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.1DX Mark II test data on DxO Mark Q test data on DxO Mark
Excellent image quality, especially from RAWs; Fantastic high ISO performance; Fast autofocus with great tracking performance; 14fps burst rate; Amazing buffer capacity; 4K 60p video; Robust build quality.
Very heavy, bulky and expensive; Dual memory card slots use different formats; 29:59 continuous video recording limit; Touchscreen feels underutilized.