If you don’t press the button in the right sequence, photos will be improperly exposed and focused. Pressing the shutter button down correctly helps prevent camera shake. Even the slightest movement during the record time of a shot can cause blurred images.
Two step process
With a film camera, the shutter button is pressed down in a single step. However, it’s a two step process with a digital camera. When the shutter button is pressed half-way, exposure and focus are locked as long as you hold it in that position.
Controlling focus and exposure
Use the first stage of pressing the shutter button to gain more control over where the camera actually focuses and exposes. Once locked correctly, take the photo. When focus and exposure are achieved, keep holding the button down halfway if you must recompose. Some digital cameras have a setting that lets you lock focus and exposure independently.
Confirming focus and exposure lock
An indicator on the LCD, electronic viewfinder or a light on the camera near an optical viewfinder glows steadily to confirm the lock. Once the camera confirms focus and exposure, then fully depress the shutter button to take the shot.
All digital camera manuals contain instructions about this important technique. Practice until you get the rhythm of the sequence and using it becomes second nature.