C'est un peu naze ça aussi :

"The camera's 39 cross-type AF points act as cross type with any f/2.8 maximum aperture lens, as well as with certain f/4 lenses or lens+teleconverter combinations that add up to f/4. (In all previous 1-series digital SLRs, only the centre point would retain its cross type detection capabilities when an f/4 lens was attached.)

The eligible Canon lenses are:
Canon EF 17-40mm f/4L
Canon EF 24-105mm f/4L IS
Canon EF 70-200mm f/2.8L IS + Extender EF 1.4x II
Canon EF 200mm f/2L IS + Extender EF 2x II
Canon EF 300mm f/2.8L IS + Extender EF 1.4x II
Canon EF 400mm f/2.8L IS + Extender EF 1.4x II
This is thought to be the complete list of f/4 glass that can reap the benefit of 39 cross-type points, which means other lenses, such as the EF 500mm f/4L IS or the Canon EF 70-200mm f/2.8L (non-IS) + Extender EF 1.4x II, will not have the benefit of cross-type operation from all 39 AF points. The centre point, however, will continue to provide cross-type sensitivity with any f/4 lens or combo not on the list above"