RU208115U1 - OPTICAL SYSTEM OF THERMAL IMAGING DEVICE WITH TWO FIELDS OF VIEW - Google Patents

Abstract

The utility model relates to infrared optical systems and can be used to create thermal imaging devices for various purposes with cooled matrix photodetectors. the third positive concave-convex lens, the second component containing the first negative concave-convex, the second biconvex and the third negative concave-convex lens, the third component containing the first biconvex, the second negative concave-convex and the third positive convex-concave lens, the fourth component, containing two positive lenses, and a photodetector with a cooled diaphragm. The second and third lenses of the first component are installed with the possibility of joint movement along the optical axis. The second and fourth components are installed with the possibility of alternate input-output into the optical path in the space between the first and third components. By providing the necessary defocusing of the cold radiation of the photodetector reflected from the optical surfaces in the calibration mode and in the operating mode, the probability of detecting and recognizing objects increases while maintaining the compactness of the optical system of a thermal imaging device with two fields of view. 3 silt, 3 tab.

Description

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

Known optical system (see patent US 8446472, IPC ⁷ H04N 5/33, publ. 05/21/2013), containing a four-lens input lens and a three-lens projection lens. The system operates in at least three modes: two modes of observation (detection and recognition) and calibration (alignment of the inhomogeneity of the sensitive elements), the switching of which is carried out by moving two optical elements of the input lens along the optical axis, while the maximum focal length f ' _max is 132 mm, the minimum f ' _min is 27 mm, the relative aperture is 1: 3, the length of the system from the first surface to the image plane is L> 160 mm, with the tele-shortening factor T _L = L / f' _max > 1.2.

The disadvantages of this system are a short focal length, a large teleshorting ratio and the inability to quickly switch modes.

Also known is an optical system for thermal imaging devices (see patent RU 2449328, IPC ⁷ G02B 13/14, G02B 23/12, publ. 04/27/2012), containing a two-lens input lens, a five-lens projection lens and a single-lens defocusing element. The system operates in two modes: observation and calibration. The calibration mode is carried out by introducing a defocusing element into the optical path in the space between the input and projection lenses, which makes it possible to transfer the image plane to the plane of the cooled diaphragm. The focal length of the system f 'is 60 mm, the relative aperture is 1: 3, the length L> 150 mm, while the tele-shortening factor T _L = L / f'> 2.5.

The disadvantages of this system are the presence of only one observation mode, a short focal length, and a large tele-shortening ratio.

The closest in technical essence to the claimed optical system, adopted as a prototype, is the optical system of a thermal imaging device with two fields of view (see patent for invention RU 2608395, IPC ⁷ G02B 13/14, G02B 15/02 publ. 18.01.2017. ), consisting of located along the optical axis of the first component containing the first positive, second negative and third positive convex-concave lenses, the second component containing the first and third negative concave-convex lenses and the second biconvex lens, the third component containing the first biconvex lens, a second negative concave-convex lens; and a third positive convex-concave lens; and a photodetector. The second and third lenses of the first component are mounted with the possibility of joint movement along the optical axis. The optical system operates in two observation modes, the switching of which is carried out by input-output of the second component into the optical path in the space between the first and third components, while the maximum focal length f ' _max is 230 mm, the minimum f' _min is 33.5 mm, the relative hole 1: 4. The length of the system from the first surface to the image plane is L = 161 mm, i.e. tele-shortening coefficient T _L = L / f ' _max = 0.7, which allows to ensure the compactness of the thermal imaging device as a whole. The disadvantages of the system include its design, which does not provide for operation in the calibration mode and does not provide the necessary defocusing of the cold radiation of the photodetector reflected from the optical surfaces, both in the calibration mode and in the operating mode, which negatively affects the probability of object detection and recognition.

The task to be solved by the utility model is to increase the probability of detection and recognition of objects by the optical system of a thermal imaging device with two fields of view by providing the necessary defocusing of the cold radiation of the photodetector reflected from optical surfaces both in the calibration mode and in the operating mode while maintaining compactness ...

This goal is achieved by the fact that in the optical system of a thermal imaging device with two fields of view, consisting of the first component located along the optical axis, containing the first positive convex-concave lens, and the second negative and third positive lenses installed with the ability to move along the optical axis, the second component installed with the possibility of input-output into the optical path and containing the first negative concave-convex lens, the second biconvex lens and the third negative concave-convex lens, the third component containing the first biconvex lens, the second negative concave-convex lens and the third positive convex-concave lens lens, and a photodetector, in accordance with the utility model in the first component, the second and third lenses are made concave-convex, and a fourth component is additionally introduced, installed with the possibility of input-output into the optical path in the space between the first and third components and containing two positive lenses.

Figure 1 shows a diagram of the optical system of a thermal imaging device with two fields of view.

Figure 2 shows a diagram of the optical system of a thermal imaging device with two fields of view in the calibration mode.

Figure 3 shows the graphs of the distribution of the relative illumination E by cold radiation of the photodetector, reflected from all surfaces of the optical parts, along the plane of the sensitive elements (the origin corresponds to the center of the plane) in the prototype system and the claimed system.

The optical system consists of the first component I located along the optical axis, containing the first positive convex-concave lens 1, the second negative 2 and the third positive 3 concave-convex lenses, the second component II containing the first negative concave-convex lens 4, the second biconvex lens 5 and a third negative concave-convex lens 6, a third component III containing a first biconvex lens 7, a second negative concave-convex lens 8 and a third positive convex-concave lens 9, a fourth component IV containing two positive lenses 10 and 11, and a photodetector 12 with cooled diaphragm! 3. Lenses 2 and 3 of the first component I are installed with the possibility of joint movement along the optical axis. The second II and fourth IV components are installed with the possibility of alternate input-output into the optical path in the space between the first I and third III components.

Table 1 shows the technical characteristics of the system operating in the mid-infrared range of the spectrum.

Table 2.1 shows the design parameters of the system, and Table 2.2 - design parameters of the fourth component IV.

In a narrow field of view corresponding to the maximum focal length, the optical system works as follows: radiation from an infinitely distant object passes through lenses 1-3 of the first component I and is focused in the plane of the intermediate image, then passes through lenses 7-9 of the third component III and enters photodetector 12, in the plane of the sensitive elements of which an image is formed, while the cooled diaphragm 13 of the photodetector 12 performs the function of the aperture diaphragm of the system.

In a wide field of view, corresponding to the minimum focal length, radiation passes through lenses 1-3 of the first I and 4-6 of the second II components and is focused in the same plane of the intermediate image, then passes through lenses 7-9 of the third component III and enters the photodetector 12, the image is formed in the same plane of the sensitive elements and the cooled diaphragm 13 of the photodetector 12 is the aperture diaphragm of the system.

The change in the field of view (focal length) of the optical system is carried out by the input-output of the second component II into the optical path in the space between the first I and third III components.

To compensate for the defocusing of the image with a change in temperature, joint movement along the optical axis of lenses 2 and 3 of the first component 1 is provided.

In the calibration mode, the fourth component IV is introduced in the space between the first I and the third III components. Radiation passes through lenses 1-3 of the first I, 10-11 of the fourth IV and 7-9 of the third III components and is focused in the plane of the cooled diaphragm 13. The photodetector 12 receives radiation defocused over the entire area of the sensitive elements, thereby forming a uniform illumination of this area ... Thereafter, the fourth component IV is removed from the optical path, and the system operates as usual.

In the presented diagram of the path of the rays in the calibration mode (figure 2), it can be seen that as a result of the combined use of lenses 2 and 3 of the first component I, which differ in design from the prototype, and two introduced positive lenses 10 and 11 of the fourth component IV, the area of the sensitive elements of the photodetector device 12 is completely illuminated.

In addition, due to the chosen design, complete defocusing of cold radiation in the region of the sensitive elements of the photodetector in the operating mode is ensured. From the examples shown in FIG. 3 graphs of the illumination distribution of the image plane of the prototype (a) and the claimed system (b), it can be seen that in the system selected as a prototype, there is a sharp difference in illumination due to insufficient defocusing of cold radiation by the lens surfaces, which leads to the presence of a defect in the form of a dark or a light circle in the center of the image, and in the inventive system the curve has a smooth appearance without sharp drops, which indicates the formation of an image without a defect, which increases the likelihood of detecting and recognizing objects of observation.

The values of the maximum focal length of 219.8 mm and the length of 161.85 mm indicated in the table provide the tele-shortening coefficient T _L = L / f ' _max = 0.73, which indicates the compactness of the claimed system.

Thus, the implementation of the optical system of a thermal imaging device with two fields of view in accordance with the proposed technical solution makes it possible to increase the probability of detection and recognition of objects by providing the necessary defocusing of the cold radiation of the photodetector both in the calibration mode and in the operating mode while maintaining compactness.

Claims (1)

Optical system of a thermal imaging device with two fields of view, consisting of a first component located along the optical axis, containing a first positive convex-concave lens, and a second negative and third positive lens installed with the ability to move along the optical axis, a second component installed with the possibility of input-output into the optical tract and containing a first negative concave-convex lens, a second biconvex lens and a third negative concave-convex lens, a third component containing a first biconvex lens, a second negative concave-convex lens and a third positive convex-concave lens, and a photoconvex lens, and in that in the first component the second and third lenses are made concave-convex, and the fourth component is additionally introduced, installed with the possibility of input-output into the optical path in the space between the first and third components, containing two positive lenses.

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