Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos.
Cameras with higher effective ISO will be better choices for indoor photography, night shooting, and indoor sports photography, especially if you intend to make large prints.
You can learn more at our glossary entry.
Maximum effective ISO test data courtesy of DxO Mark.5D Mark III test data on DxO Mark S (Typ 006) test data on DxO Mark
Superb still and video image quality; Powerful, fast, and accurate AF system with loads of cross-type points, loads of configurability and great frame coverage; Rugged, weather-sealed body with great control layout and user-interface configurability.
Dynamic range is limited by noise in deep shadows; Somewhat heavy-handed noise suppression and sharpening at default settings. (Shooting RAW avoids both.); No AF illuminator.