Reference calibration for an adaptive optics system

An adaptive optics system for providing aberration compensated detection of light from an object, the adaptive optics system comprising:

• a detecting device for detecting light from said object;
• a wavefront sensor configured to provide signals indicative of a spatial phase distribution of light incident on the wavefront sensor;
• at least one controllable wavefront modifying device arranged such that light from said object passes via said wavefront modifying device to said detecting device and to said wavefront sensor;
• a control system connected to the wavefront sensor and to the wavefront modifying device, said control system being operable in a calibration mode and in a regulation mode, wherein said control system comprises:
• an output for providing control signals to the wavefront modifying device;
• a first input for receiving signals from the wavefront sensor;
• a second input for receiving readings the detecting device;
• a wavefront modifying device controller for controlling the wavefront modifying device;
• calibration circuitry for determining calibration parameters for the adaptive optics system;
• and
• a memory for storing said calibration parameters,
• wherein:
• when said control system operates in said calibration mode:
• said wavefront modifying device controller, for each of a plurality of orthogonal wavefront modes of the wavefront modifying device, controls the wavefront modifying device to vary a magnitude of the orthogonal wavefront mode over a predetermined number of magnitude settings;
• and
• said calibration circuitry, for each of the plurality of orthogonal wavefront modes, determines a quality metric value indicative of an information content of each reading in a series of readings received from the detecting device, each reading corresponding to one of said magnitude settings, resulting in a series of quality metric values;
• determines a reference parameter set for the wavefront modifying device corresponding to an optimum quality metric value based on the series of quality metric values for each of said plurality of orthogonal wavefront modes;
• and
• when said control system operates in said regulation mode:
• said wavefront modifying device controller regulates the wavefront modifying device based on signals from the wavefront sensor and said reference parameter set.