This is the second time this has happened to me as I'm not a fast learner. There is a 1,000 acre nature reserve near my house. One of the features of the reserve is an artesian spring that was brought above ground to form a small natural waterfall. The water is chock full of iron which is why my village is called Yellow Springs. I've been drinking from the spring for almost 50 years as I love the mineral taste of the water. I was there on Friday with the XT1 and the 12mm Zeiss lens. Had a nice drink at the spring and went on to shoot some pictures of the fall colors. When I got home I found that I had a rather large, dried water spot on my filter. The top, right is just a bit of lens flare. If it had not been such a wide angle it probably would not have been quite so pronounced on the picture.