I have a #10 Cirkut in working order except for the lens (and me). The original T-R Triple Convertible was ruined due to balsam separation, although it might be salvaged, at what cost I wouldn't know. I happen to have another T-R Triple, an identical focal length combination (10.5,18,24) but a more recent vintage, with slightly larger maximum apertures. I've read that no two lenses are actually identical and that I would need to have the exact focal point of the new lens measured in order to determine the proper gears for each focal length. I find this difficult to comprehend. According to the focusing scales on the camera, each gear appears to have considerable latitude over a range of distances, a range that in my mind anyway, would exceed any variations between different lenses of the same focal length. (Whew - I hope that I've expressed this clearly). Anyway - can I use the new lens, and, if I've got this wrong, can someone explain this to me?