I've found that some discontinued teleconverters, such as the Pentax F 1.7x AF Adapter and Nikon TC16A, enable autofocus with manual focus lenses. How is this possible? Does this system have any significant limitations?
With the Pentax option, you're basically getting "close" with the manual lens using manual focus and then using the AF of the camera to move the lens elements in the teleconverter itself to adjust for more precise focus. Bear in mind that the TC is a lens itself...
At any rate, it's not perfect answer for making a manual lens do AF, but for the right sort of shooting, it's a very useful feature. I can't say for the Nikon option, but I would imagine that it's similar.