Compact large-view-field medium-wave infrared Cassegrain imaging system

Abstract

The utility model discloses a compact medium-wave infrared Cassegrain imaging system with a large view field. The imaging system comprises four parts, namely a perforated aspherical lens I (1), a main reflecting mirror (2), a secondary reflecting mirror (3) and an aspherical lens II (4). The focal length of the imaging system is 110mm, the clear aperture is 65mm, and the length from the front surface of the first perforated aspheric lens to the image plane is only 49mm which is less than half of the focal length of the system. According to the imaging system provided by the utility model, the reflector is arranged in the hole of the perforated aspheric lens I, so that the length of the system can be shortened, and more variables can be provided for aberration correction. The diameter of a defocused spot of the imaging system is smaller than 13 microns in a working wave band range of 3-5 microns, and the imaging system is suitable for a high-resolution medium-wave infrared detector; the imaging system has a large field of view of 1.3 degrees, the number of lenses is small, the transmittance is high, and imaging is clear in a wide temperature range through a mode that the second aspheric lens moves back and forth for focusing compensation.

Description

Technical Field

[0001] The utility model discloses a compact large-field mid-wave infrared Cassegrain imaging system. By adding a lens in front of the Cassegrain system and reasonably arranging the position of the secondary mirror, the system length is greatly reduced, and the miniaturized design of the system is realized. By moving the focusing mirror, the system can achieve clear imaging within a wide temperature range, belonging to the field of optical design. Background Art

[0002] Infrared imaging technology mainly uses the radiation temperature difference generated between the detected target and the background to collect information and form corresponding scene images. Infrared thermal imaging technology has strong anti-interference ability and can work all-weather. Because of such advantages, it is widely used in many fields such as reconnaissance, early warning, remote sensing, navigation, and forest fire prevention.

[0003] In recent years, infrared thermal imaging has been developing towards miniaturization. Especially in special fields with limited space such as airborne and missile-borne, the Cassegrain system adopts a catadioptric structure, which can greatly reduce the system length and is widely used in the miniaturized design of long focal lengths.

[0004] The current problem is that the existing Cassegrain system still has a relatively long system length. In some extreme cases, it still cannot be placed in areas with limited space such as airborne and missile-borne. Summary of the Invention

[0005] The purpose of the utility model is to provide a compact large-field mid-wave infrared Cassegrain imaging system. In this imaging system, by adding a lens in front of the Cassegrain system and reasonably arranging the position of the secondary mirror, the system length is greatly reduced, and the miniaturized design of the system is realized. This imaging system can be used in systems with limited space such as airborne or missile-borne and requiring a long focal length. This imaging system realizes clear imaging of wide and narrow fields within a wide temperature range of -40°C to 60°C by moving the focusing mirror.

[0006] In order to achieve the above technical purpose, the utility model adopts the following technical solutions:

[0007] A compact large-field mid-wave infrared Cassegrain imaging system, the imaging system includes an aspheric lens one with an opening along the optical axis direction, a primary mirror, a secondary mirror, and an aspheric lens two arranged in sequence; there is an opening in the middle of the aspheric lens one with an opening, and the secondary mirror is located at the opening of the aspheric lens one with an opening; the aspheric lens one with an opening is a meniscus positive lens, the primary mirror is a parabolic mirror, the secondary mirror is a spherical mirror, and the aspheric lens two is a meniscus positive lens.

[0008] Further, the focal length of the first perforated aspherical lens is f1, where 300 mm < f1 < 1000 mm. Both the front surface and the rear surface of the first perforated aspherical lens are high-order aspherical surfaces. Both the front surface and the rear surface of the second aspherical lens are high-order aspherical surfaces, and its focal length is f2, where 50 mm < f2 < 100 mm.

[0009] Further, the focal length of the imaging system is 110 mm, the F# is less than or equal to 1.67, and the clear aperture is 65 mm.

[0010] Further, the first perforated aspherical lens is made of germanium.

[0011] Further, the primary mirror is made of glass-ceramics.

[0012] Further, the second aspherical lens can be adjusted and moved as a focusing lens.

[0013] The imaging system of the present utility model has the following beneficial effects:

[0014] 1) The imaging system of the present utility model has a relatively large relative aperture and a very short length, which can meet the requirements of miniaturized design.

[0015] 2) The imaging system of the present utility model has good imaging quality and small distortion, and is applicable to high-resolution mid-wave infrared detectors. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the compact large-field-of-view mid-wave infrared Cassegrain imaging system of the present utility model;

[0017] Figure 2 It is a three-dimensional model diagram of the compact large-field-of-view mid-wave infrared Cassegrain imaging system of the present utility model;

[0018] Figure 3 It is the MTF diagram of the compact large-field-of-view mid-wave infrared Cassegrain imaging system of the present utility model at 30 lp / mm;

[0019] Figure 4 It is the spot diagram of the compact large-field-of-view mid-wave infrared Cassegrain imaging system of the present utility model;

[0020] Figure 5 It is the distortion diagram of the compact large-field-of-view mid-wave infrared Cassegrain imaging system of the present utility model. Detailed Embodiments

[0021] The following specific embodiments are used to further illustrate the present utility model:

[0022] This embodiment provides a compact mid-wave infrared Cassegrain imaging system with a large field of view. In this imaging system, by adding a lens in front of the Cassegrain system and reasonably arranging the position of the secondary mirror 3, the system length is greatly reduced, realizing the miniaturized design of the system. By moving the focusing mirror, clear imaging can be achieved within a wide temperature range of the system.

[0023] See Figure 1 , the imaging system of this embodiment includes four parts: an aspherical lens with an aperture 1, a primary mirror 2, a secondary mirror 3, and an aspherical lens 4. This imaging system is a refractive-reflective-refractive optical system, which has the advantages of a large field of view, high resolution, and miniaturization.

[0024] These lenses or mirrors are all set based on the optical axis of the imaging system. Along the optical axis direction, they are, in sequence, the aspherical lens with an aperture 1, the primary mirror 2, the secondary mirror 3, and the aspherical lens 4. Among them, the aspherical lens with an aperture 1, the primary mirror 2, and the secondary mirror 3 are all fixedly set, and their relative positions are fixed, while the aspherical lens 4, as the focusing mirror, can be adjusted and moved.

[0025] The aspherical lens with an aperture 1 is a meniscus positive lens with a focal length of f1, where 300mm < f1 < 1000mm. The front surface and the rear surface of this aspherical lens with an aperture 1 are both high-order aspherical surfaces. This aspherical lens with an aperture 1 is located in front of the primary mirror 2. There is an aperture in the middle of the aspherical lens with an aperture 1, and the diameter of the aperture is larger than the diameter of the secondary mirror 3 and as small as possible to ensure that there is no interference during assembly and adjustment.

[0026] The primary mirror 2 is a parabolic mirror, and its optical parameters are shown in Table 1.

[0027] The secondary mirror 3 is a spherical mirror, and its optical parameters are shown in Table 1. This secondary mirror 3 is located at the aperture of the aspherical lens with an aperture 1.

[0028] The aspherical lens 4 is a meniscus positive lens. The front surface and the rear surface of this aspherical lens 4 are both high-order aspherical surfaces, and its focal length is f2, where 50mm < f2 < 100mm.

[0029] The imaging system of this embodiment has a focal length of 110mm, F# is less than or equal to 1.67, the clear aperture is 65mm, and the length from the front surface of the aspherical lens with an aperture 1 to the image plane is only 49mm, which is less than half of the system focal length.

[0030] In the imaging system of this embodiment, by adding a lens in front of the Cassegrain system and reasonably arranging the position of the secondary mirror 3, the system length is greatly reduced, realizing the miniaturized design of the system.

[0031] The imaging system of this embodiment can achieve clear imaging of wide and narrow fields of view in a wide temperature range of -40°C to 60°C by moving the focusing lens.

[0032] The imaging system of this embodiment has a spot diameter of less than 13μm in the working wavelength range of 3 - 5μm, which is suitable for high-resolution mid-wave infrared detectors; this imaging system has a large field of view of 1.3°, few lens elements, and high transmittance.

[0033] The imaging system of this embodiment can achieve clear imaging in a wide temperature range by moving the aspheric lens II 4 back and forth for focusing compensation.

[0034] In the imaging system of this embodiment, a protective window 5 is also provided, and this protective window 5 is arranged behind the aspheric lens II 4.

[0035] See Figures 2 to 5 , it can be seen from the MTF curve graph and the point spread function graph that the imaging quality of this imaging system is good and can meet the imaging requirements of high resolution. It can be seen from the distortion graph that the distortion of this imaging system is less than 0.5%.

[0036] The parameters of the imaging system of the present utility model are shown in Table 1:

[0037] Table 1 Parameters of the Imaging System

[0038]

[0039]

[0040] The aspheric surface satisfies the following expression:

[0041]

[0042] Table 2 Aspheric Surface Parameters

[0043] Aspherical surface k A B C D 1 -13.3397 -6.5797e-007 4.1782e-010 1.3653e-013 -3.4584e-017 2 -20.1284 -6.8759e-007 4.71632e-010 9.77703e-014 -9.22798e-018 3 13.6972 0.00013781 2.47601e-007 -1.33098e-009 6.24299e-012 4 -0.1980 0.00010898 5.01102e-007 -6.01401e-010 2.38701e-011

[0044] The above are only the preferred embodiments of the present utility model and are not intended to limit the protection scope of the present utility model. Therefore, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A compact, large-field-of-view medium-wave infrared Cassegrain imaging system, characterized by: The imaging system includes an aspherical lens one with an aperture (1), a primary mirror (2), a secondary mirror (3), and an aspherical lens two (4) arranged in sequence along the optical axis direction; The aspherical lens one with an aperture (1) has an aperture in the middle, and the secondary mirror (3) is located at the aperture of the aspherical lens one with an aperture (1); The aspherical lens one with an aperture (1) is a meniscus positive lens, the primary mirror (2) is a parabolic mirror, the secondary mirror (3) is a spherical mirror, and the aspherical lens two (4) is a meniscus positive lens.

2. The compact large-field-of-view medium-wave infrared Cassegrain imaging system according to claim 1, characterized in that: The focal length of the aspherical lens one with an aperture (1) is f1, 300mm < f1 < 1000mm, and both the front surface and the rear surface of the aspherical lens one with an aperture (1) are high-order aspherical surfaces; Both the front surface and the rear surface of the aspherical lens two (4) are high-order aspherical surfaces, and the focal length is f2, 50mm < f2 < 100mm.

3. The compact large-field-of-view medium-wave infrared Cassegrain imaging system according to claim 1, characterized in that: The focal length of the imaging system is 110mm, F# is less than or equal to 1.67, and the clear aperture is 65mm.

4. The compact large-field-of-view medium-wave infrared Cassegrain imaging system according to claim 1, characterized in that: The aspherical lens one with an aperture (1) is made of germanium material.

5. The compact large-field-of-view medium-wave infrared Cassegrain imaging system according to claim 1, characterized in that: The primary mirror (2) is made of glass-ceramics material.

6. The compact large-field-of-view medium-wave infrared Cassegrain imaging system according to claim 1, characterized in that: The aspherical lens two (4) can be adjusted and moved as a focusing lens.

Images