D7000 and the Sigma 17-70

This is what I mean by softer sides. I feel the Sigma is a bit inadequate for shots like this. The right side appears worse than the left here, but I have some shots where the left is about the same, or worse.

Here is a landscape shot that shows more softness on the left side. It is not real bad, but if you are looking closely, there are obvious aberrations degrading the shot. The trees on the left mountain have no detail compared to the ones toward the center (and it is very clear the more you pixel peep). The far right is not that great either. Both shots are stopped down some, too (f5). And going to f8 or f11 does not really do anything to help. The 18-105 and 16-85 will be more consistent across the frame...at the expense of being slower aperture and not macro capable.

This is why I consider the Sigma to be more of a special purpose lens, not really a replacement lens for the Nikon lenses mentioned above...that's just my opinion and observation. It does things the Nikon's can't but is outdone in other areas. I love mine, but intend to add a 18-105 as a companion lens to cover the things that it does better when the lighting is adequate. The 17-70 could be used as an only lens, as some here suggest that they do, but you should be aware of the potential limitations before you commit to using it as an all-purpose single lens.
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K.B.