One of the most useful setting mode in DSLR cameras is seldom used by amateurs, mainly due to poor information on its possibilities.
This semi-automated mode, indicated by a "S" (for shutter) or "Tv" (in case of Canon, from "Time value") sets the time that the shutter is open. This way, we can decide how long will light be entering to the sensor surface. This setting can be adjusted (depending on brand and model) from 30 seconds down to 1/8000th of a second in some professional cameras.
