It was made in 1972 and it was produced in only 150 pieces for the dying Contarex system.
It’s a fisheye lens with a coverage of 180° on the diagonal. 4 filters are incorporated in the revolving turret: UV, Orange, Yellow and Blue. It’s the mother lens of the Rollei and the Contax 16mm f-distagons, with the very same optical formula.
It is so stupidly rare that I’ve lost faith I could ever complete the 16mm f-distagons collection.