I am looking for a lens to take photos of horses in action. I will need some zoom as I am standing outside of a riding ring and the horses will be moving all over the place. I have a Canon Rebel T3 and I currently use the EF 75-300 F/4-5.6 III. I think the images could be clearer, and comparing the auto focus which a friend's camera, auto focus seems slow to me. My budget is $900. I am looking at the EF 70-300mm f/4-5.6 IS USM Telephoto Zoom lens. Is this an appropriate lens for what I want to use it for? Anyone have experience with it? Any other suggestions? One with a different f stop? I contacted Canon, who is not responding Thanks!