An instrument used to view inside a small hole or structure. A long narrow tube that contains a telescope system with relay lenses. A lamp located in front illuminates the inside of the bore, and the inclusion of a small 45° mirror often permits detailed examination of the tube wall. Used to view inside pipes, oil wells, or gas mains. Some small borescopes and most types of medical endoscopes are now equipped with a fiber optic bundle for image and/or illumination transfer.