I recently purchased a Pentax K5 slr and have been using it with 16-45,10-17 and 55-300mm lenses. There is a fault that I did not notice unless there was alot of sky in the shot. There is a reverse C shape in the upper left quarter of the frame clearly visible on the photo I put on the gallery of a ship in Douglas bay. You'll see it directly over the ship.I've tried cleaning the lenses & the mirror & screen with alcohol & soft cloth to no avail. Any ideas anyone ?