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.A7S test data on DxO Mark A7 II test data on DxO Mark
Outstanding high ISO performance; excellent dynamic range; 4K video recording (via uncompressed HDMI); XAVC S option for HD video; Slightly improved battery life over A7/A7R; Built-in Wi-Fi & NFC connectivity.
4K video requires expensive external recorder; Sluggish startup time; Loud shutter; Silent Shooting mode hurts image quality; Lacks a built-in, pop-up flash; Limited selection of native Sony FE lenses.
Excellent 5-axis sensor-shift image stabilization; Sensor-shift IS brings stabilization to nearly any lens; Much-improved ergonomics and top-deck control layout; 'Mark II' maintains same impressive image quality, dynamic range and high ISO performance; XAVC S 50Mbps video format; Faster start-up time; Hybrid AF performs well with good continuous AF.
(Similar to A7): Loud shutter (but electronic first-curtain helps); Battery life could be better; Low-light AF still not as good as most DSLRs; High ISO JPEGs look over-processed; Slow buffer clearing; Limited selection of native Sony FE lenses (but it's getting better).