Determination of phases and phase differences of light reflecting from specular or diffusely reflecting, or transparent surface of object

The method for determining the phases of light or infra-red radiation reflected from an object (10) with a diffusely reflecting surface, in a displaced or distorted condition, or from a transparent or mirrored object in similar conditions, uses a movable and rotatable glass plate (23). Rays of known frequency (11) are directed at the object and reflected from it (12) through the lens (13) towards a sensor (15) made up of multiple pixels (16). A reference ray (14) of equal frequency, transmitted through the turning glass plate, changes in definition. In this way the phase position between object rays and reference rays is modified to produce, after processing, a single phase difference value (17).