After an operator has focused the zoom lens assembly of an optical measuring system on a workpiece, the zoom lens itself is adjusted to select a desired magnification. A reticle image in the form of a plurality of radially spaced, concentrically disposed circles is then projected, at the selected magnification,...http://www.google.ca/patents/US5389774?utm_source=gb-gplus-sharePatent US5389774 - Method and means for calibrating the magnification of zoom optical systems using reticle images
