Darktable's Lens Correction module correctly identifies my lenses, but doesn't correct distortion properly. I can often improve it by reducing the identified focal length to the next lower option, but unfortunately, the f number options available are in large steps with no option to specify a precise figure. So when trying to get my sea horizon line straight, I can only get it to go slightly arched or slightly sagging. I'm wondering how other users tackle this issue. It would be great if the devs could add a barrel/pincushion distortion module, wouldn't it?