GB2148663A

GB2148663A - An afocal thermal image device

Info

Publication number: GB2148663A
Application number: GB08426121A
Authority: GB
Inventors: Siegfried Roth
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1983-10-22
Filing date: 1984-10-16
Publication date: 1985-05-30
Also published as: DE3338496A1; DE3338496C2; FR2553903A1; FR2553903B1; GB2148663B; GB8426121D0

Abstract

An afocal thermal image device 3, which is an accessory for a sight 1, comprises an image pick-up part 3.1 in the infra-red for generating electrical image signals and an image reproduction part 3.2 connected thereto for producing a visible image. The pick-up part 3.1 comprises an input optical system, e.g. lens 6, a scanning device 9 and a detector device 10. The reproduction part 3.2 comprises a cathode-ray tube 11 and an output optical system, e.g. lens 13. Axis harmonisation of the two parts 3.1 and 3.2 is checked and accomplished by shifting the image in the cathode-ray tube 11 until a locating mark 7 defining the optical axis of the pick-up part 3.1, which mark appears on the screen, is in register with a further locating mark 12 defining the optical axis of the reproduction part 3.2, which mark is applied to the outside of the screen. <IMAGE>

Description

SPECIFICATION An afocal thermal image device This invention relates to an afocal thermal image device which is an accessoryforan optical device, for example a sight, said thermal image device having an image pick-up part in the infra-red for generating electrical image signals, which pick-up part comprises an input optical system, a scanning device and a detector device, and an image reproduction part, connected to the image pick-up part, for producing a visible image from the electrical image signals and including an output optical system, in which respect the image pick-up and reproduction parts together have a representation ratio of 1:1 and the optical axes thereof are aligned parallel.

Adevice ofthis kind is known from German Patent No. 2623399. In the known device it is assumed that axis harmonisation can be dispensed with when the optical axes ofthe pick-up part and of the reproduction part are parallel, since in these circumstances the afocal accessory device is adjustment-insensitive relative to the subsequently-arranged target sighting device. Such parallelism can indeed be produced by appropriatelyaccurate installation ofthe devices, but the maintenance ofthis state cannot be guaranteed particularlywhen there is rough use ofthe devices or in the event of largetemperature changes.

The object of the invention is, therefore, to provide an afocal thermal image device ofthe above-mentioned kind which makes possible problem-free axis harmonisation.

This object is achieved by a thermal image device of the above-mentioned kind characterised by the following features: a) the image pick-up part has in the image plane or in an intermediate image plane ofthe input optical system a locating mark which defines the optical axis thereof and which is effective in the infra-red, b) the image reproduction part has a cathode-ray tube, c) a locating markwhich defines the optical axis of the image reproduction part and which is effective in the visible is applied to the screen of the cathode-ray tube; and d) the locating mark ofthe image pick-up part,which appears on the screen as an image, is harmonised by electrical shifting of the image in the cathode-ray tube with the locating mark applied to the screen.

The axis harmonisation is effected in the case of the thermal image device in accordance with the invention in a simple manner by a known 'per se' shifting of theimageinthecathode-raytube untilthe locating mark appearing on the screen is brought into register with the locating mark applied on the outside of the screen. The image ofthe infra-red locating mark arranged in the beam path ofthe pick-up device appears on the screen and when this mark coincides exactly with the locating mark fixed on the cathoderay tube, the parallelism of the optical axes ofthe image pick-up and reproduction part is guaranteed.

Further locating marks which are in each case situated outside the optical axes may be provided and may be brought into registersothatthe exactness of the 1:1 representation can additionally be checked and, in the appropriate circumstances, corrected by electrical adjustment of the image size.

The invention will be described further, byway of example, with reference to the accompanying drawing in which the single Figure is a schematic diagram illustrating an exemplified embodiment ofthe afocal thermal image device of the invention.

In the diagram, a thermal image device 3 is arranged infrontofan outletapertureofa sight 1 having a directional or aiming mirror 2. The thermal image device 3 is rotatabletogetherwith the sight 1 or the directional mirror2 respectively, so that the optical axis 4 of the sight 1 is at all times parallel to the axis 5 of the thermal image device 3. The thermal image device 3 consists of an image pick-up part 3.1 and an image reproduction part 3.2. The image pick-up part 3.1 includes an infra-red optical system, e.g. lens 6, a locating mark7 which is arranged in an intermediate image plane and which is effective in the infra-red, a further infra-red optical system, e.g. lens 8, an optical scan device 9 and an infra-red detector 10.Upon use of a detectorsurfacearray, imagefield scanning would be effected in a purely electrical manner.

Conversion ofthe infra-red radiation picked up by the detector 10 into visible radiation is effected in the image reproduction part 3.2 which includes a cathoderay tube 11, a locating mark 12 which is applied to the screen thereof and which defines the optical axis 15, an output optical system, e.g. lens 13, and a partially transmissive ortranslucentoptical square orgonio- meter 14, by means of which the image ofthe cathode-ray tube is mirrored into the beam path 4 of the sight 1. Processing ofthe image signals of the detector 10 into visual signals is effected in known 'per se' manner and is therefore not explained in more detail. The optical axes 5 and 15 of the image pick-up and reproduction parts 3.1 and 3.2 are aligned parallel to one another.

The IR locating mark7 which determines the optical axis 5, and thus the image centre, is represented on the detector 10, together with the area detected by the IR-optical system 6, and thus appears on the screen of the cathode-ray tube 11 by transferto the cathode-ray tube 11. Afurther locating mark 12, which defines the optical axis ofthe image reproduction part 3.2, is fixed to the screen of the cathode-raytube 11. By comparing this mark 12 with the image mark (equal to the representation of the IR-locating mark 7) appearing in the image the axis harmonisation can be checked.

Since the image of the cathode-ray tube 11 can be shifted within the image plane by appropriate deflecting voltages, both locating marks 7, 12 can be brought into registerandthus axis harmonisation can be obtained.

An important additional criterion for axis harmonisation compared to other devices is that the image pick-up and reproduction part 3.1 and 3.2 have a representation ratio of 1: 1. This can also be checked, and in the appropriate circumstances adjusted, by having a further locating mark 7', in addition to the IR-mark7, arranged, for example, in an image corner, which mark corresponds with an appropriate locating mark 12' on the screen of the cathode-ray tube 11.

Afterthe locating marks 7 and 12 have been brought into register, the image ofthe mark 7' can also be brought into register with the mark 12' applied to the screen by electroniovariation of the image size on the screen. Thus exact maintenance ofthe representation ratio is guaranteed.

Claims

1. An afocal thermal image device which is an accessoryforan optical device, for example a sight, said thermal image device having an image pick-up part in the infra-red for generating electrical image signals, which pick-up part comprises an input optical system, a scanning device and a detector device, and an image reproduction part, connected to the image pick-up part, for producing a visible image from the electrical image signals and including an output optical system, in which respect the image pick-up and reproduction parts together have a representation ratio of 1:1 and the optical axesthereofare aligned parallel, characterised by the following features:: a) the image pick-up part has in the image plane or in an intermediate image planeofthe input optical system a locating mark which defines the optical axis thereof and which is effective in the infra-red, b) the image reproduction part has a cathode-ray tube, c) a locating mark which defines the optical axis of the image reproduction part and which is effective in the visible is applied to the screen of the cathode ray tube; and d) the locating mark of the image pick-up part, which appears on the screen as an image, is harmonised by electrical shifting ofthe image in the cathode-raytube with the locating mark applied to the screen.

2. An afocal thermal image device as claimed in claim 1, characterised in that in addition to the locating marks defining the optical axes of the image pick-up and reproduction parts, at least one further locating mark is provided outside each respective optical axis, which marks are harmonised with each other.

3. An afocal thermal image device substantiallyas hereinbefore described with reference to and as illustrated bythe accompanying drawing.