A small-f-number high-resolution middle-wave refrigeration zoom imaging system

Abstract

The application relates to a small-F-number high-resolution middle-wave refrigeration zoom imaging system, which comprises, along an optical axis, a lens L1, a lens L2, a lens L3, a lens L4 and a detector I arranged in sequence from an object side to an image side; the lens L1 is a positive focal power meniscus mirror, the convex surface of which faces the object plane; the lens L2 is a concave lens; the lens L3 is a convex lens; the lens L4 is a positive focal power meniscus mirror, the convex surface of which faces the object plane; the lens L1 constitutes a front fixed group, the lens L2 constitutes a zoom group, the lens L3 constitutes a compensation group, and the lens L4 constitutes a rear fixed group; the zoom imaging process is realized by moving the zoom group and the compensation group along the axial direction to change the focal length from short focus to long focus. The application reduces the F number of the lens focal length, can ensure that more energy is received by the detector, greatly improves the resolution capacity of the system, reduces the complexity of the lens structure, and improves the stability and reliability of the lens.

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-wavelength 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. This lens structure consists of eight lenses, employing a three-element continuous zoom and secondary imaging system design. A field stop is placed at the primary image plane, preventing stray light outside the system's field of view from passing through the stop and reaching the image plane. This effectively reduces the impact of stray light on the optical system's imaging and improves the system's signal-to-noise ratio. This lens has the following disadvantages: 1. The F-number of a mid-wave infrared zoom lens is relatively high, typically no less than 4; 2. The number of telephoto elements is relatively high, typically three or more; 3. The lens's adaptability to ambient temperatures is limited, and it cannot operate normally in harsh environments such as -40°C to +65°C. Summary of the Invention

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

[0004] In order to solve the above technical problems, the present invention provides a small F-number, high-resolution, medium-wavelength, cooled zoom imaging system comprising a lens L1, a lens L2, a lens L3, a lens L4, and a detector I, which are sequentially arranged along the optical axis from the object side to the image side; the lens L1 is a meniscus mirror with positive focal length, with its convex surface facing 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, with its convex surface facing the object side; the lens L1 constitutes a front fixed group, the lens L2 constitutes a zoom group, the lens L3 constitutes a compensation group, and the lens L4 constitutes a rear fixed group; the zoom imaging process is to achieve a change in focal length from short focus to long focus by moving the zoom 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 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 when it is in telephoto mode.

[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 eight power coefficient a4 is -6.15E-13~ -2.57E-13; the conic coefficient k of the rear surface of the lens L4 is 0, the four power coefficient a2 of the radial coordinate is 2.31E-05~2.61E-05, the six power coefficient a3 is -4.25E-07~ -1.78E-07, and the eight power coefficient a4 is 1.92E-10~5.12E-10.

[0008] Further, the application further comprises a focusing group, the focusing group is arranged between the rear fixed group and the detector I, and is composed of a lens L5, a lens L6 and a lens L7 arranged in sequence from the object side to the image side along the optical axis; the lens L5 is a negative meniscus lens with its convex surface facing the image plane; the lens L6 is a positive meniscus lens with its convex surface facing the image plane; and the lens L7 is a positive meniscus lens with its convex surface facing the object plane.

[0009] The radii of curvature of the front and rear surfaces of the lens L5 are -18.942mm~ -17.195mm and -40.791mm~ -38.687mm respectively; the radii of curvature of the front and rear surfaces of the lens L6 are -61.604mm~ -53.183mm and -33.168mm~ -32.301mm respectively; the radii of curvature of the front and rear surfaces of the lens L7 are 30.025mm~ 34.205mm and 81.426mm~ 89.927mm respectively; the thickness of the lens L5 is 6.2mm~ 6.8mm; the thickness of the lens L6 is 7.3mm~ 7.8mm; the thickness of the lens L7 is 7.4mm~ 7.8mm; the air gap between the rear surface of the lens L4 and the front surface of the lens L5 is 32.5mm~ 33.5mm; the air gap between the rear surface of the lens L5 and the front surface of the lens L6 is 1.8mm~ 2.2mm; and the air gap between the rear surface of the lens L6 and the front surface of the 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 octahedron 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 octahedron 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 conic coefficient k of the rear surface of the lens L2 is 1.03 to 1.05, the fourth power coefficient α2 of the radial coordinate is 1.817E-07 to 2.41E-07, the sixth power coefficient α3 is -3.59E-10 to -2.34E-10, and the eighth power coefficient α4 is 5.36E-12 to 7.70E-12; the circularity of the rear surface of the lens L3 is 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 octahedral 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 octahedral 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 back surface curvature radius of the lens L5 are -20.27mm~ -19.72mm and -31.21mm~ -31.08mm respectively; the front and back surface curvature radius of the lens L6 are -68.47mm~ -64.45mm and -33.13mm~ -32.30mm respectively; the front and back surface curvature radius of the lens L7 are 336.60mm~ 236.94mm and -98.95mm~ -93.35mm respectively; the thickness of the lens L5 is 5.5mm~ 5.6mm; the thickness of the lens L6 is 7.9mm~ 8.2mm; the thickness of the lens L7 is 7.3mm~ 7.5mm; the air interval between the back surface of the lens L4 and the front surface of the lens L5 is 24.7mm~ 24.9mm; the air interval between the back surface of the lens L5 and the front surface of the lens L6 is 0.4mm; the air interval between the back surface of the lens L6 and the front surface of the lens L7 is 12.2mm~ 12.3mm.

[0014] The front surface of the lens L5 is aspherical surface and the back surface is spherical surface; the front surface of the lens L6 is spherical surface and the back surface is aspherical surface; the front surface of the lens L7 is aspherical surface and the back surface is spherical surface; the conic coefficient k of the front surface of the lens L5 is 0, the fourth power coefficient of radial coordinate a2 is 2.53E-06~ 3.89E-06, the sixth power coefficient a3 is 5.87E-09~ 8.61E-09, the eighth power coefficient a4 is 4.99E-12~ 7.35E-12; the conic coefficient k of the back surface of the lens L6 is -0.63~ -0.59, the fourth power coefficient of radial coordinate a2 is 1.48E-06~ 2.84E-06, the sixth power coefficient a3 is -2.07E-09~ -1.13E-09, the eighth power coefficient a4 is 5.75E-12~ 8.57E-12; the conic coefficient k of the front surface of the lens L7 is 0, the fourth power coefficient of radial coordinate a2 is 4.07E-07~ 6.70E-07, the sixth power coefficient a3 is -8.33E-11~ -1.03E-10, the eighth power coefficient a4 is 1.24E-13~ 9.56E-14.

[0015] Beneficial effects: the lens focal length F number is reduced, the F number is 1.5, more energy can be received by the detector, the resolution of the system is greatly improved; the zoom way of 2 movement groups is adopted, the complexity of the lens structure is reduced, the stability and reliability of the lens are improved; the defocus caused by temperature change is compensated by the axial movement of the focusing group, the imaging system works normally and the image quality is excellent under the severe environment temperature of -40℃~ +65℃, the focal length is continuously zoomed from 30mm to 150mm under the condition of ensuring high resolution imaging, the zoom ratio is 5 times, the application range of the zoom lens is greatly improved. BRIEF DESCRIPTION OF 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 Examples 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 This is a diagram of the telephoto optical structure of Examples 1-1, 1-2, and 1-3 of the present invention.

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

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

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

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

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

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

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

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

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

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

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

[0031] Figure 16 This is a diagram of the telephoto optical structure of Examples 2-1, 2-2, and 2-3 of the present invention.

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

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

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

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

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

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

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

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

[0040] Figure 25 This 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. Biconcave 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 will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, rather than all structures.

[0043] In the description of this embodiment, terms such as "upper," "lower," "left," and "right" are used to refer to positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate description and simplify operation, and are not intended to indicate or imply that the devices or components referred to must be oriented, constructed, or operated in a specific manner. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and have no special meaning.

[0044] Example 1-1: Figure 2-4 As shown, the small F-number, high-resolution, medium-wavelength cooled zoom imaging system of the present invention includes 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 includes 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 to ensure that the position of the system image plane 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 when it is in telephoto mode.

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

[0047] The aspheric expression is as follows:

[0048]

[0049] z represents the sag height; 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, sixth-power, and eighth-power coefficients of the radial coordinate, respectively. α1, α5, α6, α7, and α8 represent the second-power, tenth-power, twelfth-power, fourteenth-power, and sixteenth-power coefficients of the radial coordinate, respectively, and are all 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 combination and adjusting the air spacing between each lens, the imaging system achieves a transfer function better than 0.50 @ 17 lp / mm, ensuring excellent image quality. Using an aluminum alloy lens barrel, the axial movement of lenses L5, L6, and L7 in the focusing group compensates for defocus at varying temperatures, ensuring a constant image plane position. This ensures that the entire imaging system meets operating quality requirements at temperatures between -40°C and +65°C.

[0052] The parameters of each element in this embodiment (surface shape, curvature radius, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 1-1, where the curvature radius, distance from the next optical surface, and semi-aperture are in 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, we can see that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short, medium and long focal lengths are better than 0.5 at +20°C, meeting the resolution requirements of the optical system.

[0057] Depend on Figure 8 、 9 From the modulation transfer function curves of Figure 10, we can see that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.1 at -40°C, meeting the resolution requirements of the optical system.

[0058] Depend on Figure 11 、12 From the modulation transfer function curves in Figures 13 and 14, it can be seen that at the detector cutoff frequency of 17lp / mm and at +65°C, the MTF values ​​of all fields of view of the zoom imaging system at short, medium and long focal lengths are better than 0.26, which meets the resolution requirements of the optical system.

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

[0060] The parameters of each element in this embodiment (surface shape, curvature radius, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 1-2, where the curvature radius, distance from the next optical surface, and semi-aperture are in 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 the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.47 at +20°C. At -40°C, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.10. At +65°C, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.24, meeting the resolution requirements of the optical system.

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

[0066] The parameters of each element in this embodiment (surface shape, curvature radius, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Tables 1-3, where the curvature radius, distance from the next optical surface, and semi-aperture are in 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 the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.48 at +20°C. At -40°C, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.10. At +65°C, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.25, meeting the resolution requirements of the optical system.

[0071] Example 2-1: Figures 14-16 As shown, the small F-number high-resolution medium-wave cooled zoom imaging system of the present invention includes lenses L1, L2, L3, L4, L5, L6, L7, and a detector I, which are arranged in sequence from the object side to the image side; wherein the detector I includes 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 lenses L5, L6, and L7 constitute a focusing group. The zoom imaging process is to achieve a change in 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 system image plane 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 when it is in telephoto mode.

[0072] The lens L1 is a meniscus mirror with positive optical 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 optical power, and its convex surface faces the object plane; the lens L5 is a meniscus mirror with negative optical power, and its convex surface faces the image plane; the lens L6 is a meniscus mirror with positive optical power, and its convex surface faces the image plane; the lens L7 is a convex lens; the front and back surfaces of the lens L1 are both spherical; the front surface of the lens L2 is spherical, and the back surface is aspherical; the front surface of the lens L3 is spherical, and the back surface is aspherical; the front surface of the lens L4 is spherical, and the back surface is aspherical; the front surface of the lens L5 is aspherical, and the back surface is spherical; the front surface of the lens L6 is spherical, and the back surface is aspherical; the front surface of the lens L7 is aspherical, and the back 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 combination and adjusting the air spacing between each lens, the imaging system achieves a transfer function better than 0.10 @ 17 lp / mm, ensuring excellent image quality. Using an aluminum alloy lens barrel, the axial movement of lenses L5, L6, and L7 in the focusing group compensates for defocus at varying temperatures, ensuring a constant image plane position. This ensures that the entire imaging system meets operating quality requirements at temperatures between -40°C and +65°C.

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

[0076] Table 2-1

[0077]

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

[0079] Depend on Figure 17 、 18 From the modulation transfer function curves in Figure 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, medium and long focal lengths are better than 0.6 at +20°C, meeting the resolution requirements of the optical system.

[0080] Depend on Figure 20 、 21 From the modulation transfer function curves of Figure 22, we can see that at the detector cutoff frequency of 17lp / mm, the MTF values ​​of all fields of view of the zoom imaging system at short, medium and long focal lengths are better than 0.1 at -40°C, meeting the resolution requirements of the optical system.

[0081] Depend on Figure 23 、 24 From the modulation transfer function curves of 25, we can see that at the detector cutoff frequency of 17lp / mm and +65℃, the MTF values ​​of all fields of view of the zoom imaging system at short, medium and long focal lengths are better than 0.24, meeting the resolution requirements of the optical system.

[0082] Example 2-2: The only difference between this example and Example 2-1 is the parameters of each component.

[0083] The parameters of each element in this embodiment (surface shape, curvature radius, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 2-2, where the curvature radius, distance from the next optical surface, and semi-aperture are in 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 the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.56 at +20°C. At -40°C, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.10. At +65°C, the MTF values ​​of the zoom imaging system in all fields of view, including short, medium and long focal lengths, are better than 0.23, meeting the resolution requirements of the optical system.

[0088] Example 2-3: The only difference between this example and Example 2-1 is the parameters of each component.

[0089] The parameters of each element in this embodiment (surface shape, curvature radius, distance from the next optical surface, semi-aperture, aspheric coefficient, etc.) are shown in Table 2-3, where the curvature radius, distance from the next optical surface, and semi-aperture are in 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 the zoom imaging system for all fields of view, including short, medium, and long focal lengths, are better than 0.58 at +20°C. At -40°C, the MTF values ​​of the zoom imaging system for all fields of view, including short, medium, and long focal lengths, are better than 0.10. At +65°C, the MTF values ​​of the zoom imaging system for all fields of view, including short, medium, and long focal lengths, are better than 0.23, meeting 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) Waveband: 3200~3500nm;

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

[0100] e) Distortion: <3%;

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

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

Claims

1. A small F-number, high-resolution, medium-wavelength 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, with its convex surface facing 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, with its convex surface facing the object side; the lens L1 constitutes a front fixed group, the lens L2 constitutes a zoom group, the lens L3 constitutes a compensation group, and the lens L4 constitutes a rear fixed group; the zoom imaging process is to achieve the change of focal length from short focus to long focus by moving the zoom 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 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;-0.3≤f2 / f L ≤-0.12; 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; the focusing group 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 power, with its convex surface facing the image plane; lens L6 is a meniscus mirror with positive optical power, with its convex surface facing the image plane; lens L7 has positive optical power; the entire system comprises a total of 7 lenses; the front and rear surface curvature radii of the lens L1 are 93.52mm~104.886mm and 171.663mm~217.33mm respectively; the front and rear surface curvature radii of the lens L2 are -204.095mm~-154.026mm, 102.990mm~132.92mm respectively; the front and rear surface curvature radii of the lens L3 are 211.16mm~443.995mm, -174.992mm respectively ~-128.14mm; the front and rear surface curvature radii of lens L4 are 19.336mm ~20.681mm and 17.01mm ~22.845mm respectively; 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.

2. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 1, 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~-0.78, the fourth power coefficient α2 of the radial coordinate is -6.81E-07~-1.68E-07, the sixth power coefficient α3 is -2.91E-10~-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 the lens L2 is 0, the fourth power coefficient α2 of the radial coordinate is 1.46E-07~5.91E-07, and the sixth power coefficient α3 is -3.88 The conic 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 eighth power coefficient α4 is -6.15E-13~-2.57E-13; the conic 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 eighth power coefficient α4 is 1.92E-10~5.12E-10.

3. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 2, characterized in that The lens L7 is a meniscus lens, with its convex surface facing the object plane.

4. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 3, characterized in that The front and rear surface curvature radii of the lens L5 are -18.942mm ~-17.195mm and -40.791mm ~-38.687mm respectively; the front and rear surface curvature radii of the lens L6 are -61.604mm ~-53.183mm and -33.168mm ~-32.301mm respectively; the front and rear surface curvature radii of the lens L7 are 30.025mm ~34.205mm and 81.426mm ~89.927mm respectively; the thickness of the lens L5 is 6.2mm ~6.8mm; the thickness of the lens L6 is 7.3mm ~7.8mm; the thickness of the lens L7 is 7.4mm ~7.8mm; the air gap between the rear surface of the lens L4 and the front surface of the lens L5 is 32.5mm ~33.5mm; the air gap between the rear surface of the lens L5 and the front surface of the 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.

5. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 4, 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~-1.06, the fourth power coefficient α2 of the radial coordinate is 4.39E-06~9.10E-06, the sixth power coefficient α3 is 2.04E-09~7.68E-09, the eighth power coefficient α4 is 4.88E-11~8.21E-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, and the octahedron 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 octahedron coefficient α4 is 3.45E-16~6.54E-16.

6. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 1, 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 conic 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 circularity of the rear surface of the lens L3 is The cone coefficient k is 0, the fourth power coefficient α2 of the radial coordinate is -4.38E-06~-2.97E-06, the sixth power coefficient α3 is 7.53E-09~1.165E-08, and the octahedral coefficient α4 is -3.31E-11~-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-06~7.28E-06, the sixth power coefficient α3 is -5.82E-07~-3.33E-07, and the octahedral coefficient α4 is 6.74E-09~9.87E-09.

7. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 6, characterized in that The lens L7 is a convex lens.

8. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 7, characterized in that The front and rear surface curvature radii of the lens L5 are -20.27mm ~-19.72mm and -31.21mm ~-31.08mm respectively; the front and rear surface curvature radii of the lens L6 are -68.47mm ~-64.45mm and -33.13mm ~-32.30mm respectively; the front and rear surface curvature radii of the lens L7 are 336.60mm ~236.94mm and -98.95mm ~-93.35mm respectively; the thickness of the lens L5 is 5.5mm ~5.6mm; the thickness of the lens L6 is 7.9mm ~8.2mm; the thickness of the lens L7 is 7.3mm ~7.5mm; the air gap between the rear surface of the lens L4 and the front surface of the lens L5 is 24.7mm ~24.9mm; the air gap between the rear surface of the lens L5 and the front surface of the lens L6 is 0.4mm; the air gap between the rear surface of the lens L6 and the front surface of the lens L7 is 12.2mm ~12.3mm.

9. The small F-number, high-resolution, medium-wavelength cooled zoom imaging system according to claim 8, characterized in that The front surface of the lens L5 is aspherical, and the back surface is spherical; the front surface of the lens L6 is spherical, and the back surface is aspherical; the front surface of the lens L7 is aspherical, and the back 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-06~3.89E-06, the sixth power coefficient α3 is 5.87E-09~8.61E-09, the eighth power coefficient α4 is 4.99E-12~7.35E-12, and the cone coefficient k of the back surface of the lens L6 is -0.63~-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, and the octave 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 octave coefficient α4 is 1.24E-13~9.56E-14.

Images