Nikon D6 Reference Manual page 823

Auto Distortion Control
Select [On] to reduce barrel distortion when shooting with
wide-angle lenses and to reduce pin-cushion distortion when
shooting with long lenses.
•
[Auto distortion control] is available only with type G, E, and
D lenses. Some lenses of these types, including PC and fisheye
lenses, are, however, not supported. Results are not
guaranteed with lenses that are not supported.
D
Auto Distortion Control
•
When [On] is selected, the time needed to process photographs before
recording begins may increase.
•
The greater the amount of distortion control, the greater the area
cropped from the edges of the frame.
•
Before using auto distortion control with DX lenses, choose [On] for
[Image area] > [Auto DX crop] or select [DX (24×16)] for [Choose
image area]. Selecting other options may result in heavily cropped
photographs or in photographs with severe peripheral distortion.
•
Auto distortion control does not apply to movies.
G button U C photo shooting menu
C The Photo Shooting Menu: Shooting Options 771