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Author Message   Fatbear Tinkerer Username: Fatbear Post Number: 1 Registered: 02-2012 Rating: N/A Votes: 0 Posted on Wednesday, February 22, 2012 - 07:22 pm:    I suspect the focusing distance on the scale is probably to the optical center of the lens, not to the film plane. Setting infinity focus by pointing at something infinitely far away (or into a collimator) and making sure the image is in focus on the film plane is very convenient and will remain pretty accurate at even moderate distances. But when you adjust the focus of a lens you are adjusting its optical center to and from the film plane. So it's really the distance from the subject to the optical center of the lens that should matter.