The optical system construction and exterior are the same as the ef 75 300 mm f4 56 iii usmacircrsquo the difference is that it uses a dc motor instead of a usm to drive the af this lens has the same optical system construction and exterior design as the ef 75 300mm f4 56 iii usm lens however instead of having a usm it has a micro motor diagonal angle of view 32deg 11 8deg 15 lens construction elementsgroups 139 no of diaphragm blades 7 minimum ape