SHUTTER SPEED SKILLS

Jason Parnell-Brookes introduces you to the fundamentals of using shutter priority mode to control the duration of your exposures

1 HOUR A camera's shutter 1 mechanism sits in front of the image sensor HOUR and is made up of two 'curtains: Before you take a shot, one curtain is closed, blocking the sensor, while the other is open, and raised above the sensor. As you press the shutter release button the first curtain (covering the sensor) opens, exposing the sensor to light, and at the end of the exposure the second curtain closes, blocking the sensor again.

So when we talk about the length of an exposure or shutter speed, we're referring to the time between the camera's shutter opening and closing; if we talk about a 'one-second exposure' the front curtain opens, and a second later, the rear curtain closes.

The reason two curtains are used is to ensure that light strikes the surface of the sensor evenly. At very fast shutter speeds, the rear curtain actually begins to close as the front curtain is still opening, so the exposure is made through a moving slit.