A bifocal infrared night vision lens

Abstract

This invention relates to the optical system design of an infrared night vision lens, specifically a dual-focal infrared night vision lens. The lens consists of four front lenses forming a focusless system, and three rear lenses combined with the front lenses to form a night vision imaging system with a fixed focal length, thus making it more suitable for infrared night vision thermal imaging applications. The lens system includes a focusless telescope system consisting of four front lenses. The focusless telescope system includes, in sequence, a large-aperture long-focal-length first positive lens (2), a long-focal-length second positive lens (3), a first negative lens (4), and a second negative lens (5), and also includes a positive lens group consisting of three rear lenses. The positive lens group includes, in sequence, a third positive lens (7), a fourth positive lens (8), and a fifth positive lens (9), wherein the fourth positive lens (8) and the fifth positive lens (9) are specifically meniscus lenses with two surfaces having the same radius of curvature.

Description

Technical Field

[0001] This invention relates to the optical system design of an infrared night vision lens, specifically a dual-focal infrared night vision lens. Background Technology

[0002] Visible light is the portion of the electromagnetic spectrum that the human eye can perceive. The average person can perceive electromagnetic waves with wavelengths between 400 and 760 nm, but some people can perceive electromagnetic waves with wavelengths between approximately 380 and 780 nm. Wavelengths beyond 780 nm include near-infrared, mid-infrared, and far-infrared.

[0003] In current CCTV surveillance systems, infrared technology plays an increasingly prominent role in nighttime monitoring. It's used not only in important institutions such as banks, oil depots, armories, libraries, cultural relics departments, and prisons, but also in general surveillance scenarios. Even residential CCTV systems utilize infrared cameras. This indicates that people have increasingly higher requirements for CCTV systems, demanding 24-hour continuous monitoring of important locations.

[0004] Night vision can be achieved using traditional visible light illumination, but this method is not concealed and will expose the target being monitored. Covert night vision surveillance utilizes infrared camera technology. Infrared camera technology is divided into passive infrared camera technology and active infrared camera technology.

[0005] Most infrared lenses currently designed primarily use the near-infrared spectrum, requiring the active emission of infrared light to achieve night vision monitoring. This is why we often see infrared light sources (some also using visible light sources) placed around cameras. In actual use, the image is clear during the day, but becomes blurry under infrared light conditions. Secondly, there are fewer designs for passive mid- and far-infrared lenses based on chalcogenide and germanium-based glass. Generally, these infrared lenses have a small field of view. Expanding the field of view reduces the lens resolution, resulting in poor contrast and image quality that does not meet requirements.

[0006] In conclusion, to address monitoring needs in certain special scenarios, it is particularly important to design a long-range infrared lens with a long focal length and clear imaging quality. Summary of the Invention

[0007] The purpose of this invention is to provide a dual-focal infrared night vision lens, in which the front four lenses form a focusless system, and the rear three lenses are combined with the front lenses to form a night vision imaging system with a fixed focal length, thus making it more suitable for infrared night vision thermal imaging applications.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a dual-focal infrared night vision lens, characterized in that it includes a focusless telescope system composed of four front-mounted lenses; the focusless telescope system sequentially includes a first positive lens with a large aperture and long focal length, a second positive lens with a long focal length, a first negative lens, and a second negative lens, and further includes a positive lens group composed of three rear-mounted lenses; the positive lens group sequentially includes a third positive lens, a fourth positive lens, and a fifth positive lens, wherein the fourth positive lens and the fifth positive lens are specifically meniscus lenses with two surfaces having the same radius of curvature.

[0009] Preferably, the focal length of the first positive lens is 269mm. <f2<270mm。

[0010] Preferably, the focal length of the second positive lens is 1510mm. <f3<150mm。

[0011] Preferably, the focal length of the first negative lens is -265mm. <f4<-264mm。

[0012] Preferably, the focal length of the second negative lens is -45mm. <f5<-44mm。

[0013] Preferably, the focal length of the third positive lens is 80mm. <f7<81mm。

[0014] Preferably, the focal length of the fourth positive lens is 3383mm. <f8<3384mm。

[0015] Preferably, the focal length of the fifth positive lens is 2463mm. <f9<2464mm。

[0016] Preferably, the combined focal length of the third, fourth, and fifth positive lenses is 74mm. <f789<75mm。

[0017] Preferably, a CCD or CMOS photoelectric imager can be installed at the imaging point behind the positive lens group.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The front telescope part of the dual-focal infrared night vision lens of the present invention has a large aperture and a large size. Considering the influence of aberrations, it adopts a Galilean structure design; the rear uses a positive lens group to compress the imaging surface, which compensates for the aberrations in the front and also optimizes the distortion problem caused by the large size, thus making it more suitable for optical lenses of infrared night vision thermal imaging systems. Attached Figure Description

[0019] Figure 1 This is a diagram of the optical structure of the present invention;

[0020] Figure 2 This is a graph of the MTF function of the present invention;

[0021] Figure 3 is the grid distortion diagram of the present invention;

[0022] Figure 4 is the diffraction energy circumcircle diagram of the present invention.

[0023] Description of the drawings: 1. Entrance pupil aperture; 2. First positive lens; 3. Second positive lens; 4. First negative lens; 5. Second negative lens; 6. Position symbol; 7. Third positive lens; 8. Fourth positive lens; 9. Fifth positive lens; 10. Imaging position. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] The lens designed by the present invention is applicable to the infrared band, with a wavelength range of 8 - 12 microns and a main wavelength of 10.2 microns; it includes a afocal telescopic system composed of four front lenses; the afocal telescopic system successively includes a first positive lens 2 with a large aperture and long focal length, a second positive lens 3 with a long focal length, a first negative lens 4, and a second negative lens 5, and also includes a positive lens group composed of three rear lenses; the positive lens group successively includes a third positive lens 7, a fourth positive lens 8, and a fifth positive lens 9, where the fourth positive lens 8 and the fifth positive lens 9 are specifically meniscus lenses with exactly the same curvature radii on both sides.

[0026] The focal length of the first positive lens 2 is 269mm < f2 < 270mm; the focal length of the second positive lens 3 is 1510mm < f3 < 150mm; the focal length of the first negative lens 4 is -265mm < f4 < -264mm; the focal length of the second negative lens 5 is -45mm < f5 < -44mm; for the position symbol 6, a scanning mirror or a reflecting mirror can be placed at this position as needed to change the optical path structure. The focal length of the third positive lens (7) is 80mm < f7 < 81mm; the focal length of the fourth positive lens 8 is 3383mm < f8 < 3384mm; the focal length of the fifth positive lens 9 is 2463mm < f9 < 2464mm; the combined focal length of the third positive lens 7, the fourth positive lens 8, and the fifth positive lens 9 is 74mm < f789 < 75mm.

[0027] A CCD or CMOS optoelectronic imager can be installed at the imaging position 10 behind the positive lens group.

[0028] Figure 1This is a schematic diagram of the invention. The diagram clearly shows that the front lens group (2, 3, 4, 5) forms a focalless telescope, and the rear lens group (7, 8, 9) further compresses the imaging beam to meet the imaging requirements. Figure 1 The medium aperture stop, also known as the entrance pupil diameter, is 228.6 mm and is placed to the left of the first lens. This is beneficial for controlling the beam and correcting distortion. Figure 1 The last imaging area 10 can be used to place imaging devices such as CCD or CMOS.

[0029] The front lens of this invention is designed based on the principle of Galileo's telescope, employing a separate positive and negative lens configuration, thus belonging to the category of telephoto lenses. The rear lens primarily functions to compress optics, ensuring it conforms to the requirements of the imaging plane, and can also correct distortion in infrared lenses, with a maximum grid distortion of 0.19%, fully meeting the design and usage requirements.

[0030] The parameters of the dual-focal infrared night vision lens of this invention include the thickness and spacing of each lens, the refractive index, radius of curvature, focal length F, and the refractive index of each lens material. Specific details are shown in Table 1 (Table 1 contains data on the lens surface and material refractive index of this system).

[0031]

[0032]

[0033] Table 1

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bifocal infrared night vision lens, characterized in that, The system includes a focusless telescope system consisting of four front-mounted lenses; the focusless telescope system includes, in sequence, a first positive lens (2) with a large aperture and long focal length, a second positive lens (3) with a long focal length, a first negative lens (4) and a second negative lens (5), and also includes a positive lens group consisting of three rear-mounted lenses; the positive lens group includes, in sequence, a third positive lens (7), a fourth positive lens (8) and a fifth positive lens (9), wherein the fourth positive lens (8) and the fifth positive lens (9) are specifically meniscus lenses with two surfaces having the same radius of curvature, the material of the fourth positive lens (8) is zinc selenide, and the material of the fifth positive lens (9) is germanium; The focal length of the first positive lens (2) is ; The focal length of the second positive lens (3) is ; The focal length of the first negative lens (4) is ; The focal length of the second negative lens (5) is ; The focal length of the third positive lens (7) is ; The focal length of the fourth positive lens (8) is ; The focal length of the fifth positive lens (9) is ; The combined focal length of the third positive lens (7), the fourth positive lens (8), and the fifth positive lens (9) is: .

2. The dual-focal infrared night vision lens as described in claim 1, characterized in that, A CCD or CMOS photoelectric imager is installed at the imaging point (10) behind the positive lens group.

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