Shutter Speed
Shutter speed is how long the sensor is exposed to light for a single frame, typically expressed as a fraction of a second (1/250s) or, for long exposures, in whole seconds. A faster shutter speed (a shorter time, like 1/2000s) freezes motion and admits less total light; a slower shutter speed (a longer time, like 2 seconds) blurs motion and admits more light.
It's one of the three exposure-triangle variables, and every full halving or doubling of shutter time is exactly one stop — the same unit aperture and ISO are measured in, which is why a shutter-speed change can always be exactly offset by an opposite change in either of the other two.
Frequently Asked Questions
What's a safe handheld shutter speed to avoid camera shake?
A traditional rule of thumb suggests roughly 1 over your full-frame-equivalent focal length as a starting point (1/100s for a 100mm lens, for example), though it's a rough estimate rather than a hard limit, and image stabilization can push well past it.
Why does a slow shutter speed sometimes blur a photo I didn't want blurred?
Any movement during the exposure — camera shake, subject motion, or both — shows up as blur proportional to how long the shutter stays open, which is exactly why a slow shutter speed demands either a stationary subject, a tripod, or a deliberate motion-blur intent.