Retrofocus

Glossary Terms

Retrofocus refers to a type of lens design, pioneered (and originally tradmarked) by Angénieux, which permits a short lens optical focal length while providing a greater back focus distance. This is typically required in an SLR camera, to allow space for the swinging reflex mirror; and also in some cine cameras using small image formats, to permit space for the shutter mechanism.

Sometimes known as a "reverse telephoto" design, retrofocus designs typically have outermost lens groups with negative power, with convergent elements behind them. It can be difficult to design a retrofocus lens that is fully free from barrel distortion.