I use window cleaner on a soft, ultra clean tissue, applied to the tissue (only a drop) and carefully wipe the mirror with the tissue on my finger. Then dry with a dry portion. The thing to watch for is to not even touch that foam bumper that the front of the mirror's edeg touches when taking an exposure and to not EVER touch that fresnel screen just below the prism. If you do, it gets very messy to clean up. - David Lyga