Editing Periscope (section)

{{Short description|Instrument for observation from a concealed position}}
{{Other uses}}
[[Image:Periscope simple.svg|thumb|right|Principle of the periscope. The periscope on the left uses mirrors whereas the right uses prisms.<br>
'''a''' Mirrors<br>
'''b''' Prisms<br>
'''c''' Observer's Eye ]]

[[Image:Periskop linsen.svg|thumb|right|Principle of the lens periscope.
The two periscopes differ in the way they erect the image. The left one uses an erecting prism whereas the right uses an erecting lens and a second image plane.<br>
'''a''' [[Objective lens]]<br>
'''b''' [[Field lens]]<br>
'''c''' Image erecting lens<br>
'''d''' [[Ocular lens]]<br>
'''e''' Lens of the observer's eye<br>
'''f''' Right-angled prism<br>
'''g''' Image-erecting prism]]

A '''periscope''' is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position.<ref name="Walker2000">{{cite book|author=Walker, Bruce H. |title=Optical Design for Visual Systems|url=https://books.google.com/books?id=yprWx6DfqFUC&pg=PA117|year=2000|publisher=SPIE Press|isbn=978-0-8194-3886-7|page=117}}</ref><ref>{{cite book|title=The Submarine Periscope: An Explanation of the Principles Involved in Its Construction, Together with a Description of the Main Features of the Barr and Stroud Periscopes|url=https://books.google.com/books?id=bkOUoAEACAAJ|year=1928|publisher=Barr and Stroud Limited}}</ref>

In its simplest form, it consists of an outer case with [[mirror]]s at each end set parallel to each other at a 45° angle. This form of periscope, with the addition of two simple lenses, served for observation purposes in the trenches during [[World War I]]. Military personnel also use periscopes in some [[gun turret]]s and in [[Armored car (military)|armoured vehicle]]s.<ref name="Walker2000"/>

More complex periscopes using [[Prism (optics)|prism]]s or advanced [[Optical fiber|fiber optics]] instead of mirrors and providing magnification operate on [[submarine]]s and in various fields of science. The overall design of the classical submarine periscope is very simple: two telescopes pointed into each other. If the two telescopes have different individual magnification, the difference between them causes an overall magnification or reduction.