While a 45mm f2 lens would have my favourite specs ever in a lens, I'm not sure that we'd get such an interesting lens if it had been faster.
Spherical aberration deteriorates resolution, and also goes away quickly when stopping down.
This makes it a bit of a conundrum to quantitatively balance it with faster lenses.
If it had been an f2 lens, either Sigma would have designed it to preserve as much spherical aberration at f2.8 as the current model, but resolution would have perhaps been poor enough that most lens reviews would have trashed the lens for it (like the Nikon 58). If it had had less spherical aberration to preserve resolution at f2, it wouldn't have had quite as much when stopping down.
Perhaps a solution to this conundrum would be if we saw the return of lenses that can adjust spherical aberration. I'd love to see a lens with a sort of constantly gaussian look in the transition area, even when stopping down.
I hope that this lens will lead lens reviewers to question their practices because most (but not all of course ) so far are missing what it's all about. It's a unique lens, I don't think we've ever had such a combination of solid correction of field dependent aberrations and chromatic aberrations, with lots of spherical aberration. Most older lenses aren't quite as good with the former, and most modern lenses aren't quite as aggressively designed in regards to the latter.
Now dear Sigma I'd love to see a whole series like this please ! I'll gladly take a 28mm f2, 85mm f2.8 and 130mm f4 of that kind.
) so far are missing what it's all about. It's a unique lens, I don't think we've ever had such a combination of solid correction of field dependent aberrations and chromatic aberrations, with lots of spherical aberration. Most older lenses aren't quite as good with the former, and most modern lenses aren't quite as aggressively designed in regards to the latter.