As I described at the end of October, I received a Canon 24-105 L IS USM as a birthday present, and I wasn't satisfied with its functionality, it tended to give me soft images. I rented a copy of the same lens for a day and got much sharper images across the board, but particularly above 60mm of focal length. This was evidence enough for me to go back to the store and ask them for help with my version of the lens. They cited calibration and told me to take it to Canon, who fortunately have a repair shop near where I live. This was done; the Canon report cited an improperly assembled autofocus assembly. But the lens still isn't really where I want it. It is now solid up to about 70mm but above 80mm or so it still doesn't get a very crisp focus. So now I'm wondering how to bring the whole issue back up. Returning to the Canon shop would seem my best bet but when I first took it in, it sounded as if there were only certain types of repairs they were actually authorized to do, which is confusing and calls the camera store's suggestion of micro-calibration into question.
So I guess I'd like either advice or personal experience with this sort of affair. Many thanks in advance.