I'm still learning this camera but was wondering if there is a way to choose the shutter and aperture but allow the ISO to remain in Auto. I shoot concert photos and want to force the camera to hold a shutter speed of 1/100+ and the aperture in the 4.5 range. I would like the ISO to balance the exposure. I thought I cold do this in P mode. Auto ISO is not allowed in Manual mode. Any advice on how to best approach this shooting challenge?