Most digital SLR cameras are equipped with a pop-up flash. The flash will fire automatically to illuminate dark or back-lit subjects when set to auto and in some scene modes, including portrait and close-up modes. In P, S, A, and M modes, the flash must be turned on or off manually. Turning the flash off when photographing poorly lit subjects may result in slower shutter speeds and blurred shots or heavy shadows in backlit subjects. Using the flash prevents blur and ensures that backlit subjects are not in shadow.
When using Active D-Lighting, choose a mode other than M or use matrix metering.