ISO Invariance and Noise Reference

ISO invariance is one of the more misunderstood ideas in digital photography, and this reference explains it in plain terms with a quick estimator. On an ISO invariant sensor, brightening a dark RAW file in editing gives almost the same noise as raising the ISO in camera would have, because most of the noise is set at the sensor rather than added later. This means you can protect highlights by shooting at base ISO and lifting shadows afterward. Pick your approximate scenario and the tool suggests whether to raise ISO or expose low and brighten in post, and it shows the equivalent brightening in stops. Older and smaller sensors are less invariant and prefer correct in camera ISO, while many recent full frame bodies are highly invariant. Use this to make smarter exposure choices in tricky light. Everything is computed in your browser with nothing sent to a server.