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.A9 test data on DxO Mark A58 test data on DxO Mark
Improved 20.1-megapixel resolution; Impressive image quality, especially for its price; Fast and decisive autofocus (in most conditions); Very good battery life; Good video quality (Full HD 1080p, though it doesn't support 60p frame rate).
Plastic lens mount; Slower burst mode speeds and shallower buffer than A57; LCD no longer fully articulating; Mediocre kit lens; Electronic instead of an optical viewfinder may be a turnoff for some.
New sensor offers incredible performance; Excellent image quality at low & high ISOs; Very good dynamic range; Phenomenal 20fps burst speed & deep buffer; Very good battery life for a mirrorless; 4K video; Dual card slots.
Slow buffer clearing; Only one card slot is UHS-II compatible; Touchscreen underutilized; No lossless RAW compression option; No 4K/60p option.