Dust in your camera can & will move around. When the reflex mirror rapidly swings up it will stir up the dust inside the camera. Then the shutter curtain opens and... new bits of dust can land on the sensor or bits of dust already on the sensor can move around.
Ideally you want to get the dust out of the camera.
You can:
1) Remove the lens in a dust-free environment
2) Point hte camera toward the floor
3) Invoke a manual dust-cleaning cycle
When this shakes the filter the dust will hopefully fall out of the camera.
If that doesn't work, then a hand-squeeze air blower (avoid compressed air cans because they can leave a residue on the sensor and then you have to "wet clean" the sensor using sensor cleaining fluids and sensor swabs.) A few puffs of air (without touching the sensor) will usually encourage the dust to leave.
These are usually things you can do yourself.
Just occasionally a very soft (and pristinely clean) brush can be used or ... the wet cleaning method. While I consider this to be something everyone should learn (since cleaning the sensor is something you might have to do semi-regularly), you can also just take it in to have it cleaned by a service center.
Tim Campbell
5D III, 5D IV, 60Da
