The Vivitar Macro Extension Tube Set (Set of 3) for Sony A gives you three different sized extension tubes (12 mm, 20 mm, 36 mm) that allow you to make close-up photos using your digital or film SLR camera. Simply attach the tube or tubes to your camera. By attaching one of your lenses to an extension tube, or any combination of one, two or three extension tubes, you can vary the amount of magnification and focus close, closer, or much closer, to your subject. The extension tubes have no optical components, and convert almost any lens into a close-up lens. These extension tubes are able to maintain autofocus and TTL auto exposure.