I'm looking to buy a 180mm macro lens and would like to hear comments from anyone with experience with both the Canon and Sigma versions regarding relative performance and picture quality. The reviews for the Sigma appear to be generally positive and it is a much newer design, but probably lacks weather sealing (although I don't expect to be trying to do macro photography in the rain). It's also 50% heavier than the Canon, but is the same weight as my Canon 100-400 V2, and I don't have any problem with that weight - will probably be on a tripod most of the time anyway. Not sure if OS is of much use when handheld at MFD. Also not sure F2.8 is an advantage for macro as depth of field is already too narrow at close focus, but I suppose there is an advantage in having more light for focusing. In Canada, the Sigma would cost me about $315 more than the Canon (more if I buy any filters due to the larger filter size). I only intend to use the lens for macro, not as a telephoto prime. I would be using it on a 5D III. The Sigma in Canada is a special order, meaning I can't return it.