Auto ISO sensitivity control lets the camera adjust ISO sensitivity automatically if optimal exposure can not be achieved at the value selected by the user.
Maximum sensitivity: Choose the maximum ISO sensitivity to prevent auto ISO sensitivity control selecting too high a value.
Minimum shutter speed: Auto ISO sensitivity control will automatically raise ISO sensitivity to prevent shutter speeds slower than this limit in exposure modes P and A. Choose a value, or select Auto to allow the camera to choose the minimum shutter speed according to the lens focal length (CPU lenses only). For example, the camera will select a fast minimum shutter speed with telephoto lenses to reduce the camera blur that tends to occur at long focal lengths.