Though I've used M mode before, today I was at the camera store and brought my D7000 body along. To take some test shots with a Sigma 17-50mm lens.
So I tested it. Taking double shots at min and max focal length, stopped down and wide open f stops. M mode allowed any combo of shutter/aperature. I repeated the testing outdoors. so I have can see the extreme limits of the lens.
Two things caught me by surprise. When I was outside, a few times the shutter wouldn't fire. Is the shutter disabled (in M Mode) when the exposure scale isn't centered?
Focus was fine. Definite green dot in the viewfinder.
Later, looking at the images at home on the computer (with ViewNX2), a few of the exterior shots had EC +/- exposure corrections inserted. I didn't initiate that. That was the other odd thing about today. ISO was set at about 400. What's going on with exposure?