Ok. I give... How do you clean these filters? I used them yesterday for the first time. They are very good quality and I love the thin design. However, a few hours into my trip, I noticed the one on my 24-105 lens was dirty. I had been using it a lot. I tried to clean it multiple times with a good lens cloth. It just kept smearing more and more. Do I need to use a cleaning solution or something? I did not want to do anything more until I talked to people that have used them.