Compared to other camera you might use ISO 400 or 800 just fine but hesitate to use ISO 1600 or more for Fuji X-E1 ISO 1600 still just fine and comfortable to use, you still get good quality of photo. if you follow the link to forum thread of this review you'll found the 100% original photos took by Fuji X-E1 from ISO 200 to 6400 even the photo took at ISO 6400, the quality is not just acceptable but good. 