Originally posted by biz-engineer Michael, you don't have ISO50 , you have ISO25, because pixel shift = 4 stacked frames (+time to shift the sensor... I have no idea how long it take to shift the sensor, perhaps someone could take 10 or 20 pixel shifted frame to calculate how long it takes to shift the sensor).
Or without pixel shift, instead of taking one long exposure shot of lets say 20 seconds, taking multiple shorter shots at higher ISO (lets say 10 shots at 2 seconds) and averaging them will give you the same result, as averaging reduces noise just like lower ISO does. Actually this is in some sense preferable to using an ND filter for silky water shots, as averaging multiple shots reduces noise, but ND filters do not.
I do not know how much more inconvenient it is, I have no clue if this type of averaging can be done in-camera. Its a lot easier to program than HDR, but I have not tried to find this function.