I always set ISO manually because I want to know exactly what it is and that makes it easier to work around apertures and shutter speeds in relationship to that. If it varies all the time then you don't really learn how to work with particular ISOs since the camera just does it for you. I almost always shoot at ISO 200, for example, unless I really have no choice indoors but to increase it but would not want to go beyond 800. I'm sure with many of the better cameras it is ok to go even to 1600 with clear results but I guess I like to make sure that any noise is minimized as much as possible. But in answer to your question, yes the camera can set nonstandard ISOs automatically but you cannot because it is based on stops (200 is one stop more than 100, etc.).