>I posted on this in the D7100 forum and it was confirmed that >the in camera flash respects the Auto ISO settings while >external but in hot shoe flashes do not and use, often double >the ISO. Does anyone know why or how to get around this. It >seems strange that this was not fixed on the newer D7100 >model. >My work around is Easy ISO, but it would be nice to use Auto >ISO with fill Flash in my nature work.
There have been dozens of threads over the year on this. It is clear that using Auto ISO does not work in any expected manor with flash.
The results have definitely improved with each newer camera, and maybe they will get something that works well eventually, but for now, I think it is best to simply avoid using Auto ISO with flash.