A couple of things... remember that just because your lens will open up to f1.4, it doesn't mean you should shoot there. While the 50mm f1.4 is an excellent lens, NO lens is ever at its maximum sharpness wide open; typically for portrait work I shoot with an 85mm f1.4, but at an aperture of f5.6 or f8. As well, if you're not having good results with auto-focus, you may want to try and figure out where things are going. Modern cameras and lenses are designed to auto-focus, and they do it well. For single-person portrait work, I recommend using a single AF point and placing it over/between the subject's eyes. Do not use the focus and recompose technique as this can cause problems, especially with shallow DoF shots.