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.Df test data on DxO Mark 1D Mark IV test data on DxO Mark
Same sensor and processor as professional D4; Great image quality; Arguably the best available-light shooter in its class; Handsome, retro styling; Weather-sealed design; Big, clear full-frame viewfinder; Excellent battery life
Expensive; Bulky, yet handgrip is quite modest; Some controls are clumsy; Plastic body panels don't gel with retro aesthetic; Autofocus isn't in the same league as image quality; No AF assist lamp; No movie capture; No portrait grip; Single card slot