Canon 40D - Manual (Page 127)

127
8
Sensor Cleaning
The camera has a Self Cleaning Sensor Unit attached
to the sensor’s front layer (low-pass filter) to shake off
dust automatically.
The Dust Delete Data can also be appended to the
image so that the remaining dust spots can be removed
automatically by Digital Photo Professional (provided
software).
Minimizing Dust
When changing lenses, do it in a place with minimal dust.
When storing the camera without a lens attached, be sure to
attach the body cap to the camera.
Remove dust on the body cap before attaching it.
Even while the Self Cleaning Sensor Unit is operating, you can
press the shutter button halfway to interrupt the cleaning and start
shooting immediately.