The first 50 1.4 I had worked great, sharp wide open focused great. Stupidly I sold it. Then I tried to buy another about a year later, tried three copies and none had good AF. Not sure why. So i went with a used 50 1.8 and that thing is sharp wide open and has better AF then the 3 1.4s I tried. I won't try the sigma after the issues I had with the 30 1.4 and focusing (one was so bad it front focused by ten feet!) So for me I have the 28 1.8 and 50 1.8 and love them both!