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 IV test data on DxO Mark D7000 test data on DxO Mark
Very good image quality; Better than average noise vs. detail handling at high ISOs; Very good dynamic range in JPEGs, excellent in RAW files; Lots of high-end features in a relatively compact body; 6 fps burst mode.
Viewfinder not as accurate as specified; Viewfinder doesn't show ISO unless adjusting; No live histogram in Live View mode; No phase-detect Live View AF mode.
Superb image quality from RAW files; Improved dynamic range; Excellent high ISO performance; Fast 7fps burst rate with unlimited JPEG buffer; High-quality cinema 4K video; Built-in Wi-Fi; Dual Pixel CMOS AF is very good.
JPEG files look soft at default settings; 1/200s flash sync; 4K video codec is cumbersome; 29:59 continuous video recording limit.