For those times that you need extreme reach of a distant subject, Kenko offers the Pro 300 3x DG teleconverter, designed to give optimal results with fixed focal length lenses of 200mm or more.
Like the 1.4X & 2X Pro 300 teleconverters, the Teleplus PRO 300 converter is made with high quality multicoated optical glass supplied by Hoya. Corner resolution is stellar and deterioration of light is kept to the absolute minimum. Amazingly, with lenses of f/2.8 or larger apertures, autofocus is maintained even with AF-S lenses when using current professional cameras.