I am new to photography, and just having fun with it. Not looking at going too far with it, but I have been doing shoots for people with their horses. I have a lot to learn, but I want a new lens. I have a nikon D40, with the kit lens, 18-55mm. I am looking for a little better zoom, and something to capture action. My current lens is quite fast, and want to keep it at that speed. My budget is under $200 right now, as this is a hobby only. Thanks for any and all help!