A large-aperture long-wave athermal infrared lens

Abstract

The application relates to the technical field of optical lenses, and particularly discloses a large-aperture long-wave athermal infrared lens, which comprises a first lens, a second lens, a third lens and a fourth lens; the first lens, the second lens, the third lens and the fourth lens are sequentially arranged along the light incidence direction and on the same optical axis; the first lens is a positive focal power meniscus lens; the second lens is a negative focal power meniscus lens; the third lens is a positive focal power meniscus lens; the fourth lens is a positive focal power meniscus lens; and the first lens, the second lens, the third lens and the fourth lens are all aspherical lenses; the application realizes optical passive athermalization in a wide temperature range without a mechanical focusing mechanism through specific focal power distribution and complementary combination of a chalcogenide glass and a zinc selenide material; the long-wave infrared diffraction limit is broken; the structure is compact, the weight is light, the cost is low, and the application can perfectly adapt to a new generation of high-performance infrared detectors.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and specifically discloses a large-aperture, long-wavelength, athermalized infrared lens. Background Technology

[0002] With the rapid development of uncooled infrared detector technology, small-pixel, high-resolution cooled and uncooled detectors have gradually become the mainstream trend in the industry. Long-wave infrared lenses have also been widely used in key areas such as forest fire prevention, gas detection, and UAV pods. However, existing long-wave infrared lenses still have many shortcomings in design and manufacturing. On the one hand, in pursuit of greater light transmission, traditional large-aperture lenses are often bulky, heavy, and not compact enough, making it difficult to meet the stringent lightweight requirements of payloads such as UAVs. Furthermore, to correct chromatic aberration and achieve calorimetry, existing designs often use a large amount of expensive infrared lens materials, resulting in high manufacturing costs. On the other hand, some lenses adopt a binary diffraction surface design. Although this reduces the number of lenses, the diffraction efficiency of the binary surface is low, and the risk of stray light is high. It is extremely sensitive to processing accuracy and assembly tolerances, and it also reduces image quality.

[0003] Furthermore, existing long-wave infrared lenses on the market generally have small apertures, typically with an F-number greater than or equal to 1.0. In harsh environments such as smoke, rain, and snow, insufficient light intake leads to a reduced signal-to-noise ratio, making it difficult to guarantee image quality. More importantly, due to the limitations of physical optical diffraction, the diffraction-limited Airy disk radius of a 1.0 F-number long-wave infrared lens is approximately 12µm. This means that when the detector pixel size shrinks to 12µm or even 10µm, the theoretical resolution of such lenses is close to the physical limit, failing to fully utilize the high-resolution performance of next-generation small-pixel detectors. This results in a loss of overall system imaging detail, failing to meet users' increasingly demanding high-definition imaging requirements.

[0004] In summary, existing technologies cannot simultaneously meet the requirements of large aperture, high resolution, miniaturization, and low cost. Therefore, there is an urgent need to propose a large-aperture, long-wavelength, athermalized infrared lens. Summary of the Invention

[0005] The purpose of this invention is to provide a large-aperture, long-wavelength, athermalized infrared lens to at least solve one of the aforementioned problems in the prior art.

[0006] Specifically, the present invention is achieved through the following technical solution:

[0007] A large-aperture long-wavelength athermalized infrared lens, the lens comprising a first lens, a second lens, a third lens, and a fourth lens, wherein the first lens, the second lens, the third lens, and the fourth lens are arranged sequentially along the incident light direction and on the same optical axis; the first lens is a positive power meniscus lens, the second lens is a negative power meniscus lens, the third lens is a positive power meniscus lens, and the fourth lens is a positive power meniscus lens; all of the first lens, the second lens, the third lens, and the fourth lens are aspherical lenses.

[0008] The lens satisfies the following along the optical axis:

[0009] ,in, The distance between the light-emitting surface of the first lens and the light-incident surface of the second lens on the optical axis is denoted as . The total focal length of the lens is denoted as .

[0010] Furthermore, the aperture stop of the lens is disposed on the light-incident surface of the first lens.

[0011] Furthermore, the light-incident surfaces of the first lens, the second lens, the third lens, and the fourth lens are all convex, and their light-outceasing surfaces are all concave.

[0012] Furthermore, the focal lengths of the first lens, the second lens, the third lens, and the fourth lens, together with the total focal length of the lens, satisfy the following condition:

[0013] ,

[0014] ,

[0015] ,

[0016] ,

[0017] in, , , , These are the focal lengths of the first lens, the second lens, the third lens, and the fourth lens, respectively.

[0018] Furthermore, the first, third, and fourth lenses are all made of chalcogenide glass, while the second lens is made of zinc selenide.

[0019] Furthermore, the light-incident surfaces of the first lens, the second lens, the third lens, and the fourth lens are all even-order aspherical surfaces.

[0020] Furthermore, the total optical length of the lens and the total focal length of the lens satisfy the following:

[0021] ,

[0022] in, The total optical length of the lens is given.

[0023] Furthermore, the rear focal length of the lens and the total focal length of the lens satisfy the following:

[0024] ,

[0025] in, The back focal length of the lens (i.e., the axial distance from the light-emitting surface of the fourth lens to the optical focal plane).

[0026] Furthermore, the maximum aperture number of the lens The total focal length of the lens is 0.78. The lens is 70mm in diameter and is compatible with infrared detectors with pixel sizes of 10µm or 12µm.

[0027] Compared with the prior art, the present invention has at least the following advantages and beneficial effects:

[0028] This invention successfully reduces the maximum aperture number to 0.78 by constructing a specific four-element aspherical lens group, significantly improving light transmission and signal-to-noise ratio compared to traditional lenses, enabling it to maintain excellent detection capabilities even in harsh environments such as smoke, rain, and snow. At the same time, this ultra-large aperture design effectively reduces the size of the diffraction Airy disk, breaking through the physical diffraction limit on resolution, thus perfectly adapting to and activating a new generation of high-performance infrared detectors with pixel sizes of 10µm or 12µm, ensuring high-sharpness imaging from the center to the edge.

[0029] On the other hand, this invention innovatively adopts a low-cost material combination of "chalcogenide glass with zinc selenide" and a "strong negative followed by strong positive" optical power allocation strategy, which achieves passive and heatless optical control over a wide temperature range (-45℃ to +70℃) without the need for a mechanical focusing mechanism, ensuring focal plane stability under extreme temperature differences. Moreover, this design effectively compresses the light transmission path and controls the ratio of the lens's total optical length to the focal length within a compact range. While maintaining a long focal length of 70mm, it significantly reduces the size and weight, successfully meeting the stringent requirements of lightweight, miniaturization, and low cost for payloads such as UAV pods. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0031] Figure 1These are schematic diagrams of the lens structures in Embodiments 1 and 2 of the present invention;

[0032] Figure 2 This is a dot diagram of Embodiment 2 of the present invention;

[0033] Figure 3 This is a field curvature and distortion diagram of Embodiment 2 of the present invention;

[0034] Figure 4 This is a modulation transfer function (MTF) curve of Embodiment 2 of the present invention at an ambient temperature of 25°C;

[0035] Figure 5 This is a modulation transfer function (MTF) curve of Embodiment 2 of the present invention at an ambient temperature of -45°C;

[0036] Figure 6 This is a modulation transfer function (MTF) curve of Embodiment 2 of the present invention at an ambient temperature of 70°C;

[0037] Figure 7 This is a schematic diagram of the lens structure in Embodiment 3 of the present invention;

[0038] Figure 8 This is a dot diagram of Embodiment 3 of the present invention;

[0039] Figure 9 This is a field curvature and distortion diagram of Embodiment 3 of the present invention;

[0040] Figure 10 This is a modulation transfer function (MTF) curve of Embodiment 3 of the present invention at an ambient temperature of 25°C;

[0041] Figure 11 This is a modulation transfer function (MTF) curve of Embodiment 3 of the present invention at an ambient temperature of -45°C;

[0042] Figure 12 This is a modulation transfer function (MTF) curve of Embodiment 3 of the present invention at an ambient temperature of 70°C.

[0043] In the above figures, the reference numerals represent: 1, first lens; 2, second lens; 3, third lens; 4, fourth lens. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention. The embodiments described below are some, but not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0045] In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, materials, or methods are not specifically described to avoid obscuring the invention. Unless otherwise specified, the materials, instruments, and reagents used in the following embodiments are commercially available. Unless otherwise specified, the techniques used in the embodiments are conventional methods well known to those skilled in the art.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0047] Example 1:

[0048] Please refer to the following: Figure 1 As shown, this embodiment discloses a large-aperture long-wavelength athermalized infrared lens. The lens includes a first lens 1, a second lens 2, a third lens 3, and a fourth lens 4. The first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are arranged sequentially along the incident light direction and on the same optical axis. The first lens 1 is a positive power meniscus lens, the second lens 2 is a negative power meniscus lens, the third lens 3 is a positive power meniscus lens, and the fourth lens 4 is a positive power meniscus lens. The first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are all aspherical lenses.

[0049] The lens satisfies the following along the optical axis:

[0050] ,in, The distance between the light-emitting surface of the first lens 1 and the light-incident surface of the second lens 2 on the optical axis is denoted as . The total focal length of the lens is denoted as .

[0051] It is understood that this invention provides a large-aperture, long-wavelength, athermalized infrared lens. From the object side to the image side (along the direction of light incidence), its core optical system consists of four lenses arranged coaxially: a first lens 1, a second lens 2, a third lens 3, and a fourth lens 4. Furthermore, to address the problem of large lens size and complex structure resulting from pursuing a large aperture in existing technologies, a specific "positive, negative, positive, positive" optical power allocation architecture is employed. Specifically, the first lens 1, with positive optical power, primarily performs the initial focusing function of light, effectively collecting incident light and laying the foundation for achieving high light throughput. The second lens 2, with negative optical power, mainly functions to diverge light, correcting spherical aberration caused by the positive lens and balancing the field curvature of the system—a key correction element for achieving high-resolution imaging. The third lens 3 and the fourth lens 4, both with positive optical power, further converge the beam, smoothly guiding the light onto the imaging plane while reducing the incident angle of light on each lens surface, thereby reducing the generation of higher-order aberrations.

[0052] Furthermore, in order to achieve lens miniaturization while maintaining a large aperture (high light transmission), this embodiment specifies the distance on the optical axis between the light-emitting surface of the first lens 1 and the light-receiving surface of the second lens 2. Strict limits were imposed to ensure that it meets the requirements. (in The total focal length of the lens is 4.5 mm. By controlling the spacing within the above range, the structure is kept compact while allowing reasonable space for the propagation of edge light. This helps to optimize the optical path deflection and balance off-axis aberrations within a limited space. At the same time, all four lenses are meniscus lenses and aspherical lenses. By utilizing the greater freedom of aspherical surfaces in aberration correction, the number of lenses is reduced (only 4 are needed) while achieving the image quality that traditional spherical lenses require more lenses. This avoids the low diffraction efficiency and stray light problems caused by using binary diffraction surfaces.

[0053] Optionally, based on the above embodiments, the aperture stop of the lens is disposed on the light-incident surface of the first lens 1.

[0054] Clearly, when designing long-wave infrared optical systems, the choice of aperture stop position directly affects the overall size and image quality uniformity of the lens. This design, by placing the aperture stop at the front, allows the principal rays to converge at a single point in the object space, effectively controlling the aperture angle of the incident beam. This arrangement allows for progressive control of the aperture of subsequent lens groups, preventing excessively large apertures in later lens groups. This significantly reduces the radial size and weight of the lens, meeting the stringent requirements of lightweight construction. Simultaneously, the front aperture stop helps to symmetrically remove wide beam aberrations (such as coma and astigmatism) of off-axis beams, improving the imaging quality at the edges of the field of view and ensuring consistent resolution across the entire field of view.

[0055] As a further possible implementation, the light-incident surfaces of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are all convex, and their light-outceasing surfaces are all concave.

[0056] By employing a meniscus structure design where the first lens 1, second lens 2, third lens 3, and fourth lens 4 all have convex incident surfaces and concave exit surfaces, the angle of light deflection on each lens surface can be minimized, resulting in smoother refraction of light as it passes through the lens surfaces. This smooth light deflection significantly reduces the generation of advanced spherical aberration at the source of the physical structure, alleviating the burden of aspherical coefficient correction. Compared to biconvex or plano-convex lenses, this consistent meniscus orientation design is more conducive to balancing field curvature under a large field of view, ensuring that the image center and edges are equally sharp when focused on the focal plane, thus solving the edge image quality degradation problem that is common in existing large-aperture lenses.

[0057] Furthermore, the focal lengths of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4, together with the total focal length of the lens, satisfy the following condition:

[0058] ,

[0059] ,

[0060] ,

[0061] ,

[0062] in, , , , These are the focal lengths of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4, respectively.

[0063] Obviously, this embodiment strictly defines the ratio between the focal length of each lens and the total focal length of the system through the above four conditional expressions. It constructs a special optical architecture based on strong negative optical power correction combined with strong positive optical power convergence. This is the core technical means of this invention to achieve a super large aperture (F0.78) while also taking into account passive calorimetry and structural miniaturization.

[0064] Specifically, the first lens 1 is configured as a medium positive power element with a focal length comparable to the total focal length. This ensures sufficient light-gathering aperture and performs initial light-gathering function, while the second lens 2 is endowed with extremely strong negative optical power ( ). This feature enables the second lens 2 to possess strong divergence capabilities, generating sufficient negative thermal difference to precisely compensate for the positive thermal difference generated by the chalcogenide glass positive lens group under temperature changes. This allows for focal plane stability over a wide temperature range without the need for a mechanical focusing mechanism. Meanwhile, to balance the strong divergence of the second lens 2, the third lens 3 is configured as a strong positive optical power element with strong converging capabilities. This compact "strong negative followed by strong positive" design significantly shortens the axial transmission distance of light, effectively controls the total optical length, and is finally combined with a fourth lens 4 with weak positive optical power. As a field lens, it performs fine corrections to edge field distortion and principal ray angle. The four elements work together to ensure that the lens achieves a balance between high light throughput and high resolution within an extremely compact space.

[0065] As a further preferred embodiment of the above embodiments, the first lens 1, the third lens 3 and the fourth lens 4 are all made of chalcogenide glass, and the second lens 2 is made of zinc selenide.

[0066] It should be noted that traditional lenses often use a large amount of expensive infrared materials to achieve calorific effects, resulting in high costs, and require mechanical focusing structures, leading to increased size. This embodiment adopts a combined scheme based on the principle of optical passive calorific effects. Specifically, the first, third, and fourth lenses 4 (positive lens group) are made of chalcogenide glass. Chalcogenide glass has excellent infrared transmittance, and compared to germanium single crystal, its raw material cost is lower, and it has the characteristic of being moldable, making it suitable for mass production at low cost. However, chalcogenide glass has a large temperature coefficient of refractive index, and its focal length changes significantly when heated.

[0067] Therefore, in this embodiment, the second lens 2 (negative lens) is specifically selected as zinc selenide. Zinc selenide has a small temperature coefficient of refractive index and a specific dispersion coefficient. By combining chalcogenide glass with positive optical power and zinc selenide with negative optical power, and utilizing the complementary relationship between the two in terms of thermo-optical properties (i.e., the thermal defocusing amount generated by the positive lens is approximately equal to that generated by the negative lens in value but opposite in direction), adaptive thermal compensation is achieved within the optical system.

[0068] As a further optional implementation, the light-incident surfaces of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are all even-order aspherical surfaces.

[0069] It should be understood that, in order to further overcome the limitations of physical optical diffraction on resolution and to complement the ultra-large aperture design of F0.78, the light-incident surfaces of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 in this scheme are all designed as even-order aspherical surfaces. That is to say, their surface shape sag formulas follow the standard even-order aspherical equations.

[0070] In the long-wave infrared band, conventional spherical lenses struggle to simultaneously correct spherical aberration, coma, and astigmatism with only four elements, especially under extreme conditions like f / 0.78, where aberrations at the edges increase dramatically. Therefore, this solution introduces even-order aspherical surfaces with higher-order coefficients on the aforementioned key surfaces. This introduces more correction variables, enabling precise phase modulation for light rays at different aperture heights. Based on this, the lens not only effectively corrects large-aperture spherical aberration at on-axis points and improves center resolution, but also maintains consistency in the meridional and sagittal image planes of the off-axis field of view, significantly improving the modulation transfer function (MTF). This allows the lens to perfectly adapt to high-performance detectors with pixel sizes of 10µm or 12µm, ensuring extremely high image sharpness from center to edge.

[0071] Based on the above embodiments, in a further embodiment, the total optical length of the lens and the total focal length of the lens satisfy the following:

[0072] ,

[0073] in, The total optical length of the lens is given.

[0074] Understandably, since the aperture number of this invention reaches 0.78, its beam cross-section is extremely large. If the lens length is shortened blindly, the deflection angle of light on the lens surface will be too large, thus introducing difficult-to-eliminate high-order spherical aberration and coma. It will also result in an excessively steep lens surface, greatly increasing the manufacturing difficulty and assembly tolerance sensitivity. Conversely, if the total optical length is too long, the lens will be bulky and heavy, failing to meet the stringent lightweight requirements of payloads such as UAV pods. Therefore, this invention precisely locks the ratio between 0.65 and 0.75, ensuring that the system has a just-right optical path length. This not only reserves the necessary space for smooth correction of light aberrations under large apertures and ensures the clarity of the edge field of view, but also effectively controls the axial dimension of the lens barrel. This allows this 70mm telephoto lens to maintain a compact shape suitable for integration while possessing night vision-level large light transmission, successfully solving the technical problem of existing large-aperture lenses being unable to balance size and image quality.

[0075] As a further preferred embodiment of the above embodiments, the rear focal length of the lens and the total focal length of the lens satisfy the following:

[0076] ,

[0077] in, The back focal length of the lens (that is, the axial distance from the light-emitting surface of the fourth lens 4 to the optical focal plane).

[0078] It should be noted that the present invention strictly locks the ratio between 0.12 and 0.21, which ensures that the large aperture lens can be perfectly adapted to and installed without damage on the mainstream 10um / 12um detector core, thus guaranteeing the system's versatility. At the same time, it maximizes the compression of the rear lens size while meeting the assembly clearance requirements, thereby achieving the overall miniaturization and lightweight design of the module.

[0079] As a further embodiment, the maximum aperture number of the lens The total focal length of the lens is 0.78. The lens is 70mm in diameter and is compatible with infrared detectors with pixel sizes of 10µm or 12µm.

[0080] Addressing the technical bottleneck of existing F1.0 aperture lenses having a diffraction-limited Airy disk radius of approximately 12µm, which prevents them from fully utilizing the high-resolution performance of 10µm or 12µm small pixel detectors, this embodiment designs the maximum aperture number (F-number) of the lens to be 0.78. According to the Rayleigh criterion, the diffraction-limited resolution of an optical system is proportional to the F-number. When the F-number is reduced to 0.78, the theoretical diffraction-limited Airy disk size is significantly reduced, thereby breaking through the diffraction limitation of physical optics and greatly increasing the cutoff frequency of the optical system. Combined with the 70mm focal length of this lens, this design not only greatly increases the infrared energy collection efficiency (the amount of light entering is approximately 1.6 times that of an F1.0 lens) and significantly improves the signal-to-noise ratio in harsh environments such as smoke, rain, and snow, but more importantly, it can resolve even smaller target details, truly matching and activating the high-pixel advantage of 10µm / 12µm small pixel detectors.

[0081] Example 2:

[0082] To further verify the feasibility and superiority of the technical solution of this invention, such as... Figures 2 to 6 As shown, this embodiment provides a set of specific lens design data. In this embodiment, the total focal length of the lens is... It has an F-number of 0.78, a field of view of 3.912°, and is compatible with pixel sizes of 10µm or 12µm.

[0083] The detailed optical parameters of this embodiment are shown in Table 1 below (where the length unit is millimeters).

[0084] Table 1: Lens Structure Parameters of Example 2

[0085] In this embodiment, the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are all even-order aspherical lenses. The formula for even-order aspherical lenses is as follows:

[0086] ;

[0087] in, Let be the sag of the aspherical surface along the optical axis from the vertex. Radial coordinates, Represents the curvature at the vertices of the surface. The conic coefficient, These are the higher-order aspherical coefficients.

[0088] Based on the above, it can be seen that when the incident surface of the first lens 1 is an even-order aspherical surface, its conic coefficient is... Their higher-order aspheric coefficients are as follows:

[0089] A = -1.275561027218E-007;

[0090] B = -1.410747289976E-011;

[0091] C=1.45416571081E-015;

[0092] D=-9.585820685673001E-019.

[0093] When the incident surface of the second lens 2 of the lens is an even-order aspherical surface, its conic coefficient The higher-order aspherical coefficients are as follows:

[0094] A = -1.00200207026E-005;

[0095] B = -4.5008209161E-009;

[0096] C = -4.281171639067E-012;

[0097] D=5.60866791152E-016.

[0098] When the incident surface of the third lens 3 of the lens is an even-order aspherical surface, its conic coefficient The higher-order aspherical coefficients are as follows:

[0099] A = -4.1964560630E-006;

[0100] B = -9.0784885095E-011;

[0101] C = -2.336291200702E-013;

[0102] D=-1.139157556003E-015.

[0103] When the incident surface of the fourth lens 4 of the lens is an even-order aspherical surface, its conic coefficient... The higher-order aspherical coefficients are as follows:

[0104] A = -3.714346998143E-006;

[0105] B = -4.74818977919E-010;

[0106] C=6.21576954565E-012;

[0107] D=-1.696225391085E-014.

[0108] Based on the above data, it can be seen that the distance between the light-emitting surface of the first lens 1 and the light-incident surface of the second lens 2 in this scheme is... ,satisfy Overall optical length of the lens ,satisfy .

[0109] Based on the above, the MTF curves of this solution are excellent at -45℃, 25℃ and 70℃. In particular, at the spatial frequency of 30lp / mm, the MTF value remains at a high level and the curves deviate very little at each temperature, which verifies that the structure can achieve a large aperture of F0.78 while having excellent passive calorimetry performance.

[0110] Example 3:

[0111] As another preferred embodiment of the present invention, such as Figures 7 to 12 As shown, this embodiment, while maintaining the basic structure, makes minor adjustments to the lens spacing and curvature to adapt to different assembly requirements. In this embodiment, the total focal length of the lens is... .

[0112] The detailed optical structure parameters of this embodiment are shown in Table 2 below:

[0113] Table 2: Lens Structure Parameters of Example 2

[0114]

[0115] In this embodiment, the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are all even-order aspherical lenses. The formula for even-order aspherical lenses is as follows:

[0116] ;

[0117] in, Let be the sag of the aspherical surface along the optical axis from the vertex. Radial coordinates, Represents the curvature at the vertices of the surface. The conic coefficient, These are the higher-order aspherical coefficients.

[0118] Based on the above, it can be seen that when the incident surface of the first lens 1 is an even-order aspherical surface, its conic coefficient is... Their higher-order aspheric coefficients are as follows:

[0119] A = -1.006037294936E-007;

[0120] B = -8.88803529225E-012;

[0121] C=2.77154715618E-016;

[0122] D=-3.401775599686E-019.

[0123] When the incident surface of the second lens 2 of the lens is an even-order aspherical surface, its conic coefficient The higher-order aspherical coefficients are as follows:

[0124] A = -4.40370955806E-006;

[0125] B=7.87936404637E-010;

[0126] C = -1.565109898689E-013;

[0127] D=-6.762396879164E-017016.

[0128] When the incident surface of the third lens 3 of the lens is an even-order aspherical surface, its conic coefficient The higher-order aspherical coefficients are as follows:

[0129] A = -1.78597320401E-006;

[0130] B = -3.05210835145E-010;

[0131] C=6.71143431659E-014;

[0132] D=-1.64770668990E-016.

[0133] When the incident surface of the fourth lens 4 of the lens is an even-order aspherical surface, its conic coefficient... The higher-order aspherical coefficients are as follows:

[0134] A = -6.43132301749E-006;

[0135] B=3.575532416356E-008;

[0136] C = -2.460208156411E-010;

[0137] D=5.079511096018E-013.

[0138] Based on the above data, it can be seen that the distance between the light-emitting surface of the first lens 1 and the light-incident surface of the second lens 2 in this scheme is... ,satisfy Overall optical length of the lens ,satisfy .

[0139] As can be seen from the above, thanks to the "strong negative-strong positive" optical power allocation strategy adopted in this application and the specific material combination of chalcogenide glass and zinc selenide, this embodiment achieves excellent passive pyrolysis performance and environmental adaptability while achieving an F0.78 ultra-large aperture and a compact telephoto ratio of 0.636.

[0140] The sequence numbers of the embodiments in this application are merely for descriptive purposes. Furthermore, the structures, proportions, sizes, etc., illustrated in the accompanying drawings are all schematic diagrams, intended only to complement the content disclosed in the specification and to facilitate understanding and reading by those skilled in the art. They are not intended to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by the present invention, should still fall within the scope of the technical content disclosed in this invention.

[0141] Furthermore, the terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

Claims

1. A large-aperture, long-wavelength, athermalized infrared lens, characterized in that, The lens has only four optical refractive components: a first lens, a second lens, a third lens, and a fourth lens. The first lens, the second lens, the third lens, and the fourth lens are arranged sequentially along the incident light direction and on the same optical axis. The first lens is a positive power meniscus lens, the second lens is a negative power meniscus lens, the third lens is a positive power meniscus lens, and the fourth lens is a positive power meniscus lens. The first lens, the second lens, the third lens, and the fourth lens are all aspherical lenses. The lens satisfies the following along the optical axis: ,in, The distance between the light-emitting surface of the first lens and the light-incident surface of the second lens on the optical axis is denoted as . The total focal length of the lens; The light-incident surfaces of the first lens, the second lens, the third lens, and the fourth lens are all convex, and their light-outceasing surfaces are all concave. The focal lengths of the first lens, the second lens, the third lens, and the fourth lens, together with the total focal length of the lens, satisfy the following condition: ， ， ， ， in, , , , These are the focal lengths of the first lens, the second lens, the third lens, and the fourth lens, respectively. The total optical length of the lens and the total focal length of the lens satisfy the following: ， in, The total optical length of the lens; The rear focal length of the lens and the total focal length of the lens satisfy the following: ， in, The back focal length of the lens; The maximum aperture of the lens The total focal length of the lens is 0.

78. The lens is 70mm in diameter and is compatible with infrared detectors with pixel sizes of 10µm or 12µm.

2. The large-aperture, long-wavelength, athermalized infrared lens according to claim 1, characterized in that, The aperture stop of the lens is set on the light-incident surface of the first lens.

3. The large-aperture, long-wavelength, athermalized infrared lens according to claim 1, characterized in that, The first, third, and fourth lenses are all made of chalcogenide glass, while the second lens is made of zinc selenide.

4. The large-aperture, long-wavelength, athermalized infrared lens according to claim 1, characterized in that, The light-incident surfaces of the first lens, the second lens, the third lens, and the fourth lens are all even-order aspherical surfaces.

Images