I am starting out to actually use an half-old (1930's from what I can gather) "Jos. Schneider Co. & Kreuznach Doppelanastigmat Isconar" lens, and the aperture scale progression always throws me a bit: f:6.8, then 9, 12,5, 18, 25, 36 and the 50 as the smallest stop.
Would that (sort of, leaving out the first 6.8), correspond to f:9 being f:11, and then 16, 22, 32, 45, and on to f:64?
It seems like a nice lens, but I need to dial in the process a bit, since I am using it with a lens cap - rather low contrast negatives even with a rotary process.
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