...I just got a new DSLR camera (Nikkon D5000). I want to get a fisheye lens for it but don't know which one. It will mainly be used for pics of wheeling trips, so fairly close up shots of the vehicles and terrain. Would like to get one that is reasonably priced...gently used is an option. What MM should I be looking for? The appeture seems to be f2.8 for almost all but I have seen a few at f3.5 also? So throw me some advice and schooling!