Will a Sigma 10-20mm lens fit on my Nikon d3100 body?

Tossing up whether to buy a Sigma 10-20 lens OR Tokina 11-16 lens, and whether it will fit my camera body. Do I need an adapter ring for it to fit to my body?

Sigma, Tokina, and Tamron all make lenses with Nikon mounts. All you have to do is make sure you order the Nikon mount with the lens. And yes, unless you want to manually focus, make sure the lens has the autofocus motor; they usually do.

If you specify Nikon fit, no problem. You need the HSM version if you want autofocus.

The Tokina will also fit if you specify Nikon mount, but I don't know what they call their motorised version (the D3100 needs motorised lenses because it has no body-mounted focus motor).

Specify either one with a Nikon mount and it will fit without needing an adapter.
I have the Sigma 10-20 f/4-5.6 - fantastic lens.
The Tokina also gets very good reviews.
Either would be a good buy. The Tokina has reduced focal length range but is f/2.8; the Sigma is cheaper, has bigger range but is 1-2 stops slower. You pays yer money and takes yer choice!

You have some good information above.

The lens with the best build is the Tokina. They are well known for making the most robust of all the third party lenses.

Only recently has Sigma started producing a lens line under the "ART" moniker, however those lenses cost as much or more than the lenses made by Nikon.

Retired Phil is right. Just specify the camera you are buying it for. Best in that range is said to be the Tamron 11 to 17mm at constant f2.8, but it is expensive. Once bought, no lens can be fully adapted to work in all aspects on another brand of camera.