Nikon D6 Reference Manual page 958

Lock Mirror Up for Cleaning
Use [Lock mirror up for cleaning] to lock the mirror up so that
dust that cannot be removed using the "clean image sensor"
option can be removed manually. For more information, see
"Manual Cleaning" ( 0 1078).
Image Dust Off Ref Photo
Acquire reference data for the Image Dust Off option in
Capture NX-D. Image Dust Off processes NEF (RAW) images to
mitigate effects caused by dust adhering to the low-pass filter in
front of the camera image sensor. For more information, refer to
Capture NX-D online help.
906 B The Setup Menu: Camera Setup
G button U B setup menu
G button U B setup menu