I was curious just how high the ISO on my D850 could go, within reason, and I could still have Topaz DeNoise AI remove the noise. I happened to shoot yesterday at ISO 12800 (auto ISO), this was wide open on my Nikon 500PF at 1/3200 sec. I am amazed at how well the denoise software worked. I did tweak the sliders a little bit to increase the change above what the auto did. After I used DeNoise I used LrC Transform to increase the subject size, PS to remove a feeder, LrC to again increase the size and a little bit of processing with the LrC brush tool. Not bad for an end result. This is a screen shot to show the settings. I've always pondered the whole high ISO thing instead of a dark image and trying to bring up the shadows, bringing up the shadows has never worked that well for me as I did not like the artifacts that could develop, and now technology has made it possible for us to actually shoot at very high ISO settings and still get good results.