Brass lens madman enthusiast Jim Galli offered this incredibly useful piece of advice on the Large Format Photography Forum:
Since I almost never use my antiques [lenses] at infinity, (they are usually approaching 1:1 for a portrait) I make my waterhouse stops to “known’s” like 1 inch or 30mm. Then I measure the distance from stop to ground glass and divide a whole number. ie. a stop is a 1 inch hole. I measure the bellows at 22″, I’m at f22. The bellows is stretched out to 32 inches, same lens same stop, f32. No other calcs needed. Reciprocity still needed sometimes of course, but none of the bellows factor gymnastics.
Very smart!
You can see Galli’s work at his Web site, tonopahpictures.0catch.com.