Long-wave infrared lens

Abstract

The application discloses a long-wave infrared lens, which comprises, in sequence from the object side to the image side along the optical axis, a first lens with negative refractive power, the first lens being a meniscus lens with the convex surface facing the object side, a second lens with positive refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power, wherein the effective focal length f3 of the third lens and the effective focal length ft of the long-wave infrared lens satisfy 3.4≤|f3 / ft|≤22.2.

Description

Technical Field

[0001] This application relates to the field of optical components, and more specifically, to a long-wave infrared lens. Background Technology

[0002] With the continuous development of infrared imaging technology, the demand for long-wave infrared lenses is increasing, especially in temperature measurement. Because infrared temperature measurement is a non-contact method, it is more convenient and safer than traditional contact temperature measurement, and therefore can be widely used in various fields.

[0003] Since temperature can affect optical and mechanical materials, long-wave infrared lenses are affected by temperature when performing infrared temperature measurements, which can lead to a decrease in optical imaging quality and thus affect the accuracy of temperature measurement. Summary of the Invention

[0004] This application provides a long-wave infrared lens, which includes, in sequence along the optical axis from the object side to the image side: a first lens having negative optical power, and the first lens is a meniscus lens with its convex surface facing the object side; a second lens having positive optical power; a third lens having positive optical power; and a fourth lens having positive optical power; wherein the effective focal length f3 of the third lens and the effective focal length ft of the long-wave infrared lens satisfy: 3.4≤|f3 / ft|≤22.2.

[0005] The long-wave infrared lens of this application, through the reasonable configuration of the optical power of the first, second, third, and fourth lenses, the setting of an aperture between the second and third lenses, the use of a meniscus lens with the convex surface facing the object side as the first lens, and the control of the effective focal length of the third lens and the effective focal length of the long-wave infrared lens to satisfy 3.4≤|f3 / ft|≤22.2, helps to increase the rear film aperture, achieve a large image plane, improve relative illumination, ensure the quality of optical imaging, and meet the requirement of stable imaging in a temperature range of -40° to +80°, thereby ensuring the accuracy of infrared temperature measurement and meeting the needs of use in environments with large temperature variations.

[0006] In one embodiment, at least one of the object-side and image-side surfaces of the first lens is aspherical; at least one of the object-side and image-side surfaces of the second lens is aspherical; at least one of the object-side and image-side surfaces of the third lens is aspherical, and the third lens is a meniscus lens with its concave surface facing the object side; both the object-side and image-side surfaces of the fourth lens are aspherical, and the fourth lens is a meniscus lens with its convex surface facing the object side.

[0007] In one embodiment, both the first lens and the third lens are made of germanium single crystal.

[0008] In one embodiment, it further includes an aperture which is located between the second lens and the third lens. The aperture is an adjustable variable aperture. The distance D2 between the aperture and the second lens on the optical axis satisfies: 2 mm ≤ D2 ≤ 6.5 mm, and the aperture coefficient F of the long-wave infrared lens satisfies: 1.1 ≤ F ≤ 3.

[0009] In one embodiment, the effective focal length f1 of the first lens and the effective focal length ft of the long-wave infrared lens satisfy: 1.8 ≤ |f1 / ft| ≤ 2.7.

[0010] In one embodiment, the effective focal length f2 of the second lens and the effective focal length ft of the long-wave infrared lens satisfy: 1.1 ≤ |f2 / ft| ≤ 2.5.

[0011] In one embodiment, the effective focal length f4 of the fourth lens and the effective focal length ft of the long-wave infrared lens satisfy: 1.2 ≤ |f4 / ft| ≤ 1.6.

[0012] In one embodiment, the distance BFL from the image side of the fourth lens to the imaging surface on the optical axis and the effective focal length ft of the long-wave infrared lens satisfy: 0.7 ≤ |BFL / ft| ≤ 1.1, and the effective focal length ft of the long-wave infrared lens satisfies: 15 mm ≤ ft ≤ 30 mm.

[0013] In one embodiment, the distance BFL from the image side of the fourth lens to the imaging surface on the optical axis and the distance TTL from the object side of the first lens to the imaging surface on the optical axis satisfy: 0.1 ≤ BFL / TTL ≤ 0.4.

[0014] In one embodiment, the semi-image height H of the long-wave infrared lens and the field of view FOV of the long-wave infrared lens satisfy: 18.2 < H / tan(FOV / 2), the semi-image height H of the long-wave infrared lens satisfies: H > 9.5 mm, and the field of view FOV of the long-wave infrared lens satisfies: 40° ≤ FOV ≤ 55°. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] With reference to the drawings, through the following detailed description of non-limiting embodiments, other features, objects, and advantages of the present application will become more apparent. In the drawings:

[0016] Figure 1 The structural schematic diagram of the long-wave infrared lens according to an exemplary embodiment of the present application is shown;

[0017] Figure 2 The structural schematic diagram of the long-wave infrared lens according to Embodiment 1 of the present application is shown;

[0018] Figures 3A to 3C The MTF curve, dot plot, field curvature curve, and distortion curve of the long-wave infrared lens of Example 1 are shown respectively.

[0019] Figure 4 A schematic diagram of the structure of a long-wave infrared lens according to Embodiment 2 of this application is shown;

[0020] Figures 5A to 5C The MTF curve, dot plot, field curvature curve, and distortion curve of the long-wave infrared lens of Example 2 are shown respectively.

[0021] Figure 6 A schematic diagram of the structure of a long-wave infrared lens according to Embodiment 3 of this application is shown;

[0022] Figures 7A to 7C The MTF curve, dot plot, field curvature curve, and distortion curve of the long-wave infrared lens of Example 3 are shown respectively.

[0023] Figure 8 A schematic diagram of the structure of a long-wave infrared lens according to Embodiment 4 of this application is shown;

[0024] Figures 9A to 9C The MTF curve, dot plot, field curvature curve, and distortion curve of the long-wave infrared lens of Example 4 are shown respectively. Detailed Implementation

[0025] To better understand this application, various aspects of this application will be described in more detail with reference to the accompanying drawings. It should be understood that these detailed descriptions are merely illustrative of exemplary embodiments of this application and are not intended to limit the scope of this application in any way. Throughout the specification, the same reference numerals refer to the same elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0026] It should be noted that in this specification, the terms "first," "second," etc., are used only to distinguish one feature from another and do not imply any limitation on the features. Therefore, without departing from the teachings of this application, the first optical system discussed below may also be referred to as the second optical system, and the second optical system may also be referred to as the first optical system.

[0027] In the accompanying drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for ease of illustration. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are illustrated by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to those shown in the drawings. The drawings are for illustrative purposes only and are not strictly to scale.

[0028] In this paper, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the location of the convexity is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the location of the concaveness is not defined, it means that the lens surface is concave at least in the paraxial region.

[0029] It should also be understood that the terms "comprising," "including," "having," "containing," and / or "comprising," when used in this specification, indicate the presence of the stated features, elements, and / or components, but do not exclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. Furthermore, when expressions such as "at least one of..." appear after a list of listed features, they modify the entire list of features, not individual elements in the list. Additionally, when describing embodiments of this application, the word "may" is used to mean "one or more embodiments of this application." And the term "exemplary" is intended to refer to an example or illustration.

[0030] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms (e.g., those defined in common dictionaries) shall be interpreted as having a meaning consistent with their meaning in the context of the relevant art and shall not be interpreted in an idealized or overly formalized sense, unless expressly so specified herein.

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] The features, principles and other aspects of this application are described in detail below.

[0033] Figure 1 A schematic diagram of the structure of a long-wave infrared lens 100 according to an exemplary embodiment of this application is shown. Figure 1 As shown, a long-wave infrared lens 100 according to an exemplary embodiment of this application may include: a first lens 1, a second lens 2, a third lens 4, and a fourth lens 5. The first lens 1, second lens 2, third lens 4, and fourth lens 5 are arranged sequentially along the optical axis from the object side to the image side. The first lens 1 has negative optical power, the second lens 2 has positive optical power, the third lens 4 has positive optical power, and the fourth lens 5 has positive optical power. The first lens 1 is a meniscus lens with its convex surface facing the object side.

[0034] In an exemplary embodiment, the long-wave infrared lens 100 of this application satisfies the condition: 3.4 ≤ |f3 / ft| ≤ 22.2, where f3 is the effective focal length of the third lens 4 and ft is the effective focal length of the long-wave infrared lens 100. By rationally configuring the optical power of the first lens, second lens, third lens, and fourth lens, making the first lens a meniscus lens with its convex surface facing the object side, and controlling the effective focal length of the third lens and the effective focal length of the long-wave infrared lens to satisfy 3.4 ≤ |f3 / ft|, it helps to increase the rear film aperture, achieve a large image plane, improve relative illumination, ensure the quality of optical imaging, and meet the requirement of stable imaging in a temperature range of -40° to +80°, thereby ensuring the accuracy of infrared temperature measurement and meeting the needs of use in environments with large temperature variations.

[0035] In an exemplary embodiment, at least one of the object-side and image-side surfaces of the first lens 1 of the long-wave infrared lens 100 of this application is aspherical; at least one of the object-side and image-side surfaces of the second lens 2 is aspherical, and the object-side and image-side surfaces of the second lens 2 are not limited to specific types; at least one of the object-side and image-side surfaces of the third lens 4 is aspherical, and the third lens 4 is a meniscus lens with its concave surface facing the object side; both the object-side and image-side surfaces of the fourth lens 5 are aspherical, and the fourth lens 5 is a meniscus lens with its convex surface facing the object side. The characteristic of an aspherical lens is that its curvature changes continuously from the lens center to the lens periphery. Unlike a spherical lens, which has a constant curvature from the lens center to the lens periphery, an aspherical lens has better radius of curvature characteristics, offering advantages in improving distortion aberrations and astigmatism. By using an aspherical lens, aberrations occurring during imaging can be eliminated as much as possible, thereby improving image quality. Among them, matching the shape of the fourth lens with a suitable optical back focal length helps to eliminate ghosting between the tail plate and the mechanism window, that is, between the fourth lens and the detector window.

[0036] In an exemplary embodiment, the first lens 1 and the third lens 4 of the long-wave infrared lens 100 of this application are both germanium single crystals. In one example, the first lens 1, the second lens 2, the third lens 4, and the fourth lens 5 are all made of germanium single crystals. By using germanium, which has a high refractive index, as the lens material, the use of diffraction surfaces in the lens can be avoided, the overall light transmittance of the lens can be improved, and the imaging quality of the lens can be improved, thereby improving the accuracy of temperature measurement.

[0037] In an exemplary implementation, such as Figure 1As shown, the long-wave infrared lens 100 of this application also includes an aperture stop 3, which is located between the second lens 2 and the third lens 4. The aperture stop 3 is an adjustable variable aperture stop, and the distance D2 between the aperture stop 3 and the second lens 2 on the optical axis can satisfy 2mm≤D2≤6.5mm. The aperture coefficient F of the long-wave infrared lens 100 can satisfy 1.1≤F≤3. In one example, F is 1.1. By setting an aperture stop between the second lens and the third lens, it is helpful to control the overall aperture reduction of the lens. By using an adjustable aperture stop, the amount of light transmitted by the lens can be actively controlled. Among them, the aperture stop is an adjustable aperture component. In order to ensure the temperature measurement performance, a large aperture is used to increase the energy received by the detector. However, when measuring high-temperature targets, such as temperatures of about 1600℃, the energy is too strong and will cause irreversible damage to the detector. At this time, the aperture stop can be adjusted to an elliptical small aperture stop with a major axis of 8.45mm and a minor axis of 6mm, i.e., F2.7, to perform high-temperature measurements. This can protect the detector from damage while meeting the temperature measurement requirements.

[0038] In an exemplary embodiment, the long-wave infrared lens 100 of this application can satisfy the condition 1.8≤|f1 / ft|≤2.7, where f1 is the effective focal length of the first lens 1 and ft is the effective focal length of the long-wave infrared lens 100. By controlling the above condition, it can be ensured that when the light emitted from the first lens is incident on the object side of the second lens, the incident light is relatively flat, thereby reducing the tolerance sensitivity of the long-wave infrared lens.

[0039] In an exemplary embodiment, the long-wave infrared lens 100 of this application can satisfy the condition 1.1≤|f2 / ft|≤2.5, where f2 is the effective focal length of the second lens 2 and ft is the effective focal length of the long-wave infrared lens 100. By controlling the above condition, the refractive power of the second lens can be adjusted to make the light transition smoother, which helps to improve the quality of optical imaging.

[0040] In an exemplary embodiment, the long-wave infrared lens 100 of this application can satisfy the condition 1.2≤|f4 / ft|≤1.6, where f4 is the effective focal length of the fourth lens 5 and ft is the effective focal length of the long-wave infrared lens 100. By controlling the above condition, the refractive power of the fourth lens can be adjusted, which is beneficial for correcting aberrations and thus improving the quality of optical imaging. In an exemplary embodiment, the long-wave infrared lens 100 of this application can satisfy the condition 0.7≤|BFL / ft|≤1.1, where BFL is the distance on the optical axis from the image side of the fourth lens 5 to the imaging plane, and ft is the effective focal length of the long-wave infrared lens 100. The effective focal length ft of the long-wave infrared lens 100 can satisfy 15mm≤ft≤30mm. In one example, ft is 17.6mm. By controlling the above condition, the back focal length can be reduced, making the assembly more compact.

[0041] In an exemplary embodiment, the long-wave infrared lens 100 of the present application can satisfy the conditional formula 0.1 ≤ BFL / TTL ≤ 0.4, where BFL is the distance from the image side of the fourth lens 5 to the imaging surface on the optical axis, and TTL is the distance from the object side of the first lens 1 to the imaging surface on the optical axis. By controlling the above conditional formula, space can be reserved for the installation and focusing of the optical elements of the lens, avoiding mechanical interference.

[0042] In an exemplary embodiment, the long-wave infrared lens 100 of the present application can satisfy the conditional formula 18.2 < H / tan(FOV / 2), where H is the semi-image height of the long-wave infrared lens 100, FOV is the field angle of the long-wave infrared lens, the semi-image height H of the long-wave infrared lens 100 can satisfy H > 9.5 mm, and the field angle FOV of the long-wave infrared lens can satisfy 40° ≤ FOV ≤ 55°. In one example, H is 9.84 mm and FOV is 50°. By controlling the above conditional formula, while achieving a large image plane for the lens, the requirements for the field range of the lens can be satisfied.

[0043] In an exemplary embodiment, the wavelength band applied by the long-wave infrared lens 100 of the present application is 7 to 14 μm, and it can be adapted to a non-cooled detector. The resolution of the non-cooled detector can be 1280*1024, and the pixel size can be 12 μm. By being adapted to a non-cooled detector with a resolution of 1280*1024 and a pixel size of 12 μm, a large image plane can be achieved, and the requirements of small volume and low cost can be satisfied, facilitating miniaturization and integration.

[0044] In an exemplary embodiment, as Figure 1 shown, the long-wave infrared lens 100 of the present application may further include a silicon protection window 6, a germanium protection window 7, and an imaging surface 8. Among them, the imaging surface 8 is the plane where the photosensitive element of the detector is located, and the silicon protection window 6 and the germanium protection window 7 are protection glasses for protecting the photosensitive element located on the imaging surface 8.

[0045] According to the long-wave infrared lens 100 of the above embodiment of the present application, by reasonably configuring the optical powers of the first lens, the second lens, the third lens, and the fourth lens, making the first lens a meniscus lens with the convex surface facing the object side, and controlling the effective focal length of the third lens and the effective focal length of the long-wave infrared lens to satisfy 3.4 ≤ |f3 / ft| ≤ 22.2, it helps to increase the aperture of the rear lens, achieve a large image plane, can improve the relative illumination, ensure the quality of optical imaging, meet the requirement of stable imaging within the temperature range of -40° to +80°, thereby ensuring the accuracy of infrared temperature measurement and meeting the requirement of use in an environment with large temperature changes.

[0046] Those skilled in the art will understand that, without departing from the technical solutions claimed in this application, the number of lenses constituting the long-wave infrared lens 100 can be changed to obtain the various results and advantages described in this specification.

[0047] The following describes in further detail, with reference to the accompanying drawings, specific embodiments of the long-wave infrared lens applicable to the above-described embodiments.

[0048] Example 1

[0049] The following is for reference Figure 2 Embodiment 1 of the long-wave infrared lens according to this application is described. Figure 2 A schematic diagram of the structure of a long-wave infrared lens 200 according to Embodiment 1 of this application is shown.

[0050] like Figure 2 As shown, the long-wave infrared lens 200 includes a first lens 1, a second lens 2, an aperture 3, a third lens 4, a fourth lens 5, a silicon protective window 6, a germanium protective window 7, and an imaging surface 8, arranged sequentially along the optical axis from the object side to the image side. The first lens 1 has negative optical power, with its object side S1 being convex and its image side S2 being concave. The second lens 2 has positive optical power, with its object side S3 being planar and its image side S4 being convex. The third lens 4 has positive optical power, with its object side S5 being concave and its image side S6 being convex. The fourth lens 5 has positive optical power, with its object side S7 being concave and its image side S8 being convex. The first lens 1, second lens 2, third lens 4, and fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with its convex surface facing the object side.

[0051] Table 1 shows the basic parameters of the long-wave infrared lens 200 of Example 1.

[0052] Face number face shape Radius (mm) Spacing (mm) Material Diameter (mm) S1 spherical 18.437 3.5 Single-crystal germanium 28 S2 aspherical 13.910 8.9 21.4 S3 flat endless 2.8 Single-crystal germanium 23 S4 aspherical -119.325 2.6 23 STOP flat endless 18.5 S5 aspherical -30.485 2.5 Single-crystal germanium 20.2 S6 spherical -28.220 7.97 23 S7 aspherical -220.513 3.4 Single-crystal germanium 29 S8 spherical -57.7 15.046 31 S9 flat endless 0.5 Monocrystalline silicon - S10 flat endless 0.5 - S11 flat endless 1 Single-crystal germanium - S12 flat endless 1 - IMA flat endless - -

[0053] Table 1

[0054] In Embodiment 1, the image-side surfaces of the first lens 1 and the second lens 2, and the object-side surfaces of the third lens 4 and the fourth lens 5 are all aspherical. The surface shape x of each aspherical lens can be defined using, but is not limited to, the following aspherical formula:

[0055]

[0056] Where x is the distance vector from the vertex of the aspherical surface at a height of h along the optical axis; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the reciprocal of the radius of curvature R in Table 1 above); k is the conic coefficient; Ai is the i-th order correction coefficient of the aspherical surface. Table 2 below gives the higher-order coefficients A4, A6, A8, A9, and A1 that can be used for the aspherical mirrors S2, S4, S5, and S7 in Example 1.10 A 12 and A 14 .

[0057] Number of surfaces\coefficient k A4 A6 A8 A10 A12 A14 S2 0 9.1983E-06 1.6392E-07 -3.3187E-09 7.9361E-11 -7.2125E-13 3.1068E-15 S4 0 -3.8328E-06 -3.6544E-08 -1.2358E-10 -9.4842E-13 4.7677E-15 -2.5172E-17 S5 0 -5.7965E-06 -3.6606E-08 2.6519E-10 -6.1016E-12 -4.7877E-15 3.0164E-17 S7 0 -8.371E-08 5.6649E-10 -4.6162E-11 4.6907E-13 -1.9569E-15 3.1171E-18

[0058] Table 2

[0059] Figure 3A The MTF curve of the long-wave infrared lens 200 of Example 1 is shown. Figure 3B A dot plot of the long-wave infrared lens 200 of Embodiment 1 is shown. Figure 3C The field curvature and distortion curves of the long-wave infrared lens 200 of Embodiment 1 are shown, with the field curvature curve on the left and the distortion curve on the right. According to... Figures 3A to 3C It can be seen that the MTF of the long-wave infrared lens 200 in Example 1 is close to the diffraction limit, and the diffuse spots are all close to the size of the Airy disk, which can achieve good imaging quality.

[0060] Example 2

[0061] The following is for reference Figure 4 Embodiment 2 of the long-wave infrared lens according to this application is described. In this embodiment, for the sake of brevity, descriptions similar to those in Embodiment 1 are omitted. Figure 4 A schematic diagram of the structure of a long-wave infrared lens 300 according to Embodiment 2 of this application is shown.

[0062] like Figure 4 As shown, the long-wave infrared lens 300 includes a first lens 1, a second lens 2, an aperture 3, a third lens 4, a fourth lens 5, a silicon protective window 6, a germanium protective window 7, and an imaging surface 8, arranged sequentially along the optical axis from the object side to the image side. The first lens 1 has negative optical power, with its object side S1 being convex and its image side S2 being concave. The second lens 2 has positive optical power, with its object side S3 being planar and its image side S4 being convex. The third lens 4 has positive optical power, with its object side S5 being concave and its image side S6 being convex. The fourth lens 5 has positive optical power, with its object side S7 being concave and its image side S8 being convex. The first lens 1, second lens 2, third lens 4, and fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with its convex surface facing the object side.

[0063] Table 3 shows the basic parameters of the long-wave infrared lens 300 in Embodiment 2. In this embodiment, the image-side surfaces of the first lens 1 and the second lens 2, and the object-side surfaces of the third lens 4 and the fourth lens 5 are all aspherical. Table 4 shows the higher-order coefficients A4, A6, A8, and A7 of the aspherical mirrors S2, S4, S5, and S7 that can be used in Embodiment 2. 10 A 12 and A 14Each aspherical surface shape can be defined by formula (1) given in Example 1 above.

[0064] Face number face shape Radius (mm) Spacing (mm) Material Diameter (mm) S1 spherical 18.451 3.5 Single-crystal germanium 28 S2 aspherical 13.928 8.95 21.2 S3 flat endless 2.8 Single-crystal germanium 24 S4 aspherical -117.922 2.59 24 STOP flat endless 18.5 S5 aspherical -29.017 2.5 Single-crystal germanium 20 S6 spherical -27.000 8.04 23 S7 aspherical -226.646 3.4 Single-crystal germanium 29 S8 spherical -58.691 14.89 31 S9 flat endless 0.5 Monocrystalline silicon - S10 flat endless 0.5 - S11 flat endless 1 Single-crystal germanium - S12 flat endless 1 - IMA flat endless - -

[0065] Table 3

[0066]

[0067]

[0068] Table 4

[0069] Figure 5A The MTF curve of the long-wave infrared lens 300 in Example 2 is shown. Figure 5B A dot plot of the long-wave infrared lens 300 of Embodiment 2 is shown. Figure 5C The field curvature and distortion curves of the long-wave infrared lens 300 of Embodiment 2 are shown, with the field curvature curve on the left and the distortion curve on the right. According to... Figures 5A to 5C It can be seen that the MTF of the long-wave infrared lens 300 in Example 2 is close to the diffraction limit, and the diffuse spots are all close to the size of the Airy disk, which can achieve good imaging quality.

[0070] Example 3

[0071] The following is for reference Figure 6 Embodiment 3 of the long-wave infrared lens according to this application is described. In this embodiment, for the sake of brevity, descriptions similar to those in Embodiment 1 are omitted. Figure 6 A schematic diagram of the structure of a long-wave infrared lens 400 according to Embodiment 3 of this application is shown.

[0072] like Figure 6 As shown, the long-wave infrared lens 400 includes a first lens 1, a second lens 2, an aperture 3, a third lens 4, a fourth lens 5, a silicon protective window 6, a germanium protective window 7, and an imaging surface 8, arranged sequentially along the optical axis from the object side to the image side. The first lens 1 has negative optical power, with its object side S1 being convex and its image side S2 being concave. The second lens 2 has positive optical power, with its object side S3 being planar and its image side S4 being convex. The third lens 4 has positive optical power, with its object side S5 being concave and its image side S6 being convex. The fourth lens 5 has positive optical power, with its object side S7 being concave and its image side S8 being convex. The first lens 1, second lens 2, third lens 4, and fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with its convex surface facing the object side.

[0073] Table 5 shows the basic parameters of the long-wave infrared lens 400 in Embodiment 3. In this embodiment, the image-side surfaces of the first lens 1 and the second lens 2, and the object-side surfaces of the third lens 4 and the fourth lens 5 are all aspherical. Table 6 shows the higher-order coefficients A4, A6, A8, and A7 of the aspherical mirrors S2, S4, S5, and S7 that can be used in Embodiment 3. 10 A 12 and A 14 Each aspherical surface shape can be defined by formula (1) given in Example 1 above.

[0074]

[0075]

[0076] Table 5

[0077] Number of surfaces\coefficient k A4 A6 A8 A10 A12 A14 S2 0 8.6246E-06 1.9068E-07 -4.1441E-09 8.9282E-11 -7.8348E-13 3.2146E-15 S4 0 -3.7976E-06 -3.9682E-08 8.152E-13 -2.5016E-12 1.5569E-14 -5.2577E-17 S5 0 -6.7847E-06 -4.433E-08 6.0738E-10 -9.6045E-12 5.1132E-14 -1.5229E-16 S7 0 4.2152E-07 1.8433E-09 -7.7947E-11 6.979E-13 -2.7531E-15 4.2074E-18

[0078] Table 6

[0079] Figure 7A The MTF curve of the long-wave infrared lens 400 in Example 3 is shown. Figure 7B A dot plot of the long-wave infrared lens 400 of Embodiment 3 is shown. Figure 7C The field curvature and distortion curves of the long-wave infrared lens 400 of Embodiment 3 are shown, with the field curvature curve on the left and the distortion curve on the right. According to... Figures 7A to 7C It can be seen that the MTF of the long-wave infrared lens 400 in Example 3 is close to the diffraction limit, and the diffuse spots are all close to the size of the Airy disk, which can achieve good imaging quality.

[0080] Example 4

[0081] The following is for reference Figure 8 Embodiment 4 of the long-wave infrared lens according to this application is described. In this embodiment, for the sake of brevity, descriptions similar to those in Embodiment 1 are omitted. Figure 8 A schematic diagram of the structure of a long-wave infrared lens 500 according to Embodiment 4 of this application is shown.

[0082] like Figure 8As shown, the long-wave infrared lens 500 includes a first lens 1, a second lens 2, an aperture 3, a third lens 4, a fourth lens 5, a silicon protective window 6, a germanium protective window 7, and an imaging surface 8, arranged sequentially along the optical axis from the object side to the image side. The first lens 1 has negative optical power, with its object side S1 being convex and its image side S2 being concave. The second lens 2 has positive optical power, with its object side S3 being convex and its image side S4 being convex. The third lens 4 has positive optical power, with its object side S5 being concave and its image side S6 being convex. The fourth lens 5 has positive optical power, with its object side S7 being convex and its image side S8 being convex. The first lens 1, second lens 2, third lens 4, and fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with its convex surface facing the object side.

[0083] Table 7 shows the basic parameters of the long-wave infrared lens 500 in Embodiment 4. In this embodiment, the image-side surfaces of the first lens 1 and the second lens 2, the object-side surface of the third lens 4, and the object-side and image-side surfaces of the fourth lens 5 are all aspherical. Table 8 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical mirrors S2, S4, S5, S7, and S8 that can be used in Embodiment 3. 10 A 120 A 14 and A 16 Each aspherical surface shape can be defined by formula (1) given in Example 1 above.

[0084]

[0085]

[0086] Table 7

[0087] Number of surfaces\coefficient k A4 A6 A8 A10 A12 A14 A16 S2 0 7.4605E-06 2.9445E-08 9.6719E-11 6.0884E-13 -8.1354E-15 7.572E-17 -2.2181E-19 S4 0 -4.9349E-06 -8.4174E-09 1.0542E-11 -1.0962E-14 -1.193E-16 9.4053E-19 -1.5809E-21 S5 0 -2.2434E-05 3.0408E-08 2.3363E-11 -9.2713E-12 7.6131E-14 -6.3265E-16 1.7413E-18 S7 0 2.8898E-05 -5.7565E-08 2.4568E-11 1.5197E-13 -1.2234E-15 6.9253E-18 -1.8764E-20 S8 0 2.2947E-05 2.8802E-09 -2.272E-10 3.1799E-13 1.5126E-15 -3.9906E-18 -6.4814E-21

[0088] Table 8

[0089] Figure 9A The MTF curve of the long-wave infrared lens 500 of Example 4 is shown. Figure 9B A dot plot of the long-wave infrared lens 500 of Embodiment 4 is shown. Figure 9C The field curvature and distortion curves of the long-wave infrared lens 500 of Embodiment 4 are shown, with the field curvature curve on the left and the distortion curve on the right. According to... Figures 9A to 9C It can be seen that the MTF of the long-wave infrared lens 500 in Example 4 is close to the diffraction limit, and the diffuse spots are all close to the size of the Airy disk, which can achieve good imaging quality.

[0090] Table 9 lists some optical parameters of the long-wave infrared lenses in Examples 1 to 4, as well as the conditions satisfied by each conditional expression. All optical parameters listed in Table 9 are in millimeters (mm).

[0091] Serial Number Optical parameters / conditions Example 1 Example 2 Example 3 Example 4 1 ft 17.95 17.95 17.94 17.66 2 f1 -44.92 -45.11 -45.11 -35.55 3 f2 39.73 39.27 38.04 24.11 4 f3 69.18 67.03 66.21 304.92 5 f4 25.62 25.98 26.44 25.20 6 BFL 18.05 17.89 17.75 15.77 7 TTL 52.85 52.89 52.89 58.33 8 f1 / ft -2.50 -2.51 -2.51 -2.01 9 f2 / ft 2.21 2.19 2.12 1.37 10 f3 / ft 3.85 3.73 3.69 17.27 11 f4 / ft 1.43 1.45 1.47 1.43 12 BFL / ft 1.01 1.00 0.99 0.89 13 BFL / TTL 0.34 0.34 0.34 0.27 14 H 10.01 10.01 10.01 10.01

[0092] Table 9

[0093] This application also provides a temperature measuring device, whose electronic photosensitive element can be a photocoupled device (CCD) or a complementary metal oxide semiconductor device (CMOS). This temperature measuring device can be a stand-alone temperature measuring device or a temperature measuring module integrated into a mobile electronic device such as a mobile phone. The temperature measuring device is equipped with the long-wave infrared lens described above.

[0094] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of protection involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the concept of this application. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A long-wave infrared lens characterized by, In order from the object side to the image side along the optical axis, comprises: a first lens having a negative refractive power, and the first lens is a meniscus lens convex to the object side; a second lens having a positive refractive power; a third lens having a positive refractive power; and a fourth lens having a positive refractive power; wherein the effective focal length f3 of the third lens and the effective focal length ft of the long-wave infrared lens satisfy: 3.69≤|f3 / ft|≤17.27; the effective focal length f2 of the second lens and the effective focal length ft of the long-wave infrared lens satisfy: 1.37≤|f2 / ft|≤2.

21.

2. The long wave infrared lens of claim 1, wherein, At least one of the object side surface and the image side surface of the first lens is aspherical; At least one of the object side surface and the image side surface of the second lens is aspherical; At least one of the object side surface and the image side surface of the third lens is aspherical, and the third lens is a meniscus lens concave to the object side; The object side surface and the image side surface of the fourth lens are both aspherical, and the fourth lens is a meniscus lens convex to the object side.

3. The long wave infrared lens of claim 2, wherein, The first lens and the third lens are both made of germanium single crystal.

4. The long wave infrared lens of claim 1, wherein, Further comprising a diaphragm, the diaphragm is located between the second lens and the third lens, the diaphragm is an adjustable variable diaphragm, the distance D2 of the diaphragm and the second lens on the optical axis satisfies: 2.58mm≤D2≤6.04mm, and the aperture coefficient F of the long-wave infrared lens satisfies: 1.1≤F≤3.

5. The long wave infrared lens of claim 1, wherein, The effective focal length f1 of the first lens and the effective focal length ft of the long-wave infrared lens satisfy: 2.01≤|f1 / ft|≤2.

51.

6. The long wave infrared lens of claim 1, wherein, The effective focal length f4 of the fourth lens and the effective focal length ft of the long-wave infrared lens satisfy: 1.43≤|f4 / ft|≤1.

47.

7. The long wave infrared lens of claim 1, wherein, The distance BFL of the image side surface of the fourth lens to the imaging surface on the optical axis and the effective focal length ft of the long-wave infrared lens satisfy: 0.89≤|BFL / ft|≤1.01, and the effective focal length ft of the long-wave infrared lens satisfies: 17.66mm≤ft≤17.95mm.

8. The long wave infrared lens of claim 1, wherein, The distance BFL of the image side surface of the fourth lens to the imaging surface on the optical axis and the distance TTL of the object side surface of the first lens to the imaging surface on the optical axis satisfy: 0.27≤BFL / TTL≤0.

34.

9. The long wave infrared lens of claim 1, wherein, The half image height H of the long-wave infrared lens and the field of view angle FOV of the long-wave infrared lens satisfy: 18.2mm<H / tan(FOV / 2), the half image height H of the long-wave infrared lens satisfies: 10.01mm≥H>9.5mm, and the field of view angle FOV of the long-wave infrared lens satisfies: 40°≤FOV≤50°.

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