In spite of all the high praise for this lens everyone should be aware that it's quality can vary greatly. In other words, you pay your money and you take your chances (of getting a good example). It was beyond soft at wide aperture, CA was horrible too. That junker went back. Example number 2 was a bit better but not by a lot. Example number 3 was the best but not all that good. I think there is too much hype out there for a few good examples of this lens, and they are not the norm.
It is the cheapest constructed lens I have ever laid hand to. I mean this thing feels like my grandson's plastic Chinese toy car. Horrible! Actually, in retrospect, my grandson's toy car (he's 4 years old) feels better contructed than this Canon lens.
Be advised that spending an extra $125 for the Canon 50/2.5 macro lens is likely to be the best investment you'll make. If you can say 50/2.5 macro then you can truly say SHARP! 50/1.8, well that's hit and miss. If $80 doesn't mean much to you then buy the 50/1.8. Sorry, but $80 DOES mean something to me.