| 摘要 |
1. Bifocal optic using a first focusing optic composed of two curved mirrors having the same optical axis (Z), a first concave mirror (1) pierced in its central portion and a second mirror (2) for successively reflecting the received luminous radiation, one of the mirrors being provided with an element (5) controlled by an electric signal (VC) to vary its focal distance, and d.c. current supply means (4) for producing and modifying said control signal, said bifocal optic being characterized in that said element is formed by an electrolytic cell (5, 5a) having, successively in the direction of the axial optical path reflected by the first mirror, a first transparent wall (11) the outer face of which is oriented towards the first mirror (1), a transparent conductive layer (12) convering the inner face of the first wall and forming a first electrode, an electrolyte (10) containing metallic ions, a second electrode (14) and a second wall (13), said second electrode being of annular shape and centered on the optical axis and applied against the inner face of the second wall, said electrodes being connected to the d.c. supply means (4) supplying said signal with a given sign or with the inverted sign to produce two operative states of the cell, a first state wherein a metallic deposit is produced on the first electrode (12) to form said second mirror which then forms a Cassegrain system with the first concave mirror to form said first focusing optic having a first focal length, and a second operative state wherein said metallic deposit is dissolved in a manner to obtain a second focusing optic having a second focal length (F2) different from the first (F1) and such that the focusing plane is coincident with that of the first focusing optic. |
