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.6D test data on DxO Mark 80D test data on DxO Mark
Excellent image quality on par to more expensive full-frame DSLRs (including the 5D Mark III); Responsive all-around performer; Superior HD video-shooting chops; Built-in Wi-Fi with remote control and sharing features, Built-in GPS and geotagging.
Lacks a built-in, pop-up flash; No external headphone jack; Rather basic 11-point autofocus system; Mediocre burst speed.
Very good image quality; Better RAW high ISO performance than predecessor; Improved buffer depth; Very fast AF; Dual Pixel CMOS AF is excellent; f/8 AF support; 1080/60p video; Headphone jack; Very good battery life.
New kit lens isn't very sharp; No 4K video; No clean HDMI out; 29:59 minute video recording limit; Phase detect AF not as sensitive in low-light as expected (Dual Pixel AF is better in low-light).