Originally posted by Gimbal It does happen with my K5 too, wide angle is hard for some reason. But mostly this is a problem in low light situations with my K5. I do however have a habit since the K10d days to press AF several times (when there is time) and slightly shift the camera around to make sure that the AF sort of settles at one setting. With a wide lens the AF surprisingly often hunts back and forth when doing so.
I have noticed my 18-55mm kit lens does a little dance when auto focusing; it seems to stop a little before the correct focus point and then jump to the correct point. In the case of my preferred Tamron 17-50mm, the lens always stops in exactly
one place. No dancing. For both lenses, however, if the camera actually determines the
correct focus point is hit or miss.
I'll also mention (and repeat) the fact that this AF inconsistency on the part of the K-5 was not a problem until the camera came back from CRIS for a general check and lens calibration.
There was a mention earlier in the thread about lens resolution and aberrations as a factor in my situation. I hadn't fully formed an opinion about the science of that possibility until recently. If one is to trust the reviews by guys like Photozone.de and Lenstip the Tamron lens from my test images actually has the highest center sharpness at its widest focal length which is precisely where I'm encountering the problem. In other words, if resolution is the key to all this, the lens should actually perform worse at longer focal lengths, not to mention worse resolving lenses would also be giving me problems. Of course, I've stated I know little about the alchemy that goes on with phase detection AF mechanisms, so I'm sure there's plenty I haven't considered here. Nevertheless, if I only had numbers to go by I'd be inclined to rule out the resolution of the glass.