Hello uktrbuk, and welcome to the friendly Camera Labs forum!
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As to your question: This Sigma lens has a motor built into the lens so auto-focus (AF) works perfectly fine. You can also manually override the AF.
The Nikon 10-24mm is certainly the more desirable lens, if pnly because of the additional 4mm (=20%) longer reach (maximal focal length). But taking the price into account both lenses are worthy contenders for your money.
Thomas (beware: Nikon-fanboy and moderator!) My Pictures
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