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 sure the dust is on 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.