I have just checked over some footage that I took using the Century optics 2 x converter and have noticed that the centre of the frame is quite sharp, while the majority of the rest of it is not in focus. I was shooting in fairly low light, but that shouldn't affect some of the frame and not other parts of it.
Has anyone else had similar experiance with teleconverters?

What was the focal length you were using -- zoomed out all the way wide? Full telephoto, or somewhere in between?

Maximum zoom most of the time. (maximum problem)........