Membrane mirror devices presented here are capable of large amplitude deformation for wavefront generation and correction in adaptive optics. These devices consist of micro-fabricated membranes that are actuated by an underlying electrode array and a transparent counter-electrode. Deformations of +/- 20 mum optical are demonstrated for low order deformations and 10 mum optical for high order Zernike polynomial wavefront generation. Large deformation at low voltage is enabled by the use of low stress membranes, relatively small membrane-electrode separation and the transparent counter-electrode.