Optical system for producing differently focused images

A method and system for producing two differently focused /defocused images is disclosed in which one or more beam splitting means ( 16, 18 ) are used to split a beam ( 14 ) into a plurality of resultant beams ( 20, 26, 24 ) and a plurality of separate sensors ( 30, 34, 32 ) are used to detect the beams ( 20, 26, 24 ). The path length of the resultant beams ( 20, 26, 24 ) to the respective sensors ( 30, 34, 32 ) are different for each resultant beam, which can be achieved by placing the sensors ( 30, 34, 32 ) at different distances from the respective exit points of the resultant beams (20, 26, 24) from the beam splitting means ( 16, 18 ) or by providing optical elements (such as, for instance, movable transparent wedge-shaped members) between the beam splitting means ( 16, 18 ) and the sensors 830, 34, 329. A method and system for determining movement of an object by capturing sequential images of the object are also disclosed.