Originally posted by peasant Thank you,I hope you are correct,any reason the spots would be visible at smaller apertures and not at larger apertures?
I don't know the exact scientific answer but it is basically the Depth of Field of your photo. More is in focus at the smaller apertures than the large ones. You are not seeing dust ON the sensor but rather the filter screen just in front of it. If it were On the sensor, it would show up in all photos and would probably Be White (I don't think that's the issue of the OP however because the spots are not always there and they move). As it is, you are getting an actual photo Of the dust, hair, slime, ect. Whatever happens to be on the sensor filter. The greater your DOF, the more sharp it will show. It's still there at larger apertures but is so out of focus, you cannot really see it.