Abstract: The invention relates to an apparatus for forming or working optical elements and/or optical forming elements (1) comprising a working apparatus (18) for forming surfaces of form parts by machining or an abrasive technique, wherein at least one measuring device (17) is provided for measuring changes in form and/or surface roughness of said surface when said surface is being worked and, on the basis thereof controlling said working apparatus (18).

Abstract: A method for measuring a contour variation of a measuring area on an object. The method includes the steps of: irradiating the measuring area with a light beam, wherein reflection or transmission of the beam occurs; splitting the transmitted or reflected beam; combining the split beams with each other and observing a fringe pattern representing a differential phase between the split beams; varying the phase of the split beams relative to each other, such that the differential phase is kept within the range of 2 pi; calculating an optical path length difference from the differential phase; and relating the optical path length difference to the contour variation of the object.