Hallöchen! Erik Krause writes:
> Am 08.04.2014 20:32, schrieb Torsten Bronger: > >> I think this supports my view that Hugin's focal length, >> multiplied by (1-a-b-c), results in the real one. > > Why do you want to know the focal length that precise? In the Lensfun project, we need the exact focal length for projection changes, e.g. from fisheye to rectilinear. 5% error is the difference between straight lines and visibly bent lines. The main problem -- and my main motivation for this thread -- is documentation. Lensfun must exactly tell the user how everything is defined. And Lensfun has this FOV data field inherited from Hugin. I could just write "it's the value that Hugin provides", but I find this sub-optimal. People may use other tools for calibration, or use Lensfun's data in other tools. Hugin's unfortunate definition of FOV/focal length forced us to explain this data field in a lengthy and awkward way. Even worse, Lensfun supports also non-Hugin distortion models, and for them, the FOV refers to the correct focal length. Oh well ... > Lenses are allowed to differ up to +/- 5% from the advertised > focal length. Yes, the actual mean value certainly differs, but I assume that the deviation *within* one lens model is smaller (at least for modern lens series). Besides, it is still senseful to have the correct focal length in the first place. The errors add up after all. > Many lenses change focal length during focusing. Most modern 100mm > 1:1 macro lenses f.e. have a near limit of 30cm, which means the > focal length is only 75mm at near limit. We are aware of that at Lensfun, and we have specified that all Lensfun data refers to focus @ infinity, if not stated otherwise. Tschö, Torsten. -- Torsten Bronger Jabber ID: [email protected] or http://bronger-jmp.appspot.com -- A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ --- You received this message because you are subscribed to the Google Groups "hugin and other free panoramic software" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/hugin-ptx/87k3azy012.fsf%40physik.rwth-aachen.de. For more options, visit https://groups.google.com/d/optout.
