How good is MMDM optically?

The surface quality is good enough to work with very low scattering in the whole visible spectrum. The initial figure of MMDM is flat with RMS deviation from the nearest reference plane better than 250nm. A mirror a diameter of 10mm will have less than 1 fringe of astigmatism (averaged over a number of devices), an average mirror with a diameter of 15mm has about 2 fringes of astigmatism. These aberrations can be easily corrected during the mirror operation by calibrating the bias voltage.