I do own the “Canon EF 70-200 f/4L IS USM” lens for a long time now, and have been shooting it with at least 3 different cameras. However, sorting my images by lens for the first time in darktable today, I am observing something weird: The lens is available two times with different names:
The name with USM is used for photographs between December 2021 and today, while the name without USM is used between October 2013 (I probably got it back then) and today.
The same happens for another lens: The “Canon EF 24-105mm f/4L IS” which also has variants with and without “USM”, but with another introduction date for the new name.
It seems that the newer photograph are sorted into both categories while the older photos are only in the category without USM.
The camera manufacturers haven’t always included a text nomenclature for a lens in their metadata so the software folk have had to resort to lookup tables to supply their own text. In exiftool source code, Phil Harvey has a note about ‘USM’ and it’s ambiguous application in the lens literature. This, the result of a cursory look at both exiftool and exiv2 source code, where they both maintain similar tables…
Hm, as far as I understand this would explain why different images can have different names for the same lens. However, all recent pictures seem to have 2 names at the same time. I did not yet have a look how lens information is stored in the database, but it seems that this is not a 1:1 relation. Furthermore, even relatively new images have this issue, but this would mean that the image was imported twice or at least the exif data was read twice with different results. What can trigger this re-reading? And why does it add a second lens to the image and not update the information? Seems I am still confused …
