Nikon D5100 Reference Manual page 19

Start:The message shown at right will be
displayed and "rEF" will appear in the
viewfinder.
Cleansensor andthen start: Select this option to
clean the image sensor before starting. The
message shown at right will be displayed and
"rEF" will appear in the viewfinder when
cleaning is complete.
_I_ Image Sensor Cleaning
Dust off reference data recorded before image sensor cleaning is performed can not
be used with photographs taken after image sensor cleaning is performed. Select
Clean sensor and then start only if the dust off reference data will not be used with
existing photographs.
2
Frame a featureless white object in the viewfindero
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. Note that noise reduction will be performed if the subject is poorly lit,
increasing recording times.
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.
_I_ Image Dust Off Reference Data
The same reference data can be used for photographs
taken with different lenses or at different apertures.
Reference images can not be viewed using computer
imaging software. A grid pattern is displayed when
reference images are viewed on the camera.
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