Large target surface low-distortion athermal infrared lens

Abstract

The application belongs to the field of infrared optical technology and discloses a large-target-surface low-distortion athermal infrared lens. The lens comprises a first lens, a second lens, a third lens and a fourth lens which are coaxially arranged in sequence from the object side to the image side. The first lens is a meniscus lens with negative focal power and a convex surface facing the object side. The second lens is a meniscus lens with positive focal power and a convex surface facing the object side. The third lens is a meniscus lens with positive focal power and a convex surface facing the image side. The fourth lens is a meniscus lens with positive focal power and a convex surface facing the image side. The lens has a wide field of view, a large target surface and low distortion, can effectively correct aberration, has good edge image quality and clear observation, has good athermal effect, can meet the temperature requirement of the working environment of-40 DEG C to 80 DEG C, has good thermal stability and is especially suitable for large-range monitoring in the field of security monitoring.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared optics, and in particular relates to a large-target-surface, low-distortion, and athermal infrared lens. Background Art

[0002] As security surveillance systems become increasingly prevalent and high-end, the performance of surveillance lenses, including field of view, aperture, pixel size, and image size, requires further optimization. Wide-angle infrared lenses, a type of surveillance lens, offer a wide field of view with a short focal length and are becoming increasingly popular. However, they exhibit high distortion, typically between 40% and 50% with well-controlled distortion. Furthermore, image edge resolution is low, making aberration correction and image quality difficult to control, making their optical design challenging.

[0003] Furthermore, temperature can have a certain impact on both optical and mechanical materials, leading to focal length changes, image plane drift, optical imaging quality degradation, image blur, and ultimately affecting the imaging performance of the lens. In order for the lens to be suitable for different environments, it is necessary to ensure that the lens has a certain degree of temperature adaptability.

[0004] Therefore, how to achieve a large target area and low distortion while ensuring thermal difference elimination is a difficult problem that needs to be solved urgently in this field at this stage. Summary of the Invention

[0005] To address the above issues, the present invention provides a large-target-area, low-distortion, athermal infrared lens that achieves passive athermalization while also featuring a wide field of view, a large target area, and minimal distortion. The specific technical solution is as follows.

[0006] A large-surface, low-distortion, athermal infrared lens comprises a first lens, a second lens, a third lens, and a fourth lens, arranged sequentially from the object side to the image side. The first lens is a meniscus lens with negative optical power and a convex surface facing the object side; the second lens is a meniscus lens with positive optical power and a convex surface facing the object side; the third lens is a meniscus lens with positive optical power and a convex surface facing the image side; and the fourth lens is a meniscus lens with positive optical power and a convex surface facing the image side. Along the optical axis, from the object side to the image side, the two surfaces of the first lens are sequentially the first object-side surface and the first image-side surface; the two surfaces of the second lens are sequentially the second object-side surface and the second image-side surface; the two surfaces of the third lens are sequentially the third object-side surface and the third image-side surface; and the two surfaces of the fourth lens are sequentially the fourth object-side surface and the fourth image-side surface. The first image-side surface, the third image-side surface, and the fourth object-side surface are all aspherical surfaces.

[0007] Preferably, the aspheric surfaces on the first image-side surface, the third image-side surface, and the fourth object-side surface all satisfy the following formula:

[0008]

[0009] In the formula, Z is the distance from the vertex of the aspheric surface to the vertex of the aspheric surface at the position of the height r along the optical axis direction; c=1 / R, R is the paraxial curvature fitting radius of the mirror surface; k is the conic coefficient; A, B, C, D, E are high-order aspheric surface coefficients.

[0010] Preferably, the first lens is made of germanium material, the second lens is made of zinc sulfide material, the third lens is made of IRG206 material, and the fourth lens is made of IRG209 material.

[0011] Preferably, the curvature radius of the first object side is 20.37mm, the fitting curvature radius of the first image side is 12.33mm, the curvature radius of the second object side is 31.35mm, the fitting curvature radius of the second image side is 60.71mm, the curvature radius of the third object side is -119.8mm, the fitting curvature radius of the third image side is -27mm, the curvature radius of the fourth object side is -43.3mm, and the fitting curvature radius of the fourth image side is -27.86mm.

[0012] Preferably, the central thickness of the first lens is 4mm, the central thickness of the second lens is 6mm,

[0013] the central thickness of the third lens is 4mm, and the central thickness of the fourth lens is 3mm.

[0014] Preferably, the central spacing between the first lens and the second lens is 13.26mm, there is a diaphragm between the second lens and the third lens, the central spacing from the second lens to the diaphragm is 2.8mm, the central spacing from the diaphragm to the third lens is 2.32mm, and the central spacing between the third lens and the fourth lens is 7.84mm.

[0015] Preferably, the image side of the fourth lens is sequentially provided with a germanium protective window and a detector image surface, and the spacing between the fourth lens and the focal plane is 12.73mm.

[0016] Preferably, the second image side is a binary surface, and the expression of the binary surface is

[0017]

[0018] wherein M is the diffraction order, the diffraction order is 1, B1 and B2 are binary surface phase coefficients, B1=-106.16 and B2=53.22, and the value of the normalized radius p is 10.

[0019] Preferably, the working waveband of the lens is 8-12um, the F number is 1.2, the horizontal field of view is 70°, and the vertical field of view is 58°.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. The present application realizes large target surface, low distortion, the lens focal length is 9.5 mm, and distortion can be controlled in 8%, which is very small; can effectively correct aberration, and edge image quality is good.

[0022] 2. The field of view range is large, and horizontal field of view angle can reach 70°, clear observation, especially suitable for large range monitoring, applied in security monitoring field, can reduce the number of lens deployment, and reduce cost.

[0023] 3. The athermal effect is good, can meet the temperature requirement of-40 DEG C to 80 DEG C working environment, and thermal stability is good.

[0024] The working waveband of the lens is 8-12 mu m, and the matched resolution is 1280*1024, 10 mu m detector. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows, obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained according to the drawings without creative labor for those skilled in the art.

[0026] Figure 1 It is the optical path diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application;

[0027] Figure 2 It is the MTF diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application in 20 DEG C working environment;

[0028] Figure 3 It is the Spot diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application in 20 DEG C working environment;

[0029] Figure 4 It is the MTF diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application in-40 DEG C working environment;

[0030] Figure 5 It is the Spot diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application in-40 DEG C working environment;

[0031] Figure 6 It is the MTF diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application in 80 DEG C working environment;

[0032] Figure 7 It is the Spot diagram of the large target surface low distortion athermal infrared lens in the specific embodiment of the present application in 80 DEG C working environment.

[0033] Figure 8 Figure 1 is a field curvature distortion diagram of a large target surface low distortion athermal infrared lens in the embodiment of the present application.

[0034] Figure 1 is a field curvature distortion diagram of a large target surface low distortion athermal infrared lens in the embodiment of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described in the embodiments of the present application combined with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0036] As shown in the accompanying drawings of the specification, Figure 1 The present embodiment provides a large target surface low distortion athermal infrared lens, which includes four lenses, and sequentially includes a first lens 1, a second lens 2, a third lens 4 and a fourth lens 5 along the optical axis from the object side to the image side. The first lens 1 is a meniscus lens with negative focal power, and the convex surface faces the object side. The second lens 2 is a meniscus lens with positive focal power, and the convex surface faces the object side. The third lens 4 is a meniscus lens with positive focal power, and the convex surface faces the image side. The fourth lens 5 is a meniscus lens with positive focal power, and the convex surface faces the image side.

[0037] The parameters of the four lenses 1-4 are shown in Table 1.

[0038] The curvature radius of the first object side surface S1 is 20.37 mm, the fitting curvature radius of the first image side surface S2 is 12.33 mm, the curvature radius of the second object side surface S3 is 31.35 mm, the fitting curvature radius of the second image side surface S4 is 60.71 mm, the curvature radius of the third object side surface S5 is -119.8 mm, the fitting curvature radius of the third image side surface S6 is -27 mm, the curvature radius of the fourth object side surface S7 is -43.3 mm, and the fitting curvature radius of the fourth image side surface S8 is -27.86 mm.

[0039] The center thickness of the first lens 1 is 4 mm, the center thickness of the second lens 2 is 6 mm, the center thickness of the third lens 4 is 4 mm, and the center thickness of the fourth lens 5 is 3 mm.

[0040] The center interval between the first lens 1 and the second lens 2 is 13.26 mm, the second lens 2 and the third lens 4 are provided with a diaphragm 3, the center interval between the second lens 2 and the diaphragm 3 is 2.8 mm, the center interval between the diaphragm 3 and the third lens 4 is 2.32 mm, the center interval between the third lens 4 and the fourth lens 5 is 7.84 mm, and the image side of the fourth lens 5 is sequentially provided with a germanium protective window 6 and a detector image plane 7. The interval between the fourth lens 5 and the focal plane is 12.73 mm.

[0041] As an embodiment of the preferred embodiment, the material of the first lens 1 is germanium, the material of the second lens 2 is ZnS, and the materials of the third lens 4 and the fourth lens 5 are both sulfide glass. Specifically, the third lens 4 uses IRG206, and the fourth lens 5 uses IRG209.

[0042] Table 1: Lens 1-4 parameters

[0043]

[0044] As the preferred embodiment of the present application, the first image side S2, the third image side S6 and the fourth object side S8 are all aspheric surfaces, and satisfy the following formula,

[0045]

[0046] In the formula, Z is the distance from the vertex of the aspheric surface when the aspheric surface is at a height r along the optical axis direction; c=1 / R, R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, E are high-order aspheric coefficients, and the aspheric surface data of each lens is shown in Table 2.

[0047] Table 2: Aspheric surface coefficient data of each lens

[0048]

[0049] The image side S4 of the second lens 2 is a binary surface, and the expression equation of the binary surface in Zemax is:

[0050]

[0051] Wherein, M is the diffraction order, the diffraction order is 1, B1 and B2 are binary surface phase coefficients, B1=-106.16, B2=53.22, and the value of the normalized radius p is 10.

[0052] In the embodiment, the lens realizes large target surface and low distortion through material matching of germanium-zinc sulfide-chalcogenide glass-chalcogenide glass, and reasonable design of optical power, aspheric surface and binary surface, has an ultra-short focal length of 9.5 mm, and the distortion can be controlled within 8%; can effectively correct aberration, has good edge image quality; and has a large field of view, and the horizontal field of view can reach 70°, clear observation, and is especially suitable for large-range monitoring, is applied to the field of security monitoring, can reduce the number of deployed lenses, and reduce the cost.

[0053] Figure 2 、 Figure 4 、 Figure 6 respectively, are MTF diagrams of the athermal infrared lens in working environments of 20℃, -40℃ and 80℃, the horizontal axis represents different spatial frequencies, and the vertical axis represents modulation. All field of view represents the MTF curve of the meridional plane, and the curve marked as T in the figure, and the MTF curve of the sagittal plane is the curve marked as S in the figure, and DIFF. LIMIT in the figure represents the diffraction limit. Figure 3 、 Figure 5 、 Figure 7 respectively, are Spot diagrams of the athermal infrared lens in working environments of 20℃, -40℃ and 80℃. Figure 8 indicates the field of view and distortion of the athermal infrared lens in the embodiment. It can be seen from Figures 2 to 7 that the MTF is close to the diffraction limit, the root mean square diameter of the diffuser spot is less than the diameter of the Airy disk, and the image quality is very good. Through reasonable optical structure design, the distortion of the embodiment can be reduced to below 8%. The lens provided in the embodiment has good athermal effect, can meet the temperature requirement of a working environment of -40℃ to 80℃, and has good thermal stability.

[0054] It can be seen from the above that the athermal infrared lens composed of the above lenses provided in the embodiment achieves the following optical indexes.

[0055] Working waveband: 8μm-12μm;

[0056] Focal length: f′=9.5mm;

[0057] Resolution: 1280x1024, 10μm;

[0058] F number: 1.2;

[0059] Horizontal field of view: 70°, vertical field of view: 58°.

[0060] The lens of the embodiment has good athermal effect, can meet the requirement of a working temperature range of -40℃ to 80℃, has the advantages of double field of view and ultra-low distortion, and can be matched with a large target surface detector with a resolution of 1280x1024, 10μm.

[0061] Obviously, the above embodiments are only examples for clearly illustrating the technical solutions of the present application, and are not intended to limit the manner of the present application. Any modification, equivalent replacement and improvement made on the basis of the above description by those skilled in the art shall be included in the protection scope of the claims of the present application.

Claims

1. A large target low-distortion athermal infrared lens characterized in that, The lens comprises a first lens, a second lens, a third lens and a fourth lens arranged in sequence from the object side to the image side, the first lens is a meniscus lens with negative focal length and convex surface towards the object side, the second lens is a meniscus lens with positive focal length and convex surface towards the object side, the third lens is a meniscus lens with positive focal length and convex surface towards the image side, and the fourth lens is a meniscus lens with positive focal length and convex surface towards the image side; from the object side to the image side along the optical axis, the two surfaces of the first lens are a first object side surface and a first image side surface in sequence, the two surfaces of the second lens are a second object side surface and a second image side surface in sequence, the two surfaces of the third lens are a third object side surface and a third image side surface in sequence, and the two surfaces of the fourth lens are a fourth object side surface and a fourth image side surface in sequence, wherein the first image side surface, the third image side surface and the fourth object side surface are all aspheric surfaces; The curvature radius of the first object side surface is 20.37 mm, the fitting curvature radius of the first image side surface is 12.33 mm, the curvature radius of the second object side surface is 31.35 mm, the fitting curvature radius of the second image side surface is 60.71 mm, the curvature radius of the third object side surface is -119.8 mm, the fitting curvature radius of the third image side surface is -27 mm, the curvature radius of the fourth object side surface is -43.3 mm, and the fitting curvature radius of the fourth image side surface is -27.86 mm; the center thickness of the first lens is 4 mm, the center thickness of the second lens is 6 mm, the center thickness of the third lens is 4 mm, and the center thickness of the fourth lens is 3 mm; the center interval between the first lens and the second lens is 13.26 mm, there is a diaphragm between the second lens and the third lens, the center interval from the second lens to the diaphragm is 2.8 mm, the center interval from the diaphragm to the third lens is 2.32 mm, and the center interval between the third lens and the fourth lens is 7.84 mm; The first lens is made of germanium, the second lens is made of zinc sulfide, the third lens is made of IRG206, and the fourth lens is made of IRG209; the second image side surface is a binary surface; The working temperature of the lens is -40℃ to 80℃.

2. A large target low distortion athermal infrared lens according to claim 1, characterized in that, The aspheric surfaces of the first image side surface, the third image side surface and the fourth object side surface all satisfy the following formula, In the formula, Z is the distance from the vertex of the aspheric surface to the position of the aspheric surface along the optical axis at a height r; c=1 / R, R is the fitting radius of the near-axis curvature of the mirror surface; k is the conic coefficient; A, B, C, D and E are high-order aspheric coefficients.

3. A large target low distortion athermal infrared lens according to claim 1, characterized in that, The image side of the fourth lens is sequentially provided with a germanium protective window and a detector image surface, and the interval between the fourth lens and the focal plane is 12.73 mm.

4. A large target low distortion athermal infrared lens according to claim 1, characterized in that, The second image side surface is a binary surface, and the expression of the binary surface is In the formula, M is the diffraction order, the diffraction order is 1, B1 and B2 are the phase coefficients of the binary surface, B1=-106.16 and B2=53.22, and the value of the normalized radius p is 10.

5. A large target low distortion athermal infrared lens according to claim 1, wherein, The working waveband of the lens is 8μm-12μm, the F number is 1.2, the horizontal field of view is 70°, and the vertical field of view is 58°.

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