Large zoom ratio MWIR optical system with secondary mirror switching and thermal stop F number variation

Abstract

The application discloses a kind of big zoom ratio mid-wave infrared optical systems based on secondary mirror switching and thermal light diaphragm variation F number, switching of short focal length and long focal length channel is realized by the cut-in and cut-out of secondary mirror, optical system transmits large field of view of short, medium focal length, reflects small field of view of long focal length, share rear group optical system and detector assembly, compact structure, small volume.Simultaneously, the rear group with thermal light diaphragm is designed separately, realizes variable F number design, together with the cassegrain reflective front group, realizes super long focal length structure, so that mid-wave infrared has four focal length segments of super long focal length / long focal length / medium focal length / short focal length, to realize the integration of large aperture, small field of view, long focal length compact design and large field of view, short focal length, wherein the F number of short, medium, long focal length is 4, the F number of super long focal length is 7, the lens of the application is suitable for high-resolution 640x512, 15 microns mid-wave refrigeration type detector, with the characteristics of large aperture, long focal length, large field of view, four fields of view have good imaging quality.

Description

Technical Field

[0001] This invention belongs to the field of infrared optical system technology, and more specifically, relates to a large zoom ratio mid-wave infrared optical system based on secondary mirror switching and thermal aperture F-number, especially to a four-speed zoom optical system suitable for a 640×512 mid-wave cooled 15-micron detector. Background Technology

[0002] Currently, with the continuous development of infrared thermal imaging systems, higher requirements are being placed on infrared optical systems. To meet the widespread military applications of infrared detectors, the demand for high-performance, high-zoom-ratio infrared zoom optical systems is increasing. A large field of view enables target search, while a small field of view enables target tracking and aiming, meeting the development needs of today's rapidly evolving infrared thermal imaging systems. Therefore, high-performance, high-zoom-ratio infrared zoom optical systems are one of the important development directions for future infrared imaging optical systems.

[0003] Existing high zoom ratio infrared optical systems typically employ a transmissive "zoom group + compensation group" or a switching zoom structure, which is insufficient to meet the compact optical system requirements of airborne pods. Long focal length optical systems with reflective structures, such as Cassegrain and off-axis three-mirror systems, can significantly reduce size, facilitating long focal lengths, large apertures, and compact designs. However, the corresponding field of view is limited, and the relative aperture is relatively small, failing to meet the large field of view requirements of high zoom ratio systems. Transmissive optical systems are advantageous for designing large field of view and large relative aperture optical systems, such as high zoom ratio continuous zoom optical systems, but their size limitations prevent the implementation of ultra-long focal length designs.

[0004] With the development of infrared cooled detectors in recent years, infrared imaging optical systems have been frequently used in optoelectronic equipment in fields such as navigation, early warning, and reconnaissance. Therefore, how to achieve a large zoom ratio infrared optical system that combines long focal length, large field of view, small size, and light weight is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention proposes a high zoom ratio mid-wave infrared optical system based on secondary mirror switching and thermal stop variable F-number. The secondary mirror switching structure enables an optical system that achieves both long focal length and a large field of view. The thermal stop cut-in and cut-out design enables an even longer focal length. It features long focal length, large field of view, small size, and light weight, and all four field of view settings have good imaging quality.

[0006] To achieve the above objectives, the present invention provides a high zoom ratio mid-wave infrared optical system based on secondary mirror switching and thermal stop variable F-number, comprising: a Cassegrain reflection system, a common focusing group, a common rear group, a short focal length front group, a medium focal length front group, and a thermal stop rear group. The Cassegrain reflection system includes a primary mirror and a secondary mirror; the common focusing group includes a first focusing mirror and a second focusing mirror; the common rear group includes a first rear lens and a second rear lens; the short focal length front group includes a first short focal length front lens and a second short focal length front lens; the medium focal length front group includes a first medium focal length front lens and a second medium focal length front lens; and the thermal stop rear group includes a third rear lens, a fourth rear lens, and a thermal stop.

[0007] The object-side imaging beam sequentially passes through the first short-focal-length front lens, the second short-focal-length front lens, the first focusing lens, the second focusing lens, the first rear lens, and the second rear lens to form an image on the detector, thus constituting a short-focal-length optical system.

[0008] The short focal length front group cuts out, and the middle focal length front group cuts into the optical path, forming a middle focal length optical system;

[0009] The object-side imaging beam is reflected by the primary mirror and the secondary mirror in sequence to form an image. Then, it is imaged on the detector by the first focusing mirror, the second focusing mirror, the first rear lens group and the second rear lens group, thus forming a telephoto optical system.

[0010] The first and second rear lens groups are cut out, and the third, fourth, and thermal stops are cut into the optical path, forming an ultra-long focal length optical system.

[0011] According to the above technical solution, the material of the Cassegrain reflective system is microcrystalline glass, and the other lens materials are silicon and germanium, which are commonly used in mid-wave infrared optical systems.

[0012] Following the above technical solution, the incident direction of light is the object side, and the exit direction of light is the image side. The primary mirror is a concave mirror facing the object side, the secondary mirror is a convex mirror facing the image side, the first focusing lens is a meniscus negative germanium lens facing the object side, the second focusing lens is a meniscus positive silicon lens facing the object side, the first rear lens group is a convex meniscus positive silicon lens facing the object side, the second rear lens group is a convex meniscus negative germanium lens facing the object side, the first short focal length front lens group is a biconcave silicon positive lens, the second short focal length front lens group is a biconvex germanium negative lens, the first intermediate focal length front lens group is a convex meniscus positive silicon lens facing the object side, the second intermediate focal length front lens group is a convex meniscus negative germanium lens facing the object side, the third rear lens group is a convex meniscus negative germanium lens facing the image side, the fourth rear lens group is a convex meniscus positive silicon lens facing the object side, and the thermal stop is a spherical aluminum mirror facing the image plane.

[0013] Following the above technical solution, the system includes seven aspherical surfaces, wherein the primary mirror is a parabolic surface, the secondary mirror is a hyperboloid, the first surface of the second focusing lens near the object is an aspherical surface, the second surface of the first rear lens group away from the object is an aspherical surface, the first surface of the second short focal length front lens group near the object is an aspherical surface, the second surface of the second medium focal length front lens group away from the object is an aspherical surface, and the second surface of the third rear lens group away from the object is an aspherical surface.

[0014] According to the above technical solution, the focal length range of the lens is 20mm / 150mm / 920mm / 1600mm, the zoom ratio reaches 80x, and during the zoom process, the F-number of the short, medium and long focal lengths remains constant at 4, and the F-number of the super telephoto lens is 7.

[0015] Following the above technical solution, when the system switches from a short focal length of 20mm to a medium focal length of 150mm, the front group of the short focal length is cut out and the front group of the medium focal length is cut in via gears. When switching from a medium focal length of 150mm to a telephoto focal length of 920mm, the front group of the medium focal length is cut out and the secondary lens is cut in via gears. The short, medium, and telephoto focal lengths share the first focusing lens, the second focusing lens, the first rear lens group, and the second rear lens group. When switching from a telephoto focal length of 920mm to an ultra-telephoto focal length of 1600mm, the first rear lens group and the second rear lens group are cut out via gears, and the third rear lens group, the fourth rear lens group, and the thermal stop are cut in.

[0016] The lens adopts a catadioptric-reflective combination structure. The telephoto and super telephoto lenses share the Cassegrain reflection system and the shared focusing group. The switching between telephoto and super telephoto lenses is achieved by switching between the shared rear group and the rear thermal stop group. The short focal length and medium focal length lenses share the shared focusing group, the shared rear group and the rear thermal stop group. The switching between short focal length and medium focal length lenses is achieved by switching between the front short focal length and the front medium focal length group.

[0017] Among them, the super telephoto lens adopts a variable F-number rear group with a thermal stop, which breaks through the limitation of infrared cold stop and further increases the system focal length without increasing the aperture, thus improving the performance of the optical system.

[0018] Following the above technical solution, for the main objective lens with a larger aperture, a reflection system is used to compress the aperture and avoid chromatic aberration correction; for the short and medium focal length lens group with a smaller aperture, chromatic aberration and off-axis aberration correction are achieved by combining a variety of dispersive materials.

[0019] Following the above technical solution, the optical system has four focal lengths and a focusing function. It shares a focusing lens group, and the forward and backward movement of the focusing lens can ensure that the system has good imaging quality for close-range target observation and over a wide temperature range.

[0020] Following the above technical solution, the system's primary mirror has the largest aperture, with an effective optical aperture of 230mm.

[0021] Following the above technical solution, some optical components of the system adopt aspherical surfaces, reducing the number of system lenses and improving the system's imaging quality and transmittance.

[0022] The large magnification mid-wave infrared optical system of the present invention, based on secondary mirror switching and thermal aperture F-number variation, is suitable for 640×512 mid-wave cooled detectors.

[0023] Following the above technical solution, a through hole is opened at the center of the primary lens so that the front group of the short-to-medium focal length can be inserted through the through hole in the center of the primary lens, forming a short-to-medium focal length system with the shared focusing group and the rear group.

[0024] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0025] 1. The lens is established through a reasonable initial structure. Through the structure of the catadioptric optical system, it can combine the advantages of reflection and refraction. The cassette zoom optical system can increase the field of view of the system by using the reflection of the primary lens, the entry and exit of the secondary lens, and the switching of different front groups. By using the switching of the rear group with thermal stop, it is possible to achieve variable F number design on the basis of long focal length, and expand the relative aperture of the optical system.

[0026] 2. The lens is cut in and cut out, making full use of the opening in the center of the primary lens. The front group of the short-to-medium focal length lens, together with the shared focusing lens group and the rear group, form a short-to-medium focal length lens system.

[0027] 3. The lens zoom adopts a short-to-medium telephoto front group cut-in and cut-out structure to achieve high-speed switching zoom between short and medium telephoto.

[0028] 4. The lens adopts a secondary imaging structure, which not only meets the requirement of 100% cold aperture efficiency, but also reduces the diameter of the front lens group.

[0029] 5. The lens uses a Cassegrain reflection system, which can compress the aperture and avoid chromatic aberration correction;

[0030] 6. The lens adopts a rear group with a thermal diaphragm and variable F-number, which breaks through the limitation of infrared cold diaphragm and further improves the system focal length without increasing the aperture.

[0031] 7. The image quality of the lens is close to the diffraction limit when switching between the four fields of view;

[0032] 8. The lens has good focusing performance in four field-of-view settings, and provides good image quality for close-up target observation and over a wide temperature range. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of an optical system provided in an embodiment of the present invention;

[0034] Figure 2 This is a short-focal-length two-dimensional diagram of an optical system provided in an embodiment of the present invention;

[0035] Figure 3 This is a focal two-dimensional diagram of an optical system provided in an embodiment of the present invention;

[0036] Figure 4 This is a two-dimensional diagram of a telephoto optical system provided in an embodiment of the present invention;

[0037] Figure 5 This is a two-dimensional diagram of an optical system with an ultra-long focal length provided in an embodiment of the present invention;

[0038] Figure 6 This is an MTF diagram of an optical system at a short focal length of 32 lp / mm provided in an embodiment of the present invention;

[0039] Figure 7 This is an MTF diagram of an optical system at a focal length of 32 lp / mm provided in an embodiment of the present invention;

[0040] Figure 8 This is an MTF diagram of an optical system at a focal length of 32 lp / mm provided in an embodiment of the present invention;

[0041] Figure 9 This is an MTF diagram of an optical system at an ultra-long focal length of 16 lp / mm provided in an embodiment of the present invention;

[0042] Figure 10 This is a diagram showing the short focal length endpoint of an optical system provided in an embodiment of the present invention;

[0043] Figure 11 This is a focal point array diagram of an optical system provided in an embodiment of the present invention;

[0044] Figure 12 This is a diagram showing the telephoto end of an optical system provided in an embodiment of the present invention;

[0045] Figure 13 This is a diagram showing the endpoints of an optical system with an ultra-long focal length, provided in an embodiment of the present invention.

[0046] In the diagram, 1-primary lens, 2-secondary lens, 3-first focusing lens, 4-second focusing lens, 5-first rear lens group, 6-second rear lens group, 7-first short focal length front lens group, 8-second short focal length front lens group, 9-first medium focal length front lens group, 10-second medium focal length front lens group, 11-third rear lens group, 12-fourth rear lens group, 13-thermal aperture.

[0047] The first short focal length front group lens 7, the second short focal length front group lens 8, the first focusing lens 3, the second focusing lens 4, the first rear group lens 5, and the second rear group lens 6 constitute a short focal length imaging system.

[0048] The first front group lens 9, the second front group lens 10, the first focusing lens 3, the second focusing lens 4, the first rear group lens 5, and the second rear group lens 6 constitute the central focal imaging system.

[0049] The primary mirror 1, secondary mirror 2, first focusing mirror 3, second focusing mirror 4, first rear lens group 5, and second rear lens group 6 constitute a telephoto imaging system;

[0050] The super telephoto imaging system consists of primary lens 1, secondary lens 2, first focusing lens 3, second focusing lens 4, third rear lens group 11, fourth rear lens group 12, and thermal stop 13. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0052] In the embodiments of the present invention, "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or sequence.

[0053] according to Figure 1The schematic diagram of the optical system shown in this embodiment of the invention is a large zoom ratio mid-wave infrared optical system based on secondary mirror switching and thermal stop variable F-number, including a primary mirror 1, a secondary mirror 2, a first focusing mirror 3, a second focusing mirror 4, a first rear lens group 5, a second rear lens group 6, a first short focal length front lens group 7, a second short focal length front lens group 8, a first medium focal length front lens group 9, a second medium focal length front lens group 10, a third rear lens group 11, a fourth rear lens group 12, and a thermal stop 13, for a total of 13 optical elements.

[0054] The first short focal length front group lens 7, the second short focal length front group lens 8, the first focusing lens 3, the second focusing lens 4, the first rear group lens 5, and the second rear group lens 6 constitute a short focal length 20mm imaging system.

[0055] The first front group lens 9, the second front group lens 10, the first focusing lens 3, the second focusing lens 4, the first rear group lens 5, and the second rear group lens 6 constitute a 150mm imaging system for the central focal length.

[0056] The primary lens 1, secondary lens 2, first focusing lens 3, second focusing lens 4, first rear lens group 5, and second rear lens group 6 together form a 920mm telephoto imaging system.

[0057] The primary lens 1, secondary lens 2, first focusing lens 3, second focusing lens 4, third rear lens group 11, fourth rear lens group 12, and thermal stop 13 form an ultra-telephoto 1600mm imaging system.

[0058] Furthermore, the primary and secondary mirrors of the Cassegrain reflector system are made of microcrystalline glass, and the lens materials are silicon and germanium, materials commonly used in mid-wave infrared optical systems. The primary mirror 1 is a concave mirror facing the object side, the secondary mirror 2 is a convex mirror facing the image side, the first focusing mirror 3 is a concave meniscus germanium negative lens facing the object side, the second focusing mirror 4 is a concave meniscus silicon positive lens facing the object side, the first rear lens group 5 is a convex meniscus silicon positive lens facing the object side, and the second rear lens group 6 is a convex meniscus... The first short-focus front group lens 7 is a biconcave silicon positive lens, the second short-focus front group lens 8 is a biconvex germanium negative lens, the first intermediate-focus front group lens 9 is a meniscus silicon positive lens convex towards the object, the second intermediate-focus front group lens 10 is a meniscus germanium negative lens convex towards the object, the third rear group lens 11 is a meniscus germanium negative lens convex towards the image, the fourth rear group lens 12 is a meniscus silicon positive lens convex towards the object, and the thermal stop 13 is a spherical aluminum reflector facing the image plane.

[0059] The present invention relates to a high zoom ratio mid-wave infrared optical system based on secondary mirror switching and thermal aperture F-number variation, with focal lengths of 20mm / 150mm / 920mm / 1600mm. During zooming, the F-number for short, medium, and long focal lengths remains constant at 4, while the F-number for super long focal length is 7.

[0060] Specifically, in one embodiment of the present invention, the optical system includes 13 optical elements. The primary mirror 1 is a concave mirror facing the object side with a quadratic constant K = -1; the secondary mirror 2 is a convex mirror facing the image side with a quadratic constant K = -1.652; the first focusing mirror 3 is a concave meniscus germanium negative lens facing the object side; and the second focusing mirror 4 is a concave meniscus silicon positive lens facing the object side with an aspheric coefficient A = 2.36 × 10⁻⁶. -6 B = -8.42 × 10 -9 C = 1.74 × 10 -12 The first rear lens 5 is a meniscus silicon positive lens with a convex surface facing the object side, and its aspheric coefficient is A = 8.31 × 10⁻⁶. -5 B = -6.93 × 10 -8 C = 2.97 × 10 -11 The second rear lens group 6 is a meniscus germanium negative lens with a convex object-facing surface; the first short-focus front lens group 7 is a biconcave silicon positive lens; and the second short-focus front lens group 8 is a biconvex germanium negative lens. The aspheric coefficient is A = -3.66 × 10⁻⁶. -7 B = 5.79 × 10 -9 C = -1.39 × 10 -11 The first intermediate focal front lens 9 is a meniscus positive silicon lens with a convex object-facing orientation, and the second intermediate focal front lens 10 is a meniscus negative germanium lens with a convex object-facing orientation. The aspheric coefficient is A = 1.46 × 10⁻⁶. -5 B = -6.75 × 10 -8 C = 4.52 × 10 -11 The third rear lens 11 is a meniscus germanium negative lens with a convex image-side surface and an aspheric coefficient of A = 8.76 × 10⁻⁶. -7 B = -2.89 × 10 -9 The fourth rear lens 12 is a meniscus silicon positive lens with its convex surface facing the object plane, and the thermal stop 13 is a spherical aluminum reflector facing the image plane.

[0061] Furthermore, by adopting a variable F-number rear group with a thermal diaphragm, the limitation of the infrared cold diaphragm is overcome, and the system focal length is further improved without increasing the aperture.

[0062] Furthermore, the lens adopts a short-to-medium telephoto front group cut-in and cut-out structure to achieve high-speed switching zoom between short and medium telephoto ranges;

[0063] Furthermore, the lens employs a Cassegrain reflection system, which enables aperture compression and avoids chromatic aberration correction;

[0064] Furthermore, the lens adopts a secondary imaging structure, which not only meets the requirement of 100% cold aperture efficiency, but also reduces the diameter of the front lens group.

[0065] Furthermore, the secondary lens is cut out, and a Ф50mm through hole of the same size as the secondary lens is opened at the center of the primary lens. The opening at the center of the primary lens is fully utilized, and the front group of the short-to-medium telephoto lens is cut in. Together with the shared focusing group and rear group, it forms a short-to-medium telephoto system, which compresses the size of the system, making it small in volume and compact in structure.

[0066] Furthermore, along the optical axis, the distance between the vertex of the primary mirror 1's reflecting surface and the vertex of the secondary mirror 2's reflecting surface is 135mm, and the distance between the vertex of the secondary mirror 2's reflecting surface and the vertex of the first surface of the first focusing mirror 3 is 150mm. When the focal length is short, the first short focal length front group lens 7 and the second short focal length front group lens 8 enter the optical path, and the distance between the vertex of the second surface of the second short focal length front group lens 8 and the vertex of the first surface of the first focusing mirror 3 is 140mm. When the focal length is medium, the first medium focal length front group lens 9 and the second medium focal length front group lens 10 enter the optical path, and the distance between the vertex of the second surface of the second medium focal length front group lens 10 and the vertex of the first surface of the first focusing mirror 3 is 143mm.

[0067] Figure 2 The diagram shown is a two-dimensional view of the short-focal-length optical system according to an embodiment of the present invention. The first short-focal-length front lens 7 and the second short-focal-length front lens 8 are located at... Figure 1 When the optical path is cut off from the axis, the focal length is 20mm.

[0068] Figure 3 The diagram shown is a two-dimensional focal length view of the optical system according to an embodiment of the present invention. The first intermediate focal front group lens 9 and the second intermediate focal front group lens 10 are located at... Figure 1 When the optical path is cut off from the axis, the focal length is 150mm.

[0069] Figure 4 The image shown is a two-dimensional diagram of the telephoto lens of an embodiment of the present invention, with the secondary mirror 2 located at... Figure 1 At the on-axis position, the focal length is 920mm when the optical path is cut in.

[0070] Figure 5 The diagram shown is a two-dimensional representation of the ultra-long focal length optical system according to an embodiment of the present invention. The third rear lens group 11, the fourth rear lens group 12, and the thermal stop 13 are located at... Figure 1 When the optical path is cut off from the axis, the focal length is 1600mm.

[0071] Figure 6 The figure shows the MTF diagram of the optical system at the short focal length of 32lp / mm in an embodiment of the present invention, and the transfer function curves for each field of view at a focal length of 20mm.

[0072] Figure 7 The figure shows the MTF diagram at a focal length of 32 lp / mm in the optical system of this invention, and the transfer function curves for each field of view at a focal length of 150 mm.

[0073] Figure 8The figure shows the MTF diagram of the optical system at the telephoto end of 32lp / mm in an embodiment of the present invention, and the transfer function curves of each field of view at a focal length of 920mm.

[0074] Figure 9 The figure shows the MTF diagram of the optical system of the present invention at the ultra-long focal length of 16lp / mm, and the transfer function curves of each field of view at a focal length of 1600mm.

[0075] Figure 10 The diagram shown is a short focal length endpoint diagram of the optical system according to an embodiment of the present invention, showing the size of the blur spot in each field of view at a focal length of 20mm.

[0076] Figure 11 The diagram shown is a focal length array of the optical system according to an embodiment of the present invention, showing the size of the blur spot in each field of view at a focal length of 150mm.

[0077] Figure 12 The diagram shown is a series of images of the telephoto end of the optical system according to an embodiment of the present invention, showing the size of the blur spot in each field of view at a focal length of 920mm.

[0078] Figure 13 The diagram shows the ultra-long focal length array of the optical system according to an embodiment of the present invention, with the size of the blur spot in each field of view at a focal length of 1600mm.

[0079] This invention adopts a combined catadioptric and reflective optical system structure. A suitable initial structure is established, and the aberration correction and compensation of the front and rear magnification conversion groups are optimized through switching settings of the optical system's magnification conversion groups. Switching between short-focal and medium-focal distances and long-focal distances is achieved through the entry and exit of secondary mirrors, and switching between short-focal and medium-focal distances is achieved through the entry and exit of the short-focal and medium-focal distance front groups. The optical system transmits a large field of view for short and medium focal lengths and reflects a small field of view for long focal lengths. It shares the rear optical system and detector components, resulting in a compact structure and small size. Simultaneously, a separate rear group with a thermal stop is designed to achieve a variable F-number design, overcoming the limitations of infrared cold stops. Together with the Cassegrain reflective front group, it achieves an ultra-long focal length structure, thus providing four focal lengths for mid-wave infrared: ultra-long focal length, long focal length, medium focal length, and short focal length. This integrates a large aperture, small field of view, long focal length compact design with a large field of view and short focal length.

[0080] This invention differs from conventional Cassegrain or off-axis reflection systems. While conventional Cassegrain or off-axis reflection systems can significantly reduce size, facilitating long focal lengths, large apertures, and compact designs, they suffer from limited field of view and relatively small apertures, failing to meet the large field of view requirements of high zoom ratio systems. In contrast, this invention utilizes the cutting out of the secondary mirror and the opening of the primary mirror, along with the cutting in of the short-to-medium focal length front group, to achieve a large field of view design. Furthermore, due to aperture limitations, the focal length of the optical system cannot be infinitely extended. However, by cutting in the thermal stop, a longer focal length design can be achieved without increasing the aperture.

[0081] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0082] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high zoom ratio mid-wave infrared optical system based on secondary mirror switching and thermal aperture F-number, characterized in that, include: The system comprises a Cassegrain reflection system, a shared focusing group, a shared rear group, a short focal length front group, a medium focal length front group, and a thermal stop rear group. The Cassegrain reflection system includes a primary mirror and a secondary mirror. The shared focusing group includes a first focusing mirror and a second focusing mirror. The shared rear group includes a first rear lens and a second rear lens. The short focal length front group includes a first short focal length front lens and a second short focal length front lens. The medium focal length front group includes a first medium focal length front lens and a second medium focal length front lens. The thermal stop rear group includes a third rear lens, a fourth rear lens, and a thermal stop. The object-side imaging beam sequentially passes through the first short-focal-length front lens, the second short-focal-length front lens, the first focusing lens, the second focusing lens, the first rear lens, and the second rear lens to form an image on the detector, thus constituting a short-focal-length optical system. The short focal length front group cuts out, and the middle focal length front group cuts into the optical path, forming a middle focal length optical system; The object-side imaging beam is reflected by the primary mirror and the secondary mirror in sequence to form an image. Then, it is imaged on the detector by the first focusing mirror, the second focusing mirror, the first rear lens group and the second rear lens group, thus forming a telephoto optical system. The first and second rear lens groups are cut out, and the third, fourth, and thermal stops are cut into the optical path to form an ultra-telephoto optical system. The incident light direction is on the object side, and the exit light direction is on the image side. The primary mirror is a concave mirror facing the object side, the secondary mirror is a convex mirror facing the image side, the first focusing lens is a meniscus negative germanium lens facing the object side, the second focusing lens is a meniscus positive silicon lens facing the object side, the first rear lens group is a convex meniscus positive silicon lens facing the object side, the second rear lens group is a convex meniscus negative germanium lens facing the object side, the first short focal length front lens group is a biconcave silicon negative lens, the second short focal length front lens group is a biconvex germanium negative lens, the first intermediate focal length front lens group is a convex meniscus positive silicon lens facing the object side, the second intermediate focal length front lens group is a convex meniscus negative germanium lens facing the object side, the third rear lens group is a convex meniscus negative germanium lens facing the image side, the fourth rear lens group is a convex meniscus positive silicon lens facing the object side, and the thermal stop is a spherical aluminum mirror facing the image plane. The primary mirror is a parabolic surface, the secondary mirror is a hyperboloid, the first surface of the second focusing lens near the object is aspherical, the second surface of the first rear lens away from the object is aspherical, the first surface of the second short focal length front lens near the object is aspherical, the second surface of the second medium focal length front lens away from the object is aspherical, and the second surface of the third rear lens away from the object is aspherical.

2. The system according to claim 1, characterized in that, The Cassegrain reflector system is made of microcrystalline glass, and the lens is made of silicon and germanium.

3. The system according to claim 1 or 2, characterized in that, The focal lengths of the short-focal-length optical system, the medium-focal-length optical system, the long-focal-length optical system, and the super-telephoto optical system are 20mm, 150mm, 920mm, and 1600mm, respectively. During zooming, the F-numbers of the short, medium, and long focal lengths remain constant at 4, while the F-number of the super-telephoto optical system is 7.

4. The system according to claim 3, characterized in that, When switching from a short focal length of 20mm to a medium focal length of 150mm, the front group of the short focal length is cut out and the front group of the medium focal length is cut in. When switching from a medium focal length of 150mm to a telephoto lens of 920mm, the front group of the medium focal length is cut out and the secondary lens is cut in. The short, medium, and telephoto lenses share the first focusing lens, the second focusing lens, the first rear lens group, and the second rear lens group. When switching from a telephoto lens of 920mm to a super telephoto lens of 1600mm, the first rear lens group and the second rear lens group are cut out, and the third rear lens group, the fourth rear lens group, and the thermal stop are cut in.

5. The system according to claim 4, characterized in that, The primary mirror has the largest aperture, with an effective optical aperture of 230mm.

6. The system according to claim 5, characterized in that, A through-hole is made at the center of the primary lens so that the front group of the short-to-medium focal length can be inserted through the through-hole in the center of the primary lens, forming a short-to-medium focal length system with the shared focusing group and the rear group.

Images