Got a dust problem on my sensor. I was trying to clean it with a simple blower (don't have a brush of any sort), but I couldn't seem to clean it off. After cleaning, I attached my macro lens and set it to f/20 and took a photo to see if dust was still there. Anyway, I took a photo and saw a lot of spots at the top right corner of the frame. I took off the lens, used the mirror lock-up, and tried again. I took another photo at f/20, and still got dust at the top right corner. Looking at the sensor, it doesn't seem like there's anything to clean, although dust can be smaller than I can see. Anyway, I tried flipping the camera upside-down, and took another photo of the same object. Instead of the dust appearing at the bottom-left of the new photo, it still appeared on the top-right!!! That's weird, because I flipped the camera upside down. The dust I saw at the top-right corner of the frame should then be at the bottom-left corner of the 2nd photo. When I flip the camera upside-down, the lens is upside-down as well, so I don't think it's dust in the lens. Soooooo.....what's going on?