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Originally Posted by jammie*dodger
So do nikon deliberately do this to try to prevent people from using Sigma lenses with their TC?
Canon would never stoop to those levels 
Rob. |
Probably to get people to buy AF-S lenses rather than the cheaper (and eventually obsolete) AF-D lenses, which won't AF even when attached to a modern Nikon tc... I doubt there's a Sigma factor involved in their design.
btw: the optical superiority of tc's matched to the lens are a bit of a fallacy these days, used to be the case but not anymore.