Meanwhile, in the laboratory...

I just realized I have been downgrading my photos because of a low quality UV filter. The bokeh looked horrible and focus seemed to be off so ended up setting up a test setup and shooting plenty of frames with different settings. Soon It was quite clear that cheap Jessops branded filter was the culprit. But I also learned quite a lot about how autofocus works and what might cause it to miss the spot. But more later with example photos.