Kenko Macro Extension Tube Set DG Tubes for Nikon AF AF-S -Read-
This is a handy accessory that adds extra reach to all of your Nikon lenses. They work with AI and AF lenses (including G, AF-S and DX). They are stackable.
The 36mm and 12mm work perfectly. The 20mm does not make contact so it can be used with manual lenses or as an extension but does not drive AF lenses.