Wiktionary
folded optics
n. An optical system in which prisms and/or mirrors are used to reduce the overall physical length of the system.
Wikipedia
Folded optics
Folded optics is an optical system in which the beam is bent in a way to make the optical path much longer than the size of the system. Prismatic binoculars are a well-known example.
An early conventional film (35 mm) camera was designed by Tessina that used the concept of folded optics.
Usage examples of "folded optics".
It seemed to be a lensless system depending on folded optics and a paper-thin electronics sandwich of an image plane that transmitted the pictures on its face through a pea-size FM device.