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 M3 test data on DxO Mark RX100 IV test data on DxO Mark
DSLR image quality & resolution in a mirrorless body; Higher-res 24MP APS-C sensor; Much improved AF performance; Better ergonomics with full PASM dial; Built-in Wi-Fi & NFC; Tilting LCD.
No built-in EVF; Limited native lens selection; Slow burst mode; Shallow buffer depth with RAW files; No 60p video frame rate or 4K video option.
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.