Medium wave infrared optical system for target identification

Abstract

The utility model relates to the technical field of optical lenses, in particular to a medium-wave infrared optical system for target identification, which is characterized by comprising a first lens, a second lens, a diaphragm, a third lens, a fourth lens and an image surface which are sequentially arranged along the same optical axis from an object space to an image space, the first lens and the third lens both have negative focal power, and the second lens and the fourth lens both have positive focal power; the first lens and the fourth lens are meniscus positive lenses; the second lens and the third lens are meniscus negative lenses; the first image side surface and the second object side surface are even aspheric surfaces. Common optical materials are used, aspheric surface optimization aberration is adopted, the number of lenses is reduced, and the lens is small in size and light in weight; the system has the characteristics of high resolution, long working distance, high illumination and light weight, realizes higher imaging quality, and further realizes all-weather long-distance target detection under the condition of low illumination.

Description

TECHNICAL FIELD

[0001] The utility model relates to optical lens technical field especially, it is a kind of middle wave infrared optical system for target identification. BACKGROUND

[0002] Visible light imaging system obtains the image details rich, imaging performance stable, with higher sensitivity and resolving power, but visible light imaging system depends on natural illumination, in some light poor condition, imaging quality is poor.And infrared light can penetrate cloud and fog ability, can be identified to the target after camouflage, observation time is not restricted by day and night, so it is commonly used for target identification.

[0003] Infrared reconnaissance system is a kind of passive, non-contact detection identification system with good concealment and strong anti-electromagnetic interference capability, can accurately track thermal target at long distance, accurately guide, realize all-weather monitoring, for all-weather target identification and detection in severe weather conditions, for example in thick fog or night.At present, the existing infrared lens on the market in domestic market generally has the problems of low resolution, too many lenses, large volume and heavy lens, and the long-distance target detection effect under low-illumination condition of middle wave band is poor. UTILITARY MODEL

[0004] In order to solve the problem of poor long-distance weak target detection effect of existing middle wave band infrared imaging system under low-illumination condition, the utility model provides a kind of middle wave infrared optical system for target identification, structure is light and small, resolution is high, energy concentration degree is greater than 90%, can satisfy the requirement of identification / tracking target lens.

[0005] In order to realize the above-mentioned target, the utility model provides the following technical scheme:

[0006] A kind of middle wave infrared optical system for target identification, including first lens, second lens, diaphragm, third lens, fourth lens and image plane, which are sequentially arranged from object side to image side direction with optical axis, the first lens and the third lens all have negative optical power, the second lens and the fourth lens all have positive optical power;First lens and fourth lens are both meniscus positive lens;Second lens, third lens are both meniscus negative lens;

[0007] First lens has first object side and first image side, second lens has second object side and second image side, third lens has third object side and third image side, fourth lens has fourth object side and fourth image side, the first image side and the second object side are both even aspheric surface, and even aspheric surface satisfies the relationship:

[0008] Z represents the distance from the vertex of the aspheric surface to the height r position of the aspheric surface along the optical axis, R represents the radius of curvature of the center of the aspheric surface, k represents the conic constant of the curved surface, a2, a3 and a4 represent the even aspheric surface parameters, respectively;

[0009] The incident light is sequentially deflected by the first lens, the second lens, the diaphragm, the third lens and the fourth lens and then converges on the image plane.

[0010] In a further optimized scheme, the radius of curvature of the first object side is 128.9±0.05mm, the radius of curvature of the first image side is 297.8±0.05mm, and the central thickness of the first lens is 7±0.01mm;

[0011] The radius of curvature of the second object side is 455.6±0.05mm, the radius of curvature of the second image side is 267.9±0.05mm, and the central thickness of the second lens is 7±0.01mm;

[0012] The radius of curvature of the third object side is 51.8±0.05mm, the radius of curvature of the third image side is 43±0.04mm, and the central thickness of the third lens is 6.1±0.01mm;

[0013] The radius of curvature of the fourth object side is 110.5±0.05mm, the radius of curvature of the fourth image side is 147.6±0.05mm, and the central thickness of the fourth lens is 4.1±0.01mm.

[0014] In the above scheme, such a distance combination can improve the tolerance of assembly error, reduce the difficulty of machining and assembly, enhance the stability of optical performance, and adapt to environmental changes. For germanium and silicon infrared materials, due to their low hardness and easy processing, the curvature range can be more strictly limited.

[0015] The aperture of the first object side is 88.2mm, and the aperture of the first image side is 86.8mm; the aperture of the second object side is 86.8mm, and the aperture of the second image side is 83.2mm; the aperture of the third object side is 43.3mm, and the aperture of the third image side is 60.2mm; the aperture of the fourth object side is 43.4mm, and the aperture of the fourth image side is 42.4mm.

[0016] The refractive index of the first object side is 3.4255, the refractive index of the second object side is 4.0245, the refractive index of the third object side is 4.0245, and the refractive index of the fourth object side is 3.4255.

[0017] In a further optimized scheme, the distance between the first lens and the second lens is 1.3±0.01mm; the distance between the second lens and the diaphragm is 32.5±0.01mm; the distance between the diaphragm and the third lens is 27.9±0.01mm, and the distance between the third lens and the fourth lens is 55.4±0.01mm.

[0018] In the above scheme, through the distance limitation, not only the optical performance can be guaranteed, but also the space between the lenses is large, which is convenient for installing the gasket and various mechanical structures.

[0019] The first object side, the second image side, the third object side, the third image side, the fourth object side and the fourth image side are spherical surfaces.

[0020] In the above scheme, in addition to the first image side and the second object side adopting even aspheric surfaces, the rest surfaces all adopt standard spherical surfaces, so that the implementation difficulty is reduced.

[0021] In a further optimized scheme, the first lens and the fourth lens are both made of GERMANIUM material, and the second lens and the third lens are both made of SILICON material.

[0022] GERMANIUM and SILICON have high infrared transmittance in the middle wave infrared band, and have high refractive index, so that the high refractive index material can be used to design a small optical system, reduce the system volume, and be beneficial to the design of a compact optical system. Moreover, the processing technology of the two materials is mature, and the manufacturing cost is much lower than that of expensive chalcogenide glass.

[0023] In a more perfect scheme, a lens barrel is further included, and the first lens, the second lens, the diaphragm, the third lens, the fourth lens and the image surface are all arranged in the lens barrel.

[0024] The non-cooled middle wave infrared detector has an adaptive resolution of 640x512 and a pixel size of 12μm, and the detection target distance is 2-3km.

[0025] The middle wave infrared optical system has a focal length of greater than 160mm, a working waveband of 3μm-5μm, a working F number of 2, a field of view angle of 10°, and an optical total length of 169mm.

[0026] Compared with the prior art, the utility model has the following beneficial effects:

[0027] Through cooperation of the first lens, the second lens, the diaphragm, the third lens and the fourth lens, the optical power is reasonably distributed, and high imaging quality is realized. Meanwhile, two even aspheric surfaces are introduced to correct aberration, so that the high image quality imaging requirement is achieved.

[0028] Only four pieces of lens are used, and two common optical materials are used, the number of lenses is small, the number of aspheric surfaces is small, the processing cost is low, and the structure is simple and compact, so that miniaturization can be realized.

[0029] The rear intercept is long, the space between the lenses is large, and the installation of the gasket and various mechanical structures is facilitated.

[0030] In summary, the optical system has the characteristics of high resolution, light weight, high illumination, high MTF value at the characteristic frequency, and further realizes all-weather long-distance detection of targets under low-illumination conditions. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a structure diagram of the middle wave infrared optical system for target identification.

[0032] Figure 2 It is a point column diagram of the middle wave infrared optical system for target identification.

[0033] Figure 3 It is an MTF curve diagram of the middle wave infrared optical system for target identification.

[0034] Figure 4 It is a relative illumination diagram of the middle wave infrared optical system for target identification.

[0035] Figure 5 It is a ray aberration diagram of the middle wave infrared optical system for target identification.

[0036] Marked in the figure: 1, first lens; 2, second lens; 3 third lens; 4, fourth lens; 101, first object side; 102, first image side; 201, second object side; 202, second image side; 301, third object side; 302, third image side; 401, fourth object side; 402, fourth image side. DETAILED DESCRIPTION

[0037] The utility model is further described below through examples and drawings, and the purpose is only to better understand the content of the utility model, and is not a limitation on the utility model.

[0038] As Figure 1As shown, the embodiment provides a middle wave infrared optical system for target identification, which comprises a first lens 1, a second lens 2, a third lens 3 and a fourth lens 4, the first lens 1 and the fourth lens 4 are both meniscus positive lenses; the second lens 2 and the third lens 3 are both meniscus negative lenses; a diaphragm STO is arranged between the second lens 2 and the third lens 3, and an image plane (not shown in the figure) is arranged behind the light path of the fourth lens 4. The incident light is deflected by the first lens 1, the second lens 2, the diaphragm STO, the third lens 3 and the fourth lens 4 in turn and then converges on the image plane.

[0039] In the embodiment, the first lens 1 has a negative focal power, the second lens 2 has a positive focal power, the third lens 3 has a negative focal power, and the fourth lens 4 has a positive focal power. By reasonably allocating the focal power, a high imaging quality is achieved.

[0040] In the embodiment, the distance between the first lens 1 and the second lens 2 is 1.3 mm; the distance between the second lens 2 and the diaphragm STO is 32.5 mm; the distance between the diaphragm STO and the third lens 3 is 27.9 mm, and the distance between the third lens 3 and the fourth lens 4 is 55.4 mm. The distance between the lenses can fluctuate within a certain range, for example, it can fluctuate within ±0.01 mm. That is, the distance between the first lens 1 and the second lens 2 is 1.3±0.01 mm; the distance between the second lens 2 and the diaphragm STO is 32.5±0.01 mm; the distance between the diaphragm STO and the third lens 3 is 27.9±0.01 mm, and the distance between the third lens 3 and the fourth lens 4 is 55.4±0.01 mm. The large distance between the lenses facilitates the installation of gaskets and various mechanical structures, and reduces the assembly difficulty.

[0041] In the embodiment, the first lens 1 and the fourth lens 4 are both made of GERMANIUM material, and the second lens 2 and the third lens 3 are both made of SILICON material, so as to reduce the production cost. Of course, this is only a preferred embodiment, and in other embodiments, the lenses can also be made of other materials.

[0042] The lens has two side surfaces, for the convenience of description, in the embodiment, the two side surfaces are called object side surface and image side surface, that is, the surface adjacent to the object side is called the object side surface, and the surface adjacent to the image side is called the image side surface. Therefore, as shown in the figure, the first lens 1 has a first object side surface 101 and a first image side surface 102, the second lens 2 has a second object side surface 201 and a second image side surface 202, the third lens 3 has a third object side surface 301 and a third image side surface 302, and the fourth lens 4 has a fourth object side surface 401 and a fourth image side surface 402. Since each lens is a meniscus lens bent towards the image side, the object side surface is a convex structure, and the image side surface is a concave structure. Figure 1

[0043] ​In the embodiment, the first image side surface 102 and the second object side surface 201 are both even aspheric surfaces, and the rest of the image side surfaces and the object side surfaces are standard spherical surfaces, i.e., the first object side surface 101, the second image side surface 202, the third object side surface 301, the third image side surface 302, the fourth object side surface 401 and the fourth image side surface 402 are all spherical surfaces. Two even aspheric surfaces are introduced here to correct aberrations and achieve high image quality requirements. The even aspheric surfaces in the optical system lens satisfy the following expression:

[0044]

[0045] wherein Z represents the sag of the aspheric surface at a height r along the optical axis, R represents the radius of curvature of the center of the aspheric surface, k represents the conic constant of the surface, and a2, a3 and a4 represent the even aspheric surface parameters, respectively.

[0046] The specific parameters of the lenses in the embodiment are shown in Table 1:

[0047] Table 1: Lens parameters

[0048]

[0049] wherein the radius of curvature of the lens surface is allowed to fluctuate within a certain range, for example, within 0.05 mm, and the thickness of the lens is also allowed to fluctuate within a certain range, for example, within 0.01 mm. That is, the radius of curvature of the first object side surface is 128.9±0.05 mm, the radius of curvature of the first image side surface is 297.8±0.05 mm, and the center thickness of the first lens is 7±0.01 mm; the radius of curvature of the second object side surface is 455.6±0.05 mm, the radius of curvature of the second image side surface is 267.9±0.05 mm, and the center thickness of the second lens is 7±0.01 mm; the radius of curvature of the third object side surface is 51.8±0.05 mm, the radius of curvature of the third image side surface is 43±0.04 mm, and the center thickness of the third lens is 6.1±0.01 mm; and the radius of curvature of the fourth object side surface is 110.5±0.05 mm, the radius of curvature of the fourth image side surface is 147.6±0.05 mm, and the center thickness of the fourth lens is 4.1±0.01 mm.

[0050] The optical parameters of the aspheric surfaces in the embodiment are shown in Table 2:

[0051] Table 2: Even aspheric surface parameters

[0052]

[0053]

[0054] Figure 2The point list diagram of the middle wave infrared optical system for target identification, the optical system limit diffraction Airy spot radius is 8.829 μm, three field of view RMS radiuses are 1.361 μm, 2.828 μm, 2.694 μm respectively, and are less than the diffraction limit; Figure 3 The MTF curve diagram of the middle wave infrared optical system, can reflect that the MTF is greater than 0.5 at the characteristic frequency 41 period / mm, and indicates that the imaging quality is good. Figure 4 The relative illumination diagram of the middle wave infrared optical system for target identification, is greater than 96% at the maximum field of view. Figure 5 The light aberration diagram of the middle wave infrared optical system for target identification, the aberration is very small by the degree of curve deviating from the longitudinal axis.

[0055] The optical system focal length is greater than 160 mm, the working waveband is 3 μm-5 μm, the working F number is 2, the field of view angle is 10°, the optical total length is 169 mm, the non-refrigeration middle wave infrared detector with the resolution of 640x512 and the image element size of 12 μm can be adapted, and the detection target distance is 2-3 km.

[0056] In the description of the utility model, it is understood that the orientation or position relation indicated by the terms "center", "vertical", "horizontal", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is the orientation or position relation based on the drawing shown, and is only for the convenience of describing the utility model and simplifying the description, and is not indicative or implied that the device or element indicated must have a specific orientation, a specific orientation structure and operation, and thus cannot be understood as a limitation on the protection content of the utility model.

[0057] The above-described embodiments are only specific embodiments of the utility model, but the protection scope of the utility model is not limited to this, and any skilled person in the art can easily think of various equivalent modifications, replacements and improvements within the technical range disclosed by the utility model, and these modifications, replacements and improvements should be covered in the protection scope of the utility model. Therefore, the protection scope of the utility model should be subject to the protection scope of the claims.

Claims

1. A mid-wave infrared optical system for target recognition, characterized in that, The lens comprises, from the object side to the image side, a first lens, a second lens, a diaphragm, a third lens, a fourth lens and an image plane, the first lens and the third lens have negative focal power, the second lens and the fourth lens have positive focal power; the first lens and the fourth lens are both meniscus positive lenses; the second lens and the third lens are both meniscus negative lenses; The first lens has a first object side and a first image side, the second lens has a second object side and a second image side, the third lens has a third object side and a third image side, and the fourth lens has a fourth object side and a fourth image side, the first image side and the second object side are both even aspheric surfaces, and the even aspheric surfaces satisfy the relationship: Z represents the sag of the aspheric surface at a height r along the optical axis, R represents the radius of curvature of the center of the aspheric surface, k represents the conic constant of the surface, and a2, a3 and a4 represent the even aspheric surface parameters respectively; The incident light is deflected by the first lens, the second lens, the diaphragm, the third lens and the fourth lens in sequence and then converges on the image plane.

2. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The radius of curvature of the first object side is 128.9±0.05mm, the radius of curvature of the first image side is 297.8±0.05mm, and the center thickness of the first lens is 7±0.01mm; The radius of curvature of the second object side is 455.6±0.05mm, the radius of curvature of the second image side is 267.9±0.05mm, and the center thickness of the second lens is 7±0.01mm; The radius of curvature of the third object side is 51.8±0.05mm, the radius of curvature of the third image side is 43±0.04mm, and the center thickness of the third lens is 6.1±0.01mm; The radius of curvature of the fourth object side is 110.5±0.05mm, the radius of curvature of the fourth image side is 147.6±0.05mm, and the center thickness of the fourth lens is 4.1±0.01mm.

3. The mid-wave infrared optical system for target discrimination of claim 2, wherein, The aperture of the first object side is 88.2mm, the aperture of the first image side is 86.8mm; the aperture of the second object side is 86.8mm, the aperture of the second image side is 83.2mm; the aperture of the third object side is 43.3mm, the aperture of the third image side is 60.2mm; the aperture of the fourth object side is 43.4mm, and the aperture of the fourth image side is 42.4mm.

4. The mid-wave infrared optical system for target discrimination of claim 2, wherein, The refractive index of the first object side is 3.4255, the refractive index of the second object side is 4.0245, the refractive index of the third object side is 4.0245, and the refractive index of the fourth object side is 3.4255.

5. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The distance between the first lens and the second lens is 1.3±0.01mm; the distance between the second lens and the diaphragm is 32.5±0.01mm; the distance between the diaphragm and the third lens is 27.9±0.01mm, and the distance between the third lens and the fourth lens is 55.4±0.01mm.

6. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The first object side, the second image side, the third object side, the third image side, the fourth object side and the fourth image side are all spherical surfaces.

7. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The first lens and the fourth lens are made of germanium, and the second lens and the third lens are made of silicon.

8. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The lens barrel, the first lens, the second lens, the diaphragm, the third lens, the fourth lens and the image plane are arranged in the lens barrel.

9. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The medium-wave infrared optical system is adapted to a non-cooled medium-wave infrared detector with a resolution of 640x 512 and a pixel size of 12 microns, and a detection target distance of 2-3 km.

10. The mid-wave infrared optical system for target discrimination of claim 1, wherein, The medium-wave infrared optical system has a focal length greater than 160 mm, a working waveband of 3-5 microns, an F number of 2, a field of view angle of 10 degrees and an optical total length of 169 mm.

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