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.RX1R test data on DxO Mark Q test data on DxO Mark
Significantly sharper, more detailed JPEG images than those from the RX1; JPEG processing appears to minimize moire and aliasing artifacts; Same price as the RX1; Full-frame, 24-megapixel compact camera with fast Carl Zeiss Sonnar 35mm f/2 T* lens; Blazing fast autofocus; Impressive image quality that rivals (and sometimes surpasses) full-frame DSLRs.
More prone to moire, aliasing and false color than the RX1; Only subtle improvement in sharpness in RAW files; Fixed-length lens limits shooting flexibility; Viewfinders (optical or electronic) only available as optional accessories; Extremely expensive for a compact camera.