It wasn't too many years ago that the best DSLRs had an acceptable ISO of up to 800, and then it moved up to 1600. Nowadays, it seems that the upward limit has climbed into the stratosphere. The Fuji system has also kept pace, performing well at higher ISOs. Some of my recent photos at the local zoo were at 10,000 ISO and still acceptable. This tiger was photographed in a dark corner of his cage at the Toronto Zoo. The photo is a .jpeg, with cropping and minor editing only. The other photos were from RAF files. It seems a bit strange to see red Canadian autumn leaves in a photo of a rhinoceros.