Canon EOS 7D - Manual (Page 200)

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Whenever you set the power switch to <1> or <2>, the Self
Cleaning Sensor Unit operates to automatically shake off the dust on
the front of the sensor. Normally, you need not pay attention to this
operation. However, you can execute the sensor cleaning at anytime as
well as disable it.
1
Select [Sensor cleaning].
Under the [6] tab, select [Sensor
cleaning], then press <0>.
2
Select [Clean nowf].
Turn the <5> dial to select [Clean
nowf], then press <0>.
Select [OK] on the dialog screen,
then press <0>.
X The screen will indicate that the
sensor is being cleaned. Although
there will be a shutter sound, a
picture is not taken.
In step 2, select [Auto cleaningf] and set it to [Disable].
X The sensor cleaning will no longer be executed when you set the
power switch to <1> or <2>.
f Automatic Sensor Cleaning
Cleaning the Sensor Now
Disabling Automatic Sensor Cleaning
For best results, do the sensor cleaning while the camera bottom is
placed on a table or other flat surface.
Even if you repeat the sensor cleaning, the result will not improve that
much. Right after the sensor cleaning is finished, the [Clean nowf]
option will remain disabled temporarily.