"Mirror" lenses refer to systems comprised of reflecting mirrors with lenses, a combination that allows telephotos to be lighter and more compact than conventional lenses. The effect on the image is ring blur - great for portrait work. The beauty is heightened even more when lighting is effectively used in shooting, resulting in photographs with overwhelming emotive power. Characteristics that make this lens a true classic. This improved model delivers better performance at close range with increased peripheral light. The use of rear-insertion type filters enable rapid secure filter changes. The barrel's rugged ZEN finish helps it withstand hard outdoor use.