This was shot with the old Nikkor 400mm f3.5 matched to the tc301 2x, and shot wide open. I think the image quality is good, especially considering it was shot at ISO 1250 at 1/125, twilight and shaky tripod on a wooden deck. This is resized, full frame, and body was the D700.
Funny thing about 800mm--the vibration is endless. Someday, a proper Gitzo! (and solid ground).