Medium-wave infrared continuous zoom lens with large zoom ratio

Abstract

The invention discloses a medium-wave infrared continuous zoom lens with a large zoom ratio, and belongs to the technical field of optics. The lens sequentially comprises a front fixed group, a zoom group, a compensation group I, a compensation group II, a rear fixed group and a detector part from an object side to an image side. The front fixing group is composed of specific silicon single crystal and germanium single crystal lenses, and the zoom group, the compensation group and the rear fixing group are also respectively made of corresponding optical materials and are designed in a surface type. The effective focal length of the lens is 21-420 mm, the F number is 4, the total length of the optical system is 200 mm, the optical system is adaptive to a detector with the resolution of 640 * 512 and the pixel size of 15 microns, and the horizontal field angle range is 25.8-1.3 degrees. The aspheric surface and the diffraction surface in the lens respectively satisfy a specific expression, the moving stroke of part of the lens is fixed, and the object side surface of the first lens is plated with a diamond-like carbon film. The lens adopts an eight-piece structure to realize 20 times of large zoom ratio, the structure is compact, the zoom curve is smooth, the optical axis stability is good, the full-field average MTF is greater than 0.233 lp / mm, the imaging quality is high, the defects of the existing infrared continuous zoom lens are effectively solved, and the requirements of various application scenes are met.

Description

Technical Field

[0001] The present invention relates to the field of optical technologies, and particularly to a continuous zoom lens for a mid-wave infrared cooled detector. Background Art

[0002] In recent years, significant progress has been made in infrared imaging technology, which has been widely applied in many fields such as military, security, industrial inspection, and medical. Especially in search, tracking, and recognition systems, infrared imaging technology plays a crucial role. Currently, most such systems use dual-field-of-view lenses. The large field of view is used for quickly searching and detecting targets, while the small field of view is used for precisely identifying targets.

[0003] However, dual-field-of-view lenses have obvious defects during the process of switching the field of view. Due to the sudden change in focal length when switching the field of view, it is difficult for the imaging system to quickly and accurately refocus, which easily causes the loss or blurring of the target, seriously affecting the system's ability to continuously track and stably recognize the target. In military reconnaissance scenarios, the target may break away from the monitoring range at the moment of field-of-view switching, resulting in the omission of key intelligence; in the field of security monitoring, this problem may cause the monitoring system to be unable to continuously lock suspicious targets, reducing the security guarantee.

[0004] The continuous zoom lens can theoretically effectively solve the above problems of dual-field-of-view lenses. By continuously and smoothly adjusting the focal length, it can achieve stable tracking and clear imaging of the target. However, the technology of infrared continuous zoom lenses faces many challenges. On the one hand, the selection of optical materials in the infrared band is limited, and the manufacturing process is complex, which greatly increases the difficulty of lens design and production and keeps the cost high. On the other hand, to ensure high-resolution imaging and a large field-of-view range, the lens needs to have a large size and weight, which not only increases the overall burden of the system but also limits its use in application scenarios with strict requirements for volume and weight, such as being carried by drones and portable devices.

[0005] With the continuous improvement of the performance requirements for infrared imaging systems in various fields, the market's demand for infrared continuous zoom lenses that are small in size, light in weight, have a large zoom ratio, and are suitable for mass production is becoming increasingly urgent. Developing such a lens has important practical significance for improving the performance of infrared imaging systems and expanding their application scope. Summary of the Invention

[0006] The present invention aims to provide a mid-wave infrared continuous zoom lens with a large zoom ratio to solve the problems in existing infrared imaging systems such as easy loss and blurring of targets when switching the field of view of dual-field-of-view lenses, as well as the large technical difficulty, high cost, large volume, and heavy weight of traditional infrared continuous zoom lenses, and to achieve the technical effects of short overall optical length, small volume, convenient assembly and adjustment, large zoom ratio, and high imaging quality, meeting the requirements for high-precision infrared imaging in multiple fields such as military, security, and industrial inspection.

[0007] A mid-wave infrared continuous zoom lens with a large zoom ratio, comprising: a front fixed group, a zoom group, a compensation group one, a compensation group two, a rear fixed group, and a detector part arranged in sequence from the object side to the image side.

[0008] In an embodiment of the present invention, each of the above-mentioned front fixed group to rear fixed group has an object side surface facing the object side and allowing imaging light to pass through.

[0009] In an embodiment of the present invention, each of the above-mentioned front fixed group to rear fixed group has an image side surface facing the image side and allowing imaging light to pass through;

[0010] In an embodiment of the present invention, the above-mentioned front fixed group includes a first lens and a second lens group starting from the object side and having a positive optical power. The first lens is a meniscus-shaped silicon single crystal positive lens with a convex surface facing the object side, and its surface types are all spherical surfaces;

[0011] In an embodiment of the present invention, the above-mentioned second lens is a meniscus-shaped germanium single crystal negative lens with a convex surface facing the object side, and its concave surface is an aspherical surface;

[0012] In an embodiment of the present invention, the above-mentioned zoom group has a third lens with a negative optical power. The zoom group lens is a double concave germanium single crystal negative lens, and its side facing the image side is an aspherical surface;

[0013] In an embodiment of the present invention, the above-mentioned compensation group one is a fourth lens with a positive optical power. The compensation group one lens is a double convex silicon single crystal positive lens, and its side facing the object side is a diffractive surface;

[0014] In an embodiment of the present invention, the above-mentioned compensation group two is a fifth lens with a negative optical power. The compensation group two lens is a meniscus-shaped IRG204 negative lens, and its side facing the object side is an aspherical surface;

[0015] In an embodiment of the present invention, the above-mentioned rear fixed group includes a sixth lens, a seventh lens, and an eighth lens, and has a positive optical power. The sixth lens is a meniscus-shaped germanium single crystal positive lens, and its side facing the object side is an aspherical surface;

[0016] In an embodiment of the present invention, the above-mentioned seventh lens is a meniscus-shaped calcium fluoride negative lens, and its surface types are all spherical surfaces;

[0017] In an embodiment of the present invention, the above-mentioned eighth lens is a double convex silicon single crystal positive lens, and its side facing the object side is an aspherical surface;

[0018] In an embodiment of the present invention, after the above-mentioned eighth lens is the detector optical part, including: a protection window, a cold screen, a cold stop, and an image plane. The cold stop is set as the aperture stop of the optical system.

[0019] In the embodiments of the present invention, the above lens satisfies the following parameters: effective focal length EFL = 21 - 420 mm, F number = 4, the total length of the optical system including the refrigerated detector part = 200 mm, the resolution of the adapted detector is 640×512, and the pixel size is 15 um.

[0020] In the embodiments of the present invention, the horizontal field of view angle range of the above lens is: 2w = 25.8° - 1.3°.

[0021] In the embodiments of the present invention, the aspheric surface in the above lens satisfies the following expression:

[0022]

[0023] Where, Z: the displacement in the optical axis direction, r: the height of the optical axis, c: the paraxial curvature radius, K: the conic coefficient, and A, B, C, D, E, F are aspheric coefficients.

[0024] In the embodiments of the present invention, the diffractive surface in the above lens satisfies the following expression:

[0025]

[0026] In the formula, is the phase, M is the diffraction order, the diffraction order is 1, and the normalized radius ρ is 1 mm.

[0027] In the embodiments of the present invention, the total moving stroke of the above third lens is 40.39 mm.

[0028] In the embodiments of the present invention, the total moving stroke of the above fourth lens is 24.38 mm.

[0029] In the embodiments of the present invention, the total moving stroke of the above fifth lens is 9.18 mm.

[0030] In the embodiments of the present invention, the surface of the above first lens close to the object side is coated with a diamond-like carbon film.

[0031] The embodiments of the present invention have at least the following advantages or beneficial effects:

[0032] The present invention includes the specific compositions of the front fixed group, the zoom group, the first compensating group, the second compensating group, the rear fixed group and the detector part. Based on this unique eight-lens structure design, the lens has successfully achieved a large zoom ratio of 20 times. At the same time, the effective focal length range of the lens is 21 - 420 mm, the total length of the optical system is only 200 mm, and the maximum aperture is 116 mm. This design enables the lens to achieve a high degree of compactness of the optical system while ensuring high zoom performance, greatly reducing the overall volume. Compared with traditional infrared continuous zoom lenses, it is more convenient to be integrated into various devices, meeting the requirements for miniaturization of devices. For example, it has significant application advantages in fields such as unmanned aerial vehicles and portable thermal imagers.

[0033] The special designs and moving characteristics of the third lens of the zoom group, the fourth lens of the first compensating group and the fifth lens of the second compensating group of the present invention are the key. The third lens of the zoom group is a biconcave germanium single crystal negative lens with an aspherical surface on the image side, and its total moving stroke is 40.39 mm; the fourth lens of the first compensating group is a biconvex silicon single crystal positive lens with a diffractive surface on the object side, and the total moving stroke is 24.38 mm; the fifth lens of the second compensating group is a meniscus IRG204 negative lens with an aspherical surface on the object side, and the total moving stroke is 9.18 mm. These lenses cooperate with each other to make the zoom curve of the lens smooth and can precisely control the light propagation path during the zoom process. At the same time, this design effectively ensures the stability of the optical axis, avoiding the problem of optical axis deviation caused by the movement of the lens, and laying a solid foundation for high-quality imaging.

[0034] The materials and surface characteristics of each lens group of the lens of the present invention are carefully designed. For example, the lenses with different materials and aspherical designs in the front fixed group and the rear fixed group, and the lens with a diffractive surface in the first compensating group, etc., effectively correct optical errors such as aberration and chromatic aberration. At the same time, the horizontal field of view angle range of the lens is 25.8° - 1.3°. With the above optical design, the lens has excellent imaging performance throughout the zoom range. The average MTF of the full field of view > 0.233 lp / mm, which can clearly capture target details. Whether searching for targets in a large field of view or identifying targets in a small field of view, it can provide high-quality images, meeting the strict requirements for imaging accuracy.

[0035] The surface of the first lens close to the object side is coated with a diamond-like carbon film. This coating treatment can enhance the wear resistance and corrosion resistance of the lens, effectively protecting the lens surface from the erosion of the external environment, such as dust, water vapor, chemical substances, etc. In a complex use environment, it can extend the service life of the lens, ensure that the lens maintains good optical performance stably for a long time, reduce the problem of image quality degradation caused by lens surface damage, and improve the reliability and practicality of the lens. Description of the Drawings

[0036] Figure 1It is the optical system diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 420 mm;

[0037] Figure 2 It is the spot diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 420 mm;

[0038] Figure 3 It is the optical transfer function diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 420 mm;

[0039] Figure 4 It is the astigmatism and distortion diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 420 mm;

[0040] Figure 5 It is the relative illumination diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 420 mm;

[0041] Figure 6 It is the optical system diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 21 mm;

[0042] Figure 7 It is the spot diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 21 mm;

[0043] Figure 8 It is the optical transfer function diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 21 mm;

[0044] Figure 9 It is the astigmatism and distortion diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 21 mm;

[0045] Figure 10 It is the relative illumination diagram when the focal length of the mid-wave infrared continuous zoom lens with a large zoom ratio provided by the present invention is 21 mm.

[0046] Explanation of reference numerals: 1. First lens, 2. Second lens, 3. Third lens, 4. Fourth lens, 5. Fifth lens, 6. Sixth lens, 7. Seventh lens, 8. Eighth lens. Detailed implementation manners

[0047] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0048] Figure 1-10 , an embodiment of the present invention discloses a mid-wave infrared continuous zoom lens with a large zoom ratio, which includes: a front fixed group, a zoom group, a compensation group one, a compensation group two, a rear fixed group, and a detector part arranged in sequence from the object side to the image side.

[0049] In the embodiment of the present invention, each of the above-mentioned front fixed group to rear fixed group has an object side surface facing the object side and allowing imaging light to pass through.

[0050] In the embodiment of the present invention, each of the above-mentioned front fixed group to rear fixed group has an image side surface facing the image side and allowing imaging light to pass through.

[0051] In the embodiment of the present invention, the above-mentioned front fixed group includes a first lens and a second lens group starting from the object side and having a positive optical power. The first lens is a meniscus-shaped silicon single crystal positive lens with a convex surface facing the object side, and its surface types are all spherical surfaces.

[0052] In the embodiment of the present invention, the above-mentioned second lens is a meniscus-shaped germanium single crystal negative lens with a convex surface facing the object side, and its concave surface is an aspherical surface.

[0053] In the embodiment of the present invention, the above-mentioned zoom group has a third lens with a negative optical power. The zoom group lens is a double concave germanium single crystal negative lens, and its side facing the image side is an aspherical surface.

[0054] In the embodiment of the present invention, the above-mentioned compensation group one is a fourth lens with a positive optical power. The compensation group one lens is a double convex silicon single crystal positive lens, and its side facing the object side is a diffractive surface.

[0055] In the embodiment of the present invention, the above-mentioned compensation group two is a fifth lens with a negative optical power. The compensation group two lens is a meniscus-shaped IRG204 negative lens, and its side facing the object side is an aspherical surface.

[0056] In the embodiment of the present invention, the above-mentioned rear fixed group includes a sixth lens, a seventh lens, and an eighth lens, and has a positive optical power. The sixth lens is a meniscus-shaped germanium single crystal positive lens, and its side facing the object side is an aspherical surface.

[0057] In the embodiment of the present invention, the above-mentioned seventh lens is a meniscus-shaped calcium fluoride negative lens, and its surface types are all spherical surfaces.

[0058] In an embodiment of the present invention, the eighth lens is a biconvex silicon single crystal positive lens, and the side facing the object side is an aspherical surface;

[0059] In an embodiment of the present invention, behind the eighth lens, the detector optical part includes: a protection window, a cold screen, a cold stop, and an image plane, and the cold stop is set as the aperture stop of the optical system.

[0060] In an embodiment of the present invention, the lens satisfies the following parameters: effective focal length EFL = 21 - 420 mm, F number = 4, the total length of the optical system including the refrigerated detector part = 200 mm, the resolution of the adapted detector is 640 × 512, and the pixel size is 15 um.

[0061] In an embodiment of the present invention, the horizontal field of view angle range of the lens is: 2w = 25.8° - 1.3°.

[0062] In an embodiment of the present invention, the aspherical surface in the lens satisfies the following expression:

[0063]

[0064] Wherein, Z: the displacement in the optical axis direction, r: the height of the optical axis, c: the paraxial curvature radius, K: the conic coefficient, and A, B, C, D, E, F are aspherical coefficients.

[0065] In an embodiment of the present invention, the diffractive surface in the lens satisfies the following expression:

[0066]

[0067] In the formula, is the phase, M is the diffraction order, the diffraction order is 1, and the normalized radius ρ is 1 mm.

[0068] In an embodiment of the present invention, the total moving stroke of the third lens is 40.39 mm.

[0069] In an embodiment of the present invention, the total moving stroke of the fourth lens is 24.38 mm.

[0070] In an embodiment of the present invention, the total moving stroke of the fifth lens is 9.18 mm.

[0071] In an embodiment of the present invention, the surface of the first lens close to the object side is coated with a diamond-like carbon film.

[0072] The following further describes the present invention in detail with specific embodiments.

[0073] Embodiment 1:

[0074] This embodiment is an example of the application of this invention patent to a refrigerated staring focal plane detector with a resolution of 640×512 pixels and a pixel size of 15 microns.

[0075] Figure 1 、 Figure 6 They are respectively the optical system diagrams of this invention patent when the focal lengths are 420mm and 21mm. The structures of the lenses are the same, and one of the diagrams is taken as an example for illustration.

[0076] As Figure 1 shown, this embodiment consists of a front fixed group with positive optical power, a zoom group with negative optical power, a first compensation group with positive optical power, a second compensation group with negative optical power, a rear fixed group with positive optical power, and finally a detector.

[0077] The front fixed group includes two lenses. The first lens is a positive lens made of single-crystal silicon, and both of its two surfaces are spherical surfaces; the second lens is a negative lens made of single-crystal germanium, and its S4 surface is an aspherical surface. The front fixed group uses the combination form of positive and negative lenses, which plays the role of shortening the total length of a telephoto objective; the third lens of the zoom group is a negative lens made of single-crystal germanium, and its S6 surface is an aspherical surface. This lens is a moving lens, which plays the role of zooming during the zooming process, and the total moving stroke is 40.39mm; the fourth lens of the first compensation group is a positive lens made of single-crystal silicon, and its S7 surface is a diffractive aspherical surface; the fifth lens of the second compensation group is a negative lens made of IRG204, and its S9 surface is an aspherical surface; this lens is a moving lens. When the lens of the zoom group moves, the lenses of the first compensation group and the second compensation group move accordingly to ensure that the image plane position remains unchanged. The moving curve is a straight line, and the total moving strokes are 24.38mm and 9.18mm respectively; the rear fixed group includes three lenses. The sixth lens is a positive lens made of single-crystal germanium, and its S11 surface is an aspherical surface.

[0078] In the system, the specific parameters of a large zoom ratio mid-wave infrared continuous zoom lens system are shown in Table 1. Among them, the units of the radius of curvature, thickness / distance, and focal length are all millimeters (mm):

[0079] Table 1

[0080] Surface Lens Radius of curvature Thickness / Spacing Material Aperture S1 First lens 110.85 12.76 SI 116 S2 166.83 3.03 S3 Second lens 190.58 6.5 GE 106 S4 121.989 62.39 / 22 S5 Third lens -105.482 2.5 GE 35 S6 66.26 4.27 / 65.04 S7 Fourth lens 132.234 5.7 SI 38 S8 -82.267 34.57 / 5 S9 Fifth lens -20.3 5 IRG204 21 S10 -28.7 21.6 / 30.78 S11 Sixth lens 23.04 2.8 GE 12 S12 23.65 5.48 S13 Seventh lens -8.73 2.5 CAF2 13 S14 -30.23 0.5 S15 Eighth lens 28.2 3 SI 16 S16 -41.13 4.5

[0081] The aspherical surfaces mentioned in the above eight lenses are all even aspherical surfaces, and their expressions are as follows

[0082]

[0083] Among them, Z: the displacement in the optical axis direction, r: the height of the optical axis, c: the paraxial radius of curvature, K: the conic coefficient, A, B, C, D, E, F are the aspherical coefficients.

[0084] Table 2 shows the aspheric coefficients of surfaces S4, S6, S7, S9, S11, and S15: Table 2

[0085] Surface S4 -3.8756E-6 1.7571E-9 -1.8098E-12 3.5569E-16 S6 9.4503E-9 5.8033E-15 3.0771E-19 3.3242E-21 S7 1.6813E-6 -1.3687E-8 1.825E-10 -7.8673E-13 S9 -1.402E-4 3.1854-E6 -4.4384E-8 -3.0282E-11 S11 -7.2926E-5 3.1171E-7 -2.6024E-9 2.5486E-11 S15 -2.2532E-10 7.7466E-10 7.035E-13 -1.7916E-15

[0086] For the diffractive surfaces mentioned in the above eight lenses, their expressions are as follows:

[0087] φ = M(B1ρ 2 + B2ρ 4 +... + B7ρ 14 + B8ρ 16 )

[0088] In the formula, φ is the phase, M is the diffraction order, the diffraction order is 1, and the normalized radius ρ is 1 mm.

[0089] Table 3 shows the diffraction coefficients of surface S7,

[0090] Table 3

[0091] Surface S7 -0.0338 2.1688e-4 1.7102e-6

[0092] Figure 4 and Figure 9 are the modulation transfer function curves of the example at focal lengths of 420 mm and 21 mm, indicating that the modulation transfer function values are high at different focal lengths, and the target is clear throughout the continuous zooming process; Figure 4 and Figure 9 are the field curvature distortion diagrams of the example at focal lengths of 420 mm and 21 mm, indicating that the full-field distortion at the telephoto end of the lens is ≤1%, and the full-field distortion at the wide-angle end is ≤5%, and the image has no obvious deformation.

[0093] Comparative Example 1:

[0094] Select a common traditional dual-field infrared lens on the market as a comparative example. The basic parameters of this lens are similar to those of the lens of the present invention, both are applicable to the mid-wave infrared band, the detector resolution is 640×512, and the pixel size is 15 microns.

[0095] Field of view switching test: Under the same test environment, use this traditional dual-field infrared lens to observe the same test target. When switching from the large field of view to the small field of view, the situation of target loss clearly occurs. Since the focal length changes jumpily when the dual-field lens switches the field of view, the imaging system cannot quickly refocus, resulting in the target being out of the monitoring range at the moment of field of view switching, and the target cannot be continuously tracked and stably identified.

[0096] Imaging quality comparison: At a fixed focal length, the imaging effect of the traditional dual-field-of-view lens is compared with that of the lens of the present invention. The traditional dual-field-of-view lens is significantly inferior to the lens of the present invention in terms of imaging clarity and detail restoration. For example, when observing a complex infrared test target, the lens of the present invention can clearly distinguish the tiny patterns and details on the target, and the average MTF of the full field of view > 0.233 lp / mm; while the imaging of the traditional dual-field-of-view lens is blurred, some details are lost, and it cannot meet the requirements of high-precision imaging.

[0097] Volume and weight comparison: The volume and weight of the two lenses are measured. The lens of the present invention adopts an eight-element structure, with a total optical system length of 200 mm, a maximum aperture of 116 mm, and a mass of 588 g; while the traditional dual-field-of-view lens has a larger volume due to structural design limitations, with a length of 300 mm, an aperture of 150 mm, and a weight of 800 g. In practical applications, the lens of the present invention has obvious advantages in miniaturization and light weight, and is more convenient to be integrated into various devices, such as portable infrared thermal imagers, infrared imaging systems carried by drones, etc., expanding the application scenarios.

Claims

1. A medium-wave infrared continuous zoom lens with a large zoom ratio, characterized in that include: A front fixed group, a zoom group, a compensation group 1, a compensation group 2, a rear fixed group and a detector part are arranged in sequence from the object side to the image side, and each of the front fixed group to the rear fixed group has an object side surface facing the object side and allowing imaging light to pass through, and each of the front fixed group to the rear fixed group has an image side surface facing the image side and allowing imaging light to pass through; the front fixed group includes a first lens and a second lens group starting from the object side and having positive optical power, and the first lens is a meniscus silicon single crystal positive lens with a convex surface facing the object side, and the surface type of both lenses is spherical; The second lens is a meniscus-shaped germanium single crystal negative lens with a convex surface facing the object, and a concave surface thereof is an aspherical surface; The zoom group has a third lens with negative optical power, and the zoom group lens is a double concave germanium single crystal negative lens, and the side facing the image side is aspherical; The compensation group is a fourth lens having positive optical power, and the lenses of the compensation group are biconvex silicon single crystal positive lenses, and the side facing the object is a diffraction surface; The second compensation group is a fifth lens having negative optical power, and the second compensation group lens is a meniscus IRG204 negative lens, and the side thereof facing the object side is an aspherical surface; The rear fixed group includes a sixth lens, a seventh lens and an eighth lens, and has positive optical power. The sixth lens is a meniscus germanium single crystal positive lens, and the side thereof facing the object side is an aspherical surface; The seventh lens is a meniscus calcium fluoride negative lens, and its surface type is spherical; The eighth lens is a biconvex silicon single crystal positive lens, and the side thereof facing the object is an aspherical surface; The detector optical part behind the eighth lens includes: a protection window, a cold screen, a cold stop and an image plane, and the cold stop is set as an aperture stop of the optical system.

2. The medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The lens meets the following parameters: effective focal length EFL=21-420 mm, F number=4, total length of the optical system including the cooling detector part=200 mm, the resolution of the adapted detector is 640×512, and the pixel size is 15 um.

3. The medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The horizontal field angle range of the lens is: 2w=25.8°~1.3°.

4. The medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The aspherical surface in the lens element of the lens satisfies the following expression: Among them, Z: displacement in the direction of optical axis, r: height of optical axis, c: paraxial curvature radius, K: conic coefficient, A, B, C, D, E, F are aspheric coefficients.

5. A medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 4, characterized in that: The diffraction surface in the lens satisfies the following expression: φ=M(B1ρ 2 +B2p 4 +...+B7r 14 +B8p 16 ) In the formula, φ is the phase, M is the diffraction order, the diffraction order is 1, and the normalized radius is ρ, which is 1 mm.

6. A medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The total moving stroke of the third lens is 40.39 mm.

7. A medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The total moving stroke of the fourth lens is 24.38 mm.

8. The medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The total moving stroke of the fifth lens is 9.18 mm.

9. The medium-wave infrared continuous zoom lens with a large zoom ratio according to claim 1, characterized in that: The surface of the first lens close to the object side is coated with a diamond-like carbon film.

Images