Further to my last post to confuse things futher Fed factory did produce the Industar 61 lanthanum glass lens (an f2.8 ) which was supplied with later Feds but [U]not Zorkis. Feds were never supplied with f3.5 Industar as original equipment. (source-Russian and soviet Cameras by Jean Loup Princelle) I have posted a photo taken with my own collapsible Industar 50.