A wide-angle infrared fixed-focus lens

Abstract

The invention discloses a wide-angle infrared fixed-focus lens, comprising a first lens, a second lens, a third lens, an aperture, a fourth lens, a silicon window and a detector, which are arranged in sequence from an object side to a mirror side. The first lens and the third lens are negative lenses, the second lens and the fourth lens are positive lenses, the object side surface and the mirror side surface of the first lens are convex and concave surfaces respectively, the object side surface and the mirror side surface of the second lens are convex and concave surfaces respectively, the object side surface and the mirror side surface of the third lens are concave and convex surfaces respectively, the object side surface and the mirror side surface of the fourth lens are both convex surfaces, the first lens, the second lens and the third lens are all spherical lenses, and the fourth lens is an aspherical lens. The invention can achieve the advantages of wide angle, compact structure, applicability in a high and low temperature temperature difference environment of 40 to 85°C, effective correction of aberrations in an optical system, etc., and at the same time, the cost of the infrared fixed-focus lens of the prior art is lower than that of the infrared fixed-focus lens of the prior art, and is applicable to wide-angle infrared thermal imaging equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of optical imaging, and in particular relates to a wide-angle infrared fixed-focus lens. Background Art

[0002] In recent years, infrared thermal imaging technology has developed rapidly, and the application technology of infrared thermal imaging in the field of uncooled detectors has become increasingly mature. At present, uncooled long-wave infrared thermal imagers are widely used in military, vehicle-mounted, temperature measurement, power line inspection, border security and other fields, among which the military field is particularly extensive. In order for uncooled long-wave infrared thermal imagers to meet the needs of civilian use, the field of view of the lens in the long-wave uncooled optical system is required to be large enough, but in order to maintain the balance of costs, the detector cost has to be reduced, that is, the detector frame needs to be reduced simultaneously, which will lead to a significant reduction in the image quality of the lens. In order to solve the imaging quality problem, the existing infrared system usually adopts the method of increasing the aperture of the first lens of the large field of view system, but this will inevitably lead to an increase in the volume of the product head and an increase in production costs. Summary of the invention

[0003] The purpose of the present invention is to improve the deficiencies in the prior art and provide a wide-angle infrared fixed-focus lens.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A wide-angle infrared fixed-focus lens comprises a first lens, a second lens, a third lens, an aperture, a fourth lens, a silicon window and a detector which are arranged in sequence from the object side to the mirror side;

[0006] The first lens and the third lens are negative lenses, and the second lens and the fourth lens are positive lenses; the object side surface and the mirror side surface of the first lens are convex and concave respectively, the object side surface and the mirror side surface of the second lens are convex and concave respectively, the object side surface and the mirror side surface of the third lens are concave and convex respectively, and the object side surface and the mirror side surface of the fourth lens are both convex.

[0007] Furthermore, the first lens, the second lens and the third lens are all spherical lenses, and the fourth lens is an aspherical lens; the aspherical lens meets the following conditions:

[0008]

[0009] The meanings of the relevant parameters in formula (1) are as follows:

[0010] X-the depth of the aspheric surface, in mm;

[0011] Y-the distance from the optical axis to the lens surface, i.e. the height, in mm;

[0012] C-lens curvature radius, C = 1 / R;

[0013] K-cone constant;

[0014] b, c, d, e, f, g, h - aspherical lens coefficients.

[0015] Furthermore, the fourth lens has a diffraction surface.

[0016] Furthermore, the first lens, the second lens and the third lens are all made of germanium glass, and the fourth lens is made of chalcogenide glass.

[0017] Furthermore, the focal lengths of the first to fourth lenses satisfy the following conditions:

[0018] 0.7<|f1 / f 123 ∣<1(2)

[0019] 1.9<|f2 / f 123 ∣<2.2(3)

[0020] 1.9<|f3 / f 123 ∣<2.2(4)

[0021] In formula (2) and (4), f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f 123 is the combined focal length of the first lens, the second lens, and the third lens.

[0022] Furthermore, the focal lengths of the first to fourth lenses satisfy the following conditions:

[0023] 1.5<|f 123 / f|<2 (5)

[0024] 1.4<|f1 / f|<1.6 (6)

[0025] 1.8<|f4 / f|<2.2 (7)

[0026] In formulas (5) to (7), f is the focal length of the lens optical system.

[0027] Furthermore, the focal lengths of the first lens to the fourth lens satisfy the following condition: |f1 / f 123 |=0.86, |f2 / f 123 |=2.06, |f3 / f 123 |=2.09, |f 123 / f∣=1.78, |f1 / f∣=1.53, |f4 / f∣=2.02.

[0028] Furthermore, the first lens satisfies the following condition: |R2|<4, where R2 is the image-side curvature radius of the first lens.

[0029] Furthermore, the image-side curvature radius R2 of the first lens satisfies: |R2|=3.54.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] 1. By sequentially arranging the first lens, the second lens, the third lens, the aperture, the fourth lens, the silicon window and the detector from the object side to the mirror side, the infrared fixed-focus lens obtained has the advantages of wide angle, compact structure, applicability in a high and low temperature temperature difference environment of -40 to 85°C, and the ability to effectively correct aberrations in the optical system. At the same time, it is also lower in cost than the infrared fixed-focus lens in the prior art and is suitable for large-angle infrared thermal imaging equipment. By arranging the first lens as a meniscus lens with convex and concave surfaces on the object side and the mirror side respectively, the field of view angle is effectively increased to achieve an imaging effect with a large field of view angle. At the same time, by arranging the aperture between the third lens and the fourth lens, the light flux is effectively increased and a high-quality imaging effect is guaranteed.

[0032] 2. By setting the first lens, the second lens and the third lens as spherical lenses, setting the fourth lens as an aspherical lens, and setting a diffraction surface on the aspherical lens, the aberration occurring during imaging can be fully corrected by the aspherical lens, thereby improving the imaging quality of the lens.

[0033] 3. By setting the first lens, the second lens and the third lens to use germanium glass, and the fourth lens to use chalcogenide glass, the chalcogenide material can face the large temperature difference without pressure, effectively ensuring that the fixed-focus lens is not heated and its working stability in different environments is guaranteed.

[0034] 4. By setting constraints on the focal lengths of the first to fourth lenses, a reasonable combination of different lenses is achieved, effectively ensuring the changes in lens parameters and correcting high and low temperature analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the present invention.

[0036] Figure 2 Schematic diagram of spherical aberration of a fixed focus lens at room temperature according to an embodiment.

[0037] Figure 3 Schematic diagram of astigmatism of a fixed focus lens at room temperature according to an embodiment.

[0038] Figure 4 Schematic diagram of distortion of a fixed focus lens at room temperature according to an embodiment.

[0039] Figure 5 Schematic diagram of Rayfan of a fixed focus lens at room temperature according to an embodiment.

[0040] Figure 6 Schematic diagram of MTF of a fixed focus lens at room temperature according to an embodiment.

[0041] Figure 7 Schematic diagram of spherical aberration of a fixed focus lens according to an embodiment at 85 degrees.

[0042] Figure 8 Schematic diagram of astigmatism of a fixed focus lens at 85 degrees according to an embodiment.

[0043] Fig. 9 Schematic diagram of the distortion of a fixed focus lens at 85 degrees according to an embodiment.

[0044] Fig.10 Schematic diagram of Rayfan when the fixed focus lens is at 85 degrees according to the embodiment.

[0045] Fig.11 This is a schematic diagram of the MTF of a fixed focus lens according to an embodiment when the focus angle is 85 degrees.

[0046] Fig.12 Schematic diagram of spherical aberration of the fixed-focus lens of Example 2 at room temperature.

[0047] Fig.13 Schematic diagram of astigmatism of the fixed-focus lens of Example 2 at room temperature.

[0048] Fig.14 Schematic diagram of distortion of the fixed-focus lens of Example 2 at room temperature.

[0049] Fig.15 Schematic diagram of Rayfan of the fixed-focus lens of Example 2 at room temperature.

[0050] Fig.16 Schematic diagram of MTF of the fixed-focus lens of Example 2 at room temperature.

[0051] Fig.17 Schematic diagram of spherical aberration of the fixed-focus lens of Example 2 at 85 degrees.

[0052] Fig.18 Schematic diagram of astigmatism of the fixed-focus lens of Example 2 at 85 degrees.

[0053] Fig.19 FIG. 1 is a schematic diagram of the distortion of the fixed-focus lens of Example 2 at 85 degrees.

[0054] Fig. 20 Schematic diagram of Rayfan when the fixed-focus lens of Example 2 is at 85 degrees.

[0055] Fig.21 This is a schematic diagram of the MTF of the fixed-focus lens of Example 2 at 85 degrees.

[0056] Markings in the figure: L1. first lens, L2. second lens, L3. third lens, K. aperture, L4. fourth lens, L5. silicon window. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments.

[0058] Embodiment 1:

[0059] The present invention comprises a first lens L1, a second lens L2, a third lens L3, an aperture K, a fourth lens L4, a silicon window L5 and a detector which are sequentially arranged from the object side to the mirror side. The first lens L1 and the third lens L3 are negative lenses, and the second lens L2 and the fourth lens L4 are positive lenses.

[0060] Placing the aperture K between the first lens K3 and the fourth lens K4 can ensure a larger light flux and a high-quality imaging effect.

[0061] The object side surface and mirror side surface of the first lens L1 are convex and concave respectively, the object side surface and mirror side surface of the second lens L2 are convex and concave respectively, the object side surface and mirror side surface of the third lens L3 are concave and convex respectively, and the object side surface and mirror side surface of the fourth lens L4 are both convex. The first lens L1 is set as a meniscus lens to achieve a large field of view as much as possible and improve the imaging range of the fixed focus lens.

[0062] The first lens L1, the second lens L2 and the third lens L3 are all made of germanium glass, and the fourth lens L4 is made of chalcogenide glass. The chalcogenide glass can ensure that the lens is athermal, so that it can adapt to the external environment within the temperature range of -40°C to 85°C.

[0063] The first lens L1, the second lens L2 and the third lens L3 are all spherical lenses, and the fourth lens L4 is an aspherical lens. The aberrations occurring during imaging can be fully corrected by the aspherical lens, thereby improving the imaging quality of the lens.

[0064] Aspheric lenses meet the following conditions:

[0065]

[0066] The meanings of the relevant parameters in formula (1) are as follows:

[0067] X-the depth of the aspheric surface, in mm;

[0068] Y-the distance from the optical axis to the lens surface, i.e. the height, in mm;

[0069] C-lens curvature radius, C = 1 / R;

[0070] K-cone constant;

[0071] b, c, d, e, f, g, h - aspherical lens coefficients.

[0072] The focal lengths of the first lens L1 to the fourth lens L4 satisfy the following conditions:

[0073] 0.7<|f1 / f 123 ∣<1 (2)

[0074] 1.9<|f2 / f 123 ∣<2.2 (3)

[0075] 1.9<|f3 / f 123 ∣<2.2 (4)

[0076] 1.5<|f 123 / f|<2 (5)

[0077] 1.4<|f1 / f|<1.6 (6)

[0078] 1.8<|f4 / f|<2.2 (7)

[0079] In formulas (2) to (7), f1 is the focal length of the first lens L1, f2 is the focal length of the second lens L2, f3 is the focal length of the third lens L3, f4 is the focal length of the fourth lens L4, and f 123 is the combined focal length of the first lens L1, the second lens L2 and the third lens L3. f is the focal length of the lens optical system.

[0080] The focal length of the lens is determined by the structure of the front and rear surfaces of the lens. The focal length of the lens reflects the overall situation of the combination of the front and rear surfaces of the lens. It is a structural parameter of the lens. The lens that meets the above restrictions can effectively guarantee the lens parameters and correct the changes in high and low temperature analysis.

[0081] In this embodiment, it is preferred that the focal lengths of the first lens L1 to the fourth lens L4 satisfy the following condition: |f1 / f 123 |=0.86, |f2 / f 123 |=2.06, |f3 / f 123 |=2.09, |f 123 / f∣=1.78, |f1 / f∣=1.53, |f4 / f∣=2.02.

[0082] In order to ensure the viewing angle and the size of the first lens L1 , the image-side curvature radius R2 of the first lens L1 satisfies the following condition: |R2|<4. In this embodiment, preferably, |R2|=3.54.

[0083] In order to further prove the effect of the present invention, verification is carried out in combination with specific experimental data below.

[0084] The basic lens data used in this embodiment are shown in Table 1:

[0085] Table 1:

[0086] Face number Curvature radius R Surface spacing D Material <![CDATA[Object surface of the first lens L1]]> 8.14 0.74 Germanium glass <![CDATA[Image plane of the first lens L1]]> 3.54 5.00 <![CDATA[Object surface of the second lens L2]]> 10.89 1.10 Germanium glass <![CDATA[Image plane of the second lens L2]]> 27.75 2.92 <![CDATA[Object surface of the third lens L3]]> -5.35 0.75 Germanium glass <![CDATA[Image plane of the third lens L3]]> -8.54 -0.10 Guanglan K noodles Infinity 0.36 <![CDATA[Object surface of the fourth lens L4]]> 11.51 2.15 Chalcogenide glass <![CDATA[Imaging plane of the fourth lens L4]]> -9.47 4.00 Silicon Window Infinity 0.60 Silicon glass Detector image plane Infinity 5.20

[0087] The radius of curvature R represents the radius of curvature of the corresponding surface, in mm, and the surface interval D represents the thickness of the lens of the corresponding surface or the interval between the lenses, in mm.

[0088] The specific parameters of aspherical lens coefficients are shown in Table 2:

[0089] Table 2:

[0090] <![CDATA[Object surface of the fourth lens L4]]> <![CDATA[Image plane of the fourth lens L4]]> K -9.9 -0.95 b -0.00065 0.00035 c -0.0000052 -0.000014 d 0.00000024 -0.0000045 e -0.00000058 0.0000000072 f 0.000000041 0.000000035 g 0.0000000036 0.0000000016 h -0.00000000059 -0.00000000047

[0091] The optical system parameters are shown in Table 3:

[0092] Table 3:

[0093] f FNO. 2ω TTL 1.55 1.1 161° 17.9

[0094] In Table 3, the unit of the paraxial focal length f is mm, Fno. is the aperture size, ω in the viewing angle 2ω represents the half viewing angle, and the unit of the total optical length TTL is mm.

[0095] The infrared fixed-focus lens of this embodiment is tested at room temperature, and the phase difference diagram is recorded. Figures 2 to 5 These are the spherical aberration diagram, astigmatism diagram, distortion diagram, Rayfan diagram and MTF diagram at room temperature.

[0096] Since the ambient temperature may cause the temperature of the lens to become lower or higher, the infrared fixed-focus lens of this embodiment is tested in a high temperature environment of 85°C, and the aberration diagram is recorded. Figures 7 to 11 These are the spherical aberration diagram, astigmatism diagram, distortion diagram, Rayfan diagram and MTF diagram at the wide-angle end at a high temperature of 85°C.

[0097] From Table 3 and Figures 2 to 11 It can be seen that the infrared fixed-focus lens of this embodiment has various aberrations well corrected within the temperature range of -40°C to 85°C, and has lower cost than existing infrared fixed-focus lenses, is suitable for large-angle infrared thermal imaging equipment, and has excellent development prospects.

[0098] Embodiment 2:

[0099] The difference between this embodiment and the first embodiment lies in that the first lens L1, the second lens L2 and the third lens L3 are all germanium spherical lenses, the fourth lens L4 is a chalcogenide diffractive lens, the surface L4R1 is an aspherical surface, and the surface L4R2 is a diffractive surface, that is, the object surface of the fourth lens L4 is an aspherical surface, and the image surface of the fourth lens L4 is a diffractive surface.

[0100] The basic lens data used in this embodiment are shown in Table 4:

[0101] Table 4:

[0102] Face number Curvature radius R Surface spacing D Material <![CDATA[Object surface of the first lens L1]]> 8.10 0.74 Germanium glass <![CDATA[Image plane of the first lens L1]]> 3.50 5.00 <![CDATA[Object surface of the second lens L2]]> 10.90 1.10 Germanium glass <![CDATA[Image plane of the second lens L2]]> 27.75 2.92 <![CDATA[Object surface of the third lens L3]]> -5.34 0.75 Germanium glass <![CDATA[Image plane of the third lens L3]]> -8.53 -0.10 Guanglan K noodles Infinity 0.36 <![CDATA[Object surface of the fourth lens L4]]> 11.50 2.15 Chalcogenide glass <![CDATA[Imaging plane of the fourth lens L4]]> -9.46 4.00 Silicon Window Infinity 0.60 Silicon glass Detector image plane Infinity 5.20

[0103] The specific parameters of aspherical lens coefficients are shown in Table 5:

[0104] Table 5:

[0105] <![CDATA[Object surface of the fourth lens L4]]> <![CDATA[Imaging plane of the fourth lens L4]]> K -9.9 -0.95 b -0.00064 0.00034 c -0.0000052 -0.000014 d 0.00000024 -0.0000044 e -0.00000058 0.0000000071 f 0.00000004 0.000000035 g 0.0000000036 0.0000000016 h -0.00000000059 -0.00000000047

[0106] The optical system parameters are shown in Table 6:

[0107] Table 6:

[0108] f FNO. 2ω TTL 1.54 1.1 161.3° 17.8

[0109] The infrared fixed-focus lens of this embodiment is tested at room temperature, and the phase difference diagram is recorded. Figure 12-16 These are the spherical aberration diagram, astigmatism diagram, distortion diagram, Rayfan diagram and MTF diagram at room temperature.

[0110] Since the ambient temperature may cause the temperature of the lens to become lower or higher, the infrared fixed-focus lens of this embodiment is tested in a high temperature environment of 85° C., and the aberration diagram is recorded. Figure 17-Figure 21 These are the spherical aberration diagram, astigmatism diagram, distortion diagram, Rayfan diagram and MTF diagram at the wide-angle end at a high temperature of 85°C.

[0111] From Table 6 and Appendix Figure 12-21 It can be seen that various aberrations of the infrared fixed-focus lens of this embodiment are well corrected and can be applied to infrared thermal imaging equipment.

[0112] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described herein and shown in the drawings can be arranged and designed in various different configurations.

[0113] Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0114] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

Claims

1. A wide-angle infrared fixed-focus lens, characterized in that it comprises a first lens, a second lens, a third lens, an aperture, a fourth lens, a silicon window and a detector which are arranged in sequence from the object side to the mirror side; The first lens and the third lens are negative lenses, and the second lens and the fourth lens are positive lenses; the object side surface and the mirror side surface of the first lens are convex and concave surfaces respectively, the object side surface and the mirror side surface of the second lens are convex and concave surfaces respectively, the object side surface and the mirror side surface of the third lens are concave and convex surfaces respectively, and the object side surface and the mirror side surface of the fourth lens are both convex surfaces; The first lens, the second lens and the third lens are all spherical lenses, and the fourth lens is an aspherical lens; the aspherical lens meets the following conditions: (1); The meanings of the relevant parameters in formula (1) are as follows: X-the depth of the aspheric surface, in mm; Y-the distance from the optical axis to the lens surface, i.e. the height, in mm; C-lens curvature, C=1 / R; K-cone constant; b, c, d, e, f, g, h - aspherical lens coefficients; The first lens, the second lens and the third lens are all made of germanium glass, and the fourth lens is made of chalcogenide glass; The focal lengths of the first to fourth lenses satisfy the following conditions: 0.7<|f1 / f123|<1(2) 1.9<|f2 / f123|<2.2(3) 1.9<|f3 / f123|<2.2(4) In formula (2) and (4), f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f123 is the combined focal length of the first lens, the second lens, and the third lens.

2. The wide-angle infrared fixed-focus lens according to claim 1, characterized in that: The fourth lens has a diffractive surface.

3. The wide-angle infrared fixed-focus lens according to claim 1, characterized in that: The focal lengths of the first to fourth lenses satisfy the following conditions: 1.5<|f123 / f|<2(5) 1.4<|f1 / f|<1.6(6) 1.8<|f4 / f|<2.2(7) In formulas (5) to (7), f is the focal length of the lens optical system.

4. The wide-angle infrared fixed-focus lens according to claim 3, characterized in that: The focal lengths of the first to fourth lenses satisfy the following conditions: |f1 / f123|=0.86, |f2 / f123|=2.06, |f3 / f123|=2.09, |f123 / f|=1.78, |f1 / f|=1.53, |f4 / f|=2.

02.

5. The wide-angle infrared fixed-focus lens according to claim 4, characterized in that: The first lens satisfies the following condition: |R2|<4, where R2 is the image-side curvature radius of the first lens.

6. The wide-angle infrared fixed-focus lens according to claim 5, characterized in that: The image-side curvature radius R2 of the first lens satisfies: |R2|=3.54.

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