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 test data on DxO Mark
Incredibly small body for a fully-featured, full-frame camera; Very high resolution; Hybrid autofocus is reasonably fast and confident; Significantly better burst-shooting performance than A7R; Excellent image quality even at very high sensitivities; Faster x-sync than A7R; Accepts existing Alpha-mount and E-mount lenses, and can optionally crop to APS-C image circle.
Grass-is-greener syndrome when compared to its higher-res sibling; Moderate performance; Loud shutter (but electronic first-curtain helps); Mediocre battery life when using electronic viewfinder; Weak low-light autofocus considering its price; Limited selection of native Sony FE lenses.
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.