I dont have the Zeiss 50/f2 macro, but have the 50/1.4. Also, the Zeiss 100mp.I am not sure why you mention the Zeiss 50mp instead of the Zeiss 100mp, since you are comparing them to the 100mm f/2.8L IS Macro.But anyway, the 100mm f/2.8L IS Macro is a fantastic lens. So are the Zeiss 50 & 100. Just remember that the Zeiss are manual focus only. I understand that the Zeiss 50mp is an excellent lens. You might end up using manual focus on the 100L if used as macro anyhow. You might want to visit some sites such as flickr, 500px, some Zeiss sites to see examples of images taken with all these lenses. As far as all-round quality, including build, iq, etc they are all excellent. The main differences are manual focus vs auto, and the Canon rendition vs the Zeiss rendition, and cost. I lean more toward the Zeiss look, but they are more expensive, and if you want to use them for other than macro, MF can take some getting used to.