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I understand and agree with everything posted above. I think what really annoys me about the term is that some people talk like a full frame 2.8 zoom is better than a 2.8 crop zoom because it has "more light gathering" ability. I guess that's technically true, but really kind of pointless in the real world, where your crop sensor can't use that light anyway.
So some people discredit this lens claiming that's it's really just the equivalent of a full frame 2.8 zoom, because it "gathers the same amount of light" as a full frame 2.8 zoom. As if how much light it is gathered, regardless of if the sensor can see it or not, is the really important thing.
In the real world however it allows APS-C users to get that much faster of a shutter speed, or that much lower of an ISO setting that they could have gotten before, at least not in a zoom
So I think "light gathering ability" is a confusing term at best, downright misleading at worst, thus my original comment that it's the new marketing buzz word.