A large field-of-view, large aperture low-light night vision objective and its design method

Abstract

This invention discloses a large field-of-view, large-aperture low-light night vision objective lens and its design method, relating to the field of optical imaging technology. The objective lens, along the optical axis from the object side to the image side, includes a first to an eighth lens and an image plane. The first to fifth lenses form a negative optical power front lens group to expand the incident beam angle; the seventh and eighth lenses form a positive optical power rear lens group for beam converging and imaging, forming an anti-long-range optical structure. An aperture stop is provided between the fifth and sixth lenses. The eighth lens is a positive optical power lens with an aspherical surface, used to correct aberrations. The objective lens employs a heatless structure combining glass and plastic lenses, utilizing the thermo-optical coefficient of the plastic lens for temperature compensation, ensuring stable imaging over a wide temperature range. While achieving a large field of view, large aperture, and high sensitivity, it also possesses the advantages of compact structure and strong environmental adaptability, making it suitable for low-light night vision equipment in harsh environments.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, specifically to a large field-of-view, large-aperture low-light night vision objective lens and its design method. Background Technology

[0002] In the field of low-light night vision technology, the observation objective, as the core front-end of the system, directly determines the detection range, imaging clarity, and environmental adaptability of the entire device. With the continuous expansion of application scenarios such as nighttime reconnaissance, security monitoring, and individual soldier operations, the market has placed higher demands on low-light objectives: on the one hand, they need to have a large field of view to achieve wide-area situational awareness; on the other hand, they need to have a large relative aperture to collect more light under extremely low illumination, ensuring image brightness and signal-to-noise ratio.

[0003] However, traditional low-light night vision objectives face numerous technical challenges in their design. First, a large field of view and a large aperture are often mutually exclusive. Increasing the field of view introduces severe off-axis aberrations such as distortion, coma, and astigmatism, while increasing the aperture exacerbates spherical aberration and field curvature, leading to a sharp decline in edge image quality. Second, to correct these aberrations, traditional designs often employ complex lens structures with multiple groups, increasing system size and weight, manufacturing costs, and assembly complexity. Furthermore, existing objectives generally neglect temperature adaptability design. Low-light night vision devices are often deployed outdoors, operating in environments with wide temperature ranges. The thermal expansion and contraction and refractive index changes of ordinary optical materials with temperature can cause focal length drift and image plane defocusing, resulting in image blurring in devices that do not require manual focusing, severely limiting the reliability and applicability of the equipment. Therefore, there is an urgent need for a new type of low-light night vision objective that can maintain excellent imaging performance with a large field of view and large aperture while achieving miniaturization and wide-temperature-range anechoic adaptive performance. Summary of the Invention

[0004] The purpose of this invention is to provide a large field-of-view, large-aperture low-light night vision objective lens and its design method, so as to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a large field of view, large aperture, low-light night vision observation objective lens and its design method, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, and an image plane arranged sequentially along the optical axis from the object side to the image side; The first to fifth lenses constitute a negative optical power front lens group; The seventh and eighth lenses constitute a positive optical power rear lens group; An aperture is provided between the fifth lens and the sixth lens; The eighth lens is a positive power lens having at least one aspherical surface; The negative optical power front lens group is used to expand the angle of the incident beam, and the positive optical power rear lens group is used to converge the beam to form an anti-long-distance optical structure. The RMS radius of the optical transfer function of the observation objective lens in the on-axis field of view is less than 10µm, and the RMS radius in the full field of view is smaller than the pixel size, so as to meet the resolution requirements of low-light night vision imaging.

[0006] Furthermore, at least one optical surface of the eighth lens adopts an even-order aspherical structure, which is used to correct spherical aberration, coma, and astigmatism generated by the system.

[0007] Furthermore, the observation objective lens employs a thermal optical structure combining glass and plastic lenses; Plastic lenses utilize their thermo-optical coefficient to participate in temperature compensation, while glass lenses are used to maintain the optical stability of the system.

[0008] Furthermore, the third and sixth lenses are made of plastic optical materials; The first lens, the second lens, the fourth lens, the fifth lens, the seventh lens, and the eighth lens are made of glass optical material.

[0009] Furthermore, the observation objective lens satisfies the following optical parameters: Focal length is 10mm to 25mm; The relative aperture is no greater than 1.5. The field of view is not less than 50°.

[0010] Furthermore, the focal length of the observation objective is 16.5 mm; The F-number is 1.2; The field of view is 60°; The total optical length is less than 40mm.

[0011] Furthermore, the back focal length of the objective lens is greater than 5 mm.

[0012] Furthermore, the aperture stop is positioned between the fifth lens and the sixth lens to control the effective aperture and the principal ray angle of the system. The observation objective lens has a full field-of-view distortion of less than 3% and a full field-of-view relative illumination of greater than 40%.

[0013] Furthermore, at an on-axis 0° field of view, the RMS radius of the observation objective is 4.815µm; The RMS radius at a 15° off-axis field of view is 4.060µm; The RMS radius at a 30° field of view is 8.626µm.

[0014] To achieve the aforementioned large field-of-view, large aperture low-light night vision objective lens, this invention provides the following technical solution, comprising the following steps: S1. Determine the objective lens focal length, relative aperture, and initial optical structure based on the field of view and light transmission requirements of the low-light night vision system; S2. Establish a reverse telephoto optical system consisting of a negative optical power front lens group and a positive optical power rear lens group; S3. By configuring glass lenses and plastic lenses with different thermo-optical properties, the changes in optical power caused by temperature changes can be mutually compensated. S4. Correct system aberrations by setting aspherical lenses; S5. By optimizing the lens power distribution, aperture position, and lens spacing, the system meets the imaging quality requirements.

[0015] Furthermore, by matching the thermal characteristics of the glass lens and the plastic lens, the observation objective lens can maintain stable imaging within an ambient temperature range of -40℃ to 65℃, and the focal length change is less than 0.05mm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. By adopting a negative-positive optical power separation anti-long-range structure and combining it with the even-order aspherical surface design of the eighth lens, this invention effectively corrects spherical aberration, coma and astigmatism under large field of view and large aperture conditions, making the distortion of the entire field of view less than 3% and the relative illumination at the edge higher than 40%, ensuring that a clear image with high resolution and low distortion can be obtained from the center to the edge.

[0017] 2. This invention adopts a heatless structure combining glass and plastic lenses. By utilizing the negative thermo-optical coefficient of the plastic lens and the positive thermo-optical coefficient of the glass lens to cancel each other out, the focal length change of the system is less than 0.05mm in the extreme temperature range of -40℃ to 65℃. The image plane can be kept stable without mechanical focusing, which significantly improves the reliability of the equipment under different climatic conditions.

[0018] 3. This invention achieves complex optical performance using only eight lenses, with a total optical length of less than 40mm and a simple structure. The use of aspherical lenses replaces the correction function of multiple spherical lenses, reducing the number of lenses, system weight, and assembly difficulty. It is particularly suitable for airborne, vehicle-mounted, and portable low-light night vision equipment where size and weight are strictly limited. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall assembly structure of the present invention; Figure 2 This is a schematic diagram of the lens arrangement structure of the present invention; Figure 3This is a schematic diagram of the full field-of-view distortion curve of the present invention; Figure 4 This is a schematic diagram of the relative illumination curve across the entire field of view of the present invention; Figure 5 This is a schematic diagram of the focal length stability curve under temperature changes according to the present invention; Figure 6 This is a schematic diagram of the temperature MTF variation curve at 0° field of view according to the present invention; Figure 7 This is a schematic diagram of the temperature MTF variation curve at a 15° field of view according to the present invention; Figure 8 This is a schematic diagram of the temperature MTF variation curve at a 30° field of view according to the present invention; Figure 9 This is a schematic diagram of the tolerance Monte Carlo analysis yield curve of this invention; In the diagram: 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Seventh lens; 8. Eighth lens. Detailed Implementation

[0020] 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.

[0021] Example: Figures 1-9 As shown, the present invention provides a technical solution for a large field of view, large aperture, low-light night vision observation objective lens and its design method, comprising a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7, an eighth lens 8 and an image plane arranged sequentially along the optical axis from the object side to the image side; The first lens 1 to the fifth lens 5 constitute a negative optical power front lens group; The seventh lens 7 and the eighth lens 8 constitute a positive optical power rear lens group; An aperture is provided between the fifth lens 5 and the sixth lens 6; The eighth lens 8 is a positive power lens with at least one aspherical surface; The negative optical power front lens group is used to expand the angle of the incident beam, and the positive optical power rear lens group is used to converge the beam to form an anti-long-distance optical structure. The RMS radius of the optical transfer function of the observation objective lens in the on-axis field of view is less than 10µm, and the RMS radius in the full field of view is smaller than the pixel size, so as to meet the resolution requirements of low-light night vision imaging.

[0022] In use, this invention utilizes a negative optical power front lens group to expand the angle of the incident beam, achieving a wider field of view. Simultaneously, the large aperture design allows for the collection of more low-light signals, increasing the amount of light received in low-light environments and preventing dim or blurry images. The aspherical design of the eighth lens 8 effectively corrects various aberrations caused by the large field of view and large aperture structure, ensuring clear and uniform imaging throughout the entire field of view. The aperture stop, positioned between the fifth lens 5 and the sixth lens 6, allows for reasonable control of the beam aperture, optimizing the light path within the system, and balancing the field curvature and distortion of the entire optical system. Ultimately, this results in a clear low-light image with high resolution and well-controlled distortion on the image plane, meeting the needs of wide-field, long-distance low-light night vision observation.

[0023] The eighth lens 8 has at least one optical surface with an even-order aspherical structure, which is used to correct spherical aberration, coma, and astigmatism generated by the system.

[0024] In use, the even-order aspherical surface of the eighth lens 8 effectively compensates for higher-order spherical aberrations generated under large aperture conditions, while suppressing coma and astigmatism caused by edge rays in a large field of view, thereby significantly improving imaging consistency and sharpness across the entire field of view. This aspherical structure optimizes the image quality of the optical system without increasing the number of lenses, reduces system complexity and assembly difficulty, and facilitates the design of lightweight and highly reliable low-light night vision devices.

[0025] The observation objective lens employs a thermal optical structure combining glass and plastic lenses; Plastic lenses utilize their thermo-optic coefficient to participate in temperature compensation, while glass lenses are used to maintain the optical stability of the system. During use, the plastic lens will change its refractive index according to the temperature, which complements the temperature characteristics of the glass lens. This offsets the drift of the optical system's focal length caused by temperature changes, and avoids the problem of image plane deviation and image clarity reduction caused by temperature changes. This allows the observation lens to maintain stable image quality in complex high and low temperature environments, adapt to the usage requirements of different outdoor working environments, and improve the environmental adaptability of low-light night vision equipment.

[0026] The third lens 3 and the sixth lens 6 are made of plastic optical materials; The first lens 1, the second lens 2, the fourth lens 4, the fifth lens 5, the seventh lens 7, and the eighth lens 8 are made of glass optical material; In use, the third lens 3 and the sixth lens 6, as plastic components, mainly serve the function of thermal compensation. Their negative thermo-optical coefficients can effectively offset the focal length changes caused by temperature increases in the glass lenses. Meanwhile, the remaining glass lenses, with their excellent refractive index stability and mechanical strength, ensure the consistency of the system's optical performance over a wide temperature range. This material layout takes into account aberration correction, thermal stability, and manufacturing feasibility. While ensuring imaging quality with a large field of view and large aperture, it significantly improves the system's anechoic performance under extreme temperature conditions such as -40℃ to +65℃, avoiding frequent focusing or image blurring. It is suitable for low-light night vision applications with stringent environmental adaptability requirements, such as vehicle-mounted, airborne, and individual soldier equipment.

[0027] The observation objective lens meets the following optical parameters: Focal length is 10mm to 25mm; The relative aperture is no greater than 1.5. The field of view is not less than 50°; In use, this range of optical parameters ensures that the objective lens maintains a compact structure while balancing a wide field of view and high light-gathering capability. A focal length set within the 10mm–25mm range allows for relatively long observation distances within a limited system length; a relative aperture of no more than F / 1.5 significantly improves light transmission efficiency in low-light environments and enhances the image signal-to-noise ratio; a field of view of no less than 50° effectively expands the coverage of a single frame, reduces blind spots, and improves situational awareness. The synergistic effect of these parameters makes this objective lens particularly suitable for applications requiring both wide-area surveillance and high-sensitivity imaging, such as nighttime reconnaissance, security surveillance, and special operations. It achieves reliable low-light observation performance in all weather conditions and all terrains while ensuring image clarity and uniform edge illumination.

[0028] The focal length of the observation objective is 16.5mm; The F-number is 1.2; The field of view is 60°; The total optical length is less than 40mm; In use, this parameter ratio balances the needs of large light intake, wide field of view, and miniaturized design. The 16.5mm focal length, combined with a 60° wide field of view, ensures both appropriate magnification and sufficient image coverage. The large aperture design with an F-number of 1.2 can collect enough light in extremely low-light environments to obtain imaging results with sufficient brightness and high signal-to-noise ratio. The design with a total optical length of less than 40mm makes the entire objective lens structure more compact and small, which can be adapted to the installation needs of various lightweight and miniaturized low-light night vision devices. While achieving excellent imaging performance, it controls the overall size and weight of the device, better meeting the design requirements of portable low-light night vision observation equipment.

[0029] An aperture is positioned between the fifth lens 5 and the sixth lens 6 to control the effective aperture and principal ray angle of the system. The observation objective lens has a full-field distortion of less than 3% and a full-field relative illumination of greater than 40%. In use, the aperture stop is positioned specifically between the fifth lens 5 and the sixth lens 6, effectively constraining the incident angle of edge rays and optimizing the incident angle distribution of the main ray on the image plane. This reduces the overall distortion level of the system and improves the uniformity of edge illumination. A full-field-of-view distortion of less than 3% ensures high image geometric fidelity, making it suitable for reconnaissance and identification tasks requiring high accuracy in target shape and spatial relationships. A full-field-of-view relative illumination greater than 40% significantly improves the brightness attenuation problem at the edges of the field of view, avoiding image information loss due to uneven illumination. This design maintains a large field of view and large aperture performance while also considering the geometric accuracy and energy uniformity of imaging, further enhancing the practicality and reliability of low-light night vision systems in complex scenarios.

[0030] At a 0° field of view on the axis, the RMS radius of the observation objective is 4.815µm; The RMS radius at a 15° off-axis field of view is 4.060µm; The RMS radius at a 30° field of view is 8.626µm. In use, the RMS radius data shows that the image spot size of each field of view in this embodiment is smaller than the single pixel size of the image plane detector. The energy concentration of all fields of view meets the requirements of high-resolution imaging. Clear imaging can be achieved from the center field of view to the edge field of view, which fully demonstrates the excellent effect of the aberration correction design of this invention. It can ensure uniform and clear imaging quality of the whole picture when observing low light night vision, and meet the needs of identifying target details.

[0031] A heatless design method for large field-of-view, large aperture low-light night vision objective lenses includes the following steps: S1. Determine the objective lens focal length, relative aperture, and initial optical structure based on the field of view and light transmission requirements of the low-light night vision system; S2. Establish a reverse telephoto optical system consisting of a negative optical power front lens group and a positive optical power rear lens group; S3. By configuring glass lenses and plastic lenses with different thermo-optical properties, the changes in optical power caused by temperature changes can be mutually compensated. S4. Correct system aberrations by setting aspherical lenses; S5. By optimizing the lens power distribution, aperture position, and lens spacing, the system meets the imaging quality requirements.

[0032] By matching the thermal characteristics of the glass lens and the plastic lens, the observation objective lens can maintain stable imaging within an ambient temperature range of -40℃ to 65℃, and the focal length change is less than 0.05mm.

[0033] In practice, this design method ensures that focal plane displacement of the optical system is effectively suppressed over a wide temperature range by precisely matching the thermal expansion coefficients and thermo-optical coefficients of the glass and plastic materials. When the ambient temperature varies between -40℃ and +65℃, the negative focal length drift caused by the plastic lens cancels out the positive drift caused by the glass lens, thereby controlling the overall focal length change of the system to within 0.05mm and avoiding image blurring caused by thermal defocusing.

[0034] Working principle: The low-light or near-infrared beam from the target scene first enters the negative optical power front lens group composed of the first to fifth lenses 5. This lens group is equivalent to a beam expander, which widens the angle of light from the large field of view and smoothly introduces it into the rear system, effectively reducing the incident angle of the off-axis principal ray on the image plane, laying the foundation for obtaining high edge illumination. Subsequently, the light passes through the aperture between the fifth and sixth lenses 6. This aperture effectively controls the light aperture and principal ray angle of the system, balancing the aberrations and energy distribution of the system. Then, the beam enters the positive optical power rear lens group composed of the seventh and eighth lenses 8. This group gradually converges the diverging tilted beam and finally images it onto the image plane. During this imaging process, the aspherical surface of the eighth lens 8 performs reverse compensation for the higher-order spherical aberrations and off-axis aberrations caused by the large aperture, significantly improving the full field of view sharpness. Meanwhile, the entire system achieves calorimetry through material matching: when the ambient temperature changes, the glass lens maintains high refractive index stability and provides the main optical power, while the plastic lens, due to its large negative thermo-optic coefficient, has its optical power drifting regularly with temperature. This drift is precisely used to compensate for the positive focal length drift of the glass lens caused by thermal expansion, so that the total optical power of the system remains constant in a wide temperature range. This ensures that the imaging surface always coincides with the detector target surface, and can output clear and stable night vision images under harsh temperature conditions without external focusing.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A large field-of-view, large-aperture low-light night vision objective lens and its design method, characterized in that, It includes a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7), an eighth lens (8) arranged sequentially along the optical axis from the object side to the image side, and an image plane; The first lens (1) to the fifth lens (5) constitute a negative optical power front lens group; The seventh lens (7) and the eighth lens (8) constitute a positive optical power rear lens group; An aperture stop is provided between the fifth lens (5) and the sixth lens (6); The eighth lens (8) is a positive power lens with at least one aspherical surface; The negative optical power front lens group is used to expand the angle of the incident beam, and the positive optical power rear lens group is used to converge the beam to form an anti-long-distance optical structure. The RMS radius of the optical transfer function of the observation objective lens in the on-axis field of view is less than 10µm, and the RMS radius in the full field of view is smaller than the pixel size, so as to meet the resolution requirements of low-light night vision imaging.

2. The large field-of-view, large aperture low-light night vision objective lens according to claim 1, characterized in that, The eighth lens (8) has at least one optical surface with an even-order aspherical structure, which is used to correct spherical aberration, coma and astigmatism generated by the system.

3. The large field-of-view, large aperture low-light night vision objective lens according to claim 1, characterized in that, The observation objective lens adopts a thermal optical structure combining glass and plastic lenses; Plastic lenses utilize their thermo-optical coefficient to participate in temperature compensation, while glass lenses are used to maintain the optical stability of the system.

4. The large field-of-view, large aperture low-light night vision objective lens according to claim 3, characterized in that, The third lens (3) and the sixth lens (6) are made of plastic optical material; The first lens (1), the second lens (2), the fourth lens (4), the fifth lens (5), the seventh lens (7), and the eighth lens (8) are made of glass optical material.

5. The large field-of-view, large aperture low-light night vision objective lens according to claim 1, characterized in that, The observation objective lens meets the following optical parameters: Focal length is 10mm to 25mm; The relative aperture is no greater than 1.

5. The field of view is not less than 50°.

6. The large field-of-view, large aperture low-light night vision objective lens according to claim 5, characterized in that, The focal length of the observation objective is 16.5 mm; The F-number is 1.2; The field of view is 60°; The total optical length is less than 40mm.

7. The large field-of-view, large aperture low-light night vision objective lens according to claim 1, characterized in that, The aperture is positioned between the fifth lens (5) and the sixth lens (6) to control the effective aperture and the principal ray angle of the system. The observation objective lens has a full field-of-view distortion of less than 3% and a full field-of-view relative illumination of greater than 40%.

8. The large field-of-view, large aperture low-light night vision objective lens according to claim 1, characterized in that, At a 0° field of view on the axis, the RMS radius of the observation objective is 4.815µm; The RMS radius at a 15° off-axis field of view is 4.060µm; The RMS radius at a 30° field of view is 8.626µm.

9. A design method for designing the large field-of-view, large aperture low-light night vision objective lens according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Determine the objective lens focal length, relative aperture, and initial optical structure based on the field of view and light transmission requirements of the low-light night vision system; S2. Establish a reverse telephoto optical system consisting of a negative optical power front lens group and a positive optical power rear lens group; S3. By configuring glass lenses and plastic lenses with different thermo-optical properties, the changes in optical power caused by temperature changes can be mutually compensated. S4. Correct system aberrations by setting aspherical lenses; S5. By optimizing the lens power distribution, aperture position, and lens spacing, the system meets the imaging quality requirements.

10. The design method of the large field-of-view, large aperture low-light night vision objective lens according to claim 9, characterized in that: By matching the thermal characteristics of the glass lens and the plastic lens, the observation objective lens can maintain stable imaging within an ambient temperature range of -40℃ to 65℃, and the focal length change is less than 0.05mm.

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