Raise the ISO Rather Than Accept Blur

ISO sets how strongly the camera amplifies the light it receives. Higher settings add grainy noise, which is why beginners are told to keep it low, but that advice taken too far produces something worse: a blurred picture from a shutter speed too slow to hold. A little noise in a sharp photo of a birthday cake by candlelight beats a clean smear. On a camera, Auto ISO with a sensible maximum and a minimum shutter speed lets it rise only when it must. Phones usually set ISO automatically, so this one matters most once you own a camera. Exercise: indoors at night, photograph the same scene at ISO 100, 800 and 3200, keeping shutter speed fast enough to hold. Compare the noise and the sharpness at full size.