Zeiss:
Never before has the world of photography seen such a lens. Developed for long distance wildlife photography this supertele lens provides 21x magnification. In search of the highest imaginable image quality the client decided for 6×6 medium format and the Hasselblad 203 FE as the best camera he is aware of.
At 1700 mm focal length and a speed of f/4 this lens put requirements on optical glas, lens assembly and quality assurance methods, never before encountered in photo lens manufacture. This 256 kg behemoth also required Carl Zeiss to develop totally new ways of operating a telephoto lens, including servo controlled aiming and focusing.
Here.