Nikon D5100 Reference Manual page 33

Create copies that reduce the effects of perspective taken from
the base of a tall object. Use the multi selector to adjust
perspective (note that greater amounts of perspective control
result in more of the edges being cropped out). The results can
be previewed in the edit display. Press _) to copy the
photograph, or press [] to exit to playback without creating a
copy.
Before After
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