I just got my first barrel lens. It is a Goerz apo red dot artar 8 1/4 ins. I am planning to use it in a speed graphic but I don't understand how it works. The diaphragm does not close completely. Is that normal? The aperture ring seems to work properly, but above that is another ring that turns, revealing a thin slot above the aperture numbers. What is that for? It does not seem to do anything.
I tried looking up the answer but it seems too basic a question for anyone to have had a discussion about it.
Geraldine
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