I searched the forum, but could not find an answer....thus, can someone outline the steps in determining the f-stop for an Achromatic Meniscus lens when the barrel is removed? Is the procedure different from that used to calculate/estimate the f-stop of a petzval? I have a nice 14 inch f11 Dallmeyer landscape lens and am trying to determine its f-stop when the barrel is removed. Thanks. Jon
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