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.X100 test data on DxO Mark RX100 IV test data on DxO Mark
Superb image quality; Dazzling Hybrid Viewfinder; Traditional mechanical controls; Mostly excellent optical performance.
Quirky interface; Manual dials turn easily; Manual focus is too difficult to use; Dramatic lens flare, especially at night.
Vastly improved burst speeds with deep buffer; Great performance with very fast autofocus; Very high resolution gives lots of detail in good light; High ISO noise levels much better than most pocket camera rivals; High-quality 4K video with uncompressed HDMI out; Super-fast High Frame Rate video; Same great pocket-friendly design.
Pricey for a compact camera; JPEGs can look over-processed at higher ISOs; Lens doesn't offer as much telephoto reach; Battery life not as good as predecessor; 24-70mm-equivalent lens can feel limiting.