Otto Zimmermann

" . . . Leica always had the obtainment of the best possible optical glasses for its M lenses as one aim of paramount importance, and the examples are manifold: the thorium oxide glass nD= 1,69112 vD= 54, 8 included in four of the lenses of the optical formula of the Leitz Summitar* Summicron (I) f= 5 cm 1:2 Original Project 1950 designed by Gustav Kleinberg and Otto Zimmermann (which also had a flint lead-glass plate to avoid film fogging by radiation) . . ." Source - José Manuel Serrano Esparza