Have emailed Sigma UK concerning this lens. Not at all happy with the focus. Have tried it on a test chart and taken portrait shots all at f1.4. The results are erratic both with the d700 and d300s.The d300s always locks focus immediately whist the d700 sometimes hunts and has even failed to focus. With both bodies it may focus correctly, front focus or back focus by varying amounts. One portrait shot with focus confirmed on an eye full face has the point in focus on the photo as hair just forward of the ear about 2.5 cm behind the eye. It is totally inconsistent and would find better use as a paper weight.