Yes,i have the same issue on the same camera lens. It looks like a coating issue, lens seems to be partially coated and the parts of it not covered with protective coating therefore every time you touch the lens the part of it is protected from the oil from your finger and other parts are note. You will notice, every time you touch it and clean it and touch it again, the shape of the mark will be exactly the same. You can go to Apple store and compare the phones inside if they have the same issue as yours before going go Genius Bar. Because the lens is part of the enclosure it is likely that phone will need to be replaced, so I suggest you backup your phone. I yet myself have to go to Genius Bar to solve this issue once I have time. Good luck