I want to start my career in the photography business. Particularly at horse shows. I have a small budget to begin with so I have decided that I am going to purchase the Canon Rebel Xsi. My question is about lenses. I would absolutely love to buy the 70-200mm f/2.8L IS but unfortunately it out of my budget. I am looking at purchasing a 70-200mm f/4L (is Image Stabilization a must?) and are there any other lenses that I can start off with that will work for what I want for the time being until I can afford the purchase of a better lens? The horse shows consist of Pleasure shows of horses on rail and NBHA (National Barrel Horse Association) shows.