A shutter is a device that controls how long light reaches the sensor. It is a curtain or a blade that opens and closes. When it opens, light passes through to the sensor. When it closes, the exposure ends. The length of time the shutter is open is the shutter speed. Mechanical shutters are made of metal or cloth. Electronic shutters have no moving parts. They turn the sensor on and off electronically. Each has advantages. Mechanical shutters are reliable and work with flash. Electronic shutters are silent and can achieve very fast speeds. But they can produce rolling shutter distortion, where fast-moving subjects appear skewed.

The shutter is one of the two main controls of exposure, along with the aperture. Shutter speed determines how motion is rendered. A fast shutter speed freezes motion. A slow shutter speed blurs motion. That blur can be artistic, as in a waterfall or a moving car, or it can be a mistake, as in camera shake. The shutter also affects flash sync. Most cameras have a maximum sync speed, above which the shutter curtains block the flash. Understanding the shutter helps you control time in a photograph.

Shutter facts

• Function. Controls how long light reaches the sensor.
• Speed. Measured in fractions of a second.
• Mechanical. Moving curtains or blades.
• Electronic. No moving parts, silent.
• Sync speed. Fastest speed for flash use.

The shutter is not just a mechanism. It is a way of controlling time. A photograph is a slice of time, and the shutter determines how thick that slice is.