I have a D50 and I accidently touched the mirror on the body (behind the lens), I tired to gently wipe it but it just seems to spread the smudge out instead of removing it. Also I have a B+W polarizer, which suffers from the same problem. I use one of those soft clothes but it doesn't seem to work. I was wondering are there and liquid solutions which I need to apply then wipe? If so, which ones would you recommend? Thanks.