It is optically and mechanically stronger than the predecessor of Canon. Focusing is fast and virtually inaudible. The front lens does not rotate during focusing with. Constant mesh manual focusing (with the camera turned) is also very nice. The only "disadvantage" vs.. USM lenses is that a focus without camera is turned on is not possible, but I do not really need. I have the lens cost arisen from a kit, which is significantly untzer the MSRP of Canon.