(text by P.S.) I had to go though three units before I found a good one. Sigma has a lot to improve in their factory quality control - their customer service in one of the finest, though. This is a lens for capturing small spaces, architecture and making special perspective effects. It\'s sharp from f/3.5 upwards, and f/8 has very good sharpness. It has an inbuilt lens hood which is not enough in many cases - colorful and strong lens flares are a big problem with this lens if you\'re not careful.