PT3905. Prototype lens, calculated by GOI in 1952. Focal length - 5 cm (5.2 cm), aperture range f2.0 - f22. Focusing range: the ring with metering scale is not seen on the particular lens. Number of elements/groups: 6/4. Angular field - 41º. Zorki (M39) mount. it seems to be the 1st attempt to creative an alternative lens for Jupiter-8. Very strange optical scheme (see picture below).
Lens opposite from private collection in Russia.