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.D300S test data on DxO Mark 40D test data on DxO Mark
Rugged construction; 51-point AF system capable of sophisticated AF tracking; Large, bright optical viewfinder; 7 fps JPEG or 12-bit RAW burst mode; HD Video capture.
14-bit RAW mode slows continuous shooting from 7 fps to 2.7 fps; Somewhat slow AF for a camera at this level, especially in 51-point auto-area mode; Video capture tops out at 720p24.