Well, I recently decided to get my first dslr which is the canon 500d (t1i). And I still have a lot to learn about using it. But I am having trouble trying to decide on a fisheye lens to start out with it. I currently have a NN3 and am interested in doing spherical panos with it. If price was no object, I know I probably would want to get a sigma 8mm or 4.5mm, but unfortunately I am on a budget right now. I was looking at the Opteka 6.5mm, Vivitar 7mm,Peleng 8mm, and the Rokinon 8mm. Does anyone know if these lenses can be used with filters? Also, having only one focal length means that you can't zoom right? Is there an affordable lens that lets you do both?