There are three factors that go into every photo with a DSLR - aperture (f/4, etc.), ISO (digital “film speed”) and shutter speed. Many photographers set the aperture and ISO, and let the camera determine the appropriate film speed based on the available light. 1/8000 is as high as most professional grade cameras go, it not unheard of on a bright, sunny day especially against the backdrop of the bright summer sky.