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.A5100 test data on DxO Mark M9 test data on DxO Mark
Excellent image quality, with unique film-like "Leica look"; No-nonsense controls; Solid build; Good print quality.
Difficult to focus in low light; High default contrast and saturation; Manual focus only; Lack of low-pass filter can leave moire and other artifacts.
Very small and comfortable form factor; Very good image quality for its class; New dual video record function; Quick autofocus and good dynamic range.
Lacks an EVF and external mode dial; No hot shoe; JPEG processing at higher ISOs not as good as some competing mid-level models.