Can the TC-20eiii be used successfully on this lens?
This lens will not take tack sharp photos with a teleconverter. I tried with the 1.7 and the 1.4. I took a day of photos of wood ducks and a mandarin duck and threw them all away. It was a painful lesson. My 600mm Nikkor lens works well with the 1.4 but does not auto focus with the 1.7.
Otherwise the 200-400 lens takes great photos and gives you terrific flexibility. I primarily shoot birds with these lenses, and seldom use the 200-400 any more, but do with close in subjects.
Most of my friends started with the 300mm and advanced to the 500mm. One uses the 1.4 and perhaps the 2.0 with his 300mm and he is very satisfied. An advantage with that configuration is size and weight while achieving up to 600mm.
I hope this helps.