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.EOS M5 test data on DxO Mark GX8 test data on DxO Mark
Highest resolution Micro Four Thirds camera yet; Great high ISO performance; Very fast autofocus; Fast burst mode with deep buffers; Impressive Dual I.S. system; Great 4K video.
No built-in flash; Slow buffer clearing; Below average battery life; Limited I.S. for 4K video.
Enthusiast-oriented compact camera body; Good image quality in most situations; Built-in electronic viewfinder; Impressive Dual Pixel CMOS AF; Very good overall performance.
High ISO image quality and dynamic range aren't quite up to par with some of its competition; No 4K video recording; Native EF-M lens selection is still limited; Below average battery life.