Excellent build quality. I'll leave the discussion about the sharpness to others, but I think it's very good. I was impressed by the lack of distortion commonly found in ultra wide angle lenses. You can shoot at an angle above or below the horizon line with virtually no distortion. Other reviewers complained about bright reflections from the sun, but I didn't find this an issue; Folks, if you point it at the sun, you're going to have problems. Very happy with this lens; compares very well to Nikon pro lenses, which I dismissed as too bulky and heavy.
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