borescope

thumb|Schematic view of a rigid borescope thumb|Borescope in use, showing typical view through the device

A borescope (occasionally called a boroscope, though this spelling is nonstandard) is an optical instrument designed to assist visual inspection of narrow, difficult-to-reach cavities, consisting of a rigid or flexible tube with an eyepiece or display on one end, an objective lens or camera on the other, linked together by an optical or electrical system in between. The optical system in some instances is accompanied by (typically fiberoptic) illumination to enhance brightness and contrast. An internal image of the illuminated object is formed by the objective lens and magnified by the eyepiece which presents it to the viewer's eye.