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.D610 test data on DxO Mark D5500 test data on DxO Mark
Eliminated sensor dust-and-oil spot issue from D600; Great controls for amateur or pro; Comfortable ergonomics and weight; Excellent image quality and low-light performance; Very good dynamic range; Excellent battery life; Built-in lens correction.
Not drastically different from D600; Moire with certain subjects; Auto WB still too warm in incandescent light; Slow AF in live view mode; Aliasing in videos.
Amazingly small for a DSLR; Great image quality for its class, including superb low light and high ISO performance; Generous JPEG buffer depth; High resolution.
Buffer depths are shallow when shooting RAW; Lacks GPS from the predecessor; No AA filter means it's susceptible to aliasing artifacts.