Wide-working-distance infrared radiation temperature measurement lens

Abstract

The utility model discloses a wide working distance infrared radiation temperature measuring lens, which relates to the technical field of infrared temperature measuring lenses and comprises an aperture diaphragm, a first lens, a second lens, a third lens and an infrared detector which are arranged along an optical axis, the first lens is a meniscus positive focal power lens, the second lens is a concave-convex negative focal power lens, and the third lens is a concave-convex negative focal power lens. The third lens is a biconvex positive-focal-power lens, the third lens comprises a third image side face part, the infrared detector comprises an imaging face part, the distance between the center of the third image side face part and the imaging face part is BFL, and the BFL meets the condition that BFL is larger than or equal to 11.8 mm and smaller than or equal to 14.5 mm. Through the arrangement, the temperature measurement lens can perform clear imaging from a close distance to an infinite distance, and the technical problems that when an existing lens performs imaging at a close distance, the imaging quality is poor, even focusing cannot be performed, and the temperature measurement precision is affected can be solved.

Description

TECHNICAL FIELD

[0001] The utility model relates to infrared temperature measurement lens technical field, specifically is a wide working distance infrared radiation temperature measurement lens. BACKGROUND

[0002] Infrared thermal imager has wide application in the field of security, industry, medical treatment and the like, and the market scale is huge. The radiation temperature measurement principle of the infrared thermal imager is that the infrared radiation energy of an object is converged to an infrared sensor through a lens, the sensor converts an optical signal into an electrical signal, and the processor displays the infrared thermal image of the measured object and the measured temperature on a display after processing the infrared radiation information collected by the infrared sensor.

[0003] The infrared radiation temperature measurement lens is an important component of the infrared thermal imager, and the imaging performance of the optical system of the infrared radiation temperature measurement lens affects the accuracy of temperature measurement. Excellent optical design can improve the temperature measurement precision. For example, low MTF of the lens reduces the imaging resolution and thus reduces the temperature measurement accuracy. In order to improve the imaging performance, more lenses need to be used to correct aberration, which is high in cost and increases the weight of the lens. If the cost of the lens can be reduced while the imaging quality is ensured, the product competitiveness will be improved, and the market will be very considerable.

[0004] In some fields, the lens needs to have a wide working distance, and it is required to clearly image objects at both near and far distances. Generally, lens design is only optimized for infinite distance, and the imaging quality at near distance is ignored, which leads to that the thermal imager can clearly image objects at middle and far distances, but the imaging at near distance is poor or even cannot be focused, and the temperature measurement precision is affected, which cannot meet the application requirements in some specific occasions. CONTENT OF THE UTILITY MODEL

[0005] Therefore, the utility model aims at providing a wide working distance infrared radiation temperature measurement lens to solve the technical problem that the existing lens in the background art has poor imaging quality at near distance, and even cannot be focused, and affects the temperature measurement precision.

[0006] The utility model provides a wide working distance infrared radiation temperature measurement lens, which comprises an aperture stop, a first lens, a second lens, a third lens and an infrared detector arranged along an optical axis.

[0007] The first lens is a meniscus positive focal power lens, the second lens is a concave-convex negative focal power lens, and the third lens is a double convex positive focal power lens.

[0008] The third lens comprises a third image side surface portion, the infrared detector comprises an imaging surface portion, the distance between the center of the third image side surface portion and the imaging surface portion is BFL, and BFL satisfies 11.8mm≤BFL≤14.5mm.

[0009] Further, the first lens, the second lens and the third lens are made of a chalcogenide compound.

[0010] Further, the first lens has a refractive index of n1 for light with a wavelength of 10 μm, and n1≥2.7.

[0011] The second lens has a refractive index of n2 for light with a wavelength of 10 μm, and n2≥2.6.

[0012] The third lens has a refractive index of n3 for light with a wavelength of 10 μm, and n3≥2.7.

[0013] Further, the combined focal length of the first lens, the second lens and the third lens is f.

[0014] The focal length of the first lens is f1, and f1 satisfies: 0.7≤|f1 / f|≤0.8.

[0015] The focal length of the second lens is f2, and f2 satisfies: -0.3≤|f2 / f|≤-0.4.

[0016] The focal length of the third lens is f3, and f3 satisfies: 0.4≤|f3 / f|≤0.5.

[0017] Further, the first lens comprises a first object-side surface portion provided with a spherical surface and a first image-side surface portion provided with an aspherical surface.

[0018] The second lens comprises a second object-side surface portion provided with an aspherical surface and a second image-side surface portion provided with an aspherical surface.

[0019] The third lens further comprises a third object-side surface portion provided with an aspherical surface and the third image-side surface portion provided with a spherical surface.

[0020] Further, the distance between the center of the first image-side surface portion and the center of the second object-side surface portion is d12, and d12 satisfies: 9.5mm≤d12≤10.5mm.

[0021] The distance between the center of the second image-side surface portion and the center of the third object-side surface portion is d23, and d23 satisfies: 6.5mm≤d23≤7.5mm.

[0022] Further, the aperture stop is arranged on the first object-side surface portion.

[0023] Further, the first image-side surface portion is a diffractive surface, and the diffractive surface is provided with diffractive annular zones, and the radial radius r of each annular zone at a sudden change of the diffractive annular zones satisfies: 2Nπ=B1×r2+B2×r4+…+Bi×r2i.

[0024] wherein, in the formula, N=1, 2, 3, …, n represents the nth annular zone mutation, Bi is a diffraction surface phase coefficient.

[0025] Further, the diffraction annular zone depth on the first image-side surface portion is L, and L satisfies: L=mλ / {n(λ)-1};

[0026] wherein, n(λ) is the refractive index of the second lens lens material to the wavelength λ, and m is the diffraction order.

[0027] Further, the curvature radius of the first object-side surface portion is R1, and R1 satisfies 27.4mm≤R1≤29.4mm;

[0028] The curvature radius of the first image-side surface portion is R2, and R2 satisfies 54.4mm≤R2≤56.4mm;

[0029] The curvature radius of the second object-side surface portion is R3, and R3 satisfies 118.2mm≤R3≤122.2mm;

[0030] The curvature radius of the second image-side surface portion is R4, and R4 satisfies 18.2mm≤R4≤20.2mm;

[0031] The curvature radius of the third object-side surface portion is R5, and R5 satisfies 44.5mm≤R5≤45.5mm;

[0032] The curvature radius of the third image-side surface portion is R6, and R6 satisfies -97.9mm≤R6≤-91.9mm.

[0033] Compared with the prior art, the wide working distance infrared radiation temperature measurement lens has the following beneficial effects:

[0034] In the wide working distance infrared radiation temperature measurement lens, the distance between the third image-side surface portion center and the imaging surface portion is BFL, and BFL satisfies: 11.8mm≤BFL≤14.5mm, so that the wide working distance infrared radiation temperature measurement lens can clearly image from a close distance to infinity, and can solve the technical problems of poor imaging quality and even inability to focus and influence on temperature measurement accuracy of the existing lens when imaging at a close distance. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a structural schematic view of the wide working distance infrared radiation temperature measurement lens in an embodiment of the present application;

[0036] Figure 2 is a specific structural schematic view of the wide working distance infrared radiation temperature measurement lens in an embodiment of the present application;

[0037] Figure 3 The figure is a schematic diagram of the surface shape of the diffractive surface of the first lens in an embodiment of the utility model;

[0038] Figures 4 to 6 The MTF curve of the utility model wide working distance infrared radiation temperature measurement lens focusing on 0.3 meter target under-40 DEG C, 20 DEG C, 80 DEG C ambient temperature.

[0039] Figures 7 to 9 The MTF curve of the utility model wide working distance infrared radiation temperature measurement lens focusing on 2 meter target under-40 DEG C, 20 DEG C, 80 DEG C ambient temperature.

[0040] Figures 10-12 The MTF curve of the utility model wide working distance infrared radiation temperature measurement lens focusing on infinite target under-40 DEG C, 20 DEG C, 80 DEG C ambient temperature.

[0041] Figure 13 The field of view-distortion curve diagram of the utility model wide working distance infrared radiation temperature measurement lens.

[0042] In the figure: 10, lens;0, aperture stop;1, first lens;S1, first object side surface portion;S2, first image side surface portion;2, second lens;S3, second object side surface portion;S4, second image side surface portion;3, third lens;S5, third object side surface portion;S6, third image side surface portion;4, infrared detector;41, protective window;42, imaging surface portion;X, optical system optical axis. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the utility model, the utility model will be described more fully below with reference to the relevant drawings. The drawings show several embodiments of the utility model. However, the utility model can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the utility model more thorough and comprehensive.

[0044] It should be noted that when an element is referred to as being "fixed" to another element, it can be directly on the other element or there can be an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there can be an intervening element. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. The use herein of the terms "and / or" includes a set of one or more associated listed items.

[0046] Referring to Figures 1 to 3 , a wide working distance infrared radiation temperature measurement lens 10 in an embodiment of the present application is shown, which comprises an aperture stop 0, a first lens 1, a second lens 2, a third lens 3 and an infrared detector 3 arranged along the optical axis;

[0047] The first lens 1 is a meniscus positive lens, the second lens 2 is a concave-convex negative lens, and the third lens 3 is a double convex positive lens;

[0048] The third lens 3 comprises a third image side surface S6, the infrared detector 3 comprises an imaging surface 42, the distance between the center of the third image side surface S6 and the imaging surface 42 is BFL, and BFL satisfies: 11.8mm≤BFL≤14.5mm. It should be noted that the infrared detector 3 has a protective window 41.

[0049] In the embodiment, by setting the distance between the center of the third image side surface S6 and the imaging surface 42 as BFL, and BFL satisfying: 11.8mm≤BFL≤14.5mm, the wide working distance infrared radiation temperature measurement lens 10 provided in the embodiment can clearly image from close distance to infinity, and can solve the technical problems of poor imaging quality and even inability to focus and affecting temperature measurement accuracy when the existing lens 10 images at close distance.

[0050] Specifically, in some preferred embodiments, the first lens 1, the second lens 2 and the third lens 3 are all made of a chalcogenide compound.

[0051] In some preferred embodiments, the refractive index of the first lens 1 to light with a wavelength of 10μm is n1, n1≥2.7; the refractive index of the second lens 2 to light with a wavelength of 10μm is n2, n2≥2.6; and the refractive index of the third lens 3 to light with a wavelength of 10μm is n3, n3≥2.7.

[0052] In some preferred embodiments, the combined focal length of the first lens 1 and the second lens 2 and the third lens 3 is f; wherein the focal length of the first lens 1 is f1, and f1 satisfies: 0.7≤|f1 / f|≤0.8; the focal length of the second lens 2 is f2, and f2 satisfies: -0.3≤|f2 / f|≤-0.4; the focal length of the third lens 3 is f3, and f3 satisfies: 0.4≤|f3 / f|≤0.5. In this embodiment, the optical power of each lens is reasonably distributed, so that the light rays smoothly transition in the infrared radiation thermometry lens 10 optical system, and the lens tolerance sensitivity is reduced, the requirement for lens processing precision is reduced, the overall cost is reduced, and the lens processing and optical system assembly are facilitated.

[0053] Further, the first lens 1 includes a first object side surface S1 provided with a spherical surface and a first image side surface S2 provided with an aspherical surface; the second lens 2 includes a second object side surface S3 provided with an aspherical surface and a second image side surface S4 provided with an aspherical surface; and the third lens 3 further includes a third object side surface S5 provided with an aspherical surface and a third image side surface S6 provided with a spherical surface.

[0054] It should be noted that the surface type of the aspherical surface satisfies the following formula:

[0055]

[0056] In the formula, Z is the sag of the aspherical surface at a height of Y along the optical axis X, An is the n-order coefficient of the aspherical surface, and Y is the height in the radial direction of the lens. The parameter C is the curvature corresponding to the radius of the aspherical surface (the reciprocal of the radius R), and the coefficient K is the conic quadratic curve coefficient.

[0057] Specifically, when K is less than -1, the surface curve of the lens is a hyperbola, when K is equal to -1, the surface curve of the lens is a parabola; when K is between -1 and 0, the surface curve of the lens is an ellipse, when K is equal to 0, the surface curve of the lens is a circle, and when K is greater than 0, the surface curve of the lens is a flattened circle.

[0058] Further, the aspherical surface parameters of each lens surface of the embodiment are listed in Table 1.

[0059] Surface number K A2 A4 A6 A8 A10 S2 0 0 7.0393E-07 2.4035E-09 -9.5886E-12 1.5195E-14 S4 0 0 2.4833E-05 -4.6393E-08 7.4506E-10 -4.7560E-12 S5 0 0 3.2843E-06 -2.1246E-08 4.4197E-11 -1.5754E-13

[0060] Table 1

[0061] The embodiment adopts the specific combination of the spherical surface and the aspherical surface, which improves the imaging quality, effectively reduces the number of lenses, simplifies the structure of the optical system and reduces the weight, and controls the overall cost.

[0062] Further, the first image-side surface portion S2 is a diffractive surface and is based on an aspherical surface. The introduction of the diffractive surface makes the optical system correct aberration and athermalization with fewer lenses, and provides convenience for improving image quality, reducing weight and reducing cost of the optical system.

[0063] Further, the first image-side surface portion S2 is a diffractive surface, and the diffractive surface is provided with diffractive annular zones, and the radial radius r of each annular zone mutation in the diffractive annular zones satisfies 2Nπ=B1×r2+B2×r4+…+Bi×r2i;

[0064] Wherein, N=1, 2, 3, …, n represents the nth annular zone mutation, Bi is the phase coefficient of the diffractive surface, and each annular ring corresponds to a phase change of 2π to form interference of each period of diffracted light.

[0065] Specifically, the diffractive annular zone parameters of the first image-side surface portion S2 are shown in Table 2.

[0066] Surface B1 B2 S2 -2.36E-04 7.38E-08

[0067] Table 2

[0068] The number and radius of the diffractive annular zones of the first image-side surface portion S2 are shown in Table 3.

[0069] Girdle number Girdle radius 1 6.55 2 9.33 3 11.52 4 13.40

[0070] Table 3

[0071] Further, the depth of the diffractive annular zones on the first image-side surface portion S2 is L, and L satisfies: L=mλ / {n(λ)-1}; wherein λ is the wavelength of the incident light, n(λ) is the refractive index of the second lens 2 to the incident wavelength λ, m is the diffraction order, and n means the refractive index, and n(λ) is an integral.

[0072] Specifically, the depth L parameters of the diffractive annular zones on the first image-side surface portion S2 are shown in Table 4.

[0073] m 1 Lambda 10 μm n(lambda) 2.8 L 5.62 μm

[0074] Table 4

[0075] It is worth mentioning that due to the chromatic aberration in the optical system, the conventional optical system needs to use two lenses with positive and negative optical power or increase the number of lenses to eliminate chromatic aberration. The Abbe number of the diffractive optical element is negative, which can compensate for each other with the refractive element to correct chromatic aberration. Due to the special dispersion property of the diffractive element, the difficulty of achromatization is reduced, so that achromatization can be realized by only one refractive-diffractive hybrid lens. In addition, the photo-thermal expansion coefficient of the refractive element is always negative, while the photo-thermal expansion coefficient of the diffractive element is always positive, so the refractive-diffractive hybrid optical system is easier to correct thermal aberration. The introduction of the diffractive surface makes the optical system correct aberration and eliminate thermal aberration with fewer lenses, which provides convenience for improving the image quality of the optical system and reducing weight and cost.

[0076] The embodiment according to the above optimal value of the diffractive surface, the function of eliminating thermal aberration and chromatic aberration is achieved.

[0077] Further, the curvature radius of the first object side surface S1 is R1, and R1 satisfies 27.4mm≤R1≤29.4mm;

[0078] The curvature radius of the first image side surface S2 is R2, and R2 satisfies 54.4mm≤R2≤56.4mm;

[0079] The curvature radius of the second object side surface S3 is R3, and R3 satisfies 118.2mm≤R3≤122.2mm;

[0080] The curvature radius of the second image side surface S4 is R4, and R4 satisfies 18.2mm≤R4≤20.2mm;

[0081] The curvature radius of the third object side surface S5 is R5, and R5 satisfies 44.5mm≤R5≤45.5mm;

[0082] The curvature radius of the third image side surface S6 is R6, and R6 satisfies -97.9mm≤R6≤-91.9mm.

[0083] Further, the interval between the center of the first image side surface S2 and the center of the second object side surface S3 is d12, and d12 satisfies 9.5mm≤d12≤10.5mm;

[0084] The interval between the center of the second image side surface S4 and the center of the third object side surface S5 is d23, and d23 satisfies 6.5mm≤d23≤7.5mm.

[0085] In some preferred embodiments: according to the setting of various data of one wide working distance infrared radiation thermometry lens 10 in this embodiment, a set of preferred combinations are implemented, which are listed in the following Table 5. In Table 5, the surface number refers to the order of the surface from the object surface to the image surface along the optical axis, and the surface number of the first lens 1 object side surface to the infrared detector imaging surface 42 is sequentially labeled. Table 5 also includes: the surface type of each surface, the curvature radius R of each surface, the thickness d of each lens, the interval t between the centers of two adjacent lenses, and the refractive index n of each lens material at a wavelength of 10 μm.

[0086]

[0087] Table 5

[0088] Further need to be explained is that, as shown in Figures 4-12 , the modulation transfer function curve (MTF) diagram simulated and calculated by the optical design software for the wide working distance infrared radiation thermometry lens 10 in the above preferred embodiment at the focusing distance of 0.3 m, 2 m and infinity respectively at three different temperatures of -40℃, 20℃ and 80℃. Each curve in the curve diagram refers to the modulation transfer function curve of different fields of view (distinguished by image height, such as the central field of view is 0 mm, and 2.1 mm (0.3 field of view), 3.5 mm (0.5 field of view), 4.9 mm (0.7 field of view) and the edge field of view 7.0 mm, and each field of view has two directions of meridian and sagittal, wherein the solid line is the simulation result of the meridian direction of different fields of view, and the dotted line is the simulation result of the sagittal direction of different fields of view. Through the curve diagram, it can be known that the modulation transfer function curve of the wide working distance infrared radiation thermometry lens 10 in the present application is relatively flat and changes little in the temperature range of -40℃-80℃ when the focusing distance is 0.3 m, the overall image quality is good, and each modulation transfer function curve is close to the diffraction limit of the optical system, which is sufficient to meet the resolution requirement of the infrared detector. Figures 4-6 Through the curve diagram, it can be known that the modulation transfer function curve of the wide working distance infrared radiation thermometry lens 10 in the present application is relatively flat and changes little in the temperature range of -40℃-80℃ when the focusing distance is 2 m, the overall image quality is good, and each modulation transfer function curve is close to the diffraction limit of the optical system, which is sufficient to meet the resolution requirement of the infrared detector. Figures 7-9 Through the curve diagram, it can be known that the modulation transfer function curve of the wide working distance infrared radiation thermometry lens 10 in the present application is relatively flat and changes little in the temperature range of -40℃-80℃ when the focusing distance is 2 m, the overall image quality is good, and each modulation transfer function curve is close to the diffraction limit of the optical system, which is sufficient to meet the resolution requirement of the infrared detector. Figures 10-12 Through the curve diagram, it can be known that the modulation transfer function curve of the wide working distance infrared radiation thermometry lens 10 in the present application is relatively flat and changes little in the temperature range of -40℃-80℃ when the focusing distance is 2 m, the overall image quality is good, and each modulation transfer function curve is close to the diffraction limit of the optical system, which is sufficient to meet the resolution requirement of the infrared detector.

[0089] It needs to be additionally explained that, please refer to the modulation transfer function curve (MTF) diagram simulated and calculated by the optical design software for the wide working distance infrared radiation thermometry lens 10 in the above preferred embodiment at the focusing distance of 0.3 m, 2 m and infinity respectively at three different temperatures of -40℃, 20℃ and 80℃, as shown in Figure 5As shown, the optical system distortion field curve shows that the optical system has small imaging distortion, the maximum distortion is less than or equal to 1%, the image is small, and the imaging quality is high.

[0090] The performance indicators of the temperature measurement lens 10 of the embodiment are as follows: focal length: 35mm; working wavelength: 8-12um; field of view range: 17.6°(H) x 14.1°(V); working distance: 0.3-infinity; infrared detector 4 specification: 640 x 512, image circle diameter: 17um; working temperature range: -40℃-+80℃.

[0091] Compared with the prior art temperature measurement lens, the wide working distance infrared radiation temperature measurement lens has at least the following beneficial effects:

[0092] 1. In the wide working distance infrared radiation temperature measurement lens 10, the distance between the third image side surface S6 center and the imaging surface 42 is BFL, and BFL satisfies: 11.8mm≤BFL≤14.5mm, so that the wide working distance infrared radiation temperature measurement lens 10 can clearly image from a close distance to infinity, and can solve the technical problems of poor imaging quality and even unable to focus at a close distance, and affect the temperature measurement accuracy.

[0093] 2. In the wide working distance infrared radiation temperature measurement lens 10, by reasonably distributing the lens focal power, using sulfide with different refractive indexes as the lens material, and using aspheric surface and diffraction surface, the thermal radiation in the 8-12um band can be clearly imaged using a small number of lenses, the optical system has high imaging quality, high relative luminance, and small optical distortion, and meets the imaging and temperature measurement requirements, and has simple structure, light weight, and good economic benefit.

[0094] 3. In the wide working distance infrared radiation temperature measurement lens 10, the optical system is optimized and designed, the distance between the lens 10 and the infrared core is adjusted to focus on different working distance targets, so that the lens can clearly image targets from 0.3m to infinity.

[0095] 4. In the wide working distance infrared radiation temperature measurement lens 10, the diffraction ring is machined on the lens surface, which has excellent correction of thermal aberration and chromatic aberration characteristics, and can ensure that the optical system can clearly image in a wide working temperature range of-40℃-80℃, so that the focusing mechanism does not need to be designed to compensate for the defocus of the optical system caused by temperature change, and the optical system is small in size.

[0096] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the utility model. In the specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0097] The above embodiments only express several implementation manners of the utility model, the description is more specific and detailed, but it cannot be understood as the limitation of the utility model patent scope. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the utility model, a number of modifications and improvements can be made, which belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent should be subject to the appended claims.

Claims

1. A wide working distance infrared radiation thermometry lens, characterized in that, It includes an aperture stop (0) arranged along the optical axis, a first lens (1), a second lens (2), a third lens (3), and an infrared detector (4); The first lens (1) is a meniscus positive power lens, the second lens (2) is a concave-convex negative power lens, and the third lens (3) is a biconvex positive power lens. The third lens (3) includes a third image side portion (S6), the infrared detector (4) includes an imaging face portion (42), the distance between the center of the third image side portion (S6) and the imaging face portion (42) is BFL, and BFL satisfies: 11.8mm≤BFL≤14.5mm.

2. The wide working distance infrared radiation thermometry lens according to claim 1, characterized in that, The first lens (1), the second lens (2), and the third lens (3) are all made of chalcogenide compounds.

3. The wide working distance infrared radiation thermometry lens according to claim 1, characterized in that, The first lens (1) has a refractive index for light with a wavelength of 10 μm, and the refractive index of the light is n1, n1≥2.7; The second lens (2) has a refractive index for light with a wavelength of 10 μm, and the refractive index of the light is n2, n2≥2.6; The third lens (3) has a refractive index for light with a wavelength of 10 μm, and the refractive index of the light is n3, n3≥2.

7.

4. The wide working distance infrared radiation thermometry lens according to claim 1, characterized in that, The combined focal length of the first lens (1), the second lens (2), and the third lens (3) is f; Wherein, the focal length of the first lens (1) is f1, and f1 satisfies: 0.7≤|f1 / f|≤0.8; The focal length of the second lens (2) is f2, and f2 satisfies: -0.3≤|f2 / f|≤-0.4; The focal length of the third lens (3) is f3, and f3 satisfies: 0.4≤|f3 / f|≤0.

5.

5. The wide working distance infrared radiation thermometry lens according to claim 1, characterized in that, The first lens (1) includes a first object-side portion (S1) provided on a spherical surface and a first image-side portion (S2) provided on an aspherical surface; The second lens (2) includes a second object-side portion (S3) provided with an aspherical surface and a second image-side portion (S4) provided with an aspherical surface; The third lens (3) further includes an aspherical third object side portion (S5) and a spherical third image side portion (S6).

6. The wide working distance infrared radiation thermometry lens according to claim 5, characterized in that, The distance between the center of the first image-side portion (S2) and the center of the second object-side portion (S3) is d12, and d12 satisfies 9.5mm≤d12≤10.5mm; The distance between the center of the second image side portion (S4) and the center of the third object side portion (S5) is d23, and d23 satisfies 6.5mm≤d23≤7.5mm.

7. The wide working distance infrared radiation thermometry lens according to claim 5, characterized in that, The aperture stop (0) is disposed on the first object side (S1).

8. The wide working distance infrared radiation thermometry lens according to claim 5, characterized in that, The first image-side portion (S2) is a diffraction surface, and diffraction rings are provided on the diffraction surface. The radial radius r at the abrupt change of each ring in the diffraction rings satisfies 2Nπ=B1×r2+B2×r4+…+Bi×r2i; In the formula, N = 1, 2, 3, ..., n represents the nth abrupt change in the ring, and Bi is the phase coefficient of the diffraction surface.

9. The wide working distance infrared radiation thermometry lens according to claim 8, characterized in that, The depth of the diffraction ring on the first image side (S2) is L, and L satisfies: L=mλ / {n(λ)-1}; Where n(λ) is the refractive index of the lens material of the second lens (2) for wavelength λ, and m is the diffraction order.

10. The wide working distance infrared radiation thermometry lens according to claim 5, characterized in that, The radius of curvature of the first side face (S1) is R1, and R1 satisfies 27.4mm≤R1≤29.4mm; The radius of curvature of the first image side portion (S2) is R2, and R2 satisfies 54.4mm≤R2≤56.4mm; The radius of curvature of the second object side (S3) is R3, and R3 satisfies 118.2mm≤R3≤122.2mm; The radius of curvature of the second image side portion (S4) is R4, and R4 satisfies 18.2mm≤R4≤20.2mm; The radius of curvature of the third side surface (S5) is R5, and R5 satisfies 44.5mm≤R5≤45.5mm; The radius of curvature of the third image side (S6) is R6, and R6 satisfies -97.9mm≤R6≤-91.9mm.

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