Medium-wave infrared continuous zooming thermal imaging system

Abstract

The invention belongs to a thermal imaging technology, and particularly relates to a medium-wave infrared continuous zooming thermal imaging system, which comprises an objective lens group and a detector, the zoom group, the compensation group, the focusing group and the secondary imaging group are sequentially arranged on a light path between the objective lens group and the detector; the zoom group comprises a biconcave first negative focal power lens, the compensation group comprises a first positive focal power lens, and the focusing group comprises a second positive focal power lens and a second negative focal power lens; the secondary imaging group comprises a third positive focal power lens, a third negative focal power lens and a fourth positive focal power lens which are arranged in sequence; a primary imaging surface is located between the second negative focal power lens and the third positive focal power lens, and a secondary imaging surface is located on the focal plane of the detector; and the driving unit is used for driving the zoom group and the compensation group to translate along the optical axis. The method has the advantages of clear imaging, achromatism without a diffraction part and the like, and is used for gas leakage detection.

Description

Technical Field

[0001] The present invention relates to thermal imaging technology, and particularly to a mid-wave infrared continuous zoom thermal imaging system. Background Art

[0002] Currently, on the market, there is only a continuous zoom lens for a mid-wave refrigerated detector with 320×240 and an F number of 2 based on a narrow band (3.2μm~3.4μm), which can only measure gases with absorption peaks in this wavelength range such as methane, and cannot identify toxic and harmful gases in other wavelength bands, such as carbon monoxide with an absorption peak spectrum in (4.52μm ~4.76μm).

[0003] Due to the large differences in the refractive index and dispersion of optical materials in different wavelength bands, with the addition of a mid-wave refrigerated detector with an F number of 1.2, it is very difficult to correct chromatic aberration of the optical system in the entire wide wavelength range (3μm~5μm). Coupled with the need for continuous zoom design, it is necessary to correct spherical aberration and thermal aberration of the system in both wide and narrow fields of view, which greatly increases the difficulty of designing a wide-band optical system. Summary of the Invention

[0004] To solve the deficiencies in the above-mentioned prior art solutions, the present invention provides a mid-wave infrared continuous zoom thermal imaging system.

[0005] The object of the present invention is achieved through the following technical solutions: A mid-wave infrared continuous zoom thermal imaging system, comprising an objective lens group and a detector; the imaging system further includes: A variable magnification group, a compensation group, a focusing group, and a secondary imaging group sequentially arranged on the optical path between the objective lens group and the detector; the variable magnification group includes a first negative meniscus lens, the compensation group includes a first positive lens, the focusing group includes a second positive lens and a second negative lens; the secondary imaging group includes a third positive lens, a third negative lens, and a fourth positive lens arranged in sequence; the primary imaging plane is between the second negative lens and the third positive lens, and the secondary imaging plane is at the focal plane of the detector; A driving unit, which is used to drive the variable magnification group and the compensation group to translate along the optical axis.

[0006] Compared with the prior art, the beneficial effects of the present invention are: Diffractive optical elements are not used for achromatic aberration design. Only by using two materials of silicon and germanium, optimizing the surface shape parameters of each surface, and appropriately using aspherical surfaces, continuous zoom imaging of the system with an F number of 1.2 in the wide wavelength range of 3μm~5μm is achieved, greatly reducing the system aberration and correcting the chromatic aberration of the system in the wide spectral range.

[0007] The entire thermal imaging system can achieve clear imaging from -40°C to 70°C through the focusing group, and the driving unit can use a conventional voice coil motor, which is simple and easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Referring to the accompanying drawings, the disclosure of the present invention will become more understandable. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the protection scope of the present invention. In the drawings: Figure 1 is a schematic structural diagram of the thermal imaging system of the present invention when the focal length is 180 mm; Figure 2 is a schematic structural diagram of the thermal imaging system of the present invention when the focal length is 100 mm; Figure 3 is a schematic structural diagram of the thermal imaging system of the present invention when the focal length is 30 mm; Figure 4 is an optical transfer function (MTF) graph when the focal length is 180 mm; Figure 5 is a schematic diagram of the optical system spot diagram when the focal length is 180 mm; Figure 6 is a schematic diagram of astigmatism and distortion when the focal length is 180 mm; Figure 7 is an optical transfer function (MTF) graph when the focal length is 100 mm; Figure 8 is a schematic diagram of the optical system spot diagram when the focal length is 100 mm; Figure 9 is a schematic diagram of astigmatism and distortion when the focal length is 100 mm; Figure 10 is an optical transfer function (MTF) graph when the focal length is 30 mm; Figure 11 is a schematic diagram of the optical system spot diagram when the focal length is 30 mm; Figure 12 is a schematic diagram of astigmatism and distortion when the focal length is 30 mm; Figure 13 is the continuous zoom cam curve fitted by the present invention through the dynamic optical principle.

[0009] In the drawings: 1 - the fifth positive focal length lens, 2 - the first negative focal length lens, 3 - the first positive focal length lens, 4 - the second positive focal length lens, 5 - the second negative focal length lens, 6 - the third positive focal length lens, 7 - the third negative focal length lens, 8 - the fourth positive focal length lens, 9 - the filter, 10 - the detector. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] Figures 1 - 13The following description and the following examples describe alternative specific embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. To teach the technical solution of the present invention, some conventional aspects have been simplified or omitted. Those skilled in the art should understand that variations or substitutions derived from these specific embodiments will fall within the scope of the present invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the present invention. Thus, the present invention is not limited to the following alternative specific embodiments, but is defined only by the claims and their equivalents.

[0011] Example 1.

[0012] A medium-wave infrared continuous zoom thermal imaging system, as Figures 1 - 3 shown, the thermal imaging system includes: An objective lens group, a zoom lens group, a compensating lens group, a focusing lens group, a secondary imaging lens group, a filter 9, and a detector 10 are arranged in sequence.

[0013] The objective lens group includes a fifth positive power lens 1. The zoom lens group includes a first negative power lens 2, the compensating lens group includes a first positive power lens 3, the focusing lens group includes a second positive power lens 4 and a second negative power lens 5; the secondary imaging lens group includes a third positive power lens 6, a third negative power lens 7, and a fourth positive power lens 8 arranged in sequence. The primary imaging plane is between the second negative power lens 5 and the third positive power lens 6, and the secondary imaging plane is at the focal plane of the detector 10.

[0014] The driving unit is used to drive the zoom lens group and the compensating lens group to translate along the optical axis.

[0015] To improve the imaging clarity, further, the first negative power lens 2 is a double concave lens, the first positive power lens 3 is a double convex lens, the second positive power lens 4 is a meniscus lens with the convex surface facing the objective lens group, the second negative power lens 5 is a meniscus lens with the convex surface facing the objective lens group, the third positive power lens 6 is a double convex lens, the third negative power lens 7 is a meniscus lens with the convex surface facing the objective lens group, and the fourth positive power lens 8 is a plano-convex lens with the convex surface facing the objective lens group.

[0016] To reduce the system aberration and correct the chromatic aberration, further, except for the fifth positive power lens 1, the second positive power lens 4, and the second negative power lens 5, the single surface of other lenses is aspherical, and the double surfaces of the second negative power lens 5 are aspherical. All negative power lenses are made of germanium single crystal, and positive power lenses are made of silicon single crystal.

[0017] Example 2.

[0018] An application example of the medium-wave infrared continuous zoom thermal imaging system according to Example 1 of the present invention.

[0019] In this application example, the working wavelength band is 3 μm to 5 μm, the focal length is 30 mm to 180 mm, and the F-number is 1.2.

[0020] As Figures 1 - 3 shown, on the optical path, an objective lens group, a zoom lens group, a compensation lens group, a focusing lens group, a secondary imaging lens group, a filter 9, and a detector 10 are sequentially arranged. A mid-wave infrared cooled wide-band focal plane detector 10 with an area array of 640×512 and a pixel size of 15 μm is used. The detector 10 is cooled, and the aperture stop is located on the cold aperture of the cooled detector 10, meeting the 100% cold aperture efficiency of the system. The filter 9 is replaced at any time according to different scenarios to identify different types of targets.

[0021] The objective lens group includes a meniscus-shaped fifth positive power lens 1 with its convex surface facing the object side. The zoom lens group includes a biconcave first negative power lens 2, and the compensation lens group includes a biconvex first positive power lens 3. The focusing lens group includes a meniscus-shaped second positive power lens 4 with its convex surface facing the objective lens group and a meniscus-shaped second negative power lens 5 with its convex surface facing the objective lens group. The secondary imaging lens group includes a biconvex third positive power lens 6, a meniscus-shaped third negative power lens 7 with its convex surface facing the objective lens group, and a plano-convex fourth positive power lens 8 with its convex surface facing the objective lens group arranged in sequence.

[0022] Among the above 8 lenses, all the negative power lenses are made of germanium single crystal, and all the positive power lenses are made of silicon single crystal.

[0023] Except for the fifth positive power lens 1, the second positive power lens 4, and the second negative power lens 5, one side of other lenses is aspherical, and both sides of the second negative power lens 5 are aspherical.

[0024] Table 1 shows the parameters of each lens.

[0025] .

[0026] In Table 1, the radius of curvature refers to the radius of curvature of each surface, and the spacing refers to the distance between two adjacent surfaces. For example, the spacing of surface S1 is the distance between surface S1 and surface S2. The material is the material used for manufacturing and processing of the lens.

[0027] Table 2 lists the aspherical coefficients of S3 of the first negative power lens 2, S5 of the first positive power lens 3, S9 and S10 of the second negative power lens 5, S11 of the third positive power lens 6, S15 of the third negative power lens 7, and S17 of the fourth positive power lens 8.

[0028] Table 2 is the aspherical coefficients of some lenses.

[0029] 。

[0030] The displacement in the optical axis direction of the aspherical surface with respect to the vertex of the surface is defined as follows: 。

[0031] The meanings of the parameters are as follows: Z - displacement in the optical axis direction, y - height on the optical axis, c - lens curvature, K - conic coefficient, A, B, C, D - aspherical coefficients.

[0032] Table 3 shows the parameters of the system at the long focal length end, medium focal length end, and short focal length end.

[0033] 。

[0034] Table 3 includes the focal length, F number, field of view angle, and variable spacings T1, T2, T3. Among them, T1 is the distance between the fifth positive focal length lens 1 and the first negative focal length lens 2, T2 is the distance between the first negative focal length lens 2 and the first positive focal length lens 3, and T3 is the distance between the first positive focal length lens 3 and the second positive focal length lens 4.

[0035] The present invention adopts a two - imaging - type design, in which the entrance pupil of the system is located on the first surface of the fifth positive focal length lens 1, the first imaging surface is between the second negative focal length lens 5 and the third positive focal length lens 6, and the second imaging surface is at the focal plane of the detector 10.

[0036] As Figures 4 - 12 shown, the transfer function, field curvature, distortion, and root - mean - square diameter of the point spread function of the optical system of the present invention at focal lengths of 30 mm, 100 mm, and 180 mm are all within the standard range. Thus, it can be seen that the present invention has good imaging quality.

[0037] Figure 13 is the continuous zoom cam curve fitted by the dynamic optical principle of the present invention.

Claims

1. A medium-wave infrared continuous zoom thermal imaging system, comprising an objective lens group and a detector; characterized in that: The thermal imaging system further comprises: A zoom group, a compensation group, a focusing group and a secondary imaging group are sequentially arranged on the optical path between the objective lens group and the detector; the zoom group includes a first double-concave negative power lens, the compensation group includes a first positive power lens, the focusing group includes a second positive power lens and a second negative power lens; the secondary imaging group includes a third positive power lens, a third negative power lens and a fourth positive power lens which are sequentially arranged; the primary imaging plane is between the second negative power lens and the third positive power lens, and the secondary imaging plane is on the focal plane of the detector; A driving unit, wherein the driving unit is used to drive the zoom group and the compensation group to translate along the optical axis.

2. The medium-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that: The first negative power lens is a biconcave lens, the first positive power lens is a biconvex lens, the second positive power lens is a meniscus lens with the convex surface facing the objective lens group, the second negative power lens is a meniscus lens with the convex surface facing the objective lens group, the third positive power lens is a biconvex lens, the third negative power lens is a meniscus lens with the convex surface facing the objective lens group, and the fourth positive power lens is a plano-convex lens with the convex surface facing the objective lens group.

3. The medium-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that: The objective lens group comprises a fifth positive power lens with a convex surface facing the object.

4. The medium-wave infrared continuous zoom thermal imaging system according to claim 3, characterized in that: Except for the fifth positive power lens, the second positive power lens and the second negative power lens, single surfaces of other lenses are aspherical surfaces, and both surfaces of the second negative power lens are aspherical surfaces.

5. The medium-wave infrared continuous zoom thermal imaging system according to claim 3, characterized in that: Negative power lenses are all made of germanium single crystal.

6. The medium-wave infrared continuous zoom thermal imaging system according to claim 3, characterized in that: The positive power lens is made of silicon single crystal.

7. The medium-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that: The thermal imaging system further comprises: A filter is arranged on the optical path between the secondary imaging group and the detector.

8. The medium-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that: The thermal imaging system does not need to be equipped with a diffractive optical element.

9. The medium-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that: The F number is 1.2, the working band is 3μm~5μm, and it can continuously zoom from 30mm to 180mm.

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