hi bro,your lens need to be either AF-S and AF-I to make D3100 auto focus.others then that auto focus wont work for D3100.go to link that i've pasted below for more details "look at number 7"..Im also new in photography hope this helpful dude.

But in your case your lens is AF-s,For all"F 80–200mm f/2.8, AF 35–70mm f/2.8, AF 28–85mm f/3.5–4.5 (New), or AF 28–85mm f/3.5–4.5 "lenses, you need to Focus manually until image in viewfinder is in focus.

http://imaging.nikon.com/products/imaging/...atibility02.htm

This post has been edited by fadzrul.azri: Mar 19 2011, 09:14 PM

Anyway,good nikon bag..appreciate that.thump up for you bro.