of the first lens and the center thickness of the second lens, and f is the effective focal length of the far-infrared lens.

[0008] Optionally, both the first lens and the second lens may be chalcogenide glass lenses.

[0009] Optionally, at least one of the object-side surface of the first lens, the image-side surface of the first lens, the object-side surface of the second lens, and the image-side surface of the second lens includes a diffraction surface.

[0010] Optionally, the optical power Φ1 of the first lens satisfies: -0.15≤Φ1 / Φ≤-0.004, where Φ is the overall optical power of the far-infrared lens.

[0011] Optionally, the optical power Φ2 of the second lens satisfies: 1.28≤Φ2 / Φ≤1.46, where Φ is the overall optical power of the far-infrared lens.

[0012] Optionally, the diameter D5 corresponding to the maximum image height of the image side of the second lens and the radius of curvature R5 of the image side of the second lens at the optical axis satisfy: 0.36 ≤ D5 / R5 ≤ -0.17.

[0013] Optionally, the distance L from the surface vertex of the image side of the second lens to the image plane satisfies: 0.423 < L / TTL < 0.475; TTL is the total length TTL of the far-infrared lens.

[0014] Optionally, the far-infrared lens further includes: a protective glass located on the image side of the second lens.

[0015] Optionally, the protective glass includes silica glass.

[0016] Optionally, the far-infrared lens further includes: an aperture disposed in the optical path between the first lens and the second lens.

[0017] The technical solution of the present utility model uses two aspherical lenses with positive and negative optical powers to form a far-infrared lens. By reasonably distributing the optical powers of each lens, and setting that the sum TH of the central thicknesses of the first lens and the second convex lens and the effective focal length f of the entire optical system of the far-infrared lens satisfy 0.5 ≤ TH / f ≤ 0.67, it is thus possible to ensure that the far-infrared lens takes into account the design of a large aperture, small distortion, and compact structure, and ensure that the far-infrared lens has a high imaging quality. Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of a far-infrared lens provided by an embodiment of the present utility model;

[0019] Figure 2 is Figure 1 a schematic diagram of the field curvature and distortion curve of the far-infrared lens shown;

[0020] Figure 3 is Figure 1 a schematic diagram of the axial aberration curve of the far-infrared lens shown;

[0021] Figure 4 is a schematic structural diagram of another far-infrared lens provided by an embodiment of the present utility model;

[0022] Figure 5 is Figure 4 a schematic diagram of the field curvature and distortion curve of the far-infrared lens shown;

[0023] Figure 6 is Figure 4 a schematic diagram of the axial aberration curve of the far-infrared lens shown;

[0024] Figure 7This is a schematic diagram of the structure of another far-infrared lens provided in this embodiment of the utility model;

[0025] Figure 8 yes Figure 7 A schematic diagram of the field curvature distortion curve of a far-infrared lens is shown.

[0026] Figure 9 yes Figure 7 The diagram shows the axial aberration curve of the far-infrared lens. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be fully described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Various modifications and variations can be made to this utility model without departing from its spirit or scope, which is obvious to those skilled in the art. Therefore, this utility model is intended to cover modifications and variations of this utility model that fall within the scope of the corresponding claims (the claimed technical solutions) and their equivalents.

[0028] Furthermore, the terms "first," "second," and similar terms used in the embodiments of this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, terms such as "an," "one," or "the" do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "including" or "comprising" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes. In addition, descriptions of "same" or "equal" in the embodiments of this disclosure do not mean that two objects are completely equal in size or shape; they are allowed to be approximately the same or approximately equal within a certain error range.

[0029] It should be noted that the implementation methods provided in this utility model embodiment can be combined with each other without contradiction.

[0030] Figure 1 This is a structural schematic diagram of a far-infrared lens provided in an embodiment of the present invention, for reference. Figure 1The far-infrared lens provided in this embodiment includes a first lens 10 and a second lens 20 arranged sequentially from the object side to the image side along the optical axis; the first lens 10 is a glass aspherical lens with negative optical power, and the second lens 20 is a glass aspherical lens with positive optical power; wherein, 0.5≤TH / f≤0.67; TH is the sum of the center thickness of the first lens 10 and the center thickness of the second lens 20, and f is the effective focal length of the far-infrared lens.

[0031] Optical power is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam; it characterizes the ability of an optical system to deflect light. The larger the absolute value of the optical power, the stronger the bending ability of light; the smaller the absolute value, the weaker the bending ability. When the optical power is positive, the refraction of light is converging; when the optical power is negative, the refraction of light is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., one surface of the lens), a single lens, or a system formed by multiple lenses (i.e., a lens group). The first lens 10 and the second lens 20 can be housed in a single lens barrel (…). Figure 1 Within (not shown), by reasonably setting the optical power of the first lens 10 and the second lens 20, that is, setting the first lens 10 to have a negative optical power, the incident angle of the light entering the far-infrared lens can be controlled, which can ensure that the far-infrared lens has a large amount of light transmission. Setting the second lens 20 to have a positive optical power, so that the optical power of the first lens 10 and the second lens 20 complement each other, can meet the requirements of large aperture and small distortion. For example, the aperture number F can reach 1, and the relative distortion can be less than or equal to 3%, thereby meeting the imaging requirements of high imaging quality.

[0032] Meanwhile, aspherical lenses are characterized by a continuous change in curvature from the center to the periphery. Unlike spherical lenses, which have a constant curvature from the center to the periphery, aspherical lenses have superior curvature radius characteristics, offering advantages in improving distortion and astigmatism. Using aspherical lenses can minimize aberrations that occur during image formation, thereby improving the lens's image quality. By employing aspherical lenses for both the first lens 10 and the second lens 20, aberration correction can be achieved, further reducing distortion and improving image quality.

[0033] Furthermore, by setting only two lenses with optical power in the far-infrared lens, namely the first lens 10 and the second lens, the far-infrared lens has a simple structure, which is beneficial for the small size and light weight of the far-infrared lens.

[0034] Furthermore, the center thickness of a lens can be understood as the length of the line connecting the object-side and image-side surfaces of the lens along the optical axis. By ensuring that the sum of the center thicknesses of the first lens 10 and the second lens 20 is TH, and that the ratio of TH to the effective focal length f of the entire optical system of the far-infrared lens is within the range of 0.5 to 0.67, it is possible to limit the volume of the first lens 10 and the second lens 20 to a smaller size while satisfying the requirements of a large aperture and small distortion. This further reduces the size of the far-infrared lens, enabling it to meet the requirements of small size and lightweight design, and allowing the imaging resolution of the far-infrared lens to meet the requirements of a 12μm pixel imaging sensor.

[0035] This utility model embodiment uses two aspherical lenses with positive and negative optical power to form a far-infrared lens. By reasonably allocating the optical power of each lens and setting the sum of the center thicknesses TH of the first lens and the second convex lens to satisfy 0.5≤TH / f≤0.67 with the effective focal length f of the entire optical system of the far-infrared lens, the far-infrared lens can be designed to have a large aperture, small distortion and compact structure, thus ensuring that the far-infrared lens has high imaging quality.

[0036] Based on the above embodiments, optionally, both the first lens 10 and the second lens 20 include chalcogenide glass lenses.

[0037] Chalcogenide glass offers high processing efficiency, allows for precision molding, and exhibits high refractive index, extremely low absorption loss, and excellent optical thermal stability in the far-infrared band. By incorporating chalcogenide glass lenses into both the first lens 10 and the second lens 20, the processing efficiency of both lenses is effectively improved, enhancing the overall production efficiency of the far-infrared lens and increasing its light transmittance to meet high-definition, high-quality imaging requirements. Furthermore, by including chalcogenide glass lenses in both the first lens 10 and the second lens 20, the far-infrared lens maintains high imaging quality at both high and low temperatures, such as good resolution in environments ranging from -40℃ to +80℃.

[0038] Based on the above embodiments, optionally, at least one of the object-side surface of the first lens 10, the image-side surface of the first lens 20, the object-side surface of the second lens 20, and the image-side surface of the second lens 20 includes a diffraction surface.

[0039] The diffraction surface of the lens can be provided with periodic microstructures, such as gratings or metastructures, so that when light passes through, the light rays can be diffracted on the diffraction surface, thereby achieving control of the light field. By making at least one of the object-side surface of the first lens 10, the image-side surface of the first lens 20, the object-side surface of the second lens 20, and the image-side surface of the second lens 20 include a diffraction surface, light rays can be diffracted on at least one of the object-side surface of the first lens 10, the image-side surface of the first lens 20, the object-side surface of the second lens 20, and the image-side surface of the second lens 20, thereby achieving control of the light field and meeting the imaging requirements of the far-infrared lens.

[0040] In one exemplary embodiment, one of the first lens 10 and the second lens 20 includes a diffraction surface, such that the first lens 10 and the second lens 20 can form a refractive-diffraction hybrid optical system.

[0041] Based on the above embodiments, optionally, the optical power Φ1 of the first lens 10 satisfies: -0.15≤Φ1 / Φ≤-0.004, where Φ is the overall optical power of the far-infrared lens.

[0042] By limiting the optical power of the first lens 10 to the aforementioned range, the light from the object side can be smoothly received into the imaging system of the far-infrared lens, reducing the system aberrations of the far-infrared lens and avoiding the situation where distortion is difficult to control due to excessive light angle, thereby improving the overall imaging quality of the far-infrared lens.

[0043] Based on the above embodiments, optionally, the optical power Φ2 of the second lens 20 satisfies: 1.28≤Φ2 / Φ≤1.46, where Φ is the overall optical power of the far-infrared lens.

[0044] By limiting the optical power of the second lens 20 to the aforementioned range, the residual aberrations of the optical system of the far-infrared lens can be effectively compensated, resulting in smaller overall aberrations of the optical system of the far-infrared lens. This satisfies the requirement for clear imaging under large aperture conditions, thereby enabling the far-infrared lens to have high imaging quality.

[0045] In addition, an aperture stop 30 can be set in the optical path between the first lens 10 and the second lens 20 so that the first lens 10 and the second lens 20 can be symmetrically distributed, and the aberrations before and after the aperture stop 30 can be controlled respectively to meet the high-quality imaging requirements of the far-infrared lens.

[0046] Based on the above embodiments, optionally, the aperture D5 corresponding to the maximum image height on the image side of the second lens 20 and the curvature radius R5 of the image side of the second lens 20 at the optical axis satisfy: 0.36 ≤ D5 / R5 ≤ -0.17. Thus, by reasonably allocating the ratio of the maximum aperture of the image side of the second lens 20 to the curvature radius at the optical axis, the shape of the second lens can be effectively controlled, and the manufacturing difficulty of the second lens can be reduced.

[0047] Based on the above embodiments, optionally, the distance L from the surface vertex of the image side of the second lens 20 to the image plane satisfies: 0.423 < L / TTL < 0.475; TTL is the total length TTL of the far-infrared lens. Thus, by restricting the relationship between the back focal length and the total length of the far-infrared lens, the far-infrared lens has sufficient back focal length to meet the installation requirements. At the same time, the far-infrared lens can also meet the requirement of a shorter total length, making the far-infrared lens have a compact structure and meet the requirements of small size and light weight.

[0048] Based on the above embodiments, optionally, the far-infrared lens may further include: a protective glass 40 located on the image side of the second lens 20.

[0049] Among them, by providing the protective glass 40 on the image side of the second lens 20, the protective glass 40 can play a certain protective role for the first lens 10, the second lens 20, and the imaging sensor.

[0050] Optionally, the protective glass 40 may include silicon glass.

[0051] Among them, the protective glass 40 may be monocrystalline silicon glass, so that it has excellent light transmission performance in both the mid-infrared band and the far-infrared band, thus meeting the high-quality imaging requirements of the far-infrared lens.

[0052] In summary, in the embodiments of the present invention, a far-infrared lens is composed of two lenses with positive and negative optical powers. By reasonably allocating the optical powers, surface types, and axial distances between the lenses, the far-infrared lens can meet the design requirements of large aperture, small distortion, and compact structure. Among them, the aperture number F of the far-infrared lens can reach 1, the maximum image height can reach 4.24 mm, the relative distortion can be less than or equal to 3%, and the imaging resolution can meet the use requirements of an imaging sensor with 12-μm pixels.

[0053] The following further describes specific embodiments of the far-infrared lens applicable to the above embodiments with reference to the drawings.

[0054] In a feasible embodiment, Table 1 details, in a feasible implementation manner, Figure 1 the specific optical and physical parameters of the shown far-infrared lens.

[0055] Table 1. Design of optical physical parameters for a far-infrared lens

[0056]

[0057] Table 2 shows the design parameters of each lens in a far-infrared lens, including surface type, radius of curvature, thickness, and material, which correspond to those in Table 1.

[0058] Table 2. Parameter design of each lens in a far-infrared lens

[0059]

[0060] The far-infrared lens of this embodiment includes a first lens 10, an aperture 30, a second lens 20, and a protective glass 40 arranged sequentially along the optical axis from the object side to the image side. The surface numbers are assigned according to the surface order of each lens, where "S1" represents the object side of the first lens 10, "S2" represents the image side of the first lens 10, and so on; "STO" represents the aperture 30 in the far-infrared lens; the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane, a negative value indicating that the surface bends towards the object plane, and an infinite radius of curvature indicating that the surface is flat; the thickness represents the axial distance between the central axis of the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, with a blank space indicating that the current position is air and the refractive index is 1; and the k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0061] The far-infrared lens in this embodiment has a focal length f of 9.72mm and an aperture of F# of 1.01. The focal length f and the refractive index of the material were obtained using infrared light with a reference wavelength of 10.0μm.

[0062] In this embodiment, the equation Z for the shape of the aspherical surface of the aspherical lens in the far-infrared lens can be expressed in any feasible way. For example, Z can satisfy the following formula:

[0063]

[0064] Where r represents the height of the aspherical surface, Z is the axial sagitta of the aspherical surface in the z-direction; c is the curvature of the fitted sphere; k is the conic coefficient; A, B, C, and D are the coefficients of the 4th, 6th, 8th, and 10th order terms of the aspherical polynomial, respectively.

[0065] For example, Table 3 details the aspherical coefficients of each lens in a far-infrared lens of this embodiment with a feasible implementation method.

[0066] Table 3 Design values ​​of one aspherical coefficient for each lens in far-infrared lenses

[0067]

[0068] Where -3.842898E-05 indicates that the coefficient A of surface number S1 is -3.842898 × ​​10 -5 .

[0069] In this embodiment, Figure 2 yes Figure 1 The schematic diagram of the field curvature distortion curve of the far-infrared lens is shown below. Figure 2 As shown, in the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in mm; the vertical coordinate represents the normalized image height, which has no unit; where T represents the meridion and S represents the sagitta; from Figure 2 It can be seen that the far-infrared lens provided in this embodiment can effectively control the field curvature from light with wavelengths from 8μm to 12μm, meaning that the difference in image quality between the center and the periphery is small during imaging; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage, and the vertical axis represents the normalized image height, which has no unit; from Figure 2 As can be seen, the distortion of the lens provided in this embodiment has been well corrected, and the imaging distortion is small.

[0070] Figure 3 yes Figure 1 The schematic diagram of the axial aberration curve of the far-infrared lens shown is as follows: Figure 3 As shown, the vertical direction represents the normalized aperture, 0 indicates it is on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of the system imaging, determined by... Figure 3 It can be seen that the axial aberrations at different wavelengths (12μm, 10μm, 8μm) are all controlled within the range of (-0.15mm, +0.15mm), indicating that the spherical aberration of the far-infrared lens is well controlled at each wavelength, which can meet the requirements of wide spectrum applications.

[0071] In another feasible embodiment, Figure 4 This is a schematic diagram of another far-infrared lens provided in this embodiment of the present invention. Table 4 describes in detail another feasible implementation method. Figure 4 The specific optical and physical parameters of the far-infrared lens are shown.

[0072] Table 4. Another optical physical parameter design for far-infrared lenses

[0073]

[0074] Table 5 shows the design parameters of each lens in another far-infrared lens corresponding to Table 4, including surface type, radius of curvature, thickness, and material.

[0075] Table 5. Another parameter design for each lens in a far-infrared lens.

[0076]

[0077] The far-infrared lens of this embodiment includes a first lens 10, an aperture 30, a second lens 20, and a protective glass 40 arranged sequentially along the optical axis from the object side to the image side. The surface numbers are assigned according to the surface order of each lens, where "S1" represents the object side of the first lens 10, "S2" represents the image side of the first lens 10, and so on; "STO" represents the aperture 30 in the far-infrared lens; the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane, a negative value indicating that the surface bends towards the object plane, and an infinite radius of curvature indicating that the surface is flat; the thickness represents the axial distance between the central axis of the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, with a blank space indicating that the current position is air and the refractive index is 1; and the k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0078] The far-infrared lens in this embodiment has a focal length f of 9.68mm and an aperture of F# of 1.00. The focal length f and the refractive index of the material were obtained using infrared light with a reference wavelength of 10.0μm.

[0079] In this embodiment, the equation Z for the shape of the aspherical surface of the aspherical lens in the far-infrared lens can be expressed in any feasible way. For example, Z can satisfy the following formula:

[0080]

[0081] Where r represents the height of the aspherical surface, Z is the axial sagitta of the aspherical surface in the z-direction; c is the curvature of the fitted sphere; k is the conic coefficient; A, B, C, and D are the coefficients of the 4th, 6th, 8th, and 10th order terms of the aspherical polynomial, respectively.

[0082] For example, Table 6 details the aspherical coefficients of each lens in a far-infrared lens of this embodiment with a feasible implementation method.

[0083] Table 6 Design values ​​for another type of aspherical coefficient for each lens in far-infrared lenses

[0084]

[0085] Where 1.988396E-04 indicates that the coefficient A of surface number S1 is 1.988396 × 10 -4 .

[0086] In this embodiment, Figure 5 yes Figure 4 The schematic diagram of the field curvature distortion curve of the far-infrared lens is shown below. Figure 5 As shown, in the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in mm; the vertical coordinate represents the normalized image height, which has no unit; where T represents the meridion and S represents the sagitta; from Figure 5 It can be seen that the far-infrared lens provided in this embodiment can effectively control the field curvature from light with wavelengths from 8μm to 12μm, meaning that the difference in image quality between the center and the periphery is small during imaging; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage, and the vertical axis represents the normalized image height, which has no unit; from Figure 5 As can be seen, the distortion of the lens provided in this embodiment has been well corrected, and the imaging distortion is small.

[0087] Figure 6 yes Figure 4 The schematic diagram of the axial aberration curve of the far-infrared lens shown is as follows: Figure 6 As shown, the vertical direction represents the normalized aperture, 0 indicates it is on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of the system imaging, determined by... Figure 6 It can be seen that the axial aberrations at different wavelengths (12μm, 10μm, 8μm) are all controlled within the range of (-0.1mm, +0.1mm), indicating that the spherical aberration of the far-infrared lens at each wavelength is well controlled and can meet the requirements of wide-spectrum applications.

[0088] In yet another feasible embodiment, Figure 7 This is a schematic diagram of another far-infrared lens provided in this embodiment of the present invention. Table 7 describes in detail another feasible implementation method. Figure 7 The specific optical and physical parameters of the far-infrared lens are shown.

[0089] Table 7 Another optical physical parameter design for far-infrared lenses

[0090]

[0091] Table 8 shows the design parameters of the surface type, radius of curvature, thickness, and material of each lens in another type of far-infrared lens, corresponding to Table 7.

[0092] Table 8 Another parameter design for each lens in a far-infrared lens

[0093]

[0094] The far-infrared lens of this embodiment includes a first lens 10, an aperture 30, a second lens 20, and a protective glass 40 arranged sequentially along the optical axis from the object side to the image side. The surface numbers are assigned according to the surface order of each lens, where "S1" represents the object side of the first lens 10, "S2" represents the image side of the first lens 10, and so on; "STO" represents the aperture 30 in the far-infrared lens; the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane, a negative value indicating that the surface bends towards the object plane, and an infinite radius of curvature indicating that the surface is flat; the thickness represents the axial distance between the central axis of the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, with a blank space indicating that the current position is air and the refractive index is 1; and the k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0095] The far-infrared lens in this embodiment has a focal length f of 9.72mm and an aperture of F# of 0.99. The focal length f and the refractive index of the material were obtained using infrared light with a reference wavelength of 10.0μm.

[0096] In this embodiment, the equation Z for the shape of the aspherical surface of the aspherical lens in the far-infrared lens can be expressed in any feasible way. For example, Z can satisfy the following formula:

[0097]

[0098] Where r represents the height of the aspherical surface, Z is the axial sagitta of the aspherical surface in the z-direction; c is the curvature of the fitted sphere; k is the conic coefficient; A, B, C, and D are the coefficients of the 4th, 6th, 8th, and 10th order terms of the aspherical polynomial, respectively.

[0099] For example, Table 9 details the aspherical coefficients of each lens in a far-infrared lens of this embodiment with a feasible implementation method.

[0100] Table 9 Design values ​​for another type of aspherical coefficient of each lens in far-infrared lenses

[0101]

[0102] Where 2.895081E-04 indicates that the coefficient A of surface number S1 is 2.895081 × 10 -4 .

[0103] In this embodiment, Figure 8 yes Figure 7 The schematic diagram of the field curvature distortion curve of the far-infrared lens is shown below. Figure 8 As shown, in the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in mm; the vertical coordinate represents the normalized image height, which has no unit; where T represents the meridion and S represents the sagitta; from Figure 8It can be seen that the far-infrared lens provided in this embodiment can effectively control the field curvature from light with wavelengths from 8μm to 12μm, meaning that the difference in image quality between the center and the periphery is small during imaging; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage, and the vertical axis represents the normalized image height, which has no unit; from Figure 8 As can be seen, the distortion of the lens provided in this embodiment has been well corrected, and the imaging distortion is small.

[0104] Figure 9 yes Figure 7 The schematic diagram of the axial aberration curve of the far-infrared lens shown is as follows: Figure 9 As shown, the vertical direction represents the normalized aperture, 0 indicates it is on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of the system imaging, determined by... Figure 9 It can be seen that the axial aberrations at different wavelengths (12μm, 10μm, 8μm) are all controlled within the range of (-0.1mm, +0.1mm), indicating that the spherical aberration of the far-infrared lens at each wavelength is well controlled and can meet the requirements of wide-spectrum applications.

[0105] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A far-infrared lens, characterized in that, Comprise: a first lens and a second lens arranged in order from an object side to an image side along an optical axis; the first lens is a glass aspheric lens with negative refractive power, and the second lens is a glass aspheric lens with positive refractive power; wherein 0.5≤TH / f≤0.67; TH is the sum of the center thickness of the first lens and the center thickness of the second lens, and f is the effective focal length of the far-infrared lens.

2. The far infrared lens according to claim 1, wherein, The first lens and the second lens both comprise a chalcogenide glass lens.

3. The far infrared lens according to claim 1, wherein, At least one of the object side surface of the first lens, the image side surface of the first lens, the object side surface of the second lens and the image side surface of the second lens comprises a diffractive surface.

4. The far infrared lens according to claim 1, wherein, The refractive power Φ1 of the first lens satisfies: -0.15≤Φ1 / Φ≤-0.004, Φ is the overall refractive power of the far-infrared lens.

5. The far infrared lens according to claim 1, wherein, The refractive power Φ2 of the second lens satisfies: 1.28≤Φ2 / Φ≤1.46, Φ is the overall refractive power of the far-infrared lens.

6. The far infrared lens according to claim 1, wherein, The maximum image height of the image side surface of the second lens corresponds to the aperture D5, and the curvature radius R5 of the image side surface of the second lens at the optical axis satisfies: 0.36≤D5 / R5≤-0.

17.

7. The far infrared lens according to claim 1, wherein The distance L from the surface vertex of the image side surface of the second lens to the image surface satisfies: 0.423<L / TTL<0.475; TTL is the total length TTL of the far-infrared lens.

8. The far infrared lens according to claim 1, wherein, Further comprise: a protective glass located on the image side surface of the second lens.

9. The far infrared lens according to claim 8, wherein, The protective glass comprises a silicon glass.

10. The far infrared lens according to claim 1, wherein Further comprise: a diaphragm arranged in the optical path between the first lens and the second lens.

Images