The EF 1.4x III serves as the perfect accessory to Canon EF Lenses, giving you a 1.4× increase in focal length and allowing you to get even closer to the action capturing that perfect shot. The EF 1.4x III features superlative quality, and is built with special coatings that minimize flare and ghosting, and help prevent dust and grime buildup. When using this extender, the lenses f-number is reduced by one stop, so autofocus is possible only with lenses brighter than f/4. This extender is only compatible with fixed focal length L-series lenses 135mm and over, as well as the EF 70-200/2.8L, EF 70-200/2.8L IS, EF 70-200/4L, and EF 100-400/4.5-5.6L.