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The digital photography A-Z

Shutter

Rolling shutter

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An image distortion effect caused by the way camera shutters operate at very high shutter speeds. Beyond a certain speed, focal plane shutters, as used in most interchangeable lens cameras, change the way they work. Instead of exposing the whole sensor at once, they expose it in a narrow strip between two shutter curtains passing very quickly across the sensor. This means that if a subject is moving very rapidly it may take on a skewed or twisted shape. This can be apparent not just in stills photography but in video too.

This also happens with electronic shutters, so that although they offer even higher shutter speeds than mechanical shutters, they too capture image data in ‘strips’, and while they may offer an exposure time of, say, 1/32,000sec, it actually takes considerably longer for this electronic scanning process to complete. This can only be fixed by so-called global shutters, which capture data from the entire sensor area at once.

Global shutter

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An advanced kind of electronic shutter that can capture the entire image area at once, instead of scanning it strip by strip. This should eliminate the rolling shutter effect usually associated with electronic shutters and make them much more effective for capturing moving subjects. It does, however, require advanced sensor technology, especially in larger sensor sizes, and powerful image processing, which is why it’s still in its infancy in the mass market.

Mechanical shutter

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The traditional form of camera shutter, a physical device which blocks light from the sensor until the moment you press the shutter release, then opens to expose the sensor for the required amount of time before it closes again. Mechanical shutters are either focal plane types, just in front of the sensor, or in-lens ‘leaf’ types.

Electronic shutters offer shorter shutter speeds on paper, but with current technology they’re less effective at capturing fast-moving objects.

Electronic shutter

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Some cameras now offer electronic shutters which start and stop the exposure digitally rather than with a mechanical shutter. These are silent and can offer very high shutter speeds, though most use a ‘scanning’ process which makes them unsuitable for action photography because while the exposure time for any particular strip of the sensor is very short, the length of time taken to scan the full sensor area creates distortion and ‘rolling shutter’ effects with fast-moving subjects.