I think that's the lens I'm going to get for my recently ordered Canon 50D, but have read several reviews that recommend this: "The one that you want is the Sigma 18-50 F/2.8 DC EX HSM MACRO. Don't waste money on the other ones. They've been discontinued now for a touch over 2 years." Seems like HSM exists for Nikon, but not for Canon. Does this mean that the Canon's line is older and may have the QC issues with front/back focusing? Thanks!