Ever since I got my 17-40mm 4.0 there have been spots that show up on every picture I take with it. I have gently cleaned both the front and back glass and yet, the spots have stayed. I cannot see the spots when I look at the glass from either side. Is is possible that there could be something on the glass inside of the lens?
BTW, the spots don't show up when I shoot with my 50mm, so I don't think it is an issue with the image sensor.