Carl Zeiss Jena Flexon / Pancolar 2.0/50
The Flexon 2.0 and Pancolar 2.0 is essentially the same lens with different name. However, the notion that they are the same as the later Pancolar 50/1.8 is quite incorrect. While all of them are optically a Planar deviced 6 element in 4 group configuration. The 1.8 Lens is optically different from the 2.0s

Flexon and Pancolar 50/2.0 are produced in Chrome with leatherette focsuing ring variation while the Pancolar is made in black with leatherette focsuing ring as well.

Flexon was made in Praktina mount regulary and in very small quantity for Exakta, no M42 mount Flexon was made, according to the Zeiss fabrication dates, compiled in Thiele's Fabrikationsbuch Photooptik Carl Zeiss Jena.
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