Focusing lens with focal length of 87mm

Abstract

The invention belongs to the technical field of infrared optics, and discloses a focusing lens with a focal length of 87mm. The lens is provided with two lenses with focal power, namely a first lens and a second lens which are sequentially arranged along the same optical axis from an object plane to an image plane along the optical axis direction; the first lens is a meniscus positive lens of which the convex surface faces the object side, and the second lens is a meniscus positive lens of which the convex surface faces the image side; the air gap between the first lens and the second lens is 68.066 mm. According to the invention, aberration correction and balance are carried out on a long-wave infrared spectrum range, so that the lens has excellent image quality in a wide spectrum range, and wide spectrum confocal is realized; through reasonable matching of focal power and the design of the aspheric surface and the diffraction surface, the lens can achieve a good imaging effect only by adopting two lenses, has high passing rate and low distortion, and is suitable for a detector with the pixel number of 640 * 512 and the pixel size of 12 microns.

Description

Technical Field

[0001] The present technology belongs to the field of infrared optical technology, and particularly relates to a focusing lens with a focal length of 87 mm. Background Art

[0002] Infrared detection has a certain ability to penetrate smoke, fog, haze, snow, etc. and to identify camouflage. It is not disturbed by strong light or flash, and can achieve long-distance, all-weather observation. It is especially suitable for target detection at night and in adverse weather conditions.

[0003] However, in complex environments, the focal length of infrared lenses will be affected by many factors, which will lead to unclear imaging and affect the normal operation of the detector. For example, temperature will not only affect the refractive index of optical materials, but also cause thermal expansion and contraction of the lens barrel material, resulting in changes in optical power and displacement of the best image plane, reducing the optical imaging quality, blurring the image, and reducing the contrast, which ultimately affects the imaging performance of the lens.

[0004] In order to eliminate or reduce the impact of temperature changes on the imaging of the optical system, keep the optical system stable within a large temperature difference range, and ensure good imaging quality, corresponding compensation technology can be used. Existing compensation methods include optical passive compensation and mechanical active compensation, and the lenses are usually more than three.

[0005] Therefore, it is necessary to design a focusing lens with fewer lenses, better imaging quality, and the ability to match smaller chip pixels. Summary of the invention

[0006] In order to solve the above problems, the present invention proposes a focusing lens with a focal length of 87 mm. The specific technical solution is as follows: A focusing lens with a focal length of 87 mm, wherein the lens is provided with two lenses with optical power, namely a first lens and a second lens which are arranged in sequence along the optical axis from the object plane to the image plane; the first lens is a positive meniscus lens with a convex surface facing the object side, and the second lens is a positive meniscus lens with a convex surface facing the image side; and the air gap between the first lens and the second lens is 68.066 mm.

[0007] Furthermore, the center thickness of the first lens is 7.0 mm, the object side curvature radius is 135.690 mm, and the image side curvature radius is 194.522 mm; the center thickness of the second lens is 5 mm, the object side curvature radius is -164.772 mm, and the image side curvature radius is -110.682 mm.

[0008] Furthermore, the two lenses are both made of germanium single crystal.

[0009] Furthermore, the image side surface of the first lens is an aspherical surface and satisfies the aspherical surface formula: Among them, Z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror; k is the cone coefficient; A, B, C, D, and E are high-order aspherical coefficients.

[0010] Furthermore, the image side surface of the second lens is a binary surface, which satisfies the aspheric surface formula and satisfies the expression equation of the binary surface in Zemax: M(B1ρ 2 +B2ρ 4 );wherein, M is the diffraction order, the diffraction order is 1, B1 and B2 are the binary surface phase coefficients, B1 = -20.653, B2 = 5.191, and the normalized radius ρ is 30.

[0011] Furthermore, a stop is provided between the first lens and the second lens.

[0012] Furthermore, the lens has an operating band of 8 μm to 12 μm and an F number of 0.9, and is suitable for a detector with a pixel number of 640×512 and a pixel size of 12 μm.

[0013] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: The present invention performs aberration correction and balance on the long-wave infrared spectral range, so that the lens has excellent image quality in a wide spectral range, and realizes wide-spectrum confocality; through reasonable matching of optical focal lengths and the design of aspheric and diffractive surfaces, the lens can achieve good imaging effects with only two lenses, and has high pass rate and low distortion, and can match smaller chip pixels, such as 640×512, 12μm chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0015] Figure 1 This is a lens composition diagram of the focusing lens with a focal length of 87mm in Example 1.

[0016] Figure 2 This is the optical path diagram of the focusing lens with a focal length of 87 mm in Example 1.

[0017] Figure 3 This is the point diagram of the focusing lens with a focal length of 87 mm in Example 1.

[0018] Figure 4 This is the MTF diagram of the focusing lens with a focal length of 87mm in Example 1.

[0019] Reference numerals: 1, first lens; 2, second lens; 3, third lens; 4, protection window; 5, image plane. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It should be noted that the terms "first" and "second" are only used for the purpose of convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a focusing lens with a focal length of 87 mm. The lens is provided with two lenses with optical power, namely, a first lens 1 and a second lens 3 which are arranged in sequence along the optical axis from the object plane to the image plane 5; the first lens 1 is a positive meniscus lens with a convex surface facing the object side, and the second lens 3 is a positive meniscus lens with a convex surface facing the image side. A stop 2 is provided between the first lens 1 and the second lens 3.

[0022] like Figure 2 As shown, the light beam converges from left to right through the first lens 1, passes through the aperture 2, and then converges through the second lens 3, and then forms an image on the image plane 5 through the protective window 4. When the ambient temperature changes, the distance between the second lens 3 and the first lens 1 is adjusted to balance the aberration caused by temperature.

[0023] As shown in Table 1, as a specific implementation, the center thickness of the first lens 1 is 7.0 mm, the object side curvature radius is 135.690 mm, and the image side curvature radius is 194.522 mm; the center thickness of the second lens 3 is 5 mm, the object side curvature radius is -164.772 mm, and the image side curvature radius is -110.682 mm; the air gap between the first lens 1 and the second lens 3 is 68.066 mm; the air gap between the second lens 32 and the protective window 4 is 38.876 mm, and the air gap between the protective window 4 and the image plane 5 is 1.37 mm.

[0024] It can be understood that the side of the lens where light is incident is the object side, and the side where light is emitted is the image side. For example, the S1 surface of the first lens 1 is the object side, and the S2 surface is the image side. Other lenses are not described here. Table 1 Parameters of each component As a specific implementation, the material of the first lens 1 and the second lens 3 is germanium single crystal.

[0025] Table 2 Aspheric surface data of lens As a specific implementation, as shown in Table 2, the image side surface S2 of the first lens 1 is an aspherical surface and satisfies the aspherical surface formula: Among them, Z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror; k is the cone coefficient; A, B, C, D, and E are high-order aspherical coefficients.

[0026] The image side surface S5 of the second lens 3 is a binary surface, which satisfies the above aspheric surface formula and satisfies the expression equation of the binary surface in Zemax: M(B1ρ 2 +B2ρ 4 );wherein, M is the diffraction order, the diffraction order is 1, B1 and B2 are the binary surface phase coefficients, B1 = -20.653, B2 = 5.191, and the normalized radius ρ is 30.

[0027] Figure 3 , Figure 4 These are the spot diagram and MTF diagram of the lens at a focal length of 87mm. In the MTF diagram, the horizontal axis represents different spatial frequencies and the vertical axis represents the modulation degree. All fields of view represent the MTF curve of the meridian plane. It can be seen that the MTF is close to the diffraction limit, the RMS diameter of the diffuse spot is smaller than the Airy disk diameter, and the image quality is good.

[0028] The focusing lens of this embodiment has a focal length of 87 mm, an operating band of 8 μm to 12 μm, an F number of 0.9, and is suitable for a detector with a pixel number of 640×512 and a pixel size of 12 μm.

[0029] The lens of this embodiment performs aberration correction and balance in a wide spectral range by reasonably allocating optical focal length and designing optical materials, aspherical surfaces and diffraction surfaces, so that the lens has excellent image quality in a wide spectral range, realizes wide spectrum confocality, and can form clear images in the medium and long wave ranges.

[0030] Obviously, the above embodiments are merely examples for clearly explaining the technical solutions of the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the protection of the claims of the present invention.

Claims

1. A focusing lens with a focal length of 87 mm, characterized in that: The lens is provided with two lenses with optical focal length, which are a first lens and a second lens arranged in sequence along the optical axis from the object plane to the image plane; the first lens is a positive meniscus lens with a convex surface facing the object side, and the second lens is a positive meniscus lens with a convex surface facing the image side; the air gap between the first lens and the second lens is 68.066 mm.

2. The focusing lens with a focal length of 87 mm according to claim 1, characterized in that: The center thickness of the first lens is 7.0 mm, the object side curvature radius is 135.690 mm, and the image side curvature radius is 194.522 mm; the center thickness of the second lens is 5 mm, the object side curvature radius is -164.772 mm, and the image side curvature radius is -110.682 mm.

3. The focusing lens with a focal length of 87 mm according to claim 1, characterized in that: The two lenses are both made of germanium single crystal.

4. The focusing lens with a focal length of 87 mm according to claim 1, characterized in that: The image side surface of the first lens is an aspherical surface and satisfies the aspherical surface formula: Among them, Z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror; k is the cone coefficient; A, B, C, D, and E are high-order aspherical coefficients.

5. The focusing lens with a focal length of 87 mm according to claim 4, characterized in that: The image side surface of the second lens is a binary surface, which satisfies the aspheric surface formula and satisfies the expression equation of the binary surface in Zemax: M(B1ρ 2 +B2ρ 4 ), where M is the diffraction order, the diffraction order is 1, B1 and B2 are the binary surface phase coefficients, B1 = -20.653, B2 = 5.191, and the normalized radius ρ is 30.

6. The focusing lens with a focal length of 87 mm according to claim 1, characterized in that: An aperture is provided between the first lens and the second lens.

7. The focusing lens with a focal length of 87 mm according to any one of claims 1 to 6, characterized in that: The lens has an operating band of 8 μm to 12 μm and an F number of 0.9, and is suitable for a detector with a pixel number of 640×512 and a pixel size of 12 μm.

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