How close are you trying to get, filling the frame with just a head or more pulled back? I have shot a number of portraits pretty close, and i find that in terms of the focus, weather you are wide open or super closed down that you still have to be precise with the focus. Sure the additional DOF from shooting at say f22 compared to f5.6 will make parts of the face that you didn't focus on (everything but the eyes) closer to being in focus, but I could always see distinctly what was actually in focus. One thing that I found out very quick was to make sure the tripod I was using was very sturdy, this has a huge effect when working close up (with a flimsy tripod its easy to move the camera when you are adjusting the lens/shutter and putting in the film holder). Also try to re-focus as often as you, I usually try to not shoot more than 3 frames with out opening up and checking focus. Hope this helps.