I made 3 photos; manual mode, same subject, same focus. (1) 1/100, F8, Auto ISO2800; (2) 1/200, F8, Auto ISO9000, (3)1/400. F8, Auto ISO12800. I use single-servo AF mode (AF-S),EV Compensation for each photo was O, GrP Group Area (5 point). Why did the auto ISO change so much: 2800 to 9000...