Russian FED rangefinder-coupled wide angle lens for M39, the first fast 28mm wide-angle lens for Leica mount.
Originally released in mid-1930's, on the outside the FED 4,5/28mm resemble Leitz Elmar 35mm f/3,5, but it's deluxe optical formula (British Ross-Wide-Angle formula) is pretty advanced when compared the famous German competitors, Leitz Hektor (6,3/28mm) and Zeiss Jena Tessar from the same period.
The miniature dimensions of the entire optical block is impressive achievement for a 1930's wide-angle lens. The frontal disc of the lens has a diameter of approximately 7mm (analogous dimensions also have the other elements), while the thickness of the third optical glass element does not exceed the 6-7 tenths of millimeter. Imagine the difficulties in the grinding and the assembly of each of these elements bu hand, maintaining a reasonable precision. 6 elements in 4 groups, the outside element pairings are cemented. 6-blade aperture f4,5-f18.
Photo credit: © WestLicht Photographica Auction