The Sigma APO Teleconverter 2x EX DG for Pentax Digital SLR Cameras is a dedicated APO teleconverter that can be mounted between select lenses and the camera body to increase the focal length by the power of 2. The multi-layer coating reduces flare and ghosting, which is a common problem with digital cameras. The lens also offers maximum magnification without any variation in the minimum focusing distance. Compact and lightweight, this teleconverter can convert your lenses into longer focal-length lenses, so you don't have to do a lot of unnecessary footwork. A case for the lens is included. more info