Nikon D750 DSLR Camera (Body Only) - Manual (Page 407)

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2
Frame a featureless white object in the viewfinder.
With the lens about ten centimeters (four inches) from a well-
lit, featureless white object, frame the object so that it fills the
viewfinder and then press the shutter-release button
halfway.
In autofocus mode, focus will automatically be set to infinity;
in manual focus mode, set focus to infinity manually.
3
Acquire dust off reference data.
Press the shutter-release button the rest of the way down to
acquire Image Dust Off reference data. The monitor turns off
when the shutter-release button is pressed.
If the reference object is too bright or
too dark, the camera may be unable
to acquire Image Dust Off reference
data and the message shown at right
will be displayed. Choose another
reference object and repeat the
process from step 1.