Well I am ecstatic over my new 200mm f2 but.... The 200mm is spot on, no AF fine tune required. I slapped on my Kenko 1.4 pro 300 TC and the combo back focuses, even -20 is not enough to correct it fully. The Kenko worked fine on my 70-200mm VR and 300mm f4 both AFS and AFD. I wasn't too concerned because I had a new Nikon 1.7 TCE II on the way. Slap on the 1.7 TC and same thing. I can't test the 1.7 with another lens because I don't have one that is compatable. When using MF the combo is very good. The problem is more pronounced at moderate distance. So I am now looking at sending the combo to Nikon. Any ideas or similiar experiences?