ahsanford said:
1) How fast to focus is Nano USM vs. Micro USM vs. Ring USM? LensTip measures focusing speed, but it doesn't have either of the two nano USM lenses tested. What might we expect here on a 50? Faster than the micro USM? Slower adjustments but less hunting?
Just to join the chorus, I was very, very impressed by the Nano USM, the one time I got a chance to try it (an 18-135mm on an 80D).
Speed is definitely impressive. It felt almost instantaneous, at all focal lengths of the zoom, focusing from very close to infinity. Faster than any of my current lenses on any of my current cameras. I don't know how that generalizes to other implementations of Nano USM, and to use on other cameras, though ...
As for accuracy, I can't really tell, I would need more than a half hour with one camera. All I can say is that the focusing felt very decisive. No hunting, not even the minor split-second fine adjustment hunting before confirmation.
Bottom line, I'm personally very happy to hear that it will have Nano USM, looking forward to seeing it in action.
(Of course if you're into manual focusing, you're probably not as happy. If I'm not mistaken, Nano USM means focus by wire, unfortunately.)