It's nicely built, very fast thanks to it's F/1.4 and has very smooth and quite autofocus.As most of reviews noted, it is very soft in the corners when stopped down but with this kind of lens, you don't really care for the edges, especially as you get a wider angle than most of it's competitors in the category.I am very pleased with it, but if you are looking for a good portrait lens i would recommend the CANON 50mm F/1.4 instead.it will be much sharper at corners and will cost less.