Please forgive me for "raining on the parade" here, but in the tests conducted by Photodo, the Zeiss Macro-Planar T* 100mm f/2 beat the Canon EF 100mm f/2.8L IS Macro in virtually every optical parameter. Most particularly, its resolution was significantly better than the Canon. Yes, the Zeiss needs an extension tube to reach 1:1, but with the time, diligence, and tripod already required for macro work, that doesn't strike me as much of an issue (either lens will need an extension to go beyond 1:1 which is a fun zone as well). Lack of IS on the Zeiss when used for normal photography at 100mm focal length is perhaps an issue. Just my 2 cents.