I am looking at a lense on craigslist. The seller says "The lens is in pretty good shape, with the exception of a little dust inside the lens barrel, which is fairly normal for a used lens. The dust doesn't show up in images unless the aperture is in the f/16 - f/22 range. The dust spots that DO show up at that point are usually pretty easy to remove in post processing using Photoshop or other similar programs." Is this something that can be cleaned or not?