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Light enters the top lens of a periscope, reflects off a mirror set at a 45 degree angle, travels down the periscope tube, and reflects off a second mirror, also set at a 45 degree angle. Light that reflects off the second mirror exits through the bottom lens and into the eye of the user.
Any of various tubular optical instruments that contain reflecting elements, such as mirrors and prisms, to permit observation from a position displaced from a direct line of sight.
per′i·scop′ic (-skŏp′ĭk), per′i·scop′i·cal (-ĭ-kəl) adj.
(of a lens) having a wide field of view
per•i•scop•ic(ˌpɛr əˈskɒp ɪk)
1. (of certain lenses in special microscopes, cameras, etc.) giving distinct vision obliquely, or on all sides.
2. pertaining to periscopes or their use.