Ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system

Abstract

The invention discloses a medium-wave infrared optical system with a super large zoom ratio of 50×, which comprises a front group, a rear group and two folding reflectors from the object side to the image side, wherein: the front group comprises a coaxial front lens group 1, a zoom lens, a compensating lens and a focusing lens, and the front group also comprises a reflector 1; the rear group comprises a rear lens group 1, a rear lens group 2, a reflector 2 and a rear lens group 3; the imaging light beam of the object side is incident on the front lens group 1, the zoom lens, the compensating lens and the focusing lens, and is folded and reflected on the reflector 1 for a primary imaging, and then passes through the rear lens group 1 and the rear lens group 2, and is folded and reflected on the reflector 2, and is formed on the detector for a secondary imaging through the rear lens group 3. The invention has the characteristics of long focal length, small size, light weight and high resolution, and has good imaging quality at all focal lengths.

Description

Technical Field

[0001] The invention discloses an infrared optical system, in particular to a medium-wave infrared optical system with a super large zoom ratio of 50× and continuous zoom suitable for a high-resolution medium-wave refrigeration detector. Background Art

[0002] Infrared optical systems have strong nighttime penetration, good concealment, and are not easily interfered with. With the development of infrared cooling detectors in recent years, infrared imaging optical systems are frequently used in optoelectronic equipment in the fields of navigation, alert, and reconnaissance. Continuous zoom infrared systems can search, track, and aim at targets. In the process of switching between large and small fields of view, the stability and continuity of the image can be maintained, and the target image will not be lost and can remain clear, while taking into account large field of view search and small field of view resolution. Continuous zoom optical systems are divided into optical compensation and mechanical compensation according to different image plane compensation methods. Optical compensation is the linear movement of one or more lenses in the lens, which can only make the system overlap the image plane at a limited number of focal length positions and cannot meet the requirements of continuous zoom. Mechanical compensation is the linear movement of the zoom lens group to change the focal length. The compensation lens group compensates for the image plane displacement caused by the movement of the zoom lens group through nonlinear movement of the cam, which can meet the requirements of continuous zoom.

[0003] Compared with conventional equipment, the ultra-large zoom ratio continuous zoom optical system can simultaneously have a larger search range and higher detail capture capability, has great military application value, and is the main development direction of future infrared imaging. Summary of the invention

[0004] The purpose of the present invention is to provide a medium-wave infrared optical system with an ultra-large zoom ratio of 50× continuous zoom, which has the characteristics of large zoom ratio, large field of view, long focal length, small size, light weight and high resolution, and has good imaging quality in the entire focal length.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] Provided is a medium-wave infrared optical system with a super large zoom ratio of 50× continuous zoom, which includes a front group, a rear group and two folding reflectors from the object side to the image side, wherein:

[0007] The front group includes a coaxial front lens group 1, a zoom lens, a compensating lens, and a focusing lens, and the front group also includes a reflecting mirror 1 to change the optical path;

[0008] The rear group includes rear lens group 1, rear lens group 2, reflector 2, and rear lens group 3;

[0009] The imaging beam on the object side enters the front lens group 1, the zoom lens, the compensation lens, and the focusing lens, and is folded and reflected on the reflector 1 to form an image. Then, it passes through the rear lens group 1 and the rear lens group 2, and is folded and reflected on the reflector 2. It passes through the rear lens group 3 to form a secondary image on the detector.

[0010] During continuous zooming, the zoom lens moves linearly along the optical axis in a direction away from the front lens group, and the compensation lens moves nonlinearly in a direction close to the front lens group to compensate for the image plane movement caused by the focal length change.

[0011] Following the above technical solution, the front lens group 1 is a meniscus silicon positive lens with a convex surface facing the object, the zoom lens is a double concave silicon negative lens, the compensation lens is a double convex germanium positive lens, the focusing lens is a meniscus silicon negative lens with a convex surface facing the image side, the rear lens group 1 is a plano-convex silicon positive lens, the rear lens group 2 is a meniscus germanium negative lens with a convex surface facing the image side, the rear lens group 3 is a meniscus silicon positive lens with a convex surface facing the object side, and the reflector 1 and the reflector 2 are both plane reflectors turned 45°.

[0012] According to the above technical solution, the focal length range of the lens of the optical system is 13.2 mm to 665 mm, and the F number is 5.5.

[0013] According to the above technical solution, the second surface of the zoom lens is an aspherical diffraction surface, and the first surface of the focusing lens and the second surface of the rear lens group 1 are both aspherical surfaces.

[0014] According to the above technical solution, along the optical axis direction, the distance between the vertex of the first surface of the magnification mirror and the vertex of the second surface of the front lens group is 49mm~98mm, the distance between the vertex of the second surface of the magnification mirror and the vertex of the first surface of the compensation mirror is 110mm~7mm, and the distance between the vertex of the second surface of the compensation mirror and the vertex of the first surface of the focusing mirror is 19.8mm~73.8mm.

[0015] According to the above technical solution, the zoom curve of the optical system is smooth without inflection point.

[0016] The ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system of the present invention can be applied to a 640*512 medium-wave refrigerated detector.

[0017] The beneficial effects of the present invention are as follows: the continuous zoom medium-wave infrared optical system of the present invention adopts a secondary imaging structure, which not only meets 100% cold aperture efficiency, but also can compress the aperture of the front lens group; in addition, the lens adopts two folding reflectors to perform U-shaped folding of the light path, compressing the lateral and longitudinal dimensions of the system, with a small volume and a compact structure; and the lens has a wide focal length range and a zoom ratio of up to 50×, which can simultaneously have a larger search range and a higher detail capture capability.

[0018] Furthermore, the continuous zoom medium-wave infrared optical system of the present invention is well corrected for the aberration of each zoom point by means of establishing a reasonable initial structure, appropriately complicating the front fixed group, and reasonably constructing the optical focal length and materials. The present invention adopts a secondary imaging and positive group compensation zoom structure. The secondary imaging component can compress the aperture of the front group lens to meet 100% cold aperture efficiency. The positive group compensation structure can achieve better imaging quality. The system includes a front group, a rear group and two folding reflectors, and the reflectors are mainly used to compress the size. In the process of zooming, the zoom lens and the compensation lens are moved back and forth along the optical axis to achieve the purpose of continuous zooming. The present invention has the characteristics of long focal length, small size, light weight and high resolution, and has good imaging quality at all focal lengths.

[0019] Furthermore, the zoom cam curve of the continuous zoom medium-wave infrared optical system of the present invention is smooth without inflection points, and the imaging quality of the entire focal length is good.

[0020] Furthermore, the continuous zoom medium-wave infrared optical system of the present invention strictly controls the cold reflection effect, that is, controls the RMS value of the detector and the cold screen after being reflected by various surfaces of the lens and finally appearing on the detector target surface, and no ghost image occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0022] Figure 1 is a schematic diagram of an optical system of the present invention;

[0023] In the figure, 1-front lens group 1, 2-variator, 3-compensator, 4-focusing lens, 5-reflector 1, 6-rear lens group 1, 7-rear lens group 2, 8-reflector 2, 9-rear lens group 3;

[0024] Figure 2 is a short-focus two-dimensional diagram of the optical system of the present invention;

[0025] Figure 3 A two-dimensional diagram of the focus in the optical system of the present invention;

[0026] Figure 4 is a two-dimensional diagram of the optical system of the present invention;

[0027] Figure 5 This is the MTF diagram of the optical system of the present invention at the short focal end of 32lp / mm;

[0028] Figure 6 This is the MTF diagram of the optical system of the present invention when the focal end is 32lp / mm;

[0029] Figure 7 This is the MTF diagram of the optical system of the present invention at the telephoto end of 32lp / mm;

[0030] Figure 8 It is a diagram of the short focal end points of the optical system of the present invention;

[0031] Fig. 9 A diagram of focal end points in the optical system of the present invention;

[0032] Fig.10 It is a diagram of the telephoto end points of the optical system of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] like Figure 1 As shown, the ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system of the embodiment of the present invention includes a front group, a rear group and two folding reflectors, wherein the front group includes a front lens group 1, a zoom lens 2, a compensating lens 3, a focusing lens 4 and a total of four lenses, and the rear group includes a rear lens group 1 6, a rear lens group 2 7, and a rear lens group 3 9 and a total of three lenses. The object-side imaging light beam passes through the front lens group 1, the zoom lens 2, the compensating lens 3, and the focusing lens 4 in sequence, and is folded and reflected on the reflector 1 5 to form an image once, and then passes through the rear lens group 1 6, the rear lens group 2 7, and is folded and reflected on the reflector 2 8, and is formed on the detector for a second time through the rear lens group 3 9, and a clear image of the full focal length is obtained by the relative movement of the zoom lens 2 and the compensating lens 3 along the optical axis. Figure 1 The solid line of the medium optics is the short focal position and the dashed line is the long focal position.

[0035] Furthermore, the optical lens materials are silicon and germanium, which are commonly used materials in infrared optical systems. The incident direction of light is the object side, and the emitting direction of light is the image side. The front lens group 1 is a meniscus silicon positive lens convex to the object side, the zoom lens 2 is a double concave silicon negative lens, the compensation lens 3 is a double convex germanium positive lens, the focusing lens 4 is a meniscus silicon negative lens convex to the image side, the rear lens group 6 is a plano-convex silicon positive lens, the rear lens group 2 7 is a meniscus germanium negative lens convex to the image side, the rear lens group 3 9 is a meniscus silicon positive lens convex to the object side, the reflector 1 5 and the reflector 2 8 are both plane reflectors turned 45°, and the materials are all k9 glass.

[0036] The ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system of the present invention has a focal length of 13.2 mm to 665 mm, and during the zooming process, the F number is kept constant at 5.5.

[0037] The imaging beam from the object side passes through the front lens group 1, the zoom lens 2, the compensating lens 3, and the focusing lens 4 in sequence, and is folded on the reflector 15 to form an image, and then passes through the rear lens group 16 and the rear lens group 27, and is folded on the reflector 28, and then passes through the rear lens group 3 9 and the cold aperture to form a secondary image on the detector. When the optical system switches from the short focal length 13.2mm to the long focal length 665mm, the zoom lens 2 performs linear movement along the optical axis away from the front lens group 1 to achieve zooming, and the compensating lens 3 performs nonlinear movement toward the front lens group 1 to compensate for the image plane movement caused by the focal length change, and achieves a continuous zoom of 50×.

[0038] Specifically, in one embodiment of the present invention, the optical system includes 7 lenses and two folding reflectors. The front lens group 1 is a meniscus silicon positive lens convex to the object side, and the zoom lens 2 is a biconcave silicon negative lens, whose second surface is an aspheric diffraction surface, and the aspheric coefficient is K = 0, A = -3.56×10 -6 , B = -8.29 × 10 -9 , the diffraction surface coefficient is C1=1.05×10 -4 , C2=4.37×10 -8 The compensation lens 3 is a biconvex germanium positive lens, and the focusing lens 4 is a meniscus silicon negative lens convex to the image side, the first surface of which is aspherical, and the aspheric coefficient is A = 3.77 × 10 -7 , B = -2.55 × 10 -10 , C = 1.79 × 10 -13 , the reflector 5 is a K9 plane glass folded 45°, the rear lens 6 is a plano-convex silicon positive lens, the second surface of which is aspherical, and the aspherical coefficient is A = -6.82×10 -7 , B=9.62×10 -9 The rear lens group 27 is a meniscus germanium negative lens convex to the image side, the rear lens group 39 is a meniscus silicon positive lens convex to the object side, and the reflector 29 is a K9 plane glass folded 45°.

[0039] Furthermore, one or two surfaces of the front lens group with the largest aperture adopt a spherical design, avoiding the use of an aspherical design, simplifying the processing technology, reducing costs, and easily ensuring accuracy.

[0040] Furthermore, the lens adopts a secondary imaging structure, which not only meets 100% cold aperture efficiency, but also can compress the aperture of the front lens group; two folding mirrors are used to perform U-shaped folding of the light path, compressing the lateral and longitudinal dimensions of the system, with a small size and compact structure.

[0041] Furthermore, along the optical axis direction, the distance between the vertex of the first surface of the zoom lens 2 and the vertex of the second surface of the front lens group 1 is 49mm~98mm, the distance between the vertex of the second surface of the zoom lens 2 and the vertex of the first surface of the compensation lens 3 is 110mm~7mm, and the distance between the vertex of the second surface of the compensation lens 3 and the vertex of the first surface of the focusing lens 4 is 19.8mm~73.8mm. The zoom curve of the optical system is smooth without inflection point, which is suitable for processing and installation.

[0042] Furthermore, in the embodiment of the present invention, the distance between the vertex of the first surface of the front lens group 1 and the reflector 6 along the optical path is 261 mm, the distance between the reflector 6 and the reflector 2 9 along the optical path is 76.15 mm, and the reflector 2 9 is 53.5 mm away from the image plane.

[0043] In a preferred embodiment of the present invention, specific parameters of each optical structure in the ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system are shown in Table 1 below.

[0044] Table 1 Specific parameters of the optical system

[0045]

[0046] Figure 2 The short-focus two-dimensional diagram of the optical system of the present invention, the zoom lens and the compensating lens are located at Figure 1 Solid line position, focal length 13.2mm.

[0047] Figure 3 This is a two-dimensional diagram of the focal length of the optical system of the present invention. The zoom lens and the compensating lens move relative to each other and are located between the solid line and the dotted line positions. The focal length is 320 mm.

[0048] Figure 4 The optical system of the present invention is a two-dimensional diagram of the telephoto focus, where the zoom lens and the compensating lens are located Figure 1 At the dotted line, the focal length is 665mm.

[0049] Figure 5 This is the MTF diagram of the optical system of the present invention at the short focal end of 32lp / mm, with the zoom lens and the compensation lens located at Figure 1 Solid line position, transfer function curve of each field of view with focal length of 13.2mm.

[0050] Figure 6 It is the MTF diagram of the optical system of the present invention when the focal end is 32lp / mm. The magnification changer and the compensation mirror move relatively and are located between the solid line and the dotted line positions. It is the transfer function curve of each field of view of the 320mm focal length.

[0051] Figure 7 This is the MTF diagram of the optical system of the present invention at the telephoto end of 32lp / mm, with the zoom lens and the compensation lens located at Figure 1 The dotted line shows the transfer function curves for each field of view at a focal length of 665mm.

[0052] Figure 8 The short focal point diagram of the optical system of the present invention, the zoom lens and the compensating lens are located at Figure 1 The solid line shows the size of the diffuse spot in each field of view with a focal length of 13.2 mm.

[0053] Fig. 9 This is a diagram of focal point ends in the optical system of the present invention. The zoom lens and the compensating lens move relative to each other and are located between the solid line and the dotted line positions. The size of the diffuse spot in each field of view at a focal length of 320 mm.

[0054] Fig.10 The optical system of the present invention is a telephoto end point diagram, where the zoom lens and the compensating lens are located Figure 1 The dotted line shows the size of the diffuse spot in each field of view with a focal length of 665 mm.

[0055] The invention has a wide focal range and a large zoom ratio, and has a larger search range and higher detail capture capability. The smaller the focal length, the larger the field of view. The field of view of the optical system of the invention reaches more than 40°, which can quickly realize the search for the target. The larger the focal length, the easier it is to realize the resolution and tracking of the target. The optical system of the invention only uses seven lenses and two reflectors to achieve 50× continuous zoom. The fewer the number of lenses, the higher the transmittance and the stronger the energy. The optical system of the invention only uses three aspherical surfaces, and the aperture is not large, the cost is low, and it is easy to process. The transfer function of each focal position of the system of the invention is close to the diffraction limit, the diffuse spot is small, and it can focus clearly in an environment of -40℃ to +70℃.

[0056] The shorter the focal length, the more likely it is to have cold reflections. When designing an optical system, it is necessary to control the RMS value of the light from the detector and the cold screen after being reflected by each lens surface and imaged on the detector target surface. The continuous zoom medium-wave infrared optical system of the present invention has a short focal length of only 13.2mm, which is prone to ghost images. The cold reflection effect is strictly controlled, that is, the RMS value of the light from the detector and the cold screen after being reflected by each lens surface and finally imaged on the detector target surface is controlled, so that ghost images will not appear.

[0057] The short focal length of the optical system is too short, the long focal length is too long, and if the zoom ratio needs to reach 50 times, the long and short focal length aberrations are extremely difficult to correct, and it is difficult to simultaneously meet the requirements of good imaging quality in the full focal length range. The present invention establishes a reasonable initial structure, appropriately complicates the front fixed group, and adopts aspherical surfaces on the zoom lens and the focusing lens in order to effectively correct chromatic aberration and balance aberration. The compensation method adopts the form of positive group compensation, and in order to make the optical system achieve good high and low temperature focusing effects, the focal length of the focusing lens is adjusted and the optical focal length is distributed, and finally a system with good imaging quality in the full focal length range is obtained.

[0058] In summary, the ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system of the present invention adopts the structural form of secondary imaging and positive group compensation zoom. The secondary imaging component can compress the aperture of the front group lens to meet 100% cold aperture efficiency. The positive group compensation structural form can achieve better imaging quality. The system includes a front group, a rear group and two folding reflectors, and the reflectors are mainly used to compress the size. In the process of zooming, the zoom lens 2 and the compensation lens 3 are moved forward and backward along the optical axis to achieve the purpose of continuous zooming. The present invention has the characteristics of long focal length, small size, light weight and high resolution, and has good imaging quality at all focal lengths.

[0059] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A medium-wave infrared optical system with a super large zoom ratio of 50× continuous zoom, characterized in that: From the object side to the image side, it includes the front group, the rear group and two folding reflectors, among which: The front group includes a coaxial front lens group 1, a zoom lens, a compensating lens, and a focusing lens, and the front group also includes a reflecting mirror 1 to change the optical path; The rear group includes rear lens group 1, rear lens group 2, reflector 2, and rear lens group 3; The imaging beam on the object side enters the front lens group 1, the zoom lens, the compensation lens, and the focusing lens, and is folded and reflected on the reflector 1 to form an image. Then, it passes through the rear lens group 1 and the rear lens group 2, and is folded and reflected on the reflector 2. It passes through the rear lens group 3 to form a secondary image on the detector. During continuous zooming, the zoom lens moves linearly along the optical axis in a direction away from the front lens group, and the compensating lens moves nonlinearly in a direction close to the front lens group to compensate for the image plane movement caused by the change in focal length. Among them, the front lens group 1 is a meniscus silicon positive lens with a convex surface facing the object, the zoom lens is a double concave silicon negative lens, the compensation lens is a double convex germanium positive lens, the focusing lens is a meniscus silicon negative lens with a convex surface facing the image, the rear lens group 1 is a plano-convex silicon positive lens, the rear lens group 2 is a meniscus germanium negative lens with a convex surface facing the image, the rear lens group 3 is a meniscus silicon positive lens with a convex surface facing the object, and the reflector 1 and the reflector 2 are both plane reflectors folded 45°; The second surface of the zoom lens is an aspherical diffraction surface, and the first surface of the focusing lens and the second surface of the rear lens group 1 are both aspherical surfaces; The lens focal length range of this optical system is 13.2mm to 665mm, and the F number is 5.

5.

2. The ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system according to claim 1, characterized in that: Along the optical axis, the distance between the vertex of the first surface of the magnification mirror and the vertex of the second surface of the front lens group is 49mm~98mm, the distance between the vertex of the second surface of the magnification mirror and the vertex of the first surface of the compensation mirror is 110mm~7mm, and the distance between the vertex of the second surface of the compensation mirror and the vertex of the first surface of the focusing mirror is 19.8mm~73.8mm.

3. The ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system according to any one of claims 1-2, characterized in that: The zoom curve of this optical system is smooth without inflection point.

4. Application of the ultra-large zoom ratio 50× continuous zoom medium-wave infrared optical system according to any one of claims 1 to 3 in a 640*512 medium-wave cooled detector.

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