Low-cost long-wave infrared continuous zoom lens adaptive to large target surface

Abstract

The invention provides a low-cost long-wave infrared continuous zoom lens adaptive to a large target surface, and relates to the technical field of infrared thermal imaging. The low-cost long-wave infrared continuous zoom lens adaptive to the large target surface comprises a front fixed group, a zoom group, a compensation group, a rear fixed group and a long-wave uncooled detector which are sequentially arranged from an object space to an image space along an optical axis, the effective focal length of the lens is 25 mm to 75 mm, the F number of the short focal end is 0.92, the F number of the long focal end is 1.2, and the total length of the optical system is 133 mm. The invention provides the long-wave infrared uncooled continuous zoom lens which is low in cost and adapts to a large target surface, and the air interval between the lenses is changed by controlling the zoom group and the compensation group to perform linear motion along the optical axis, so that the continuous zoom adjustment of the system is realized. Meanwhile, mature, widely-used and economical chalcogenide glass is used as materials of the three lenses including the first lens, and the other two lenses are made of germanium single crystals, so that the material cost of the lenses is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of infrared thermal imaging technology, in particular to a low-cost long-wave infrared continuous zoom lens suitable for large target surface. BACKGROUND

[0002] Infrared thermal imagers are widely used in various fields such as industrial detection, field hunting, weapon guidance, etc. due to their ability to detect infrared light emitted by objects and to sense temperature differences in the external environment. In recent years, long-wave infrared bands corresponding to non-cooled detectors have gradually opened up the market in the civilian field due to their low cost and lightweight structure. However, with the increasing international tension, the price of traditional infrared lens material germanium has been rising, and the prices of infrared lenses and even complete machine products have also been rising. Therefore, it is of great significance to find new and inexpensive materials to replace germanium to reduce the cost of products, especially for products such as continuous zoom lenses that have more lenses and larger lens apertures.

[0003] The existing patent (CN 118311752 A) uses chalcogenide glass to design a long-wave infrared continuous zoom lens with a focal length of 10mm-60mm, which is suitable for a 640x512 / 12μm detector. However, the chalcogenide glass used in this patent contains a large amount of Te, Ge, and Sb elements, which does not belong to the cost-friendly category of chalcogenide glasses. The compatible detector is relatively small, which limits the viewing angle. CN117170074 A uses germanium and ZnSe, chalcogenide glass to design a three-group linkage 13.5-75mm long-wave infrared zoom lens suitable for a 640x512 / 15μm detector. This patent uses expensive germanium single crystals as the material for the three lenses including the first lens. The three-group linkage design also increases the construction difficulty of the mechanical structure and reduces the tolerance limit of the entire system. The existing patent (CN 116243469 A) also has the above-mentioned problems: germanium is used in multiple lenses including the first lens, which increases the material cost of the system.

[0004] Therefore, in order to better apply non-cooled long-wave infrared continuous zoom lenses to a wider range of fields, designers need to further compress costs while ensuring imaging quality and mechanical structure adaptability, and at the same time, try to adapt to larger target surface detectors to increase the viewing angle. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a low-cost long-wave infrared continuous zoom lens suitable for large target surface, which solves the problem of high cost of the prior art.

[0006] To achieve the above purpose, the present application realizes the following technical scheme: a low-cost long-wave infrared continuous zoom lens suitable for large target surface, comprising a front fixed group, a variable group, a compensation group, a rear fixed group and a long-wave non-cooled detector arranged in order along the optical axis from the object side to the image side.

[0007] The effective focal length of the lens is 25mm to 75mm, the short-focus end F number is 0.92, the long-focus end F number is 1.2, and the total length of the optical system is 133mm;

[0008] The front fixed group is a meniscus lens with positive refractive power;

[0009] The variable magnification group is a double-concave lens with negative refractive power;

[0010] The compensation group is a double-convex lens with positive refractive power;

[0011] The rear fixed group is composed of a meniscus lens with negative refractive power and a meniscus lens with positive refractive power arranged in sequence along the optical axis;

[0012] The variable magnification group and the compensation group are adjustable in position in the direction of the optical axis.

[0013] Preferably, the rear surface of the front fixed group, the rear surface of the variable magnification group, the front surface of the compensation group, the front surface of the rear fixed group, and the front surface of the rear fixed group are all aspherical surfaces, and the surface expression thereof is:

[0014]

[0015] Wherein, c is the curvature, k is the conic coefficient; r is the normalized radius coordinate; 、 、 、 、 、 is the aspherical coefficient.

[0016] Preferably, the rear surface of the front fixed group is a binary diffractive surface, and the dispersion characteristic expression thereof is:

[0017]

[0018] Wherein, λm represents the central wavelength, which is 10μm, λl represents the long wave, which is 12μm, λs represents the short wave, which is 8μm, and v represents the Abbe number, which is -2.5.

[0019] Preferably, the diffractive surface topography of the rear surface of the front fixed group and the rear surface of the variable magnification group is characterized by the following formula:

[0020]

[0021] Wherein, m=1, n=2.7781, and both are constants, and C1, C2 are diffractive surface coefficients.

[0022] Preferably, the lens material of the front fixed group, the variable magnification group and the rear fixed group is chalcogenide glass, and the composition is Se and As, and the ratio is 3:2; the lens material of the compensation group and the rear fixed group is germanium single crystal.

[0023] Preferably, in the process of continuously zooming from the long focal end to the short focal end, the variable magnification group moves monotonously to the object side, and the compensation group moves monotonously to the image side.

[0024] Preferably, the rear fixed group has a focusing stroke of 2-3 mm, for compensating for the image plane shift caused by temperature change and target distance.

[0025] Preferably, the lens is adapted to a probe resolution of 1280*1024 pixels, and the pixel size is 12 mu m, and the system effective field of view ranges from 36.8*29.0 to 11.7*9.4.

[0026] The application provides a low-cost long-wave infrared continuous zoom lens adapted to a large target surface.

[0027] The application provides a low-cost long-wave infrared continuous zoom lens adapted to a large target surface, compared with the prior art, the application provides a low-cost long-wave infrared continuous zoom lens adapted to a large target surface, which is composed of a front fixed group, a variable magnification group, a compensation group and a rear fixed group, and the application applies a large amount of chalcogenide glass, which is economical, mature and widely used, to lens materials on the basis of ensuring the adaptability to a large target probe and optical imaging capability, thereby increasing the cost competitiveness of the system in the example.

[0028] The application provides a low-cost long-wave infrared continuous zoom lens adapted to a large target surface, the application uses diffraction surfaces and even aspheric surfaces reasonably, compensates for the low refractive index and large dispersion of chalcogenide glass relative to germanium single crystal, ensures the imaging quality, and controls the processing cost and tolerance within an acceptable range, the application realizes 3 times of continuous zooming of the focal length of the optical system from 75 mm to 25 mm by moving the variable magnification group with negative focal power and the compensation group with positive focal power along the optical axis, and the optical system has good imaging quality in the whole focal length range, and meets the use requirements. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The optical system diagram of the low-cost long-wave infrared continuous zoom lens adapted to a large target surface of the application at a focal length of 75 mm;

[0030] Figure 2 The optical system diagram of the low-cost long-wave infrared continuous zoom lens adapted to a large target surface of the application at a focal length of 50 mm;

[0031] Figure 3Optical system diagram of the low-cost large target surface long-wave infrared continuous zoom lens at a focal length of 25 mm according to the present application;

[0032] Figure 4 MTF curve diagram of the present application at a focal length of 75 mm and a spatial frequency of 42 lp / mm;

[0033] Figure 5 MTF curve diagram of the present application at a focal length of 50 mm and a spatial frequency of 42 lp / mm;

[0034] Figure 6 MTF curve diagram of the present application at a focal length of 25 mm and a spatial frequency of 42 lp / mm.

[0035] Wherein, A is a front fixed group, B is a zoom group, C is a compensation group, D is a rear fixed group, D-1 is a first piece of the rear fixed group, and D-2 is a second piece of the rear fixed group. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to 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. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0037] As shown in FIGS. Figure 1 , Figure 2 and Figure 3 , the present application provides a low-cost large target surface long-wave infrared continuous zoom lens, and gives optical system diagrams of the low-cost large target surface long-wave infrared continuous zoom lens at 75 mm, 50 mm and 25 mm, the low-cost large target surface long-wave infrared continuous zoom lens is composed of a front fixed group, a zoom group, a compensation group, a rear fixed group and a detector, which are sequentially distributed along an optical axis from an object side to an image side, the front fixed group is composed of a positive focal length meniscus lens A with a convex surface facing the object side, the zoom group is composed of a double-concave lens B with a negative focal length, the compensation group is composed of a double-convex lens C with a positive focal length, and the rear fixed group is composed of a lens D-1 with a negative focal length and a meniscus lens D-2 with a positive focal length and a convex surface facing the object side, which are sequentially distributed along the optical axis.

[0038] Specifically, in the low-cost large target surface long-wave infrared continuous zoom lens, the effective focal length is 25-75 mm, the F number at the short focal end is 0.92, the F number at the long focal end is 1.2, the total length of the optical system is 133 mm, the resolution of the adapted detector is 1280*1024 pixels, the pixel size is 12 μm, and the effective field of view of the system ranges from 36.8°*29.0° to 11.7°*9.4°.

[0039] The zoom group and the compensation group can reciprocate along the optical axis to change the focal length of the system, so that the real-time switching of short-focus search and long-focus observation is realized

[0040] In the embodiment of the application, the lens materials of the front fixed group A, the zoom group B, and the rear fixed group D-1 are the same kind of chalcogenide glass, and the component ratio is Se:As=3:2, and the lens materials of the compensation group C and the rear fixed group D-2 are germanium single crystal.

[0041] The low-cost large-target long-wave infrared continuous zoom lens of the application is characterized in that the rear surface of the front fixed group A, the rear surface of the zoom group B, the front surface of the compensation group C, the front surface of the rear fixed group D-1, and the front surface of the rear fixed group D-2 are all aspheric surfaces, and the rear surface of the front fixed group A and the rear surface of the zoom group B further have diffraction surfaces on the aspheric surface base.

[0042] The aspheric surface equation is as follows:

[0043]

[0044] The conic coefficient k of all the aspheric surfaces is 0, c is the surface curvature, and the multiple term coefficient is as follows

[0045]

[0046] The diffraction surface equation is as follows:

[0047]

[0048] Wherein, m=1, and n=2.7781.

[0049]

[0050] The distance from the front fixed group A to the image surface is maintained constant during zooming and focusing, as shown in Figs. Figure 1 、 2 , 3, only the zoom group and the compensation group are in trajectory coupling motion in the lens, and the rear fixed group D-2 also has a small movement during focusing, which does not affect the overall optical length of the system. In the specific example, the total optical length of the system is 133 mm. In actual use, there may be different types of cores, and their window thickness and position are different (in the specific example, the window specification is a 0.7 mm silicon window, and the air gap between the window and the image surface is 2.175 mm). In order to better adapt to different cores, the final detector position may be slightly offset, that is, the total optical length of the system is slightly offset from the value of 133 mm, but it does not affect the imaging quality.

[0051] In the present application, the surfaces of each lens group are marked along the optical axis direction from the object side to the image side, the front and rear surfaces of the front fixed group A are S1 and S2 in turn, the front and rear surfaces of the variable group B are S3 and S4 in turn, the front and rear surfaces of the compensation group C are S5 and S6 in turn, the front and rear surfaces of the rear fixed group D-1 are S7 and S8 in turn, and the front and rear surfaces of the rear fixed group D-2 are S9 and S10 in turn. In the zooming process of the lens of the present application, the distance between the rear surface of the front fixed group A and the front surface of the variable group B is Z1, the distance between the rear surface of the variable group B and the front surface of the compensation group C is Z2, and the distance between the rear surface of the compensation group C and the front surface of the rear fixed group D-1 is Z3. The optical structure parameters of the present application at the focal lengths of 75 mm, 50 mm and 25 mm are shown in Table 1.

[0052] Table 1

[0053]

[0054] In Table 1, 7 mm, 3 mm, 4.6 mm, 3.2 mm and 4.8 mm correspond to the center thicknesses of the front fixed group A, the variable group B, the compensation group C, the rear fixed group D-1 and the rear fixed group D-2 in turn, and the center thicknesses of the lenses remain unchanged in the continuous zooming process. The distance between the rear surface of the front fixed group A and the front surface of the variable group B is Z1, the distance between the rear surface of the variable group B and the front surface of the compensation group C is Z2, and the distance between the rear surface of the compensation group C and the front surface of the rear fixed group D-1 is Z3. In the zooming process, the variable group B and the compensation group C are continuously changed in a mutual coupling manner: they are fixed on the designed cam tracks, and when the variable group B moves a distance to a certain position, the compensation group C correspondingly moves a distance to a uniquely determined position. The air gap changes of the three focal lengths are listed in Table 2:

[0055] Table 2

[0056]

[0057] In the continuous zooming process of the present application, the trajectories of the two moving elements monotonously move in opposite directions as the focal length of the system gradually changes from 75 mm to 25 mm, and there is no inflection point in the process.

[0058] Figure 4 、 Figure 5 、 Figure 6 The optical transfer function (MTF) curves of the present application at the spatial frequency of 42 lp / mm when the focal length is the long focal length (75 mm), the medium focal length (50 mm) and the short focal length (25 mm) are shown in Figures 1, 2 and 3 respectively, in which the abscissa is the logarithm of the line per millimeter, and the ordinate is the normalized contrast. As can be seen from the figures, the modulation transfer function value of the present application is high at different focal lengths, indicating that clear imaging of the target can be realized throughout the continuous zooming process.

[0059] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to the details of the embodiments described, since numerous changes, modifications, substitutions and variations can be made thereto without departing from the spirit and scope of the application as defined by the appended claims and their equivalents.

Claims

1. A low-cost long-wave infrared continuous zoom lens adapted to a large target surface, characterized in that: The lens comprises, from the object side to the image side along the optical axis, a front fixed group (A), a zoom group (B), a compensation group (C), a rear fixed group (D) and a long-wave uncooled detector; The front fixed group (A) is a meniscus lens with positive focal power; The zoom group (B) is a double-concave lens with negative focal power; The compensation group (C) is a double-convex lens with positive focal power; The rear fixed group (D) is composed of a meniscus lens (D-1) with negative focal power and a meniscus lens (D-2) with positive focal power arranged in sequence along the optical axis; The zoom group (B) and the compensation group (C) are adjustable in position along the optical axis.

2. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The rear surface of the front fixed group (A), the rear surface of the zoom group (B), the front surface of the compensation group (C), the front surface of the rear fixed group (D-1) and the front surface of the rear fixed group (D-2) are all aspherical surfaces, and the surface expression thereof is as follows: ； where c is the curvature, k is the conic constant; r is the normalized radial coordinate; , , , , , are aspherical coefficients.

3. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The rear surface of the front fixed group (A) is a binary diffractive surface, and the dispersion characteristic expression thereof is as follows: ； wherein denotes the center wavelength, denotes the long wave, denotes the short wave, denotes the Abbe number.

4. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The diffractive surface topography of the rear surface of the front fixed group (A) and the rear surface of the zoom group (B) is characterized by the following formula: ； wherein m and n are both constants, and are diffraction surface coefficients.

5. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The lens material of the front fixed group (A), the zoom group (B) and the rear fixed group (D-1) is chalcogenide glass, and the composition thereof is Se and As, with a ratio of 3:2; the lens material of the compensation group (C) and the rear fixed group (D-2) is germanium single crystal.

6. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: In the process of continuous zooming from the long focal end to the short focal end, the zoom group (B) monotonically moves towards the object side, and the compensation group (C) monotonically moves towards the image side.

7. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The rear fixed group (D-2) has a focusing stroke of 2-3 mm, which is used to compensate for the image plane shift caused by temperature change and target distance.

8. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The lens is adapted to a detector with a resolution of 1280×1024 pixels.

9. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The lens is adapted to a detector with a pixel size of 12 μm, and the effective field of view of the system ranges from 36.8°×29.0° to 11.7°×9.4°.

10. The low-cost long-wave infrared continuous zoom lens adapted to a large target surface according to claim 1, characterized in that: The effective focal length of the lens is 25-75 mm, the F number at the short focal end is 0.92, the F number at the long focal end is 1.2, and the total length of the optical system is 133 mm.

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