Demystifying ISO invariance (Full Edition - Living Document)

ISO invariance is one of the most misunderstood — and underused — concepts in digital photography. In this highly technical yet accessible article, the author breaks down the theory behind ISO invariance, read noise, photon noise, and the ETTR (Exposing To The Right) technique, revealing how digital amplification can be used strategically to maximize image quality and dynamic range.

Going beyond theory, the article presents real-world applications of these concepts in challenging photographic scenarios, including lunar timelapses, high-contrast scenes, and astrophotography. Whether you're a seasoned photographer or someone looking to master exposure under extreme conditions, this guide offers valuable insight into how to shoot smarter when it comes to ISO.

This full edition is continuously evolving, including new applications, examples and insights.

Last updated on June 5, 2025.

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