I was looking some photos on web made with Leitz Thambar lens, and specially with this special filter with black dot in the center. Very crazy and unusual.
What I don't understand is how this filter works. Can this filter effect be done with other lenses (for example I modify one 52mm filter for nikon lens)?
Considering high price of this lens, and also relative simple design - I am wondering how difficult would be in general to make some lens at home (without f stops, just simple wide open lens, without mount, to be used on large format camera or Rollei SL66)? Is there a shop where one can buy lens glass elements with different spherical curves?