Borescope is a long, thin, rigid rod like optical device that allows an inspector to see into inaccessible areas by transmitting an image from one end of the scope to the other. Borescopes are designed to provide direct, forward oblique, right angle, and retrospective viewing of the area in question. It is used in aircraft/engine maintenance programs to reduce or eliminate the need for costly teardowns. It comes in three general types: rigid, flexible and charge-coupled devices. Rigid and fiberoptic borescopes are capable of providing access to small openings. The rigid borescopes utilize a lens train; this is called the lens optic technique.

Borescopes are inspection devices with a rigid or flexible optical tube for insertion into bores and cavities for visualization. They are used in a wide range of industrial quality control and inspection applications. A borescope consists of an objective lens positioned in front of a long relay tube containing an image relay and an illumination relay. Borescopes have four common relay lens type such as achromatic doublet, gradient index, fused quartz fibers and rod lens. Its feature includes integral illumination and the ability to attach a video camera for image display & capture.