So I'm looking at picking up the Sigma 18-50 f2.8 Macro lens. Not so fast says Mr. Sigma, we have (at least) 2 varieties of that particular lens! According to Sigma's site they only have two varieties of the 18-50 f2.8, the HSM and non-HSM versions, but amazon explicitly has a version with SLD and ELD glass, but neither with HSM. Try as I might I've only found one place that sells a Canon mount HSM version and they are in the UK (I'm in the US). Amazon sells the HSM version, but only for a Nikon mount. Is it worth getting the HSM version, or is it mostly just noise reduction on focus? Is the SLD and ELD on all their glass for this lens? EX DC Macro http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3320&navigator=6 EX DC Macro HSM http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3328&navigator=6 HSM version for sale http://www.i-source-global.com/epages/ce_fr.sf/en_US/?ObjectPath=/Shops/170990/Products/S1850C Amazon with SLD & ELD http://www.amazon.com/Sigma-18-50mm...1?ie=UTF8&s=electronics&qid=1205642067&sr=8-1 Any help would be appreciated!!