Radiant energy – Infrared-to-visible imaging
Reexamination Certificate
1998-11-23
2001-01-23
Hannaher, Constantine (Department: 2878)
Radiant energy
Infrared-to-visible imaging
C359S350000, C359S353000
Reexamination Certificate
active
06177671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an infrared telescope comprising means to harmonize its input and output axes. It may be recalled that the telescope is a device used to observe a distant scene. The telescope gives an image of the scene at infinity. By analogy, an infrared telescope enables the observation of an infrared scene and gives an image thereof that is visible at infinity.
Many sighting systems such as for example a gun sighting device, a laser telemeter or a missile firing station use a telescope working in the visible light spectrum. This telescope, called a day telescope, defines an axis by means of a reticule. It may be necessary to make these sighting systems work in a frequency spectrum other than the visible spectrum, such as for example the infrared spectrum. A usual frequency band of the infrared spectrum ranges for example between about three and five &mgr;m. Another band commonly used in the infrared spectrum is located approximately between eight and twelve &mgr;m. The invention of course is not limited to these frequency bands. To make these sighting systems work at such frequencies, advantageous use is made of an infrared telescope with a magnification of unity. The infrared telescope is placed before this day telescope.
2. Description of the Prior Art
Embodiments of this type of telescope exist but they nevertheless have a particular difficulty. It is indeed important to harmonize the input and output optical axes of the infrared telescope in such a way that an observer can look at the same scene with or without the infrared telescope. In particular, the aiming axis defined by the reticule of the day telescope must be preserved when an infrared telescope is placed before this day telescope. In the particular case of an infrared telescope placed before the day telescope, the input and output axes of the infrared telescope have to be parallel. Harmonizing the input and output axes of a telescope of this kind implies reducing possible defects of parallelism of these axes, ideally so as to cancel these defects or, at least, to bring them within acceptable tolerances. The invention of course is not limited to a telescope comprising parallel axes. It can also be implemented for a telescope whose input and output axes are not parallel. Harmonizing axes, in this case, means limiting their defects of relative position.
The example of an infrared telescope with a magnification of unity has being chosen for a better understanding of the problem raised, but it is clear that the invention is not limited to this type of telescope. The invention can be implemented for any type of telescope whatever its magnification.
It is an aim of the invention to harmonize the input and output axes of the telescope with a precision that is compatible with the application envisaged. This precision may, for example, be lower than 100 &mgr;rd.
SUMMARY OF THE INVENTION
To achieve this goal, an object of the invention is an infrared telescope comprising:
an infrared camera enabling the observation of an infrared scene and delivering a video signal representing the infrared scene, said infrared camera having a sighting axis that constitutes the input axis,
a display screen receiving the video signal and displaying the corresponding image in the visible frequency spectrum,
a bispectral, visible and infrared collimator, collimating the image displayed on the display screen at infinity, said collimator having an optical axis that constitutes the output axis,
an infrared source positioned in a predefined way with respect to the output axis and positioned so that its radiation is collimated at infinity by the collimator,
means for the reflection of the radiation coming from the infrared source at output of the collimator towards the infrared camera, said means enabling the formation on the display screen of an image of the infrared source,
means to measure the shift between the predefined position of the infrared source and the image of the infrared source on the display screen,
means for adjusting the telescope to reduce the shift.
One advantage related to the invention is that it enables the harmonizing of the axes to be done in a simple way. This implementation can be done during operation. It is not necessary to place the telescope on a measuring stand in the factory in order to harmonize the axes.
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Fouilloy Jean-Pierre
Seugnet Patrick
"Thomson-CSF"
Gagliardi Albert
Hannaher Constantine
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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