Nikon D300 Complete Manual page 694

4. Use the Direction pad to navigate to the Dust off ref
photo option and press the > key to select it.
5. Use the Direction pad to highlight Start and press the
> key to select it.
The Clean sensor and then start option performs
the camera's automatic dust removal function prior to
taking a dust off photo.
6. Follow the instructions on the display, which instruct
you to take a picture of a white object (card or sheet
of paper) 10cm (4") from the front of the lens. Fill the
frame with this object.
7. Press the shutter release. If you get the message
INAPPROPRIATE EXPOSURE CONDITIONS
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 694