It's not an answer to your problem per se so much as a piece of photographic trivia. Some time ago, I read a review of a couple of 15mm lenses, and noticed that one of them showed a noticeably narrower angle of view when two images of the same subject from the same position were placed side by side. As a exercise, I put the one with the wider angle into Photoshop and corrected the barrel distortion evident in that image but not the other. The resulting image then showed the same angle of view after the unusable bits had been cut out. The first lens showed the image straight out of camera apparently, so it would seem that the camera's firmware was correcting the image automatically to remove distortion.