Fed prototype 50mm macro lens, circa 1936.
Apertures: f. 3.5 - f. 16.
Focus: 20cm - infinity.
Similar to the example in the Moscow Polytechnic Museum, pictured on page 108 of Princelle 2nd Edition, but has a vertically textured ring at the lens mount, rather than a cross-hatched texture like the one in Princelle.
No engraving on front ring. No serial number. The production FED 50mm Macro Lens has engraving on the front ring.