A long-wave infrared continuous zoom optical system

Abstract

The present invention belongs to the technical field of long-wave infrared zoom optical system, and relates to a long-wave infrared continuous zoom optical system, which is composed of a front fixed group, a zoom group, a compensation group, and a rear fixed group arranged in sequence along the positive direction of the optical axis; the front fixed group adopts a first meniscus lens L1 with positive focal length, the zoom group adopts a biconcave lens L2, the compensation group adopts a biconvex lens L3, and the rear fixed group is composed of a second meniscus lens L4 with negative focal length and a third meniscus lens L5 with positive focal length arranged in sequence along the positive direction of the optical axis; the object side surfaces of the first meniscus lens L1 and the third meniscus lens L5 are convex, and the image side surface of the second meniscus lens L4 is convex. The present invention realizes 4x continuous zoom within the focal length range of 15mm~60mm, and has the characteristics of small FNO, high resolution, large relative aperture, strong light-gathering ability, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of long-wave infrared zoom optical systems and relates to a long-wave infrared continuous zoom optical system. Background Art

[0002] With the development of infrared technology, the demand for zoom optical lenses in optoelectronic systems in airborne and security fields is increasing. Traditional fixed-focus optical systems can only search or identify targets at a specific distance, which has certain limitations. Zoom lenses can meet both target search in a large field of view and target identification in a small field of view, and have great flexibility. While the total volume remains unchanged, the image quality in large and small fields of view is clear and coherent. However, traditional continuous zoom optical systems often find it difficult to meet requirements such as large relative aperture and miniaturization. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a long-wave infrared continuous zoom optical system, which uses a small number of lenses, reduces the total length of the system and reduces the cost.

[0004] In order to solve the above technical problems, the long-wave infrared continuous zoom optical system of the present invention is composed of a front fixed group, a zoom group, a compensation group, and a rear fixed group arranged in sequence along the positive direction of the optical axis. The front fixed group adopts a first meniscus lens L1 with positive focal length, the zoom group adopts a biconcave lens L2, the compensation group adopts a biconvex lens L3, The rear fixed group consists of a second meniscus lens L4 with negative optical focal length and a third meniscus lens L5 with positive optical focal length which are arranged in sequence along the positive direction of the optical axis; the object side surfaces of the first meniscus lens L1 and the third meniscus lens L5 are convex, and the image side surface of the second meniscus lens L4 is convex; the focal length f1 of the first meniscus lens L1, the focal length f2 of the biconcave lens L2, the focal length f3 of the biconvex lens L3, the focal length f4 of the second meniscus lens L4, and the focal length f5 of the third meniscus lens L5 satisfy the following relationship: 0.73≤f1 / f≤1.13, -0.37≤f2 / f≤-0.17, 0.25≤f3 / f≤0.45, -1.18≤f4 / f≤-0.78, 0.16≤f5 / f≤0.56, where f is the focal length of the optical system in the telephoto state.

[0005] Furthermore, the air gap between the first meniscus lens L1 and the biconcave lens L2 is 4.6mm~20.54mm, the air gap between the biconcave lens L2 and the biconvex lens L3 is 30.27mm~3.4mm, the air gap between the biconvex lens L3 and the second meniscus lens L4 is 4.11mm~16.06mm, and the air gap between the second meniscus lens L4 and the third meniscus lens L5 is 26.91mm~27.58mm; during the zooming process, as the focal length gradually increases, the biconcave lens L2 moves in the positive direction along the optical axis, and the biconvex lens L3 moves in the reverse direction along the optical axis.

[0006] Furthermore, the front and rear surface curvature radii of the first meniscus lens L1 are 68.78mm~85.65mm and 95.73mm~155.48mm respectively; the front and rear surface curvature radii of the biconcave lens L2 are -180.35mm~-85.15 mm and 57.84mm~107.27mm respectively; the front and rear surface curvature radii of the biconvex lens L3 are 95.48mm~178.55 mm and -145.18mm~-87.25mm respectively; the front and rear surface curvature radii of the second meniscus lens L4 are -60.87mm ~-46.65mm and -120.48mm~-110.45mm respectively; the front and rear surface curvature radii of the third meniscus lens L5 are 20.86mm~42.45mm and 65.25mm~71.98mm respectively.

[0007] Furthermore, the thicknesses of the first meniscus lens L1, the biconcave lens L2, the biconvex lens L3, the second meniscus lens L4, and the third meniscus lens L5 are 7.18 mm to 8.00 mm, 2.96 mm to 3.25 mm, 4.52 mm to 5.40 mm, 2.92 mm to 3.18 mm, and 2.86 mm to 3.35 mm, respectively.

[0008] Furthermore, the first meniscus lens L1 and the biconvex lens L3 are made of single crystal germanium, the biconcave lens L2 is made of zinc selenide, the second meniscus lens L4 is made of IRG201, and the third meniscus lens L5 is made of zinc sulfide.

[0009] Furthermore, a curvature radius R8 of the image side surface of the second meniscus lens L4 and a curvature radius R9 of the object side surface of the third meniscus lens L5 satisfy: -5≤R8 / R9≤0.

[0010] Furthermore, the rear surface of the first meniscus lens L1 is aspherical; the front and rear surfaces of the biconcave lens L2 and the second meniscus lens L4 are both aspherical, the front surface of the biconvex lens L3 is a diffraction surface, and the rear surface is a spherical surface; the front surface of the third meniscus lens L5 is aspherical, and the rear surface is spherical.

[0011] The quadratic surface coefficient K of the rear surface of the first meniscus lens L1 is 1.21E-02~2.15E-02, the 4th order aspheric coefficient A is 2.73E-09~2.78E-09, the 6th order aspheric coefficient B is 4.13E-12~4.50E-12, and the 8th order aspheric coefficient C is -6.98E-16~-6.12E-16; the quadratic surface coefficient K of the front surface of the biconcave lens L2 is -1.34E-01~-3.12E+00, the 4th order aspheric coefficient A is -2.56E-08~1.57E-06, the 6th order aspheric coefficient B is -7.78E-10~-1.83E-10, and the 8th order aspheric coefficient C is 2.7 5E-13~3.15E-13; the quadric surface coefficient K of the back surface of the biconcave lens L2 is -2.47E-01~-4.21E+00, the 4th order aspheric coefficient A is -2.86E-08~1.72E-06, the 6th order aspheric coefficient B is -8.21E-10~-1.32E-10, and the 8th order aspheric coefficient C is 2.75E-13~3.55E-13; the quadric surface coefficient K of the front surface of the biconvex lens L3 is 0, the 4th order aspheric coefficient A is 1.43E-06~1.76E-06, the 6th order aspheric coefficient B is -3.51E-10~-2.21E-10, and the 8th order aspheric coefficient C is -3.85E -14~-2.83E-14, diffraction order HOR=1, diffraction surface coefficient C1=6.48E-04~1.14E-06, C2=-2.81E-10~7.54E-07, C3=-4.23E-14~-4.22E-08; the quadratic surface coefficient K=-7.82E-01~-1.23E+00 of the front surface of the second meniscus lens L4, the 4th order aspheric coefficient A=1.22E-06~7.21E-08, the 6th order aspheric coefficient B=2.59E-09~8.79E-10; the 8th order aspheric coefficient C=-6.11E-12~-4.48E-12, the quadratic surface coefficient K=-7.82E-01~-1.23E+00 of the front surface of the second meniscus lens L4, the 4th order aspheric coefficient A=1.22E-06~7.21E-08, the 6th order aspheric coefficient B=2.59E-09~8.79E-10; the 8th order aspheric coefficient C=-6.11E-12~-4.48E-12, the quadratic surface coefficient K=-7.82E-01~-1.23E+00 of the rear surface of the second meniscus lens L4 The secondary surface coefficient K=-7.12E-01~-1.25E+00, the 4th order aspheric coefficient A=1.56E-06~6.78E-08, the 6th order aspheric coefficient B=1.43E-09~8.51E-10, and the 8th order aspheric coefficient C=-5.46E-12~-4.20E-12; the secondary surface coefficient K=-1.78E+00~-1.75E+00, the 4th order aspheric coefficient A=1.77E-06~2.21E-06, the 6th order aspheric coefficient B=1.59E-09~1.95E-09, and the 8th order aspheric coefficient C=-5.26E-12~-4.78E-12 of the front surface of the third meniscus lens L5.

[0012] Beneficial effects: The present invention realizes continuous zoom of the system by moving the biconcave lens, realizes continuous zoom compensation by moving the biconvex lens, realizes 4x continuous zoom within the focal length range of 15mm~60mm, and the imaging quality is high within this focal length range; the distance from the object side to the image plane of the first meniscus lens is 100mm, which realizes the miniaturization of the system and can be adapted to the long-wave infrared detector with a resolution of 640×512 and a pixel size of 10um / 12um. The present invention has the characteristics of small FNO (aperture coefficient), high resolution, large relative aperture, and strong light-gathering ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the optical path diagram of the present invention when the telephoto focal length is 60mm.

[0014] Figure 2 This is the optical path diagram of the present invention at a medium to long focal length of 45mm.

[0015] Figure 3 This is the optical path diagram of the present invention at a medium-short focal length of 30 mm.

[0016] Figure 4 This is the optical path diagram of the present invention when the short focus is 15mm.

[0017] Figure 5 This is a modulation transfer function diagram of Example 1 of the present invention at a telephoto focal length of 60 mm.

[0018] Figure 6 It is a modulation transfer function diagram of Example 1 of the present invention at a medium-long focal length of 45 mm.

[0019] Figure 7 This is a modulation transfer function diagram of Example 1 of the present invention at a medium-short focal length of 30 mm.

[0020] Figure 8 This is a modulation transfer function diagram of Example 1 of the present invention at a short focal length of 15 mm.

[0021] Fig. 9 It is a cam curve diagram of the zoom group and the compensation group in the zoom overshoot of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description. However, the present invention is not limited to the following embodiments.

[0023] like Figures 1 to 4As shown, the long-wave infrared continuous zoom optical system of the present invention is composed of a front fixed group, a zoom group, a compensation group, and a rear fixed group arranged in sequence along the positive direction of the optical axis; the focal lengths of the front fixed group, the zoom group, the compensation group, and the rear fixed group are distributed in sequence according to positive, negative, positive, and positive; the first meniscus lens L1 with positive focal power serves as the front fixed group, the biconcave lens L2 with negative focal power serves as the zoom group, the biconvex lens L3 with positive focal power serves as the compensation group, and the second meniscus lens L4 with negative focal power and the third meniscus lens L5 with positive focal power arranged in sequence along the positive direction of the optical axis serve as the rear fixed group; in the figure, A is the protective glass in front of the detector, and B is the image plane of the detector. The concave surface of the first meniscus lens L1 faces the image side; the concave surface of the second meniscus lens L4 faces the object side; and the concave surface of the third meniscus lens L5 faces the image side.

[0024] The material of the first meniscus lens L1 is single crystal germanium, the material of the biconcave lens L2 is zinc selenide, the material of the biconvex lens L3 is single crystal germanium, the material of the second meniscus lens L4 is IRG201, and the material of the third meniscus lens L5 is zinc sulfide.

[0025] In the present invention, as the focal length gradually increases, the biconcave lens L2 moves in the positive direction along the optical axis, moving a total of 15.26 mm from the short focus state to the long focus state; the biconvex lens L3 moves in the reverse direction along the optical axis, moving a total of 11.57 mm from the short focus state to the long focus state. In the process of increasing the focal length, the magnification group and the compensation group gradually approach each other.

[0026] The distance between the vertex of the surface of the first meniscus lens L1 facing the image side and the vertex of the object side surface of the biconcave lens L2 is 5.28mm~20.54mm, the distance between the vertex of the image side surface of the biconcave lens L2 and the vertex of the object side surface of the biconvex lens L3 is 30.27mm~3.46mm, and the distance between the vertex of the image side surface of the biconvex lens L3 and the vertex of the object side surface of the second meniscus lens L4 is 4.20mm~15.77mm; the front fixed group and the rear fixed group remain in position during the zooming process.

[0027] The rear surface of the first meniscus lens L1 is aspherical; the front and rear surfaces of the biconcave lens L2 and the second meniscus lens L4 are both aspherical, the front surface of the biconvex lens L3 is a diffraction surface, and the rear surface is a spherical surface; the front surface of the third meniscus lens L5 is aspherical, and the rear surface is spherical.

[0028] The present invention adopts a variable F number method to reduce the aperture of the system as much as possible when the optical system is in a telephoto state, thereby further miniaturizing the system. The aperture stop of the system is arranged on the object side of the compensation group.

[0029] The detector specifications applicable to the present invention are uncooled long-wave infrared detectors such as 640×512 / 10um and 640×512 / 12um.

[0030] The working band of the present invention is 8um~12um; the F number is 0.95~1; the focal length is 15mm~60mm, 4x zoom, the image plane size is 9.84mm, and the total length of the system is 100mm (the distance from the object side of the first meniscus lens L1 to the image plane), and it has the characteristics of large relative aperture and short total length.

[0031] Embodiment 1: The optical system parameters of this embodiment are shown in Table 1-1, in which ti is the center thickness of the ith optical element, and di is the air gap between the vertex of the rear surface of the ith optical element and the vertex of the next optical surface.

[0032] Table 1-1

[0033] The aspheric surface equations of the image side of the first meniscus lens L1, the biconcave lens L2, the second meniscus lens L4, and the object side of the third meniscus lens L5 are as follows:

[0034] (1)

[0035] Wherein, z is the axial sagitta of different lens heights r, which is the axial distance from the vertex of the aspheric surface to the lens surface at different heights, where r is the radial distance of the lens surface. c is the curvature, which is equal to the inverse of the radius of curvature R. k is the quadratic surface coefficient, A is the 4th order aspheric coefficient, B is the 6th order aspheric coefficient, and C is the 8th order aspheric coefficient.

[0036] The aspheric coefficients of each aspheric surface are shown in Table 1-2.

[0037] Table 1-2

[0038] Among them, the object side of the biconvex lens L3 is added with a diffraction surface on the basis of the aspheric surface, and the diffraction surface equation is:

[0039] (2)

[0040] Among them, HOR is the diffraction order, C1, C2, C3 are the diffraction surface coefficients. λ0 is the central wavelength, n is the refractive index of the lens, and n0 is the refractive index of air. The aspheric coefficients and diffraction surface coefficients are shown in Table 1-3.

[0041] Table 1-3

[0042] from Figure 5~Figure 8It can be seen that the modulation transfer function (MTF) of this embodiment is greater than 0.3 at focal lengths of 60 mm, 45 mm, 30 mm, and 15 mm.

[0043] Embodiment 2: The optical system parameters of this embodiment are shown in Table 2-1, in which ti is the center thickness of the ith optical element, and di is the air gap between the vertex of the rear surface of the ith optical element and the vertex of the next optical surface.

[0044] Table 2-1

[0045]

[0046] The aspheric coefficients of each aspheric surface are shown in Table 2-2.

[0047] Table 2-2

[0048]

[0049] The aspheric coefficients and diffraction surface coefficients of the biconvex lens L3 are shown in Table 2-3.

[0050] Table 2-3

[0051]

[0052] The modulation transfer function (MTF) of this embodiment is greater than 0.3 at focal lengths of 60 mm, 45 mm, 30 mm, and 15 mm.

[0053] Embodiment 3: The optical system parameters of this embodiment are shown in Table 3-1, in which ti is the center thickness of the ith optical element, and di is the air gap between the vertex of the rear surface of the ith optical element and the vertex of the next optical surface.

[0054] Table 3-1

[0055]

[0056] The aspheric coefficients of each aspheric surface are shown in Table 3-2.

[0057] Table 3-2

[0058]

[0059] The aspheric coefficients and diffraction surface coefficients of the biconvex lens L3 are shown in Table 3-3.

[0060] Table 3-3

[0061]

[0062] The modulation transfer function (MTF) of this embodiment is greater than 0.3 at focal lengths of 60 mm, 45 mm, 30 mm, and 15 mm.

[0063] The present invention adopts a variable F number method to reduce the aperture of the system as much as possible when the optical system is in a telephoto state, thereby further miniaturizing the system. The aperture stop of the system is arranged on the object side of the compensation group.

[0064] The detector specifications applicable to the present invention are uncooled long-wave infrared detectors such as 640×512 / 10um and 640×512 / 12um.

[0065] The technical parameters of the optical system are: working band is 8um~12um; F number is 0.95~1; focal length is 15mm~60mm, 4x zoom, image plane size is 9.84mm, and the total length of the system is 100mm (the distance from the object side of the first meniscus lens L1 to the image plane). The system has the characteristics of large relative aperture and short total length.

[0066] The above are only preferred embodiments of the present invention, which describe the basic principles, main features and advantages of the present invention, and are not intended to limit the present invention in any form. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A long-wave infrared continuous zoom optical system, characterized in that The system consists of a front fixed group, a zoom group, a compensation group, and a rear fixed group which are sequentially arranged along the positive direction of the optical axis. The front fixed group adopts a first meniscus lens L1 with positive focal length, the zoom group adopts a biconcave lens L2, the compensation group adopts a biconvex lens L3, and the rear fixed group consists of a second meniscus lens L4 with negative focal length and a third meniscus lens L5 with positive focal length which are sequentially arranged along the positive direction of the optical axis. The system has 5 lenses with different focal lengths. The object side surfaces of the first meniscus lens L1 and the third meniscus lens L5 are convex, and the image side surface of the second meniscus lens L4 is convex. The focal length f1 of the first meniscus lens L1, the focal length f2 of the biconcave lens L2, the focal length f3 of the biconvex lens L3, the focal length f4 of the second meniscus lens L4, and the focal length f5 of the third meniscus lens L5 are convex. The focal length f5 of the three-meniscus lens L5 satisfies the following relationship: 0.73≤f1 / f≤1.13, -0.37≤f2 / f≤-0.17, 0.25≤f3 / f≤0.45, -1.18≤f4 / f≤-0.78, 0.16≤f5 / f≤0.56, where f is the focal length of the optical system in the telephoto state; during the zooming process, as the focal length gradually increases, the biconcave lens L2 moves in the positive direction along the optical axis, and the biconvex lens L3 moves in the reverse direction along the optical axis.

2. The long-wave infrared continuous zoom optical system according to claim 1, characterized in that The air gap between the first meniscus lens L1 and the biconcave lens L2 is 4.6mm~20.54mm, the air gap between the biconcave lens L2 and the biconvex lens L3 is 30.27mm~3.4mm, the air gap between the biconvex lens L3 and the second meniscus lens L4 is 4.11mm~16.06mm, and the air gap between the second meniscus lens L4 and the third meniscus lens L5 is 26.91mm~27.58mm.

3. The long-wave infrared continuous zoom optical system according to claim 1, characterized in that The front and rear surface curvature radii of the first meniscus lens L1 are 68.78mm~85.65 mm and 95.73mm~155.48mm respectively; the front and rear surface curvature radii of the biconcave lens L2 are -180.35mm~-85.15 mm and 57.84mm~107.27mm respectively; the front and rear surface curvature radii of the biconvex lens L3 are 95.48mm~178.55 mm and -145.18mm~-87.25mm respectively; the front and rear surface curvature radii of the second meniscus lens L4 are -60.87mm ~-46.65mm and -120.48mm~-110.45mm respectively; the front and rear surface curvature radii of the third meniscus lens L5 are 20.86mm~42.45mm and 65.25mm~71.98mm respectively.

4. The long-wave infrared continuous zoom optical system according to claim 3, characterized in that The thicknesses of the first meniscus lens L1, the biconcave lens L2, the biconvex lens L3, the second meniscus lens L4, and the third meniscus lens L5 are 7.18 mm to 8.00 mm, 2.96 mm to 3.25 mm, 4.52 mm to 5.40 mm, 2.92 mm to 3.35 mm, and 2.86 mm to 3.18 mm, respectively.

5. The long-wave infrared continuous zoom optical system according to claim 1, characterized in that The first meniscus lens L1 and the biconvex lens L3 are made of single crystal germanium, the biconcave lens L2 is made of zinc selenide, the second meniscus lens L4 is made of IRG201, and the third meniscus lens L5 is made of zinc sulfide.

6. The long-wave infrared continuous zoom optical system according to claim 1, characterized in that The curvature radius R8 of the image side surface of the second meniscus lens L4 and the curvature radius R9 of the object side surface of the third meniscus lens L5 satisfy: -5≤R8 / R9≤0.

7. The long-wave infrared continuous zoom optical system according to claim 1, characterized in that The rear surface of the first meniscus lens L1 is aspherical; the front and rear surfaces of the biconcave lens L2 and the second meniscus lens L4 are both aspherical; the front surface of the biconvex lens L3 is a diffraction surface, and the rear surface is a spherical surface; the front surface of the third meniscus lens L5 is aspherical, and the rear surface is spherical.

8. The long-wave infrared continuous zoom optical system according to claim 7, characterized in that The quadratic surface coefficient K of the rear surface of the first meniscus lens L1 is 1.21E-02~2.15E-02, the 4th order aspheric coefficient A is 2.73E-09~2.78E-09, the 6th order aspheric coefficient B is 4.13E-12~4.50E-12, and the 8th order aspheric coefficient C is -6.98E-16~-6.12E-16; the quadratic surface coefficient K of the front surface of the biconcave lens L2 is -1.34E-01~-3.12E+00, the 4th order aspheric coefficient A is -2.56E-08~1.57E-06, the 6th order aspheric coefficient B is -7.78E-10~-1.83E-10, and the 8th order aspheric coefficient C is 2.75 E-13~3.15E-13; the quadric surface coefficient K of the back surface of the biconcave lens L2 is -2.47E-01~-4.21E+00, the 4th order aspheric coefficient A=-2.86E-08~1.72E-06, the 6th order aspheric coefficient B=-8.21E-10~-1.32E-10, and the 8th order aspheric coefficient C=2.75E-13~3.55E-13; the quadric surface coefficient K of the front surface of the biconvex lens L3 is 0, the 4th order aspheric coefficient A=1.43E-06~1.76E-06, the 6th order aspheric coefficient B=-3.51E-10~-2.21E-10, and the 8th order aspheric coefficient C=-3.85E- 14~-2.83E-14, diffraction order HOR=1, diffraction surface coefficient C1=6.48E-04~1.14E-06, C2=-2.81E-10~7.54E-07, C3=-4.23E-14~-4.22E-08; the quadratic surface coefficient K=-7.82E-01~-1.23E+00 of the front surface of the second meniscus lens L4, the 4th order aspheric coefficient A=1.22E-06~7.21E-08, the 6th order aspheric coefficient B=2.59E-09~8.79E-10; the 8th order aspheric coefficient C=-6.11E-12~-4.48E-12, the quadratic surface coefficient of the rear surface of the second meniscus lens L4 The surface coefficient K=-7.12E-01~-1.25E+00, the 4th-order aspheric coefficient A=1.56E-06~6.78E-08, the 6th-order aspheric coefficient B=1.43E-09~8.51E-10, and the 8th-order aspheric coefficient C=-5.46E-12~-4.20E-12; the quadratic surface coefficient K=-1.78E+00~-1.75E+00 of the front surface of the third meniscus lens L5, the 4th-order aspheric coefficient A=1.77E-06~2.21E-06, the 6th-order aspheric coefficient B=1.59E-09~1.95E-09, and the 8th-order aspheric coefficient C=-5.26E-12~-4.78E-12.

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