This chapter explains how shutter speed and subject movement affects photographic exposure. Shutter speed is about time—the time during which the shutter is open to record an image on an image sensor. That length of time affects subject movement. Shutter speeds on digital SLRs and mirrorless cameras can range from 1/8000th of a second or so to as long as photographers want to leave the shutter open. The chapter shows an image of the famous waterfall in Thingvellir National Park. A photographer wanted to create a "silky water" type photograph. At this waterfall, the water was flowing faster than at Hraunfossar and he was much closer. Those two factors required a slower shutter speed to create the effect. To prevent a blurry photograph caused by the movement of the boat and the telephoto lens factor, he needed to set a shutter speed of 1/320th of a second, which is fast enough for a hand-held shot.