Tele Converters

[Blackberner]

FWIW.......I have used my 70-200 F4 with a 2xII and found the resulting quality not bad. Just had to compensate for the lack of AF and the min F8 aperture. However I am hanging for a 70-200 2.8..............

[vk2gwk]

It actually says the 2x works with this lens in the 5D mkiii manual as well, maybe not the case with other bodies.
I expect this setup to have limitations and will/might not work in all conditions but would expect it to work in good light etc
I am also expecting the have to manual focus on those many occasions when the AF won't work.
Am I wasting time thinking that the 2x iii on the 100-400mm is an option?

I think you are mistaken.... Look in the 5D MkIII manual on the page where the 100-400mm L is mentioned (page 82 and 83, lens group E). It does not mention an Extender, like in a number of other (faster) lenses in that group.

[wasnapper]

Glad I found this thread as I have been thinking of buying a tele-converter.
As I don't have / cant afford a fast telephoto I wont be buying one = money saved.