Low-cost infrared fisheye lens

Abstract

The utility model discloses a low-cost infrared fisheye lens, and relates to the technical field of optical systems. The six lenses are arranged from the object side to the image side in sequence. The first lens is a meniscus negative-focal-power lens with the convex face facing the object side. The second lens is a negative-focal-power meniscus lens, and the convex surface of the second lens faces the object side; the third lens is a meniscus lens with positive focal power, and the convex surface of the third lens faces the image side; the fourth lens is a meniscus lens with positive focal power, and the convex surface of the fourth lens faces the image side; the fifth lens is a meniscus lens with positive focal power, and the convex surface of the fifth lens faces the image side; the sixth lens is a meniscus lens with positive focal power, and the concave surface of the sixth lens faces the object side. The infrared lens is matched with a low-cost 384 * 288 resolution long-wave uncooled detector, the pixel is 12 microns, only one aspheric surface is adopted, and excellent imaging in a 200-degree fisheye view field is realized. And a low linear distortion design is adopted to lay a foundation for lens calibration. The lens not only can be suitable for a common infrared panoramic monitoring system, but also can be used in military fields such as low-cost infrared alarm and the like.

Description

Technical Field

[0001] The utility model relates to a low-cost infrared fish-eye lens, belonging to the field of infrared optical technology. Background Art

[0002] A fish-eye lens is an extreme wide-angle lens with a short focal length and a large field of view (the field angle is close to or exceeds 180°). Since a single lens can achieve 2π airspace imaging coverage, it is often used in the fields of security monitoring and optoelectronic warning. The infrared fish-eye lens is also often used in the fields of forest fire prevention, environmental protection, hot spot monitoring, etc. due to its temperature difference imaging characteristics. Due to the large field of view and large marginal ray aberration of the fish-eye lens, multiple aspherical surfaces or binary diffractive surfaces are often used to correct the aberration. For example, a large field of view long-wave infrared fish-eye lens disclosed in Chinese Patent CN208984871.U has a field of view of up to 190°, but uses 5 aspherical surfaces, which will greatly increase the lens processing cost. Summary of the Invention

[0003] In view of the above problems, the long-wave infrared fish-eye lens of the utility model only uses one even aspherical surface to achieve 200° wide-angle field of view imaging, matches the existing low-cost 384×288 uncooled long-wave detector on the market, and the materials used are all common infrared materials, which is beneficial to realizing the cost control of the product.

[0004] To solve the above problems, the solution adopted by the utility model is: a low-cost infrared fish-eye lens, which sequentially includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens from the object side to the image side; the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are all in a meniscus structure; only the surface of the fifth lens facing the object side is an even aspherical surface, and the rest of the surfaces are spherical surfaces;

[0005] The first lens is in a meniscus shape, with the convex surface facing the object side, the optical power is negative, and the material is single crystal germanium;

[0006] The second lens is in a meniscus shape, with the convex surface facing the object side, the optical power is negative, and the material is single crystal germanium;

[0007] The third lens is in a meniscus shape, with the convex surface facing the image side, the optical power is positive, and the material is single crystal germanium;

[0008] The third lens is in a meniscus shape, with the convex surface facing the image side, the optical power is positive, and the material is single crystal germanium;

[0009] The fifth lens is in a meniscus shape, with the convex surface facing the image side, the optical power is positive, the surface facing the object side is an aspherical surface, and the material is chalcogenide glass;

[0010] The sixth lens is in a meniscus shape, with the convex surface facing the image side, the optical power is positive, and the material is single crystal germanium.

[0011] Furthermore, the diaphragm surface is located between the fourth lens and the fifth lens, and the distance from the fifth lens towards the vertex of the object-side surface S8 is 1.41 mm.

[0012] Furthermore, the parameters of the infrared fish-eye lens are as follows: the working wavelength is 8 μm to 12 μm, the central working wavelength is 10 μm, the effective focal length is 1.65 mm, the F-number is 1.0, it is matched with a 384×288 resolution long-wave uncooled detector, the pixel size is 12 μm, the diagonal field of view is 200°, and the total optical system length is 65.49 mm.

[0013] Furthermore, the diagonal field of view of the infrared fish-eye lens is 200°, and the horizontal field of view angle 2w = 160°.

[0014] Furthermore, the relative aperture F-number of the infrared fish-eye lens is 1.0, the optical focal length is 1.65 mm, it is adapted to a 384×288 resolution uncooled long-wave detector, the pixel size is 12 μm, and the total optical system length is 65.49 mm.

[0015] Compared with the prior art, the present utility model has the following advantages and features:

[0016] (1) Only one aspherical surface is used to correct aberrations, and it is designed on a chalcogenide glass material, which is beneficial to reducing the lens processing cost.

[0017] (2) It is matched with a 384×288 resolution long-wave uncooled detector that is relatively mature and low-cost on the market, which is beneficial to reducing the usage cost of the core device.

[0018] (3) The imaging field of view is large, the diagonal field of view reaches 200°, and a single fish-eye lens can achieve 2π spatial imaging coverage.

[0019] (4) The infrared fish-eye lens adopts a low linear distortion design, and the linear distortion value is lower than 0.1%, which is beneficial to the later calibration of the lens and the improvement of the relative illuminance in the edge field of view. The average value of the relative illuminance in the full field of view is better than 96%.

[0020] (5) The materials used for the infrared fish-eye lens are single crystal germanium and chalcogenide glass, which are common typical infrared materials and the materials are not special.

[0021] (6) The processing and assembly tolerance levels of the infrared fish-eye lens are loose, which is beneficial to reducing the processing and assembly costs.

[0022] (7) All lenses of the infrared fish-eye lens adopt a meniscus structure, which is beneficial to aberration correction. Description of the Drawings

[0023] For the convenience of more clearly describing the specific implementation of the infrared fish-eye lens, some design results are selected as illustrative drawings according to needs.

[0024] Figure 1 In a preferred embodiment of the present utility model, it is the optical structure diagram of an infrared fish-eye lens;

[0025] Figure 2 In a preferred embodiment of the present utility model, it is the MTF diagram of the optical system of an infrared fish-eye lens;

[0026] Figure 3 In a preferred embodiment of the present utility model, it is the distribution diagram of the spot diagram of the optical system of an infrared fish-eye lens;

[0027] Figure 4 In a preferred embodiment of the present utility model, it is the field curvature and linear distortion diagram of the optical system of an infrared fish-eye lens;

[0028] Figure 5 In a preferred embodiment of the present utility model, it is the relative illuminance diagram of each field of view of the optical system of an infrared fish-eye lens;

[0029] Figure 1 Among them, L1 - the first lens, L2 - the second lens, L3 - the third lens, L4 - the fourth lens, L5 - the fifth lens, L6 - the sixth lens, O - the object space, A - the detector window, B - the image plane, S1 to S12 respectively represent the surfaces of L1 to L6 lenses in sequence, and ST is the aperture stop plane. Specific embodiments

[0030] The following will describe the best embodiment of the present utility model in detail with reference to the accompanying drawings, which does not represent a limitation to the present utility model. Any initial structure and optimized structure based on this best embodiment fall within the protection scope of the present utility model.

[0031] The structure of the best embodiment is as Figure 1 shown. From the object side to the image side, in sequence are: the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens, and the lenses share the same optical axis. The first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are all in a meniscus shape. The surface S9 of the fifth lens facing the object space is an even aspheric surface.

[0032] The first lens is in a meniscus shape, and the surface of the first lens facing the object direction is convex, which compresses and converges the light rays within a 200° field of view. The fifth lens adopts a meniscus shape with a positive optical power, and the surface facing the object direction adopts an even aspheric surface, which is beneficial to further contracting the light rays, correcting aberration, and improving the image quality.

[0033] The main optical parameters of the infrared fish-eye lens are as follows: the optical diagonal field of view is 200°, the horizontal field of view angle 2w = 160°, the effective focal length is 1.65 mm, the F number is 1.0, it is adapted to a 384×288 resolution uncooled long-wave detector, the pixel size is 12 μm, and the total length of the optical system is 65.49 mm.

[0034] The curvature radii of the first lens are 22.89 mm and 11.99 mm respectively, the center thickness of the lens is 3.53 mm, and the material is single-crystal germanium.

[0035] The curvature radii of the second lens are 112.00 mm and 22.92 mm respectively, the center thickness of the lens is 1.77 mm, and the material is single-crystal germanium.

[0036] The curvature radii of the third lens are -56.10 mm and -28.25 mm respectively, the center thickness of the lens is 2.47 mm, and the material is single-crystal germanium.

[0037] The curvature radii of the fourth lens are -27.02 mm and -21.42 mm respectively, the center thickness of the lens is 3.10 mm, and the material is single-crystal germanium.

[0038] The lens aperture is located between the fourth lens and the fifth lens. The distance value from the vertex of the spherical surface S8 of the fourth lens is 1.41 mm, the air gap with the sixth lens is 1.84 mm, and the effective aperture of the aperture is 9.00 mm.

[0039] The curvature radii of the fifth lens are -264.24 mm and -143.67 mm respectively, the center thickness of the lens is 3.53 mm, and the material is single-crystal germanium.

[0040] The curvature radii of the sixth lens are -91.87 mm and -22.42 mm respectively, the center thickness of the lens is 3.53 mm, and the material is single-crystal germanium.

[0041] The aspheric surface S9 of the fifth lens satisfies the following expression:

[0042]

[0043] Among them, z is the distance sagitta from the vertex of the aspheric surface when the aspheric surface is along the optical axis direction at a position with a height of r, c represents the vertex curvature of the surface, k is the conic coefficient, α 2 、α 3 、α 4 are the high-order aspheric coefficients.

[0044] The coefficients of the aspheric surface of the fifth lens are shown in Table 1 below.

[0045] Table 1

[0046] Aspherical surface k c <![CDATA[α 2 > <![CDATA[α 3 > <![CDATA[α 4 > S9 0 -3.78444E-003 -1.65879E-004 -1.17914E-006 -4.13858E-008

[0047] The air gaps between the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are respectively: 12.47 mm, 3.96 mm, 15.79 mm, 3.25 mm, 4.15 mm.

[0048] The air gap between the sixth lens and the detector window is 5.09 mm.

[0049] The parameters of the infrared fish-eye lens are shown in Table 2 below.

[0050] Table 2

[0051]

[0052]

[0053] The following describes the optical performance of the best embodiment long-wave fish-eye lens in conjunction with the accompanying drawings.

[0054] It can be seen from Figures 2 to 4 that the MTF of the long-wave fish-eye lens is close to the diffraction limit at the Nyquist frequency of 42 lp / mm, reaching 0.35. The diameter of the blur spot is less than one pixel size of 12 μm. The maximum field curvature value is less than 0.05 mm, and the linear distortion value is less than 0.1%. It shows that the lens has excellent imaging quality, high resolution and low linear distortion, which is convenient for subsequent lens calibration; It can be seen from Figure 5 that the average relative illuminance of the lens in the full field of view is better than 96%, the illuminance is uniform, and there is no edge shadow.

Claims

1. A low-cost infrared fisheye lens, characterized in that: The lens comprises, from the object side to the image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens, all of which are meniscus-shaped structures; The first lens is meniscus-shaped, convex to the object side, and has negative focal power; The second lens is meniscus-shaped, convex to the object side, and has negative focal power; The third lens is meniscus-shaped, convex to the image side, and has positive focal power; The fourth lens is meniscus-shaped, convex to the image side, and has positive focal power; The fifth lens is meniscus-shaped, convex to the image side, with positive focal power and an aspherical surface facing the object side; The sixth lens is meniscus-shaped, with a convex surface facing the image side and positive optical power.

2. The low-cost infrared fisheye lens as claimed in claim 1, characterized in that: The aperture surface is located between the fourth lens and the fifth lens, and the distance from the vertex of the fifth lens facing the object surface S8 is 1.41 mm.

3. The low-cost infrared fisheye lens as claimed in claim 1, characterized in that: The infrared fisheye lens has an operating wavelength of 8 μm to 12 μm, and a central operating wavelength of 10 μm.

4. The low-cost infrared fisheye lens according to claim 1, characterized in that: The infrared fisheye lens has a diagonal field of view of 200° and a horizontal field of view of 2w=160°. 0 .

5. The low-cost infrared fisheye lens according to claim 1, characterized in that: The infrared fisheye lens has a relative aperture F number of 1.0, an optical focal length of 1.65 mm, is suitable for a 384×288 resolution uncooled long-wave detector, has a pixel size of 12 μm, and a total length of the optical system of 65.49 mm.

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