Seems reasonably sharp to me Mark but there seems to be a bit of noise around. Have you cropped it much? What ISO were you using?
I have a 1.4 converter that I occasionally use with a 70- 300 Nikkor. The success rate is not high. You lose at least a stop but more significantly, on a Nikon at least, the auto focus is degraded and I get a lot of hunting.
200mm isn't much lens for shooting birds, Mark. You should do OK with a 1.4x on that lens. What body are you shooting? If it is one of the current gen bodies that focus to f8 you could even try a 2x. I've used a 2x on a 70-200 2.8 with decent results.
Thanks Dan. A D600. I'll talk to the folks at the place I shop. Would be nice not to have to do so much cropping.