RU2754310C1 - Infrared system with three fields of view - Google Patents

Abstract

FIELD: optical instrumentation.SUBSTANCE: invention relates to the field of optical instrumentation and relates to an infrared system with three fields of view. The system contains a focusing lens, a projection lens and a photodetector with a cooled diaphragm. The focusing lens consists of a first component sequentially located along the optical axis, containing a positive and negative convex-concave lens, a second component containing a biconcave lens, and a third component containing a positive convex-concave lens. The projection lens consists of a first and second positive concave-convex lens and a third positive convex-concave lens. The second and third components are installed with the ability to move the lenses along the optical axis independently of each other. All lenses are aspherical.EFFECT: invention decreases the tele-shortening coefficient and the amount of movement of the second movable component.1 cl, 2 dwg, 4 tbl

Description

The invention relates to infrared optical systems and can be used in thermal imagers built on the basis of cooled matrix detectors of thermal radiation.

Known invention under the patent RU 2400784 C1, IPC ⁷ G02B 13/14, publ. 09/27/2010 The essence of the known technical solution is an infrared lens with two fields of view and a remote aperture diaphragm, located between the last component of the lens and the image plane, containing optically coupled first and last positive components located along the path of the rays and a movable component located between them, including negative and positive lenses, which have two fixed positions on the optical axis for changing fields of view; the first component is made in the form of two meniscus facing the concave side of the image plane, the last component includes two positive meniscus facing the convex sides to each other, and a negative meniscus facing the concave side to the image plane, and in the first component the first meniscus is positive, the second - negative, after the first positive component, a movable negative meniscus is introduced, facing the convex side to the image plane, having two fixed positions on the optical axis, while the distances between the vertices of the refracting surfaces of the movable negative meniscus and the movable component are different in each of the two fixed provisions; the movable component is made positive, a negative meniscus is inserted into it, facing the convex side to the image plane, located close to the negative lens of this component, a negative meniscus is inserted into the last component, located close to the positive meniscus of this component, all refractive surfaces of the infrared lens are spherical.

The lens operates in the spectral range of 7.7-10.3 μm and has the following characteristics: relative aperture 1: 2, maximum focal length ƒ ' _max = 210 mm, minimum focal length ƒ' _min = 70 mm, lens length L = 290 mm ...

The disadvantages of this infrared lens are the small multiplicity of changes in the focal length M = ƒ ' _max / ƒ' _min = 3 ^x and a high tele-shortening ratio T _L = L / ƒ ' _max = 1.38.

The closest to the claimed technical solution in terms of the combination of essential features and purpose is an infrared optical system with three fields of view, described in patent CN 103064184 A, IPC ⁷ G02B 27/00, 7/04, publ. 12.12.2012, which includes a focusing lens, consisting of a first component sequentially located along the optical axis, containing a positive convex-concave lens, a second movable component, which includes a biconcave and a negative convex-concave lens, a third movable component, consisting of a biconvex lens, a fourth component containing a negative concave-convex lens, a system of breaking mirrors, a projection lens consisting of sequentially arranged along the optical axis of the first and second convex-concave positive lenses and the third convex-concave negative lens, and a photodetector with a cooled diaphragm.

The system operates in the spectral range of 8-12 microns and has the following characteristics: relative aperture 1: 2, 1: 3, 1: 4; ƒ ' _max varies from 250 to 480 mm, ƒ' _cp - from 100 to 200 mm, ƒ ' _min - from 10 to 30 mm. The compactness of the system is ensured by the use of two breaking mirrors.

The description shows the version of the system with a relative opening of 1: 2, for ƒ ' _max = 250 mm, ƒ' _cp = 100 mm, ƒ ' _min = 30 mm. The length of the system from the first surface of the entrance lens to the image plane is L = 310 mm.

The disadvantages of this technical solution are the large length of the optical system, as a result of which the system has a high tele-shortening coefficient T _L = 1.24, and a large amount of movement of the second movable lens, equal to 42.4 mm.

The problem to be solved by the invention is to create an infrared system with three fields of view with a reduced tele-shortening ratio and the amount of movement of the second movable component.

The problem is solved by the fact that in an infrared system with three fields of view, containing a focusing lens, consisting of a first component sequentially located along the optical axis, containing a positive convex-concave lens, mounted with the ability to move along the optical axis of the second component containing a biconcave aspherical lens, and a third component containing a positive lens, a projection lens consisting of first and second positive lenses and a third convex-concave aspherical lens, as well as a photodetector with a cooled diaphragm, in the focusing lens in the first component, the first lens is made aspherical and an aspherical negative convexity is additionally introduced - concave lens, the lens of the third component is made convex-concave, aspherical, in the projection lens the first and second lenses are made aspherical concave-convex, the third lens is made positive.

Figure 1 shows an optical diagram of an infrared system with three fields of view;

Figure 2 shows an optical diagram showing the path of the rays in a narrow field of view;

Figure 3 shows an optical diagram showing the path of the rays in the middle field of view;

Figure 4 shows an optical diagram showing the path of the rays in a wide field of view.

The infrared system contains a focusing lens FO, consisting of sequentially located along the optical axis of the first component I, containing positive 1 and negative 2 convex-concave lenses, the second component II, containing a biconcave aspherical lens 3, and the third component III, containing a positive convex-concave lens 4. The projection lens PO, consists of the first 5 and second 6 positive concave-convex lenses, and the third 7 positive convex-concave lenses, as well as a photodetector 8 with a cooled diaphragm 9. The second II and third III components are installed with the ability to move the lenses along optical axis independently of each other.

Table 1 shows the main parameters of the inventive infrared system.

Table 2 shows the design parameters of an example of a specific implementation of the inventive infrared system.

d ₂ , d ₃ , d ₄ - variable air gaps.

Table 3 shows the values of variable air gaps.

Table 4 shows the main ratios performed in the claimed infrared system.

The infrared system with three fields of view works as follows.

Radiation from an infinitely distant object falls on the input lens (1), sequentially refracted by the lenses (2-4) of the focusing lens (FO), and is focused in the plane of the intermediate image. Further, the radiation is transferred by the lenses (5-7) of the projection lens (PO) into the plane of the sensitive elements of the photodetector (8). The exit pupil of the optical system coincides with the cooled diaphragm (9) of the photodetector (8). The third (3) and fourth (4) lenses of the second (II) and third (III) components, moving independently of each other along the optical axis in accordance with the values given in Table 3, provide a change in the focal length and field of view of the system. Figures 2-4 show the ray paths for narrow, medium and wide fields of view, respectively. The position of the plane of the intermediate image and the plane of the sensitive elements of the radiation receiver remain unchanged when the focal length is changed.

The optical system with three fields of view has a displacement of the third component equal to 10 mm, which is 4.2 times less than in the prototype. The length of the infrared system from the first surface to the image plane is 180 mm, which is 1.72 times less than in the prototype, as a result of which the teleshorting coefficient is 0.49, which is 2.55 times less than in the prototype.

The results obtained were achieved due to the design of the optical elements and the choice of the ratios for them, given in Table 4.

Thus, the implementation of the infrared system with three fields of view in accordance with the proposed technical solution provides a decrease in the tele-shortening coefficient and a decrease in the amount of movement of the second movable component.

Claims (1)

Infrared system with three fields of view, containing a focusing lens, consisting of a first component sequentially located along the optical axis, containing a positive convex-concave lens, mounted with the possibility of movement along the optical axis of a second component containing a biconcave aspherical lens, and a third component containing a positive lens , a projection lens consisting of the first and second positive lenses and the third convex-concave aspherical lens, as well as a photodetector with a cooled diaphragm, characterized in that in the focusing lens in the first component the first lens is made aspherical and an aspherical negative convex-concave lens, the lens of the third component is made convex-concave, aspherical, in the projection lens the first and second lenses are made aspherical concave-convex, the third lens is made positive.

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