Thanks for the feedback.
The submission I made us actually of an entirely different building that's
walking distance from my home that I suddenly thought about yesterday.
Sent from mobile.... I have big thumbs so sorry for for typos... I hope
they were amusing and not offensive. 😀
On 2 Jan 2018 7:39 a.m., <junkyardspar...@yepmail.net> wrote:
>
>
> 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
>
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