Konica Hexanon ARM 2000mm f/11
Maybe only prototypes of the Reflex 2000mm Hexanons were ever made by Konica, and none were ever sold, according to a knowledgeable Konica dealer. One on display at the Konica offices when they company merged with Minolta. In an internet discussion a mentioning in promotional material is reported. Present location is unknown.
The 2000mm is massive. It uses a rear mounted bellows type focusing mechanism.
It and the smaller 1000mm Reflex Hexanon are unique among "mirror" lenses, having some form of aperture control. At the rear is mounted a disc with, effectively, Waterhouse stops (various size holes) in it. It can be dialed into place, to achieve different aperture settings.
Better known but nearly as rare is the heavy glass lens variant with 9 elements in 8 groups plus a set of filters.