How does a periscope work?

Answer 1

Old trench periscopes worked by using two mirrors to bounce light from one place to another. A typical periscope uses two mirrors at 45 degree angles to the direction one desires to see. The light bounces from one to the other and

then out to the persons eye.

If there is an object in front of you, any nearby light source (i.e the sun, a lamp etc.) bounces straight rays of light onto the object and then into your eyes, enabling you to see it. However, if the object is not within straight lines of your eyes, the light will not find them and you will not be able to see the object (since light only travels in straight lines).

But a periscope works using the laws of reflection. Reflective objects like mirrors work by bouncing light so it carries on in a straight line but alters it's route, according to the angle of the mirror to the light source. This means that if the mirror was at a 45 degree angle to the light source then it would bounce off at a perpendicular (90 degree) angle. That is how a periscope works.

The important fact to note when considering a periscope is that the laws of reflection mean that the light hitting a mirror at an angle is reflected off at twice the angle of the mirror. Thus a 45 degree mirror reflects light rays through 90 degrees.

Submarine Periscopes

Submarine optical periscopes don't use mirrors due to their fragility and susceptibility to environmental conditions/changes, requiring special coatings. Instead, they use refractive prisms.

The newer U.S. Virginia-class and British Astute-class boats use neither; they use a Photonics Mast, which is essentially a hi-resolution camera array that is raised above the waterline. This has many advantages, the primary one being that the Control Room need not be directly under the main sail as in all previous modern submarine designs.