Below shows the effects of varying the ISO on my Canon T3i. I should have had the camera on a tripod to do this, but it gives you a pretty good idea about the ISO settings on the camera. The higher the ISO, the lower quality the photos become. I like the quality up to about 400. I could probably live with ISO 800 in better lighting. The door shot shows a lower lighted area. The curtains are much brighter and look okay at higher ISOs.