Quote Originally Posted by fingel
I believe that after WW2 all the patents of the German optical companies became public domain.
The Tessar, Protar, Celor (Artar), Dagor, Planar, etc. patents all expired long before WWII. These designs all date from the 1890s through early 1900s. Most had expired by the late 1910s or early 1920s.

So, patents have not been an issue concerning these designs for over 80 years. The real issue isn't technical - these designs are pretty simple by today's standards (which is part of the appeal). The real issue concerns manufacturing cost, return on investment, potential market, etc.