catoptrics n : branch of optics dealing with formation of images by mirrors
Catoptrics deals with the phenomena of reflected light and image-forming optical systems using mirrors. From the Greek κατοπτρικός (specular).
The book Catoptrics attributed to Euclid covered the mathematical theory of mirrors, particularly the images formed by plane and spherical concave mirrors.
The first practical catoptric telescope (the "Newtonian reflector") was built by Isaac Newton as a solution to the problem of chromatic aberration exhibited in telescopes using lenses as objectives (dioptric telescopes).