A focusing lens with a focal length of 87 mm

Abstract

The present application belongs to the field of infrared optical technology, and discloses a focusing lens with a focal length of 87mm. The lens is provided with two lenses with optical power, namely a first lens and a second lens which are sequentially arranged along the optical axis from an object plane to an image plane. The first lens is a convex moon positive lens with a convex surface facing the object side, and the second lens is a convex moon positive lens with a convex surface facing the image side. The air gap between the first lens and the second lens is 68.066mm. The present application corrects and balances aberration in the long-wave infrared spectral range, so that the lens has excellent image quality in a wide spectral range, and wide-spectrum confocal is realized. Through reasonable matching of optical power and design of aspheric surface and diffractive surface, the lens can achieve good imaging effect by using only two lenses, and has high pass rate and low distortion, and is suitable for a detector with 640x512 image elements and 12um image element size.

Description

Technical Field

[0001] This technology belongs to the field of infrared optical technology, and specifically relates to a focusing lens with a focal length of 87mm. Background Technology

[0002] Infrared detection has a certain ability to penetrate smoke, fog, haze, snow and other forms of camouflage, and is not affected by strong light or flashes. It can achieve long-distance, all-weather observation and is especially suitable for target detection at night and under adverse weather conditions.

[0003] However, in complex environments, the focal length of an infrared lens is affected by various factors, leading to unclear imaging and affecting the normal operation of the detector. For example, temperature not only affects the refractive index of optical materials but also causes thermal expansion and contraction of the lens barrel material, resulting in changes in optical power and a shift in the optimal image plane, reducing optical imaging quality, blurring the image, decreasing contrast, and ultimately affecting the lens's imaging performance.

[0004] To eliminate or reduce the impact of temperature changes on the imaging of optical systems, and to ensure the stability of the optical system within a large temperature range, thereby guaranteeing good image quality, appropriate compensation techniques can be employed. Existing compensation methods include passive optical compensation and active mechanical compensation, which typically involve three or more lenses.

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

[0006] To address the above problems, this invention proposes a focusing lens with a focal length of 87mm. The specific technical solution is as follows:

[0007] A focusing lens with a focal length of 87mm is provided, the lens having two lenses with optical power, namely a first lens and a second lens arranged sequentially along the optical axis from the object plane to the image plane; the first lens is a meniscus lens with its convex surface facing the object side, and the second lens is a meniscus lens with its convex surface facing the image side; the air gap between the first lens and the second lens is 68.066mm.

[0008] Furthermore, the center thickness of the first lens is 7.0 mm, the object-side radius of curvature is 135.690 mm, and the image-side radius of curvature is 194.522 mm; the center thickness of the second lens is 5 mm, the object-side radius of curvature is -164.772 mm, and the image-side radius of curvature is -110.682 mm.

[0009] Furthermore, both lenses are made of germanium single crystal.

[0010] Furthermore, the image-side surface of the first lens is aspherical and satisfies the aspherical formula:

[0011]

[0012] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0013] Furthermore, the image-side surface of the second lens is a binary surface, satisfying the aspherical formula and the equation for 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 phase coefficients of the binary surface, B1 = -20.653, B2 = 5.191, and the normalization radius ρ is 30.

[0014] Furthermore, an aperture stop is provided between the first lens and the second lens.

[0015] Furthermore, the lens operates in the 8μm~12μm band, has an F-number of 0.9, and is suitable for detectors with a pixel count of 640×512 and a pixel size of 12μm.

[0016] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0017] This invention corrects and balances aberrations in the long-wave infrared spectral range, enabling the lens to have excellent image quality across a wide spectral range and achieving wide-spectral confocal focusing. Through reasonable matching of optical power and the design of aspherical and diffractive surfaces, the lens can achieve good imaging results with only two lens elements, and has high transmittance, low distortion, and can be matched with smaller chip pixels, such as 640×512, 12μm chips. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a diagram showing the lens composition of the focusing lens with a focal length of 87mm in Example 1.

[0020] Figure 2 The optical path diagram is for the focusing lens with a focal length of 87mm in Example 1.

[0021] Figure 3 This is a dot plot of the focusing lens with a focal length of 87mm in Example 1.

[0022] Figure 4 The MTF diagram is for the focusing lens with a focal length of 87mm in Example 1.

[0023] Reference numerals: 1. First lens; 2. Second lens; 3. Third lens; 4. Protective window; 5. Image plane. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features.

[0025] Example 1

[0026] like Figure 1 As shown, this embodiment provides a focusing lens with a focal length of 87mm. The lens has two lenses with optical power, a first lens 1 and a second lens 3 arranged sequentially along the optical axis from the object plane to the image plane 5; the first lens 1 is a meniscus lens with its convex surface facing the object side, and the second lens 3 is a meniscus lens with its convex surface facing the image side. An aperture stop 2 is provided between the first lens 1 and the second lens 3.

[0027] 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 through the second lens 3 before being imaged 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 aberrations caused by temperature.

[0028] As shown in Table 1, in one specific embodiment, the center thickness of the first lens 1 is 7.0 mm, the object-side radius of curvature is 135.690 mm, and the image-side radius of curvature is 194.522 mm; the center thickness of the second lens 3 is 5 mm, the object-side radius of curvature is -164.772 mm, and the image-side radius of curvature 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.

[0029] It is understandable that the side of a lens where light enters is the object-side surface, and the side where light exits is the image-side surface. For example, in the first lens 1, surface S1 is the object-side surface, and surface S2 is the image-side surface. Other lenses will not be described in detail here. Table 1 shows the parameters of each component.

[0030]

[0031] In a specific implementation, the first lens 1 and the second lens 3 are made of germanium single crystal.

[0032] Table 2 Aspherical data of lenses

[0033]

[0034] As one 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 formula:

[0035]

[0036] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0037] The image-side surface S5 of the second lens 3 is a binary surface, satisfying the above aspherical surface formula and the expression equation for a 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 phase coefficients of the binary surface, B1 = -20.653, B2 = 5.191, and the normalization radius ρ is 30.

[0038] Figure 3 , Figure 4 The images show a dot plot and an MTF (Mean Transformer Factor) plot for the lens at a focal length of 87mm. In the MTF plot, the horizontal axis represents different spatial frequencies, and the vertical axis represents modulation. All fields of view represent the MTF curves in the meridional plane. It can be seen that the MTF is close to the diffraction limit, the root mean square diameter of the spot of confusion is smaller than the Airy disk diameter, and the image quality is good.

[0039] The focusing lens in this embodiment has a focal length of 87mm, a working wavelength of 8μm~12μm, an F number of 0.9, and is suitable for detectors with a pixel count of 640×512 and a pixel size of 12μm.

[0040] This embodiment of the lens, through the reasonable allocation of optical power and the design of optical materials, aspherical surfaces and diffraction surfaces, performs aberration correction and balance over a wide spectral range, enabling the lens to have excellent image quality over a wide spectral range, achieving wide spectral confocal imaging, and clear imaging in the mid-to-long wavelength range.

[0041] Obviously, the above embodiments are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A focusing lens with a focal length of 87mm, characterized in that, The lens includes a lens with optical power; the lens with optical power consists of a first lens and a second lens arranged sequentially along the optical axis from the object plane to the image plane; the first lens is a meniscus lens with its convex surface facing the object side, and the second lens is a meniscus lens with its convex surface facing the image side; the air gap between the first lens and the second lens is 68.066 mm; the center thickness of the first lens is 7.0 mm, the radius of curvature of the object side is 135.690 mm, and the radius of curvature of the image side is 194.522 mm; the center thickness of the second lens is 5 mm, the radius of curvature of the object side is -164.772 mm, and the radius of curvature of the image side is -110.682 mm; the lens operates in the wavelength range of 8 μm to 12 μm, has an F-number of 0.9, and is suitable for detectors with a pixel count of 640×512 and a pixel size of 12 μm; the image side of the first lens is aspherical; the image side of the second lens is a binary surface; both the first lens and the second lens are made of germanium single crystal.

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

3. The focusing lens with a focal length of 87mm according to claim 2, characterized in that, The image-side surface of the second lens satisfies the aspherical formula and the equation for a 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 phase coefficients of the binary surface, B1 = -20.653, B2 = 5.191, and the normalization radius ρ is 30.

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

Images