On Fri, Jan 03, 2014 at 07:07:37AM +0100, Torsten Bronger wrote: > > I'm actually having a bit of difficulty with this bit, actually. > > I'm trying to do calibration of a fairly wide angle lens (14mm > > with a 2.0 crop) and am finding it hard to get what appears to be > > even illumination - I certainly don't have a light source that can > > apply an even enough illumination to my ceiling. Does this mean > > that my diffusion material isn't diffusy enough (I have tried a > > white plastic trash bag)? > > Doesn't such a plastic trash bag wrinkle up? The diffuser must be > even. > > As far as illumination is concerned: Two steps of diffusing are > enough. So, illuminate your ceiling, and point the diffusor on the > lens to the ceiling. Then, the ceiling scatters the light, and the > diffusor does it again. > > It wouldn't work if the left half of the diffuser area got less > light than the right half. But this should only happen if you point > a lamp directly to the diffuser, possibly even in short distance. > Therefore, the ceiling as an intermediate step: It enlarges the > effective distance to the light source, and adds scattering. Yah, my initial material wasn't diffusy enough. I got some opaque white contact paper which seemed to provide the right amount of translucence and have gotten some calibrations which seem to do the right thing with my pictures (stuck it to some clear plastic to provide the flat surface). lensfun & your supporting scripts are really spectacular - with my Canon gear corrections could be nice but were mostly not necessary. Having switched to micro 4/3, the kit lens is a total non-starter without distortion correction and the vignetting with it can be very distracting as well.
One quirk is that even though I only calibrated at infinity, the lensfun database has identical entries for 10 and 1000 (cm?). Darktable doesn't pick up distance information (exiftool at least doesn't see anything either) and so just fills distance with 0, which means that it doesn't get detected. What is the right answer here? Should either Darktable or lensfun be enhanced so that if there is not calibration at multiple distances, it used whatever is found? Should I tweak the database to list a distance of "0" rather than "10"? Something else? I don't see an issue in the darktable bug tracker that seems to address this offhand. The lack of distance information supplied by the exif also seems to make bothering to calibrate at different focal distances of dubious value... Thanks again! -- [ [email protected] | [email protected] ] [ http://www.chiappa.net/~chris/ ] ------------------------------------------------------------------------------ CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments & Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk _______________________________________________ Darktable-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/darktable-users
