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 III test data on DxO Mark 7D test data on DxO Mark
Excellent 18-megapixel sensor with impressively low noise and superb detail; Very good high ISO performance, especially for 18-megapixel subframe sensor; Rugged construction with magnesium body and weather sealing; Fast autofocus and fast burst rate of 8 fps; Full HD (1920x1080) movies at 30/25/24p, 60/50p at 1280x720.
No dedicated AF-assist lamp (flash is used), and AF-assist adjustment is buried in the Flash Settings menu; Kit lens (28-135mm) isn't quite up to the resolving power of the 18-megapixel sensor, odd focal length for subframe DSLR; No continuous autofocus in Movie mode.
Superb still and video image quality; Powerful, fast, and accurate AF system with loads of cross-type points, loads of configurability and great frame coverage; Rugged, weather-sealed body with great control layout and user-interface configurability.
Dynamic range is limited by noise in deep shadows; Somewhat heavy-handed noise suppression and sharpening at default settings. (Shooting RAW avoids both.); No AF illuminator.