I am referring to inspecting the glass of the lens, front, back and internally with a magnifying glass. But, even dust within the lens might not be so obvious at first. A test that you might try sometime . . . for each frame exposed, make a duplicate exposure on the next frame with the camera inverted (upside down). If in the first frame the smudges end up in the sky as usual, and in the subsequent frame (inverted frame) they end up elsewhere; ie; 180 degrees out, then my guess is still that it's something on the glass of the lens internally or externally. I think you have already proven this by your example above, the exposure that was made in portrait (vertical). Notice how the "C" shaped smudge moved when the camera was rotated. It moved with regards to the real horizon, but stayed in the same place with regard to the camera's frame.
Last edited by DannL.; 11-25-2013 at 10:27 PM. Click to view previous post history.