HI,
Two, no three reasons I guess:
1) I really want it to PDAF autofocus for people stuff. My suspicion is that a pukka Canon lens is more likely to be in Metabones firmware's capability than third party lenses. I'll take slow AF over not at all.
2) EBay had some second hand in reasonable nick, but didn't of the Sigma 2.8.
and 3) I don't really know how useful it'll be, and I don't really know forgiving it will be for people pics. My previous experience of macros is that they tend to be too harsh and contrasty for photographing beautiful girls, which is why the Tamron 90 mm f/2.8 Adaptall is still my go-to macro.
I've tried a couple of others in the past and just didn't like the rendition. All of these macros are likely to be too sharp, so I might end up diffusing or mucking around with them or just flogging them again because I hate them (which happened to my 100mm Canon macro. I hated the look SOOOO much). All the reviews of the 180mm Canon mention it is super-sharp, so if the Sigma is sharper, that's not in its favour for my purposes!
Hence, a second-hand copy of a lens which stands a fighting chance of getting useable autofocus on the A7Rii seemed worth a punt as an impulse buy at the end of the tax year If there'd been a Sigma on eBay I might have risked it but there wasn't so I didn't.
Cheers, Hywel
Oh and 4) it'll take the Canon extenders too in case I want to get even further away and flatten the perspective more on very tight close-ups.
1. I have owned 3 copies of the Canon 180, 2 copies of the Sigma 180, and Sigma's AF blows Canon's out of the water;
2. Can't help you here, and don't know how much of an emergency it is for you to have one "right now," but I would rather wait 3 months and get the better of the two than "immediately" buy an inferior product;
3. The Sigma is better at pretty much everything than the Canon, including sharpness, so if this is a deal-breaker, then buy the Canon if you want soft images.
As for the reviews of the Canon 180 being "super-sharp," that might have been in comparison to "other Canons" ... but the lens is rated at the bottom of the barrel
compared to the competition. I did
a complete review of the most common macro lens (albeit for nature photography).
While the intended purpose of my article may be completely different from your intended purpose,
you can still use the information to your benefit.
For example, while the Sigma may be very sharp, it also has an f/2.8 aperture (unlike any other long macro)
and the Sigma rates the highest in bokeh as well, so this combination should make it very favorable for portraiture. (
The Sigma 180 also comes with outstanding image stabilization, unlike the Canon 180, which is another plus for hand-held portraiture.)
Regarding your issue with sharpness, if you don't want the photograph to be sharp as it can be, simply move the clarity slider in the negative direction (problem solved).
Jack