Hello, hoping someone can help. I have an old brass lens from around 1895 and I have attached a pic of its description from an old catalog. My problem is that it uses 0-5, all spaced equally, as the “stops”, AND it’s a convertible. Does the minimum, wide-open f-stop change as I make the lens “longer” or “shorter”? All of the screw-on front and rear lens cells are the same thickness. Is “0” the same then when it’s a 203mm lens and when it’s a 356mm lens? How do I properly figure out what “0” is considering there are multiple combinations and by design the iris, when wide open, doesn’t fully expand to the inner surface of the tube?
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