RU2614167C1 - Optical system of thermal imaging device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: optical system consists of the input object lens sequentially arranged along the optical axis, forming an intermediate image and including the first positive, the second negative and the third positive convex-concave lenses of the projection object lens comprising the first bi-convex, the second negative concavo-convex and the third positive convexo-concave lens, and the photodetector with a cooled diaphragm.

EFFECT: improving the quality of the system image in the entire view field maintaining the size and reducing weight.

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Description

The invention relates to infrared optical systems and can be used to create thermal imaging devices for various purposes with cooled matrix photodetectors.

A known optical system for thermal imaging devices (see patent for the invention RU 2449328 A, IPC ⁷ G02B 13/14, 23/12, publ. 04/27/2010), containing an input lens of two lenses and a projection lens of five lenses, this focal length f is 60 mm.

An optical system for thermal imaging devices is also known (see patent for invention RU 2338227 C1, IPC7 G02B 13/14, 9/64, publ. 10.11.2008), containing an input lens of three lenses and a projection lens of four lenses, when this focal length f is 150 mm.

The disadvantage of these systems is the small value of the focal length.

The closest in technical essence to the claimed optical system adopted for the prototype is the optical system of a thermal imaging device (see patent for invention RU 2525463 U1, IPC G02B 13/14, 13/16, 9/64, published on 08/20/2014 ), consisting of an input lens located along the optical axis that forms an intermediate image and contains the first negative and second positive convex-concave lenses and the third negative concave-convex lens, a projection lens containing the first positive and second negative NLRB-convex lens, a positive third convex-concave lens and a positive fourth concave-convex lens, and photodetector. The optical system operates with a relative aperture of 1: 4, the focal length of the lens f = 230 mm, the length L = 159.7 mm, and the tele-shortening factor T _L = L / f = 0.69. In the given design parameters of an example of a specific embodiment of the system, there are no data on lens materials. Given the limited range of optical materials used in the infrared region, obtaining the claimed system characteristics is possible only when the first and third lenses of the input lens and the second and fourth lenses of the projection lens are made from Germany, and the second lenses of the input lens, the first and third lenses of the projection lens are made of silicon . With this embodiment, the mass of the optical elements of the entire system m is 270 g, and the mass of the input lens m _I is 263 g due to the presence of two large diameter and thick germanium lenses in it. In the described system, the design of the input lens provides high image quality in the center of the field of view due to the implementation of the first component of two lenses with a larger number of correction parameters. The design of the third lens does not allow to provide good image quality over the entire field of view. For this particular embodiment, the energy concentration in a circle with a diameter of 30 μm is 75% in the center of the field of view, 66% in the middle, and 25% at the edge (with an image size of 12 mm diagonally).

The problem to which the invention is directed, is to improve the image quality of the system in the entire field of view while maintaining dimensions and reducing weight.

This goal is achieved by the fact that in the optical system of a thermal imaging device, consisting of a sequentially arranged along the optical axis of the input lens, forming an intermediate image and containing the first and second convex-concave and third lenses, a projection lens containing the first positive, second negative concave-convex and the third positive convex-concave lens, and a photodetector, in the input lens, the first lens is positive, the second is negative and three your lens is positive convex-concave; in the projection lens, the first lens is biconvex.

The figure 1 presents a diagram of the optical system of a thermal imaging device.

The figure 2 presents graphs of the function of the energy concentration (FFE) of the system according to the field of view in a scattering circle with a diameter of 30 μm.

The optical system consists of a sequentially located along the optical axis of the input lens I, containing the first positive 1, the second negative 2 and the third positive 3 convex-concave lenses, the projection lens II, containing the first biconvex lens 4, the second negative concave-convex lens 5 and the third positive convex-concave lens 6, and a photodetector 7 with a cooled diaphragm 8.

Table 1 shows the technical characteristics of a system operating in the mid-infrared range of the spectrum (3.0-5.0 microns).

Table 2 shows the design parameters of an example of a specific optical system.

The optical system operates as follows. The radiation from an infinitely distant object passes through the lenses 1-3 of the input lens I and focuses in the plane of the intermediate image, then passes through the lenses 4-6 of the projection lens II and enters the photodetector 7, in the plane of the sensitive elements of which an image is formed, while the cooled diaphragm 8 of the photodetector 7 performs the function of the aperture diaphragm of the system.

The optical system of a thermal imaging device works with a relative aperture of 1: 4, focal length f _max = 230 mm, length L = 161 mm. The total mass of the optical elements m = 82 g, while the mass of the input lens is m _I = 77 g.

From the graph shown in figure 2, it follows that the optical system provides high image quality within the entire field of view. The energy concentration in a circle with a diameter of 30 μm is 75% in the center of the field of view, 71% in the middle, and 50% at the edge (with an image size of 12 mm diagonally). At the same time, the mass of the optical elements of the system is 3.3 times less than in the prototype.

Thus, the implementation of the optical system of the thermal imaging device in accordance with the proposed technical solution allows to ensure high image quality within the entire field of view while maintaining overall dimensions and a significant reduction in the mass of its optical elements.

Claims (1)

An optical system of a thermal imaging device, consisting of a sequentially located along the optical axis of the input lens forming an intermediate image and containing the first and second convex-concave and third lenses, a projection lens containing the first positive, second negative concave-convex and third positive convex-concave lenses and a photodetector, characterized in that in the input lens, the first lens is positive, the second is negative and the third lens is ene positive convexo-concave first lens in the projection lens is formed of a biconvex.

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