Long-focus compact high-resolution athermalization type visible light imaging system

Abstract

The invention discloses a long-focus compact high-resolution athermalization type visible light imaging system, and relates to the technical field of optical system design, and the system comprises an optical window, and a reflector group, a first fixed group, a relay lens group and an aberration correction group which are arranged on the same optical axis in sequence from front to back in the light beam incidence direction; the reflector group comprises a secondary reflector and a primary reflector which are arranged in sequence; the first fixed group comprises a first lens and a second lens which are arranged in sequence, and a first image surface is formed between the front of the first fixed group and the secondary reflector; the relay lens group comprises a third lens, a fourth lens and a fifth lens which are arranged in sequence, and the third lens is arranged on the side, away from the first lens, of the second lens; the aberration correction group comprises a sixth lens and a seventh lens which are sequentially arranged, and the sixth lens is arranged on the side, away from the fourth lens, of the fifth lens. According to the system, system aberration can be eliminated and thermal defocus can be compensated through cooperation of the lens groups, so that a passive athermalization effect is achieved.

Description

Technical Field

[0001] The present invention generally relates to the technical field of optical system design, and in particular to a long-focus, compact, high-resolution, athermal visible light imaging system. Background Art

[0002] Long focal length, compact, high resolution, athermal visible light imaging systems have been widely used in military and civilian fields, such as security, traffic monitoring, forest fire prevention, border inspection, etc. Especially when imaging long-distance targets in harsh environments, they have irreplaceable advantages.

[0003] However, the longer the focal length and the higher the resolution of the optical system, the more complex its structure will be, and it will be more difficult to achieve a compact design of its outer envelope. At the same time, optical passive athermalization is to reasonably match the temperature characteristics of different optical materials, thereby compensating for the thermal defocusing caused by temperature changes in the system, so that the system has excellent imaging effects in a wider temperature range. Compared with infrared systems, the surface shape of optical elements in visible light systems is relatively simple, which makes it relatively difficult to achieve optical passive athermalization in visible light systems. Therefore, a long-focus compact high-resolution athermalized visible light imaging system that can take into account both compact design and passive athermalization is urgently needed to fill the gap in the field of visible light imaging. Summary of the invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a compact, long-focus, compact, high-resolution, athermalized visible light imaging system having optical passive athermalization characteristics;

[0005] The present application provides a long-focus, compact, high-resolution, athermal visible light imaging system, the visible light imaging system comprising:

[0006] The optical window, a reflector group, a first fixed group, a relay group and an aberration correction group are sequentially included from front to back along the incident direction of the light beam;

[0007] The reflector group comprises: a secondary reflector and a primary reflector which are arranged in sequence, and the secondary reflector is arranged close to the optical window relative to the primary reflector; a light-through hole is opened in the middle of the primary reflector, and the light-through hole forms a space for placing the first fixed group, the relay mirror group and the aberration correction group; a side of the primary reflector close to the optical window is a primary reflective surface, and a side of the secondary reflector close to the primary reflector is a secondary reflective surface;

[0008] The first fixed group includes: a first lens and a second lens arranged in sequence, and the first lens is arranged on a side of the secondary reflector away from the optical window; a first image plane is formed between the front of the first fixed group and the secondary reflector;

[0009] The relay lens assembly comprises: a third lens, a fourth lens and a fifth lens which are arranged in sequence, and the third lens is arranged on a side of the second lens away from the first lens;

[0010] The aberration correction group comprises: a sixth lens and a seventh lens which are arranged in sequence, and the sixth lens is arranged on a side of the fifth lens away from the fourth lens;

[0011] The light beam incident from the optical window will be reflected to the secondary reflection surface via the primary reflection surface, and the secondary reflection surface will converge the light beam to the first image plane, and then be incident to the first fixed group, the relay lens group and the aberration correction group in sequence through the light hole.

[0012] According to the technical solution provided in the embodiment of the present application, in the reflector assembly,

[0013] The mirror surface of the secondary reflector close to the primary reflector is a convex surface;

[0014] The mirror surface of the primary reflector close to the secondary reflector is a concave surface, and an aperture stop of the visible light imaging system is placed on the concave surface of the primary reflector.

[0015] According to the technical solution provided in the embodiment of the present application, in the first fixed group,

[0016] The mirror surface of the first lens close to the secondary reflector is a concave surface, and the mirror surface of the first lens close to the second lens is a convex surface;

[0017] The second lens is a cemented lens, the second lens is composed of a negative power lens and a positive power lens, and the negative power lens is arranged close to the first lens relative to the positive power lens; the mirror surface of the negative power lens close to the negative power lens is a concave surface, and both side mirrors of the negative power lens are convex surfaces;

[0018] The first fixed group is used to diverge the light beams converged on the first image plane and compensate for thermal defocusing generated by the reflector group.

[0019] According to the technical solution provided in the embodiment of the present application, in the relay mirror assembly,

[0020] The mirror surface of the third lens close to the second lens is convex, and the mirror surface of the third lens close to the fourth lens is concave;

[0021] Both side surfaces of the fourth lens are convex surfaces;

[0022] The mirror surface of the fifth lens close to the fourth lens is a concave surface, and the mirror surface of the fifth lens close to the sixth lens is a convex surface;

[0023] The relay lens group is used to collimate the light beam incident through the first fixed group and correct part of the aberration.

[0024] According to the technical solution provided in the embodiment of the present application, in the aberration correction group,

[0025] The mirror surface of the sixth lens close to the fifth lens is a plane, and the mirror surface of the sixth lens close to the seventh lens is a convex surface;

[0026] The mirror surface of the seventh lens close to the sixth lens is a convex surface, and the mirror surface of the seventh lens away from the sixth lens is a concave surface, and a detector image plane is arranged on a side of the seventh lens away from the sixth lens;

[0027] The aberration correction group is used to converge the light beam collimated by the relay lens group to the detector image plane and correct the remaining aberration.

[0028] According to the technical solution provided in the embodiment of the present application, the material of the primary reflector is silicon single crystal, and it adopts a spherical structure;

[0029] The secondary reflector adopts an even-order aspherical structure;

[0030] The surface equation of the secondary reflector is as follows:

[0031]

[0032] Among them, Z represents the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis, c represents the vertex curvature of the surface, k represents the cone coefficient, α2, α3, α4 and α5 represent the aspherical coefficients.

[0033] According to the technical solution provided in the embodiment of the present application, taking the direction pointing to the object as positive, the curvature of the concave surface of the first lens is -5mm to -6mm, and the curvature radius of the convex surface is: 8mm to 9mm;

[0034] The thermal expansion coefficient of the negative power lens is 6.7×10 -6 / ℃, and its optical power is 0.03;

[0035] The curvature ratio of the front and rear surfaces of the negative power lens is 4.2, and its refractive index and Abbe number are between 1.7 and 1.8 and 36 and 38 respectively;

[0036] The thermal expansion coefficient of the positive power lens is 7.1×10 -6 / ℃, and its optical power is 0.067;

[0037] The curvature ratio of the front and rear mirror surfaces of the positive power lens is 0.63, and the refractive index and Abbe number thereof are respectively between 1.6 and 1.7 and between 57 and 60.

[0038] According to the technical solution provided in the embodiment of the present application, the refractive index and Abbe number of the third lens are respectively between 1.75 and 1.83 and 42 and 46, and the ratio of the curvature radii of the front and rear mirror surfaces thereof is 1.33;

[0039] The refractive index and Abbe number of the fourth lens are between 1.48 and 1.65 and 55 and 63 respectively, and the convex curvature of the fourth lens close to the third lens is between 22 mm and 30 mm; the diameter-to-thickness ratio of the fourth lens is 0.37;

[0040] The refractive index and Abbe number of the fifth lens are between 1.9 and 2.2 and 16 and 20 respectively, and the diameter-to-thickness ratio is 3.3; the curvature ratio of the front and rear surfaces of the fifth lens is 1:2.

[0041] According to the technical solution provided in the embodiment of the present application, the refractive index and Abbe number of the sixth lens are between 1.55 and 1.65 and 70 and 72 respectively, and its diameter-to-thickness ratio is 3.3; the convex curvature of the sixth lens is between 30 and 35 mm;

[0042] The refractive index and Abbe number of the seventh lens are between 1.6 and 1.68 and 20 and 24 respectively, and its diameter-to-thickness ratio is 2.8; the curvature ratio of the front and rear surfaces of the seventh lens is 1:1.

[0043] In summary, the technical solution specifically discloses a long-focus compact high-resolution athermal visible light imaging system, which comprises: an optical window and a reflector group arranged on the same optical axis, a first fixed group, a relay mirror group and an aberration correction group are sequentially included from front to back along the incident direction of the light beam; the reflector group comprises: a secondary reflector and a main reflector are sequentially arranged, and the secondary reflector is arranged close to the optical window relative to the main reflector; a light-through hole is opened in the middle of the main reflector, and a space is formed by the hole to place the first fixed group, the relay mirror group and the aberration correction group; the side of the main reflector close to the optical window is the main reflection surface, and the side of the secondary reflector close to the main reflector is the secondary reflection surface; the first fixed group comprises: A first lens and a second lens are arranged, and the first lens is arranged on a side of the secondary reflector away from the optical window; a first image plane is formed in front of the first fixed group and between the secondary reflector; the relay lens group includes: a third lens, a fourth lens and a fifth lens arranged in sequence, and the third lens is arranged on a side of the second lens away from the first lens; the aberration correction group includes: a sixth lens and a seventh lens arranged in sequence, and the sixth lens is arranged on a side of the fifth lens away from the fourth lens; a light beam incident from the optical window will be reflected to the secondary reflective surface via the main reflective surface, and the secondary reflective surface will then converge the light beam to the first image plane, and will be incident to the first fixed group, the relay lens group and the aberration correction group in sequence through the light hole.

[0044] The existing optical systems with longer focal lengths and higher resolutions have complex structures, which brings difficulties to compact design. At the same time, compared with infrared systems, the surface shape of optical elements in visible light systems is relatively simple, which makes it relatively difficult to achieve optical passive athermalization in visible light systems. Combining the above two situations, designing a long-focus, high-resolution visible light imaging system that takes into account compact design and achieves passive athermalization is a difficulty in the field of visible light imaging systems. This application designs an optical window and a reflector group, a first fixed group, a relay mirror group, and an aberration correction group arranged on the same optical axis, so that the coordination between the mirror groups can eliminate system aberrations, compensate for thermal defocus, and achieve the effect of passive athermalization. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0046] Figure 1 Schematic diagram of the structure of a long-focus, compact, high-resolution, athermal visible light imaging system.

[0047] Figure 2 This is the optical transfer function curve of a long-focus, compact, high-resolution, athermal visible light imaging system at room temperature of 20°C.

[0048] Figure 3This is the optical transfer function curve of a long-focus, compact, high-resolution athermal visible light imaging system at low temperature of -40℃.

[0049] Figure 4 This is the optical transfer function curve of a long-focus, compact, high-resolution athermal visible light imaging system at a high temperature of 60°C.

[0050] Figure 5 Field curvature distortion curve of a long-focus, compact, high-resolution, athermal visible light imaging system.

[0051] Numbers in the figure: 100, optical window; 101, secondary reflector; 102, primary reflector; 103, first image plane; 201, first lens; 202, second lens; 301, third lens; 302, fourth lens; 303, fifth lens; 401, sixth lens; 402, seventh lens; 501, detector image plane. DETAILED DESCRIPTION

[0052] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0053] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0054] Example 1

[0055] Please refer to Figure 1 The structure diagram of a telephoto compact high-resolution athermal visible light imaging system provided by the present embodiment is shown, wherein the visible light imaging system comprises: an optical window 100 and a reflector group, a first fixed group, a relay group, and an aberration correction group arranged on the same optical axis in sequence from front to back along the incident direction of the light beam;

[0056] The reflector group includes: a secondary reflector 101 and a primary reflector 102 which are arranged in sequence, and the secondary reflector 101 is arranged close to the optical window 100 relative to the primary reflector 102; a light-through hole is opened in the middle of the primary reflector 102, and the light-through hole forms a space for placing the first fixed group, the relay mirror group and the aberration correction group; a side of the primary reflector 102 close to the optical window 100 is a primary reflective surface, and a side of the secondary reflector 101 close to the primary reflector 102 is a secondary reflective surface;

[0057] The first fixed group includes: a first lens 201 and a second lens 202 arranged in sequence, and the first lens 201 is arranged on a side of the secondary reflector 101 away from the optical window 100; a first image plane 103 is formed between the front of the first fixed group and the secondary reflector 101;

[0058] The relay lens assembly includes: a third lens 301, a fourth lens 302 and a fifth lens 303 which are arranged in sequence, and the third lens 301 is arranged on a side of the second lens 202 away from the first lens 201;

[0059] The aberration correction group includes: a sixth lens 401 and a seventh lens 402 which are arranged in sequence, and the sixth lens 401 is arranged on a side of the fifth lens 303 away from the fourth lens 302;

[0060] The light beam incident from the optical window 100 will be reflected to the secondary reflection surface via the primary reflection surface, and the secondary reflection surface will then converge the light beam to the first image plane 103, and will be incident to the first fixed group, the relay lens group and the aberration correction group in sequence through the light hole.

[0061] Due to the widespread use of long focal length, compact, high resolution, athermal visible light imaging systems, the corresponding design requirements are becoming increasingly higher. In addition to the basic requirements of imaging clarity and resolution, they are also required to have a compact structure and good passive athermal performance. For example, the system disclosed in patent document CN110579859A has a total length of only 207.8 mm but still does not solve the athermal problem, and the system disclosed in patent document CN109597187A has a certain athermal effect, but has a low resolution and a relatively large spatial envelope.

[0062] In view of this, the present invention proposes a visible light imaging system with a spectral band of 450-650nm, a focal length of 500mm, a relative aperture of F5.5, a total length of 240mm, a resolution of 1920×1080, a pixel size of 3.45 microns, and optical passive athermalization characteristics. At the same time, when matching the detector, the system can maintain excellent imaging quality within the range of -40℃ to +60℃, and in order to effectively control the system stray light and reduce the spatial envelope of the system rear group, the system adopts a secondary imaging configuration.

[0063] In this embodiment, the visible light imaging system includes: an optical window 100 and a coaxially arranged reflector group, a first fixed group, a relay mirror group and an aberration correction group from front to back along the incident direction of the light beam.

[0064] See also Figure 1Here, the front and back in the position definition of each lens group is that the optical window 100 is the front and the detector image plane 501 that appears later is the back; similarly, the position definition of each lens group can also be set in sequence from the object side to the image side, see Figure 1 , actually refers to the direction from left to right.

[0065] Next, specifically, the reflector group includes: a secondary reflector 101 and a main reflector 102 which are arranged in sequence, and the secondary reflector 101 is arranged close to the optical window 100 relative to the main reflector 102, and the side of the main reflector 102 close to the optical window 100 is a primary reflective surface, and the side of the secondary reflector 101 close to the main reflector 102 is a secondary reflective surface. Such a design enables the reflector group to be responsible for first reflecting the light beam from the object side (i.e., the light beam injected through the optical window 100) through the primary reflective surface of the main reflector 102 to the secondary reflective surface of the secondary reflector 101. In order to reduce the proportion of light beam obstruction by the secondary reflector, the light beam incident on the secondary reflective surface is then converged on the first image plane 103 through the secondary reflective surface to form an image in front of the first fixed group.

[0066] It should be noted that the optical window 100 is composed of a cost-effective optical glass material with a refractive index between 1.5 and 1.7 and an Abbe number between 63 and 68. In order to ensure the strength of the window, the window diameter-to-thickness ratio is approximately 10:1. At the same time, the existence of the optical window 100 also provides a guarantee for the airtightness of the system.

[0067] In addition, a light-through hole is opened in the middle of the main reflector 102, and the light-through hole forms a space for placing the first fixed group, the relay lens group and the aberration correction group, thereby forming a co-optical axis setting of multiple lens groups, that is, the co-optical axis setting of the first fixed group, the relay lens group and the aberration correction group and the main reflector 102 is based on the opening of the light-through hole. The design of the light-through hole can facilitate the light beam to pass through the subsequent lens groups and finally converge to the detector image plane 501.

[0068] In a preferred embodiment, the mirror surface of the secondary reflector 101 close to the primary reflector 102 is convex; the mirror surface of the primary reflector 102 close to the secondary reflector 101 is concave, and the aperture stop of the visible light imaging system is placed on the concave surface of the primary reflector 102, thereby reducing the obstruction ratio of the secondary reflector 101 to the system; in addition, the ratio of the curvature of the primary reflector 102 to the focal length of the system is approximately 0.85.

[0069] Furthermore, in order to ensure that the system has no thermal effect, the main reflector 102 is made of silicon single crystal and has a spherical structure, which can also provide convenience for processing, testing, and assembly.

[0070] At the same time, in order to better correct the system aberration, the secondary reflector 101 adopts an even-order aspheric structure, so as to converge the light beam to the first image plane 103. At the same time, the curvature ratio of the secondary reflector 101 and the primary reflector 102 is 0.7, and the surface equation of the secondary reflector 101 is as follows:

[0071]

[0072] Among them, Z represents the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis, c represents the vertex curvature of the surface, k represents the cone coefficient, α2, α3, α4 and α5 represent the aspherical coefficients, and the aspherical coefficients (α2, α3, α4 and α5) of the secondary reflector 101 described in the present application are: -3.18799E-07, -5.87543E-1, 7.6888E-12, -4.62772E-14 and 2.44614E-17 respectively; k represents the cone coefficient and generally defaults to 0, and the vertex curvature can refer to the parameter introduction of the secondary reflector 101.

[0073] In a preferred embodiment, in order to further reduce the shielding coefficient of the secondary reflector 101 on the light beam, the ratio of the interval between the secondary reflector 101 and the primary reflector 102 to the focal length of the system can be set to about 0.3.

[0074] In a preferred embodiment, the first fixed group is responsible for diverging the light beam converged at the first image plane 103, and can also partially supplement the thermal defocus generated by the reflector group. The thermal defocus is defined as the phenomenon that temperature changes cause changes in the size of optical elements and supporting structures, thereby affecting the focal position of the system.

[0075] In the first fixed group, the mirror surface of the first lens 201 close to the secondary reflector 101 is a concave surface, and the mirror surface close to the second lens 102 is a convex surface, and the whole is a meniscus lens;

[0076] The second lens 202 is a cemented lens, which is composed of a negative power lens and a positive power lens, and the negative power lens is arranged close to the first lens 201 relative to the positive power lens; the mirror surface of the negative power lens close to the negative power lens is concave, and the two side mirrors of the negative power lens are convex; wherein the negative power lens and the positive power lens are, for example, a meniscus lanthanum flint lens J2 and a double convex lanthanum crown lens J3, respectively.

[0077] In addition, the first lens 201 and the second lens 202 also have the following design parameters:

[0078] The first lens 201 is made of low-refractive-index, high-dispersion barium crown meniscus glass.

[0079] Taking the direction pointing to the object as positive, the curvature of the concave surface of the first lens 201 is -5mm to -6mm, and the curvature radius of the convex surface is: 8mm to 9mm;

[0080] The thermal expansion coefficient of the negative power lens is 6.7×10 -6 / ℃, and its optical power is 0.03;

[0081] The curvature ratio of the front and rear surfaces of the negative power lens is 4.2, and its refractive index and Abbe number are between 1.7 and 1.8 and 36 and 38 respectively;

[0082] The thermal expansion coefficient of the positive power lens is 7.1×10 -6 / ℃, and its optical power is 0.067;

[0083] The curvature ratio of the front and rear mirror surfaces of the positive power lens is about 0.63, and its refractive index and Abbe number are between 1.6 and 1.7 and 57 and 60 respectively.

[0084] In a preferred embodiment, in order to effectively control system stray light, the first image plane 103 is located 10 mm in front of the first lens 201, and the aperture of a single field of view full-aperture light incident on the first lens 101 is about 3 mm.

[0085] In a preferred embodiment, the relay lens group is used to collimate the light beam incident through the first fixed group and correct partial aberrations. In addition, it also plays a certain role in compensating for the thermal defocus generated by the system. The partial aberrations here are mainly spherical aberration and vertical axis chromatic aberration.

[0086] Specifically, the mirror surface of the third lens 301 close to the second lens 202 is convex, and the mirror surface close to the fourth lens 302 is concave. The third lens 301 can be a meniscus lanthanum flint lens with a high refractive index.

[0087] Both sides of the fourth lens 302 are convex, and a high-dispersion biconvex barium crown lens can be used;

[0088] The mirror surface of the fifth lens 303 close to the fourth lens 302 is concave, and the mirror surface of the fifth lens 303 close to the sixth lens 401 is convex. The fifth lens 303 can be used for high-refractive-index, low-dispersion meniscus heavy flint glass.

[0089] In addition, the third lens 301, the fourth lens 302 and the fifth lens 303 also have the following design parameters:

[0090] The refractive index and Abbe number of the third lens 301 are between 1.75 and 1.83 and 42 and 46 respectively, the ratio of the curvature radii of the front and rear surfaces is 1.33, and the ratio of its focal length to the system focal length is 0.3.

[0091] The refractive index and Abbe number of the fourth lens 302 are between 1.48 and 1.65 and 55 and 63 respectively, and the convex curvature of the fourth lens 302 close to the third lens 301 is between 22 mm and 30 mm; the diameter-to-thickness ratio of the fourth lens 302 is 0.37;

[0092] In addition, the focal length of the fourth lens 302 and the system focal length are approximately 0.08, and the blocking ratio (ratio of diameter to curvature) of the mirror surface away from the third lens 301 is approximately 0.09.

[0093] The refractive index and Abbe number of the fifth lens 303 are between 1.9 and 2.2 and 16 and 20 respectively, and the diameter-to-thickness ratio is 3.3; the curvature ratio of the front and rear surfaces of the fifth lens 303 is 1:2.

[0094] In a preferred embodiment, the aberration correction group is responsible for converging the light beam collimated by the relay lens group to the detector image plane 501, and correcting the residual aberrations so that the aberrations of the system reach a balanced state. Here, the residual aberrations mainly refer to residual distortion, field curvature and dispersion, etc.

[0095] Specifically, in the aberration correction group, the mirror surface of the sixth lens 401 close to the fifth lens 303 is a plane, and the mirror surface of the sixth lens 401 close to the seventh lens 402 is a convex surface, and the whole is a plano-convex lens;

[0096] The mirror surface of the seventh lens 402 close to the sixth lens is convex, and the mirror surface away from the sixth lens 401 is concave. A detector image plane 501 is provided on the side of the seventh lens 402 away from the sixth lens 401;

[0097] The refractive index and Abbe number of the sixth lens 401 are between 1.55 and 1.65 and between 70 and 72 respectively, and its diameter-to-thickness ratio is 3.3; the convex curvature of the sixth lens 401 is between 30 and 35 mm;

[0098] The sixth lens 401 may be a heavy phosphorus crown plano-convex lens with low refractive index and high dispersion, so as to have higher dispersion capability and better balance system-related chromatic aberration.

[0099] The refractive index and Abbe number of the seventh lens 402 are between 1.6 and 1.68 and 20 and 24 respectively, and its diameter-to-thickness ratio is 2.8; the curvature ratio of the front and rear surfaces of the seventh lens 402 is 1:1, and the seventh lens 402 can be a heavy barium flint meniscus lens with extremely small optical power.

[0100] It should be noted that this system has excellent temperature adaptability under the premise of using an aluminum alloy lens barrel by reasonably matching lens materials with different linear expansion coefficients. It can produce clear images in the range of -40℃ to +60℃ without focusing. At the same time, compared with the existing visible light telephoto system, this system can match extremely small pixels, and the object space resolution is as high as 0.0138mrad. Although the system effect depends on the design parameters, most of the aforementioned parameters are range settings, and the specific selection needs to be determined based on the actual situation, so there is no special limitation.

[0101] Combine the following Figure 2-Figure 5 The performance of this system is described.

[0102] in, Figure 2-Figure 4 They are the optical transfer function curves of the visible light imaging system at room temperature 20℃, low temperature -40℃ and high temperature 60℃.

[0103] The optical transfer function curve is an important parameter for describing the imaging quality of an optical imaging system. It reflects the response of the optical system to different spatial frequencies of an object, that is, the aberration and astigmatism of the imaging system. Each optical transfer function curve uses the spatial frequency as the horizontal coordinate and the optical transfer function value as the vertical coordinate.

[0104] from Figure 2-Figure 4 It can be seen that when the system is at 20℃, -40℃ and 60℃, the optical transfer function value at the cutoff frequency of 145lp / mm is greater than 0.2, indicating that the system has a good ability to maintain the contrast and clarity of the image.

[0105] Figure 5 The field curvature distortion curve of the system is used to describe the field curvature distortion in the optical system. Field curvature distortion refers to the deviation between the image points at different positions and the ideal image points after the light passes through the optical system. It is used to reflect the imaging quality of the system and perform distortion correction.

[0106] Specifically, by Figure 5 It can be seen that the maximum distortion of the system is only 0.5, and the field curvature of each band is only 0.2, indicating that the system distortion and field curvature are well corrected, further indicating that the system has high imaging quality.

[0107] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A long-focus, compact, high-resolution, athermal visible light imaging system, characterized in that: The visible light imaging system comprises: an optical window (100) and a reflector group, a first fixed group, a relay mirror group and an aberration correction group arranged on the same optical axis, from front to back along the incident direction of the light beam; The reflector group comprises: a secondary reflector (101) and a primary reflector (102) which are arranged in sequence, and the secondary reflector (101) is arranged close to the optical window (100) relative to the primary reflector (102); a light-through hole is provided in the middle of the primary reflector (102), and the light-through hole forms a space in which the first fixed group, the relay mirror group and the aberration correction group can be placed; a side of the primary reflector (102) close to the optical window (100) is a primary reflective surface, and a side of the secondary reflector (101) close to the primary reflector (102) is a secondary reflective surface; The first fixed group comprises: a first lens (201) and a second lens (202) which are arranged in sequence, and the first lens (201) is arranged on a side of the secondary reflector (101) away from the optical window (100); a first image plane (103) is formed between the front of the first fixed group and the secondary reflector (101); The relay lens assembly comprises: a third lens (301), a fourth lens (302) and a fifth lens (303) which are arranged in sequence, and the third lens (301) is arranged on a side of the second lens (202) away from the first lens (201); The aberration correction group comprises: a sixth lens (401) and a seventh lens (402) which are arranged in sequence, and the sixth lens (401) is arranged on a side of the fifth lens (303) away from the fourth lens (302); The light beam incident from the optical window (100) is reflected from the primary reflection surface to the secondary reflection surface, and the secondary reflection surface then converges the light beam to the first image plane (103), and sequentially enters the first fixed group, the relay lens group, and the aberration correction group through the light hole.

2. The long-focus compact high-resolution athermal visible light imaging system according to claim 1, characterized in that: In the reflector assembly, The mirror surface of the secondary reflector (101) close to the primary reflector (102) is a convex surface; The mirror surface of the primary reflector (102) close to the secondary reflector (101) is a concave surface, and an aperture stop of the visible light imaging system is placed on the concave surface of the primary reflector (102).

3. The long-focus compact high-resolution athermal visible light imaging system according to claim 1, characterized in that: In the first fixed group, The mirror surface of the first lens (201) close to the secondary reflector (101) is a concave surface, and the mirror surface of the first lens (201) close to the second reflector (102) is a convex surface; The second lens (202) is a cemented lens, the second lens (202) is composed of a negative power lens and a positive power lens, and the negative power lens is arranged closer to the first lens (201) relative to the positive power lens; the mirror surface of the negative power lens close to the negative power lens is a concave surface, and both side mirror surfaces of the negative power lens are convex surfaces; The first fixed group is used to diverge the light beam converged on the first image plane (103) and compensate for thermal defocusing generated by the reflector group.

4. The long-focus compact high-resolution athermal visible light imaging system according to claim 1, characterized in that: In the relay lens assembly, The mirror surface of the third lens (301) close to the second lens (202) is a convex surface, and the mirror surface of the third lens (301) close to the fourth lens (302) is a concave surface; Both side surfaces of the fourth lens (302) are convex surfaces; The mirror surface of the fifth lens (303) close to the fourth lens (302) is a concave surface, and the mirror surface of the fifth lens (303) close to the sixth lens (401) is a convex surface; The relay lens group is used to collimate the light beam incident through the first fixed group and correct part of the aberration.

5. The long-focus compact high-resolution athermal visible light imaging system according to claim 1, characterized in that: In the aberration correction group, The mirror surface of the sixth lens (401) close to the fifth lens (303) is a plane, and the mirror surface of the sixth lens (401) close to the seventh lens (402) is a convex surface; The mirror surface of the seventh lens (402) close to the sixth lens is a convex surface, and the mirror surface of the seventh lens (402) far from the sixth lens (401) is a concave surface, and a detector image plane (501) is provided on a side of the seventh lens (402) far from the sixth lens (401); The aberration correction group is used to converge the light beam collimated by the relay lens group to the detector image plane (501) and correct the residual aberration.

6. The long-focus compact high-resolution athermal visible light imaging system according to claim 2, characterized in that: The main reflector (102) is made of silicon single crystal and has a spherical structure; The secondary reflector (101) adopts an even-order aspherical structure; The surface equation of the secondary reflector (101) is as follows: Among them, Z represents the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis, c represents the vertex curvature of the surface, k represents the cone coefficient, α2, α3, α4 and α5 represent the aspherical coefficients.

7. The long-focus compact high-resolution athermal visible light imaging system according to claim 3, characterized in that: Taking the direction pointing toward the object as positive, the curvature of the concave surface of the first lens (201) is -5mm to -6mm, and the curvature radius of the convex surface is 8mm to 9mm; The thermal expansion coefficient of the negative power lens is 6.7×10 -6 / ℃, and its optical power is 0.03; The curvature ratio of the front and rear surfaces of the negative power lens is: 4.2, and its refractive index and Abbe number are between 1.7 and 1.8 and 36 and 38 respectively; The thermal expansion coefficient of the positive power lens is 7.1×10 -6 / ℃, and its optical power is 0.067; The curvature ratio of the front and rear surfaces of the positive power lens is: 0.63, and its refractive index and Abbe number are between 1.6 and 1.7 and 57 and 60 respectively.

8. The long-focus compact high-resolution athermal visible light imaging system according to claim 4, characterized in that: The refractive index and Abbe number of the third lens (301) are respectively between 1.75 and 1.83 and between 42 and 46, and the ratio of the curvature radii of the front and rear surfaces thereof is 1.33; The refractive index and Abbe number of the fourth lens (302) are between 1.48 and 1.65 and between 55 and 63 respectively, and the curvature of the convex surface of the fourth lens (302) close to the third lens (301) is between 22 mm and 30 mm; the diameter-to-thickness ratio of the fourth lens (302) is 0.37; The refractive index and Abbe number of the fifth lens (303) are respectively between 1.9 and 2.2 and between 16 and 20, and the diameter-to-thickness ratio is 3.3; the curvature ratio of the front and rear surfaces of the fifth lens (303) is 1:

2.

9. The long-focus compact high-resolution athermal visible light imaging system according to claim 5, characterized in that: The refractive index and Abbe number of the sixth lens (401) are between 1.55 and 1.65 and between 70 and 72 respectively, and its diameter-to-thickness ratio is 3.3; the convex curvature of the sixth lens (401) is between 30 and 35 mm; The refractive index and Abbe number of the seventh lens (402) are between 1.6 and 1.68 and between 20 and 24 respectively, and its diameter-to-thickness ratio is 2.8; the curvature ratio of the front and rear surfaces of the seventh lens (402) is 1:1.

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