I have a question about rangefinder focusing with LF lenses. I am getting my Technika cammed and calibrated for a 150mm lens. I have been told by one of our commercial authorities that I will only be able to use that particular cam to focus that particular lens and that it will not work to focus other lenses of 150mm focal length. The more I think (actually thinking is a poor word for the processes that occur in my mind) about this, the more confused I become. It seems to me that any 150mm lens should have the same focusing distance from the rear nodal point to the ground glass (one focal length or 150mm) when focused at infinity as any other lens of that focal length. Similarly, if I shoot at 1:1 reproduction ratio, all 150mm lenses ought to focus at twice that distance, or 300mm from the rear nodal point to the ground glass. If these two points are the same, it seems to me that most likely the relationship between the object distance and the image distance for any 150mm lens ought to be linear and superimposed, otherwise the focusing object/image distance relationships for different 150mm lenses would have to be some kind of awfully funky curves with a pair of surprisingly coincident points. Thus, it seems to me that a cam made for one 150mm lens ought to work with other lenses of the same focal length. The only difficulty that I can think (again that probably inaccurate verb) of is that the rear nodal point may differ between lenses, although within a single focal length I wouldn't think that it would differ by much, and the effect of differing rear nodal points would cause the most misfocusing at infinity when the image distance is least, and the effect would decrease as object distance decreased and image distance increased making the difference due to differing rear nodal points a smaller percentage of the image distance.
So, does any of this make any sense? Can multiple lenses of the same focal length be used with the single cam, or would the error be too large at any distance? What other problems are there that I have not thought of (undoubtedly many)? I look forward to once more benefiting from the collective knowledge, expertise, and experience of the group.
Thanks ahead of time,
Larry
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