We should keep in mind that lenses are optimized for their strongest feature. The 50/1.4 is optimized for fast performance. Indeed, the large aperture is the main reason for this lens's existence.
A macro, on the other hand, is optimized to meet different requirements. Flatness of field, total lack of distortion, and even resolution across the field are the most important requirements for a lens designed for copy work. And make no mistake, the sort of macro that is the intent of a 50mm lens is copy work rather than insects, for which longer macro lenses are better suited. That's why 1:2 is generally just fine for me.
The Canon 50/2.5 macro is sharper than the 50/1.4, and scores a tiny bit higher on 40 lines/mm MTF (i.e., resolution) and not quite as high on 10 lines/mm MTF (i.e. contrast). That's just what you want in a macro lens. And it has that flat field and lack of distortion that isn't so important with a lens built for speed.
I'm sure the Sigma benefitted from the same design decisions that when into the Canon macro lens. Thus, it's a bit tough to compare them on absolute terms. Even so, Photodo rated the Sigma macro lens at 4.2, instead of 4.4. for the two Canon lenses. That difference is probably not noticeable and is still quite excellent.
I own the Canon 50/2.5, but recently bought the 50/1.4, simply because there are things the fast lens can do that the macro lens cannot do, particularly regarding selective focus.
And it should be noted that both the 1.4 and the macro Canon 50's performed the very best of all non-L Canon lenses. In fact, the Canon 50/1.4 is the best 50/1.4 in Photodo's database--better than the Nikkor and better even than the Summilux (I'll probably get a load of Leica hate mail for saying that, but hey I'm just reporting what Photodo published). And the Compact Macro was better than the 60mm Micro-Nikkor. Only the famed f/2 Summicron provided a better overall MTF score among normal lenses.
A lens is more than MTF scores, of course, it is properly measured in terms of artistic potential or suitability for a particular purpose (such as copy work). For general sharpness, the macro lenses are almost always the best performers, but none of them have that extra two full stops of wide-open speed, and it's that speed that opens a whole range of artistic possibility.
Rick "who thinks the Sigma performed very nicely" Denney
just kidding. Nice test.
