Shutter Release button
Explanation: The shutter release button reacts in two steps:
- Slightly pressing it until you feel the first resistance will activate autofocus and exposure metering
- Pressing it further will actually take a picture.
The exposure metering will be continuously adjusted as long as you hold the button pressed – unless you have changed this in custom setting menu c1 shutter release button AE-L.
Recommendation: Use it frequently! But think beforehand 