This little, tiny mirror, about the size of a dime, has an array of 225 actuators that can move to slightly (10 mm) to adjust the mirror surface to correct for wavefront aberrations.

To see the whole paper: https://cfaom.soe.ucsc.edu/sites/default/files/High-aspect-ratio%20microelectromechanical%20systems%20deformable%20mirrors%20for%20adaptive%20optics%20(JM3).pdf