Last weekend I spent some time writing a manufacturer lens correction module for Darktable. The idea is to take advantage of the fact that most cameras embed distortion, chromatic aberration, and vignetting correction data into their RAW files. Thus, by interpreting these we can correct iens issues without waiting for a lens/camera combination to first be supported by lensfun (something which can take months or even years, and whose results depend heavily on the quality of the calibration).
Currently the module understands Sony and Fuji (APS-C) correction data. The models themselves were all derived through a combination of reverse engineering along with trial and error. As an example here is an image taken with a Fuji 16mm F2.8 lens in Darktable.
Notice the extreme amount of vignetting and distortion. Enabling the correction module we find:
Which has straightened everything up and produces results which are reasonably similar to the out of camera JPEG’s. (In case anyone is wondering that is what -11.6% distortion looks like.)
The module is reasonably adept at handling edge cases including Sony full frame cameras in 1.5x crop mode and Fuji cameras with their 1.25x crop mode. For those who are interested the relevant PR can be found at https://github.com/darktable-org/darktable/pull/7092/ although there is still quite a bit of work to do.