Medium-wave infrared continuous zooming optical system with large relative aperture and application of medium-wave infrared continuous zooming optical system

Abstract

The invention relates to a medium-wave infrared continuous zooming optical system with a large relative aperture and application thereof. The optical system comprises a front fixed group, a zoom group, a compensation group, a rear fixed group, a secondary imaging fixed group, a refrigeration detector cold diaphragm and a focal plane which are sequentially arranged on the same optical axis, the front fixed group comprises a first positive meniscus lens 1 and a first negative meniscus lens 2, the zoom group is a biconcave lens 3 with negative focal power, the compensation group is a biconvex lens 4 with positive focal power, and the rear fixed group is a biconvex lens 5 with negative focal power. The rear fixing group comprises a second negative meniscus lens 5 and a second positive meniscus lens 6. The secondary imaging fixing group comprises a third negative meniscus lens 7 and a third positive meniscus lens 8. The relative aperture of the optical system is 1 / 2, the diameter is greater than 200 mm, the total length does not exceed 360 mm, the focal length range is 50-400 mm, the working wave band is 3-5 [mu] m, the matching surface width is greater than 20.5 mm, the optical system has the advantages of large relative aperture, compact structure, large target surface and the like, and the problem that the existing medium-wave refrigeration zoom system has weak target detection capability for long distance and small temperature difference is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical lens, in particular to a large relative aperture mid-wave infrared continuous zoom optical system and application thereof. BACKGROUND

[0002] The infrared imaging system has a series of advantages such as not being limited by light, good concealment, strong anti-interference ability, long action distance, and all-weather work, and has a broad application prospect in many fields. The existing infrared optical system mainly applies two atmospheric window bands of 3~5μm and 8~14μm, and the mid-wave refrigeration type detector has the advantages of high sensitivity, and the action distance and imaging effect are incomparable to the non-refrigeration type detector.

[0003] The infrared imaging system mainly detects the thermal radiation of the target itself, and extracts the target by using the temperature difference between the target and the background. When it is raining and snowing, the target temperature difference and the environment temperature difference are small, and the target recognition is not obvious, so it is necessary to improve the minimum resolvable temperature difference (MRTD) of the infrared imaging system to improve its resolution capability. However, the minimum resolvable temperature difference is affected by the relative aperture of the infrared imaging system, and the relative aperture of the existing mid-wave refrigeration zoom system is generally 1 / 4, and the detection capability of the long-distance target and the target with small temperature difference is weak. In summary, it is particularly important to develop a large relative aperture mid-wave infrared continuous zoom optical system. SUMMARY

[0004] The present application aims to solve the above-mentioned problems existing in the prior art, and provides a large relative aperture mid-wave infrared continuous zoom optical system. The aperture of the system is greater than 200mm, the total length of the system is <360mm, the relative aperture is 1 / 2, the focal length range is 50mm~400mm, and the overall structure is relatively compact.

[0005] The large relative aperture mid-wave infrared continuous zoom optical system comprises, in order from the object side to the image side, a front fixed group, a variable group, a compensation group, a rear fixed group, a secondary imaging fixed group, a refrigeration detector cold light barrier and a focal plane.

[0006] Further, the air gap between the front fixed group and the variable group is 79.03~147.17mm, the air gap between the variable group and the compensation group is 73.29~2mm, the air gap between the compensation group and the rear fixed group is 5.15~8.3mm, and the air gap between the rear fixed group and the secondary imaging fixed group is 57.81mm.

[0007] Further, the front fixed group comprises a meniscus positive lens A (i.e. a first meniscus positive lens 1) and a meniscus negative lens B (i.e. a first meniscus negative lens 2).

[0008] Further, the variable magnification group is specifically a double-concave lens 3 with a negative focal length, which can move linearly along the optical axis to realize the variable magnification function.

[0009] Further, the compensation group is specifically a double-convex lens 4 with a positive focal length, which can move linearly along the optical axis to realize the compensation function.

[0010] Further, the rear fixed group comprises a meniscus negative lens C (i.e. a second meniscus negative lens 5) and a meniscus positive lens D (i.e. a second meniscus positive lens 6). The meniscus negative lens C is close to the compensation group, and the convex surface thereof faces the convex surface of the meniscus positive lens D, and the concave surface of the meniscus positive lens D faces the secondary imaging fixed group.

[0011] Further, the secondary imaging fixed group comprises a meniscus negative lens E (i.e. a third meniscus negative lens 7) and a meniscus positive lens F (i.e. a third meniscus positive lens 8). The meniscus negative lens E is close to the rear fixed group, and the concave surface thereof faces the meniscus positive lens F, and the concave surface of the meniscus positive lens F faces the cold light stop of the refrigeration detector.

[0012] Further, the image side of the double-concave lens 3, the object side of the double-convex lens 4, the object side of the meniscus negative lens C, the image side of the meniscus positive lens D, and the object side of the meniscus positive lens F are all even aspheric surfaces.

[0013] The second object of the present application is to provide the application of the above-mentioned large relative aperture mid-wave infrared continuous zoom optical system in thermal imaging, especially the thermal imaging of long-distance targets and targets with small temperature differences.

[0014] Compared with the prior art, the present application has the following advantages: (1) outstanding comprehensive performance. The relative aperture of the optical system reaches 1 / 2, the focal length is 50mm~400mm, the working waveband is 3um~5um, and the optical system can match a detector with a face width greater than 20.5mm, and has the advantages of large relative aperture, wide focusing range, large target, etc. (2) compact structure. The aperture of the optical system is slightly larger than 200mm, and the total length is less than 360mm, and a relatively small number of lenses are used to achieve good imaging effect. (3) solves the problem of weak detection capability of the prior art when facing long-distance targets and targets with small temperature differences, and realizes optical imaging and observation in special situations. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1Optical schematic of the MWIR continuous zoom optical system at short focus.

[0016] Figure 2 Optical schematic of the MWIR continuous zoom optical system at mid focus.

[0017] Figure 3 Optical schematic of the MWIR continuous zoom optical system at long focus.

[0018] Figure 4 Optical schematic of the MWIR continuous zoom optical system at short focus. Figure 1 MTF plot at short focus.

[0019] Figure 5 Optical schematic of the MWIR continuous zoom optical system at mid focus. Figure 2 MTF plot at mid focus.

[0020] Figure 6 Optical schematic of the MWIR continuous zoom optical system at long focus. Figure 3 MTF plot at long focus.

[0021] Figure 7 Optical schematic of the MWIR continuous zoom optical system at short focus. Figure 1 Point spread function plot at short focus.

[0022] Figure 8 Optical schematic of the MWIR continuous zoom optical system at mid focus. Figure 2 Point spread function plot at mid focus.

[0023] Figure 9 Optical schematic of the MWIR continuous zoom optical system at long focus. Figure 3 Point spread function plot at long focus.

[0024] Reference numerals: 1 - first meniscus positive lens, 2 - first meniscus negative lens, 3 - double concave lens, 4 - double convex lens, 5 - second meniscus negative lens, 6 - second meniscus positive lens, 7 - third meniscus negative lens, 8 - third meniscus positive lens, 9 - first window protection mirror, 10 - second window protection mirror. DETAILED DESCRIPTION

[0025] In order to fully understand the technical solutions and beneficial effects of the present application, the following will be further described in detail in combination with specific embodiments and drawings. It is emphasized that the following embodiments are only the preferred implementation of the present application, and on this basis, there can be many other embodiments of the present application, and any simple improvement or replacement based on these embodiments will fall within the protection scope of the present application.

[0026] As Figures 1-3The large relative aperture mid-wave infrared continuous zoom optical system is shown. From the object side on the left to the image side on the right, there are a front fixed group, a variable group, a compensation group, a rear fixed group, a secondary imaging fixed group, a refrigeration detector cold light barrier and a focal plane arranged along the optical axis. The front fixed group is composed of a first meniscus positive lens 1 and a first meniscus negative lens 2, the variable group is a double concave lens 3 with a negative focal power, the compensation group is a double convex lens 4 with a positive focal power, the rear fixed group is composed of a second meniscus negative lens 5 and a second meniscus positive lens 6, the secondary imaging fixed group is composed of a third meniscus negative lens 7 and a third meniscus positive lens 8, the refrigeration detector cold light barrier is composed of a first window protection mirror 9 (the left and right faces correspond to S17 and S18 respectively) and a second window protection mirror 10 (the left and right faces correspond to S19 and S20 respectively), and the focal plane is specifically an imaging surface IMA (S21). The parameters of each lens are shown in the following table:

[0027] As shown in the above table, the first meniscus positive lens 1, the double concave lens 3, the double convex lens 4, the second meniscus positive lens 6, the third meniscus positive lens 8 and the first window protection mirror 9 are all made of silicon, the first meniscus negative lens 2, the second meniscus negative lens 5 and the second window protection mirror 10 are all made of germanium, and the third meniscus negative lens 7 is made of a chalcogenide glass.

[0028] The large relative aperture mid-wave infrared continuous zoom optical system adopts a positive mechanical compensation, secondary imaging and continuous zoom design. In the zooming process, the variable group (i.e. the double concave lens 3) moves left and right along the optical axis according to different movement rules. The air gap between the front fixed group and the variable group (i.e. the distance between the first meniscus negative lens 2 and the double concave lens 3) is 79.03-147.17 mm, the air gap between the variable group and the compensation group (i.e. the distance between the double concave lens 3 and the double convex lens 4) is 73.29-2 mm, the air gap between the compensation group and the rear fixed group (i.e. the distance between the double convex lens 4 and the second meniscus negative lens 5) is 5.15-8.3 mm, and the air gap between the rear fixed group and the secondary imaging fixed group (i.e. the distance between the second meniscus positive lens 6 and the third meniscus negative lens 7) is 57.81 mm.

[0029] As shown in the above table, in the large relative aperture mid-wave infrared continuous zoom optical system, the image side of the double concave lens 3 (i.e. the S6 face), the object side of the double convex lens 4 (i.e. the S7 face), the object side of the second meniscus negative lens 5 (i.e. the S9 face), the image side of the second meniscus positive lens 6 (i.e. the S12 face) and the object side of the third meniscus positive lens 8 (i.e. the S15 face) all adopt even aspheric surfaces, and the surface equation is:

[0030] Wherein, Z is the distance from the vertex of the aspheric surface to the position of the aspheric surface along the optical axis direction at the height of Y, R is the radius of curvature of the lens surface, Y is the radial coordinate of the lens surface perpendicular to the optical axis direction, k is the quadratic curve constant of the lens surface, A is the fourth-order aspheric surface coefficient of the lens surface, B is the sixth-order aspheric surface coefficient of the lens surface, C is the eighth-order aspheric surface coefficient of the lens surface, and D is the tenth-order aspheric surface coefficient of the lens surface. The specific values of the parameters are as follows:

[0031] The total length (i.e. the distance from the S1 surface of the first meniscus positive lens 1 to the S21 surface of the IMA) of the large relative aperture mid-wave infrared continuous zoom optical system is not more than 360 mm, the diameter is greater than 200 mm, the focal length range is 50 mm-400 mm, the relative aperture is 1 / 2, the working waveband is 3 μm-5 μm, and the cold shield efficiency is 100% in the full focal length range.

[0032] The target surface diameter of the system is greater than 20.5 mm (compatible with a detector with a target surface diagonal ≤20 mm), and the matching pixel array is a mid-wave refrigeration infrared detector with a pixel size of 12 μm and an F# of 2, compatible with a pixel array of 1024×768 and a pixel size of 15 μm\12 μm.

[0033] The optical schematic diagrams of the large relative aperture mid-wave infrared continuous zoom optical system in the short focus (focal length of 50 mm), the medium focus (focal length of 200 mm) and the long focus (focal length of 400 mm) states are respectively as shown in Figures 1-3 The corresponding MTF curve diagrams and point column diagrams are respectively as shown in Figures 4-6 、 Figures 7-9 According to the pixel size of 12 μm, the limit resolution of the detector is 41.6 lp / mm, and from the MTF curve diagrams of different focal lengths, it can be seen that the central field transmittance is >0.5 at 40 lp / mm, and the edge field transmittance is >0.2 at 33 lp / mm, indicating that the resolution effect is good and the imaging is clear. From the point column diagrams, it can be seen that the diffraction spots of each field are within the Airy disk and are less than one pixel (12 μm) in the whole zoom range of 50 mm-400 mm, reaching the spatial domain diffraction limit, indicating that the imaging quality is good.

[0034] The above examples are only used to illustrate the technical solutions of the present application, but not limit it; the present application is not limited to the details of the above exemplary embodiments, and can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. The scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and range of the equivalent elements of the claims are intended to be included in the present application.

Claims

1. A medium-wave infrared continuous zoom optical system with a large relative aperture, characterized by: The system includes a front fixed group, a zoom group, a compensation group, a rear fixed group, a secondary imaging fixed group, a cold stop of a refrigerated detector and a focal plane, which are arranged coaxially from the object space to the image space.

2. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The air gap between the anterior fixation group and the zoom group was 79.03-147.17 mm, the air gap between the zoom group and the compensation group was 73.29-2 mm, the air gap between the compensation group and the posterior fixation group was 5.15-8.3 mm, and the air gap between the posterior fixation group and the secondary imaging fixation group was 57.81 mm.

3. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The front fixed group includes a meniscus positive lens A and a meniscus negative lens B. The meniscus positive lens A is close to the object side, and its concave surface faces the convex surface of the meniscus negative lens B. The concave surface of the meniscus negative lens B faces the zoom group.

4. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The zoom group is specifically a biconcave lens with negative optical power that can move linearly along the optical axis.

5. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The compensation group is specifically a biconvex lens with positive optical power and movable along the optical axis.

6. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The rear fixed group includes a meniscus negative lens C and a meniscus positive lens D. The meniscus negative lens C is close to the compensation group, and its convex surface faces the convex surface of the meniscus positive lens D. The concave surface of the meniscus positive lens D faces the secondary imaging fixed group.

7. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The secondary imaging fixed group includes a meniscus negative lens E and a meniscus positive lens F. The meniscus negative lens E is close to the rear fixed group, and its concave surface faces the meniscus positive lens F. The concave surface of the meniscus positive lens F faces the cold aperture of the refrigerated detector.

8. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The image side surface of the biconcave lens, the object side surface of the biconvex lens, the object side surface of the meniscus negative lens C, the image side surface of the meniscus positive lens D, and the object side surface of the meniscus positive lens F are all even-order aspherical surfaces.

9. The large relative aperture medium-wave infrared continuous zoom optical system according to claim 1, characterized in that: The aperture of the system is greater than 200mm, the total length of the system is less than 360mm, the relative aperture is 1 / 2, and the focal length range is 50mm~400mm.

10. Use of the medium-wave infrared continuous zoom optical system with large relative aperture according to any one of claims 1 to 9 in thermal imaging of distant targets or targets with small temperature differences.

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