When I looked at the photos I took in Hamburg last Saturday, at first I thought "oh dear, in some the focus is not right", to only later see that they look blurred only IN PART - and now I fear my second Sigma lens is getting defective (the first would - after some time - "fall into focus" or "fall out of focus", just as it pleased, randomly, and I had no influence over it). Again, not every photo shows the blurred part, but some do. In horizontal frames it is in the lower right, and in vertical photos in the upper right corner: Any idea what might cause this? Any idea what could be done ABOUT it? Will I need to get myself a THIRD lens of the kind (no money for anything better than that one!)?