I am assisting someone with selling off remainders of the collection of an esteemed former president of LHSA. She has an old Thambar in user condition without the filter having a central blocking disc. I have found an old Leitz 48mm UV filter of that vintage and want to paint the requisite patch in center of the glass so as to evaluate the lens. Could someone tell me the particulars such as diameter of the opaque section, whether it is "solid" or on just the inner or outer surface, and anything else that might assist. I understand the new version is 49mm but presumably same patch. Thanks, Harry in Florida