2 X Extender Canon fit.

The Canon EF 2X II Extender is a teleconverter. These high-performance accessories multiply the effective focal length of the attached lens by 2x. For example, a 200mm lens with the Extender 2x, increases to 400mm. Extenders are only compatible with selected EF lenses, including the EF 70-200mm f/2.8L USM, EF 70-200mm f/2.8L IS USM, EF 70-200mm f/4L, EF 100-400mm f/4.5-5.6L USM, EF 400mm f/4 DO IS

asking price £190