An objective lens is secured in an afocal mode to a support for movement vertically toward and away from a workpiece. An illumination collimator fixed on the support above the objective lens projects the image of a reticle downwardly and successively through a second lens assembly, a beamsplitter plate,...http://www.google.ca/patents/US5668665?utm_source=gb-gplus-sharePatent US5668665 - Telecentric, parfocal, multiple magnification optical system for videoinspection apparatus
