A method of determining a reference calibration setting for an adaptive optics system comprising: a detecting device for detecting light from an object; and at least one controllable wavefront modifying device arranged such that light from said object passes via said wavefront modifying device to said detecting device, said method comprising the steps of: arranging a light-source between said object and said wavefront modifying device to provide a reference light beam to the detecting device via the wavefront modifying device; for each of a plurality of orthogonal wavefront modes of the wavefront modifying device: controlling the wavefront modifying device to vary a magnitude of the orthogonal wavefront mode over a predetermined number of magnitude settings; acquiring a series of readings of the detecting device, each reading corresponding to one of said magnitude settings; determining a quality metric value indicative of an information content of the reading for each reading in said series of readings, resulting in a series of quality metric values; and determining a reference parameter set for the wavefront modifying device corresponding to an optimum quality metric value based on the series of quality metric values. a detecting device for detecting light from an object; and at least one controllable wavefront modifying device arranged such that light from said object passes via said wavefront modifying device to said detecting device, said method comprising the steps of: arranging a light-source between said object and said wavefront modifying device to provide a reference light beam to the detecting device via the wavefront modifying device; for each of a plurality of orthogonal wavefront modes of the wavefront modifying device: controlling the wavefront modifying device to vary a magnitude of the orthogonal wavefront mode over a predetermined number of magnitude settings; acquiring a series of readings of the detecting device, each reading corresponding to one of said magnitude settings; determining a quality metric value indicative of an information content of the reading for each reading in said series of readings, resulting in a series of quality metric values; and determining a reference parameter set for the wavefront modifying device corresponding to an optimum quality metric value based on the series of quality metric values. arranging a light-source between said object and said wavefront modifying device to provide a reference light beam to the detecting device via the wavefront modifying device; for each of a plurality of orthogonal wavefront modes of the wavefront modifying device: controlling the wavefront modifying device to vary a magnitude of the orthogonal wavefront mode over a predetermined number of magnitude settings; acquiring a series of readings of the detecting device, each reading corresponding to one of said magnitude settings; determining a quality metric value indicative of an information content of the reading for each reading in said series of readings, resulting in a series of quality metric values; and determining a reference parameter set for the wavefront modifying device corresponding to an optimum quality metric value based on the series of quality metric values. controlling the wavefront modifying device to vary a magnitude of the orthogonal wavefront mode over a predetermined number of magnitude settings; acquiring a series of readings of the detecting device, each reading corresponding to one of said magnitude settings; determining a quality metric value indicative of an information content of the reading for each reading in said series of readings, resulting in a series of quality metric values; and determining a reference parameter set for the wavefront modifying device corresponding to an optimum quality metric value based on the series of quality metric values.