Abstract: A method and apparatus for determining angular displacement of one or more parts of an object (10) comprising detecting in at least one first image sensor first and second one or more distributions of Fourier-transformed speckles before and after angular displacement, respectively, and determining the displacement of the detected images; a method and apparatus for determining twist of a rotating shaft between two or more parts of the shaft subjected to a load; a method and apparatus for simultaneously determining angular displacements and surface translations of one or more parts of an object, and a method of determining the radius of angular displacement of one or more parts of an object.