lensfun database location is goofy. It relies on GLib, which they don’t really explain fully in the lensfun docs.
It’s important to know the location of the lensfun database RawTherapee is using. Really IMHO, the best way to do this in Windows is to:
- specify a specific location in the options file. This is describe in https://rawpedia.rawtherapee.com/Lens/Geometry#Updating_your_Lensfun_database_in_Linux, scroll to “Should you need to use a Lensfun database in a custom location…”
- use my Windows lensfun_updatedb to update that specific location. You can get the .zip file containing the dbupdate.exe file here: https://github.com/butcherg/lensfun_dbupdate/releases, put the dbupdate.exe in a directory pointed to by your PATH variable, or in the directory containing the lensfun database director, then open a shell cd to that directory, and run dbupdate 1|2, pick 1 or 2 corresponding to the version number of the lensfun database RawTherapee is using. That’ll check the installed version and if it’s behind (or non-existent), it’ll download the current database from the recommended URL and unpack it to a version_x directory, x being either 1 or 2, depending on the version you specified.
You can change the database to include your data, but if you do this, don’t run dbupdate again or it’ll write the update right over your change. The lensfun docs apparently are not clear on where user mods can be placed in Windows, but what they do tell you in the most recent documentation might give you some clues.
Anyway, use the RT options to point to the directory you want to use, rather than let lensfun determine it for you…