Abstract: A wavefront, such as from a laser, is sampled, preferably at a beam splitter to break off only a fraction of the total light energy. The sampled beam is adjusted and sized--either by expansion or contraction at a conventional telescope--and thereafter sent through paired crossed Ronchi gratings and onto a CCD camera located at the first wave distance of constructive interference from the crossed Ronchi gratings. The crossed Ronchi gratings--in the order of 200 lines per inch and preferably with 200 equally spaced gaps per inch--project an array of square spots onto the focus of the CCD camera. The image of the array of square spots at the CCD camera is frozen via a frame grabber and digitized in a conventional format. The digitized image is played through a disclosed computer program to locate the spots. Thereafter, the located spots are compared to a standard spots.