<p>An apparatus and method for measuring wavefront aberrations. The apparatus comprises a reflecting device (128) for reflecting selected portions of the wavefront (126), an imaging device (132) for capturing information related to the selected portions, and a processor (136) for calculating aberrations of the wavefront from the captured information. The method comprises reflecting selected portions of a wavefront (126) onto the imaging device (132), capturing information related to the selected portions, and processing the captured information to derive the aberrations.</p>