Hi Stuart. I find that my 18-200mm Sigma lens is very capable and is my most used lens because its focal range almost covers most subjects. I also have a 10-20mm f3.5 ultra wide angle which is fine for groups shots in small spaces, and it's amazing how much can be crammed into the frame. For long shots I use my Sigma 120-400mm and I find the quality just great for Motor Cycle Racing, you can see some of my shots in the gallery of this subject. All the best. Mike.
Humility is an endearing quality and gains many friends, whereas arrogance loses them. Mike, 2012