17-40mm f/4 is film lens. Thus, it is a lenses for FF camera like the 5D. It was created during the film days, thus it is a bit soft for me in low light on digital SLR camera. But still harder than 16-35mm f/2.8 version 1. On a 5D, 17mm is truely 17mm ultra wide-angle lens. Good for big object in limited working space and small and tight interiors. As for the curvical distortion and perspective distortion ones needs to handle well to get great shoots.