11-07-2017, 09:24 AM
Quote:I reckon it is caused by the camera not being able to determine exactly what to use for AF exactly, as the AF points cover quite a bit more territory than they do with e.g. tele-lenses. Having a slower aperture helps a lot in those cases, I would think.Almost never, there is something a lot in front of what you want to focus on with UWA lenses. It can be that you focus on a small target where behind it the background can become a target of the AF point. However, AF points are small enough to rule that out in tests.
Spherical aberrations in a lens can throw off the PD AF system, depending on which colours the AF sensor is sensitive to. And the steps a lens makes can also be an issue.
In this case, from what Klaus describes, I suspect aberrations to be the/a culprit. Testing my 10-18mm on 14mm yesterday in MF, the focus confirmation range was very, very small.