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.D3300 test data on DxO Mark K-500 test data on DxO Mark
Excellent image quality with lots of fine detail; Very good high ISO performance; Good dynamic range; Good print quality; Deep buffers with JPEGs; 1080/60p video; Uncompressed HDMI output.
AF struggles in low-light; Contrast-detect AF in live view is slow; Buffer depth is shallow with RAW files; No AE bracketing; No built-in Wi-Fi.