RU2525463C1 - Optical system for thermal imaging device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: optical system for a thermal imaging device comprises, arranged in series on the beam path, an input lens which constructs a real intermediate image and comprises a negative and a positive meniscus, and a projection lens mounted in front of a photodetector and comprising, arranged in series on the beam path, a first meniscus, a second negative meniscus whose convex side faces the photodetector, a third positive meniscus whose convex side faces the object space, and a fourth positive meniscus whose convex side faces the photodetector. In the input lens, the negative meniscus lies first on the beam path and after the positive meniscus there is an additional negative meniscus whose convex side faces the real intermediate image. In the projection lens, the first meniscus is positive and its convex side faces the photodetector, and the fourth meniscus is located between the third meniscus of the projection lens and the photodetector.

EFFECT: high resolution of the optical system of the thermal imaging device while maintaining compactness thereof.

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Description

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

Known optical system of a thermal imager with a cooled photodetector (patent EP No. 1684105 A1, publ. 07/27/2006), containing an input lens that builds a valid intermediate image, and a projection lens that transfers the intermediate image to the plane of the sensing elements of the matrix photodetector.

The disadvantage of this optical system is the large number of lenses of significant diameter in the input lens, which leads to an increase in the mass of the optical system, and a large assortment of materials from which the lenses of the optical system are made.

An optical system for thermal imaging devices was taken as the closest to the claimed technical solution (RF patent No. 2449328, IPC G02B 13/14, G02B 23/12, publ. 04/27/12, paragraphs 1 and 4 of the formula), containing at least , an input lens that builds a valid intermediate image, including a positive meniscus convex to the space of objects sequentially located along the rays, a negative meniscus convex to the space of objects, and a projection lens that transfers the intermediate about the image in the plane of the arrangement of the sensitive elements of the photodetector, made as a part of sequentially located along the rays of the negative meniscus, convex to the space of objects, a biconvex lens, negative meniscus, convex to the image plane, positive meniscus, convex to the image plane and positive meniscus convex to the space of objects.

The disadvantage of this technical solution is the significant total length of the optical system, equal to 150 mm with a small equivalent focal length of 60 mm, which means the low resolution of this optical system with dimensions significantly exceeding its focal length. An indicator of shortening the length K in the system (Theory of optical systems. A textbook for high schools / BN Begunov et al. M: Mechanical Engineering, 1981, p.266), characterized by the ratio of the length from the first surface to the focal plane to the focal length, in the prototype is K = 2.5.

The task to which the invention is directed is to increase the resolution of the optical system of a thermal imaging device while maintaining its compactness.

The problem is solved in that in the optical system of a thermal imaging device containing an input lens sequentially located along the rays, constructing a valid intermediate image and containing negative and positive menisci, and a projection lens mounted in front of the photodetector and containing the first meniscus sequentially installed along the rays, the second negative meniscus convex to the photodetector, the third positive meniscus convex to the space of objects, and the fourth positive meniscus, convex to the photodetector, characterized in that the negative meniscus is placed first in the input lens along the rays, and an additional negative meniscus is introduced behind the positive meniscus, which is convex to the plane of the actual intermediate image, in the projection lens the first meniscus is made positive and convex side is directed to the photodetector, and the fourth meniscus is located between the third meniscus ektsionnogo lens and the photodetecting device.

Figure 1 shows a diagram of the optical system of a thermal imaging device. The optical system of the thermal imaging device contains an input lens sequentially located along the rays, constructing a valid intermediate image containing a negative meniscus 1, convex to the space of objects, a positive meniscus 2, convex to the space of objects, a negative meniscus 3, convex to the plane of the actual intermediate image 4, and a projection lens mounted in front of the photodetector 5, comprising sequentially mounting along the rays of the first positive meniscus 6, the second negative meniscus 7, convex to the photodetector 5, the third positive meniscus 8, convex to the space of objects, and the fourth positive meniscus 9, convex to the photodetector 5, and located between the third meniscus 8 of the projection lens and photodetector 5. The input window 10 is part of the design of the photodetector 5, the cooled diaphragm 11 limits the aperture of the rays incident on the matrix in sensitive elements 12 of the photodetector unit 5, and the real intermediate image plane 4 is located between the negative meniscus lens 3 and the first input meniscus projection lens 6.

The optical design works as follows. An input lens containing menisci 1, 2, and 3 builds a valid intermediate image in plane 4, a projection lens containing menisci 6, 7, 8, and 9 transfers it to the image plane that matches the sensor array 12 of the photodetector 5.

A possible variant of such a compact optical system may have the following parameters shown in the table.

Position Radii, mm Light diameter mm Thickness mm one r ₁ = 92.26 66.0 7.0 r ₂ = 68.55 59.5 Air gap 2.0 2 r ₃ = 70.31 61.3 10.0 r ₄ = 183.65 59.0 Air gap 24.0 3 r ₅ = -148.94 40.2 6.0 r ₆ = -187.93 35.8 Air gap 69.2 6 r ₇ = -80.17 12.8 2.0 r ₈ = -18.75 12.8 Air gap 1.0 7 r ₉ = -15.996 12.4 3.0 r ₁₀ = -22.39 14.0 Air gap 1.0 8 r ₁₁ = 15.382 13.4 3.0 r ₁₂ = 19.861 11.8 Air gap 3.0 9 r ₁₃ = -15.066 10.6 2.0 r ₁₄ = -16.255 11.4 Air gap 2.5 Protective window 10 one The distance to the plane of the sensing elements 12 23

Thus, the implementation of the optical system in accordance with the formula of the claimed materials allows to increase the resolution by increasing the focal length up to 230 mm from 60 mm from the closest analogue with a slight increase in the total length of the optical system from 150 mm in the analogue to 159.7 mm in the claimed device. The length shortening indicator in the claimed device is K = 0.694.

Claims (1)

An optical system of a thermal imaging device, containing an input lens sequentially located along the rays, building a valid intermediate image and containing negative and positive menisci, and a projection lens mounted in front of the photodetector and containing the first meniscus and the second negative meniscus, convex to photodetector, the third positive meniscus, convex to the space of objects, and the fourth a false meniscus convex to the photodetector, characterized in that the negative meniscus is placed first in the input lens in the input lens, and an additional negative meniscus is introduced behind the positive meniscus, convex to the plane of the actual intermediate image, the first meniscus is positive and convex in the projection lens side facing the photodetector, and the fourth meniscus is located between the third meniscus of the projection lens and the photodetector a triple.