Large-aperture short-focus infrared prime lens

Abstract

The utility model provides a large-aperture short-focus infrared prime lens. The large-aperture short-focus infrared prime lens comprises a first lens, a diaphragm, a second lens, a third lens, a window and a detector which are sequentially arranged from an object side to an image side, the first positive lens is a biconvex surface, the object side surface and the image side surface of the second positive lens are a concave surface and a convex surface in sequence, and the object side surface and the image side surface of the third positive lens are a concave surface and a convex surface in sequence; the first lens is a spherical lens with positive focal power, the second lens is an aspherical lens with positive focal power, and the third lens is a spherical lens with positive focal power. The infrared prime lens provided by the utility model has a large aperture and a compact structure, meets the infrared imaging requirement, and effectively controls the weight and cost of the lens.

Description

Technical Field

[0001] This utility model relates to the field of infrared lens technology, and in particular to a large aperture short focal length infrared fixed focal length lens. Background Technology

[0002] Drones equipped with infrared lenses can achieve clear imaging in complex environments such as complete darkness, smoke, and dust, making them crucial for nighttime inspections, search and rescue operations, agricultural monitoring, and power line inspections. However, existing short-focal-length infrared fixed-focus lenses, such as those in patent document CN206515547U (6 lenses) and patent document CN107193114B (7 lenses), increase the overall cost of the lens. Therefore, there is a need to develop a new type of lens that meets the performance requirements of infrared thermal imaging while also being cost-effective. Utility Model Content

[0003] This invention proposes a large-aperture, short-focal-length infrared fixed-focus lens, which features a large aperture and a compact structure, meets the requirements of infrared imaging, and effectively controls the lens weight and cost.

[0004] The technical solution of this utility model is implemented as follows: A large aperture short focal length infrared fixed-focus lens includes a first lens, an aperture stop, a second lens, a third lens, a window, and a detector arranged sequentially from the object side to the image side; the first positive lens is biconvex, the object side and image side of the second positive lens are concave and convex respectively, and the object side and image side of the third positive lens are concave and convex respectively; the first lens is a spherical lens with positive optical power, the second lens is an aspherical lens with positive optical power, and the third lens is a spherical lens with positive optical power.

[0005] Furthermore, the aperture number Fno of the infrared fixed-focus lens is ≤1.0.

[0006] Furthermore, 2.5 < |f2 / f| < 3.5, 1.3 < |f3 / f| < 1.8, where f2 is the focal length of the second lens, f3 is the focal length of the third lens, and f is the focal length of the lens.

[0007] Furthermore, the second lens is an aspherical lens and satisfies the following equation:

[0008]

[0009] Where X is the depth (mm) of the aspherical lens; Y is the distance (height) from the optical axis to the lens surface (mm); C is the radius of curvature of the lens, C=1 / R; K is the conic constant; and b, c, d, e, f, g, and h are the aspherical lens coefficients.

[0010] Furthermore, Nd1(10.6)>4, Nd2(10.6)>4, where Nd1(10.6) represents the refractive index of the first lens at a wavelength of 10.6μm; and Nd2(10.6) represents the refractive index of the second lens at a wavelength of 10.6μm.

[0011] The beneficial effects of this utility model are:

[0012] This invention provides a large-aperture, short-focal-length infrared fixed-focus lens, employing a three-lens structure: a first spherical lens, a second aspherical lens, and a third spherical lens. The resulting infrared fixed-focus lens features a large aperture, a compact structure, and lower cost compared to existing infrared fixed-focus lenses. It is suitable for use on unmanned aerial vehicles (UAVs). Since UAVs have high requirements for image quality and weight when using infrared lenses, this invention meets the infrared imaging needs while effectively controlling lens weight and cost. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the structure of this utility model;

[0015] Figure 2 This is a schematic diagram of spherical aberration in an infrared fixed-focus lens.

[0016] Figure 3 This is a schematic diagram of astigmatism in an infrared fixed-focus lens at room temperature.

[0017] Figure 4 This is a schematic diagram of the distortion of an infrared fixed-focus lens at room temperature.

[0018] Figure 5 This is a schematic diagram of the infrared fixed-focus lens at room temperature.

[0019] First lens 1, aperture 2, second lens 3, third lens 4, window 5, detector 6. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0021] like Figure 1 As shown, a large-aperture, short-focal-length infrared fixed-focus lens includes a first lens 1 with positive optical power, an aperture 2, a second lens 3 with positive optical power, a third lens 4 with positive optical power, a window 5, and a detector 6, arranged sequentially from the object side to the image side. The aperture 2 is located between the first and second positive lenses, ensuring a large light throughput and high-quality imaging effect.

[0022] The object-side and image-side surfaces of the first lens 1 are both convex; the object-side and image-side surfaces of the second lens 3 are concave and convex, respectively; and the object-side and image-side surfaces of the third lens 4 are concave and convex, respectively. The first lens 1 is a spherical lens, the second lens 3 is an aspherical lens, and the third lens 4 is a spherical lens. The design of the second lens 3 and the third lens 4 with one concave and one convex surface respectively facilitates fabrication and assembly with the platform. The object-side surface is the side of the lens closest to the object, and the image-side surface is the side of the lens closest to the image.

[0023] The aperture number of the infrared fixed-focus lens is Fno≤1.0. The smaller the aperture number, the greater the overall light transmission, which can ensure that the detector 6 receives stronger light and the temperature measurement is more accurate.

[0024] The focal length satisfies the following conditions: 2.5 < |f2 / f| < 3.5, 1.3 < |f3 / f| < 1.8, where f2 is the focal length of the second lens 3, f3 is the focal length of the third lens 4, and f is the focal length of the lens. The focal length of a lens is determined by the structure of its front and rear surfaces and the material of the lens. The focal length reflects the overall situation after the front and rear surfaces of the lens are combined, and is a structural parameter of the lens. In a single-lens system, the smaller the focal length, the larger the field of view; the larger the focal length, the smaller the field of view; different focal lengths can achieve different field of view angles.

[0025] The refractive indices satisfy the following conditions: Nd1(10.6)>4, Nd2(10.6)>4, where Nd1(10.6) represents the refractive index of the first lens 1 at a wavelength of 10.6 μm; and Nd2(10.6) represents the refractive index of the second lens 3 at a wavelength of 10.6 μm. Using a high-refractive-index material for the lenses allows for better control of the field of view, is beneficial for short-focal-length lens design, and also reduces the outer diameter of the lens.

[0026] Taking Fno = 1.0, the lens as germanium material, and f = 4.3 as an example.

[0027] Table 1 Basic Lens Data

[0028]

[0029]

[0030] In the table above, the surface number uses the side of the lens closest to the object as the object-side surface and the other side as the image-side surface. The radius of curvature R represents the radius of curvature value of the corresponding surface in mm. The surface spacing D represents the lens thickness or the spacing between lenses on the corresponding surface in mm. The table also provides the lens material.

[0031] The second lens 3 is an aspherical lens. The coefficient of an aspherical lens is expressed with the center of the lens surface as the origin and the optical axis as the x-axis. The expression for the aspherical surface shape of the lens surface satisfies the following formula:

[0032]

[0033] Where X is the depth of the aspherical lens in mm, Y is the distance from the optical axis to the lens surface in mm, C is the radius of curvature of the aspherical lens, C = 1 / R, k is the conic constant, and b, c, d, e, f, g, and h are the coefficients of the aspherical lens.

[0034] Table 2. Specific parameters of the coefficients of aspherical lenses.

[0035]

[0036] Table 3 Optical System Parameters

[0037] f FNO. 2ω TTL 4.3 1.0 49 19

[0038] In the table above, the lens focal length f is in mm, Fno. is the aperture size, ω in the angle of view 2ω represents the half angle of view, and the total optical length TTL is in mm.

[0039] The infrared fixed-focus lens of this embodiment was tested at room temperature. Figures 2-5 The diagrams show the spherical aberration, astigmatism, distortion, and RI at room temperature. (See Table 3 and Appendix). Figure 2-4 As can be seen, the various aberrations of the infrared fixed-focus lens in this embodiment are well corrected, making it suitable for use in drones.

[0040] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A large aperture short focal length infrared prime lens characterized by: The infrared focusing lens comprises, in order from the object side to the image side, a first lens, a diaphragm, a second lens, a third lens, a window and a detector; the first positive lens is a double convex lens, the object side surface and the image side surface of the second positive lens are a concave surface and a convex surface in order, and the object side surface and the image side surface of the third positive lens are a concave surface and a convex surface in order; the first lens is a spherical lens with positive focal power, the second lens is an aspherical lens with positive focal power, and the third lens is a spherical lens with positive focal power.

2. The large-aperture short-focal-length infrared fixed-focus lens according to claim 1, characterized in that: The aperture number Fno of the infrared focusing lens is less than or equal to 1.

0.

3. The large-aperture short-focal-length infrared fixed-focus lens according to claim 1 or 2, characterized in that: 2.5 < |f2 / f| < 3.5, 1.3 < |f3 / f| < 1.8, wherein f2 is the focal length of the second lens, f3 is the focal length of the third lens, and f is the focal length of the lens.

4. The large-aperture short-focal-length infrared fixed-focus lens according to claim 1 or 2, characterized in that: Nd1(10.6) > 4, Nd2(10.6) > 4, wherein Nd1(10.6) represents the refractive index of the first lens at a wavelength of 10.6 μm, and Nd2(10.6) represents the refractive index of the second lens at a wavelength of 10.6 μm.

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