Hallöchen! junkyardspar...@yepmail.net writes:
> On Sat, Apr 16, 2016, at 15:16, Owen Mays wrote: > > [...] > >> For Vignetting correction, I read Torsten's instructions here: >> http://wilson.bronger.org/lens_calibration_tutorial/ >> >> How even does the even illumination need to be? [...] > > [...] > > Probably the most important thing to watch for is that the > diffusing material fits perfectly against the front of the lens > tube with no gaps, since light leaking in could potentially skew > the results as much as uneven lighting, maybe more so. Right, this is worst case. > I like to visually sanity check my calibration images before > running the script on them; rotating them by 90-degree jumps in > your viewer makes it easier to detect any odd variations. Equivalently, you may look at the Gnuplot graphs that are generated: Very broad dot distribution means lack of rotational symmetry. >> For TCA correction: I haven't found a good target for TCA. Does >> this calibration need a regular geometry (like the buildings used >> for distortion?) Or are trees against an overcast sky ok? > > Regularity isn't important, you just need sharp contrasty (but not > overexposed) non-radial lines that are fairly near the outermost > parts of the image. Diagonal lines in corners will probably show > the most detectable TCA. But the diagonal must be perpendicular to the line to the image centre. > Your mileage may vary, but I've found that for my purposes, TCA > also changes with focus distance, and since lensfun doesn't handle > this, I don't enable it by default, since it's wrong as often as > it's right. [...] Indeed, unfortunately, all three aberrations (distortion, TCA, vignetting) also depend on focus distance. Lensfun's database contains (well, hopefully) data for focus at infinity because this is the kind of photos that need correction most (architecture, landscape). In case of vignetting, different distances are possible, but infinity focus is still the default, and mostly the only available. One must say that deviations due to focus breathing occur only at really short distance (usually 3 times close focus distance). Tschö, Torsten. -- Torsten Bronger Jabber ID: torsten.bron...@jabber.rwth-aachen.de ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic patterns at an interface-level. Reveals which users, apps, and protocols are consuming the most bandwidth. Provides multi-vendor support for NetFlow, J-Flow, sFlow and other flows. Make informed decisions using capacity planning reports. http://pubads.g.doubleclick.net/gampad/clk?id=1444514421&iu=/41014381 _______________________________________________ Lensfun-users mailing list Lensfun-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lensfun-users
