Canon EF 1.4X l Telephoto Extender for Canon Super Telephoto Lenses Lens Elements/Groups 5/4 Canon EF Mount Dimensions:2-11/16" x 1-1/16" Usable lenses: EF 200mm f/1.8 L, EF 300mm f/2.8 L, EF 400mm f/2.8L, EF 600mm f/4L Canon date code: UF1002