Hello. Anybody know what the differences are between these two Rollei films? They are both orthochromatic and super fine grain. So what is different besides ATO 2.1 having a fancier name ("Advanced Technical Orthographic")? The only thing I can find different in anything I see on the web is that ATO is described as "pure lith". But I've never quite understood specifically what that means. I take it to mean ATO 2.1 is higher contrast than Ortho 25, but what else if anything? I also thought lith films were inherently very grainy, but ATO 2.1 has the same "extremely fine grain" description as Ortho 25.