90mm telephoto lens produced by Futura Kamerawerk in Freiburg, Breisgau, Germany during the (likely late) 1950's.
8-bladed diaphragm; circular at 1:5.6, remaining circular to 1:22.
This particular lens (serial
T77xx) has a non-backwards-compatible lens mount, hereby referred to as the S variant.
This incompatibility takes the form of a tab at 9 o'clock (looking at the lens from the flange side) which mates with a groove in the shutter's shroud baffle; earlier cameras lack this groove and attempting to mount this lens will damage their baffling. This tab (visible to the left) allows the 50mm focus helicoid to drive the longer lens through its travel.