If I'm not mistaken, this has to do with technical & feasibility issues. Actual lens diameter for crop can be smaller than for ff bodies, thus making it easier to produce f/1.8. Or am I completely wrong right now?
I was flummoxed when I heard that this thing is APS-C only. Why?! If this is a premium lens aimed at serious shooters, why go crop? This is not a screaming need for the relatively few APS-C guys who spend big money on glass (i.e. birders, sports guys), so I can't make heads or tails of this.
Why not push for (idk) a 24-50 F/2 for the FF guys? That would likely have a larger interest level.
You're not wrong, but for those saying this is no big deal, I disagree. This is something that has not been done before for either crop or FF (an f/1.8 zoom), so to dismiss it outright is absurd. Yes, developing for full frame is more challenging, but this is clearly a step in the right direction and will put more pressure on Canon. As a consumer, I see that as a good thing
Agreed that it's a big deal, as it's not been done before. But I don't think it makes it any more likely for full frame equivalent lens to be made, as that one would have to be larger.
Value is in closing the gap between APS-C and full frame, and if you're Nikon shooter, you have 27-52.5 f2.7 FF equivalent, for serious, but not FF money.
And as to why Sigma did this - I think they were looking for a gap where they can play by themselves for awhile. Crop sensor shooters looking for best/fastest glass they can get (in normal range) is probably not a huge market segment, but they own it now. And then there is a 'hallo' effect of 1.8, increasing value of their lineup. Smart play...