I was overseas for holiday and found my sensor to have a few large specks of dust that was clearly visible at F8 and even vague visible at F5.6. Since my cam warranty was over and I did not want the dust to spoil my pics for the rest of my trip, I used in desperation my lenspen brush to sweep the sensor. I swept gingerly at first but the dust was still there. So I did it again and swept more vigoursly in circular motion. And guess what? It worked brilliantly...haha. Dust was not visible anymore even at F16 and only a few minor, almost invisible specks at F22. Looks like our cam sensor is not that fragile and the camera makers are just scaring us so that we are willing pay to have our sensors cleaned by them.