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.D500 test data on DxO Mark DSLR-A580 test data on DxO Mark
Superb image quality; Great high ISO performance; Rugged, comfortable camera body; Sharp articulating touchscreen display; Excellent AF point frame coverage; Fast continuous shooting speeds; 4K UHD video; Built-in Wi-Fi, NFC and Bluetooth.
Somewhat large for an APS-C camera; Expensive for a DX camera; 4K UHD video doesn't offer full DX field-of-view; No built-in flash; Still uses contrast-detect for Live View AF; Dual slots use two different card types (XQD and SD).