First, for accuracy's sake, focal length has little to do with DOF (depth of field). Believe it or not, if the subject takes up the same amount of space in the frame, and the aperture settings are the same, then the depth of field will be the same for a 28mm lens, or a 200mm lens. Try it. Shoot something with something wide, and then shoot it again with something long. Use the same aperture setting but make sure the subject is the same size within the frame. The DOF will be the same!

First, for accuracy's sake, focal length has little to do with DOF (depth of field). Believe it or not, if the subject takes up the same amount of space in the frame, and the aperture settings are the same, then the depth of field will be the same for a 28mm lens, or a 200mm lens. Try it. Shoot something with something wide, and then shoot it again with something long. Use the same aperture setting but make sure the subject is the same size within the frame. The DOF will be the same!