JJC Automatic Extension Tube for Canon EOS allows your lens to focus closer than its normal minimum focus distance.By placing distance between your camera body and lens,focusing distance is shortened and the effect of magnifying your subject is created. Extension tubes are thus commonly used for macro photography and sometimes for closeup portraits.JJC Automatic Extension Tubes are available as a set (12mm,20mm and 36mm), also can be used individually or together to create the desired magnification effect. These tubes are fully automatic tubes,so they are able to communicate all electronic functions from lens to camera including auto focus and auto exposure. Extension tubes have no optical elements so they will not degrade the quality of your lenses.