Un document Canon (qui a l'air officiel) dit :

http://media.onecall.com/Image_Produ...artyLenses.pdf

"A variety of lenses from third-party manufacturers — Sigma, Tokina, Tamron, and
others — are available in Canon EF mounts to fi t Canon EOS camera bodies. However,
contrary to popular belief, these companies are not “licensed” to produce these lenses;
instead, their designers must basically take apart and analyze EOS cameras and lenses,
and then “reverse-engineer” them to fi t and operate on EOS camera bodies."