An ultra-large-aperture large-target-surface athermalized long-wave infrared optical system suitable for an 8um pixel core

Abstract

This invention discloses an ultra-large aperture, large target surface, thermal-free long-wave infrared optical system suitable for 8µm pixel modules, comprising, from object to image: a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5; the first lens L1 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the object; the second lens L2 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the image; the third lens L3 is a meniscus aspherical lens with positive optical power and a convex surface bent towards the object; the fourth lens L4 is a plano-convex diffraction lens with positive optical power and a convex surface bent towards the object; and the fifth lens L5 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the object. The optical system of this invention features an ultra-large aperture, sufficient energy, high sensitivity, and high spatial resolution; it has a large target surface field of view and can be matched with a 15.36mm×8.64mm target surface long-wave camera; under the premise of large aperture, it achieves a thermal design with a temperature range of -40℃ to 80℃; and it has excellent image quality.

Description

Technical Field

[0001] This invention relates to an ultra-large aperture, large target surface, athermalized long-wave infrared optical system suitable for 8µm pixel modules, belonging to the technical field of athermalized long-wave infrared optical systems. Background Technology

[0002] The pixel size of mainstream long-wave cameras on the market is mainly 12um, 17um, etc., and their main matching infrared lenses have an F# of 1.0. Smaller pixel size corresponds to higher spatial resolution and resolution, requiring the lens to have a larger light-transmitting aperture and higher imaging quality.

[0003] The Nyquist frequency for a 12µm pixel chip is 42 lp / mm, for a 17µm pixel chip it is 29.4 lp / mm, and for an 8µm pixel chip it is 62.5 lp / mm. Current mainstream long-wavelength lenses have an aperture of F#1.0 and a maximum resolution of 57 lp / mm, primarily designed for 12µm and 17µm pixel cameras. They cannot fully accommodate the resolution capabilities of 8µm pixel cameras, resulting in a waste of camera performance.

[0004] Secondly, due to the limitation of large aperture, long-wavelength optical lenses cannot be designed to be thermal, which makes it impossible to achieve clear imaging without focusing in different temperature environments. This limits their usage environment, or they have to use electronic adjustment to achieve the imaging effect, which greatly reduces the reliability of the lens and increases manufacturing costs.

[0005] To adapt to the resolution capability of an 8µm pixel infrared camera, this invention provides a large-aperture, athermalized long-wave infrared optical system with an F#0.8 aperture, a focal length of 25mm, and a field of view of 40.8°. Summary of the Invention

[0006] This invention provides a long-wave infrared optical system with a large aperture and large target surface, which features good imaging quality, high sensitivity, and high resolution.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A super-large aperture, large target surface, calorimetric long-wave infrared optical system suitable for 8µm pixel cores, comprising, from object to image, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5.

[0009] The first lens L1 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the object side; the second lens L2 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the image side; the third lens L3 is a meniscus aspherical lens with positive optical power and a convex surface bent towards the object side; the fourth lens L4 is a plano-convex diffraction lens with positive optical power and a convex surface bent towards the object side; and the fifth lens L5 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the object side.

[0010] The above-mentioned anechoic long-wave infrared optical system has a focal length of 25mm, an operating wavelength of 8um to 12um, an F / # of 0.8, a full field of view of 40.8°, distortion ≤ -5%, and a spatial resolution greater than 65lp / mm.

[0011] From the object side to the image side, the first lens L1 with negative optical power and the second lens L2 with negative optical power constitute the front group of the entire optical system, which compresses the light rays in the large field of view; the third lens L3, the fourth lens L4 and the fifth lens L5 constitute the rear group of the optical system, which performs focusing and imaging. At the same time, placing the aperture stop on the convex surface of the third lens helps to reduce the lens aperture of the entire optical system.

[0012] The convex surface of the fourth lens is a diffraction surface to achieve thermal imaging at temperatures ranging from -40℃ to 80℃. In other words, the fourth object-side surface is a diffraction surface, while the fourth image-side surface is a plane.

[0013] Let the focal length of the system be F, the focal length of the first lens L1 be f1, the focal length of the second lens L2 be f2, the focal length of the third lens L3 be f3, the focal length of the fourth lens L4 be f4, and the focal length of the fifth lens L5 be f5. In order to improve the imaging effect, -5F < f1 < -4F, -3F < f2 < -2F, 0.8F < f3 < 1.5F, 0.9F < f4 < 1.6F, and -2.5F < f5 < -1.5F.

[0014] From the object side to the image side, the two sides of the first lens L1 are the first object side and the first image side, respectively; the two sides of the second lens L2 are the second object side and the second image side, respectively; the two sides of the third lens L3 are the third object side and the third image side, respectively; the two sides of the fourth lens L4 are the fourth object side and the fourth image side, respectively; and the two sides of the fifth lens L5 are the fifth object side and the fifth image side, respectively.

[0015] To improve imaging quality, both the first lens L1 and the third lens L3 are single-sided aspherical lenses (only one side is aspherical). The aspherical surface of the first lens L1 is the first image-side surface, and the aspherical surface of the third lens L3 is the third object-side surface. Both the second lens L2 and the fifth lens L5 are double aspherical lenses.

[0016] To further improve imaging quality, the radius of curvature of the first object-side surface is 90.5578±0.0003mm, and the radius of curvature of the first image-side surface is 57.8689±0.0003mm; the radius of curvature of the second object-side surface is -20.4554±0.0003mm, and the radius of curvature of the second image-side surface is -37.7666±0.0003mm; the radius of curvature of the third object-side surface is 47.2551±0.0003mm, and the radius of curvature of the third image-side surface is 227.4418±0.0003mm; the radius of curvature of the fourth object-side surface is 49.5524±0.0003mm, and the radius of curvature of the fourth image-side surface is infinite; the radius of curvature of the fifth object-side surface is -190.8611±0.0003mm, and the radius of curvature of the fifth image-side surface is ±135.62850.0003mm.

[0017] As one specific implementation scheme, in order to ensure imaging quality, the center interval between the first lens L1 and the second lens L2 is 10.52±0.01mm; the center interval between the second lens L2 and the third lens L3 is 2.05±0.01mm; the center interval between the third lens L3 and the fourth lens L4 is 17.29±0.01mm; and the center interval between the fourth lens L4 and the fifth lens L5 is 1.36±0.01mm.

[0018] To balance image quality and stability, the center thickness of the first lens L1 is 3.00±0.01mm, the center thickness of the second lens L2 is 8.00±0.01mm, the center thickness of the third lens L3 is 9.00±0.01mm, the center thickness of the fourth lens L4 is 8.30±0.01mm, and the center thickness of the fifth lens L5 is 7.80±0.01mm.

[0019] To improve imaging stability, the materials of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are chalcogenide glass or zinc sulfide.

[0020] To achieve better imaging quality, the optical system uses even-order aspherical surfaces and diffraction surfaces to reduce various aberrations, including chromatic aberration, and appropriately combines lens materials to eliminate focus shift caused by surface shape changes due to temperature variations at high and low temperatures.

[0021] Any techniques not mentioned in this invention are based on existing technologies.

[0022] This invention is applicable to ultra-large aperture, large target surface, calorimetric long-wave infrared optical systems with 8µm pixel cores, and has the following beneficial effects:

[0023] 1) It has an ultra-large aperture, reaching F#0.8, with sufficient energy, high sensitivity, and high spatial resolution;

[0024] 2) It has a large target surface field of view and can be matched with a long-wavelength camera with a target surface of up to 15.36mm×8.64mm;

[0025] 3) Under the premise of large aperture, it achieves a heatless design from -40℃ to 80℃, and does not require multiple focusing during use. It is suitable for use requirements such as temperature measurement and observation in different temperature environments.

[0026] 4) Excellent image quality, fully matching the resolution capability of 8µm pixel size cameras. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the optical principle system of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the optical system according to a detailed embodiment of the present invention;

[0029] Figure 3 The graph shows the transfer function of the optical system of the present invention at an ambient temperature of 20°C.

[0030] Figure 4 The transfer function curve of the optical system of the present invention at an ambient temperature of -40°C is shown.

[0031] Figure 5 The transfer function curve of the optical system of the present invention at an ambient temperature of 80°C is shown.

[0032] Figure 6 This is a full-field distortion curve diagram of the optical system of the present invention;

[0033] Figure 7 This is a diagram showing the relative illumination curve of the optical system of the present invention across the entire field of view; Detailed Implementation

[0034] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0035] like Figure 1-2 As shown, an ultra-large aperture, large target surface, athermalized long-wave infrared optical system suitable for 8µm pixel cores includes, from object to image, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5; the F# is 0.8, the focal length is 25mm, the field of view is 40.8°, and the spatial resolution is greater than 60lp / mm.

[0036] From the object side to the image side, the first lens L1 with negative optical power and the second lens L2 with negative optical power constitute the front group of the entire optical system, which compresses the light rays in the large field of view; the third lens L3, the fourth lens L4 and the fifth lens L5 constitute the rear group of the optical system, which performs focusing and imaging. At the same time, placing the aperture stop on the convex surface of the third lens helps to reduce the lens aperture of the entire optical system.

[0037] The first lens L1 has two surfaces, namely the first object side S1 and the first image side S2, respectively; the second lens L2 has two surfaces, namely the second object side S3 and the second image side S4, respectively; the third lens L3 has two surfaces, namely the third object side S5 and the third image side S6, respectively; the fourth lens L4 has two surfaces, namely the fourth object side S7 and the fourth image side S8, respectively; and the fifth lens L5 has two surfaces, namely the fifth object side S9 and the fifth image side S10, respectively.

[0038] Let the focal length of the system be F, and the focal lengths of the first to fifth lenses be f1, f2, f3, f4, and f5, respectively. Each lens has the following characteristics:

[0039] The first lens L1 is a meniscus single-sided aspherical lens with negative optical power and a convex surface bent towards the object side. The aspherical surface is the first image side surface, and -5F < f1 < -4F.

[0040] The second lens L2 is a meniscus double aspherical lens with negative optical power and a convex surface bent towards the image side, -3F < f2 < -2F;

[0041] The third lens L3 is a meniscus aspherical lens with positive optical power and a convex surface curved towards the object side. The aspherical surface is the third object-side surface, and 0.8F < f3 < 1.5F.

[0042] The fourth lens L4 is a plano-convex diffraction lens with positive optical power and a convex surface bent towards the object side. The diffraction surface is the fourth object-side surface (convex surface), and the plane is the fourth image-side surface. 0.9F < f4 < 1.6F.

[0043] The fifth lens L5 is a meniscus double aspherical lens with negative optical power and a convex surface bent towards the object side, -2.5F < f5 < -1.5F;

[0044] Table 1 shows the technical specifications of the optical system in this embodiment, Table 2 shows the specific optical parameters of the optical system in this embodiment, and Table 3 shows the aspherical coefficients specifically used in the optical system described in this embodiment.

[0045] Table 1 Technical Specifications of the Optical System

[0046]

[0047]

[0048] Table 2 Specific optical parameters of the optical system

[0049]

[0050] In Table 2, radius of curvature refers to the radius of curvature of each lens surface, thickness or spacing refers to the lens thickness or the distance between adjacent lens surfaces, material refers to the material used in the lens, and air refers to the medium between two lenses being air.

[0051] To achieve better imaging quality, even-order aspherical surfaces and diffractive surfaces are used in the optical system to reduce various aberrations, including chromatic aberration. In addition, lens materials are appropriately matched to eliminate focus shift caused by surface shape changes due to temperature variations at high and low temperatures.

[0052] Table 3 shows the aspheric coefficients used in specific embodiments.

[0053]

[0054] The aspherical equations used for each surface in Table 3 are as follows:

[0055]

[0056] The meanings of each quantity are as follows:

[0057] ZA: The lens sagitta along the optical axis of the aspherical surface;

[0058] R: Radius of curvature at the intersection of the surface and the optical axis OO';

[0059] Y: Half-aperture of the lens perpendicular to the optical axis;

[0060] k: Conic coefficient;

[0061] A, B, C, and D aspheric coefficients;

[0062] Table 4. Diffraction surface coefficients of the S7 plane

[0063]

[0064] The diffraction surface equations used in Table 4 are as follows:

[0065] Φ=A1Y 2 +A2Y 4 +A3Y 6

[0066] in:

[0067] Φ: Phase of the diffraction plane;

[0068] Y: Half-aperture of the lens perpendicular to the optical axis;

[0069] A1, A2, and A3 are the phase coefficients of the diffraction surface.

[0070] Figure 3 The transfer function curve of the optical system of the present invention at room temperature (20°C) is shown below. Figure 3 It can be seen that the transfer function values ​​of 62lp / mm are all greater than 0.3; Figure 4 The transfer function curve of the optical system of the present invention at a low temperature of -40°C is shown below. Figure 4 It can be seen that the transfer function values ​​of 62lp / mm are all greater than 0.3; Figure 5 The figure shows the transfer function curve of the optical system of this invention at a high temperature of 80°C. As can be seen from the figure, the transfer function value of 62 lp / mm is greater than 0.3, indicating excellent image quality and fully matching the resolution capability of an 8µm pixel-size camera. Figure 6 It can be seen that the distortion across the entire field of view is ≤-5%. Figure 7 It can be seen that the relative illumination across the entire field of view is ≥90%, and the image plane uniformity is good.

Claims

1. An ultra-large aperture large target surface athermalized long-wave infrared optical system suitable for an 8um pixel core, characterized in that: From the object side to the image side, it consists of: first lens L1, second lens L2, third lens L3, fourth lens L4 and fifth lens L5; The first lens L1 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the object side; the second lens L2 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the image side; the third lens L3 is a meniscus aspherical lens with positive optical power and a convex surface bent towards the object side; the fourth lens L4 is a plano-convex diffraction lens with positive optical power and a convex surface bent towards the object side; and the fifth lens L5 is a meniscus aspherical lens with negative optical power and a convex surface bent towards the object side. Let the focal length of the system be F, the focal length of the first lens L1 be f1, the focal length of the second lens L2 be f2, the focal length of the third lens L3 be f3, the focal length of the fourth lens L4 be f4, and the focal length of the fifth lens L5 be f5; where -5F < f1 < -4F, -3F < f2 < -2F, 0.8F < f3 < 1.5F, 0.9F < f4 < 1.6F, and -2.5F < f5 < -1.5F.

2. The super-aperture large-format uncooled LWIR optical system suitable for 8um pixel core as claimed in claim 1, wherein: From the object side to the image side, the first lens L1 with negative optical power and the second lens L2 with negative optical power constitute the front group of the entire optical system, which compresses the light rays in the large field of view; the third lens L3, the fourth lens L4 and the fifth lens L5 constitute the rear group of the optical system, which performs focusing and imaging, and at the same time, the aperture stop is placed on the convex surface of the third lens to reduce the lens aperture of the entire optical system.

3. The super-aperture large-format uncooled LWIR optical system suitable for 8um pixel core according to claim 1 or 2, characterized in that: The convex surface of the fourth lens is a diffraction surface.

4. The super-aperture large-format uncooled LWIR optical system suitable for 8um pixel core as claimed in claim 1 or 2, characterized in that: From the object side to the image side, the two sides of the first lens L1 are the first object side and the first image side, respectively; the two sides of the second lens L2 are the second object side and the second image side, respectively; the two sides of the third lens L3 are the third object side and the third image side, respectively; the two sides of the fourth lens L4 are the fourth object side and the fourth image side, respectively; and the two sides of the fifth lens L5 are the fifth object side and the fifth image side, respectively. The first lens L1 and the third lens L3 are both single-sided aspherical lenses. The aspherical surface of the first lens L1 is the first image-side surface, and the aspherical surface of the third lens L3 is the third object-side surface. The second lens L2 and the fifth lens L5 are both double aspherical lenses.

5. The super-aperture large-format uncooled LWIR optical system suitable for 8um pixel core as claimed in claim 4, characterized in that: The radius of curvature of the first object side is 90.5578±0.0003mm, and the radius of curvature of the first image side is 57.8689±0.0003mm; the radius of curvature of the second object side is -20.4554±0.0003mm, and the radius of curvature of the second image side is -37.7666±0.0003mm; the radius of curvature of the third object side is 47.2551±0.0003mm, and the radius of curvature of the third image side is 227.4418±0.0003mm; the radius of curvature of the fourth object side is 49.5524±0.0003mm, and the radius of curvature of the fourth image side is infinite; the radius of curvature of the fifth object side is -190.8611±0.0003mm, and the radius of curvature of the fifth image side is ±135.62850.0003mm.

6. The ultra-large aperture, large target surface, calorimetric long-wave infrared optical system suitable for 8µm pixel modules as described in claim 1 or 2, characterized in that: The center-to-center distance between the first lens L1 and the second lens L2 is 10.52±0.01mm; the center-to-center distance between the second lens L2 and the third lens L3 is 2.05±0.01mm; the center-to-center distance between the third lens L3 and the fourth lens L4 is 17.29±0.01mm; and the center-to-center distance between the fourth lens L4 and the fifth lens L5 is 1.36±0.01mm.

7. The super-aperture large-format uncooled LWIR optical system suitable for 8um pixel core as claimed in claim 1 or 2, characterized in that: The center thickness of the first lens L1 is 3.00±0.01mm, the center thickness of the second lens L2 is 8.00±0.01mm, the center thickness of the third lens L3 is 9.00±0.01mm, the center thickness of the fourth lens L4 is 8.30±0.01mm, and the center thickness of the fifth lens L5 is 7.80±0.01mm.

8. The super-aperture large-format uncooled long-wave infrared optical system suitable for 8um pixel core according to claim 1 or 2, characterized in that: Its focal length is 25mm, its working band is 8um~12um, its F / # is 0.8, its full field of view is 40.8°, and its distortion is ≤-5%.

9. The ultra-large aperture, large target surface, calorimetric long-wave infrared optical system suitable for 8µm pixel modules as described in claim 1 or 2, characterized in that: The materials of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are chalcogenide glass or zinc sulfide.

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