Nikon D5100 Reference Manual page 46

A
The Shutter-Release Button
The camera has a two-stage shutter-release button. The camera focuses when the shutter-
release button is pressed halfway. To take the photograph, press the shutter-release button
the rest of the way down.
A
Auto Meter-Off
The viewfinder and information display will turn off if no operations are performed for about
s
8 seconds (auto meter-off ), reducing the drain on the battery. Press the shutter-release
button halfway to reactivate the display. The auto meter-off delay can be selected using
Custom Setting c2 (Auto off timers; 0 160).
Exposure meters on
A
The Built-in Flash
If additional lighting is required for correct exposure in i mode, the
built-in flash will pop up automatically when the shutter-release
button is pressed halfway. If the flash is raised, photographs can only
be taken when the flash-ready indicator (M) is displayed. If the flash-
ready indicator is not displayed, the flash is charging; remove your
finger briefly from the shutter-release button and try again.
To save battery power when the flash is not in use, return it to its
closed position by pressing it gently downward till the latch clicks
into place.
28
Focus: press halfway
8 s
Exposure meters off
Shoot: press all the way down
Exposure meters on