Long telephotos are notorious for their shallow depth of field (DOF). When shooting close-up wildlife shots with long glass, seldom can the entire subject fit within the narrow range. It is imperative for the animals eye, if visible, to be tack sharp. With this in mind I regularly attempt to spot focus on the eye. If this isn’t the composition I desire I then recompose the shot while holding the shutter button down halfway.
In this instance a cooperative young whitetail buck inquisitively watched as I photographed him. Using the 400mm lens at F7.1 the DOF was too shallow to keep both the eyes and nose sharp when using his eyes as the focus point.