A method of edge detection with an optical measuring machine including aligning a test object with a lens system having a variable size aperture, wherein the lens system is operable to form an image of the test object on a digital sensor having an array of addressable pixels, and wherein the variable size aperture is operable to image points of the test object on the digital sensor at different spot sizes. Setting the variable size aperture to a first size and binning contiguous clusters of the addressable pixels into image pixels having a first size in accordance with the number of addressable pixels within each of the image pixels. Identifying contrast variations of the test object imaged onto the digital detector over a number of image pixels at the variable aperture first size, whereby an area of the test object is imaged at a first effective magnification.