YONGNUO YN2.0X III Teleconverter Extender Auto Focus Lens for Canon EOS EF Lens The Magnification: 2 times Mount:EF mount(Electronically controlled) Lens construction: 9elements in 5 groups Dimensions(max.dia. length): 5573.9mm When Extender EF2X is attached,the lens maximum aperture will be smaller by 2 stop.In the above two case, the camera will compensate the exposure automatically.