Abstract: An actuator device of particular use in changing the configuration of a deformable mirror faceplate includes an electrically deformable actuator confined between a grounded electrode disposed on a front surface of a support and an end cap of a tensioning unit which further includes an elongated tensioning element secured to the end cap and passing through a central opening of the actuator and a passage in the support with a free end portion thereof extending beyond the other surface of the support. A tensioning assembly for imposing a preloading force on the actuator includes an externally threaded sleeve surrounding and secured to the free end portion of the tensioning element, and an internally threaded nut meshing with the sleeve and acting on the support.