A periscope is constructed and functions similarly to a telescope, with a long tube containing a mirror at each end. The mirrors are mounted on the tube so that they are parallel to each other at a 45° angle to the axis or imaginary centerline of the tube.
In more advanced periscopes, additional lenses have been added to enlarge the image. Underwater periscopes are even more complicated. They have reflective prisms on the top and bottom of the tube, with two telescopes and several lenses between the two ends, and an eyepiece on the observer's side. The underwater periscope also has a thick, rigid waterproof cover and can withstand water pressure at great depths.
In addition to submarines, war tanks also use periscopes to search for enemy targets. Both vehicles have a periscope that can be raised or lowered, as well as turned in a 360° circle.
Periscopes can also be built so that they see around corners!
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