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Many optical instruments use prisms to reflect light (by total internal reflection). Cameras and binoculars are two common examples.
When light is reflected internally by a 45°
prism as shown below, inversion takes place.
Two such prisms are used in "prismatic binoculars" in order to produce an image which is "the same way round" and "the same way up" as the object.
This system also has the advantage of including a longer optical path in a given length of instrument. This allows for greater magnification.