The shutter has two primary functions :
- By opening and closing when the trigger is pressed, it lets in light for a specific duration. This controls the amount of light reaching the sensor and hence the exposure.
- The shutter also affects the appearance of the image in terms of its freezing power. At high shutter speeds, the image looks sharp and the action is frozen. As the shutter speed becomes slower the images show blur and have a softer effect.
Shutter speeds are written as a fractions of a second. 1/1000 means that the shutter is open for one thousandth of a second.
This video shows how the shutter works. When the trigger is pressed, the mirror will first flip open. The next stage is when the shutter rolls down. The shutter does not open and close fully but rolls down as a small slit. Once the shutter movement is complete, the mirror drops down to it normal position.