A dual-field long-wave infrared lens

Abstract

The present invention provides a dual-field-of-view long-wave infrared lens, which comprises a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along an optical axis from an object side to an image side, wherein: the object-side surface of the first lens is convex, the image-side surface of the first lens is concave, and the first lens has a positive refractive power; the object-side surface of the second lens is concave, the image-side surface of the second lens is concave, and the second lens has a negative refractive power; the object-side surface of the third lens is convex, the image-side surface of the third lens is concave, and the third lens has a positive refractive power; the object-side surface of the fourth lens is concave, the image-side surface of the fourth lens is convex, and the fourth lens has a negative refractive power. By reasonably allocating the positions and gluing relationships of the various lenses to form a lens group, the lens of the present invention adopts a total of four aspherical lenses with a total length of less than 65 mm, and can realize a dual-field-of-view zoom system with focal lengths of 20 mm and 40 mm, respectively. The working object distance range of the optical system is 10 m to infinity, and the working temperature range is ‑40° C. to 60° C.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared lenses, and in particular to a dual-field-of-view long-wave infrared lens. Background Art

[0002] Most existing zoom infrared lenses have one or more of the following defects: First, conventional continuous zoom lenses usually contain more than two moving components, which are generally moved by a cam mechanism. The movement of the components usually does not follow a linear pattern, so the switching speed is slow during the movement. Second, conventional zoom lenses are relatively complex in structure and bulky in size, which is not convenient for carrying and using. Third, the image stabilization range of a zoom lens is usually determined by the focal length variation range. For a zoom lens with a large magnification, the longer the telephoto focal length, the closer the minimum object distance for image stabilization cannot be, which easily reduces the convenience of user use. Fourth, since the price of infrared materials on the market is relatively expensive, the more complex the structure of the zoom lens, the higher its price. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the purpose of the present invention is to propose a dual-field-of-view long-wave infrared lens that adopts a four-lens architecture. By rationally allocating the refractive power of each lens and optimizing the surface shape, thickness, and distance between lenses, the lens can have good imaging quality, thereby solving the problems mentioned in the above background technology section.

[0004] The present invention is achieved through the following technical solutions:

[0005] A dual-field-of-view long-wave infrared lens, consisting of a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis from the object side to the image side, wherein: the object-side surface of the first lens is convex, the image-side surface of the first lens is concave, and the first lens has positive refractive power; the object-side surface of the second lens is concave, the image-side surface of the second lens is concave, and the second lens has negative refractive power; the object-side surface of the third lens is convex, the image-side surface of the third lens is concave, and the third lens has positive refractive power; the object-side surface of the fourth lens is concave, the image-side surface of the fourth lens is convex, and the fourth lens has negative refractive power; the first lens is used for fine-tuning the focal length, and the second lens is used for switching between long and short focal lengths of the lens; the thickness of the first lens is 5.9 mm; the thickness of the second lens is 4.0 mm; the thickness of the third lens is 5.9 mm; the thickness of the fourth lens is 4.0 mm; and the thickness distance between the third and fourth lenses is 9.3 mm.

[0006] Furthermore, the lens satisfies the following relationship: nd1=4, 55≤| f1 |≤65, where nd1 is the refractive index of the first lens, and f1 is the focal length of the first lens.

[0007] Furthermore, the optical back focus of the lens is equal to 11.09 mm, the telephoto F number is less than 1.2, and the total movement of the second lens is equal to 13.4 mm.

[0008] Furthermore, the lens can be adjusted to a focal length between 20 mm and 40 mm.

[0009] Furthermore, the lens satisfies the following relationship: 0.246≤|y / f|≤0.492; wherein y is the image height of the lens, and f is the focal length of the lens.

[0010] Furthermore, the lens satisfies the following relationship: 0.277≤|BFL / f|≤0.5545; wherein BFL is the optical back focus of the lens, and f is the focal length of the lens.

[0011] The beneficial effects of the present invention are as follows: a dual-field long-wave infrared lens, composed of a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the optical axis from the object side to the image side, wherein: the object side surface of the first lens is convex, the image side surface of the first lens is concave, and the first lens has positive refractive power; the object side surface of the second lens is concave, the image side surface of the second lens is concave, and the second lens has negative refractive power; the object side surface of the third lens is convex, the image side surface of the third lens is concave, and the third lens has positive refractive power; the object side surface of the fourth lens is concave, the image side surface of the fourth lens is convex, and the fourth lens has negative refractive power; the first lens is used for fine-tuning focus The second lens is used to switch between long focus and short focus of the lens; the thickness of the first lens is 5.9 mm; the thickness of the second lens is 4.0 mm; the thickness of the third lens is 5.9 mm; the thickness of the fourth lens is 4.0 mm; the thickness interval between the third lens and the fourth lens is 9.3 mm, and the fourth lens has a negative refractive power. By rationally allocating the positions and gluing relationships of the lenses that form the lens group, the lens of the present invention adopts a total of four aspherical lenses, the overall structure is relatively compact, the total length is less than 65 mm, and a dual-field zoom system with focal lengths of 20 mm and 40 mm can be realized. The working object distance range of the optical system is 10 m to infinity, and the working temperature range is -40°C to 60°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the optical system structure diagram of the lens at long focal length.

[0013] Figure 2 This is the MTF diagram of the lens at long focal length.

[0014] Figure 3 This is the relative illumination diagram of the lens at long focal length.

[0015] Figure 4 This is a diagram of the optical distortion and field curvature of a medium lens at a long focal length.

[0016] Figure 5 This is the optical system structure diagram of the lens in the short focal length section.

[0017] Figure 6 This is the MTF diagram of the lens at short focal length.

[0018] Figure 7 This is the relative illumination diagram of the lens at short focal length.

[0019] Figure 8 This is a diagram of the optical distortion and field curvature of the lens at short focal length.

[0020] The above drawings include the following reference numerals:

[0021] 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Protective sheet. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. It should be noted that the description of these embodiments is intended to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0023] Reference Figures 1 to 8 As shown, a dual-field long-wave infrared lens (hereinafter referred to as the lens) includes a first lens 1, a second lens 2, a third lens 3, and a fourth lens 4 arranged in sequence along the optical axis from the object side to the image side. An aperture (not shown in the figure) is provided between the third lens 3 and the fourth lens 4, and a protective sheet 5 is provided behind the fourth lens 4.

[0024] The object-side surface of the first lens 1 is convex, the image-side surface of the first lens 1 is concave, and the first lens 1 has positive refractive power;

[0025] The object side surface of the second lens 2 is concave, the image side surface of the second lens 2 is concave, and the second lens 2 has negative refractive power;

[0026] The object side surface of the third lens 3 is convex, the image side surface of the third lens 3 is concave, and the third lens 3 has positive refractive power;

[0027] The object-side surface of the fourth lens 4 is concave, the image-side surface of the fourth lens 4 is convex, and the fourth lens 4 has negative refractive power.

[0028] The lens utilizes four aspherical lenses, resulting in a compact overall structure with a total length of less than 65mm. It enables a dual-field zoom system with focal lengths of 20mm and 40mm, respectively. The optical system operates from a distance of 10m to infinity and in a temperature range of -40°C to 60°C, capable of outputting high-definition images within these operating ranges. A multi-point zoom structure achieves focal length variation, simplifying the system architecture and reducing its size. The lens can be used with an uncooled 640*512@12um detector, achieving excellent imaging quality at both focal lengths, approaching the diffraction limit.

[0029] Furthermore, the first lens 1 is used for fine-tuning the focal length. This embodiment has the following beneficial effects: by using the first lens 1 as a fine-focusing mechanism for fine-tuning the focal length, the minimum image stabilization distance can be effectively maintained at 10 meters, and the focusing stroke can be greatly reduced. When the lens object distance or the ambient temperature of the lens changes, the focus can be adjusted through the first lens 1, thereby ensuring the output of a high-definition image.

[0030] Furthermore, the lens satisfies the following relationship: nd1=4, 55≤|f1|≤65, where nd1 is the refractive index of the first lens element 1, and f1 is the focal length of the first lens element 1. This embodiment has the beneficial effect of satisfying the above range, facilitating correction of higher-order aberrations and optimizing image quality at long focal lengths.

[0031] Furthermore, the second lens 2 is used to switch between long and short focal lengths. This embodiment has the following beneficial effects: the second lens 2 is the only moving component in the lens system, primarily responsible for the system's zoom function. This satisfies the principle of object-image exchange, enabling the lens to achieve a dual-field zoom system with focal lengths of 20mm and 40mm, respectively. Field switching can be achieved through a single moving component, accelerating the switching speed.

[0032] Furthermore, the lens satisfies the following relationship: f2<0, where f2 is the focal length of the second lens 2. The beneficial effects of this embodiment are: satisfying the above range is beneficial for correcting aberrations, improving imaging quality, and facilitating athermal design.

[0033] Furthermore, the lens satisfies the following relationship: f3>0, f4>0, where f3 is the focal length of the third lens element 3, and f4 is the focal length of the fourth lens element 4. This embodiment has the beneficial effect of: the third lens element 3 and the fourth lens element 4 primarily correct residual aberrations, and satisfying the above range facilitates aberration correction, improves imaging quality, and facilitates athermal design.

[0034] Furthermore, the optical back focus of the lens is equal to 11.09 mm, the telephoto F number is less than 1.2, and the total movement of the second lens 2 is equal to 13.4 mm. The beneficial effect of this embodiment is that the lens can meet the miniaturization design as much as possible and the total length of the lens is no more than 65 mm.

[0035] Furthermore, the lens can be adjusted in focal length between 20 mm and 40 mm. The beneficial effect of this embodiment is that the lens realizes a dual-field zoom system.

[0036] Furthermore, the lens satisfies the following relationship: 0.246≤|y / f|≤0.492; where y is the image height of the lens and f is the focal length of the lens. This embodiment has the beneficial effect of satisfying the above range, further facilitating the realization of a large target area, optimizing distortion, and meeting the requirement of zero distortion.

[0037] Furthermore, the lens satisfies the following relationship: 0.277≤|BFL / f|≤0.5545, where BFL is the optical back focus of the lens and f is the focal length of the lens. This embodiment has the beneficial effect of satisfying the above relationship, allowing light to transition properly to the image plane, thereby improving the resolution of the lens.

[0038] The present invention will be described in more detail below with reference to Tables 1 to 4. It should be noted that the following tables are only specific embodiments of the present invention and are not intended to be limiting examples.

[0039] Please refer to Table 1 and Table 2, where surface number 1 and surface number 2 in the table are the object measurement surface and image side surface of the first lens 1 respectively; surface number 3 and surface number 4 are the object measurement surface and image side surface of the second lens 2 respectively; surface number 5 and surface number 6 are the object measurement surface and image side surface of the third lens 3 respectively; surface number 7 and surface number 8 are the object measurement surface and image side surface respectively.

[0040] Table 1 shows the specific arrangement parameters of each lens, such as the curvature radius, thickness interval, etc., when the lens is in telephoto state.

[0041]

[0042] Table 2 shows the specific arrangement parameters of each lens, such as the curvature radius, thickness interval, etc., when the lens is in the short focus state.

[0043]

[0044] Table 3 shows the focal lengths of the various lenses.

[0045]

[0046] Table 4 shows the specific arrangement of the long focus and short focus lenses of the present invention. In the table, f is the focal length, BFL is the optical back focus, y is the image height of the lens, and TTL is the total optical length of the lens.

[0047]

[0048] The following is an explanation of the various figures:

[0049] Figure 2 The MTF graph for the lens at long focal lengths shows that the contrast across the entire field of view is greater than 0.36 at 42 lp / mm, indicating uniform image quality and high resolving power.

[0050] Figure 3 This is the relative illumination diagram of the lens at long focal length. As can be seen from the figure, the relative illumination of the lens is greater than 88%, and the energy utilization rate is high.

[0051] Figure 4 This graph shows the optical distortion and field curvature of a medium-length lens at long focal lengths. As can be seen from the graph, the lens exhibits less than 2% optical distortion, effectively controls field curvature, and produces high image fidelity.

[0052] Figure 6 The MTF graph for the lens at short focal length shows that the contrast ratio across the entire field of view is greater than 0.38 at 42 lp / mm, indicating uniform image quality and high resolving power.

[0053] Figure 7 This is the relative illumination diagram of the lens at short focal length. As can be seen from the figure, the relative illumination of the lens is greater than 88%, and the energy utilization rate is high.

[0054] Figure 8 This graph shows the optical distortion and field curvature of the lens at short focal lengths. As can be seen from the graph, the lens has less than 4% optical distortion, well-controlled field curvature, and high image fidelity.

[0055] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0056] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0057] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A dual-field long-wave infrared lens, characterized by: It consists of the first lens, the second lens, the third lens and the fourth lens arranged in sequence along the optical axis from the object side to the image side, wherein: The object-side surface of the first lens is convex, the image-side surface of the first lens is concave, and the first lens has positive refractive power; The object-side surface of the second lens is concave, the image-side surface of the second lens is concave, and the second lens has negative refractive power; The object-side surface of the third lens is convex, the image-side surface of the third lens is concave, and the third lens has positive refractive power; The object side surface of the fourth lens is concave, the image side surface of the fourth lens is convex, and the fourth lens has negative refractive power; The first lens is used to fine-tune the focal length, and the second lens is used to switch between long focus and short focus; The thickness of the first lens is 5.9 mm; the thickness of the second lens is 4.0 mm; the thickness of the third lens is 5.9 mm; and the thickness of the fourth lens is 4.0 mm. The thickness distance between the third lens and the fourth lens is 9.3 mm.

2. The dual-field-of-view long-wave infrared lens according to claim 1, characterized in that: The lens satisfies the following relationship: nd1=4, 55≤| f1 |≤65, where nd1 is the refractive index of the first lens, and f1 is the focal length of the first lens.

3. The dual-field-of-view long-wave infrared lens according to claim 1, characterized in that: The optical back focus of the lens is equal to 11.09 mm, the telephoto F number is less than 1.2, and the total movement of the second lens is equal to 13.4 mm.

4. The dual-field-of-view long-wave infrared lens according to claim 1, characterized in that: The lens can be adjusted between a focal length of 20 mm and 40 mm.

5. The dual-field-of-view long-wave infrared lens according to claim 1, characterized in that: The lens satisfies the following relationship: 0.246≤|y / f|≤0.492; wherein y is the image height of the lens, and f is the focal length of the lens.

6. The dual-field-of-view long-wave infrared lens according to claim 1, characterized in that: The lens satisfies the following relationship: 0.277≤|BFL / f|≤0.5545; wherein BFL is the optical back focus of the lens, and f is the focal length of the lens.

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