Dust on sensor
			 
			 
			
		
		
		
			
			This might be a naive question but where does the dust come from? 
  
Is it airborne and consequently when you change lenses, it winds up on the sensors?  Are you better off not changing  your lenses that often or is there some way to insure a relatively dust free atmosphere when changing lenses?
		 
		
		
		
		
		
		
		
		
	
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