Abstract: An actuator device of particular use in changing the configuration of a deformable mirror faceplate includes an electrically deformable actuator confined between a back surface of a support and a nut that is threaded onto a threaded end portion of elongated tensioning element that has an end cap secured to the other end portion. The tensioning element passes through a central opening of the actuator and a passage in the support. A spring is interposed between the front surface of the support and the end cap. Tightening of the nut imparts causes the spring to exert its restoring force on the actuator to subject the same to a mechanical preload pressure. Another nut may be threaded onto the threaded end portion of the tensioning element to be received in a corresponding recess of the support and pre-deform the spring in the absence of the actuator.