In order to freeze the action in this photograph of two stallions battling for dominance, I used 400 ISO in the bright, early morning sunlight. This gave me a shutter speed of 1/2500th of a second, and my aperture was f/6.3. Depth of field wasn’t a factor here; it was the shutter that was of primary concern so I could capture each hair as sharp as possible. It would be easy to assume that 1/250th or even 1/500th of a second would be fast enough here, but that wasn't the case. When the two horses came together, things happened extremely fast, and only the super fast shutter could freeze all of the elements with tack sharp clarity.
I used Program mode in this situation, knowing that ‘P’ would give me virtually the fastest shutter possible (because it assumes I’m hand holding the camera, which I was). I shot this with a 70 – 200mm lens set to 140mm during my photo tour in southern France.