I have used both the Nikon 500mm and the Vivitar 450 4.5 Series 1 and like the Vivitar as well as the Nikon, Vivitar also marketed a 600 and 800 F 8 and F 11 but I dont how good these were compaired to either Nikon or the earlier series 1. I have been thinking about picking up a older 450 in a K mount.