On Sun, Dec 31, 2017, at 16:14, John J Bloomfield wrote: > > I'll shoot them all on FF (as I basic geometry makes me believe a FF > calibration should be able to be applied to APSC - but the opposite isn't > true) even though some are technically APSC lenses many do cover the whole > frame so are being commonly used.
Yes, that's how it works. > Might not be the 100% accurate name as displayed in exif but I have; > > > - Pentax FA 77mm Ltd f1.8 > - Pentax DFA 100mm f2.8 WR > - Pentax DA 50mm f1.8 > - Pentax DA 35mm f2.4 > - Pentax FA 28-70mm f4 > - Pentax DAL 18-50mm RE WR > - Pentax DAL 50-200mm WR > - Sigma 17-50 f2.8 I think there may be a Pentax lens or two in the backlog for calibration, unfortunately when I went to take a look today the server holding the files (including your recent upload) wasn't responding; I contacted Torsten Bronger, the owner, and hopefully it will be up and running soon. > I have spotted a couple of other buildings that should do for the job too. > > 1. - Is this Asda Store > 2. - University building The second one, assuming you can reasonably loiter there without attracting negative attention, looks ideal... a grid like that is always nice, even if not strictly needed. Otherwise, the important thing is at least one good, reliably straight line of sufficient length to allow you to stay at a reasonable distance even at wide angles. This line should be placed as close as possible to the edge of the frame, and fully span it. Many uploaded pictures don't get the line as close to the edge as they should, possibly due to differences between the viewfinder and what the RAW actually captures, so this is one issue to keep in mind. The importance of having a second line at 1/3 of the frame depends on the complexity of the distortion; if it displays any divergence towards "mustache" from simple barrel distortion, then this line is used for additional correction. Since this can make finding and using a suitable target more difficult, I've been thinking about the possibility of using two images with the camera simply tilted to position the line differently in each. I think this could be made to work, if need be. Also note that it's ok to change distance for different focal lengths on a zoom to get the best lines; the shots don't need to be taken from the same position. An additional consideration with crop lenses on full-frame bodies is to ensure that the frame-edge line is visible at both ends despite any corner shading the lens may produce. For TCA correction images, it would be good if the corners are fairly sharp and retain as much contrast as possible, even at the expense of the center of the frame being slightly less sharp and/or overexposed. Hopefully that clarifies some of the criteria for good calibration shots. It's also convenient if the uploader has a github account and can communicate directly within the numbered "issues" that each upload generates there, in the event that communication is needed. Oh, and for zooms, the ideal focal lengths (besides both ends of the range) are the point where distortion changes from barrel to pincushion (where applicable), and a few on either side of this, weighted towards the wider end. Often, once the distortion changes to pincushion, it doesn't change drastically over the rest of the range. I hope to have some time for working on profiles this week, knock on wood! -- jys ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Lensfun-users mailing list Lensfun-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lensfun-users
