Originally posted by Yoda boy I've had 4 failures with SDM on two DA* lenses in less than 3 years so I think there is a problem.
There are any number of threads about SDM failures on the forum. A few of them have made a bit of senses. Apparently SDM relies on a capacitor for power. If the capacitor loses its charge, which all do over time, SDM will not work. However, if you take the time before taking the SDM lens out to recharge the capacitor everything will work again.
Yesterday my wife and I went for a walk on a local urban trail. I felt like taking the K-3 and a single lens, the DA* 16-50/2.8. I had not used it for over a month. I mounted it, pressed the AF button and nothing happened, so I left the camera turned on with the lens attached an had another coffee. When I came back, it moved slowly, but it focused. I exercised the focus mechanism by focusing near and far alternately for a couple of minutes, and the old girl was like new. Worked like a charm during the walk. As snappy as it has ever been since I bought it in 2007.
I think I made a mistake when I gave up on my DA* 50-135/2.8 a few years ago. I wish I had known this trick back then. My DA 55-300 is performing as well as can be, but there was a snap to the 50-135 that I miss.