During the 1979, the Tamron SP 500mm F/8 Tele-Macro Catadioptric (Model 55B) lens was the smallest and lightest 500mm mirror telephoto lens. The lens employs mangin mirrors, continuous focusing down to 1:3 macro, and 30.5mm rear filter thread. Macro performance is good but with softness in the corners due to off-axis coma. Light transmission is very close to F/8 and light fall-off is a mere 0.75 stop.
"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.