Mid-wave infrared continuous zoom thermal imaging system

Abstract

The present invention belongs to the field of thermal imaging technology, and particularly relates to a mid-wave infrared continuous zoom thermal imaging system, which includes an objective lens group and a detector; it also includes a zoom group, a compensating group, a focusing group, and a secondary imaging group that are sequentially arranged on the optical path between the objective lens group and the detector; the zoom group includes a first negative power lens with a double concave shape, the compensating 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 that 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 at the detector focal plane. The drive unit is used to drive the zoom group and the compensating group to translate along the optical axis. The present invention has advantages such as clear imaging and achromatism without diffraction components, 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, there is only a continuous zoom lens for a mid-wave refrigeration detector with 320×240 and an F number of 2 based on a narrow band (3.2μm~3.4μm) in the market, which can only measure gases such as methane with absorption peaks in this wavelength range 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 refrigeration 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 a continuous zoom design, it is necessary to correct spherical aberration and thermal aberration of the system in both narrow and wide fields of view, which greatly increases the difficulty of designing a wide wavelength 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:

[0006] A mid-wave infrared continuous zoom thermal imaging system includes an objective lens group and a detector; the imaging system further includes:

[0007] A variable magnification 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 variable magnification group includes a first negative meniscus lens, the compensation group includes a first positive meniscus lens, the focusing group includes a second positive meniscus lens and a second negative meniscus lens; the secondary imaging group includes a third positive meniscus lens, a third negative meniscus lens, and a fourth positive meniscus lens arranged in sequence; the primary imaging plane is between the second negative meniscus lens and the third positive meniscus lens, and the secondary imaging plane is at the focal plane of the detector;

[0008] A driving unit, which is used to drive the variable magnification group and the compensation group to translate along the optical axis.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] An achromatic design is not achieved by using diffractive optical elements. Instead, by using only two materials, silicon and germanium, optimizing the surface profile parameters of each surface, and appropriately adopting aspherical surfaces, continuous zoom imaging of a system with an F-number of 1.2 is realized within a wide wavelength range of 3 μm to 5 μm, significantly reducing the system aberration and correcting the chromatic aberration of the system within a wide spectral range.

[0011] The entire thermal imaging system achieves clear imaging from -40°C to 70°C through a focusing group, and a conventional voice coil motor can be used as the driving unit, which is simple and easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Referring to the accompanying drawings, the disclosure of the present invention will become more readily understood. It is easily understood by those skilled in the art 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 figures:

[0013] Figure 1 is a schematic structural diagram of the thermal imaging system of the present invention when the focal length is 180 mm;

[0014] Figure 2 is a schematic structural diagram of the thermal imaging system of the present invention when the focal length is 100 mm;

[0015] Figure 3 is a schematic structural diagram of the thermal imaging system of the present invention when the focal length is 30 mm;

[0016] Figure 4 is an optical transfer function (MTF) graph when the focal length is 180 mm;

[0017] Figure 5 is a schematic diagram of the optical system spot diagram when the focal length is 180 mm;

[0018] Figure 6 is a schematic diagram of astigmatism and distortion when the focal length is 180 mm;

[0019] Figure 7 is an optical transfer function (MTF) graph when the focal length is 100 mm;

[0020] Figure 8 is a schematic diagram of the optical system spot diagram when the focal length is 100 mm;

[0021] Figure 9 is a schematic diagram of astigmatism and distortion when the focal length is 100 mm;

[0022] Figure 10 is an optical transfer function (MTF) graph when the focal length is 30 mm;

[0023] Figure 11 is a schematic diagram of the optical system spot diagram when the focal length is 30 mm;

[0024] Figure 12 It is a schematic diagram of astigmatism and distortion when the focal length is 30 mm;

[0025] Figure 13 It is the continuous zoom cam curve fitted by the dynamic optical principle of the present invention.

[0026] In the attached 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 implementation manners

[0027] Figures 1 - 13 The following description and illustration describe alternative specific embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. Some conventional aspects have been simplified or omitted for the purpose of teaching the technical solutions of the present invention. 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.

[0028] Example 1.

[0029] A mid-wave infrared continuous zoom thermal imaging system, as Figures 1 - 3 shown, the thermal imaging system includes:

[0030] An objective lens group, a zoom group, a compensation group, a focusing group, a secondary imaging group, a filter 9 and a detector 10 are arranged in sequence.

[0031] The objective lens group includes the fifth positive focal length lens 1. The zoom group includes the first negative focal length lens 2, the compensation group includes the first positive focal length lens 3, the focusing group includes the second positive focal length lens 4 and the second negative focal length lens 5; the secondary imaging group includes the third positive focal length lens 6, the third negative focal length lens 7 and the fourth positive focal length lens 8 arranged in sequence. The primary imaging plane is between the second negative focal length lens 5 and the third positive focal length lens 6, and the secondary imaging plane is at the focal plane of the detector 10.

[0032] The driving unit is used to drive the zoom group and the compensation group to translate along the optical axis.

[0033] In order to improve the imaging clarity, further, the first negative focal length lens 2 is a double concave lens, the first positive focal length lens 3 is a double convex lens, the second positive focal length lens 4 is a meniscus lens with the convex surface facing the objective lens group, the second negative focal length lens 5 is a meniscus lens with the convex surface facing the objective lens group, the third positive focal length lens 6 is a double convex lens, the third negative focal length lens 7 is a meniscus lens with the convex surface facing the objective lens group, and the fourth positive focal length lens 8 is a plano-convex lens with the convex surface facing the objective lens group.

[0034] In order to reduce the system aberration and correct the chromatic aberration, further, except for the fifth positive focal length lens 1, the second positive focal length lens 4 and the second negative focal length lens 5, the single surfaces of other lenses are aspherical surfaces, and the two surfaces of the second negative focal length lens 5 are aspherical surfaces. All the negative focal length lenses are made of germanium single crystal, and the positive focal length lenses are made of silicon single crystal.

[0035] Embodiment 2.

[0036] An application example of the mid-wave infrared continuous zoom thermal imaging system according to Embodiment 1 of the present invention.

[0037] In this application example, the working band is 3μm to 5μm, the focal length is 30mm to 180mm, and the F number is 1.2.

[0038] As Figures 1 - 3 shown, on the optical path, an objective lens group, a zoom group, a compensation group, a focusing group, a secondary imaging group, a filter 9 and a detector 10 are sequentially arranged. A mid-wave infrared cooled wide-band focal plane detector 10 with an array of 640×512 and a pixel size of 15μm is used. The detector 10 is cooled, and the aperture stop is located on the cold aperture stop of the cooled detector 10, meeting the 100% cold aperture stop efficiency of the system. The filter 9 is replaced at any time according to different scenarios to identify different types of targets.

[0039] The objective lens group includes a meniscus fifth positive focal length lens 1 with the convex surface facing the object side. The zoom group includes a double concave first negative focal length lens 2, and the compensation group includes a double convex first positive focal length lens 3. The focusing group includes a meniscus second positive focal length lens 4 with the convex surface facing the objective lens group and a meniscus second negative focal length lens 5 with the convex surface facing the objective lens group. The secondary imaging group includes a double convex third positive focal length lens 6, a meniscus third negative focal length lens 7 with the convex surface facing the objective lens group, and a plano-convex fourth positive focal length lens 8 with the convex surface facing the objective lens group arranged in sequence.

[0040] Among the above 8 lenses, all the negative focal length lenses are made of germanium single crystal, and all the positive focal length lenses are made of silicon single crystal.

[0041] Except for the fifth positive power lens 1, the second positive power lens 4 and the second negative power lens 5, single surfaces of other lenses are aspherical surfaces, and both surfaces of the second negative power lens 5 are aspherical surfaces.

[0042] Table 1 shows the parameters of each lens.

[0043] .

[0044] 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 the lens.

[0045] Table 2 lists the aspheric 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.

[0046] Table 2 shows the aspheric coefficients of some lenses.

[0047] .

[0048] The displacement of the optical axis direction of an aspherical surface based on the vertex is defined as follows:

[0049] .

[0050] The meanings of the parameters are: Z—position change in the direction of the optical axis, y—height of the optical axis, c—lens curvature, K—quadratic surface coefficient, A, B, C, D—aspheric surface coefficients.

[0051] Table 3 shows the parameters of the system at the long focal length, medium focal length and short focal length.

[0052] .

[0053] Table 3 includes focal length, F number, field angle and variable spacing T1, T2, T3. T1 is the distance between the fifth positive power lens 1 and the first negative power lens 2, T2 is the distance between the first negative power lens 2 and the first positive power lens 3, and T3 is the distance between the first positive power lens 3 and the second positive power lens 4.

[0054] The present invention adopts a secondary imaging design, wherein the system entrance pupil is located on the first surface of the fifth positive power lens 1, 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 in the focal plane of the detector 10.

[0055] like Figures 4 - 12As shown, the transfer function, field curvature, distortion, and root mean square diameter of the spot diagram of the optical system of the present invention are all within the standard range at focal lengths of 30 mm, 100 mm, and 180 mm. It can be seen therefrom that the present invention has good imaging quality.

[0056] Figure 13 This is the continuous zoom cam curve fitted by the dynamic optical principle of the present invention.

Claims

1. A mid-wave infrared continuous zoom thermal imaging system, comprising an objective lens group and a detector; characterized in that, The thermal imaging system further includes: A zoom group, a compensation group, a focusing group, and a secondary imaging group that are sequentially arranged on the optical path between the objective lens group and the detector; the objective lens group includes a fifth positive focal length lens with a convex surface facing the object side; the zoom group includes a first negative focal length lens with a double concave shape, the compensation group includes a first positive focal length lens, the focusing group includes a second positive focal length lens and a second negative focal length lens; the secondary imaging group includes a third positive focal length lens, a third negative focal length lens, and a fourth positive focal length lens that are sequentially arranged; the primary imaging plane is between the second negative focal length lens and the third positive focal length lens, and the secondary imaging plane is at the focal plane of the detector; A driving unit, which is used to drive the zoom group and the compensation group to translate along the optical axis; There are only 8 lenses with optical power in the thermal imaging system.

2. The mid-wave infrared continuous zoom thermal imaging system according to claim 1, wherein The first negative focal length lens is a double concave lens, the first positive focal length lens is a double convex lens, the second positive focal length lens is a meniscus lens with a convex surface facing the objective lens group, the second negative focal length lens is a meniscus lens with a convex surface facing the objective lens group, the third positive focal length lens is a double convex lens, the third negative focal length lens is a meniscus lens with a convex surface facing the objective lens group, and the fourth positive focal length lens is a plano-convex lens with a convex surface facing the objective lens group.

3. The mid-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that, Except for the fifth positive focal length lens, the second positive focal length lens, and the second negative focal length lens, the single surface of other lenses is aspherical, and the double surfaces of the second negative focal length lens are aspherical.

4. The mid-wave infrared continuous zoom thermal imaging system according to claim 1, characterized in that, All negative focal length lenses are made of single crystal germanium.

5. The mid-wave infrared continuous zoom thermal imaging system according to claim 1, wherein The positive focal length lenses are made of single crystal silicon.

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

7. The mid-wave infrared continuous zoom thermal imaging system according to claim 1, wherein The thermal imaging system does not need to be configured with diffractive optical elements.

8. The mid-wave infrared continuous zoom thermal imaging system according to claim 1, wherein The F number is 1.2, the working wavelength band is 3μm to 5μm, and continuous zooming is performed from 30mm to 180mm.

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