Catadioptric lens
From The Glossary of Digital Photography
More commonly known as a mirror lens. Catadioptric refers to optical systems that are made up of both mirrors and lenses. Mirror lenses actually include both, even though the name doesn't suggest it. Catadioptric lenses are much lighter and shorter than the equivalent, traditional telephoto lens, but they usually lack the speed and adjustable diaphragm of the latter.
