gradient said it well. Dust does come from lenses too while they zoom in.I thoughtt I had a worse problem on the my sensor, but it was just a bit of dust on the viewfinder. That shakes off after awhile. I'm not a huge fan of blowing dust. I have found a good strong vac is best. Look at it this way. Blowing a particle against some fragile surface in my opinion is wrong. Sucking it away seems more logical. Just be very gentle lifting the mirror up and letting it back down. Never let it shut by itself.Don't use anything inside to lift mirror that can scratch or drop particles itself IE: Q-tips. Better to make up something similar using a rubber tip. Anyways I don't lose too much sleep over the dust anymore.

"The happiness of a man in this life does not consist in the absence but in the mastery of his passions."