Small-F-number high-resolution medium-wave refrigeration zoom imaging system

Abstract

The invention relates to a small-F-number high-resolution medium-wave refrigeration zoom imaging system. The system comprises a lens L1, a lens L2, a lens L3, a lens L4 and a detector I which are sequentially arranged from an object space to an image space along an optical axis, the lens L1 is a meniscus lens with positive focal power, and the convex surface of the lens L1 faces the object surface; the lens L2 is a concave lens; the lens L3 is a convex lens; the lens L4 is a meniscus lens with positive focal power, and the convex surface of the lens L4 faces the object surface; the lens L1 forms a front fixed group, the lens L2 forms a zoom group, the lens L3 forms a compensation group, and the lens L4 forms a rear fixed group; in the zoom imaging process, the zoom group and the compensation group move oppositely along the axial direction to realize the change of the focal length from the short focal length to the long focal length. According to the invention, the F number of the focal length of the lens is reduced, more energy can be ensured to be received by a detector, the resolution capability of the system is greatly improved, the complexity of the lens structure is reduced, and the stability and reliability of the lens are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical imaging systems and relates to a small F-number high-resolution medium-wave cooling zoom imaging system. Background Art

[0002] The existing optical structure of visible light medium wave cooling zoom lens is as follows: Figure 1 As shown, it consists of a first meniscus positive lens, a double concave negative lens, a second meniscus positive lens, a third meniscus positive lens, a fourth meniscus positive lens, a first meniscus negative lens, a fifth meniscus positive lens, a sixth meniscus positive lens, and an infrared detector; the first meniscus positive lens is a front fixed mirror, the double concave negative lens is a first zoom lens, and the second meniscus positive lens is a second zoom lens, and the focal length of the system is changed by the movement of the double concave negative lens and the second meniscus positive lens along the optical axis; the third meniscus positive lens is a compensation lens, and the movement of the compensation lens along the optical axis compensates for the image plane defocus caused by the movement of the zoom lens; the fourth meniscus positive lens, the first meniscus negative lens, the fifth meniscus positive lens, and the sixth meniscus positive lens are a rear fixed group. The structure consists of 8 lenses, and adopts a three-element continuous zoom and secondary imaging system design; a field diaphragm is set at the position of the primary image plane, and the stray light outside the field of view of the system cannot pass through the field diaphragm to reach the image plane, effectively reducing the impact of stray light on the imaging of the optical system and improving the system signal-to-noise ratio. The lens has the following disadvantages: 1. The F number of the medium-wave infrared zoom lens is relatively large, generally not less than 4; 2. There are many tele-dynamic components, greater than or equal to 3; 3. The adaptability to environmental temperature is general, and it cannot work normally in harsh environmental temperatures such as -40℃~+65℃. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a medium-wave cooling zoom imaging system with a small F number and high resolution, which has a simple structure and good stability and reliability.

[0004] In order to solve the above technical problems, the small F number high resolution medium wave cooling zoom imaging system of the present invention comprises a lens L1, a lens L2, a lens L3, a lens L4 and a detector I which are arranged in sequence from the object side to the image side along the optical axis; the lens L1 is a meniscus mirror with positive focal length, and its convex surface faces the object side; the lens L2 is a concave lens; the lens L3 is a convex lens; the lens L4 is a meniscus mirror with positive focal length, and its convex surface faces the object side; the lens L1 constitutes a front fixed group, the lens L2 constitutes a variable magnification group, the lens L3 constitutes a compensation group, and the lens L4 constitutes a rear fixed group; the zoom imaging process is to realize the change of focal length from short focus to long focus by moving the variable magnification group and the compensation group toward each other along the axial direction; the focal length f1 of the front fixed group, the focal length f2 of the variable magnification group, the focal length f3 of the compensation group, and the focal length f4 of the rear fixed group satisfy the following relationship: 0.3≤f1 / f L ≤0.7;-0.12≤f2 / f L≤-0.3; 0.2≤f3 / f L ≤0.4; 0.2≤f4 / f L ≤0.5; where f L is the focal length of the system at telephoto.

[0005] The front and rear surface curvature radii of the lens L1 are 93.52mm to 104.886mm and 171.663mm to 217.33mm respectively; the front and rear surface curvature radii of the lens L2 are -204.095mm to -154.026mm and 102.990mm to 132.92mm respectively; the front and rear surface curvature radii of the lens L3 are 211.16mm to 443.995mm and -174.992mm to -128.14mm respectively; the front and rear surface curvature radii of the lens L4 are 19.336mm to 20.681mm and 17 .01mm~22.845mm; the thickness of lens L1 is 10.5mm~12.4mm; the thickness of lens L2 is 3.6mm~4.3mm; the thickness of lens L3 is 7mm~8.8mm; the thickness of lens L4 is 7.2mm~8.1mm; the air gap between the rear surface of lens L1 and the front surface of lens L2 is 23.2mm~42.9mm; the air gap between the rear surface of lens L2 and the front surface of lens L3 is 4.0mm~56.9mm; the air gap between the rear surface of lens L3 and the front surface of lens L4 is 13.0mm~41.7mm.

[0006] The front and rear surfaces of the lens L1 are both spherical; the front and rear surfaces of the lens L2 are both aspherical; the front surface of the lens L3 is aspherical, and the rear surface is spherical; the front surface of the lens L4 is spherical, and the rear surface is aspherical; the cone coefficient k of the front surface of the lens L2 is -0.96 to -0.78, the fourth power coefficient α2 of the radial coordinate is -6.81E-07 to -1.68E-07, the sixth power coefficient α3 is -2.91E-10 to -1.58E-10, and the eighth power coefficient α4 is 1.26E -13~3.16E-13; the cone coefficient k of the rear surface of lens L2 is 0, the fourth power coefficient α2 of the radial coordinate is 1.46E-07~5.91E-07, the sixth power coefficient α3 is -3.88E-10~-2.88E-10, and the eighth power coefficient α4 is 1.23E-13~3.50E-13; the cone coefficient k of the front surface of lens L3 is 0, the fourth power coefficient α2 of the radial coordinate is -5.69E-07~-2.55E-07, and the sixth power coefficient α3 is

[0007] 1.43E-10~2.34E-10, the octal coefficient α4 is -6.15E-13~-2.57E-13; the cone coefficient k of the rear surface of lens L4 is 0, the fourth power coefficient α2 of the radial coordinate is 2.31E-05~2.61E-05, the sixth power coefficient α3 is -4.25E-07~-1.78E-07, and the octal coefficient α4 is 1.92E-10~5.12E-10.

[0008] Furthermore, the present invention also includes a focusing group, which is arranged between the rear fixed group and the detector I, and is composed of lens L5, lens L6, and lens L7 arranged in sequence along the optical axis from the object side to the image side; lens L5 is a meniscus mirror with negative optical focal length, and its convex surface faces the image plane; lens L6 is a meniscus mirror with positive optical focal length, and its convex surface faces the image plane; lens L7 is a meniscus mirror with positive optical focal length, and its convex surface faces the object plane.

[0009] The front and rear surface curvature radii of the lens L5 are -18.942mm to -17.195mm and -40.791mm to -38.687mm respectively; the front and rear surface curvature radii of the lens L6 are -61.604mm to -53.183mm and -33.168mm to -32.301mm respectively; the front and rear surface curvature radii of the lens L7 are 30.025mm to 34.205mm and 81.426mm to 89.927mm respectively; The thickness of lens L5 is 6.2mm~6.8mm; the thickness of lens L6 is 7.3mm~7.8mm; the thickness of lens L7 is 7.4mm~7.8mm; the air gap between the rear surface of lens L4 and the front surface of lens L5 is 32.5mm~33.5mm; the air gap between the rear surface of lens L5 and the front surface of lens L6 is 1.8mm~2.2mm; the air gap between the rear surface of lens L6 and the front surface of lens L7 is 0.4mm~0.6mm.

[0010] The front surface of the lens L5 is spherical, and the rear surface is aspherical; the front surface of the lens L6 is spherical, and the rear surface is aspherical; the front surface of the lens L7 is aspherical, and the rear surface is spherical; the cone coefficient k of the rear surface of the lens L5 is -1.21 to -1.06, the fourth power coefficient α2 of the radial coordinate is 4.39E-06 to 9.10E-06, the sixth power coefficient α3 is 2.04E-09 to 7.68E-09, the eighth power coefficient α4 is 4.88E-11 to 8.21E-11, and the cone coefficient k of the rear surface of the lens L6 is 0, the fourth power coefficient α2 of the radial coordinate is 1.86E-07~3.11E-07, the sixth power coefficient α3 is -9.09E-10~-2.03E-10, the octapower coefficient α4 is 3.51E-14~8.38E-14, the cone coefficient k of the front surface of lens L7 is 0, the fourth power coefficient α2 of the radial coordinate is 1.69E-07~4.73E-07, the sixth power coefficient α3 is -2.98E-11~-2.01E-11, and the octapower coefficient α4 is 3.45E-16~6.54E-16.

[0011] The front and rear surfaces of the lens L1 are both spherical; the front surface of the lens L2 is spherical, and the rear surface is aspherical; the front surface of the lens L3 is spherical, and the rear surface is aspherical; the front surface of the lens L4 is spherical, and the rear surface is aspherical; the cone coefficient k of the rear surface of the lens L2 is 1.03-1.05, the fourth power coefficient α2 of the radial coordinate is 1.817E-07-2.41E-07, the sixth power coefficient α3 is -3.59E-10--2.34E-10, and the eighth power coefficient α4 is 5.36E-12-7.70E-12; the cone coefficient k of the rear surface of the lens L3 ... The cone coefficient k is 0, the fourth power coefficient α2 of the radial coordinate is -4.38E-06 to -2.97E-06, the sixth power coefficient α3 is 7.53E-09 to 1.165E-08, and the octapower coefficient α4 is -3.31E-11 to -2.02E-11; the cone coefficient k of the back surface of lens L4 is 0, the fourth power coefficient α2 of the radial coordinate is 4.27E-06 to 7.28E-06, the sixth power coefficient α3 is -5.82E-07 to -3.33E-07, and the octapower coefficient α4 is 6.74E-09 to 9.87E-09.

[0012] Furthermore, the present invention also includes a focusing group, which is arranged between the rear fixed group and the detector I, and is composed of lens L5, lens L6, and lens L7 arranged in sequence along the optical axis from the object side to the image side; lens L5 is a meniscus mirror with negative optical focal length, and its convex surface faces the image plane; lens L6 is a meniscus mirror with positive optical focal length, and its convex surface faces the image plane; lens L7 is a convex lens.

[0013] The front and rear surface curvature radii of the lens L5 are -20.27mm to -19.72mm and -31.21mm to -31.08mm respectively; the front and rear surface curvature radii of the lens L6 are -68.47mm to -64.45mm and -33.13mm to -32.30mm respectively; the front and rear surface curvature radii of the lens L7 are 336.60mm to 236.94mm and -98.95mm to -93.35mm respectively; The thickness of L5 is 5.5mm~5.6mm; the thickness of lens L6 is 7.9mm~8.2mm; the thickness of lens L7 is 7.3mm~7.5mm; the air gap between the rear surface of lens L4 and the front surface of lens L5 is 24.7mm~24.9mm; the air gap between the rear surface of lens L5 and the front surface of lens L6 is 0.4mm; the air gap between the rear surface of lens L6 and the front surface of lens L7 is 12.2mm~12.3mm.

[0014] The front surface of the lens L5 is aspherical, and the rear surface is spherical; the front surface of the lens L6 is spherical, and the rear surface is aspherical; the front surface of the lens L7 is aspherical, and the rear surface is spherical; the cone coefficient k of the front surface of the lens L5 is 0, the fourth power coefficient α2 of the radial coordinate is 2.53E-06 to 3.89E-06, the sixth power coefficient α3 is 5.87E-09 to 8.61E-09, the eighth power coefficient α4 is 4.99E-12 to 7.35E-12, and the cone coefficient k of the rear surface of the lens L6 is -0.63 to -0.59 The fourth power coefficient α2 of the radial coordinate is 1.48E-06~2.84E-06, the sixth power coefficient α3 is -2.07E-09~-1.13E-09, the octapower coefficient α4 is 5.75E-12~8.57E-12, the cone coefficient k of the front surface of lens L7 is 0, the fourth power coefficient α2 of the radial coordinate is 4.07E-07~6.70E-07, the sixth power coefficient α3 is -8.33E-11~-1.03E-10, and the octapower coefficient α4 is 1.24E-13~9.56E-14.

[0015] Beneficial effects: The present invention reduces the F number of the lens focal length to 1.5, which can ensure that more energy is received by the detector, greatly improving the resolution of the system; adopts a zoom method with two moving components, reduces the complexity of the lens structure, and improves the stability and reliability of the lens; compensates for the defocus caused by temperature changes through the axial movement of the focusing group, and realizes the normal operation of the imaging system with excellent image quality under the harsh ambient temperature of -40℃ ~ +65℃; while ensuring high-resolution imaging, it realizes continuous zooming of the focal length from 30mm to 150mm, and the magnification ratio is 5 times, which greatly improves the application range of the zoom lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the optical structure of the prior art.

[0017] Figure 2 It is a short-focus optical structure diagram of embodiments 1-1, 1-2, and 1-3 of the present invention.

[0018] Figure 3 It is a mid-focus optical structure diagram of Examples 1-1, 1-2, and 1-3 of the present invention.

[0019] Figure 4 It is a telephoto optical structure diagram of embodiments 1-1, 1-2, and 1-3 of the present invention.

[0020] Figure 5 It is the short-focus optical transfer function diagram of Example 1-1 of the present invention at +20°C.

[0021] Figure 6 It is the mid-focus optical transfer function diagram of Example 1-1 of the present invention at +20°C.

[0022] Figure 7 It is the long-focus optical transfer function diagram of Example 1-1 of the present invention at +20°C.

[0023] Figure 8 It is the short-focus optical transfer function diagram of Example 1-1 of the present invention at -40°C.

[0024] Fig. 9 It is the mid-focus optical transfer function diagram of Example 1-1 of the present invention at -40°C.

[0025] Fig.10 It is the long-focus optical transfer function diagram of Example 1-1 of the present invention at -40°C.

[0026] Fig.11 It is the short-focus optical transfer function diagram of Example 1-1 of the present invention at +65°C.

[0027] Fig.12 It is the mid-focus optical transfer function diagram of Example 1-1 of the present invention at +65°C.

[0028] Fig.13 It is the long-focus optical transfer function diagram of Example 1-1 of the present invention at +65°C.

[0029] Fig.14 It is a short-focus optical structure diagram of embodiments 2-1, 2-2, and 2-3 of the present invention.

[0030] Fig.15 It is a mid-focus optical structure diagram of Examples 2-1, 2-2, and 2-3 of the present invention.

[0031] Fig.16 It is a telephoto optical structure diagram of embodiments 2-1, 2-2, and 2-3 of the present invention.

[0032] Fig.17 It is the short-focus optical transfer function diagram of Example 2-1 of the present invention at +20°C.

[0033] Fig.18 It is the mid-focus optical transfer function diagram of Example 2-1 of the present invention at +20°C.

[0034] Fig.19 It is the long-focus optical transfer function diagram of Example 2-1 of the present invention at +20°C.

[0035] Fig. 20 It is the short-focus optical transfer function diagram of Example 2-1 of the present invention at -40°C.

[0036] Fig.21 It is the mid-focus optical transfer function diagram of Example 2-1 of the present invention at -40°C.

[0037] Fig. 22 It is the long-focus optical transfer function diagram of Example 2-1 of the present invention at -40°C.

[0038] Fig.23 It is the short-focus optical transfer function diagram of Example 2-1 of the present invention at +65°C.

[0039] Fig.24 It is the mid-focus optical transfer function diagram of Example 2-1 of the present invention at +65°C.

[0040] Fig.25 It is the long-focus optical transfer function diagram of Example 2-1 of the present invention at +65°C.

[0041] Figure 1 Middle: 1. First meniscus positive lens; 2. Double concave negative lens; 3. Second meniscus positive lens; 4. Third meniscus positive lens; 5. Fourth meniscus positive lens; 6. First meniscus negative lens; 7. Fifth meniscus positive lens; 8. Sixth meniscus positive lens; 9. Infrared detector. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0043] In the description of this embodiment, the terms "upper", "lower", "left", "right" and other directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplified operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0044] Example 1-1: Figure 2-4 As shown, the small F-number high-resolution medium-wave cooled zoom imaging system of the present invention comprises a lens L1, a lens L2, a lens L3, a lens L4, a lens L5, a lens L6, a lens L7, and a detector I which are arranged in sequence from the object side to the image side; wherein the detector I comprises a window WIN, a detector protection glass FIL, a cold stop STOP, and a target surface IMAGE; and the detector I is a cooled infrared detector.

[0045] The lens L1 constitutes the front fixed group, the lens L2 constitutes the zoom group, the lens L3 constitutes the compensation group, the lens L4 constitutes the rear fixed group, and the lens L5, lens L6 and lens L7 constitute the focusing group. The zoom imaging process is to achieve the change of focal length from short focus to long focus by axially moving the zoom group and the compensation group toward each other, and ensure that the image position of the system does not change. The defocus caused by temperature change can be compensated by the axial movement of the focusing group as a whole in the lens barrel, ensuring clear imaging of the system at different temperatures. The focal length f1 of the front fixed group, the focal length f2 of the zoom group, the focal length f3 of the compensation group, and the focal length f4 of the rear fixed group satisfy the following relationship: 0.3≤f1 / f L ≤0.7;-0.12≤f2 / f L ≤-0.3; 0.2≤f3 / f L ≤0.4; 0.2≤f4 / f L ≤0.5; where f L is the focal length of the system at telephoto.

[0046] The lens L1 is a meniscus mirror with positive focal power, and its convex surface faces the object plane; the lens L2 is a concave lens; the lens L3 is a convex lens; the lens L4 is a meniscus mirror with positive focal power, and its convex surface faces the object plane; the lens L5 is a meniscus mirror with negative focal power, and its convex surface faces the image plane; the lens L6 is a meniscus mirror with positive focal power, and its convex surface faces the image plane; the lens L7 is a meniscus mirror with positive focal power, and its convex surface faces the object plane; the front and rear surfaces of the lens L1 are both spherical; the front and rear surfaces of the lens L2 are both aspherical; the front surface of the lens L3 is aspherical, and the rear surface is spherical; the front surface of the lens L4 is spherical, and the rear surface is aspherical; the front surface of the lens L5 is spherical, and the rear surface is aspherical; the front surface of the lens L6 is spherical, and the rear surface is aspherical; the front surface of the lens L7 is aspherical, and the rear surface is spherical.

[0047] The aspheric expression is as follows:

[0048]

[0049] z represents the height of the sag; c represents the vertex curvature of the lens; r represents the aperture radius of the lens; k represents the cone coefficient, α2, α3, and α4 represent the fourth power coefficient, sixth power coefficient, and eighth power coefficient of the radial coordinate respectively. α1, α5, α6, α7, and α8 represent the second power, tenth power, twelfth power, fourteenth power, and sixteenth power coefficient of the radial coordinate respectively, and all are 0.

[0050] The materials of the lens L1, lens L3, lens L4, lens L5, lens L6 and lens L7 are all Si, and the material of the lens L2 is Ge.

[0051] By calculating the material matching and adjusting the air space between each lens, the imaging system transfer function is finally achieved to be better than 0.50@17lp / mm, ensuring excellent imaging quality. Under the condition that the lens barrel is made of aluminum alloy, the focusing group of lenses L5, L6 and L7 move axially together to compensate for the defocusing of the imaging system at different temperatures, ensuring that the image plane position remains unchanged. The imaging quality of the entire imaging system meets the use requirements at a temperature of -40 to +65°C.

[0052] The parameters of each element of this embodiment (surface shape, radius of curvature, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 1-1, where the radius of curvature, distance from the next optical surface, and semi-aperture are in units of mm.

[0053] Table 1-1

[0054]

[0055]

[0056] The effect data corresponding to this embodiment are as follows: Figure 5 , 6 From the modulation transfer function curves of Figure 7, it can be seen that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short focus, medium focus and long focus are better than 0.5 at +20℃, which meets the resolution requirements of the optical system.

[0057] Depend on Figure 8 , 9 From the modulation transfer function curves of 10, it can be seen that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short focus, medium focus and long focus are better than 0.1 at -40℃, which meets the resolution requirements of the optical system.

[0058] Depend on Fig.11 ,12 From the modulation transfer function curves of Figure 13, it can be seen that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short focus, medium focus and long focus are better than 0.26 at +65℃, which meets the resolution requirements of the optical system.

[0059] Embodiment 1-2: The difference between this embodiment and embodiment 1-1 is only that the parameters of each component are different.

[0060] The parameters of each element of this embodiment (surface shape, radius of curvature, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 1-2, where the radius of curvature, distance from the next optical surface, and semi-aperture are in units of mm.

[0061] Table 1-2

[0062]

[0063] The effect data corresponding to the parameters of this embodiment are as follows:

[0064] At the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.47 at +20℃, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.10 at -40℃, and the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.24 at +65℃, which meets the resolution requirements of the optical system.

[0065] Embodiment 1-3: The difference between this embodiment and embodiment 1-1 is only that the parameters of each component are different.

[0066] The parameters of each element of this embodiment (surface shape, radius of curvature, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 1-3, where the radius of curvature, distance from the next optical surface, and semi-aperture are in units of mm.

[0067] Table 1-3

[0068]

[0069] The effect data corresponding to the parameters of this embodiment are as follows:

[0070] At the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.48 at +20℃, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.10 at -40℃, and the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.25 at +65℃, which meets the resolution requirements of the optical system.

[0071] Example 2-1: Figures 14 to 16 As shown, the small F-number high-resolution medium-wave cooling zoom imaging system of the present invention comprises lens L1, lens L2, lens L3, lens L4, lens L5, lens L6, lens L7, and detector I, which are arranged in sequence from the object side to the image side; wherein the detector I comprises a window WIN, a detector protection glass FIL, a cold stop STOP, and a target surface IMAGE; the lens L1 constitutes a front fixed group, the lens L2 constitutes a zoom group, the lens L3 constitutes a compensation group, the lens L4 constitutes a rear fixed group, and the lens L5, lens L6, and lens L7 constitute a focusing group. The zoom imaging process is to achieve the change of focal length from short focus to long focus by axially moving the zoom group and the compensation group toward each other, and to ensure that the position of the image plane of the system does not change. The defocus caused by temperature change can be compensated by the axial movement of the focusing group as a whole in the lens barrel, so as to ensure clear imaging of the system at different temperatures. The focal length f1 of the front fixed group, the focal length f2 of the zoom group, the focal length f3 of the compensation group, and the focal length f4 of the rear fixed group satisfy the following relationship: 0.3≤f1 / f L ≤0.7;-0.12≤f2 / f L ≤-0.3; 0.2≤f3 / f L ≤0.4; 0.2≤f4 / f L ≤0.5; where f L is the focal length of the system at telephoto.

[0072] The lens L1 is a meniscus mirror with positive focal power, and its convex surface faces the object plane; the lens L2 is a concave lens; the lens L3 is a convex lens; the lens L4 is a meniscus mirror with positive focal power, and its convex surface faces the object plane; the lens L5 is a meniscus mirror with negative focal power, and its convex surface faces the image plane; the lens L6 is a meniscus mirror with positive focal power, and its convex surface faces the image plane; the lens L7 is a convex lens; the front and rear surfaces of the lens L1 are both spherical; the front surface of the lens L2 is spherical, and the rear surface is aspherical; the front surface of the lens L3 is spherical, and the rear surface is aspherical; the front surface of the lens L4 is spherical, and the rear surface is aspherical; the front surface of the lens L5 is aspherical, and the rear surface is spherical; the front surface of the lens L6 is spherical, and the rear surface is aspherical; the front surface of the lens L7 is aspherical, and the rear surface is spherical.

[0073] The materials of lens L1, lens L2, lens L3, lens L4, lens L5, lens L6 and lens L7 are Si, Ge, Si, Ge, Si, Ge, and Si respectively.

[0074] By calculating the material matching and adjusting the air space between each lens, the imaging system transfer function is finally achieved to be better than 0.10@17lp / mm, ensuring excellent imaging quality. Under the condition that the lens barrel is made of aluminum alloy, the focusing group of lenses L5, L6 and L7 move axially together to compensate for the defocusing of the imaging system at different temperatures, ensuring that the image plane position remains unchanged. The imaging quality of the entire imaging system meets the use requirements at a temperature of -40 to +65°C.

[0075] The parameters of each element of this embodiment (surface shape, radius of curvature, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 1-1, where the radius of curvature, distance from the next optical surface, and semi-aperture are in units of mm.

[0076] Table 2-1

[0077]

[0078] The effect data corresponding to the parameters of this embodiment are as follows:

[0079] Depend on Fig.17 , 18 From the modulation transfer function curves of 19, it can be seen that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short focus, medium focus and long focus are better than 0.6 at +20℃, which meets the resolution requirements of the optical system.

[0080] Depend on Fig. 20 , 21 From the modulation transfer function curves of 22, it can be seen that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short focus, medium focus and long focus are better than 0.1 at -40℃, which meets the resolution requirements of the optical system.

[0081] Depend on Fig.23 , 24 From the modulation transfer function curves of 25, it can be seen that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short focus, medium focus and long focus are better than 0.24 at +65℃, which meets the resolution requirements of the optical system.

[0082] Embodiment 2-2: This embodiment differs from Embodiment 2-1 only in that the parameters of the components are different.

[0083] The parameters of each component of this embodiment (surface shape, radius of curvature, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 2-2, where the radius of curvature, distance from the next optical surface, and semi-aperture are in units of mm.

[0084] Table 2-2

[0085]

[0086] The effect data corresponding to the parameters of this embodiment are as follows:

[0087] At the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.56 at +20℃, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.10 at -40℃, and the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.23 at +65℃, which meets the resolution requirements of the optical system.

[0088] Embodiment 2-3: The difference between this embodiment and embodiment 2-1 is only that the parameters of each component are different.

[0089] The parameters of each component of this embodiment (surface shape, radius of curvature, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 2-3, where the radius of curvature, distance from the next optical surface, and semi-aperture are in units of mm.

[0090] Table 2-3

[0091]

[0092]

[0093] The effect data corresponding to the parameters of this embodiment are as follows:

[0094] At the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.58 at +20℃, the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.10 at -40℃, and the MTF values ​​of all fields of view of the zoom imaging system in short focus, medium focus and long focus are better than 0.23 at +65℃, which meets the resolution requirements of the optical system.

[0095] The embodiments of the present invention can achieve the following indicators:

[0096] a) Focal length: 30.0~150.0mm;

[0097] b)F / #: 1.5;

[0098] c) Wavelength: 3200~3500nm;

[0099] d) Field of view: 18.2°×14.6°~3.62°×2.91°;

[0100] e) Distortion: <3%;

[0101] f)MTF:>0.10@17lp / mm;

[0102] g) Working temperature: -40℃~+65℃.

Claims

1. A small F-number high-resolution medium-wave cooled zoom imaging system, characterized in that The invention comprises lens L1, lens L2, lens L3, lens L4 and detector I which are arranged in sequence from the object side to the image side along the optical axis; the lens L1 is a meniscus mirror with positive focal length, and its convex surface faces the object side; the lens L2 is a concave lens; the lens L3 is a convex lens; the lens L4 is a meniscus mirror with positive focal length, and its convex surface faces the object side; the lens L1 constitutes a front fixed group, the lens L2 constitutes a variable magnification group, the lens L3 constitutes a compensation group, and the lens L4 constitutes a rear fixed group; the zoom imaging process is to change the focal length from short focal length to long focal length by moving the variable magnification group and the compensation group toward each other along the axial direction; the focal length f1 of the front fixed group, the focal length f2 of the variable magnification group, the focal length f3 of the compensation group, and the focal length f4 of the rear fixed group satisfy the following relationship: 0.3≤f1 / f L ≤0.7;-0.12≤f2 / f L ≤-0.3; 0.2≤f3 / f L ≤0.4; 0.2≤f4 / f L ≤0.5; where f L is the focal length of the system at telephoto.

2. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 1, characterized in that The front and rear surface curvature radii of the lens L1 are 93.52mm to 104.886mm and 171.663mm to 217.33mm respectively; the front and rear surface curvature radii of the lens L2 are -204.095mm to -154.026mm and 102.990mm to 132.92mm respectively; the front and rear surface curvature radii of the lens L3 are 211.16mm to 443.995mm and -174.992mm to -128.14mm respectively; the front and rear surface curvature radii of the lens L4 are 19.336mm to 20.681mm and 17 .01mm~22.845mm; the thickness of lens L1 is 10.5mm~12.4mm; the thickness of lens L2 is 3.6mm~4.3mm; the thickness of lens L3 is 7mm~8.8mm; the thickness of lens L4 is 7.2mm~8.1mm; the air gap between the rear surface of lens L1 and the front surface of lens L2 is 23.2mm~42.9mm; the air gap between the rear surface of lens L2 and the front surface of lens L3 is 4.0mm~56.9mm; the air gap between the rear surface of lens L3 and the front surface of lens L4 is 13.0mm~41.7mm.

3. The small F-number high-resolution medium-wavelength cooling zoom imaging system according to claim 2, characterized in that The front and rear surfaces of the lens L1 are both spherical; the front and rear surfaces of the lens L2 are both aspherical; the front surface of the lens L3 is aspherical, and the rear surface is spherical; the front surface of the lens L4 is spherical, and the rear surface is aspherical; the cone coefficient k of the front surface of the lens L2 is -0.96 to -0.78, the fourth power coefficient α2 of the radial coordinate is -6.81E-07 to -1.68E-07, the sixth power coefficient α3 is -2.91E-10 to -1.58E-10, and the eighth power coefficient α4 is 1.26E-13 to 3.16E-13; the cone coefficient k of the rear surface of the lens L2 is 0, the fourth power coefficient α2 of the radial coordinate is 1.46E-07 to 5.91E-07, and the sixth power coefficient α3 is -3.88 E-10~-2.88E-10, and the octapower coefficient α4 is 1.23E-13~3.50E-13; the cone coefficient k of the front surface of lens L3 is 0, the fourth power coefficient α2 of the radial coordinate is -5.69E-07~-2.55E-07, the sixth power coefficient α3 is 1.43E-10~2.34E-10, and the octapower coefficient α4 is -6.15E-13~-2.57E-13; the cone coefficient k of the back surface of lens L4 is 0, the fourth power coefficient α2 of the radial coordinate is 2.31E-05~2.61E-05, the sixth power coefficient α3 is -4.25E-07~-1.78E-07, and the octapower coefficient α4 is 1.92E-10~5.12E-10.

4. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 3, characterized in that It also includes a focusing group, which is arranged between the rear fixed group and the detector I, and is composed of lens L5, lens L6, and lens L7 arranged in sequence along the optical axis from the object side to the image side; lens L5 is a meniscus mirror with negative optical focal length, and its convex surface faces the image plane; lens L6 is a meniscus mirror with positive optical focal length, and its convex surface faces the image plane; lens L7 is a meniscus mirror with positive optical focal length, and its convex surface faces the object plane.

5. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 4, characterized in that The front and rear surface curvature radii of the lens L5 are -18.942mm to -17.195mm and -40.791mm to -38.687mm respectively; the front and rear surface curvature radii of the lens L6 are -61.604mm to -53.183mm and -33.168mm to -32.301mm respectively; the front and rear surface curvature radii of the lens L7 are 30.025mm to 34.205mm and 81.426mm to 89.927mm respectively; The thickness of lens L5 is 6.2mm~6.8mm; the thickness of lens L6 is 7.3mm~7.8mm; the thickness of lens L7 is 7.4mm~7.8mm; the air gap between the rear surface of lens L4 and the front surface of lens L5 is 32.5mm~33.5mm; the air gap between the rear surface of lens L5 and the front surface of lens L6 is 1.8mm~2.2mm; the air gap between the rear surface of lens L6 and the front surface of lens L7 is 0.4mm~0.6mm.

6. The small F-number high-resolution medium-wave cooling zoom imaging system according to claim 5, characterized in that The front surface of the lens L5 is spherical, and the rear surface is aspherical; the front surface of the lens L6 is spherical, and the rear surface is aspherical; the front surface of the lens L7 is aspherical, and the rear surface is spherical; the cone coefficient k of the rear surface of the lens L5 is -1.21 to -1.06, the fourth power coefficient α2 of the radial coordinate is 4.39E-06 to 9.10E-06, the sixth power coefficient α3 is 2.04E-09 to 7.68E-09, the eighth power coefficient α4 is 4.88E-11 to 8.21E-11, and the cone coefficient k of the rear surface of the lens L6 is 0, the fourth power coefficient α2 of the radial coordinate is 1.86E-07~3.11E-07, the sixth power coefficient α3 is -9.09E-10~-2.03E-10, the octapower coefficient α4 is 3.51E-14~8.38E-14, the cone coefficient k of the front surface of lens L7 is 0, the fourth power coefficient α2 of the radial coordinate is 1.69E-07~4.73E-07, the sixth power coefficient α3 is -2.98E-11~-2.01E-11, and the octapower coefficient α4 is 3.45E-16~6.54E-16.

7. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 2, characterized in that The front and rear surfaces of the lens L1 are both spherical; the front surface of the lens L2 is spherical, and the rear surface is aspherical; the front surface of the lens L3 is spherical, and the rear surface is aspherical; the front surface of the lens L4 is spherical, and the rear surface is aspherical; the cone coefficient k of the rear surface of the lens L2 is 1.03-1.05, the fourth power coefficient α2 of the radial coordinate is 1.817E-07-2.41E-07, the sixth power coefficient α3 is -3.59E-10--2.34E-10, and the eighth power coefficient α4 is 5.36E-12-7.70E-12; the cone coefficient k of the rear surface of the lens L3 ... The cone coefficient k is 0, the fourth power coefficient α2 of the radial coordinate is -4.38E-06 to -2.97E-06, the sixth power coefficient α3 is 7.53E-09 to 1.165E-08, and the octapower coefficient α4 is -3.31E-11 to -2.02E-11; the cone coefficient k of the back surface of lens L4 is 0, the fourth power coefficient α2 of the radial coordinate is 4.27E-06 to 7.28E-06, the sixth power coefficient α3 is -5.82E-07 to -3.33E-07, and the octapower coefficient α4 is 6.74E-09 to 9.87E-09.

8. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 7, characterized in that It also includes a focusing group, which is arranged between the rear fixed group and the detector I, and is composed of lens L5, lens L6, and lens L7 arranged in sequence along the optical axis from the object side to the image side; lens L5 is a meniscus mirror with negative optical focal length, and its convex surface faces the image plane; lens L6 is a meniscus mirror with positive optical focal length, and its convex surface faces the image plane; lens L7 is a convex lens.

9. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 8, characterized in that The front and rear surface curvature radii of the lens L5 are -20.27mm to -19.72mm and -31.21mm to -31.08mm respectively; the front and rear surface curvature radii of the lens L6 are -68.47mm to -64.45mm and -33.13mm to -32.30mm respectively; the front and rear surface curvature radii of the lens L7 are 336.60mm to 236.94mm and -98.95mm to -93.35mm respectively; The thickness of L5 is 5.5mm~5.6mm; the thickness of lens L6 is 7.9mm~8.2mm; the thickness of lens L7 is 7.3mm~7.5mm; the air gap between the rear surface of lens L4 and the front surface of lens L5 is 24.7mm~24.9mm; the air gap between the rear surface of lens L5 and the front surface of lens L6 is 0.4mm; the air gap between the rear surface of lens L6 and the front surface of lens L7 is 12.2mm~12.3mm.

10. The small F-number high-resolution medium-wavelength cooled zoom imaging system according to claim 9, characterized in that The front surface of the lens L5 is aspherical, and the rear surface is spherical; the front surface of the lens L6 is spherical, and the rear surface is aspherical; the front surface of the lens L7 is aspherical, and the rear surface is spherical; the cone coefficient k of the front surface of the lens L5 is 0, the fourth power coefficient α2 of the radial coordinate is 2.53E-06 to 3.89E-06, the sixth power coefficient α3 is 5.87E-09 to 8.61E-09, the eighth power coefficient α4 is 4.99E-12 to 7.35E-12, and the cone coefficient k of the rear surface of the lens L6 is -0.63 to -0.59 The fourth power coefficient α2 of the radial coordinate is 1.48E-06~2.84E-06, the sixth power coefficient α3 is -2.07E-09~-1.13E-09, the octapower coefficient α4 is 5.75E-12~8.57E-12, the cone coefficient k of the front surface of lens L7 is 0, the fourth power coefficient α2 of the radial coordinate is 4.07E-07~6.70E-07, the sixth power coefficient α3 is -8.33E-11~-1.03E-10, and the octapower coefficient α4 is 1.24E-13~9.56E-14.

Images