I'm gona try a few tricks to increase the smoothness of the pics.
From what I've been reading you can over expose the pic say to 1.0 in raw format then bring it in to say Pshop and reduce the exposure to -1.0. This is supposed to decrease the ISO from 200 to 100. Doing the same with a over exposure of 2.0 and then decreasing with -2.0 should achieve a ISO 50. I'll try some tests to verify.