A long focal length mid-wave infrared continuous zoom optical system

Abstract

This application discloses a long-focal-length mid-wave infrared continuous zoom optical system, comprising a primary imaging lens group and a secondary imaging lens group. The primary imaging lens group includes: a first lens and a second lens forming a front fixed group; a third lens forming a zoom group; a fourth lens forming a compensation group; and a fifth lens forming a rear fixed group. During imaging, the focal length is changed by the movement of the zoom group along the optical axis, and the movement of the compensation group along the optical axis compensates for the image plane defocusing caused by the movement of the zoom group, thereby achieving clear imaging throughout the zoom process. Furthermore, a secondary imaging lens group is provided after the primary imaging lens group for re-correcting the image after the primary imaging, which can significantly reduce the lens aperture of each lens in the optical system. In addition, the optical system provided by this invention uses three plane mirrors to deflect the light path, further reducing the length of the entire optical system, thereby realizing a compact high-magnification continuous zoom optical system.

Description

Technical Field

[0001] This application belongs to the field of infrared optical technology, and specifically relates to a long focal length mid-wave infrared continuous zoom optical system. Background Technology

[0002] As devices using infrared continuous zoom optical systems develop towards higher integration, more requirements are being placed on these systems. These requirements include achieving both high zoom ratios and high image quality, without sacrificing image quality. Additionally, the overall length of the optical system should be as short as possible, and the aperture should be as small as possible, in order to reduce the size of the optical system in all aspects and facilitate the high integration of the entire device. Summary of the Invention

[0003] Based on this, the present invention proposes a long focal length mid-wave infrared continuous zoom optical system. The specific technical solution is as follows.

[0004] A long-focal-length mid-wave infrared continuous zoom optical system includes a primary imaging lens group and a secondary imaging lens group arranged sequentially along the optical axis transmission direction.

[0005] The primary imaging lens group includes, in sequence along the optical axis transmission direction, a front fixed group, a movable group, and a rear fixed group.

[0006] The front fixing group includes a first lens and a second lens arranged sequentially along the optical axis transmission direction. The first lens is a positive meniscus lens with its convex surface facing the object side, and the second lens is a negative meniscus lens with its convex surface facing the object side.

[0007] The active group includes a third lens and a fourth lens arranged sequentially along the optical axis transmission direction. The third lens is a biconcave lens and the fourth lens is a biconvex lens. Both the third lens and the fourth lens are capable of reciprocating along the optical axis.

[0008] The rear fixing group includes a fifth lens, which is a meniscus negative lens with its convex surface facing the object side;

[0009] The secondary imaging lens group includes a sixth lens, a seventh lens, and an eighth lens arranged sequentially along the optical axis transmission direction. The sixth lens is a biconvex lens, the seventh lens is a meniscus lens with its convex surface facing the image side, and the eighth lens is a meniscus lens with its convex surface facing the image side.

[0010] Preferably, the focal length of the first lens is 57.25 mm, the focal length of the second lens is -73.95 mm, the focal length of the third lens is -14.02 mm, the focal length of the fourth lens is 25.23 mm, the focal length of the fifth lens is -40.22 mm, the focal length of the sixth lens is 35.15 mm, the focal length of the seventh lens is 118.65 mm, and the focal length of the eighth lens is 19.84 mm.

[0011] Preferably, when the focal length of the optical system is 15mm, the air gap between the second and third lenses is 10.4mm, the air gap between the third and fourth lenses is 88.04mm, and the air gap between the fourth and fifth lenses is 2.25mm; when the focal length of the optical system is 300mm, the air gap between the second and third lenses is 62.40mm, the air gap between the third and fourth lenses is 15.08mm, and the air gap between the fourth and fifth lenses is 23.21mm.

[0012] Preferably, the optical system includes three plane mirrors, with a first plane mirror and a second plane mirror arranged sequentially between the fifth and sixth lenses, and a third plane mirror between the seventh and eighth lenses.

[0013] Preferably, the normals of the three planar mirrors are all at a 45° angle to the optical axis of the optical system.

[0014] Preferably, the air gap between the first lens and the second lens is 7.300 mm; the air gap between the second lens and the third lens is adjustable from 10.4 mm to 62.40 mm; the air gap between the third lens and the fourth lens is adjustable from 88.04 mm to 15.08 mm; the air gap between the fourth lens and the fifth lens is adjustable from 2.25 mm to 23.21 mm; the air gap between the fifth lens and the first plane mirror is 14.00 mm; the air gap between the first plane mirror and the second plane mirror is 20.000 mm; the air gap between the second plane mirror and the sixth lens is 34.000 mm; the air gap between the sixth lens and the seventh lens is 5.000 mm; the air gap between the seventh lens and the third plane mirror is 26.260 mm; and the air gap between the third plane mirror and the eighth lens is 14 mm.

[0015] Preferably, the center thickness of the first lens is 10.390 mm, the object side radius of curvature is 75.490 mm, and the image side radius of curvature is 149.370 mm.

[0016] The second lens has a center thickness of 4.680 mm, an object-side radius of curvature of 77.450 mm, and an image-side radius of curvature of 54.910 mm.

[0017] The third lens has a center thickness of 3.840 mm, an object-side radius of curvature of -142.240 mm, and an image-side radius of curvature of 61.600 mm.

[0018] The fourth lens has a center thickness of 6.100 mm, an object-side radius of curvature of 64.540 mm, and an image-side radius of curvature of -77.620 mm.

[0019] The fifth lens has a center thickness of 3.750 mm, an object-side radius of curvature of 34.420 mm, and an image-side radius of curvature of 24.630 mm.

[0020] The sixth lens has a center thickness of 5.000 mm, an object-side radius of curvature of 231.830 mm, and an image-side radius of curvature of -200.000 mm.

[0021] The seventh lens has a center thickness of 4.720 mm, an object-side radius of curvature of -63.020 mm, and an image-side radius of curvature of -80.000 mm.

[0022] The eighth lens has a center thickness of 2.970 mm, an object-side radius of curvature of -33.830 mm, and an image-side radius of curvature of -111.870 mm.

[0023] Preferably, the first lens and the eighth lens are made of silicon single crystal, the second lens, the third lens, the fifth lens, the sixth lens and the seventh lens are all made of germanium single crystal, and the fourth lens is made of zinc selenide.

[0024] Preferably, the image-side surfaces of the first lens, the second lens, the fourth lens, the fifth lens, the sixth lens, and the eighth lens, as well as the object-side surfaces of the third lens and the seventh lens, are all aspherical surfaces and satisfy the aspherical formula:

[0025]

[0026] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0027] Preferably, the light-emitting side of the fourth lens is a diffractive aspherical surface and satisfies the diffraction formula:

[0028]

[0029] +

[0030] Wherein, c5 is the radius of curvature of the light-incident surface of the fourth lens, r5 is the radial coordinate of the light-incident surface of the fourth lens perpendicular to the optical axis, k5 is the quadratic curve constant of the light-incident surface of the fourth lens, A5 is the fourth-order aspherical coefficient of the light-incident surface of the fourth lens, B5 is the sixth-order aspherical coefficient of the light-incident surface of the fourth lens, C5 is the eighth-order aspherical coefficient of the light-incident surface of the fourth lens; HOR is the diffraction order of the light-incident surface of the fourth lens, C1, C2, and C3 are the diffraction coefficients of the light-incident surface of the fourth lens, n is the refractive index of the optical material of the fourth lens, n0 is the refractive index of air, and λ0 is the center wavelength of the optical system design.

[0031] The long-focal-length mid-wave infrared continuous zoom optical system provided by this invention has the following technical advantages:

[0032] The continuous zoom infrared optical system provided by this invention includes a primary imaging lens group and a secondary imaging lens group. The primary imaging lens group includes a front fixed group, a movable group, and a rear fixed group. The movable group includes a zoom group and a compensation group. During the imaging process, when the optical system is at a short focal length, the zoom group is closer to the object side, and the compensation group is closer to the image side. During the transition from short focal length to long focal length, the zoom group and the compensation group move from their positions closer to the object side and image side, respectively, towards the center. The movement of the zoom group along the optical axis achieves the focal length change, and the movement of the compensation group along the optical axis compensates for the image plane defocusing caused by the movement of the zoom group, thereby achieving clear imaging throughout the zoom process. This provides a large zoom ratio of 20x while ensuring high image quality throughout the entire zoom process.

[0033] Furthermore, a secondary imaging lens group is provided after the primary imaging lens group to re-correct the image after the primary imaging, ensuring that the entire system can obtain a clear image again. On the other hand, it can reduce the lens aperture of each lens in the optical system of this embodiment. Since the optical system of this invention can achieve a continuous zoom of 20x from 15mm to 300mm, the requirement for lens aperture is relatively large. Compared with using only primary imaging, the lens aperture requirement is about 200mm. By using the secondary imaging lens group to correct the image quality again, this invention can significantly reduce the requirement for the lens aperture of each lens in the optical system, and the lens aperture only needs to be about 80mm.

[0034] Furthermore, this embodiment also includes three planar mirrors to deflect the light path, further reducing the length of the entire optical system, thereby enabling a compact high-magnification continuous zoom optical system. Attached Figure Description

[0035] The accompanying drawings are provided to further understand this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof.

[0036] Figure 1 A schematic diagram of the optical system provided in this application embodiment with a focal length of 15mm;

[0037] Figure 2 A schematic diagram of the optical system provided in this application embodiment at a focal length of 150mm;

[0038] Figure 3 A schematic diagram of the optical system provided in this application embodiment at a focal length of 300mm;

[0039] Figure 4 The optical transfer function diagram of the optical system with a focal length of 15mm is provided for the embodiments of this application;

[0040] Figure 5 The optical transfer function diagram of the optical system with a focal length of 150mm is provided for the embodiments of this application;

[0041] Figure 6 The optical transfer function diagram provided for an optical system with a focal length of 300mm is shown in the embodiment of this application.

[0042] Figure 7 A dot plot of the optical system with a focal length of 15mm provided in the embodiments of this application;

[0043] Figure 8 A dot plot of an optical system with a focal length of 150mm, provided for an embodiment of this application;

[0044] Figure 9 A dot plot of an optical system with a focal length of 300mm, provided for an embodiment of this application;

[0045] Figure 10 This is a schematic diagram showing the relationship between the phase period and radial distance of the diffraction element in an optical system provided in an embodiment of this application.

[0046] Among them, 1. First lens, 2. Second lens, 3. Third lens, 4. Fourth lens, 5. Fifth lens, 6. First plane mirror, 7. Second plane mirror, 8. Sixth lens, 9. Seventh lens, 10. Third plane mirror, 11. Eighth lens. Detailed Implementation

[0047] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0048] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the equipment 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 limitations on this application.

[0049] This application provides a long-focal-length mid-wave infrared continuous zoom optical system, adaptable to a cooled mid-wave infrared detector with 640×512 pixels and a pixel size of 15μm. The optical system has a focal length of 15mm to 300mm, a zoom ratio of 20x, an operating wavelength of 3.2μm to 4.8μm, an operating temperature range of -40℃ to 60℃, and a relative aperture of 4.0.

[0050] like Figure 1 As shown, the long focal length mid-wave infrared continuous zoom optical system of this embodiment includes a primary imaging lens group and a secondary imaging lens group arranged sequentially along the optical axis transmission direction. The primary imaging lens group includes a front fixed group, a movable group, and a rear fixed group.

[0051] In the primary imaging lens group, the front fixed group includes a first lens 1 and a second lens 2 arranged sequentially along the optical axis transmission direction. The first lens 1 is a meniscus positive lens with its convex surface facing the object side, and the second lens 2 is a meniscus negative lens with its convex surface facing the object side. In the movable group, the third lens 3 is a zoom lens, and the fourth lens 4 is a compensation lens. The rear fixed group includes a fifth lens 5, which is also a meniscus positive lens with its convex surface facing the object side. The secondary imaging lens group includes a sixth lens 8, a seventh lens 9, and an eighth lens 11. The sixth lens 8 is a biconvex lens, the seventh lens 9 is a meniscus positive lens with its convex surface facing the image side, and the eighth lens 11 is a meniscus positive lens with its convex surface facing the image side.

[0052] The two surfaces of each lens in the optical system provided in this embodiment are defined, such as... Figure 1 As shown, along the direction of light transmission on the optical axis from left to right, the left side is the object side and the right side is the image side. For example, the S1 surface of the first lens 1 is the object side surface and the S2 surface is the image side surface. Other lenses will not be described in detail here.

[0053] As shown in Table 1, the first lens 1 has a focal length of 57.25 mm, a center thickness T1 of 10.390 mm, an object-side surface S1 radius of curvature of 75.490 mm, and an image-side surface S2 radius of curvature of 149.370 mm; the second lens 2 has a focal length of -73.95 mm, a center thickness T2 of 4.680 mm, an object-side surface S3 radius of curvature of 77.450 mm, and an image-side surface S4 radius of curvature of 54.910 mm. The third lens 3 has a focal length of -14.02 mm, a center thickness T3 of 3.840 mm, an object-side surface S5 radius of curvature of -142.240 mm, and an image-side surface S6 radius of curvature of 61.600 mm; the fourth lens 4 has a focal length of 25.23 mm, a center thickness T4 of 6.1 mm, an object-side surface S7 radius of curvature of 64.540 mm, and an image-side surface S8 radius of curvature of -77.620 mm; the fifth... Lens 5 has a focal length of -40.22mm, a center thickness T5 of 3.75mm, an object-side surface S9 radius of curvature of 34.420mm, and an image-side surface S10 radius of curvature of 24.630mm; the sixth lens 8 has a focal length of 35.15mm, a center thickness T6 of 5.000mm, an object-side surface S13 radius of curvature of 231.830mm, and an image-side surface S14 radius of curvature of -200.000mm; the seventh lens... Lens 9 has a focal length of 118.65 mm, a center thickness T7 of 4.72 mm, an object-side surface S15 radius of curvature of -63.020 mm, and an image-side surface S16 radius of curvature of -80.000 mm; Lens 11 has a focal length of 19.84 mm, a center thickness T9 of 2.970 mm, an object-side surface S18 radius of curvature of -33.830 mm, and an image-side surface S10 radius of curvature of -111.870 mm.

[0054] Furthermore, between the fifth lens 5 and the sixth lens 8, there is a first plane mirror 6 and a second plane mirror 7 in sequence, and between the seventh lens 9 and the eighth lens 11, there is a second plane mirror 10. The normals of the first plane mirror 6, the second plane mirror 7 and the third plane mirror 10 are all at a 45° angle to the optical axis.

[0055] The air gap D1 between the first lens 1 and the second lens 2 is 7.300 mm; the air gap adjustment range D2 between the second lens 2 and the third lens 3 is 10.4 mm to 62.40 mm; the air gap adjustment range D3 between the third lens 3 and the fourth lens 4 is 88.04 mm to 15.08 mm; the air gap adjustment range D4 between the fourth lens 4 and the fifth lens 5 is 2.25 mm to 23.21 mm; the air gap D5 between the fifth lens 5 and the first plane mirror 6 is 14.00 mm; the air gap D6 between the first plane mirror 6 and the second plane mirror 7 is 20.000 mm; the air gap D7 between the second plane mirror 7 and the sixth lens 8 is 34.000 mm; the air gap D8 between the sixth lens 8 and the seventh lens 9 is 5.000 mm; the air gap D9 between the seventh lens 9 and the third plane mirror 10 is 26.260 mm; and the air gap D10 between the third plane mirror 10 and the eighth lens 11 is 14 mm.

[0056] It should be noted that, Figure 1 , Figure 2 and Figure 3 These are lens composition diagrams for optical systems with focal lengths of 15mm, 150mm, and 300mm, respectively. The arrangement of each lens remains unchanged, and the individual parameters of each lens are identical. Figure 1 The center thickness T and air gap D are marked in the middle. The air gap D represents the air gap between the two corresponding lenses.

[0057] Specifically, when the focal length of the optical system is 15mm, the air gap between the second lens 2 and the third lens 3 is 10.4mm, the air gap D3 between the third lens 3 and the fourth lens 4 is 88.04mm, and the air gap D4 between the fourth lens 4 and the fifth lens 5 is 2.25mm; when the focal length of the lens is 300mm, the air gap D2 between the second lens 2 and the third lens 3 is 62.40mm, the air gap D3 between the third lens 3 and the fourth lens 4 is 15.08mm, and the air gap D4 between the fourth lens 4 and the fifth lens 5 is 23.21mm.

[0058] Among them, the first lens 1 and the eighth lens 11 are made of silicon single crystal; the second lens 2, the third lens 3, the fifth lens 5, the sixth lens 8 and the seventh lens 9 are made of germanium single crystal; and the fourth lens 4 is made of zinc selenide.

[0059] Table 1 Parameters of each lens

[0060]

[0061] As shown in Table 2, the image-side surfaces of the first lens 1, the second lens 2, the fourth lens 4, the fifth lens 5, the sixth lens 8, and the eighth lens 11, as well as the object-side surfaces of the third lens and the seventh lens 9, are all aspherical surfaces and satisfy the aspherical surface formula:

[0062]

[0063] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0064] Table 2 Aspherical data of lenses

[0065]

[0066] As shown in Table 3, the light-emitting side of the fourth lens 4 is a diffractive aspherical surface, meaning that the diffractive surface and the aspherical surface act together on the light-emitting side surface of the fourth lens 4, and this light-emitting side surface satisfies the following diffraction formula.

[0067]

[0068] +

[0069] Table 3 Diffraction surface coefficients of the fourth lens on the light-emitting side

[0070]

[0071] Wherein, c5 is the radius of curvature of the incident surface of the fourth lens 4, r5 is the radial coordinate of the incident surface of the fourth lens 4 in the direction perpendicular to the optical axis, k5 is the quadratic curve constant of the incident surface of the fourth lens 4, A5 is the fourth-order aspherical coefficient of the incident surface of the fourth lens 4, B5 is the sixth-order aspherical coefficient of the incident surface of the fourth lens 4, C5 is the eighth-order aspherical coefficient of the incident surface of the fourth lens 4; HOR is the diffraction order of the incident surface of the fourth lens 4, C1, C2, and C3 are the diffraction coefficients of the incident surface of the fourth lens 4, n is the refractive index of the optical material of the fourth lens 4, n0 is the refractive index of air, and λ0 is the center wavelength of the optical system design.

[0072] The continuous zoom infrared optical system provided in this embodiment includes a primary imaging lens group and a secondary imaging lens group. The primary imaging lens group includes: a first lens 1 and a second lens 2 forming a front fixed group; a third lens 3 forming a zoom group; a fourth lens 4 forming a compensation group; and a fifth lens 5 forming a rear fixed group. The secondary imaging lens group includes: a sixth lens 8, a seventh lens 9, and an eighth lens 11. During imaging, when the focal length is short, the third lens 3 of the zoom group is closer to the object side, and the fourth lens 4 of the compensation group is closer to the image side. During the transition from short to long focal length, the third lens 3 of the zoom group and the fourth lens 4 of the compensation group move from their positions closer to the object side and image side, respectively, towards the center. The movement of the zoom group along the optical axis achieves the focal length change, and the movement of the compensation group along the optical axis compensates for the image plane defocusing caused by the movement of the zoom group, thereby achieving clear imaging throughout the zoom process. Furthermore, a secondary imaging lens group is provided after the primary imaging lens group to re-correct the image after the primary imaging. This not only obtains a clear image quality but also reduces the lens aperture of each lens in the optical system of this embodiment. Since the optical system in this embodiment can achieve 20x continuous zoom from 15mm to 300mm, if only a single imaging is used, the lens aperture requirement would need to be around 200mm, resulting in a large overall optical system size, which is not conducive to system packaging and use. However, in this embodiment, multiple lenses are used to re-correct the quality of the single image after imaging, which can significantly reduce the lens aperture requirement in the optical system; the lens aperture only needs to be around 80mm. Furthermore, this embodiment also includes three plane mirrors to deflect the light path, further reducing the length of the entire optical system, thereby realizing a compact high-magnification continuous zoom optical system.

[0073] Therefore, the continuous zoom infrared optical system provided in this application embodiment can keep the target image clear throughout the 20x zoom process from 15mm to 300mm, and can realize the transformation of any field of view within the zoom range. It is the optimal choice for modern observation systems to solve the problem of switching between large and small fields of view.

[0074] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A long-focal-length mid-wave infrared continuous zoom optical system, characterized in that, It consists of a primary imaging lens group and a secondary imaging lens group arranged sequentially along the optical axis transmission direction; The primary imaging lens group consists of a front fixed group, a movable group, and a rear fixed group in sequence along the optical axis transmission direction. The front fixing group is composed of a first lens and a second lens in sequence along the optical axis transmission direction. The first lens is a positive meniscus lens with its convex surface facing the object side, and the second lens is a negative meniscus lens with its convex surface facing the object side. The active group is composed of a third lens and a fourth lens in sequence along the optical axis transmission direction. The third lens is a biconcave lens and the fourth lens is a biconvex lens. Both the third lens and the fourth lens can reciprocate along the optical axis. The rear fixing group is the fifth lens, which is a meniscus negative lens with its convex surface facing the object side; The secondary imaging lens group is composed of a sixth lens, a seventh lens, and an eighth lens in sequence along the optical axis transmission direction. The sixth lens is a biconvex lens, the seventh lens is a meniscus lens with its convex surface facing the image side, and the eighth lens is a meniscus lens with its convex surface facing the image side. The first lens has a focal length of 57.25 mm, the second lens has a focal length of -73.95 mm, the third lens has a focal length of -14.02 mm, the fourth lens has a focal length of 25.23 mm, the fifth lens has a focal length of -40.22 mm, the sixth lens has a focal length of 35.15 mm, the seventh lens has a focal length of 118.65 mm, and the eighth lens has a focal length of 19.84 mm.

2. The long focal length mid-wave infrared continuous zoom optical system according to claim 1, characterized in that, When the focal length of the optical system is 15mm, the air gap between the second and third lenses is 10.4mm, the air gap between the third and fourth lenses is 88.04mm, and the air gap between the fourth and fifth lenses is 2.25mm; when the focal length of the optical system is 300mm, the air gap between the second and third lenses is 62.40mm, the air gap between the third and fourth lenses is 15.08mm, and the air gap between the fourth and fifth lenses is 23.21mm.

3. The long focal length mid-wave infrared continuous zoom optical system according to claim 2, characterized in that, The optical system includes three plane mirrors: a first plane mirror and a second plane mirror are arranged sequentially between the fifth and sixth lenses, and a third plane mirror is arranged between the seventh and eighth lenses.

4. The long focal length mid-wave infrared continuous zoom optical system according to claim 3, characterized in that, The normals of the three plane mirrors are all at a 45° angle to the optical axis of the optical system.

5. A long focal length mid-wave infrared continuous zoom optical system according to claim 3, characterized in that, The air gap between the first lens and the second lens is 7.300 mm; the air gap between the second lens and the third lens is adjustable from 10.4 mm to 62.40 mm; the air gap between the third lens and the fourth lens is adjustable from 88.04 mm to 15.08 mm; the air gap between the fourth lens and the fifth lens is adjustable from 2.25 mm to 23.21 mm; the air gap between the fifth lens and the first plane mirror is 14.00 mm; the air gap between the first plane mirror and the second plane mirror is 20.000 mm; the air gap between the second plane mirror and the sixth lens is 34.000 mm; the air gap between the sixth lens and the seventh lens is 5.000 mm; the air gap between the seventh lens and the third plane mirror is 26.260 mm; and the air gap between the third plane mirror and the eighth lens is 14 mm.

6. The long focal length mid-wave infrared continuous zoom optical system according to claim 1, characterized in that, The first lens has a center thickness of 10.390 mm, an object-side radius of curvature of 75.490 mm, and an image-side radius of curvature of 149.370 mm. The second lens has a center thickness of 4.680 mm, an object-side radius of curvature of 77.450 mm, and an image-side radius of curvature of 54.910 mm. The third lens has a center thickness of 3.840 mm, an object-side radius of curvature of -142.240 mm, and an image-side radius of curvature of 61.600 mm. The fourth lens has a center thickness of 6.100 mm, an object-side radius of curvature of 64.540 mm, and an image-side radius of curvature of -77.620 mm. The fifth lens has a center thickness of 3.750 mm, an object-side radius of curvature of 34.420 mm, and an image-side radius of curvature of 24.630 mm. The sixth lens has a center thickness of 5.000 mm, an object-side radius of curvature of 231.830 mm, and an image-side radius of curvature of -200.000 mm. The seventh lens has a center thickness of 4.720 mm, an object-side radius of curvature of -63.020 mm, and an image-side radius of curvature of -80.000 mm. The eighth lens has a center thickness of 2.970 mm, an object-side radius of curvature of -33.830 mm, and an image-side radius of curvature of -111.870 mm.

7. The long focal length mid-wave infrared continuous zoom optical system according to claim 1, characterized in that, The first lens and the eighth lens are made of silicon single crystal, the second lens, the third lens, the fifth lens, the sixth lens and the seventh lens are all made of germanium single crystal, and the fourth lens is made of zinc selenide.

8. A long focal length mid-wave infrared continuous zoom optical system according to claim 1, characterized in that, The image-side surfaces of the first lens, the second lens, the fourth lens, the fifth lens, the sixth lens, and the eighth lens, as well as the object-side surfaces of the third lens and the seventh lens, are all aspherical surfaces and satisfy the aspherical formula: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

9. A long focal length mid-wave infrared continuous zoom optical system according to claim 1, characterized in that, The light-emitting side of the fourth lens is a diffractive aspherical surface, and the radial sag of the light-emitting side surface of the fourth lens is z5(r5), which satisfies the following diffraction formula: + Wherein, c5 is the radius of curvature of the light-incident surface of the fourth lens, r5 is the radial coordinate of the light-incident surface of the fourth lens perpendicular to the optical axis, k5 is the quadratic curve constant of the light-incident surface of the fourth lens, A5 is the fourth-order aspherical coefficient of the light-incident surface of the fourth lens, B5 is the sixth-order aspherical coefficient of the light-incident surface of the fourth lens, C5 is the eighth-order aspherical coefficient of the light-incident surface of the fourth lens; HOR is the diffraction order of the light-incident surface of the fourth lens, C1, C2, and C3 are the diffraction coefficients of the light-incident surface of the fourth lens, n is the refractive index of the optical material of the fourth lens, n0 is the refractive index of air, and λ0 is the center wavelength of the optical system design.

Images