GB1584556A

GB1584556A - Spectral converters

Info

Publication number: GB1584556A
Application number: GB2208677A
Authority: GB
Original assignee: Industrie Automation GmbH and Co
Current assignee: Industrie Automation GmbH and Co
Priority date: 1976-05-25
Filing date: 1977-05-25
Publication date: 1981-02-11
Also published as: NL189623B; NL7705783A; SE436664B; DE2623399C2; NL189623C; FR2366591A1; IT1115481B; DE2623399A1; FR2366591B1; CH612768A5; SE7705977L

Abstract

The attachment unit comprises a spectral converter for converting a thermal image into a visible image. An infrared image recording unit (1) is combined in the attachment unit with an image rendition unit (2) in such a way as to produce a linear magnification of 1:1. The parallel beam of the image rendition unit (2) is fed into the main device (4) in such a way that the thermal image of the attachment unit (5) is superimposed on the optical image of the main device (4) without any influence on the optical axis of the main device (4). The main device can be used with the attachment unit both at night and by day in the case of good and bad visibility. <IMAGE>

Description

(54) IMPROVEMENTS IN SPECTRAL CONVERTERS (71) We, INDUSTRIE AUTOMA TION GmbH & COMPANY, a German body corporate of P.O. Box 10 3029 Heidelberg, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to afocal spectral converters which are adopted for attachment to main sighting and aiming devices and which are for converting heat images into visible images.

Afocal attachments are known from geometrical optics, the purpose of which is to effect a change in enlargement. All these attachments cause a change in the direction of aim, unless the optical axis of the telescopic sight coincides with the optical axis of the afocal attachment. Only with a magnification of 1:1 and an incident ray parallel to the emergent ray does such an attachment not alter the direction of aim, even if the optical axis of the attachment does not coincide with the optical axis of the telescopic sight. In visible optics, however, attachments with a magnification of 1:1 are of no interest because they do not produce any optical effect.

It is an object of the invention to provide an afocal spectral converter as an attachment device of simple and light construction, wherein the incoming infrared rays are converted into visible rays which can be observed through the main device. The view through the main device should not be adversely affected in the course of this.

The present invention consists in an afocal spectral converter which is adapted for attachment to a main sighting and aiming device and which is for the conversion of a heat image into a visible image, wherein the converter comprises an infrared image pickup unit and an image-reproduction unit which together have a magnification of 1, the converter is adapted for attachment to the main device so that the optical axis of the image pick-up unit extends parallel to the optical axis of the main device and so that a parallel bundle of rays from the image reproduction unit is reflected into the main device withou disturbing the use of the main device with visible radiation.

In converters according to the invention, conversion from thermal into visible radiation may be effected with high efficiency on the principle of a frequency converter. As a result of the magnification of 1:1, the effect is achieved that, in the parallel path of rays, the heat image may correspond in its contours precisely to the visible image and can therefore be reflected in register with this.

The parallelism of the optical axis of the image pick-up unit with the optical axis of the main device renders it possible to reflect the parallel bundle of rays of the imagereproduction unit into the main device so that no adverse influencing of the main device is effected The principle of which the invention is based permits normal operation by day, the thermal image being reflected in on the same scale as the visible one and with the contours in register. Thus a mixed image results, in which the spectral lines red and green with their thermal image content are blended into the visible spectral range. In this case, the thermal image is adjustable in intensity. The mixed image combines the advantages of daytime vision with those of thermal vision. For example, optically camouflaged targets can easily be made out in the thermal range.

If the device is formed so that the optical axis of the reproduction unit extends parallel to the optical axis of the image pick-up unit, then a polygonal prism serving to pick up the thermal image can be mounted on a common shaft with the polygonal prism reproducing the visible image, thus rendering precisely synchronous scanning possible in both cases. The conversion of the heat signals picked up by a detector into an optical image can be carried out in known manner through one or more luminescent diodes.

Afocal attachments for changing the magnification are known from geometrical optics. All these attachments cause an alteration of the direction of aim unless the optical axis of the telescopic sight coincides with the optical axis of the afocal attachment.

Only with the magnification of 1:1 and when the incident rays and emergent rays are parallel does such an attachment not alter the direction of aim even if the optical axis of the attachment does not coincide with the optical axis of the main device.

Applying this basic idea to a heat image means that the image pick-up unit and the image-reproduction unit of a heat image device are adapted to one another so that the whole system has a magnification of 1:1 and the optical axis of the image pick-up unit extends parallel to that of the image reproduction unit.

Thus a reversal of the infrared bundle of rays entering at the angle into the plane of an infrared detector is effected on the same optical axis. After conversion of the infrared radiation into radiation visible to the eye through luminescent diodes, the rays leave the attached device (converter) at the same angle and can enter the entrance pupil of an optical sighting or aiming device in a suitable manner. Thus the condition for the case of entry into a parallax-free system is fulfilled, namely that the axis of the attachment extends parallel for the ray entrance and emergence and so is independent of the adjustment to the main device.

Therefore. the device only shows an offsetting of the field of vision in the heat image on observation through the sight of the main device without detracting from the accuracy of sighting, if the sight line of the main device does not coincide exactly with that of the attachment.

Naturally, in principle, an adaptation of the heat-image converter can also be effected in separate pupils. Then it would be necessary to ensure that the inner instrument angle of the main device was identical with the angle of the attached device for entrance and emergence of the rays.

With normal polygonal prisms, the line offset must be effected by means of an additional element, for example an oscillating mirror. The line offset can be effected more simply and easily by using a polygon with dihedral surfaces. Each surface of such a polygonal prism scans another line of the whole image so that during one revolution, the whole image is scanned from left to right and from top to bottom. By appropriate selection of the adjustable angle of the sides to the axis of the prism, it is also possible to produce a representation via a coarse-fine resolution. This means that the targets, which normally have a higher temperature than the background, appear coarse while the background is fine.

In order to be able to readjust the parallel position of the pick-up unit and of the reproduction unit of the device, if necessary, it is advisable for an element for the parallel adjustment to be disposed in one of the two optical channels.

The reflection of the heat image which has been made visible into the main device is effected through a spectral divider which, when the attached device is fitted, is disposed in front of the entrance pupil of the main device. This spectral divider is so constructed that it lets through rays of the visible range and reflects the rays originating from the luminescent diodes. As a result, the daytime vision through the main device is not hindered, but the rays coming from the attached device are reflected and reflected into the path of rays of the main device.' Thus the heat image which has been made visible is superimposed on the natural image observed through the main device.

Together with the main device, the attached device forms a whole combination which can be used both as a daytime sight and as a nighttime sight. Even during normal operation by day, the thermal image can be reflected into the visible one, on the same scale. With approaching dusk or in misty weather, the tracking of the target with the pure daytime sight is often suddenly disturbed so that the wish arises to introduce the nighttime sight. For this case, it is advisable if the attached device can be placed on the main device and secured thereto with a few movements of the hand.

It is therefore further proposed to equip the device with an easily detachable securing element for connection to the main device.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically a spectral converter according to the invention attached to a main aiming and sighting device; Figure 2 shows diagrammatically the optical construction of the converter of Figure 1; and Figure 3 shows the attachment of the converter of Figures 1 and 2 to a conventional observation and aiming device.

Referring to Figure 1, the converter consists of two units, a pick-up unit 1, in which infrared rays emitted by an object are scanned and conveyed to a detector, and a reproduction unit 2, in which rays emitted from luminescent diodes are combined to form an image and passed on. The dividing line 6 in Figure 1 represents an electronic system in which the infrared rays detected are converted into visible rays via a video signal and luminescent diodes.

The incoming infrared rays 17 are first reflected by a mirror 15 and then focussed by a group of lenses 11/21 before reaching the detector. The visible rays from the luminescent diodes are converted into parallel rays by a collimator and so reach a spectral divider 3, which reflects them into the path of visible rays from the object.

Both rays enter the main device through an exit pupil 32 and an entrance pupil 41. The optical system of the main device is designated 46. The beam splitter 3 is so constructed that it lets through the natural visible rays and reflects the rays coming from the luminescent diodes. Disposed opposite the exit pupil 32 is the entrance pupil 31 through which the visible rays can enter the attached device. In this manner, a heat image in which the different temperatures occurring at the observed object are displayed in various colours, is superimposed on the natural image which is detected via the main device. As a result of the magnification being 1:1, the two images are in register.

In Figure 2, the internal construction of the attached spectral converter is represented diagrammatically. The entrance objective is designated by 11. Reference numeral 12 designates a polygonal prism which is mounted together with a second polygonal prism 22 on a common shaft driven by a motor 15. As a result, a precisely synchronous rotary movement of the two polygonal prisms is achieved.

Disposed behind the polygonal prism 12 is a transformation optical system 13 from which the incoming infrared rays are conveyed to a detector 14. The conversion of the infrared rays received by the detector into visible rays is effected in known manner through video signal and luminescent diodes 24. The visible rays emerging from the luminescent diodes enter the polygonal prism 22, which reproduces the visible heat image, and then pass through the collimator 23 to a deflecting mirror 25. The deflecting mirror 25 reflects the rays and conveys them to the spectral divider, from which they are reflected into the path of visible rays entering directly into the main device in the manner described. The exit pupil 32 is provided for this purpose in the housing which surrounds the spectral divider 3.

Opposite the exit pupil 32 is the entrance pupil of the main device after passing through the spectral divider 3. There is a hole for test purposes in the beam splitter.

Figure 3 shows the attachment of the attached device 5 to the main device 4. For the parts already discussed, the same reference numerals apply as in the previous Figures. Disposed behind the entrance pupil 41 of the main device there is here a deflecting prism 42 which deflects the rays from the converter and the direct rays and conveys them to a second deflecting prism 43. After again being deflected by prism 43, the rays enter the eyepiece 44.

WHAT WE CLAIM IS: 1. An afocal spectral converter which is adapted for attachment to a main sighting and aiming device and which is for the conversion of a heat image into a visible image, wherein the converter comprises an infrared image pick-up unit and an imagereproduction unit which together have a magnification of 1, the converter is adapted for attachment to the main device so that the optical axis of the image pick-up unit extends parallel to the optical axis of the main device and so that a parallel bundle of rays from the image reproduction unit is reflected into the main device without disturbing the use of the main device with visible radiation.

2. A spectral converter as claimed in Claim 1, wherein the optical axis of the image reproduction unit extends parallel to the optical axis of the pick-up unit.

3. A spectral converter as claimed in Claim 1 or 2, wherein the pickup unit comprises a rotatable polygonal prism for effecting a cartesian scanning of the heat image, the reproduction unit comprises a polygonal prism for converting visible rays derived from electric signals delivered by the pick-up unit into a visible image, and both prisms are mounted on a common shaft which is driven by a common drive motor.

4. A spectral converter as claimed in Claim 1, 2 or 3, wherein each of the two polygonal prisms is a dihedral polygonal prism.

5. A spectral converter as claimed in any one of Claims 1 to 4 wherein an element for parallel adjustment is disposed in one of the two optical channels.

6. A spectral converter as claimed in any one of Claims 1 to 5, wherein a beam splitter or a spectral divider is disposed in the parallel path of rays of the image reproduction unit.

7. A spectral converter as claimed in any one of Claims 1 to 6, comprising an easily detachable attachment element for connecting the converter to the main device.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. from luminescent diodes are combined to form an image and passed on. The dividing line 6 in Figure 1 represents an electronic system in which the infrared rays detected are converted into visible rays via a video signal and luminescent diodes. The incoming infrared rays 17 are first reflected by a mirror 15 and then focussed by a group of lenses 11/21 before reaching the detector. The visible rays from the luminescent diodes are converted into parallel rays by a collimator and so reach a spectral divider 3, which reflects them into the path of visible rays from the object. Both rays enter the main device through an exit pupil 32 and an entrance pupil 41. The optical system of the main device is designated 46. The beam splitter 3 is so constructed that it lets through the natural visible rays and reflects the rays coming from the luminescent diodes. Disposed opposite the exit pupil 32 is the entrance pupil 31 through which the visible rays can enter the attached device. In this manner, a heat image in which the different temperatures occurring at the observed object are displayed in various colours, is superimposed on the natural image which is detected via the main device. As a result of the magnification being 1:1, the two images are in register. In Figure 2, the internal construction of the attached spectral converter is represented diagrammatically. The entrance objective is designated by 11. Reference numeral 12 designates a polygonal prism which is mounted together with a second polygonal prism 22 on a common shaft driven by a motor 15. As a result, a precisely synchronous rotary movement of the two polygonal prisms is achieved. Disposed behind the polygonal prism 12 is a transformation optical system 13 from which the incoming infrared rays are conveyed to a detector 14. The conversion of the infrared rays received by the detector into visible rays is effected in known manner through video signal and luminescent diodes 24. The visible rays emerging from the luminescent diodes enter the polygonal prism 22, which reproduces the visible heat image, and then pass through the collimator 23 to a deflecting mirror 25. The deflecting mirror 25 reflects the rays and conveys them to the spectral divider, from which they are reflected into the path of visible rays entering directly into the main device in the manner described. The exit pupil 32 is provided for this purpose in the housing which surrounds the spectral divider 3. Opposite the exit pupil 32 is the entrance pupil of the main device after passing through the spectral divider 3. There is a hole for test purposes in the beam splitter. Figure 3 shows the attachment of the attached device 5 to the main device 4. For the parts already discussed, the same reference numerals apply as in the previous Figures. Disposed behind the entrance pupil 41 of the main device there is here a deflecting prism 42 which deflects the rays from the converter and the direct rays and conveys them to a second deflecting prism 43. After again being deflected by prism 43, the rays enter the eyepiece 44. WHAT WE CLAIM IS:

1. An afocal spectral converter which is adapted for attachment to a main sighting and aiming device and which is for the conversion of a heat image into a visible image, wherein the converter comprises an infrared image pick-up unit and an imagereproduction unit which together have a magnification of 1, the converter is adapted for attachment to the main device so that the optical axis of the image pick-up unit extends parallel to the optical axis of the main device and so that a parallel bundle of rays from the image reproduction unit is reflected into the main device without disturbing the use of the main device with visible radiation.

8. An afocal spectral converter con

structed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, "the accompanying drawings.