I have this lens and love it. It's very versatile, and can be found relatively cheap these days. I can use a 1.4 on it but only on cameras that can f8 autofocus (5d3 and 1 series),and even then it's pretty slow. In its native form though, it has excellent image quality and pretty speedy focus.
20120824-AQ4E0085-Edit by
lennycarl08, on Flickr