The Biogon was the fastest 35mm lens Zeiss sold for the Contax. It was introduced with Contax II and III cameras in chrome only. The pre-war design featured a rear element the projected so far back into the camera, that it could not be used on the Contax IIa and IIIa cameras.
After the war, there were two versions of the Biogon. The East German was very much like the pre-war version, but the rear element was redesigned with a protective ring, and was a bit shorter than the earlier lens. It was given an aluminum barrel, as were most of the Jena lenses of that period.
In 1950, Zeiss Ikon released their new Biogon that is marked Zeiss-Opton. It was a chrome over brass construction.
The 35/2.8 Biogon, T coated.
The high point of the rear element is actually the glass itself.