I used a primitive setup: Flashlight mounted on camera and "guided" to the back of the negative, so not even remote flashlight because I didn't have that for th

I used a primitive setup: Flashlight mounted on camera and "guided" to the back of the negative, so not even remote flashlight because I didn't have that for the camera. I used Darktable for the conversion process and there were 3 key points: Exposing the negative to fully exploit the RAW channels of the camera, setting a proper black and white point in the conversion process, apply white balance as needed and maybe manually tune the green/magenta slider a bit. Usually, if all that went well, I received pretty clean results. If something got botched in the process, I would see the same noise as the top right image shows. As the article notes the resulting dynamic range is really low then, which makes noise pop out. Noise is also in the bottom right example image, but the larger resulting DR (and downscaling) hides it well enough.