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.7D Mark II test data on DxO Mark S (Typ 006) test data on DxO Mark
Excellent image quality; High ISO performance improved over predecessor; Excellent burst speeds (up to 10fps); Significantly improved buffer depths; 65-pt AF system; Dual Pixel CMOS AF; Can focus down to f/8 (great for teleconverters); 1080/60p video; Headphone and mic jacks; Rugged build quality.
Autofocus speed (AF shutter lag) slower than 7D and 70D; Mediocre battery life for a pro DSLR; Dynamic range at low to moderate ISOs not as good as competitors; Phase-detect AF did not perform as well as expected in our low-light AF tests; No built-in Wi-Fi; No autofocus for 1080/60p video.