I rode safari with my zoomiest lens recently, my 200-600mm, and everything was so close that I ended up spending the first half of the ride trying to zoom out enough to get all of any animal into my frame. I just wanted this guy (or gal?) from the neck up though, so this shot worked out just fine.
Taken at 200mm, f/6.3, 1/500 sec, ISO 2000. Sometimes you have to embrace a little ISO grain to get the shot on a moving safari vehicle.