Infrared Channel. The scanner needs to have the hardware for this. V850 has it, 12000 does not. It recognizes anything that is denser than film, like dust, and can eliminate it like a big spot healing brush.
The V850 comes bundled with SilverFast SE scanning software. You will have to upgrade to the SF8 Ai software to take best advantage of the IR feature, and have the best scanning software.
The 12000 comes with SF8 Ai. I think it is expensive because it is large format, high quality, and has a smaller pool of buyers.