Usable lenses: Lens Focal Length & Maximum Aperture EF 1.4 X III EF 2 X III EF 135mm f/2L USM 189mm f/2.8 270mm f/4 EF 180mm f/3.5L Macro USM 252mm f/4.5 360mm f/6.7 EF 200mm f/2.8L USM 280mm f/ 4 400mm f/5.6 EF 200mm f/2.8L II USM 280mm f/4
When the EF 1.4 x III is attached, the lens maximum aperture will be smaller (darker) by 1 stop. The camera will compensate the exposure automatically.