Nikon D3100 Reference Manual page 23

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Hiding Shooting Information
To turn the monitor off, press the R button. Note that the monitor turns off automatically
while the shutter-release button is pressed or if no operations are performed for about 8 s
(for information on choosing how long the monitor stays on, see Auto off timers on page
143). The information display can be restored by pressing the R button again.
R button
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Rotating the Camera
When the camera is rotated 90 °, shooting information rotates to
match camera orientation.
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The Shutter-Speed and Aperture Displays
These displays provide visual indications of shutter speed and aperture.
Fast shutter speed, large aperture
(small f-number).
While the mode dial is rotated, this display is replaced by an image of the mode dial.
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See Also
For information on choosing a design for the information display, see Info display format,
(0 137). For information on choosing whether information is displayed when the shutter-
release button is pressed; see Auto info display (0 139).
Information display
Slow shutter speed, small aperture
Monitor off
(large f-number).
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