You mean, setting your CAMERA with this lens mounted on it? Well, I guess you will need to set the AF (auto focus) mode to AF-A, in order to let the AF system re-focus as you re-compose (move your camera, while tracking the dog, keeping your shutter half-pressed). Set the number of "focus points" to "one", found at the center of the frame. Set the metering to "matrix", so that the light meter takes care of the "average" intensity of the light across the frame. Use mainly a "shutter priority" whenever you are afraid that the "action" could render your photo blurred, due to the fast moving of your dog, and a "aperture priority" if the "depth of field" (field of sharpness, before and behind your dog) matters to you. Set the ISO so that it is automatically changed (raised!) as needed , relative to the available light, starting with, say, 400 ISO (dog on the run will probably require the exposure times of above 1/500 sec. at the focal length of 300mm, with or without VR).
If you want to "freeze" the dog's motion, you'll need even shorter exposure times, say, 1/1000 sec and beyond that. If you're aiming at "catching" the dogs movement by "blurring" it (as opposed to the "frozen" and perfectly sharp background) you will have to use VR (VR "on", if your version of lens is equipped with VR) or the tripod (VR "off") and the exposures of 1/100 sec and longer ("slower")... Use "panning" (moving the camera so that it is tracking the dog as it runs, and you'll get the dog "frozen" and the background/foreground "motion-blurred").
Useful review:
http://www.dummies.com/how-to/content/how-to-take-photos-of-dogs-runningfetching.html
Thanks Kevin
