Although I've had this lens for about 15 years it's always worked perfectly. It's in excellent cosmetic and optical condition, and it's never been dropped, etc.. However, very recently I found that it won't focus any more. Both the lens and the camera are set to AF but when I try to focus the lens hunts back and forth briefly then comes to rest a long way out of focus and the camera's screen shows a large red box. During that brief attempt to focus I can sometimes see the lens pass through the focus point, so the camera ought to stop it right there but somehow the lens just carries on past that point to somewhere a long way off. None of my other lenses have a problem, including my other EF lens (a 50mm f/1.8 II), which is also attached with the same EF-M adapter, so I don't think it can be the camera or the adapter that's at fault. All the contacts on the lens look perfectly clean. Clearly the focusing motor in the lens works, as it attempts to focus - it just doesn't stop at the right place. And focusing manually feels smooth and works fine. It was working on the M6 Mk II for about 18 months, so this is a new problem. I've tried the lens in both focus range settings (0.34m or 0.48m to infinity) with the same result. Any ideas, or do I need to get Canon to service the lens? Or maybe just give up and always use it in MF, which I often do for macros anyway.
