Originally posted by Rondec I would go to iso 3200 and then push the photo in post processing. Marc Sabatella has a number of examples where in low light he deliberately under exposed a photo to keep his shutter speed decent and then pushed the photo afterward.
Just to be clear for those wondering - no, I am not imagining that I am somehow getting better results from this than from simply raising the ISO higher. I do it simply because my camera (K200D) maxes out at ISO 1600 - there is no ISO 3200 or 6400 to choose from. So deliberate underexposure and push processing is the only way to get similar results - the same final exposure at the same shutter speed as a camera that shoots 3200 or 6400 natively.
Actually, on all cameras I know of that have ISO 3200 or 6400, that's how it's implemented in the camera anyhow. The shot is taken at a lower ISO as far as the electronics are concerned, and then the results are simply brightened digitally in the firmware. The results are no better (or worse) than one can do oneself in PP. So it's really no particular loss to have to do things my way except for a few additional moments spent in PP. The noise levels I see when pushing one stop to the equivalent of ISO 3200 look about as good as any other camera that shoots 3200 natively, except the K-x which does look slightly (like maybe about half a stop) better. Pushing two stops to 6400 is usually considerably iffier. Every once in a while, if the light and subject are right, the results will surprise me, but it's not a risk I like to take, so I usually try to keep within one stop of the correct exposure.
To be honest, I actually find it a little liberating *not* to have too many options for high ISO. I don't have to think hard before or while shooting about what ISO to choose in order to get the best compromise between shutter speed and noise. I simply go straight for ISO 1600, open up the lens, pick a shutter speed I can live with in M mode, and let the exposures go where they will. Takes all of a few seconds in PP to select a bunch of similarly-exposed images and push them at once. So I'm not so sure I wouldn't continue to shoot in this way with a K-x.