A borescope's an optical device consisting of a rigid or flexible tube with an eyepiece on one end, an objective lens on the other linked together by a relay optical system in between. The optical system's usually surrounded by optical fibers used for illumination of the remote object and a rigid or flexible protective outer sheath. The remote object's illuminated and an internal image formed by the objective lens's relayed to the eyepiece which magnifies the internal image and presents it to t… (More on Borescope)