Long-wave athermal optical imaging lens

Abstract

The application provides a long-wave athermal optical imaging lens, comprising, in sequence from an object side to an image side of a light path, a first lens of a meniscus lens with positive refractive power, a second lens of a double-concave lens with negative refractive power, a third lens of a meniscus lens with positive refractive power, and a fourth lens of a meniscus lens with negative refractive power; wherein the lens material types of the first lens, the second lens, the third lens and the fourth lens are at least three; the lens material comprises sulfide glass, ZnS crystal and germanium crystal. The application eliminates the thermal difference and the chromatic aberration of the optical system through the combination of different lens materials and the surface type design of the aspheric lens, so that the optical imaging lens can clearly image without re-focusing under the condition that the working spectrum is 8-12 mu m and the working temperature is -40 DEG C to 60 DEG C, and is suitable for application in the fields of security and protection, unmanned aerial vehicle, industrial monitoring, temperature measurement, forest fire prevention and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical imaging information technology, in particular to a long-wave athermal optical imaging lens. BACKGROUND

[0002] Infrared imaging is based on the difference between the radiation of the target and the background, according to the Planck blackbody radiation law, long-wave infrared with a wavelength of 8-12 μm is used to detect the profile of a normal temperature object.

[0003] There are three main methods for athermal design of common infrared optical systems: mechanical passive, electromechanical active and optical passive. Although the mechanical passive and electromechanical active methods are easy to implement, they only compensate for the displacement of the image plane and cannot guarantee the compensation of the focal length. Moreover, due to the use of mechanical devices, the system is inevitably complicated, the volume is increased, the weight is increased, and the reliability is reduced. The optical passive athermal technology not only guarantees the compensation of the focal length of the system, but also has the advantages of relatively simple structure, small size, light weight, high system reliability, etc., and has been widely used in the athermal design of infrared optical systems.

[0004] However, infrared optical materials are sensitive to environmental temperature, and with the change of environmental temperature, the focal length, image plane position and aberration of the infrared optical system will change, and the imaging quality will decrease. SUMMARY

[0005] The purpose of the present application is to provide a long-wave athermal optical imaging lens that can solve at least one of the above technical problems. The specific scheme is as follows:

[0006] According to the specific embodiment of the present application, a long-wave athermal optical imaging lens is disclosed, comprising:

[0007] arranged in order from the object side to the image side are:

[0008] a first lens, the first lens being a meniscus lens with positive refractive power;

[0009] a second lens, the second lens being a double-concave lens with negative refractive power;

[0010] a third lens, the third lens being a meniscus lens with positive refractive power;

[0011] a fourth lens, the fourth lens being a meniscus lens with negative refractive power;

[0012] wherein the lens materials of the first lens, the second lens, the third lens and the fourth lens are at least three kinds;

[0013]

[0014] ​The lens material comprises: a chalcogenide glass, a ZnS crystal, and a germanium crystal.

[0015] Preferably, the lens material of the first lens and the fourth lens is a chalcogenide glass.

[0016] The lens material of the second lens is a ZnS crystal.

[0017] The lens material of the third lens is a germanium crystal.

[0018] Preferably, the image-side surface of the second lens, the image-side surface of the third lens, and the image-side surface of the fourth lens are all aspheric surfaces.

[0019] Preferably, the aspheric surface of the second lens, the aspheric surface of the third lens, and the aspheric surface of the fourth lens satisfy the expression:

[0020]

[0021] wherein c is the curvature at the vertex, and r is the radial coordinate length.

[0022] k is a quadratic curve coefficient.

[0023] a, a2, a3, a4 are high-order term coefficients, respectively.

[0024] Preferably, in the expression of the aspheric surface of the second lens: k = 4.634,

[0025] a = 4.689 x 10-4, a2 = 4.898 x 10-3, a3 = 8.560 x 10-2, and a4 = 2.056 x 10-1; -7 -11 -13 -15

[0026] In the expression of the aspheric surface of the third lens: k = -0.257,

[0027] a = 2.163 x 10-2, a2 = 1.235 x 10-1, a3 = 6.503 x 10-0, and a4 = 2.969 x 10-1; -6 -8 -12 -15

[0028] In the expression of the aspheric surface of the fourth lens: k = -4.621,

[0029] a = 1.762 x 10-2, a2 = 1.373 x 10-1, a3 = 8.675 x 10-0, and a4 = 3.919 x 10-1. -5 -9 -10 -12 ​​​​​​​​​​​​

[0030] Preferably, the center thickness of the first lens is 10.8mm;

[0031] The center thickness of the second lens is 8.0mm;

[0032] The center thickness of the third lens is 8.6mm;

[0033] The center thickness of the fourth lens is 10.0mm.

[0034] Preferably, the brand of the chalcogenide glass is HWS6.

[0035] Preferably, the focal length of the first lens and the focal length of the near-infrared optical imaging lens satisfy: 1.3

[0036] The focal length of the second lens and the focal length of the near-infrared optical imaging lens satisfy: -4.7

[0037] The focal length of the third lens and the focal length of the near-infrared optical imaging lens satisfy: 0.8

[0038] The focal length of the fourth lens and the focal length of the near-infrared optical imaging lens satisfy: 8.3

[0039] Preferably, the parallel flat plate is further included.

[0040] The air gap between the second lens and the first lens is 25.4mm;

[0041] The air gap between the third lens and the second lens is 27.2mm;

[0042] The air gap between the fourth lens and the third lens is 6.0mm;

[0043] The air gap between the parallel flat plate and the fourth lens is 5.7mm.

[0044] Preferably, the focal length of the optical imaging lens is 60mm, the F / # is 1, the working waveband is 8-12μm, and the working temperature is -40℃-60℃.

[0045] Compared with the prior art, the above scheme of the embodiment of the present application has at least the following beneficial effects:

[0046] The application eliminates the thermal difference and chromatic aberration of the optical system through the combination of different lens materials and the surface type design of the aspheric mirror, so that the optical imaging lens can clearly image without re-focusing under the condition that the working spectrum is 8-12 mu m and the working temperature is-40 DEG C~60 DEG C, and is suitable for application in the fields of security and protection, unmanned aerial vehicle, industrial monitoring, temperature measurement, forest fire prevention and the like. BRIEF DESCRIPTION OF DRAWINGS

[0047] The drawings incorporated by reference in the specification and forming part of the specification illustrate embodiments consistent with the present disclosure and, together with the specification, serve to explain the principles of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained according to these drawings without creative labor for those skilled in the art. In the drawings:

[0048] Figure 1 The structural schematic diagram of the optical imaging lens provided by the embodiment of the present application is shown in the figure;

[0049] Figure 2 The MTF curve diagram of the embodiment of the present application at-40 DEG C is shown in the figure;

[0050] Figure 3 The MTF curve diagram of the embodiment of the present application at-20 DEG C is shown in the figure;

[0051] Figure 4 The MTF curve diagram of the embodiment of the present application at 0 DEG C is shown in the figure;

[0052] Figure 5 The MTF curve diagram of the embodiment of the present application at 20 DEG C is shown in the figure;

[0053] Figure 6 The MTF curve diagram of the embodiment of the present application at 40 DEG C is shown in the figure;

[0054] Figure 7 The MTF curve diagram of the embodiment of the present application at 60 DEG C is shown in the figure;

[0055] Figure 8 The optical field curvature-distortion curve diagram of the embodiment of the present application is shown in the figure.

[0056] Reference signs:

[0057] L1, first lens; S1, object side surface of the first lens; S2, image side surface of the first lens;

[0058] L2, second lens; S3, object side surface of the second lens; S4, image side surface of the second lens;

[0059] L3, third lens; S5, object side surface of the third lens; S6, image side surface of the third lens;

[0060] L4, fourth lens; S7, object side surface of the fourth lens; S8, image side surface of the fourth lens;

[0061] L5, parallel flat; S9, entrance surface of the parallel flat; S10, exit surface of the parallel flat;

[0062] S11, detection surface. DETAILED DESCRIPTION

[0063] In order to make the purposes, technical solutions and advantages of the present disclosure clearer, further detailed description will be made to the long-wave athermalization optical imaging lens according to the present disclosure with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present disclosure, but not all the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present disclosure.

[0064] It should also be noted that the terms "comprising", "containing" or any other variant thereof are intended to cover non-exclusive inclusion, so that the products or devices including a series of elements not only include those elements, but also include other elements not explicitly listed or inherent to such products or devices. Without more limitations, the element defined by the statement "comprising one" does not exclude the presence of another identical element in the product or device including the element.

[0065] In the accompanying drawings, the thickness, size and shape of the lenses have been slightly exaggerated for ease of illustration. Specifically, the shape of the spherical or aspherical surface shown in the drawings is shown by way of example. That is, the shape of the spherical or aspherical surface is not limited to the shape of the spherical or aspherical surface shown in the drawings. The drawings are merely examples and are not strictly drawn to scale.

[0066] The following will be described in detail with reference to the accompanying drawings. Figures 1-8 Detailed description of the alternative embodiments of the present disclosure.

[0067] In the present embodiment, the surface of each lens close to the detection surface S11 is the image side surface of the lens, and the surface of each lens close to the object side is the object side surface of the lens. If the object side surface of the lens is away from the detection surface, the object side surface of the lens is a convex surface; otherwise, the object side surface is a concave surface. If the image side surface of the lens is away from the detection surface, the image side surface of the lens is a concave surface; otherwise, the image side surface is a convex surface.

[0068] As Figure 1As shown, according to the specific embodiment of the present application, the present application provides a long-wave athermal optical imaging lens, which comprises, in sequence from the object side to the image side of the light path: a first lens L1, a second lens L2, a third lens L3, a diaphragm S7, a fourth lens L4, a fifth lens L5, and a parallel flat plate.

[0069] Specifically, the first lens L1 is a meniscus lens with positive refractive power; the second lens L2 is a double-concave lens with negative refractive power; the third lens L3 is a meniscus lens with positive refractive power; and the fourth lens L4 is a meniscus lens with negative refractive power. The focal length of the optical imaging lens is 60 mm, the F / # is 1, the working waveband is 8-12 μm, and the working temperature is -40℃-60℃.

[0070] Further, the lens materials of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are at least three types, and the lens materials include: chalcogenide glass, ZnS crystal, and germanium crystal.

[0071] Preferably, the grade of the chalcogenide glass is HWS6.

[0072] In the embodiment, the chalcogenide glass, the ZnS crystal, and the germanium crystal are combined to eliminate thermal aberration and chromatic aberration in the long-wave infrared waveband (8-12 μm) because the chalcogenide glass has high transmittance, small refractive index temperature coefficient, high Abbe number, and small Abbe number.

[0073] Preferably, the materials of the first lens L1 and the fourth lens L4 are HWS6.

[0074] The material of the second lens L2 is ZnS crystal, and the material of the third lens L3 is germanium crystal.

[0075] The present application eliminates the thermal aberration of the optical system by the combination of different lens materials, so that the optical imaging lens can clearly image without re-focusing under the condition that the working waveband is 8-12 μm and the working temperature is -40℃-60℃.

[0076] In the embodiment, the image side S4 of the second lens, the image side S6 of the third lens, and the image side S8 of the fourth lens are all aspheric surfaces, which are used to reduce the monochromatic aberration of the optical system.

[0077] Specifically, the aspheric surface adopts even aspheric surface, which cannot only use curvature to define the shape, but also needs other parameters to represent the degree of deviation from the reference sphere. The most commonly used even aspheric surface in the optical design software is defined according to the sag, and the expression of the aspheric surface type is as follows:

[0078]

[0079] In the expression, c is the curvature at the vertex.

[0080] k is a quadratic curve coefficient;

[0081] a, a2, a3, a4 are high order term coefficients, respectively.

[0082] In a preferred embodiment of the present application,

[0083] The parameters in the surface expression of the image side surface S4 of the second lens are as follows: k = 4.634,

[0084] a = 4.689 x 10 -7 , a2 = 4.898 x 10 -11 , a3 = 8.560 x 10 -13 , a4 = 2.056 x 10 -15 .

[0085] The parameters in the surface expression of the image side surface S6 of the third lens are as follows: k = -0.257,

[0086] a = 2.163 x 10 -6 , a2 = 1.235 x 10 -8 , a3 = 6.503 x 10 -12 , a4 = 2.969 x 10 -15 .

[0087] The parameters in the surface expression of the image side surface S8 of the fourth lens are as follows: k = -4.621,

[0088] a = 1.762 x 10 -5 , a2 = 1.373 x 10 -9 , a3 = 8.675 x 10 -10 , a4 = 3.919 x 10 -12 .

[0089] Further,

[0090] The central thickness of the first lens is 10.8 mm, the radius of curvature of the object side surface S1 of the first lens is 63.94 mm, and the radius of curvature of the image side surface S2 of the first lens is 91.00 mm;

[0091] The central thickness of the second lens is 8.0 mm, the radius of curvature of the object side surface S3 of the second lens is -771.03 mm, and the radius of curvature of the image side surface S4 of the second lens is 511.97 mm;

[0092] The central thickness of the third lens is 8.6 mm, the radius of curvature of the object side surface S5 of the third lens is 29.84 mm, and the radius of curvature of the image side surface S6 of the third lens is 31.74 mm;

[0093] The center thickness of the fourth lens is 10.0 mm, the curvature radius of the object side S5 of the fourth lens is 68.31 mm, and the curvature radius of the image side S6 of the fourth lens is 63.01 mm.

[0094] Further,

[0095] The air gap between the second lens and the first lens is 25.4 mm, the air gap between the third lens and the second lens is 27.2 mm, and the air gap between the fourth lens and the third lens is 6.0 mm.

[0096] Further,

[0097] The focal length of the first lens and the focal length f of the near-infrared optical imaging lens satisfy: 1.3 < f1 / f < 1.8;

[0098] The focal length of the second lens and the focal length f of the near-infrared optical imaging lens satisfy: -4.7 < f2 / f < -3.8;

[0099] The focal length of the third lens and the focal length f of the near-infrared optical imaging lens satisfy: 0.8 < f3 / f < 1.5;

[0100] The focal length of the fourth lens and the focal length f of the near-infrared optical imaging lens satisfy: 8.3 < f4 / f < 13.4.

[0101] In a preferred embodiment of the present application, a parallel flat plate is arranged as a protective glass in front of the detection surface S11.

[0102] The thickness of the parallel flat plate is 1.0 mm, the air gap between the parallel flat plate and the fourth lens is 5.7 mm, and the air gap between the parallel flat plate and the detection surface S11 is 2.1 mm.

[0103] Table 1 is the parameters of each lens in a preferred embodiment of the present application.

[0104] Table 1 Lens Parameters

[0105]

[0106]

[0107] Figures 2-7 The MTF test result curves of the long-wave athermal optical imaging lens of the present application in the working waveband of 8-12 μm at -40℃, -20℃, 0℃, 20℃, 40℃ and 60℃ are shown in the following table.

[0108] The image quality evaluation standard of the optical design is based on the optical transfer function (Modulation Transfer Function, MTF) at the Nyquist frequency (at 34 mm / lp). It can be seen that the image quality of the long-wave athermalization optical imaging lens of the present application is close to the diffraction limit within the working distance,

[0109] It can be seen from the curves shown in FIG. 6 that the field curvature and distortion of the long-wave athermalization optical imaging lens of the present application are corrected under the corresponding field of view. Figure 8

[0110] Finally, it should be noted that: the various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts of each embodiment can be referred to. For the system or device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0111] The above embodiments are only used to illustrate the technical solutions disclosed in the present application, but not limit them. Although the foregoing embodiments of the present application are described in detail, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents. The modification or replacement does not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the present application.​

Claims

1. A long-wave athermal optical imaging lens characterized in that, Comprise sequentially arranged on the light path from the object side to the image side: The first lens is a meniscus lens with positive refractive power; The second lens is a double-concave lens with negative refractive power; The third lens is a meniscus lens with positive refractive power; The fourth lens is a meniscus lens with negative refractive power; Wherein, the lens material of the first lens, the second lens, the third lens and the fourth lens is at least three kinds; The lens material includes: chalcogenide glass, ZnS crystal and germanium crystal; The aspheric surface type of the second lens, the third lens and the fourth lens satisfies the expression: Wherein, c is the curvature at the vertex, r is the radial coordinate length; K is the quadratic curve coefficient; a, a2, a3, a4 are high-order coefficients respectively; In the aspheric surface expression of the second lens: k=4.634, a = 4.689 x 10 -7 , a2= 4.898 x 10 -11 , a3= 8.560 x 10 -13 , a4= 2.056 x 10 -15 ; In the aspheric surface expression of the third lens: k=-0.257, a = 2.163 x 10 -6 , a2= 1.235 x 10 -8 , a3= 6.503 x 10 -12 , a4= 2.969 x 10 -15 ; In the aspheric surface expression of the fourth lens: k=-4.621, a = 1.762 x 10 -5 , a2= 1.373 x 10 -9 , a3= 8.675 x 10 -10 , a4= 3.919 x 10 -12 .

2. The optical imaging lens according to claim 1, wherein: The lens material of the first lens and the fourth lens is chalcogenide glass; The lens material of the second lens is ZnS crystal; The lens material of the third lens is germanium crystal.

3. The optical imaging lens according to claim 1, characterized in that, The image side surface of the second lens, the image side surface of the third lens and the image side surface of the fourth lens are all aspheric surfaces.

4. The optical imaging lens according to claim 1, wherein: The center thickness of the first lens is 10.8mm; The center thickness of the second lens is 8.0mm; The center thickness of the third lens is 8.6mm; The center thickness of the fourth lens is 10.0mm.

5. The optical imaging lens according to claim 1, characterized in that, The grade of the chalcogenide glass is HWS6.

6. The optical imaging lens according to claim 1, wherein: The focal length of the first lens and the focal length of the optical imaging lens satisfy: 1.3 The focal length of the second lens and the focal length of the optical imaging lens satisfy: -4.7 The focal length of the third lens and the focal length of the optical imaging lens satisfy: 0.8 The focal length of the fourth lens and the focal length of the optical imaging lens satisfy: 8.3 7.The optical imaging lens according to claim 1, wherein, Further comprising: Parallel flat plate; The air gap between the second lens and the first lens is 25.4mm; The air gap between the third lens and the second lens is 27.2mm; The air gap between the fourth lens and the third lens is 6.0mm; The air gap between the parallel flat plate and the fourth lens is 5.7mm. 8.The optical imaging lens according to any one of claims 1-7, wherein, The focal length of the optical imaging lens is 60mm, F / # is 1, the working waveband is 8-12μm, and the working temperature is -40℃-60℃.

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