Extension tube is made to distance the focal point of the lens film plane to get the opportunity to approach closer to the object to be photographed and thus have a higher ratio of Magnification and thus better fulfill the format of the shooting or see the most important details. This replaces the bellows with the benefit of transmitting lens data to the device when the rings have ad hoc linkages. It is expected in general a set of 3 different lengths that can add up. The greater the distance of the optics, the greater the magnification but the depth of field is short.