1. I am pretty sure that you are in one of the AF area modes, probably one of the more advanced ones. I don't have a D600 (or any recent model) but I think this is changed by pressing the control button in the center of the AF/M switch, and then rotating the front command dial. I have no idea how to tell which mode you're in, although I suspect that if you go fiddle this control, it will be fairly apparent.
2. I find adjusting diopters kind of a pain on all of the cameras, but in general I think you should be looking at individual pixels of the viewfinder display to adjust the diopter control, NOT the image.
_____ Brian... a bicoastal Nikonian and Team Member
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