Konica Hexanon ARM 2000mm f/11
It is believed only two or three of the 2000mm Hexanons were ever made by Konica, and none were ever sold, according to a knowledgeable Konica dealer. One was on display at the Konica offices when they company merged with Minolta. 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.