Could the veteran collectors please walk us through (with pictures) the earliest prewar filter styles and date ranges, for the Elmar 5cm lens?
I know of the small (19mm?) screw-in style, the slip-on style (with slotted tabs to simply pinch it on the lens rim), and the common clamp-on style with the screw-clamp to tighten a tab.
Question 1: I assume that all the earliest Elmars had a screw-in thread (for the small 19mm filters) in front of the front lens element, but maybe that is not so?
Question 2: are all these early Leitz filters marked Leitz or Leica?
Or are some unmarked, but likely original Leitz/Leica?
Question 3: are there other prewar filter styles?
I believe I have seen (on the internet auction site) two types of "slip-on" style: one with a full-diameter (about 33mm?) filter glass, and one with a smaller (about 22mm?) diameter filter glass in the middle, to cover the lens element. The full-diameter slip-on filters are marked Leitz, and the smaller diameter type does not appear to be marked (perhaps NOT a Leitz product).
Question 4: are the earliest filters identified in late 1920s and early 1930s catalogues or literature, with illustrations and product numbers?
We appreciate your information that will inform those of us who would like to find and use correct-period, original Leitz filters, with our oldest Elmars.
And a follow-up Question 5: are filters for the earliest Hector 5cm lenses any different (style, type, size) from those for the Elmar?