Shutter Speed Skills

Jason Parnell-Brookes guides you through your first steps in using the Shutter Priority mode to effectively control exposure time

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.

The shutter mechanism sits in front of the image sensor and is made up of two ‘curtains’. Before you take a shot, one curtain is open, raised above the sensor, while the other is closed, blocking the sensor.

As you press the shutter release button the first curtain (covering the sensor) opens, exposing the sensor to light, followed by the second curtain closing, blocking the sensor again. So when we talk about a ‘one second exposure’, the front curtain opens, exposing the sensor, and a second later, the rear curtain closes to cover it.

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.