Infrared lens system with high telephoto ratio and long focal length

Abstract

The invention relates to an infrared lens system with high telephoto ratio and long focal length, which comprises five lenses with meandering force, and sequentially comprises a first lens with positive focal power, a second lens with negative focal power, a third lens with positive focal power, a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with negative focal power, a seventh lens with positive focal power and a seventh lens with negative focal power from an object plane to an image plane along an optical axis. The fifth lens has negative focal power; the fifth lens is an aspheric lens made of glass; according to the invention, the imaging is clear and is close to aberration-free, the lens groups and the focal power for forming each lens group are reasonably distributed in distortion control, the special problem of optical distortion is solved, the optical distortion of the system is less than 1% on the premise of achieving high image quality, the length of the optical system is greatly shortened, and more possibilities are provided for the integration and modularization of the subsequent system.

Description

Technical Field

[0001] The present invention relates to the technical field of optical imaging, and in particular to an infrared lens system with a high telephoto ratio and a long focal length. Background Art

[0002] An infrared telephoto lens is a lens specifically used for an infrared optical system, which has a telephoto function and can capture infrared radiation at a long distance. At the same time, infrared rays have a penetration ability for some materials and fabrics relative to visible light, and can produce a magical perspective effect. In addition to the above technical applications, infrared photography can also be used to capture scenes that are invisible to the naked eye in a completely dark environment. Nowadays, there are various infrared telephoto lenses to meet the needs of different scenarios. The optical system of the previous telephoto infrared lens was relatively large in size, which was not conducive to system integration, and the imaging at the far end was not clear, bringing great difficulties to subsequent detectors and computer data processing. Due to the expansion of applications and the growth of market demand, it is an urgent problem to provide an infrared lens with a high telephoto ratio and a long focal length. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides an infrared lens system with a high telephoto ratio and a long focal length, so as to solve the problems that the telephoto optical system is relatively large in size, not conducive to system integration, and it is difficult to clearly image the details of distant targets, bringing great difficulties to subsequent detectors and computer data processing.

[0004] The technical solution provided by the present invention to achieve the above object is as follows: An infrared lens system with a high telephoto ratio and a long focal length provided by the present application includes a first positive lens, a second negative lens, a third positive lens, a fourth positive lens, and a fifth negative lens arranged in sequence along the optical axis from the object plane to the image plane. The refractive index of the first positive lens satisfies 1.48 < n1 < 1.5, where n1 is the refractive index of the first positive lens. The refractive index of the second negative lens satisfies 1.85 < n2 < 1.95, where n2 is the refractive index of the second negative lens. The refractive index of the third positive lens satisfies 1.48 < n3 < 1.5, where n3 is the refractive index of the third positive lens. The refractive index of the fourth positive lens satisfies 1.6 < n4 < 1.7, where n4 is the refractive index of the fourth positive lens. The refractive index of the fifth negative lens of the system satisfies 1.48 < n5 < 1.5, where n5 is the refractive index of the fifth negative lens. The surface types of the first positive lens, the second negative lens, the third positive lens, and the fourth positive lens are all standard spherical surfaces. The fifth negative lens is an aspherical glass lens, and the fifth negative lens satisfies the conditional formula: 81 < vd < 82, where vd is the Abbe number of the fifth negative lens; A diaphragm is disposed between the third positive lens and the fourth positive lens, and the diaphragm is used to adjust the size of the imaging range.

[0005] Furthermore, the lens system satisfies the relational formula: Y = TTL / f < 0.75, where Y is the telephoto ratio of the lens system, TTL is the distance from the object side of the first lens to the imaging surface of the lens system on the optical axis, and f is the focal length of the lens system.

[0006] Furthermore, the high-telephoto-ratio long-focal-length infrared lens system satisfies the conditional formula: , where w is the half field of view angle of the lens system, f is the focal length of the lens system, and H is the Gaussian image height of the lens system.

[0007] Furthermore, the high-telephoto-ratio long-focal-length infrared lens system satisfies the conditional formula: , where FNUM is the relative aperture of the lens system and w is the half field of view angle of the lens system.

[0008] Furthermore, the high-telephoto-ratio long-focal-length infrared lens system satisfies the conditional formula: , where f is the focal length of the lens system, θ is the field of view angle of the lens system, and D is the diagonal length of the imaging surface of the lens system.

[0009] Furthermore, the high-telephoto-ratio long-focal-length infrared lens system satisfies the conditional formula: , where x is the transmittance of the wavelength of the lens of the lens system, e is the base of the natural logarithm, a is the absorption coefficient of the lens of the lens system, and d is the thickness of the lens of the lens system; the transmittances of the respective lenses of the lens system satisfy the conditional formula: , where α is the transmittance of the wavelength of the lens system, x1 is the transmittance of the wavelength of the first positive lens of the lens system, x2 is the transmittance of the wavelength of the second negative lens of the lens system, x3 is the transmittance of the wavelength of the third positive lens of the lens system, x4 is the transmittance of the wavelength of the fourth positive lens of the lens system, and x5 is the transmittance of the wavelength of the fifth negative lens of the lens system.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention relates to a high-telephoto-ratio long-focal-length infrared lens system, which employs one glass aspherical lens and four glass spherical lenses. The overall structure can well balance aberration, so that the imaging of a distant object is clear and almost aberration-free. Moreover, the thermal expansion coefficients of the respective lenses of the present invention are all less than In terms of distortion control, the lens groups and the optical focal lengths of each lens group are reasonably distributed to solve the special problem of optical distortion. Under the premise of achieving high image quality, the distortion of the lens system is less than 1%, the spot of the lens system in the full field of view is less than 0.01mm, and the lateral chromatic aberration of the lens system is less than 0.01mm. In addition, the length of the lens system is greatly shortened, providing more possibilities for subsequent system integration and modularization. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 It is a schematic structural diagram of a high telephoto ratio and long focal length infrared lens system of Example 1 of the present invention.

[0013] Figure 2 This is a lateral chromatic aberration diagram of the high telephoto ratio and long focal length infrared lens system of Example 1 of the present invention.

[0014] Figure 3 3 is a distortion diagram of the infrared lens system with a high telephoto ratio and a long focal length according to Example 1 of the present invention.

[0015] Figure 4 3 is a RMS graph of the diffuse spots of the infrared lens system with a high telephoto ratio and a long focal length according to Example 1 of the present invention.

[0016] Figure 5 This is a point diagram of the high telephoto ratio and long focal length infrared lens system of Example 1 of the present invention.

[0017] Figure 6 It is a modulation transfer function analysis diagram of the high telephoto ratio and long focal length infrared lens system of Example 1 of the present invention.

[0018] Figure 7 It is a schematic structural diagram of a high telephoto ratio and long focal length infrared lens system of Example 2 of the present invention.

[0019] Figure 8 This is a lateral chromatic aberration diagram of the high telephoto ratio and long focal length infrared lens system of Example 2 of the present invention.

[0020] Fig. 9 3 is a distortion diagram of the high telephoto ratio and long focal length infrared lens system of Example 2 of the present invention.

[0021] Fig.10 It is the RMS diagram of the diffuse spots of the infrared lens system with a high telephoto ratio and a long focal length according to Example 2 of the present invention.

[0022] Fig.11 This is a point diagram of the high telephoto ratio and long focal length infrared lens system of Example 2 of the present invention.

[0023] Fig.12 It is a modulation transfer function analysis diagram of the high telephoto ratio and long focal length infrared lens system of Example 2 of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0025] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0026] In the present invention, the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like are based on the directions or positional relationships shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific direction, or to be constructed and operated in a specific direction.

[0027] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those skilled in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0028] In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0029] The technical solution of the present invention will be further described below in conjunction with embodiments and drawings.

[0030] The present application provides a long focal length infrared lens system with a high telephoto ratio. The lens system has a total of five lenses. The lens system includes a first positive lens, a second negative lens, a third positive lens, a fourth positive lens, and a fifth negative lens arranged in sequence from the object plane along the optical axis towards the image plane. The overall structure can well balance many aberrations, improve resolution, enhance contrast, and achieve miniaturization of the lens system.

[0031] The refractive index of the first positive lens satisfies 1.48 < n1 < 1.5, where n1 is the refractive index of the first positive lens; The refractive index of the second negative lens satisfies 1.85 < n2 < 1.95, where n2 is the refractive index of the second negative lens; The refractive index of the third positive lens satisfies 1.48 < n3 < 1.5, where n3 is the refractive index of the third positive lens; The refractive index of the fourth positive lens satisfies 1.6 < n4 < 1.7, where n4 is the refractive index of the fourth positive lens; The refractive index of the fifth negative lens satisfies 1.48 < n5 < 1.5, where n5 is the refractive index of the fifth negative lens; As an optional embodiment, the surface types of the first positive lens, the second negative lens, the third positive lens, and the fourth positive lens all include standard spherical surfaces; The fifth negative lens is an aspherical glass lens, and the fifth negative lens satisfies the condition: 81 < vd < 82, where vd is the Abbe number of the fifth negative lens; A diaphragm is provided between the third positive lens and the fourth positive lens, and the diaphragm is used to adjust the size of the imaging range.

[0032] The long focal length infrared lens system with a high telephoto ratio satisfies the relationship: Y = TTL / f < 0.75, where Y is the telephoto ratio of the lens system, TTL is the distance from the object side of the first lens to the imaging plane of the lens system on the optical axis, and f is the focal length of the lens system. When the lens system satisfies this formula, by limiting the relationship between the total length and the focal length of the lens system, the total length of the lens system can be made smaller, thus providing more possibilities for subsequent integration.

[0033] The long focal length infrared lens system with a high telephoto ratio satisfies the conditional formula: , where w is the half field of view angle of the lens system, f is the focal length of the lens system, and H is the Gaussian image height of the lens system. Considering that the lens is a long focal length infrared lens system with a high telephoto ratio, combining the focal length and the Gaussian image height, the specific embodiments of the present invention select the full field of view angle to be .

[0034] The long focal length infrared lens system with a high telephoto ratio satisfies the conditional formula: , FNUM is the relative aperture of the lens system, w is the half field angle of the lens system, and the depth of field of the lens system satisfies the following relationship: , where: f is the focal length of the lens system; F is the aperture number of the lens system under paraxial operation; δ is the allowable diameter of the confusion circle of the lens system; L is the focusing distance of the lens system, and ΔL is the depth of field of the lens system. It can be seen from the formula of the depth of field that in order to obtain a larger depth of field, the F number of the lens system needs to be larger, but when the F number increases, the luminous flux entering the lens system will be relatively reduced, and the resolution will be reduced. Therefore, setting a suitable F number requires comprehensive consideration of other factors; considering that the lens system is a high telephoto ratio long focal length infrared lens, combined with the characteristics of such lens systems, as well as the working depth of field and imaging quality, the system F number of the specific embodiment of the present invention is set to 5.6.

[0035] The high telephoto ratio and long focal length infrared lens system satisfies the conditional formula: , where f is the focal length of the lens system, θ is the field of view of the lens system, and D is the diagonal length of the imaging surface of the lens system. Since the lens system is a high telephoto ratio and long focal length infrared lens system, the focal length value will be relatively large. Considering the size of the field of view angle and the size of the diagonal of the imaging surface, the specific embodiment of the present invention selects f as 240 mm.

[0036] The high telephoto ratio and long focal length infrared lens system satisfies the conditional formula: , x is the transmittance of the wavelength of the lens of the lens system, e is the base of the natural logarithm, a is the absorption coefficient of the lens of the lens system, and d is the thickness of the lens of the lens system; the transmittance of each lens of the lens system satisfies the conditional formula: , α is the transmittance of the wavelength of the lens system, x1 is the transmittance of the wavelength of the first positive lens of the lens system, x2 is the transmittance of the wavelength of the second negative lens of the lens system, x3 is the transmittance of the wavelength of the third positive lens of the lens system, x4 is the transmittance of the wavelength of the fourth positive lens of the lens system, x5 is the transmittance of the wavelength of the fifth negative lens of the lens system. When the lens system satisfies the transmittance of the wavelength of the lens system greater than 0.9, it can ensure that the field of view of the system is bright and the imaging is real and clear.

[0037] Embodiment 1: In this embodiment, the F number is 5.6, the field of view angle is 4°, the focal length is 240 mm, the total length is 100 mm, and the back focal length is 60 mm.

[0038] like Figure 1This embodiment provides an infrared lens system with a high telephoto ratio and a long focal length, which includes, along the direction from the object side to the image side of the optical axis, a first positive power lens group and a second negative power lens group, wherein the aperture L4 is located between the first positive power lens group and the second negative power lens group, i.e., surface S7, and the image surface L7 is surface S12; along the direction from the object side to the image side of the optical axis, the first positive power lens group includes, along the direction from the object side to the image side of the optical axis, a first positive lens L1, a second negative lens L2 and a third positive lens L3; with respect to the lens shape, along the direction from the object side to the image side of the optical axis, the first positive lens L1 is a convex-convex lens, the second negative lens L2 is a concave-concave lens, and the third positive lens L3 is a concave-concave lens. is a convex-concave lens, wherein S1 is the object end of the first lens, S2 is the image end of the first lens, S3 is the object end of the second lens, S4 is the image end of the second lens, S5 is the object end of the third lens, and S6 is the image end of the third lens; along the direction from the object side to the image side of the optical axis, the second negative optical focal length lens group includes: a fourth positive lens L5 and a fifth negative lens L6 in sequence; with respect to the lens shape, along the direction from the object side to the image side of the optical axis, the fourth positive lens L5 is a concave-convex lens, and the fifth negative lens L6 is a concave-concave lens, wherein S8 is the object end of the fourth lens, S9 is the image end of the fourth lens, S10 is the object end of the fifth lens, and S11 is the image end of the fifth lens.

[0039] The telephoto ratio of this embodiment is Y=TTL / f=0.67, where Y is the telephoto ratio of the lens system, TTL is the distance from the object side of the first lens to the imaging surface of the lens system on the optical axis, and f is the focal length of the lens system, which meets the requirements.

[0040] The curvature radius, thickness and thermal expansion coefficient of the system described in this embodiment are shown in Table 1.1, where the units of curvature radius and thickness are both mm.

[0041] Table 1.1

[0042] In Table 1.1, surface 1 is the front surface of the first positive lens, surface 2 is the back surface of the first positive lens, surface 3 is the front surface of the second negative lens, surface 4 is the back surface of the second negative lens, surface 5 is the front surface of the third positive lens, surface 6 is the back surface of the third positive lens, surface 7 is the aperture, surface 8 is the front surface of the fourth positive lens, surface 9 is the back surface of the fourth positive lens, surface 10 is the front surface of the fifth negative lens, surface 11 is the back surface of the fifth negative lens, and surface 12 is the image plane; From Table 1.1, it can be seen that the thermal expansion coefficients of the five lenses of the lens system are all lower than , meet the requirements; From Table 1.1, it can be seen that the Abbe number of the aspherical lens of the lens system is 81.61, which meets the requirements; In this implementation case, the transmittance of the long wavelength 1.97um of the lens system is 0.93549554, the transmittance of the medium wavelength 1.53um of the lens system is 0.99437362, and the transmittance of the short wavelength 1.06um of the lens system is 0.99319942, all of which are greater than 0.9 and meet the requirements.

[0043] Table 1.2

[0044] As shown in Table 1.2, assuming that the Z axis is the optical axis, the origin of the rectangular coordinate system coincides with the origin of the aspheric surface, and the rotation axis coincides with the optical axis of the system, the surface shape of the aspheric surface of the fifth negative lens can be expressed as:

[0045] in, is the incident height of the light on the aspheric surface, k is the cone coefficient, A2, A4, A6, ... are the high-order aspheric coefficients, c is the curvature at the vertex of the aspheric surface, and Z is the distance vector height from the vertex of the aspheric surface at a height of h along the optical axis. c is the curvature at the optical axis O, c = 1 / R (that is, the paraxial curvature c is the reciprocal of the curvature radius R in Table 1.2); k is the cone coefficient; Ai is the correction coefficient of the i-th order of the aspheric surface, and the high-order coefficients of each aspheric mirror are given in Table 1.2.

[0046] Among them, as a further test of the present invention, reference is made to Figure 2-Figure 6 , Figure 2 is the lateral chromatic aberration diagram of this system, where the vertical axis represents the lateral chromatic aberration and the horizontal axis represents the relative field of view. Figure 2 It can be seen that the full-field chromatic aberration from long wave to medium wave, long wave to short wave, and medium wave to short wave is no higher than 0.0036, indicating that the chromatic aberration has been well optimized.

[0047] Figure 3 This is the distortion diagram of the system, where the vertical axis represents the field of view and the horizontal axis represents the linear distortion. Figure 3 It can be seen that the curves of light in the three wavelength bands of 1.97um, 1.53um and 1.06um of the lens system overlap together, and the distortion is less than 1% in the full field of view, indicating that the distortion has been well optimized.

[0048] Figure 4 is the RMS diagram of the diffuse spot of this lens system, where the vertical axis is the diffuse spot size and the horizontal axis is the relative field of view. Figure 4 It can be seen that the diffuse spot size does not exceed 0.0047mm in the full field of view.

[0049] Figure 5is the full field of view point diagram of this lens system, where both the horizontal and vertical axes represent size. Figure 5 It can be seen that the energy of the point array images in each field of view is almost concentrated in the Airy disk, and the imaging quality is close to the diffraction limit.

[0050] Figure 6 The modulation transfer function curve of this lens system, the ordinate is the transfer function, the abscissa is the number of line pairs per millimeter, Figure 6 It can be seen that the meridian and sagittal of the diffraction limit overlap, the sagittal of the 0.5 field of view and the 0.75 field of view overlap, the sagittal of the 1.0 field of view and the meridian of the 0.5 field of view overlap, and the meridian and sagittal of the 0 field of view overlap. All of them are very close to the diffraction limit under different fields of view. It can be seen that this system can capture images with richer layers and stronger contrast.

[0051] Embodiment 2: In this embodiment, the F number is 5.6, the field of view angle is 6°, the focal length is 240 mm, the total length is 118 mm, and the back focal length is 60 mm.

[0052] like Figure 7 , this embodiment provides an infrared lens system with a high telephoto ratio and a long focal length, which includes, in sequence along the direction from the object side to the image side of the optical axis: a first positive power lens group and a second negative power lens group, wherein the aperture is located between the first positive power lens group and the second negative power lens group, i.e., surface S7, and the image plane L7 is surface S12; in the direction from the object side to the image side of the optical axis, the first positive power lens group includes, in sequence: a first positive lens L1, a second negative lens L2 and a third positive lens L3; with respect to the lens shape, in the direction from the object side to the image side of the optical axis, the first positive lens L1 is a convex-convex lens, the second negative lens L2 is a concave-concave lens, and the third positive lens L3 is A convex-concave lens, wherein S1 is the object end of the first lens, S2 is the image end of the first lens, S3 is the object end of the second lens, S4 is the image end of the second lens, S5 is the object end of the third lens, and S6 is the image end of the third lens; along the direction from the object side to the image side of the optical axis, the second negative optical focal length lens group includes in sequence: a fourth positive lens L5 and a fifth negative lens L6; with respect to the lens shape, along the direction from the object side to the image side of the optical axis, the fourth positive lens L5 is a concave-convex lens, and the fifth negative lens L6 is a concave-concave lens, wherein S8 is the object end of the fourth lens, S9 is the image end of the fourth lens, S10 is the object end of the fifth lens, and S11 is the image end of the fifth lens.

[0053] The telephoto ratio of this embodiment is Y=TTL / f=0.74, where Y is the telephoto ratio of the lens system, TTL is the distance from the object side of the first lens to the imaging surface of the lens system on the optical axis, and f is the focal length of the lens system, which meets the requirements.

[0054] The radius of curvature, thickness and thermal expansion coefficient of the lens system described in this embodiment are shown in Table 2.1, where the units of the radius of curvature and thickness are both mm.

[0055] Table 2.1

[0056] In Table 2.1, surface 1 is the front surface of the first positive lens, surface 2 is the back surface of the first positive lens, surface 3 is the front surface of the second negative lens, surface 4 is the back surface of the second negative lens, surface 5 is the front surface of the third positive lens, surface 6 is the back surface of the third positive lens, surface 7 is the aperture, surface 8 is the front surface of the fourth positive lens, surface 9 is the back surface of the fourth positive lens, surface 10 is the front surface of the fifth negative lens, surface 11 is the back surface of the fifth negative lens, and surface 12 is the image plane; From Table 2.1, it can be seen that the thermal expansion coefficients of the five lenses of the lens system are all lower than , meet the requirements; From Table 2.1, it can be seen that the Abbe number of the aspherical lens of the lens system is 81.61, which meets the requirements; In this implementation case, the transmittance of the long wavelength 1.97um of the lens system is 0.93563508, the transmittance of the medium wavelength 1.53um of the lens system is 0.99446751, and the transmittance of the short wavelength 1.06um of the lens system is 0.99328832, all of which are greater than 0.9 and meet the requirements.

[0057] Table 2.2

[0058] As shown in Table 2.2, assuming that the Z axis is the optical axis, the origin of the rectangular coordinate system coincides with the origin of the aspheric surface, and the rotation axis coincides with the optical axis of the system, the surface shape of the aspheric surface of the fifth negative lens can be expressed as:

[0059] in, is the incident height of the light on the aspheric surface, k is the cone coefficient, A2, A4, A6, ... are the high-order aspheric coefficients, c is the curvature at the vertex of the aspheric surface, and Z is the distance vector height from the vertex of the aspheric surface at a height of h along the optical axis. c is the curvature at the optical axis O, c = 1 / R (that is, the paraxial curvature c is the reciprocal of the curvature radius R in Table 2.2); k is the cone coefficient; Ai is the correction coefficient of the i-th order of the aspheric surface, and the high-order coefficients of each aspheric mirror are given in Table 2.2.

[0060] Among them, as a further test of the present invention, reference is made to Figure 8-Figure 12 , Figure 8 is the lateral chromatic aberration diagram of this lens system, where the vertical axis represents the lateral chromatic aberration and the horizontal axis represents the relative field of view. Figure 8It can be seen that the full-field chromatic aberration from long wave to medium wave, long wave to short wave, and medium wave to short wave is no higher than 0.0038, indicating that the chromatic aberration has been well optimized.

[0061] Fig. 9 This is the distortion diagram of the lens system, where the vertical axis represents the field of view and the horizontal axis represents the linear distortion. Fig. 9 It can be seen that the curves of light in the three wavelength bands of 1.97um, 1.53um and 1.06um of the lens system overlap together, and the distortion is less than 1% in the full field of view, indicating that the distortion has been well optimized.

[0062] Fig.10 is the RMS diagram of the diffuse spot of this lens system, where the vertical axis is the diffuse spot size and the horizontal axis is the relative field of view. Fig.10 It can be seen that the size of the diffuse spot does not exceed 0.0051mm in the full field of view.

[0063] Fig.11 is the full field of view point diagram of this lens system, where both the horizontal and vertical axes represent size. Fig.11 It can be seen that the energy of the point array images in each field of view is almost concentrated in the Airy disk, and the imaging quality is close to the diffraction limit.

[0064] Fig.12 The modulation transfer function curve of this lens system, the ordinate is the transfer function, the abscissa is the number of line pairs per millimeter, Fig.12 It can be seen that the sagittal and meridian of the 0 field of view, the meridian of the 0.5 field of view, the meridian of the 0.75 field of view, and the sagittal and meridian of the 1.0 field of view all coincide, and are very close to the diffraction limit under different fields of view. This shows that this system can capture images with richer layers and stronger contrast.

[0065] In summary, the infrared telephoto lens system of the present invention is composed of only 5 lenses, which reduces the design cost as much as possible, of which 4 lenses are domestic glass spherical lenses and 1 lens is a glass aspherical lens, which has both cost-effectiveness and miniaturized design; while meeting the use requirements and providing low distortion and high imaging quality, the total length and weight of the system are greatly reduced, making the overall structure more stable and providing more possibilities for subsequent integration.

[0066] The description of the embodiments of the specification should be combined with the corresponding drawings, and the drawings should be considered as part of the complete specification. In the above description of the embodiments, any reference to directions and orientations are only for the convenience of description and should not be construed as any limitation on the scope of protection of the invention. The description of the preferred embodiments will involve a combination of features, which may exist independently or in combination. The present invention is not particularly limited to the preferred embodiments. The description of the above embodiments is only used to help understand the optical lens of the present invention and its core design concept. At the same time, for those of ordinary skill in the art, according to the concept of the present invention, there will be changes in the specific implementation method and scope of application. In summary, the content of this specification should not be construed as a limitation on the present invention. The scope of the present invention is defined by the claims.

Claims

1. An infrared lens system with a high telephoto ratio and a long focal length, characterized in that : It includes a first positive lens, a second negative lens, a third positive lens, a fourth positive lens, and a fifth negative lens arranged in sequence from the object surface along the optical axis towards the image surface; The refractive index of the first positive lens satisfies 1.48 < n1 < 1.5, where n1 is the refractive index of the first positive lens; The refractive index of the second negative lens satisfies 1.85 < n2 < 1.95, where n2 is the refractive index of the second negative lens; The refractive index of the third positive lens satisfies 1.48 < n3 < 1.5, where n3 is the refractive index of the third positive lens; The refractive index of the fourth positive lens satisfies 1.6 < n4 < 1.7, where n4 is the refractive index of the fourth positive lens; The refractive index of the fifth negative lens satisfies 1.48 < n5 < 1.5, where n5 is the refractive index of the fifth negative lens; The surface types of the first positive lens, the second negative lens, the third positive lens, and the fourth positive lens are all standard spherical surfaces; The fifth negative lens is an aspherical glass lens, and the fifth negative lens satisfies the conditional formula: 81 < vd < 82, where vd is the Abbe number of the fifth negative lens; An aperture stop is provided between the third positive lens and the fourth positive lens, and the aperture stop is used to adjust the size of the imaging range.

2. The high telephoto ratio and long focal length infrared lens system according to claim 1, characterized in that: The lens system satisfies the relational formula: Y = TTL / f < 0.75, where Y is the telephoto ratio of the lens system, TTL is the distance from the object side surface of the first lens to the imaging surface of the lens system on the optical axis, and f is the focal length of the lens system.

3. The high telephoto ratio and long focal length infrared lens system according to claim 1, characterized in that: The lens system satisfies the condition: , where w is the half field of view angle of the lens system, f is the focal length of the lens system, and H is the Gaussian image height of the lens system.

4. The high telephoto ratio and long focal length infrared lens system according to claim 1, characterized in that: The lens system satisfies the condition: , FNUM is the relative aperture of the lens system, and w is the half field of view angle of the lens system.

5. The high telephoto ratio and long focal length infrared lens system according to claim 1, characterized in that: The lens system satisfies: , where f is the focal length of the lens system, θ is the field of view of the lens system, and D is the diagonal length of the imaging surface of the lens system.

6. The high telephoto ratio and long focal length infrared lens system according to claim 1, characterized in that: The lens system satisfies: , x is the transmittance of the wavelength of the lens of the lens system, e is the base of the natural logarithm, a is the absorption coefficient of the lens of the lens system, and d is the thickness of the lens of the lens system; the transmittance of each lens of the lens system satisfies the conditional formula: , α is the transmittance of the lens system with respect to the wavelength, x1 is the transmittance of the first positive lens with respect to the wavelength, x2 is the transmittance of the second negative lens with respect to the wavelength, x3 is the transmittance of the third positive lens with respect to the wavelength, x4 is the transmittance of the fourth positive lens with respect to the wavelength, and x5 is the transmittance of the fifth negative lens with respect to the wavelength.

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