>Thanks guys for all of the information. I think I am going >to stick with what I have for now. For my own education, can >the 2.0 III work with this lens. In reading through different >blogs, there was a lot of conflicting information. Nikon say >it can't. Many people say it works just fine in all >capacities. Being new to this is hard. The more I read, it >seems like I can find many different answers for the same >questions. I am starting to feel like there are a lot of >different ways to get good results. It seems like not >everyone does things the same way. I am wrong?
The 2x converter with the 200-400 will physically attach and will meter properly, etc. The issue is that it drops you down to F8. Older cameras will not reliably focus at F8, newer cameras are supposed to (D800, D4, I think D600). As you get to the F5.6 range though auto focus becomes more challenging generally, and on the 51 area cameras you only have a few focus points which can focus all the way to its limit, so you reduce the number of focus points available not only for focus but for tracking focus.
But short answer is "yes - with the right camera". The reason you find conflicting info is when the lens was released you didn't have cameras that could AF at F8, so the official answer at that time was "no".