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Album: German Submarines
Image: 238 / 473
Date: 2010-04-15 15:47:13
Tags: Bremerhaven, Germany, Submarines, Type XXI, U 2540

Periscope Type ASC 17 A2

The periscope (from greek Peri "around" and skopéin, "to watch"), is an optical instrument to observe from a cover. The invention goes back to Johannes Hevelius (published 1647).

Use

The periscope is mainly used in war to safely observe the surroundings from the submarine.

Layout and Operation

The basic set-up of the periscope is a tube which has mirrors or prisms at each end. These direct the incoming light rays into the tube and shifted parallely to the original direction out again. To an observer, looking into the bottom opening of a periscope, it looks like he's looking at the surroundings from a higher point of view. The mirrors are arranged in a 45° angle to the incoming and outgoing light ray which results in a perpendicular deviation. Prisms have the advantage that because of their total internal reflection, less light is lost compared to a mirror.

Often, a magnification factor if 1.5 is used, which, for psychological reasons, seems create the impression of a natural, plain 1-time magnification.

Because the image in common magnification systems is rotated by 180°, an image reversal is used, as with binoculars or telescopes for terrestrial observation, either a reversal prism or lens.