I currently own a 50mm f/1.2 AIS. I've seen pictures of the AIS version side-by-side with the older AI, and the latter (like most if not all AI and pre-AI lenses) seems to have a longer focusing throw, meaning the distances are more spread out, facilitating more accurate but slower focusing. Has anyone used both the AIS and AI versions? Is there a noticable difference in the ease of focusing accurately? I ask because I get frustrated when trying to critically focus with my sample; the focusing ring doesn't feel precise enough. There's also a little bit of play when focusing back and forth, meaning when I switch directions, I can turn the focusing ring a fraction of a rotation before the helicoids move.