Hi Rick, It is a delayed response, but maybe it is still relevant. I've seen a similar trend with several Pentax lenses that had "SDM" (aka Micro Ultrasonic, or "old style" micro SDM aka piezoelectric motor). It's been an issue since the very beginning of 16-50 lens, which, AFAIR, was the very first lens with then a new type of AF mechanism, and was very prone to that problem. It's been a while since I was looking into it, so, I do not remember all the details of why it was happening, but the main advice was to "excercise" the AF of these lenses on a regular basis. Based on my observation, the issue will likely come back, but if you "excercise" the AF regularly, it might work well for quite long time. If/when it doesn't seem to work, try autofocusing with it several time, so that the motor would be activated both ways. In some cases after some (5-30) back-and-forth attempts, it might start moving, first, slightly, then getting back to the normal range. Sometimes, if it doesn't work on the first excercise attempt, try again a bit later. HTH, Igor Rick Womer Wed, 19 Mar 2025 18:50:11 -0700 wrote: Today I took a photo walk with the photo class I enrolled in. I had intended to substitute another lens for the 17-70, but forgot to. I focused manually for several shots, and then the lens woke up and autofocused without problems for the rest of the morning. Not sure I trust it, of course… Rick