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Author Topic: Not getting lens correction  (Read 1224 times)
CHoffman
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« on: October 12, 2021, 02:08:45 AM »

Hi- noticed that I'm not getting lens correction with my Nikon Z6 and 24-70 mm f/4 S lens in the raw files. Strong pincushion distortion. Is there something I need to do to turn it on? It gets corrected in other programs that do raw conversion. This isn't anything new or related to recent versions AFAIK, just something I noticed when shooting rectangular objects.
Thanks!
CH
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« Reply #1 on: October 12, 2021, 11:56:21 AM »

Raw developing libraries like LibRaw used in Qimage do not perform lens distortion correction; that's an add-on.  We add those as we get the data for them.  You can submit files to us for the purpose of building a lens distortion profile if you like.  Just take a few shots of a cross-hatch pattern like tile in a shower, evenly spaced bricks, etc. and take several shots at different focal lengths throughout the 24-70 range.  Put them on Google drive and give us a link and we can create a lens profile.

Regards,
Mike
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CHoffman
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« Reply #2 on: October 12, 2021, 03:04:01 PM »

OK. Reading here- https://www.ddisoftware.com/qimage-u/tech-raw.htm#lens it wasn't clear to me that you had to do this for each lens yourself. Seems like a massive undertaking! I know that Affinity has a huge database but I don't think they did it themselves. Lensfun maybe, though I don't see my lens listed there. If the data is in the raw file, even if not optimum, it seems that would be far better than nothing. Regardless, I'll see if I can come up with a set of grid patterns for you.

Thanks & best regards,
Conrad
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CHoffman
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« Reply #3 on: October 14, 2021, 11:46:13 PM »

Man, no brick buildings or anything else useful close by. I'll have to drive over to RIT, which is massively brick!
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« Reply #4 on: October 15, 2021, 02:22:01 PM »

It can be anything with a crosshatch pattern: straight horizontal and vertical lines.  They just have to cover the frame and there has to be enough of them, typically 8 or more in both directions.  I printed a 13x19 of a grid but you can use shower tiles, brick, or even something like chain link fence.  I even had one person use a critter cage, similar to this: https://images.globalindustrial.com/images/enlarge/184087_04.jpg?t=1631868254122.  It'll work if they are straight lines and you shoot it straight-on.

Regards,
Mike
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CHoffman
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« Reply #5 on: October 15, 2021, 04:48:08 PM »

I know my lens goes barrel to pincushion with zoom, but does distance/focus have much to do with it?
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« Reply #6 on: October 15, 2021, 06:10:50 PM »

Very little.  I've done the lens distortion tests using everything from macro to far field and both return very close to the same results.

Mike
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CHoffman
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« Reply #7 on: October 16, 2021, 09:11:53 PM »

Hi Mike,  I've uploaded a zip file of raw images:

DSC_1971.NEF - 24mm
DSC_1972.NEF - 28mm
DSC_1973.NEF - 35mm
DSC_1975.NEF - 50mm
DSC_1976.NEF - 59mm
DSC_1982.NEF - 70mm

The lens is the Nikkor Z 24-70 f/4 S-series.

Hopefully you can get them at www.conradhoffman.com/rawtest/Nikkor_24_70_Distortion.zip

Thanks,
Conrad
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« Reply #8 on: October 16, 2021, 10:50:22 PM »

OK.  I'm done.  Good shots!  I've attached the lens corrections.  Here are the instructions:

(1) First make sure you are running the latest Qimage Ultimate (2022.105).
(2) Go into Qimage Ultimate and click "Utilities" on the top menu, then click "Explore Qimage Application Data" and click "OK" on the confirmation dialog.
(3) A File Explorer window will open: in that window, open the "profiles" subfolder.
(4) Take the "Z 6.lens" file in the attached ZIP and put the "Z 6.lens" file in the "profiles" folder you opened in the previous step.

That's it.  You'll get the lens corrections from that point forward: be sure to rebuild the thumbs/cache so Qimage updates your raws.  That is, go to a folder with some raws and click "View" from the top menu and then "Rebuild Thumbs/Raws".  You'll have to do this in each folder you visit so that Qimage will rebuild the raws with the new lens corrections.

Regards,
Mike
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CHoffman
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« Reply #9 on: October 17, 2021, 02:35:35 AM »

That's just fantastic, thanks! I assume it will only apply corrections to that lens and will ignore other lenses that would need their own corrections?

As an aside, I seem to shoot a lot of close-ups of straight sided objects at the full zoom, where the pincushion was driving me crazy.
« Last Edit: October 17, 2021, 02:55:34 AM by CHoffman » Logged
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« Reply #10 on: October 17, 2021, 12:18:28 PM »

Yes.  That file only applies lens corrections to photos shot with the NIKKOR Z 24-70mm f/4 lens.

Mike
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CHoffman
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« Reply #11 on: October 17, 2021, 12:38:04 PM »

Hey, do you want me to put anything in the cookie jar for this? Seems like you spend a lot of time supporting everybody!
CH
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« Reply #12 on: October 17, 2021, 12:56:41 PM »

Thanks but no; just part of the job.  Plus you already helped out because the next release will have that lens file included to support another lens in QU.  Smiley

Mike
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