Calibration upload 60193d

[bronger]

Calibration images were uploaded to the directory that starts with “60193d_”.

Please read the workflow description for further instructions about the calibration.

[uchrisu]

@uploader: We need pictures for the whole focal length range. The lens has a range from 70mm to 210mm but the uploaded pictures are only at 160mm and 210mm. As distortion may vary very much over the focal length range it is important to have the whole focal length covered. It is suggested to use at least 5 different focal lengths within this range, including the limits.

[misin100]

Hi, the uploader here. Seems like there is a problem with the EXIF data (I took all photos from the exact same spot so the first few a 70mm, but I'm not sure about the exact intermediate steps until Exif writing seems to started working at 160mm). Sorry, I obviously did not check that properly before uploading. I will try to get another set of photos. Should I then just create a new upload or somehow attach them to this issue?

[uchrisu]

I had also a look at the file names, they also said 160 and 210mm. Maybe it is the best if you re-upload the files with corrected exif information and corrected file names, so that we can double-check if it is the right focal length.

But there might be another problem. When applying the corrections below 160mm the software will grab wrong correction data (at a wrong focal length) if this is a general problem ob recognizing focal lengths on this lens. Do you have a second camera or do you know someone who can check this with a second camera or the same lens, if this might be a general problem to this lens?

[misin100]

Thanks for the support @uchrisu I checked the lens with a second camera and it reported wrong focal lengths there, too. It seems like focal length reporting ceased to work after shooting in the rain a few weeks back. Before that, the lens reported somewhat correct EXIF data, that seems to be normal for that model. I.e. 70mm is reported as 75mm and in general rather big steps in reported focal length, most likely due to the vintage design.

I will try to investigate this further and reupload a set of pictures with correct focal lengths. This leads to another follow-up question (sorry for all the trouble): It seems that in general the lens (Minolta AF 70-210 / 4) does not seem to report exact focal lengths even if in proper working order. Searching the web, I found multiple reports that the minimal reported EXIF focal length of the lens is 75mm when shooting at 70mm. This is supported by some older shoots in my archive. Should this skewed focal length reporting turn out to be the normal behaviour of all those lenses, would it be more sensible to report the test shots with the original somewhat "correct" focal lengths or should I manually correct those?

I figure, although being technically incorrect, it might be more useful for automatic profile applications in darktable and the like, if the test pictures would report the indicated focal length. However, I would correct those if you think that's more sensible. Thanks again for all the help! :)

[junkyardsparkle]

Searching the web, I found multiple reports that the minimal reported EXIF focal length of the lens is 75mm when shooting at 70mm.

In a situation like this, it would be good to include a correction line for 70mm in the profile, just to keep software happy (darktable, for instance, tries to be "smart" about which focal lengths it offers for manual selection, based on the nominal zoom range). This can just be a duplicate of the "75mm" (actually shot at 70mm) entry with the FL value changed.

As for other focal lengths, I suppose it would be best to try to take calibration shots near the center of the range for each value it actually reports, at least in theory... but probably automatic correction for such a lens will never be perfect, no matter what you do.

[junkyardsparkle]

@uchrisu Something to keep in mind: when you add the "unsuccessful" label to an issue, the uploaded images are removed from the server's calibration directory and can no longer be accessed by anyone else... so you might want to avoid doing that until after any discussion referencing them is resolved. :grin:

[uchrisu]

As for other focal lengths, I suppose it would be best to try to take calibration shots near the center of the range for each value it actually reports, at least in theory... but probably automatic correction for such a lens will never be perfect, no matter what you do.

I think this is the way to go. This would mean we have good fitting results for automatic correction (automatic focal length search) but are still able to manually choose manually intermediate steps.

@uchrisu Something to keep in mind: when you add the "unsuccessful" label to an issue, the uploaded images are removed from the server's calibration directory and can no longer be accessed by anyone else... so you might want to avoid doing that until after any discussion referencing them is resolved. grin

Okay, next time I will only leave a comment and mark it unsuccessful if there is no answer within one week.

[misin100]

Thanks again for the feedback and help. I got the lens dried, cleaned, and reporting different somewhat correct focal distances again, and hope for some decent weather this weekend to get some new test shots in. I will create a new upload once I have them in the bag.