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.A7 III test data on DxO Mark K-1 test data on DxO Mark
Unlocks the full potential of full-frame Pentax lenses; Excellent image quality; Great ergonomics and build; Very compact for full-frame; Decent performance; Fast autofocus with great low-light capabilities; Very wide sensitivity range; Bright, accurate viewfinder; Articulated LCD; Stabilization, Wi-Fi and GPS in-camera
No built-in flash strobe; Quite heavy compared to APS-C flagships; Somewhat soft images and blown highlights by default in JPEG mode; Warm Auto white balance indoors; Slow startup and buffer clearing; Small top-deck status display; Weak viewfinder illumination; Below-average battery life for DSLR
New 24MP sensor offers excellent image quality; Outstanding high ISO performance and dynamic range; Improved JPEG colors; Improved build quality; Fast autofocus; Excellent 4K video; Very good battery life.
Buffer clearing can be slow even with fast UHS-II cards; UHS-II support only on one card slot; No losslessly compressed RAW option; Dedicated battery charger not included; Menus are still confusing; No built-in flash.