The Varifocal, as it is often simply known, was a radical lens design for its day, the mid-1970s.

It's a very large and heavy lens, and was offered with an equally over-sized, clamp-on, rectangular metal lens hood.

"Varifocal" means that when the focal length is changed, the lens must be re-focused. A "true zoom" lens will maintain focus even when focal length is zoomed.