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.RX100 V test data on DxO Mark S120 test data on DxO Mark
Pocket-friendly design; Unbelievably fast burst capture; Generous buffer depth, even for raw; Fast and confident 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
Very pricey for a compact camera; Still no touch screen; Slow buffer clearing; JPEGs can look over-processed at higher ISOs; Lens doesn't offer much telephoto reach; Battery life is very modest; 4K movies are limited to five minute clips