An adaptive optics system consists of a wavefront sensor, a wavefront compensator and a control computer. The wavefront sensor produces M wavefront measurements which are given as input signals to a control computer. The computer delivers P output voltage values to be applied to the wavefront compensator. Wavefront compensators generally consist of a deformable mirror with P actuators. Usually the figure of the deformable mirror at rest is not perfect but corrects itself in a closed loop. In order to do that the number M of wavefront measurements has to be higher or equal to the number P of actuators.