Long-wave infrared lens

Abstract

The invention discloses a long-wave infrared lens, and the lens sequentially comprises a first lens which has negative focal power and is a meniscus lens with a convex surface facing the object side from the object side to the image side along an optical axis; the second lens has positive focal power; the third lens has positive focal power; the fourth lens has positive focal power; the effective focal length f3 of the third lens and the effective focal length ft of the long-wave infrared lens meet the condition that f3 / ft is larger than or equal to 3.4 and smaller than or equal to 22.2.

Description

Technical Field

[0001] The present application relates to the field of optical elements, and more specifically, to a long-wave infrared lens. Background Art

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

[0003] Since temperature will have a certain impact on optical and mechanical materials, the long-wave infrared lens will be affected by temperature when performing infrared temperature measurement, resulting in a decrease in optical imaging quality, thereby affecting the accuracy of temperature measurement. Summary of the invention

[0004] The present application provides a long-wave infrared lens, which includes, in order from the object side to the image side along the optical axis: a first lens having negative optical power, and the first lens is a meniscus lens with a 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 the present application reasonably configures the optical power of the first lens, the second lens, the third lens and the fourth lens, sets an aperture between the second lens and the third lens, makes the first lens adopt a meniscus lens with the convex surface facing the object side, and controls the effective focal length of the third lens and the effective focal length of the long-wave infrared lens to meet 3.4≤|f3 / ft|≤22.2, which helps to increase the aperture of the rear film, realize a large image surface, improve the relative illumination, ensure the quality of optical imaging, meet the demand for stable imaging in the temperature range of -40° to +80°, thereby ensuring the accuracy of infrared temperature measurement and meeting the demand for use in an environment with large temperature changes.

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

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

[0008] In one embodiment, it further includes a diaphragm, the diaphragm is located between the second lens and the third lens, the diaphragm is an adjustable variable diaphragm, and the distance D2 between the diaphragm 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] In conjunction with 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 shows a schematic structural diagram of a long-wave infrared lens according to an exemplary embodiment of the present application;

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

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

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

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

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

[0022] 7A to 7C The MTF curve, the spot diagram, the field curvature curve and the distortion curve of the long-wave infrared lens of Example 3 are respectively shown;

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

[0024] 9A to 9C The MTF curve, point diagram, field curvature curve and distortion curve of the long-wave infrared lens of Example 4 are respectively shown. DETAILED DESCRIPTION

[0025] In order to better understand the present application, a more detailed description will be made of various aspects of the present application with reference to the accompanying drawings. It should be understood that these detailed descriptions are only descriptions of exemplary embodiments of the present application, and are not intended to limit the scope of the present 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 expressions first, second, etc. are only used to distinguish one feature from another feature, and do not represent any limitation on the feature. Therefore, without departing from the teaching 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 drawings, the thickness, size and shape of the lenses have been slightly exaggerated for ease of explanation. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are shown by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to the shapes of the spherical or aspherical surfaces shown in the drawings. The drawings are only examples and are not drawn strictly to scale.

[0028] In this article, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the convex position 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 concave position 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 "comprises", "including", "having", "includes" 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. In addition, when expressions such as "at least one of..." appear after a list of listed features, they modify the entire listed features rather than modifying the individual elements in the list. In addition, when describing embodiments of the present application, "may" is used to mean "one or more embodiments of the present application". And, the term "exemplary" is intended to refer to an example or illustration.

[0030] Unless otherwise defined, all terms (including technical terms and scientific terms) used in this article have the same meaning as commonly understood by ordinary technicians in the field to which this application belongs. It should also be understood that terms (such as terms defined in commonly used dictionaries) should be interpreted as having the same meaning as their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined in this article.

[0031] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

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

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

[0034] In an exemplary embodiment, the long-wave infrared lens 100 of the present application can satisfy the conditional formula: 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 reasonably configuring the optical power of the first lens, the second lens, the third lens, and the fourth lens, the first lens is a meniscus lens with a convex surface facing the object side, and the effective focal length of the third lens and the effective focal length of the long-wave infrared lens are controlled to satisfy 3.4≤|f3 / ft|, which helps to increase the aperture of the rear film, realize a large image plane, improve relative illumination, ensure the quality of optical imaging, and meet the requirements of stable imaging in the temperature range of -40° to +80°, thereby ensuring the accuracy of infrared temperature measurement and meeting the requirements of use in environments with large temperature changes.

[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 the present application is an aspherical surface, at least one of the object side and image side surfaces of the second lens 2 is an aspherical surface, the second lens 2 does not limit the mirror type of the object side and image side surfaces, at least one of the object side and image side surfaces of the third lens 4 is an aspherical surface, and the third lens 4 is a meniscus lens with a concave surface facing the object side, the object side and image side surfaces of the fourth lens 5 are both aspherical surfaces, and the fourth lens 5 is a meniscus lens with a convex surface facing the object side. The characteristic of an aspherical lens is that the curvature changes continuously from the center of the lens to the periphery of the lens. Unlike a spherical lens with a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has a better curvature radius characteristic, and has the advantages of improving distortion aberration and improving astigmatism aberration. After adopting an aspherical lens, the aberration occurring during imaging can be eliminated as much as possible, thereby improving the imaging quality. Among them, the shape of the fourth lens and the appropriate optical back focus help to eliminate the ghost image between the tail piece and the movement 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 the present 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 with a high refractive index as the material of the lens, the use of a diffraction surface of 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 embodiment, Figure 1As shown, the long-wave infrared lens 100 of the present application also includes an aperture 3, which is located between the second lens 2 and the third lens 4. The aperture 3 is an adjustable variable aperture. The distance D2 between the aperture 3 and the second lens 2 on the optical axis can satisfy 2mm≤D2≤6.5mm, and 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 the aperture 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, the light throughput of the lens can be actively controlled. Among them, the aperture is a component with an adjustable aperture. 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 a temperature of about 1600°C, too much energy will cause irreversible damage to the detector. At this time, the aperture can be adjusted to a small elliptical aperture with a major axis of 8.45mm and a minor axis of 6mm, that is, F2.7, for high-temperature measurement, which can protect the detector from damage while meeting the temperature measurement requirements.

[0038] In an exemplary embodiment, the long-wave infrared lens 100 of the present application may satisfy the conditional expression 1.8≤|f1 / ft|≤2.7, wherein 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 conditional expression, it can be ensured that when the light emitted from the first lens is incident on the object side surface of the second lens, the incident light is relatively gentle, thereby reducing the tolerance sensitivity of the long-wave infrared lens.

[0039] In an exemplary embodiment, the long-wave infrared lens 100 of the present application may satisfy the conditional expression 1.1≤|f2 / ft|≤2.5, wherein 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 conditional expression, the refractive power of the second lens may be adjusted to make the light transition smoothly, which helps to improve the quality of optical imaging.

[0040] In an exemplary embodiment, the long-wave infrared lens 100 of the present application may satisfy the conditional formula 1.2≤|f4 / ft|≤1.6, wherein 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 conditional formula, the refractive power of the fourth lens can be adjusted, which is beneficial to correct aberrations, thereby improving the quality of optical imaging. In an exemplary embodiment, the long-wave infrared lens 100 of the present application may satisfy the conditional formula 0.7≤|BFL / ft|≤1.1, wherein BFL is the distance from the image side surface of the fourth lens 5 to the imaging surface on the optical axis, 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 may satisfy 15mm≤ft≤30mm. In one example, ft is 17.6mm. By controlling the above conditional formula, 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 expression 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 expression, 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 expression 18.2 < H / tan(FOV / 2), where H is the semi-image height of the long-wave infrared lens 100, FOV is the field of view 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 of view 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 expression, while achieving a large image plane for the lens, the requirements for the field of view 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 adapting 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] For the long-wave infrared lens 100 according to 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 rear lens aperture, 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 should understand that, without departing from the technical solution claimed in the present 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] Specific embodiments of the long-wave infrared lens applicable to the above-mentioned embodiments are further described below with reference to the accompanying drawings.

[0048] Example 1

[0049] The following reference Figure 2 Embodiment 1 of the long-wave infrared lens according to the present application is described. Figure 2 A schematic structural diagram of a long-wave infrared lens 200 according to Embodiment 1 of the present 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 protection window 6, a germanium protection window 7 and an imaging surface 8 arranged in sequence from the object side to the image side along the optical axis. Among them, the first lens 1 has a negative optical focal length, and its object side surface S1 is a convex surface, and the image side surface S2 is a concave surface. The second lens 2 has a positive optical focal length, and its object side surface S3 is a plane, and the image side surface S4 is a convex surface. The third lens 4 has a positive optical focal length, and its object side surface S5 is a concave surface, and the image side surface S6 is a convex surface. The fourth lens 5 has a positive optical focal length, and its object side surface S7 is a concave surface, and the image side surface S8 is a convex surface. The first lens 1, the second lens 2, the third lens 4 and the fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with the convex surface facing the object side.

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

[0052] Face number Face type Radius(mm) Spacing(mm) Material Diameter(mm) S1 Spherical 18.437 3.5 Single Crystal Germanium 28 S2 Aspheric 13.910 8.9 21.4 S3 flat endless 2.8 Single Crystal Germanium 23 S4 Aspheric -119.325 2.6 23 STOP flat endless 18.5 S5 Aspheric -30.485 2.5 Single Crystal Germanium 20.2 S6 Spherical -28.220 7.97 23 S7 Aspheric -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 Example 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 surfaces, and the surface shape x of each aspherical lens can be defined by, but not limited to, the following aspherical surface formula:

[0055]

[0056] Wherein, x is the distance vector height of the aspheric surface from the vertex of the aspheric surface when the aspheric surface is at a height of h along the optical axis; c is the paraxial curvature of the aspheric surface, c=1 / R (i.e., the paraxial curvature c is the reciprocal of the curvature radius R in Table 1 above); k is the cone coefficient; Ai is the correction coefficient of the i-th order of the aspheric surface. Table 2 below gives the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A29, A30, A31, A32, A33, A34, A35, A36, A37, A310 , A 12 and A 14 .

[0057] Face number\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 FIG. 2 shows the MTF curve of the long-wave infrared lens 200 of Example 1. Figure 3B FIG. 2 shows a point diagram of the long-wave infrared lens 200 of Example 1. Figure 3C The field curvature curve and distortion curve of the long-wave infrared lens 200 of Example 1 are shown, wherein the left side is the field curvature curve and the right side is the distortion curve. FIG. 3A to FIG. 3C It can be seen that the MTF of the long-wave infrared lens 200 of Example 1 is close to the diffraction limit, and the diffuse spots are close to the size of the Airy disk, which can achieve good imaging quality.

[0060] Example 2

[0061] The following reference Figure 4 Embodiment 2 of the long-wave infrared lens according to the present application is described. In this embodiment, for the sake of brevity, some descriptions similar to those of Embodiment 1 will be omitted. Figure 4 A schematic structural diagram of a long-wave infrared lens 300 according to Embodiment 2 of the present 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 protection window 6, a germanium protection window 7 and an imaging surface 8, which are arranged in sequence from the object side to the image side along the optical axis. Among them, the first lens 1 has a negative optical focal length, and its object side surface S1 is a convex surface, and the image side surface S2 is a concave surface. The second lens 2 has a positive optical focal length, and its object side surface S3 is a plane, and the image side surface S4 is a convex surface. The third lens 4 has a positive optical focal length, and its object side surface S5 is a concave surface, and the image side surface S6 is a convex surface. The fourth lens 5 has a positive optical focal length, and its object side surface S7 is a concave surface, and the image side surface S8 is a convex surface. The first lens 1, the second lens 2, the third lens 4 and the fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with the convex surface facing the object side.

[0063] Table 3 shows the basic parameters of the long-wave infrared lens 300 of Example 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 surfaces. Table 4 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A29, A30, A31, A32, A33, A34, A35, A36, A37, A38, A39, A40, A41, A42, A43, A44, A45, A46, A47, A48, A49, A50, A 10 , A 12 and A 14, wherein each aspheric surface shape can be defined by the formula (1) given in the above embodiment 1.

[0064] Face number Face type Radius(mm) Spacing(mm) Material Diameter(mm) S1 Spherical 18.451 3.5 Single Crystal Germanium 28 S2 Aspheric 13.928 8.95 21.2 S3 flat endless 2.8 Single Crystal Germanium 24 S4 Aspheric -117.922 2.59 24 STOP flat endless 18.5 S5 Aspheric -29.017 2.5 Single Crystal Germanium 20 S6 Spherical -27.000 8.04 23 S7 Aspheric -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 FIG. 4 shows the MTF curve of the long-wave infrared lens 300 of Example 2. Figure 5B FIG. 4 shows a point diagram of the long-wave infrared lens 300 of Example 2. Figure 5C The field curvature curve and distortion curve of the long-wave infrared lens 300 of Example 2 are shown, wherein the left side is the field curvature curve and the right side is the distortion curve. FIG. 5A to FIG. 5C It can be seen that the MTF of the long-wave infrared lens 300 of Example 2 is close to the diffraction limit, and the diffuse spots are close to the size of the Airy disk, which can achieve good imaging quality.

[0070] Example 3

[0071] The following reference Figure 6 Embodiment 3 of the long-wave infrared lens according to the present application is described. In this embodiment, for the sake of brevity, some descriptions similar to those of Embodiment 1 will be omitted. Figure 6 A schematic structural diagram of a long-wave infrared lens 400 according to Embodiment 3 of the present 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 protection window 6, a germanium protection window 7 and an imaging surface 8, which are arranged in sequence from the object side to the image side along the optical axis. Among them, the first lens 1 has a negative optical focal length, and its object side surface S1 is a convex surface, and the image side surface S2 is a concave surface. The second lens 2 has a positive optical focal length, and its object side surface S3 is a plane, and the image side surface S4 is a convex surface. The third lens 4 has a positive optical focal length, and its object side surface S5 is a concave surface, and the image side surface S6 is a convex surface. The fourth lens 5 has a positive optical focal length, and its object side surface S7 is a concave surface, and the image side surface S8 is a convex surface. The first lens 1, the second lens 2, the third lens 4 and the fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with the convex surface facing the object side.

[0073] Table 5 shows the basic parameters of the long-wave infrared lens 400 of Example 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 surfaces. Table 6 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A29, A30, A31, A32, A33, A34, A35, A36, A37, A38, A39, A40, A41, A42, A43, A44, A45, A46, A47, A48, A49, A50, A51, A52, A53, A54, A55, A56, A57, A58, A59, A60, A61, A71, A72, A73, A74, A75 10 , A 12 and A 14 , wherein each aspheric surface shape can be defined by the formula (1) given in the above embodiment 1.

[0074]

[0075]

[0076] Table 5

[0077] Face number\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] Fig. 7A FIG. 4 shows the MTF curve of the long-wave infrared lens 400 of Example 3. Figure 7B FIG. 4 shows a point diagram of the long-wave infrared lens 400 of Example 3. Figure 7C The field curvature curve and distortion curve of the long-wave infrared lens 400 of Example 3 are shown, wherein the left side is the field curvature curve and the right side is the distortion curve. 7A to 7C It can be seen that the MTF of the long-wave infrared lens 400 of Example 3 is close to the diffraction limit, and the diffuse spots are close to the size of the Airy disk, which can achieve good imaging quality.

[0080] Example 4

[0081] The following reference Figure 8 Embodiment 4 of the long-wave infrared lens according to the present application is described. In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. Figure 8 A schematic structural diagram of a long-wave infrared lens 500 according to Embodiment 4 of the present 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 protection window 6, a germanium protection window 7 and an imaging surface 8, which are arranged in sequence from the object side to the image side along the optical axis. Among them, the first lens 1 has a negative optical focal length, and its object side surface S1 is a convex surface, and the image side surface S2 is a concave surface. The second lens 2 has a positive optical focal length, and its object side surface S3 is a convex surface, and the image side surface S4 is a convex surface. The third lens 4 has a positive optical focal length, and its object side surface S5 is a concave surface, and the image side surface S6 is a convex surface. The fourth lens 5 has a positive optical focal length, and its object side surface S7 is a convex surface, and the image side surface S8 is a convex surface. The first lens 1, the second lens 2, the third lens 4 and the fourth lens 5 are all germanium single crystals. The first lens 1 is a meniscus lens with the convex surface facing the object side.

[0083] Table 7 shows the basic parameters of the long-wave infrared lens 500 of Example 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 surface and image side surface of the fourth lens 5 are all aspherical surfaces. Table 8 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A29, A30, A31, A32, A33, A34, A35, A36, A37, A38, A39, A40, A41, A42, A43, A44, A45, A46, A47, A48, 10 , A 120 , A 14 and A 16 , wherein each aspheric surface shape can be defined by the formula (1) given in the above embodiment 1.

[0084]

[0085]

[0086] Table 7

[0087] Face number\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] Fig.9A The MTF curve of the long-wave infrared lens 500 of Example 4 is shown. Fig. 9B FIG. 4 shows a point diagram of the long-wave infrared lens 500 of Example 4. Fig. 9C The field curvature curve and distortion curve of the long-wave infrared lens 500 of Example 4 are shown, wherein the left side is the field curvature curve and the right side is the distortion curve. 9A to 9C It can be seen that the MTF of the long-wave infrared lens 500 of Example 4 is close to the diffraction limit, and the diffuse spots are 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 lens of each embodiment from Example 1 to Example 4 and the conditions satisfied by each conditional formula. The units of the optical parameters listed in Table 9 are all 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] The present application also provides a temperature measuring device, whose electronic photosensitive element can be a photosensitive coupled device (CCD) or a complementary metal oxide semiconductor element (CMOS). The temperature measuring device can be an independent temperature measuring device, or a temperature measuring module integrated in 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 only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of protection involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the concept of the present application. For example, the above features are replaced with the technical features with similar functions disclosed in the present application (but not limited to) to form a technical solution.

Claims

1. A long-wave infrared lens, characterized in that: It sequentially includes from the object side to the image side along the optical axis: A first lens, having a negative focal power, and the first lens is a meniscus lens with its convex surface facing the object side; A second lens, having a positive focal power; A third lens, having a positive focal power; and A fourth lens, having a positive focal 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.

2. The long-wave infrared lens according to claim 1, characterized in that: At least one of the object side surface and the image side surface of the first lens is an aspherical surface; At least one of the object side surface and the image side surface of the second lens is an aspherical surface; At least one of the object side surface and the image side surface of the third lens is an aspherical surface, and the third lens is a meniscus lens with its concave surface facing the object side; Both the object side surface and the image side surface of the fourth lens are aspherical surfaces, and the fourth lens is a meniscus lens with its convex surface facing the object side.

3. The long-wave infrared lens according to claim 2, characterized in that: Both the first lens and the third lens are made of germanium single crystal.

4. The long-wave infrared lens according to claim 1, characterized in that: It further includes a diaphragm, the diaphragm is located between the second lens and the third lens, the diaphragm is an adjustable variable diaphragm, the distance D2 between the diaphragm and the second lens on the optical axis satisfies: 2mm ≤ D2 ≤ 6.5mm, and the aperture coefficient F of the long-wave infrared lens satisfies: 1.1 ≤ F ≤ 3.

5. The long-wave infrared lens according to claim 1, characterized in that: 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.

6. The long-wave infrared lens according to claim 1, characterized in that: 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.

7. The long-wave infrared lens according to claim 1, characterized in that: 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.

8. The long-wave infrared lens according to claim 1, characterized in that: The distance BFL from 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: 0.7 ≤ |BFL / ft| ≤ 1.1, and the effective focal length ft of the long-wave infrared lens satisfies: 15mm ≤ ft ≤ 30mm.

9. The long-wave infrared lens according to claim 1, characterized in that: The distance BFL from the image side surface of the fourth lens to the imaging surface on the optical axis and the distance TTL from the object side surface of the first lens to the imaging surface on the optical axis satisfy: 0.1 ≤ BFL / TTL ≤ 0.

4.

10. The long-wave infrared lens according to claim 1, characterized in that: 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 > 9.5mm, and the field of view FOV of the long-wave infrared lens satisfies: 40° ≤ FOV ≤ 55°.

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