The EF 100mm f/2 USM Lens from Canon is a medium telephoto lens with a fast maximum aperture. It is ideal for many telephoto applications including portraiture, as ;the f/2 aperture provides shallow depth of field focus and its 8-blade diaphragm creates pleasing out-of-focus areas. Its ultrasonic focus motor provides quick and quiet autofocus action and the internal focus system means that the front element does not extend when focusing. Also, lens multi-coating reduces reflections and minimizes flare and ghosting. This is a very sharp prime lens and despite ;the large maximum aperture, ;it remains compact. The filter thread and barrel front ;are metal to add an element of durability.