| 摘要 |
<p>An optimised optical system is composed of an entrance optical unit (1), an image transport means and a unit (C) for focusing onto a detector (D). In order to compensate for the thermal defocusing introduced by the entrance optical unit (1), the image transport means consists of a specular system having two mirrors (M1, M2), one (M1) of the two mirrors surrounding the other (M2), creating an entrance aperture and an exit aperture for respectively introducing the beams coming from the observed scene and projecting them towards the focusing unit (C). The image transport system is constituted by a specular system such that the entire optical system is catadioptric. This specular system is formed by at least two mirrors (M1, M2), the surfaces of which face each other, one of the two surfaces surrounding the other. Such a specular reflection system, of the Hoffner system type, is known per se. Such a system offers compensating defocusing possibilities when it is combined with other dioptric image transporters, whilst keeping conventional materials, aluminium for example, for its holding ties (spacers). The positive contribution to the thermal defocusing provided by the specular system and its holding ties (spacers) is paramount for compensating for the negative contribution induced by the upstream elements of the optical system. The compensation depends more significantly on the choice available for the expansion coefficients of the mirrors M1 and M2 than on the other factors involved in f and can therefore be adjusted on account of the choice of the component materials; in particular, this compensation is achieved more "rapidly" the more the coefficient alpha M1 of the surrounding mirror (M1) exceeds the coefficient alpha M2 of the other mirror (M2). A systematic study shows that, among the materials mentioned by way of example, two pairs enable the defocusing dl2 to be cancelled out: these are the pairs Ge/ZnS and Ge/ZnSe. Application to the athermalisation of infrared cameras. <IMAGE></p> |
