The mechanism which controls the duration which light is allowed in.
Low shutter speed allows more light in.
High shutter speed allows less light in.
Measured in "stops" which are halved or doubled units.
- 1/30 sec. lets in double the light of 1/60 and quadruple of 1/125
- 1/60 sec. lets in half the light of 1/30 and double of 1/125
1/125 sec. lets in half the light of 1/60 and one quarter of 1/30
A slower shutter gives more opportunity for blurring. The movement of either the camera or the subject can can cause blur. A fast shutter speed is useful for moving objects (like pets or with sports photography).