For what it's worth to those of you considering such a procedure: don't! I had a very annoying black speck on my focusing screen and attempted to dislodge it with a bulb blower. That didn't work. It made matters worse, adding some big dust spots to the black speck. So then I had the brilliant idea of using the blower's brush to remove the dust. REALLY bad idea. That made the focusing screen look like it fell in a pile of dirt. So then what did I do? Yup, I decided to put on an even bigger dunce hat. I then attempted to get that stuff off with some lint-free lens cleaning paper. That process just moved the dust around and caused me to smudge my mirror. I think I may have even scuffed the focusing screen and the mirror. And in my great wisdom, I decided to carry out this series of procedures about 10 days before I fly to Europe for the summer, so I have no time to get it professionally cleaned before I depart. Yay me!