Nikon D300 Complete Manual page 495

3. Use the Direction pad to navigate to Rotate tall and
press the > key on the Direction to select it.
4. Use the Direction pad to navigate to On and press the
> key or the OK button to complete the setting.
Not rotated
Personally, I don't like the Rotate tall option, as it starts to
make the review image too small to quickly evaluate (not how
little of the LCD space is taken up by the image in the rotated
example, above). That's especially true if you use the RGB
Histogram page as your primary review page. I leave this
option Off on my D300 and just tilt the camera or my head.
Thom Hogan's Complete Guide to the Nikon D300
Rotated
V1.02
Page 495