In fact, a Nikon tele-converter will NOT mount on this particular lens, because of a mechanical stop they engineered into their teleconverters. But, that doesn't stop other manufacturers from omitting this mechanical stop...such as the Kenko I have....it happily mounts just fine.
But the question remained: would the auto-focus work, and would the picture quality be so bad that it wouldn't be worth having a "100-420mm zoom"?
Well, I can tell you the AF works great on a sunny day. (haven't tried it in overcast conditions yet). The AF speed seemed to be just as fast as without the converter, and it did not "hunt" around at all. Furthermore, the metering works just as it should, the proper f-stop is reported to the camera, and the effective 100-420mm magnification also shows up in the EXIF data. AND: the VR still worked just fine
! I just could not believe it: all of a sudden I had a very compact super-telephoto with VR
! I wondered what would happen if I dared to take a few shots at 420mm handheld
....no tripod? So...I tried it with the lens aperature cranked wide open. Judge for yourself the results.
Ok, so it seems to work if the light is good. I need to experiment more in other light conditions. And with a tripod to see what the difference might be. The bad: the maximum wide-open f-stop you can get with this particular setup is only f/8....meaning a slow lens that needs lots of light to work. No, it's not as good as a prime 300 f4 lens with this same teleconverter on a tripod, but I had a lot of fun doing this experiment. You Canon guys might want to try this if you happen to own the 70-300 IS USM...I'd be interested in hearing if it works and how the picture quality is.