ExifTool > Bug Reports / Feature Requests

Nikon D850 AF Points Used - changes not work

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I have a problem changing the tag: AFPointsUsed in files from Nikon D850.
For example, this file: https://4.img-dpreview.com/files/p/sample_galleries/5682971467/7312607286.jpg

Reading values gives me this:
AF Points Used: A9
Primary AF Point: A9

When changing these values using ExifTool values are saved to the file but does not change anything when I view this photo with Nikon Capture NX-D which displays the active AF point.
exiftool.exe -AFPointsUsed=C6 d850.jpg

Everything works fine on older cameras: D800, D750, D600. The D850 is a newer generation, so the data on the active focus point is probably saved in a different place.
So where does ExifTool get the value of A9 by reading it and is it correct?

Phil Harvey:
Yes, I saw this github issue.  It will take me some time to research this because I have to dig out the backups of my old emails to see if I have tried to decode this in the past.  Best case is that I will need lots of samples to be able to decode this.  Worst case is that I have already tried this and failed.  It will be next week before I can look into this in detail.

- Phil

Thanks for your interest, I think the problem will also apply to the D5 and D500 models because they have the same focus mechanism. Unfortunately, I do not have any of them so when it comes to sample photos I will not help, but I hope that you will be able to solve it, because the situation will probably also apply to newer models that will be released.

Hayo Baan:
I have a D500 and can provide example files.

Phil Harvey:
I have a D500 too. :)

- Phil


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