I believe this is the postwar Tenax that was produced by the Eastern unit of Zeiss Ikon.
The Tenax is a name that Goerz used for one of its cameras before the megamerger that formed Zeiss Ikon.
Zeiss Ikon used the Tenax name on three cameras: Tenax I, Tenax II and the postwar Tenax. Tenax I and Tenax II shots square photos (24mm x 24mm), while The postwar Tenax yielded a normal 35mm negative (36x24).
After World War II, there existed two Zeiss Ikon units in the Eastern and Western Zones. Eventually, the Eastern Zeiss Ikon became Pentacon after the courts granted the Western unit the rights to the name.
For a short time, the Eastern Zeiss Ikon produced the Tenax under the Zeiss Ikon name. That's the camera that you have. The focal length on my camera is marked 37.5 (which is 37.5mm or 3.75cm or 3 3/4cm).
The Tessar on your camera is a coated lens as indicated by the "T." Like the prewar Tenax I, it also shoots square photos (24x24) and can use standard 35mm film.
It's a very nice camera. The lever to the left is the film advance, which also tensions the shutter.
I have a
short writeup about this camera on my site.