Hi guys,I have a Nikkor 50mm 1.8D mounted on my D3100 and I've been using it for a while now for portraits. However, I still can't seem to get that really sharp shot. My usual settings are ISO 100 @ F1.8 and F2.8 in aperture prio mode. Could this be the reason why some of my shots are not that sharp? What settings should be appropriate for portrait shots to get that correct sharpness? Thank you guys.