Abstract: An electro-optical device for generating data signals representing relative displacement between a master reticle with an optical aperture pattern in an object plane and a workpiece with an image of the aperture pattern in an image plane comprises a reference detector for sensing reference radiation directed towards the aperture pattern and a convolution detector for sensing the reference radiation reflected by the image pattern. A processor compares the phase of a signal generated by the convolution detector to the phase of a signal generated by the reference detector and generates the data signals defining the relative displacement between the master and the workpiece.