EOS 5D Mark III - Incorrect exif data re: focal length

[MNshutterbug]

I have a Canon 5D Mark 111 and just acquired a Canon 17-40 lens. Everything looks good and performs well but anytime I have the focal length at wider than 28mm, the exif still shows 28mm. It's correct from 28 - 40 but it's as if the camera isn't capable of registering the correct exif at anything below 28mm. I tried both jpeg and raw. Anybody else have this issue?

[MNshutterbug]

I opened a file in DPP4 and performed a lens correction for this lens and instead of 28mm, it now shows 24mm in my exif viewer. I was going to run it again to see if it changes but once it's been done once, it doesn't give me the option of a 2nd time. It was an interesting experiment anyway.

[Peter]

I mean that your lens correction will be wrong when you want to apply one. DPP will not be able to read the right focal length and will over/undercorrect vignetting.

[MNshutterbug]

Why won't DPP be able to read the right focal length? 

[johnrmoyer]

I have EOS R5, so this might be different. But, I hope some of this might be helpful anyway.

To find a photo made with this lens at 17mm on my web server, I ran the command: 

egrep -i -l "17-40" ~/public_html/*/*.html | xargs egrep -i "focal.*len"

I had previously used exiftool free software and a Korn shell script to make the html files and did some manual edits of the html files after.

This is one I made with that lens at 17mm: 

https://www.rsok.com/~jrm/2023Feb14_birds_and_cats/2023feb013_thunderbird_IMG_3165c.html 

Lake Thunderbird in Norman, Oklahoma, United States on February 13, 2023