Having taught Medical Physics this year, I got to experience it at first hand. The endoscope is the black fibre that goes diagonally from top right to bottom left across the middle of the picture. Part of that went a long way up my nose! An endoscope is made of two optic fibres. One runs from the box on the bottom of the trolley. The box contains a bright light source that strongly illuminates the tip of the fibre. That's so the inside of my nose is lit up. The other fibre runs back from the tip to the wider black section which is clearer in the top right of the photograph below. The doctor looks into this. The second fibre brings the reflected light back, which is the image of the inside of my nose. It must be lensed.
