I have recently acquired a Hexanon 50mm f1.9 Leica thread mount lens which I believe is a "Planar" type lens of the mid to late 1950's.My copy has a Leotax lens cap so I assume that it was originally fitted to Leotax cameras.
I have also read that it was available on the rare Honor camera.
I have recently come across a very informative article about the history of the "Sonnar" lens and thought that it might be of interest to other members who are interested in "Sonnar" lenses.
The article is in Italian but Google Chrome on Windows will translate it into English.
Please see:- L