Carl Zeiss Jena in leica mount

Here is another angle of the lens.

And another.

See:

http://www.taunusreiter.de/Cameras/Zeiss_Fakes.html

http://www.zeisscamera.com/services_35RBiogon.shtml

Much has been written about fake f/1.5 50mm Sonnars (in rigid mount), and f/2.0 50mm Sonnars in Contax/Kiev mount. I am not an expert in this field but I have never heard about f/2.0 50mm Sonnar fakes in LTM. Actually, I do not remember having heard anything about russian lenses in collapsible mounts in LTM versions other than the f/3.5 50mm FED/Zorki lens.
During wartime, quite a few Zeiss lenses were manufactured in LTM mount. It is not unlikely that these were coated like yours with the T engraving, since probably most, if not all, were made for government/military use, and these were the first to use coated optics back then. Also, I have heard about a certain batch of Zeiss lenses in LTM mount manufactured post-war which were all shipped to the Soviet Union to fit FED and Zorki cameras.
There are experts out there on Zeiss lens serial numbers (until 1945), it might be possible to find out about the batch of lenses yours belongs to.

It looks like a custom remount of the optics module into LTM. I've seena few jobs done like this, not in collapsible mount quite like yours. The SN is late wartime. I have a SN285xxxx lens that is German wartime, and one that is 286xxxx that is made from wartime parts and "copy" parts. I suspect that the period just after the war ended saw a lot of semi-custom one-offs, as opposed to regular production items. Just an opinion, but I have seen a lot of "fakes" with real parts from the same batches.

Hi Brian, thank you for your comment. It appears there is no real answer. I suppose I am just hoping it is a rare lens. One interesting thing is that the lens has quite a few air bubbles in it which I heard indicates quality glass for the time.

Note that it can be stopped down to f22. Most of today's 50mm lenses only go to f16.
That old time precision!

I have two such lenses that look exactly like the one you have, including the odd colored material that the distance scale ring is made of. Also Hartmut Theile's book of CZJ lens numbers shows that Zeiss in Russian-occupied Germany manufactured a couple of batches of collapsible 50/2 Sonnars in 1946 and 1947. Both of my lenses show up in Theile's book as 1946 manufacture. The serial number on your lens corresponds to this time frame. I have taken apart my two lenses, and found that they contained parts numbers from three different batches of lens numbers. although manufacturing dates for the various numbers are very close (within months). I am guessing that my lenses were cobbled together from leftover wartime parts, but who knows. Follow this link to ZIForum for pics and additional information, post #7 and #9
http://www.ziforums.com/showthread.php?t=466

My lenses are both great performers.

Hi Mark, thank you for the link, I found it very interesting. It look like the lens is very close to yours, I should take it apart but I am not very mechanical minded. It is amazing how Zeiss were producing lenses in such a poor quality alloy.