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.5D Mark IV test data on DxO Mark 645D test data on DxO Mark
Very high-resolution 40-megapixel sensor; Plentiful controls with great placement; Excellent optical viewfinder; Dual SDHC card slots; Infrared remote sensors front and back.
High price tag; Aliasing artifacts; Produces ~70MB RAW files.
Superb image quality from RAW files; Improved dynamic range; Excellent high ISO performance; Fast 7fps burst rate with unlimited JPEG buffer; High-quality cinema 4K video; Built-in Wi-Fi; Dual Pixel CMOS AF is very good.
JPEG files look soft at default settings; 1/200s flash sync; 4K video codec is cumbersome; 29:59 continuous video recording limit.