Yesterday I was photographing an event and had to change a lot between lenses (50mm and 18-55mm). Surprise, surprise, today when I looked on the viewfinder I saw a little piece of fabric and a little black dot.
I cleaned with a brush and blower (click for example): the lenses, the eye piece, the base of the pentaprism (which is that pink line in the figure below), and even the mirror. After the "cleaning" I looked again and the viewfinder was even dirtier, now with small translucent fragments, and the original dust still there.
I'm sure the dust is over the "focussing screen" (according to the pink line in the figure), because I observed the mirror and it's clean and I took a photo and it's also clear of dust. How can I effectively clean that base of the pentaprism? I even tried using the corner of a paper sheet and scrub it but without success.
Any ideas? Get a better blower?
P.S: I have a Nikon 3100.