Near-infrared, short-wave infrared and medium-wave infrared long-focus common-aperture imaging system

Abstract

The invention provides a near-infrared, short-wave infrared and medium-wave infrared long-focus common-aperture imaging system, and belongs to the technical field of optical design. Comprising a primary mirror, a secondary mirror, a spectroscope, a beam splitter prism, a near-infrared television rear-end mirror group, a CMOS black-and-white camera, a short-wave infrared rear-end mirror group, a short-wave infrared camera, a reflex mirror, a medium-wave infrared rear-end mirror group and a medium-wave infrared refrigeration detector. The imaging system is suitable for an airborne spherical photoelectric pod, near-infrared, short-wave infrared and medium-wave infrared common-aperture imaging can be realized under the constraint of compact size and weight, the focal lengths of three wavebands of the photoelectric pod within the sphere diameter of 410mm can reach more than 900mm, and the short-wave infrared has a laser spot monitoring function.

Description

Technical Field

[0001] This invention belongs to the field of optical design technology, specifically relating to a near-infrared, short-wave infrared and mid-wave infrared long-focal-width common aperture imaging system. Background Technology

[0002] Electro-optical pods are a crucial payload for advanced fighter jets, primarily providing support for optical search and reconnaissance, target identification and tracking, and target designation and localization. Due to the radiation characteristics of the target and target camouflage, single-band optical systems acquire relatively limited information. During detection, if the target's radiation characteristics change, the imaging system can easily lose sight of the target or experience a decrease in detection accuracy, potentially generating false signals. Three-band optical systems can simultaneously acquire radiation information from the target in near-infrared television, short-wave infrared, and mid-wave infrared bands, effectively avoiding these issues. Therefore, electro-optical pods typically include independent sensor components such as infrared thermal imagers, short-wave infrared cameras, and television cameras. The ever-increasing demands of modern warfare on sensor operating range have led to the adoption of longer focal lengths for infrared thermal imagers, short-wave infrared cameras, and television cameras. Longer focal lengths mean larger apertures, further exacerbating the conflict between these factors and the size and weight constraints of electro-optical pods.

[0003] Regarding co-aperture imaging, an article titled "Third Generation Infrared Optics" published in Proc. of SPIE Vol. 6940, 69400S, (2008) discloses a dual-band co-aperture imaging system for mid-wave infrared and long-wave infrared, sharing an off-axis three-mirror system with beam splitting located in a parallel optical path; an article titled "Optical system design for the aerial camera with dual band, common optical path, long focal, oblique view and focusing" published in Proc. of SPIE Vol. 9677 96771O-2 discloses a co-aperture imaging system for mid-wave infrared and near-infrared. Both of these existing co-aperture imaging systems have low space utilization and lack short-wave infrared / laser monitoring imaging. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems so as to realize a common aperture imaging system for near-infrared, short-wave infrared and mid-wave infrared under compact size and weight constraints.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system for realizing near-infrared, short-wave infrared, and mid-wave infrared co-aperture imaging. This includes a primary mirror, secondary mirrors, beam splitters, beam splitting prisms, near-infrared television back-end mirror assembly, a CMOS monochrome camera, a short-wave infrared back-end mirror assembly, a short-wave infrared camera, a folding mirror, a mid-wave infrared back-end mirror assembly, and a mid-wave infrared cooled detector. A near-infrared imaging system consists of a primary mirror, a secondary mirror, a beam splitter, a beam splitter prism, a near-infrared television back-end mirror assembly, and a CMOS monochrome camera; a short-wave infrared imaging system consists of a primary mirror, a secondary mirror, a beam splitter, a beam splitter prism, a short-wave infrared back-end mirror assembly, and a short-wave infrared camera; and a mid-wave infrared imaging system consists of a primary mirror, a secondary mirror, a beam splitter, a folding mirror, a mid-wave infrared back-end mirror assembly, and a mid-wave infrared cooled detector. The beam splitter is used for reflecting near-infrared and short-wave infrared beams and transmitting mid-wave infrared beams. The beam splitter prism is used for splitting near-infrared and short-wave infrared beams. The three different optical paths split by the beam splitter and beam splitter prism are arranged behind the primary mirror as a pure refraction system in the rear optical path. The shortwave infrared camera is equipped with a filter in front of it for switching between different working modes.

[0006] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common aperture imaging system provided by this invention also has the following technical features: the mid-wave infrared working band is 3.7μm-4.8μm, the near-infrared television working band is 0.6μm-0.9μm, and the short-wave infrared working band is 0.9μm-1.7μm.

[0007] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system provided by this invention also has the technical feature that the primary mirror and secondary mirror constitute a common-aperture cartridge system. The primary mirror is a rotationally symmetric parabolic surface; the secondary mirror is a rotationally symmetric quadric surface.

[0008] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system provided by this invention also has the following technical features: the beam splitter is used to fold the near-infrared beam and the short-wave infrared beam behind the main mirror for compact arrangement; the folding mirror is used to fold the mid-wave infrared beam behind the main mirror for compact arrangement.

[0009] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system provided by the present invention also has the following technical features: the beam splitter is a prism with a apex angle, the front surface is coated with a beam splitting film, and the rear surface is coated with an anti-reflection film.

[0010] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system provided by this invention also has the following technical feature: the cemented surface of the beam-splitting prism is coated with a dichroic film for transmitting short-wave infrared beams and reflecting near-infrared beams.

[0011] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-length common aperture imaging system provided by the present invention also has the following technical features: the filter includes two types, and the two types of filter are coated with 900-1700nm and 1064±50nm filter films respectively.

[0012] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system provided by the present invention also has the following technical features: the mid-wave infrared back-end mirror group is used to achieve three-stage imaging; the near-infrared television back-end mirror group is used to achieve secondary imaging; the short-wave infrared back-end mirror group is used to achieve secondary imaging; and the near-infrared imaging system, the short-wave infrared imaging system, and the mid-wave infrared imaging system are all equipped with focusing lenses.

[0013] The near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system provided by this invention also has the following technical features: the mid-wave infrared back-end mirror group is a U-shaped relay mirror group, which images the primary image plane onto the focal plane of the detector. The two lenses of the U-shaped relay mirror group are combined as a focusing mirror group to compensate for defocus; the short-wave infrared back-end mirror group has a field stop at the primary image plane, and behind the primary image plane is a U-shaped relay mirror group, which images the primary image plane onto the focal plane of the short-wave infrared camera. The first lens of the U-shaped relay mirror group serves as a focusing mirror group to compensate for defocus; the near-infrared television back-end mirror group has an L-shaped relay mirror group behind the primary image plane, which images the primary image plane onto the focal plane of the CMOS camera. The first lens of the L-shaped relay mirror group serves as a focusing mirror group to compensate for defocus.

[0014] Beneficial effects: The imaging system provided by this invention is suitable for airborne spherical optoelectronic pods. It can achieve near-infrared, short-wave infrared, and mid-wave infrared common aperture imaging under compact size and weight constraints. For optoelectronic pods with a spherical diameter of less than 410mm, the focal length of all three bands can reach more than 900mm. Among them, the short-wave infrared has a laser spot monitoring function. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the imaging system provided in an embodiment of the present invention; Figure 2 Optical path tracing diagram of the common aperture Cassegrain system provided in the embodiments of the present invention; Figure 3 The optical path transfer function diagram of the common aperture Cassegrain system provided in the embodiments of the present invention; Figure 4 This is a mid-wave infrared optical path tracing diagram provided in an embodiment of the present invention; Figure 5 This is a mid-wave infrared optical path transfer function diagram provided in an embodiment of the present invention; Figure 6 This is a short-wave infrared optical path tracing diagram provided in an embodiment of the present invention; Figure 7 This is a shortwave infrared band transfer function diagram provided in an embodiment of the present invention; Figure 8 This is a near-infrared television optical path tracing diagram provided in an embodiment of the present invention; [Xiao Liu 1] Figure 9 This is a near-infrared band transfer function diagram provided in an embodiment of the present invention. Among them, 1: primary mirror; 2: secondary mirror; 3: beam splitter; 4: beam splitter prism; 5: near-infrared television back-end mirror group; 6: CMOS monochrome camera; 7: short-wave infrared back-end mirror group; 8: short-wave infrared camera; 9: folding mirror; 10: mid-wave infrared back-end mirror group; 11: mid-wave infrared cooled detector. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the protection scope of the present invention.

[0018] In the description of the embodiments of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the invention.

[0019] Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0020] The terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of these terms in this invention based on the specific circumstances.

[0021] like Figure 1-9 As shown, this embodiment of the invention provides a near-infrared, short-wave infrared, and mid-wave infrared long-focal-aperture imaging system for realizing near-infrared, short-wave infrared, and mid-wave infrared co-aperture imaging. The technical specifications are as follows: A. Near-infrared mode: The near-infrared mode uses a CMOS monochrome camera with a resolution of 1920×1080 and a pixel size of 4.5μm. The optical system design parameters are as follows: 1) Operating wavelength: 0.6μm~0.9μm; 2) Field of view: 0.55° × 0.44°; 3) Maximum F-number: ≤5.5; 4) MTF: >0.3@110lp / mm (on the shaft) >0.2@110lp / mm (outside the shaft).

[0022] B-wave infrared mode: The mid-wave infrared mode uses a mid-wave cooled detector with a resolution of 1280×1024 and a pixel size of 10μm. The optical system design parameters are as follows: 1) Operating wavelength: 3.7μm~4.8μm; 2) Field of view: 1.02° × 0.81°; 3) Number of F: 4; 4) MTF: >0.18@40lp / mm (on the shaft); >0.10@40lp / mm (outside the shaft).

[0023] B-mode shortwave infrared: The shortwave infrared mode uses a shortwave TEC cooled detector with a resolution of 640×512 and a pixel size of 15μm. The optical system design parameters are as follows: 1) Operating wavelength: 0.9μm~1.7μm; 2) Field of view: 0.55° × 0.44°; 3) F-number: 5.7; 4) MTF: >0.50@30lp / mm (on the shaft); >0.40@30lp / mm (outside the shaft).

[0024] It includes a primary mirror 1, a secondary mirror 2, a beam splitter 3, a beam splitter prism 4, a near-infrared television back-end mirror group 5, a CMOS monochrome camera 6, a short-wave infrared back-end mirror group 7, a short-wave infrared camera 8, a folding mirror 9, a mid-wave infrared back-end mirror group 10, and a mid-wave infrared cooled detector 11. The near-infrared imaging system consists of a primary mirror 1, a secondary mirror 2, a beam splitter 3, a beam splitter prism 4, a near-infrared television back-end mirror group 5, and a CMOS monochrome camera 6; the short-wave infrared imaging system consists of a primary mirror 1, a secondary mirror 2, a beam splitter 3, a beam splitter prism 4, a short-wave infrared back-end mirror group 7, and a short-wave infrared camera 8; and the mid-wave infrared imaging system consists of a primary mirror 1, a secondary mirror 2, a beam splitter 3, a folding mirror 9, a mid-wave infrared back-end mirror group 10, and a mid-wave infrared cooled detector 11. The beam splitter 3 is used for reflecting near-infrared and short-wave infrared beams and transmitting mid-wave infrared beams. The beam splitter prism 4 is used for splitting near-infrared and short-wave infrared beams. The three different optical paths split by the beam splitter 3 and beam splitter prism 4 are arranged behind the main mirror 1 as a pure refraction system in the back end optical path. The shortwave infrared camera 8 is equipped with a filter for switching between different operating modes. The different operating modes refer to target reconnaissance and laser spot monitoring modes.

[0025] In the above embodiment, a beam-splitting prism 4 with equivalent parallel incident and exit surfaces is disposed behind the beam splitter 3. All three incident and exit surfaces of the prism 4 are perpendicular to the optical axis, thus avoiding the introduction of additional aberrations. The beam-splitting prism 4 reflects short-wave infrared light and transmits near-infrared light. The mid-wave infrared cooled detector 11 has a resolution of 640×512 and a pixel size of 15μm.

[0026] In some embodiments, the mid-wave infrared operating band is 3.7μm-4.8μm, the near-infrared television operating band is 0.6μm-0.9μm, and the short-wave infrared operating band is 0.9μm-1.7μm.

[0027] In some embodiments, the primary mirror 1 and the secondary mirror 2 form a common aperture cassette system, wherein the primary mirror 1 is a rotationally symmetric parabolic surface; and the secondary mirror 2 is a rotationally symmetric quadric surface. Light rays from the target scene are converged by the primary mirror and then incident on the secondary mirror 2. The secondary mirror 2 magnifies the focal length of the primary mirror 1 and images it on the back of the primary mirror 1.

[0028] like Figure 3As shown, the on-axis field of view forms a perfect image at the focal plane of the common aperture cassette system, and the MTF is close to the diffraction limit, which can be used as a control and monitoring tool for assembly quality during the assembly process.

[0029] In some embodiments, the beam splitter 3 is also used to fold the near-infrared beam and the short-wave infrared beam behind the main mirror 1 for compact arrangement; the folding mirror 4 is used to fold the mid-wave infrared beam behind the main mirror 1 for compact arrangement.

[0030] In some embodiments, the beam splitter 3 is a prism with a apex angle, a beam-splitting film coated on the front surface, and an anti-reflection film coated on the rear surface. The beam splitter 3 is a light wedge rotated 45 degrees along a local X-axis, transmitting mid-wave infrared (MWIR) beams and reflecting near-infrared and short-wave infrared beams.

[0031] In some embodiments, the near-infrared and short-wave infrared beams reflected by the beam splitter 3 are split again by the beam splitter prism 4 into two independent single-band optical paths: short-wave infrared and near-infrared. The adhesive surface of the beam splitter prism is coated with a dichroic film to transmit the short-wave infrared beam and reflect the near-infrared beam.

[0032] In some embodiments, the filter includes two types, which are coated with 900-1700nm and 1064±50nm filter films respectively. By switching the filter, there are two imaging bands: short-wave infrared (900-1700nm) and laser spot monitoring (1064±50nm).

[0033] In some embodiments, the mid-wave infrared back-end mirror group 10 is used to achieve three-stage imaging, the near-infrared television back-end mirror group 5 is used to achieve secondary imaging, and the short-wave infrared back-end mirror group 7 is used to achieve secondary imaging. The near-infrared imaging system, the short-wave infrared imaging system, and the mid-wave infrared imaging system are all equipped with focusing lenses.

[0034] In some embodiments, the mid-wave infrared back-end mirror group 10 is a U-shaped relay mirror group, which images the primary image plane onto the focal plane of the detector. The two lenses of the U-shaped relay mirror group are combined as a focusing mirror group to compensate for defocus. The short-wave infrared back-end mirror group 7 has a field stop at the primary image plane, and a U-shaped relay mirror group is located behind the primary image plane to image the primary image plane onto the focal plane of the short-wave infrared camera. The first lens of the U-shaped relay mirror group is used as a focusing mirror group to compensate for defocus. The near-infrared television back-end mirror group 5 has an L-shaped relay mirror group behind the primary image plane to image the primary image plane onto the focal plane of the CMOS camera. The first lens of the L-shaped relay mirror group is used as a focusing mirror group to compensate for defocus.

[0035] like Figure 4As shown, the folding mirror 9 is used to fold the optical path, facilitating the arrangement of the back-end infrared optical path behind the primary mirror 1. Three-stage imaging is achieved using the mid-wave infrared back-end mirror group 10, which is a U-shaped relay mirror group that images the primary image onto the detector's focal plane. The detector's cold screen serves as the aperture of the infrared optical system. By rationally selecting and optimizing design parameters, the entrance pupil of the optical system is located near the primary mirror, thereby minimizing the system size. The two lenses of the relay mirror group act as a focusing mirror group, compensating for defocusing caused by near-field imaging and high / low temperatures. Figure 5 As shown, the optical system's transfer function at room temperature (20℃) has an on-axis MTF > 0.18 @ 40 lp / mm and an off-axis MTF > 0.10 @ 40 lp / mm, which is close to the diffraction limit and meets the design requirements.

[0036] like Figure 6 As shown, secondary imaging is achieved using the short-wave infrared back-end mirror group 7. Short-wave infrared light is reflected by the beam splitter 3 and transmitted through the beam splitter prism 4 before reaching the short-wave infrared back-end mirror group 7. A field stop is placed at the primary image plane, and a U-shaped relay mirror group is placed behind the primary image plane to image the primary image plane onto the focal plane of the short-wave infrared camera 8. Reasonable selection of design parameters ensures that the entrance pupil of the entire near-infrared television optical system is located near the primary mirror, minimizing the system size. The first lens of the relay mirror group acts as a focusing lens, compensating for defocusing caused by near-field imaging and high / low temperatures. Figure 7 As shown in the figure, the transfer function of the short-wave infrared optical system at room temperature (20℃) is as follows. The figure shows that the on-axis MTF of this optical system is better than 0.50@30lp / mm, and the off-axis MTF is greater than 0.40@30lp / mm, approaching the diffraction limit and meeting the design requirements.

[0037] like Figure 8 As shown, secondary imaging is achieved using the near-infrared television back-end mirror group 5. Near-infrared light is reflected by the beam splitter 3 and beam splitter prism 4 before reaching the near-infrared television back-end mirror group 5. Behind the primary image plane is an L-shaped relay mirror group, which images the primary image plane onto the focal plane of the CMOS camera 6. A variable aperture is designed into the system to ensure the entrance pupil of the entire near-infrared television optical system is located near the primary mirror, minimizing the system size. The first lens of the relay mirror group acts as a focusing lens, compensating for defocusing caused by near-field imaging and extreme temperatures. Figure 9 As shown in the figure, the near-infrared transfer function of the optical system at room temperature (20℃) is as follows. The figure shows that the on-axis MTF of this optical system is better than 0.30@110lp / mm, and the off-axis MTF is greater than 0.20@110lp / mm, approaching the diffraction limit and meeting the design requirements.

[0038] 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 protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A near-infrared, short-wave infrared, and mid-wave infrared long-focal-width co-aperture imaging system, used to achieve near-infrared, short-wave infrared, and mid-wave infrared co-aperture imaging, characterized in that, This includes a primary mirror, secondary mirrors, beam splitters, beam splitting prisms, near-infrared television back-end mirror assembly, a CMOS monochrome camera, a short-wave infrared back-end mirror assembly, a short-wave infrared camera, a folding mirror, a mid-wave infrared back-end mirror assembly, and a mid-wave infrared cooled detector. A near-infrared imaging system consists of a primary mirror, a secondary mirror, a beam splitter, a beam splitter prism, a near-infrared television back-end mirror assembly, and a CMOS monochrome camera; a short-wave infrared imaging system consists of a primary mirror, a secondary mirror, a beam splitter, a beam splitter prism, a short-wave infrared back-end mirror assembly, and a short-wave infrared camera; and a mid-wave infrared imaging system consists of a primary mirror, a secondary mirror, a beam splitter, a folding mirror, a mid-wave infrared back-end mirror assembly, and a mid-wave infrared cooled detector. The beam splitter is used for reflecting near-infrared and short-wave infrared beams and transmitting mid-wave infrared beams. The beam splitter prism is used for splitting near-infrared and short-wave infrared beams. The three different optical paths split by the beam splitter and beam splitter prism are arranged behind the primary mirror as a pure refraction system in the rear optical path. The shortwave infrared camera is equipped with a filter in front of it for switching between different working modes.

2. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 1, characterized in that, The operating wavelength range is 3.7μm-4.8μm for mid-wave infrared, 0.6μm-0.9μm for near-infrared television, and 0.9μm-1.7μm for short-wave infrared.

3. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 1, characterized in that, The primary and secondary mirrors form a common aperture cassette system. The primary mirror is a rotationally symmetric parabolic surface; the secondary mirror is a rotationally symmetric quadric surface.

4. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 1, characterized in that, The beam splitter is also used to fold the near-infrared beam and the short-wave infrared beam behind the main mirror for compact arrangement; the folding mirror is used to fold the mid-wave infrared beam behind the main mirror for compact arrangement.

5. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 4, characterized in that, The beam splitter is a prism with a apex angle, with a beam splitting film coated on the front surface and an anti-reflection film coated on the rear surface.

6. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 1, characterized in that, The adhesive surface of the beam splitter is coated with a color-separating film for transmitting short-wave infrared beams and reflecting near-infrared beams.

7. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 1, characterized in that, The filter includes two types, which are coated with 900-1700nm and 1064±50nm filter films respectively.

8. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 1, characterized in that, The mid-wave infrared back-end mirror group is used to achieve three-stage imaging, the near-infrared television back-end mirror group is used to achieve secondary imaging, and the short-wave infrared back-end mirror group is used to achieve secondary imaging. The near-infrared imaging system, the short-wave infrared imaging system, and the mid-wave infrared imaging system are all equipped with focusing lenses.

9. The near-infrared, short-wave infrared, and mid-wave infrared long-focal-width common-aperture imaging system according to claim 8, characterized in that, The mid-wave infrared back-end mirror group is a U-shaped relay mirror group, which images the primary image plane onto the focal plane of the detector. The two lenses of the U-shaped relay mirror group are combined as a focusing mirror group to compensate for defocus. The short-wave infrared back-end mirror group has a field stop at the primary image plane, and behind the primary image plane is a U-shaped relay mirror group, which images the primary image plane onto the focal plane of the short-wave infrared camera. The first lens of the U-shaped relay mirror group is used as a focusing mirror group to compensate for defocus. The near-infrared television back-end mirror group has an L-shaped relay mirror group behind the primary image plane, which images the primary image plane onto the focal plane of the CMOS camera. The first lens of the L-shaped relay mirror group is used as a focusing mirror group to compensate for defocus.

Images