I'm looking to get a fisheye lens for my D300. I'm looking for something like the Tokina 10-17mm or a Sigma fisheye. Are there any pros or cons to having the 10-17mm as opposed to a fixed 10mm or 12mm? Also, if anyone has any experience with either of these lenses, please share. EDIT: Just realized that the Sigma I linked actually isn't a fisheye. Can't seem to find the real one I was looking at.