I use a Nikon 500mm F4 ED-EF II lens in conjunction with either a D2Hs or D2H body and find it absolutely useless for any wildlife photography in motion. It is barely adequate for sports. It is quite incapable of tracking any bird in flight and is constantly jumping in and out of focus. And it will not autofocus with any teleconverter. The same applies to my Nikon 80-200mm F2.8 zoom (converters are OK but slow) I am seriously considering changing to a Canon system, i.e. EOS 1d II or III and a 500mm IS lens, despite the crazy white colour (for wildlife photography anyway) Can anyone tell me if Canon lenses are any better at autofocus tracking, faster, and do work with teleconverters? I'm a professional press photographer using Nikon gear for over 40 years so I have a fair idea of camera equipment. But this lot is driving me crazy, with so many missed shots. I would be better off with my ancient 600mm F5.6 manual focus lens. I have sent the 500 lens away for checking and even through the repair man couldn't find anything wrong, he did suggest that I might need a new motor!