Within the last years, the Adaptive Optics (AO) systems built or designed are growing in complexity: their optics are numerous and they aim at better performances on-axis and/or in the Field of View. A limiting factor to those performances can be the Non-Common Path Aberrations (NCPA), i.e. static aberrations present in the optical path of the instrument after the dichroic, which therefore are not seen by the AO Wave Front Sensor. Since long the Deformable Mirror of the system has been used to partially compensate for them, in a more or less efficient and complex way. This paper will present a rapid to implement, rather simple and all-measured method of compensation for the NCPA tanks to the use of Phase Diversity and of a calibration matrix of the modes constituting the aberrations. Moreover for systems composed of several DMs, we will present how a clever use of those can reduce significantly the aberrations in the whole FoV. All those techniques will be illustrated by their application to ESO'S MCAO Demonstrator (MAD).
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