A laser-optical apparatus for measuring blade tip clearance, e.g. of a compressor or gas turbine, uses a laser beam, fiber optics, a light probe and electrical circuits (14, 25) for processing data from the probe, and includes a light probe (16) having a lens (17) for making parallel a light beam from...http://www.google.de/patents/US5017796?utm_source=gb-gplus-sharePatent US5017796 - Moving blade tip clearance measurement apparatus and method with moveable lens
