Can i use sigma AF 3.5-4.5 lens on nikon D5100?

Can i use sigma AF 3.5-4.5 lens on nikon D5100?

If it has a Nikon mount then probably. But 3rd party lenses don't always have compatible firmware with cameras released after they left the factory, so your lens may have to go back to Sigma for an update.

If it is a F mount, then yes. However, you will not be able to auto focus because the D5100 does not have a built in autofocus motor. It can only auto focus with AF-S lenses.

Ah, you left out some major information. You gave us the aperture range of the lens, but not the focal lengths (e.g.: 35-85mm)

On entry level Nikons like the D5100, you need lenses with built-in autofocus motors. In Nikon lens-talk, it's AF-S. With Sigma lenses, it's HSM.

Here's a complete list of lenses that mount, meter, and autofocus on your camera.
http://en.wikipedia.org/...cus_motors

BTW, I don't see any Sigma lenses with an aperture range of f/3.5-4.5 on the list, so I'm afraid the mystery lens in question won't work in autofocus, though you may be able to use it in manual, IF it's a Nikon mount optic.

If it has a Nikon F-mount I'm guessing it will connect to your camera. As to AF compatibility, I'm not so sure about it.