The branch of optics dealing with systems that use both reflection and refraction to focus and manipulate light.
Greek roots 'kata' (down) + 'dia' (through) + 'optikos' (sight) + '-ics' (study of), formalized as a scientific field in the 1600s.
NASA uses catadioptrical systems in their telescopes and rovers because they're lighter and more powerful than using just mirrors or just lenses alone!
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