The effective aperture of the lens is increased by one stop. Auto-focusing does not operate if the effective maximum aperture is greater than f/5.6 (greater than f/8 on the EOS 1V and EOS 3). Features Dust and moisture resistant construction Extends the master lens focal length by 1.4x Minimum loss of lens performance Reduces inner reflection for higher image quality The new version II maintains the outstanding optics of the previous version, and adds enhanced weather- resistant construction, and improved anti-reflective surfaces in the barrel