Polaroid Auto Focus DG Macro Extension Tube Set (12mm, 20mm, 36mm) For Nikon Digital SLR Cameras The Extension Tubes Enable Your Lens To Focus Closer Than Its Normal Minimum Focusing Distance Resulting In The Magnification Of The Subject Includes Electrial Contacts To Maintain Auto Focus And Auto Exposure Capabilities Tube Sizes: 12mm, 20mm, 36mm