This mirror-reflex lens is so compact and light that many photographers will perfer it to larger, but less powerful telephoto lenses. Optically, it is superb, focusing past infinity (for use in extremely cold weather) and featuring Super Spectra Coating for flare reduction. Measuring just 5 3/4 inches in length, this high-powered lens can travel anywhere. And, it's light enough to be used hand-held or on a monopod at higher shutter speeds. Special Canon 34mm ND filters are inserted into a special filter slot at the rear of the lens for exposure adjustment, as the reflex design does not incorporate a diaphragm. Lenshood: built-in.