I Get darn Frustrated in this matter can never remember when Dealing with a Brass lens! From what point on the barrel lens does one measure to determine the focal point of the lens
In the foto I have attached I shined the light straight down thru the lens on to a piece of paper and have ruler set up there : When the lens board is at 3.25 inches, I get a sharpe focus of the light bulb bright spot! on the paper:
I know on a shutter lens one uses the center of the shutter as center point to the film plane , I Believe that to be correct !:
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