Polaroid Auto Focus DG Macro Extension Tubes are designed to enable your lens to focus closer than its normal set minimum focusing distance, this way you can magnify your subject. The tubes are very useful for macro photography. The extension tubes have no glass. The Extension tubes are attached between the camera body and the lens. This set consists of three tubes, the tubes may be used singly or in combination with one another for a total of seven different lengths. Each tube is provided with a mounting bayonet and electrical contacts which match those of your particular camera choice. The contacts allow the camera’s lens to respond to its automatic exposure system giving you a perfect exposure each time.