The ef 100mm f2 usm is a short telephoto lens with a wide aperture making it ideal for portraits the lens compresses facial features and ensures the subject stands out against a blurred backdrop long focal length and compact size the ef 100mm f2 usm has a large maximum aperture but is still relatively compact the 100mm focal length lets photographers maintain a comfortable working distance from their subjects and also helps to compress perspective sharp crisp pictures are obtained at a