A compact long-wave infrared zoom lens

Abstract

The present invention discloses a compact long-wave infrared zoom lens. Along the optical axis, from the object side to the image side, the lens comprises a first lens with positive refractive power, a convex surface on the object side, and a concave surface on the image side; a second lens with negative refractive power, a concave surface on the object side and a concave surface on the image side; a third lens with positive refractive power, a convex surface on the object side and a convex surface on the image side; a fourth lens with negative refractive power, a convex surface on the object side and a concave surface on the image side; and a fifth lens with positive refractive power, a concave surface on the object side and a convex surface on the image side. Through a rational distribution of optical power, the present invention achieves a 20-60mm continuous zoom optical system design. The lens utilizes a total of five optical lenses, resulting in a compact overall structure with a total length of less than 85mm. This not only enables clear imaging at different focal lengths, but also meets the design requirements of miniaturization.

Description

Technical Field

[0001] The invention relates to a zoom lens, in particular to a compact long-wave infrared zoom lens for a non-cooling detector. Background Art

[0002] Infrared systems can search, identify, and track targets around the clock, and are widely used in military reconnaissance, air defense, and guidance. Due to their unique infrared imaging technology, they can remain operational even in extreme weather conditions such as heavy fog and haze. However, conventional infrared zoom lenses currently have complex structures and are relatively large in size. This is especially true for zoom lenses in the medium and long focal length range. The larger the focal length, the larger the front diameter of the lens, making them less convenient to carry and use. In addition, infrared materials are relatively expensive, making it difficult to optimize both the cost and imaging quality of the lens. Conventional long-wave infrared zoom lenses currently have a minimum image stabilization distance that cannot be too close, with medium and long focal length lenses typically around 100 meters. Furthermore, their operating temperature range is relatively small, and the image quality tends to blur in high and low temperature environments. Summary of the Invention

[0003] In view of this, an object of the present invention is to provide a compact long-wave infrared zoom lens capable of solving at least one of the technical problems mentioned in the background art.

[0004] According to one aspect of the present invention, a compact long-wave infrared zoom lens is provided, which comprises, in order from the object side to the image side along the optical axis, a first lens, a second lens, a third lens, an aperture, a fourth lens, and a fifth lens; wherein the first lens is a front fixed lens group, the second lens is a zoom lens group, the third lens is a compensating lens group, the fourth lens is a focusing lens group, and the fifth lens is a rear fixed lens group;

[0005] The first lens has positive refractive power, a convex object-side surface, and a concave image-side surface;

[0006] The second lens has a negative refractive power, a concave object side surface, and a concave image side surface;

[0007] The third lens has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0008] The fourth lens has a negative refractive power, a convex object-side surface, and a concave image-side surface;

[0009] The fifth lens element has positive refractive power, and its object-side surface is concave and its image-side surface is convex.

[0010] In some embodiments, the working object distance range of the lens is 10m to infinity, and the working temperature range is -40°C to 60°C; the fourth lens is a fine-focusing lens group of the system, and when the object distance or temperature changes, focusing is performed through the fine-focusing lens group.

[0011] In some embodiments, the lens satisfies the following formula:

[0012] 0.5<|f1| / f<0.67

[0013] 0.17<|f2| / f<0.25

[0014] 0.3<|f3| / f<0.33

[0015] 1.17<|f4| / f<1.25

[0016] 0.42<|f5| / f<0.5

[0017] Where f1, f2, f3, f4, and f5 are the focal lengths of the first, second, third, fourth, and fifth lenses, and f is the telephoto focal length of the lens, 60 mm.

[0018] In some embodiments, the lens satisfies the following conditions:

[0019] The optical back focus BFL of the lens is greater than 13.7mm, the telephoto F number is less than 1.2, the total movement of the zoom lens group is 7.4mm, and the total movement of the supplementary lens group is 10.8mm.

[0020] In some embodiments, the lens has a long focal length of 60 mm and a short focal length of 20 mm.

[0021] The lens satisfies the following formula:

[0022] 3.9<nd1<4.1

[0023] 3.9<nd2<4.1

[0024] 3.9<nd3<4.1

[0025] 2.7<nd4<2.9

[0026] 3.9<nd5<4.1

[0027] Wherein, nd1, nd2, nd3, nd4, and nd5 are the refractive indices of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens.

[0028] In some embodiments, the lens is provided with a housing, and the outer dimensions of the whole machine formed by the housing and the lens are φ73mm*82mm, the weight is less than 400g, and the outer diameter of the largest lens is less than 58mm.

[0029] In some embodiments, the focal length of the first lens is defined as f1, and the refractive index is defined as nd1, satisfying the following relationship: nd1>4, 30<|f1|<40; and correcting high-order aberrations is utilized to optimize the image quality in the long focal length segment.

[0030] In some embodiments, the focal length of the second lens is defined as f2, which satisfies the following relationship: f2<0; and the second lens mainly performs the function of system magnification in the system.

[0031] In some embodiments, the focal length of the third lens is defined as f3, which satisfies the following relationship: f3>0; and the third lens mainly performs the function of compensating for image plane movement in the system.

[0032] In some embodiments, the focal length of the fourth lens is defined as f4, and the focal length of the fifth lens is defined as f5, satisfying the following relationship: f4<0, f5>0; which is beneficial to the correction of residual aberrations.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] This application uses five lenses to achieve a 20-60mm continuous zoom optical system design. Through reasonable optical power distribution and the use of aspheric surfaces, the lens is miniaturized as much as possible while ensuring clear imaging. The total length is no more than 85mm, and the structure is compact, which not only reduces production costs but also simplifies the assembly of the system. The lens can be used with a 640*512@12um non-cooled detector to achieve high resolution across the entire target surface, and relatively consistent imaging quality from the center to the edge. The system implements an athermal design, which can output high-definition images in high and low temperature environments of -40℃ to 60℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above features and advantages of the present invention will become more clear and easily understood through the following description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0036] Figure 1 This is a schematic structural diagram of one embodiment of the compact long-wave infrared zoom lens of the present invention at telephoto focus;

[0037] Figure 2 This is a schematic diagram of the structure of one embodiment of the compact long-wave infrared zoom lens of the present invention at short focal length;

[0038] Figure 3 This is an MTF diagram of one embodiment of the compact long-wave infrared zoom lens of the present invention at a long focal length;

[0039] Figure 4 This is a diagram of optical distortion and field curvature of one embodiment of the compact long-wave infrared zoom lens of the present invention at a long focal length;

[0040] Figure 5 This is a relative illumination diagram of one embodiment of the compact long-wave infrared zoom lens of the present invention at a long focal length;

[0041] Figure 6 This is an MTF diagram of one embodiment of the compact long-wave infrared zoom lens of the present invention at a short focal length;

[0042] Figure 7 This is a diagram of optical distortion and field curvature of one embodiment of the compact long-wave infrared zoom lens of the present invention at a short focal length;

[0043] Figure 8 This is a relative illumination diagram of one embodiment of the compact long-wave infrared zoom lens of the present invention at a short focal length;

[0044] Figure 9 This is an MTF graph of one embodiment of the compact long-wave infrared zoom lens of the present invention at a low temperature of -40°C in the short focal length range;

[0045] Figure 10 This is an MTF graph of one embodiment of the compact long-wave infrared zoom lens of the present invention at a low temperature of -40°C in the long focal length range;

[0046] Figure 11 This is an MTF graph of one embodiment of the compact long-wave infrared zoom lens of the present invention at a high temperature of 60°C in the short focal length section;

[0047] Figure 12 This is an MTF diagram of one embodiment of the compact long-wave infrared zoom lens of the present invention at a high temperature of 60°C in the long focal length range. DETAILED DESCRIPTION

[0048] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It is particularly noted that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Similarly, the following examples are only some embodiments of the present invention and are not intended to be exhaustive. All other embodiments obtained by those of ordinary skill in the art without creative effort are intended to fall within the scope of protection of the present invention.

[0049] The present invention provides a compact long-wave infrared zoom lens, which can solve at least one technical problem mentioned in the background technology.

[0050] Example 1

[0051] See also Figure 1-2 Schematic diagram of the lens structure of a compact long-wave infrared zoom lens. Along the optical axis, from the object side to the image side, the following sequence is: first lens 1, second lens 2, third lens 3, aperture ST, fourth lens 4, and fifth lens 5.

[0052] The first lens 1 has positive refractive power, a convex object side surface, and a concave image side surface;

[0053] The second lens 2 has a negative refractive power, a concave object side surface, and a concave image side surface;

[0054] The third lens 3 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0055] The fourth lens 4 has a negative refractive power, a convex object-side surface, and a concave image-side surface;

[0056] The fifth lens element 5 has positive refractive power, and its object-side surface is concave and its image-side surface is convex.

[0057] The aperture is placed on the second surface of the third lens.

[0058] The first lens 1 and the fifth lens 5 are fixed lens groups, the second lens 2 is a zoom lens group, the third lens 3 is a compensation lens group, and the fourth lens 4 is a fine-focus lens group.

[0059] The optical back focus BFL of the lens is greater than 13.7mm, the telephoto F number is less than 1.2, the total movement of the zoom lens group is 7.4mm, and the total movement of the supplementary lens group is 10.8mm; the telephoto focal length of the lens is 60mm and the short focal length is 20mm; the maximum outer diameter of the lens is less than 58mm, and the total length is less than 85mm.

[0060] Reference numerals in the figure are: object side surface A, image side surface B, first lens 1, second lens 2, third lens 3, aperture ST, fourth lens 4, fifth lens 5, and protective sheet 6.

[0061] Other parameters of the lens of this embodiment are as follows:

[0062] Table 1. Parameters of the lens in the embodiment

[0063]

[0064]

[0065] Note: f represents focal length, BFL represents back focal length, TTL represents total lens length, y represents image plane size, surface numbers represent object side surface of first lens 1, image side surface of first lens 1, and object side surface of second lens 2 in sequence, and thickness intervals corresponding to surface numbers represent center thickness of first lens 1, center distance between first lens 1 and second lens 2, and center thickness of second lens 2 in sequence.

[0066] Table 2 Conditional formulas corresponding to the lenses of the embodiment

[0067] Telephoto Short focus f 60 20 BFL 13.78 13.78 BFL / f 0.23 0.69 y 9.84 9.84 y / f 0.16 0.49 TTL 85 85 BFL / TTL 0.16 0.16

[0068] Table 3 Aspheric coefficients of the lens in the embodiment

[0069] Surface number K A4 A6 A8 A10 A12 1 -1.35 -1.77E-06 5.28E-10 8.23E-13 2.17E-15 -2.28E-18 2 -12.04 -2.45E-06 1.56E-09 3.79E-12 -3.44E-15 6.40E-20 3 87.95 -2.20E-06 2.16E-10 -5.62E-11 3.13E-13 -3.69E-16 4 -9.52 4.61E-06 -1.50E-09 -1.73E-10 7.26E-13 -7.87E-16 5 12.15 1.61E-08 1.21E-08 -1.53E-10 5.65E-13 -6.18E-16 6 0.00 6.42E-06 -1.19E-08 -6.06E-11 4.03E-13 -4.94E-16 7 4.82 -1.72E-05 -1.05E-07 7.82E-10 -2.34E-12 2.59E-15 8 -8.77 -6.06E-06 -5.29E-08 5.44E-10 -1.83E-12 2.23E-15 9 0.00 -4.45E-05 6.81E-08 7.25E-10 -1.64E-11 5.88E-14 10 21.12 -3.27E-05 1.76E-07 -7.59E-10 -2.22E-12 1.68E-14

[0070] The above aspheric lens coefficients satisfy the following expressions:

[0071]

[0072] Where Z is the distance from the vertex of the aspheric surface to the height Y along the optical axis, Sag, R is the paraxial curvature radius of the mirror, K is the conic coefficient, A4, A6, A8, A 10 、A 12 =High-order aspheric coefficient. The first through fifth lenses are aspheric lenses. The first, second, third, and fifth lenses can be made of single-crystal germanium glass, while the fourth lens can be made of chalcogenide glass.

[0073] from Figure 3-5 As can be seen from the figure, at telephoto, the contrast of the entire field of view is greater than 0.28 at 42lp / mm, the image quality is uniform, and it has high resolution; the optical distortion is less than 2%, the field curvature is well controlled, and the image restoration is high; the relative illumination is greater than 90%, and the energy utilization rate is high. Figure 6-8 It can be seen that at short focus, the contrast of the entire field of view is greater than 0.28 at 42lp / mm, the imaging quality is uniform, and it has high resolving power; the optical distortion is less than 3%, the field curvature is well controlled, and the image restoration is high; the relative illumination is greater than 93%, and the energy utilization rate is high.

[0074] Based on the above embodiments, the advantages of the present invention are as follows:

[0075] 1. This patented lens uses a total of five aspherical lenses, with a relatively compact overall structure and a total length of less than 85mm, which can achieve a focal length variation of 20mm-60mm.

[0076] 2. The working object distance range of the optical system is 10m to infinity, and the working temperature range is -40℃ to 60℃. The fourth lens is the system's fine-focusing lens group, which can be used to focus when the object distance or temperature changes.

[0077] 3. The overall dimensions of the machine are φ73mm*82mm, the weight is less than 400g, and the outer diameter of the largest lens is less than 58mm.

[0078] 4. The system can be used with a 640*512@12um uncooled detector, and the imaging quality at each focal length is good.

[0079] It should be noted that the specific parameters in the above table are merely illustrative, and the parameters of each lens are not limited to the values ​​shown in the above numerical embodiments. Other values ​​can be used to achieve similar technical effects.

[0080] Although the principles and specific embodiments of the present invention have been described above, those skilled in the art may make various improvements and modifications based on the above embodiments based on the above teachings of the present invention, and such improvements or modifications fall within the scope of protection of the present invention. Those skilled in the art should understand that the above detailed description is only for the purpose of explaining the present invention and is not intended to limit the present invention. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A compact long-wave infrared zoom lens, characterized in that: Along the optical axis, from the object side to the image side, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are arranged in order. The first lens is the front fixed lens group, the second lens is the zoom lens group, the third lens is the compensating lens group, the fourth lens is the focusing lens group, and the fifth lens is the rear fixed lens group. The first lens has positive refractive power, a convex object-side surface, and a concave image-side surface; The second lens has a negative refractive power, a concave object-side surface, and a concave image-side surface; The third lens has positive refractive power, a convex object-side surface, and a convex image-side surface; The fourth lens has a negative refractive power, a convex object-side surface, and a concave image-side surface; The fifth lens has positive refractive power, the object side surface is concave, and the image side surface is convex; The lens satisfies the following formula: 0.5<|f1| / f<0.67 0.17<|f2| / f<0.25 0.3<|f3| / f<0.33 1.17<|f4| / f<1.25 0.42<|f5| / f<0.5 Wherein, f1, f2, f3, f4, and f5 are the focal lengths of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens, and f is the telephoto focal length of the lens; the telephoto focal length of the lens is 60 mm, and the short focal length is 20 mm.

2. The compact long-wave infrared zoom lens according to claim 1, wherein: The working object distance range of the lens is 10m to infinity, and the working temperature range is -40℃ to 60℃; the fourth lens is the system's fine-focus lens group, and when the object distance or temperature changes, the focus is adjusted through the fine-focus lens group.

3. The compact long-wave infrared zoom lens according to claim 1, wherein: The lens meets the following conditions: The optical back focus BFL of the lens is greater than 13.7mm, the telephoto F number is less than 1.2, the total movement of the zoom lens group is 7.4mm, and the total movement of the compensation lens group is 10.8mm.

4. The compact long-wave infrared zoom lens according to claim 1 or 2, characterized in that: The lens satisfies the following formula: 3.9<nd1<4.1 3.9<nd2<4.1 3.9<nd3<4.1 2.7<nd4<2.9 3.9<nd5<4.1 Wherein, nd1, nd2, nd3, nd4, and nd5 are the refractive indices of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens.

5. The compact long-wave infrared zoom lens according to claim 1 or 2, wherein: The lens is provided with a housing. The outer dimensions of the whole device formed by the housing and the lens are φ73mm*82mm, the weight is less than 400g, and the outer diameter of the largest lens is less than 58mm.

6. The compact long-wave infrared zoom lens according to claim 1, wherein: The focal length of the first lens is defined as f1, and the refractive index is defined as nd1, which satisfy the following relationship: nd1>4, 30<|f1|<40.

7. The compact long-wave infrared zoom lens according to claim 1, wherein: The focal length of the second lens is defined as f2, which satisfies the following relationship: f2<0.

8. The compact long-wave infrared zoom lens according to claim 1, wherein: The focal length of the third lens is defined as f3, which satisfies the following relationship: f3 >0.

9. The compact long-wave infrared zoom lens according to claim 1 or 2, wherein: The focal length of the fourth lens is defined as f4, and the focal length of the fifth lens is defined as f5, which satisfy the following relationship: f4<0, f5>0.

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