United States Patent, No.: US 9,139,468 B2, Date of Patent: Sep. 22, 2015, Appl. No.: 14/172,486; Filed: Feb. 4, 2014, Prior Publication Data US 2014/0153865 A1, Jun. 5, 2014, Int. Cl. G02B 6/00, G03B 37/14, G01B 11/16, G01D 6/26